Laser-material interactions for tailoring future applications

Resume : After decades of intensive nanoresearch, nanoparticles are widely implemented as functional elements on surfaces, into volumes and as nanohybrids, with a wide spectrum of applications such as catalysis and biomedicine. However, integration of the “nanofunction” into products is still limited due to drawbacks of gas phase and chemical synthesis methods regarding particle aggregation and contaminantion causing deactivation of the building blocks´surface. As an alternative synthesis route, nanoparticle generation by lasers in liquids has proven its capability to generate and conjugate totally ligand-free colloidal nanoparticle building blocks, recently started getting commercial. Recent studies highlight unique properties of laser-generated nanoparticles potentially harvested in real-world applications. In biomedical research, scale-up of the method is shown at the example of polymer matrix embedding, fabricating kilogram scale of polymer membrane nanocomposites essential in artificial lung implants. First in vivo studies with neural electrodes modified by ligand.free platinum nanopartiucles show application prospects in treatment of Parkinson deasease. Laser-generated monophasic gold-silver-alloy nanoparticles particularly profit from purity, which allows their application in biomedicine without cross effects. This alloy reference material series represents a grayscale of toxicity, used to model unintended implant debris toxicity using a very sensitive biofunctional system: mammalian reproduction biology. The studies involve life cell imaging and intracellular quantification of single, 60 femtogram plasmonic nanoobjects. General Ref´s: • Asahi, T. ; Mafune, F. ; Rehbock, C. ; Barcikowski, S.: Strategies to harvest the unique properties of laser-generated nanomaterials in biomedical and energy applications. Applied Surface Science 348 (2015), S. 1-3 • Rehbock, C. ; Jakobi, J. ; Gamrad, L. ; van der Meer, S. ; Tiedemann, D. ; Taylor, U. ; Kues, W. ; Rath, D. ; Barcikowski, S.: Current state of laser synthesis of metal and alloy nanoparticles as ligand-free reference materials for nano-toxicological assays. Beilstein Journal of Nanotechnology 5 (2014), 1523–1541. • Wagener, P. ; Barcikowski, S. ; Baersch, N.: Fabrication of nanoparticles and nanomaterials using laser ablation in liquids. In: Photonik international (2011), 20–23 • YouTube Channel (of published videos shown during the talk): http://youtube.com/nanofunction BioMed Ref´s: • Klein, S. ; Petersen, S. ; Taylor, U. ; Rath, D. ; Barcikowski, S.: Quantitative visualization of colloidal and intracellular gold nanoparticles by confocal microscopy. Journal of Biomedical Optics 15 (2010), Nr. 3, S. 036015. • Gamrad, L.; Rehbock, C.; Krawinkel, J.; Tumursukh, B.; Heisterkamp, A.; Barcikowski, S.; Charge Balancing of Model Gold-Nanoparticle-Peptide Conjugates Controlled by the Peptide's Net Charge and the Ligand to Nanoparticle Ratio. Journal of Physical Chemistry C (2014), 118 (19), 10302-10313. • Taylor, U. ; Tiedemann, D. ; Rehbock, C. ; Kues, W.A. ; Barcikowski, S. ; Rath, D.: Influence of gold, silver and gold-silver alloy nanoparticles on germ cell function and embryo development. Beilstein Journal of Nanotechnology (2015), 6, 651-66

Resume : TiO2 is one of the most studied photocatalysts due to its stability, abundance, non-toxicity and high activity. Its main deficiency relies on the wide band gap, making it inefficient for solar-driven applications. The so-called “black-TiO2” may overcome this issue. Unfortunately, the commonly presented synthesis routes of black-TiO2 require high pressures of hydrogen (up to 20 bar) and long annealing treatments (up to 15 days). Such conditions are clearly not suitable for low cost production. In this work we present a new, versatile, industrially scalable and environmental friendly laser synthesis of black-TiOx nanostructured film that overcomes the above mentioned issues. We used a Q-switched Nd:Yag laser operating at 1064 nm in order to realize a nanostructured photochemical diode. The device is composed by a titanium foil, sandwiched between a nanostructured titanate film (TiOx) and a layer of Pt nanoparticles (PtNps). The black-TiOx film was obtained by ablating the Ti foil in pure water. We deposited Pt nanoparticles (synthetized by laser ablation in water) on the back side of our samples realizing a stacked layered structure (TiOx/Ti/PtNps). This structure exhibits a high photoactivity with a quantum efficiency of 0.058 % (double than commercial glasses). We ascribe such high photo efficiency to both the presence of Pt nanoparticles on the rear side of the film, and the presence of surface states in amorphous hydrogenated TiOx layer.

Resume : Silver (Ag) nanoparticle (NP) films have been prepared using atmospheric pulsed laser deposition (APLD). In this novel technique a rotating Ag target is ablated, in flowing argon at atmospheric pressure, with a 248 nm, 25 ns excimer laser. The ablation plume is captured by the gas and forms a NP aerosol, which is carried to the substrate using a gas flow of 8 litres per min. The substrate was positioned at 5 – 20 mm from the ablation spot and the laser fluence and the number of laser shots was varied. Silicon, quartz and glass substrates were used. The NP size distribution was examined using scanning electron microscopy. The distribution of Feret diameters ranged up to 50 nm, with a mean value of 11 -19 nm, depending on the deposition conditions. In optical absorption the as-deposited films showed the usual surface plasmon resonance (SPR) in the region 350 - 500 nm, with the strength of the resonance depending on the laser fluence, number of laser shots and the target-substrate distance. The as-deposited NP films were thermally annealed in argon, nitrogen, and hydrogen at 400 °C, and in air for temperatures in the range 200 - 900 °C. For all gases annealing at 400 °C leads to increase of the amplitude, and a decrease of the width, of the SPR, with annealing in air around 400 °C showing the most pronounced effect. Annealing in air in the range 200 – 400 °C leads to a strong enhancement and a red shift of the SPR, while temperatures in the range 600 – 900 °C leads to a blue shifted SPR with lower amplitude. Annealing was found to lead to a significant enhancement of the detection sensitivity when the NP films are used as substrates for surface enhanced Raman spectroscopy (SERS).

Resume : Metallic nanoparticles (NPs), either on the surface or embedded in dielectric matrices, have received great attention due to their linear and non-linear optical properties. Since these properties depend on their size, shape and their surrounding media, there is a great interest in developing methods able to produce NPs of low dimensions and size dispersion. A suitable technique for the synthesis of metallic NPs is pulsed laser irradiation of thin films in which the irradiation converts metal films in nanoislands, beads or NPs. This technique can be applied at room temperature and atmospheric conditions and it is free of chemical wastes [1]. In this work we study the formation of gold nanoparticles by laser irradiation of Au films of thickness up to 65 nm. The films, grown by discharge sputtering on glass substrates, were irradiated with nanosecond laser pulses at 355 nm with fluences in a range from 100 to 400 mJ/cm2. The irradiation was performed both at atmospheric pressure and in vacuum conditions in order to determine the background pressure effect. The influence of the film thickness and the laser fluence on the characteristics of the NPs was also studied. With the aim of better understanding the mechanisms involved during the NPs formation, the light of a stabilized HeNe, transmitted through the sample, was measured in real time [2]. The changes in the optical transmission signal of the films last for hundreds of microseconds after the laser pulse. The obtained NPs were later characterized by SEM and UV-Vis optical absorption. It was found that both, the size and the size distribution of the NPs are smaller when irradiating in vacuum than at atmospheric pressure. Moreover, the influence of the laser fluence on the size of the NPs is less noticeable when the irradiation is performed in vacuum. [1] S.J. Henley, M.J. Beliatis, V. Stolojan, S.R.P. Silva, "Laser implantation of plasmonic nanostructures into glass", Nanoscale 5, 1054 (2013). [2] R.J. Peláez, T. Kuhn, C.E. Rodríguez, C.N. Afonso, "Dynamics of laser induced metal nanoparticle and pattern formation", Appl. Phyis. Lett. 106, 061914 (2015). This work was partially supported by the DGAPA-UNAM under project PAPIIT IG100415.

Resume : Laser-induced self-organization of matter is a guarantee of efficient and cost-effective processes. Ultrafast laser-induced ripples at material surface are probably the most representative example of precise material patterning. In addition, ultra-fast laser has also been successfully used to induce organization of metallic nanoparticles embedded in polymer films, which opened new ways to the fabrication of plasmonic nanostructures with tailored morphological and, thus, optical properties. Our group have shown that self-organization of nanoparticles could be also obtained in the case of thin films loaded with metallic ions using CW lasers. In particular, we have already demonstrated that one dimensional (1D) metallic-nanoparticle grating-like structure can be obtained when an amorphous titania (TiO2) thin film loaded with Ag salt, deposited on glass substrate, is illuminated with ArKr CW laser. Such periodic structures can be produced with different wavelengths lying in the plasmon resonance of Ag nanoparticles, their period is a fraction of the laser wavelength and their orientation parallel to the laser polarization. In this work, we use a similar approach to induce the formation of a two dimensional (2D) grating-like structure. With the help of a solid state laser working at 532 nm and of a half-wave plate to rotate the laser linear polarization, we first demonstrate our capability of producing 1D gratings with different orientations, and we explore the effect that the scan direction has on the quality of the grating itself. Then, we study the effect of exposing a same sample area to two consecutive illumination processes exhibiting perpendicular polarization orientations. Scanning electron microscopy (SEM) is used to study the morphology of samples after laser exposure, while Raman spectroscopy is used to figure out any phase change in the TiO2 amorphous matrix. We thus present a very simple method to induce large-scale and long-range order 2D self-organization of Ag nanoparticles in TiO2 thin films, a composite with high potential in photochromic and photocatalytic applications.

Resume : Femtosecond laser material processing has become an excellent option to produce micro and nanostructures with precision and repeatability. However, large scale production in certain industrial applications is still challenging. Direct processing using high power ultrafast lasers is not a viable option for the particular case of plastic materials as damage and melting in the surface degrades the surface relief in the micrometer scale. Hence, our approach for the definition of surface textures in plastic parts is the laser process of the metallic master surface and the replication of the injected plastic part surface. The purpose is to study the scale limits of this technique and the replication rates that are achievable. The first part is the fabrication of micro and nano structures in the stainless steel master surface with the femtosecond laser and its characterization. Microgrooves with different ablated depths and widths structures from 1 to 10 µm high and 5 to 50 µm width were obtained on the metallic master surface. Also different types of LIPSS were generated. The second part consist in the injection of polystyrene (PS) and polycarbonate (PC) and the adjustment of the injection parameters to characterize the replication accuracy. Given the successful achieved results, we can conclude that this approach is highly promising for large scale production of polymeric functional parts for applications such as superhydrophobicity, decorative functions or light diffusers.

Resume : Laser processing and machining of dielectrics, like for instance silica or sapphire, is a growing field, involving increasingly complex laser temporal and spatial pulse shaping. The situation is intricate due to the feedback between electronic excitation and pulse propagation. Obviously, a detailed knowledge of all elementary processes involved in the interaction is mandatory for optimizing any laser manufacturing process. In particular, the critical step is energy deposition, which must be controlled to achieve precise laser induced modification. In order to improve our understanding of the interaction, we use three different experimental technique: time resolved holography and interferometry, and photoelectron spectroscopy. We will show that the combination of these technique allow to get a complete picture of the beam propagation, and to quantitatively characterize in 3D the energy deposition in the solid. Also, we will show that the use of a double excitation scheme gives detailed information on the excitation and relaxation mechanisms. The consequence of the results to improve laser machining of dielectrics will be discussed.

Resume : The existence of two different solid phases in Silicon, crystalline and amorphous, with very different properties has paved its way into many sectors of the electronic industry. The phase can be switched using laser radiation, with the amorphous phase being typically obtained by melting and fast quenching, whereas recrystallization is achieved by laser thermal annealing. Another attractive phenomenon observed in Si is the formation of Laser-Induced Periodic Surface Structures (LIPSS), yielding topographic ripples with an orientation typically perpendicular to the laser polarization and periods in the order of the laser wavelength. This effect is produced by an interference process between the incident light and a scattered surface wave, and is found in virtually all material classes, but mainly limited to the ablation regime. In this study, we report the formation of amorphous and crystalline ripples induced in c-Si by multi-pulse fs laser irradiation at different wavelengths (400, 800 and 1030 nm) and angles of incidence. By scanning the laser beam over the surface with an adequate spot size, repetition rate and scan velocity we are able to fabricate long-range ordered, high-precision, amorphous-crystalline grating structures. By means of fs-resolved microscopy, we reveal the phase transformation dynamics (from fs to ns) that leads to the formation of these amorphous-crystalline ripples.

Resume : The interaction of ultrashort infrared laser with bulk silicon is known to produce high free-carrier densities. This regime is thus attractive for contactless reliability tests inside silicon embedded technologies. We detail a method to inject free-carriers by backside irradiation of silicon-supported transistor structures and report on the tunneling of the laser-induced carriers across gate oxide layers, emulating in this way a process on the basis of modern microelectronics. Firstly, we present our experimental setup relying on a customized infrared microscope in which a femtosecond laser is injected. This allows us to irradiate and observe micro-devices through silicon. A probe station enables us to apply electrical signals on the structures and measure their characteristics after irradiation. To measure the carriers generated by ionization that are injected through an oxide, a structure that traps them for subsequent electrical measurements is needed. For this reason we choose to irradiate flash memory cells. The free electrons can be thus injected and stored in the cell. By measuring the drain current versus the gate voltage, we detect electrons trapped in the memory cell. The impact of various laser parameters, and the voltage applied on the cell is investigated. The threshold conditions for tunneling allow us to discuss the characteristics of free-carriers generated by ultrafast laser inside silicon, improving the understanding of this emerging regime of interaction.

Resume : In order to check the manufacturing quality of electronic components using electron microscopy, the area of interest must be exposed. This requires the removal of large quantity of matter without damaging the surrounding area. This step can be accomplished using ion milling but the processing time is long. In order to accelerate the preparation of the samples, picosecond laser micromachining is considered. Laser ablation allows the fast removal of matter but induces damages around the ablated area. Therefore the process has to be optimized in order to limit the size of the heat affected and induced dislocations zones. For this purpose, cavities have been engraved in silicon and in electronic components, using a picosecond laser (~ 50 ps) at three different wavelengths (343, 515 and 1030 nm). Results showed that the cross sectional shapes and the surface topologies can be tuned by the laser fluence and the number of shots. Clear cross sections of bumps and cavity openings, exposing multilayer interfaces, are demonstrated. The silicon removal rates, tuned by the applied energy density, have been measured. Removal rates were typically hundred times higher than those achieved by ion milling and the best efficiency was obtained at 343 nm. Acknowledgement : This work has been carried out thanks to the support of the A*MIDEX project (n° ANR-11-IDEX-0001-02) funded by the « Investissements d’Avenir » French Government program, managed by the French National Research Agency (ANR).

Resume : Laser-induced periodic surface structures, known as LIPSS, have been increasingly studied during recent years since they provide an efficient way to fabricate high quality micro- or nano-structures over large area [1]. Many LIPSS phenomena have been reported for different materials; however, few studies have been performed in metal/oxide composite materials. Recently, self-organization of metallic nanoparticles (NPs) in metal oxide layers has been achieved under visible continuous-wave (cw) laser illumination [2]. Such composite structures can lead to applications such as photo-catalysis and solar energy harvesting thanks to “hot electrons” generated by the plasmonic absorption of each nanoparticle and the electromagnetic interaction between these self-arranged NPs. The work reported here focuses on the simultaneous formation of LIPSS and self-organized embedded silver nanoparticle gratings in TiO2 thin films under visible femtosecond laser (370 fs pulse duration) irradiation at 515 nm wavelength. Compared to the cw-laser produced structures, the fs-laser process can combine the properties of the two periodic structures in a single step and can give various types of grating structures by changing the laser parameters The TiO2 thin layer used in this work is initially mesoporous and amorphous and contains small silver NP of 1-3 nm as described in a previously published process [2]. By changing the fs-laser scan speed and power, simultaneous LIPSS/NP self-organized structures were observed within a large fluence range, where two main types of structures, named S1 and S2, were identified respectively under low and high laser fluence. In S1 (Fig. 1 a), LIPSS and NP gratings are all perpendicular to the laser polarization with a period of about 500 nm (close to the laser wavelength λ). STEM studies of a S1 cross-section reveal local crystallization of TiO2 in the valley of the LIPSS together with the formation of silver NPs of 25nm in average diameter. In S2 (Fig. 1 b), the LIPSS are always perpendicular to the laser polarization whereas the NP gratings are parallel to it with a period of 310nm. In that case, the NP gratings have similar properties to what is usually obtained with cw-lasers [2]. Further AFM measurements show that the LIPSS have a period of ~λ/3. Optical properties of such laser-induced nanostructures are also investigated, featuring efficient white light diffraction and selective absorption bands that can be achieved over large areas (Fig. 1 c). [1] A. Ruiz de la Cruz et al., High speed inscription of uniform, large-area laser-induced periodic surface structures in Cr films using a high repetition rate fs laser, OPTICS LETTERS, vol. 39, pp. 2491-2494, (2014). [2] N. Destouches et al., Self-organized growth of metallic nanoparticles in a thin film under homogeneous and continuous wave light excitation, J. Mater. Chem. C, vol. 2, pp. 6256-6263, (2014).

Resume : Low dimensional ZnO is an extremely promising material for optoelectronic applications due to the strong quantum confinement effects. The only limitation for successful application is the conductivity. Doping of ZnO nanostructures by appropriate metal atoms such as Al, Ga, Sn, and In can significantly change electrical and optical properties. In recent years, Al-doped ZnO nanostructures have been considered as the most promising candidate. Here we present fast, effective and environmental friendly synthesis approach for preparation of ZnO nanostructures by pulsed laser ablation (PLA) in water media. The advantages of this technique are numerous but still not fully exploited. In order to investigate the influence of Al-doping on optical and structural properties of ZnO nanoparticles produced by PLA in water, two different targets were used: i) ZnO target (99.999% ZnO) and ii) ZnO:Al2O3 target (98% ZnO, 2% Al2O3). Both targets were irradiated by a Nd:YAG laser (λ = 1064 nm), 100 mJ of output energy and operating at 5 Hz. The morphology of nanoparticles was investigated by electron microscopy techniques. Spherical-shaped particles with diameter around 120 nm were recorded when the ZnO:Al2O3 target was used. Optical properties were investigated by means of UV-Vis, and the measurements have clearly indicate a ZnO surface plasmon peak at 335 nm for both targets, but with different intensity. The ZnO nanoparticles prepared by PLA of the ZnO:Al2O3 target give much better absorption, compared to the case when the pure ZnO target was used. Our results indicate that PLA in water media can be applied as an efficient and fast approach for synthesis of Al-doped ZnO nanoparticles with improved UV absorption.

Resume : Manipulating the size of matters has been previously demonstrated a powerful means of creating unprecedented optical properties in metals and semiconductors. Here we report an insulator system composed of NaYbF4:Tm in which size effect can be harnessed to enhance multiphoton upconversion. Our mechanistic investigations suggest that the phenomenon stems from spatial confinement of energy migration in the nanosized frameworks. We show that confining energy migration constitutes a general and versatile strategy to manipulating multiphoton upconversion, demonstrating an efficient five-photon upconversion emission of Tm3 in a stoichiometric Yb lattice without suffering from concentration quenching. The high emission intensity is unambiguously substantiated by realizing room-temperature lasing emission at around 311 nm after 980-nm pumping, recording an optical gain two orders of magnitude larger than that of a conventional Yb/Tm-based system operating at 650 nm. Our findings thus highlight the viability of realizing diode-pumped lasing in deep ultraviolet regime for various practical applications.

Resume : We here introduce a laser-driven method to pattern Ag nanowire (AgNW) transparent electrode without material removal. Our approach is to block the current flow in selected areas by cutting nanowires, which is fundamentally based on the Rayleigh instability. AgNW film spin-coated onto a glass substrate was selectively irradiated using a nanosecond-pulsed ultraviolet laser beam. This made it possible to fabricate a patterned structure consisting of spatially separated conducting and insulating regions. The feasibility of this electrical property patterning was demonstrated with white light emitting diodes attached to the fabricated pattern.

Resume : It is known that X-ray and light beams are not interacted in the vacuum. But the interaction is possible in principle at the material medium presence. For realization of such interaction we used new device of X-ray nanophotonics – Planar X-ray Waveguide-Resonator (PXWR) [1]. This device transports X-ray radiation through generation of the uniform interference field of X-ray standing wave in own air planar slit clearance formed by quartz polished reflectors. In these reflectors it is possible to excite the interference fields of optical standing wave by laser beam in conditions of the total interval reflection. Interference fields periods can be variated by incidence angles changing. Our investigations shown that under certain combination of the fields periods experimental parameters of X-ray beam formed by the PXWR demonstrate real variation. It is supposed that the effect has resonance nature. [1] V.K. Egorov, E.V. Egorov // X-ray Spectrometry. V33. 2004. pp. 360-371.

Resume : Biodegradable polymers have receiving growing interest as materials for tissue engineering. Among other methods for modification of biodegradable polymers, laser processing is a simple technique which provides high spatiotemporal controllability. In addition, surface processing of materials after molding is capable on a complex surface without using any toxic chemicals. In this study, we investigated the wettability modification of poly (lactic-co-glycolic acid) (PLGA) treated by femtosecond laser at different wavelengths. Femtosecond laser pulses from a Ti:sapphire chirped pulse amplification laser system (pulse width 100 fs, repetition rate 1 kHz) operating at a central wavelength of 800 nm or 400 nm were loosely focused onto PLGA films. The wettability of PLGA was analyzed by using the water contact angle measurement. Although the contact angle of PLGA irradiated at 800 nm exhibits little difference, the contact angle of PLGA irradiated at 400 nm showed significant increase compared to the initial surface, indicating hydrophobic property. PLGA irradiated at the laser fluence of 0.25 J/cm2 showed the contact angle of 98°, which is the largest angle obtained in our experiments. Since hydrophobization of PLGA surface is obtainable with laser fluences far below the ablation threshold, the change in wettability is attributable to the change in chemical structure as well as to the morphology of PLGA surface. The mechanism of femtosecond laser-induced wettability modification will be discussed based on the measurements of morphological and chemical change of PLGA surface.

Resume : A large class of quasi-periodic surface structures has been observed on crystalline silicon irradiated with femtosecond laser pulses, among which subwavelength ripples have been largely investigated. In this communication, we report on the seldom considered issue of quasi-periodic, micron spaced grooves formation. We characterize the morphological evolution of the grooves generation experimentally, singling out how the threshold fluence for their formation varies with the number of pulses N. The typical ripples simultaneously produced are considered for comparison. Our results evidence a power law variation on N of the threshold fluence both for ripples and grooves formation, addressing a typical incubation behavior. We observe incubation factor and single pulse threshold of (0.84±0.03) and (0.54±0.08) J/cm2 for the grooves, while the corresponding values for ripples are (0.76±0.04) and (0.20±0.04) J/cm2. Our experimental findings are interpreted by introducing a simple, empirical scaling approach for the excitation level that allows associating the surface structures generated in multiple-pulse experiments with the predictions of the surface scattered wave theory, at laser fluencies around the grooves formation threshold. This, in turn, allows proposing a physical mechanism interpreting the grooves generation and explaining the coexistence and relative prominence of grooves and ripples formed over the irradiated area.

Resume : We applied Pulsed Laser Deposition (PLD) and Matrix Assisted Pulsed Laser Evaporation (MAPLE) in order to synthesize hydroxyapatite thin films on Ti substrates. An enhanced chemical and biological activity is expected for the films deposited by MAPLE from nanopowders due to the extended surface area in contact with the reactive media. The experiments were conducted in a reaction chamber using a KrF* excimer laser source (λ=248nm, τFWHM≈25ns). The films were grown on 12 mm diameter Ti disks which were previously cleaned in an ultrasonic bath with acetone, ethanol and deionized water. All films were post-deposition thermally treated in a flux of water vapors in order to improve stoichiometry and crystallinity. Half of the samples were bioactivated with a top layer of fibronectin (FN). The selected samples were subjected to physical-chemical analysis. Specific coating surface morphologies were evidenced by optical, scanning electron (SEM) and atomic force microscopy (AFM) investigations. They were shown to depend on deposition technique and also on the post-deposition treatment. The crystalline structure of the coatings was monitored by X-ray diffraction (XRD) before and after thermal treatment. To evaluate the biocompatibility of coatings, cellular adhesion, proliferation and differentiation tests were conducted.

Resume : In this work results on laser assisted formation of gold nanoparticles in glass are presented. The sample material is borosilicate glass obtained by conventional melt quenching method. In the fabrication stage AuCl3 is added in order to obtain gold ion doped material. The produced glass samples are then irradiated by laser pulses with a wide variety of parameters – wavelength, fluence, pulse duration. At certain conditions femtosecond laser radiation induces defects associated with formation of color centers in the material. After annealing of the samples the irradiated areas express red color whit clear dip in the transmission spectra. This effect is related to formation of gold nanoparticles and their optical properties defined by plasmon resonance. The optical properties of the irradiated areas are found to depend on the laser processing parameters. Irradiation with nanosecond laser pulses may also induce color change of the glass, but at laser fluences where a permanent damage of the material is observed. The properties of the material at the processed areas are studied on the basis of generalized multiparticle Mie theory that is used to correlate the experimentally obtained optical spectra and the characteristics of the nanoparticles. The influence of the processing condition on the characteristics of the formed particles and the mechanism of their formation are discussed. This method can be used in fabrication of 3D nanoparticles systems in transparent materials that can be applied in the design of new optical components as metamaterials and in plasmonics.

Resume : Fiber-integrated nanosecond laser sources at 1550 nm wavelength allow modifications in the bulk silicon. Even if many characterizations of these modifications can be performed by conventional infrared microscopy, information about the change in the refractive index is needed to intend the manufacturing of optically-functionalized silicon micro-devices. Thereby, we have developed a phase-shift interference setup by which we are able to map out refractive index variations in the range [-10^-2; +10^-3] for laser-induced modifications in bulk silicon. This setup relies on a Mach-Zender interferometer in which a femtosecond laser beam at 1.3 µm wavelength or a white light source is injected for phase or amplitude measurements, respectively. The modified areas are measured following a four-step phase-shifting procedure to obtain phase images that are then numerically unwrapped and flattened. The comparison between phase and amplitude images shows that phase measurements not only give access to the refractive index change, but also provide very interesting information about the nature of the modifications likely composed of voids and densified material. A parametric study of the morphology for modifications initiated with various energies and number of pulses will be presented. The magnitude of the observed index changes is enough to envision the laser writing of optical functionalities paving a way toward the micro-fabrication of monolithic silicon photonics chips.

Resume : Laser direct writing techniques have the ability to transfer a wide variety of materials, both in solid or liquid state, from a certain source to a selected substrate without altering their properties. The most extended laser-based approach to transfer inks and solutions is laser-induced forward transfer (LIFT). It consists on propelling a tiny portion of the desired material from a donor film to an acceptor substrate by means of a focused laser pulse. The donor substrate is covered with the liquid film to transfer and separated a convenient gap from the acceptor. Then, a laser pulse is focused onto the donor film where a bubble is induced and it evolves into a jet that is propelled forward. Once the jet contacts the acceptor substrate, the material is deposited. If the material to transfer does not absorb the laser radiation an absorbing sacrificial layer is used. LIFT has been usually carried out with short laser pulses (from a few nanoseconds to femtoseconds). However, the use of longer pulses would allow reducing production costs since less expensive lasers could be employed. In this work we investigate the LIFT of low viscosity inks with long laser pulses through a systematic study of the main process parameters, such as laser pulse energy or laser focusing conditions.

Resume : We report on the deposition of chitosan-biomimetic nanocrystalline apatite coatings by Combinatorial-Matrix Assisted Pulsed Laser Evaporation technique, with potential application in medicine. A KrF* excimer laser source was used (? = 248 nm, ?FWHM ? 25 ns). The structures were studied by GIXRD, SEM, EDS, TEM, AFM, FTIR, RAMAN, XPS and submitted to antimicrobial assays. FTIR spectra of the thin films were found to be highly similar to the spectrum of the initial powders. Scanning electron microscopy evidenced a typical morphology characteristic to deposition technique, advantageous for envisaged application. The nanoscale roughness increases with chitosan concentration. It was observed the gradual substance variation from pure apatite to chitosan. The results demonstrated that the chitosan - biomimetic nanocrystalline apatite composite coatings improve bone formation and facilitate anchorage between the bone and the prosthesis validating the method used. Two microbial strains were tested. It was shown that S. aureus biofilm is more susceptible to chitosan action than E. coli, while hydroxiapatite favorized bone growth process against to bone resorption.

Resume : Polymer foams are suitable for a wide range of applications. The foam physico-chemical properties and, thus, the applications are defined by the polymer and the foam morphology. Therefore, the study of the foam morphology evolution is of great interest. Processes such as nucleation of bubbles, bubble growth and coalesce predestinate the final foam morphology. However, especially the early stages of nucleation are still not fully explained because the processes are very fast and some physical parameters describing the nucleation are experimentally inaccessible. In this work, we present our preliminary experimental results of the observation of early nucleation stages in polymer foams. In order to observe the early stages we designed a new methodology using a laser beam, which evokes foaming in a polymer sample. For this purpose, we designed and constructed an apparatus on which we conducted the laser induced foaming. The foaming procedure was the following. The polymer sample was impregnated with a blowing agent in a pressure cell at an elevated temperature. Then, we applied a laser beam on the polymer sample, which caused foaming in the area of the laser spot. The resulting foam morphology was analyzed by optical microscopy, X-ray micro-tomography, SEM and/or AFM. The final foam morphology was then compared with the laser beam energy density and the concentration of blowing agent in order to determine their effect on the morphology. Surprisingly, even a neat polystyrene sample foamed under laser irradiation. The knowledge of the early stages of nucleation will help not only to better understand the foaming process but also to be able to prepare foams with improved physical properties so-called nano- and microcellular foams.

Resume : Here we report on the fabrication of a microfluidic system designed to amplify the DNA from E-coli. Micro-channels and micro-cavities have been fabricated by laser writing in different polymers i.e. PDMS, PMMA for their application in microfluidic systems. An ArF (193 nm) laser has been used for irradiation. Channel and micro-cavity morphology, dimensional accuracy, and surface conditions have been investigated by optical microscopy, atomic force microscopy, and scanning electron microscopy. The difference in width between bottom and top surface has been also studied. In addition, the heating elements for DNA amplification have been fabricated from metallic and dielectric thin films. Hydrogenated silicon carbide (a-SiC:H) and Ni thin films have deposited by pulsed laser deposition as insulating and conducting materials with high temperature coefficient of resistance. Our results indicate that the laser micromachining techniques applied here represent an important technical support for the realization of low-cost microfluidic chip systems with wide-ranging applications in chemical and biological analysis and clinical diagnostics. This work was supported by a grant from MEN-UEFISCDI, project PN-PCCA 34/2014.

Resume : Vanadium dioxide (VO2) is one of the most interesting thermochromic materials due to a reversible first order metal to insulator transition (MIT) at 68°C (TMIT) followed by abrupt changes in its physical properties: up to 5 orders in magnitude for electrical conductivity and more than 80% for optical transmittance contrast in near IR range. This transition - which can be described as a Mott-Peierls transition - is accompanied by a transformation from tetragonal to monoclinic structure. Thanks to their ultrafast MIT switching time (some hundred femtoseconds) near room temperature, VO2 thin films are particularly attractive for optoelectronic switching devices. Most previous studies showed that the films could be switched by thermal, optical, strain and electrical triggerings. In this work, our aim is to use fluids as switching stimulus. VO2 thermochromic films were grown on C-sapphire by reactive pulsed laser deposition (KrF, 248 nm) using a metallic vanadium target. Films were thus analyzed before and after fluid interaction using X-ray diffraction, XPS, AFM, four-point probe measurement and optical transmittance analysis. Different fluids were tested such as water, alcohol solutions and biologic liquids. Micro-fluidic systems integrating VO2 films made by PLD are developed in order to get more accurate and statistical results, including in situ evolution of the transition characteristics under fluid stimuli.

Resume : Pulsed laser deposition (PLD) is a versatile technique to deposit films with complex compositions. It mainly involves three steps, namely laser-matter interaction, plasma plume expansion and deposition. Besides substrate properties and deposition temperature, the dynamics in the plume expansion is the key factor influencing the film properties. Previous studies have shown that plume dynamics and composition have a strong correlation with film crystallinity and composition. Thus characterization of the laser induced plasma is always necessary for a thorough understanding of PLD process. In this work, we apply combined techniques to characterize plasma plumes from single metallic target ablation as well as perovskite compound ablation. Plume expansion in vacuum and in background gas is characterized by energy-resolved mass spectrometry, Langmuir probe measurements, plasma imaging and emission spectroscopy. Differences between techniques are discussed and plume expansion dynamics is mapped both spatially and temporally.

Resume : Structure improvement of light-weighted metals by adding of hard ceramic particles in metal matrix has promised perspectives for aerospace industry. In the present study, titanium carbides of micron (m-) and nano (n-) sizes were incorporated to the titanium substrate by a selective laser melting (SLM) of Ti+(10, 15, 20 wt.%) TiC powder mixtures via an Ytterbium fiber laser with 1.075 mm wavelength. Optimal regimes of 3D laser additive process were determined. We compared how the interfacial properties would change due to the difference in composition in case of the m- and n- carbides reinforces titanium matrix composites (TMC). Phase analysis of the fabricated TMC showed that the initial carbide particles are dissolved after the remelting with different velocities. Special attention was paid on carbide dilution and secondary carbides formation mechanisms when the TiC is mixed with titanium. Microstructure, phase constitution and mechanical properties of the TMCs were investigated by OM, SEM, XRD and microhardness measurement. It was shown that the microstructure had two types of heterogeneity: the TiC particles at the interlayer interfaces and element chemical segregation on the boundaries of the tracks.

Resume : Laser fusion cutting is a well-established process in industry, mainly for cutting commonly used metallic materials such as steels. However, the utilization of this laser technique to process advanced materials, such as ceramics or some aluminium alloys is restricted due to the formation of large heat affected zones, rough cut edges, presence of dross, or thermal cracks. These defects are intimately related to the assist gas performance during the removal of molten material. Previous works have demonstrated the impressive improvement in cut quality due to the utilization of off-axial axisymmetric converging-diverging nozzles to inject the assist gas. This is due to the higher removal of molten material. However, these results can be even improved if the geometry of the gas jet is tailored to the cutting kerf. In the present work, a cutting head assisted by an off-axis non-axisymmetric converging-diverging nozzle, working at supersonic regime, was developed to improve the efficiency of current assist gas injection systems. Fundamentals and main factors determining the efficiency of the system are reviewed. Furthermore, a comparison with other assist gas injection systems, such as a converging coaxial nozzle, or alternatively, an-off axis axisymmetric converging-diverging nozzle is also analysed during the processing of Al2024-T3 sheets. Results demonstrate the superior performance of the new assist gas injection system in terms of cut quality and productivity.

Resume : Metal nanoparticles, especially gold nanoparticles, are broadly used in electronic devices, display, solar cells and bio-sensors. For high quality nanoparticle applications, regular shape and narrow size distribution are important. Laser based fragmentation of nanoparticles is found to be a promising method of control over a nanoparticle size distribution and shape. However, most researches are focused on size reduction of originally uniform gold nanoparticles. There is still remained problem to employ this technique in industry due to an exorbitant price of uniform size distributed gold nanoparticles. In this study, we manufactured broad size distributed and unstable commercial gold nanopowders to narrow size distributed and stabilized spherical high quality nanoparticles by using Nd-YAG nanosecond pulse laser. First, to disperse the nanopowders in water, gold nanoparticle colloidal solution was ultra-sonicated for 5 min. After sonication, nanoparticles were still agglomerated like cluster and it colored gray. When it was irradiated by 532 nm pulse laser (pulse width = 5 ns) for 5 min, nanoparticle clusters were melted and formed around 100 nm ~ 1 um large spherical particles. After 532 nm pulse laser irradiation, the aqueous solution exposed to 1064 nm pulse laser (pulse width = 6 ns) for 30 sec to split large spherical particles into sub-100 nm particles. As a result, we obtained spherical gold nanoparticles with a narrow size distribution. Furthermore, the gold aqueous solution was well dispersed for 1 month without dispersant such as SDS.

Resume : Laser beam radii increases cause decreasing ablation threshold fluences for nanosecond [1] and femtosecond [2,3] pulses. The two reported quantitative models attempting to describe this dependence are based on defect densities [1] and on heat accumulation [3]. Both models do not comply with experimental results and omit to consider incubation phenomena at all [2]. In this study, an extended defect model is introduced where incubation is attributed to optically active high-density defects with a separation below the laser wavelength [4]. The reduction of threshold fluence for large beam radii is ascribed to the laser spot covering a finite number of optically active low-density defects embedded in the matrix material. This new model combining the spot size and pulse number dependence of femtosecond pulse ablation thresholds is successfully demonstrated with organic and inorganic materials. The average distance of the optically active low-density defects obtained from the model could be confirmed by scanning electron microscopy. [1] L.G. Deshazer, B.E. Newnam, K.M. Leung, Applied Physics Letters 23, 607-609 (1973). [2] S. Martin, A. Hertwig, M. Lenzner, J. Krüger, W. Kautek, Applied Physics A 77, 883-884 (2003). [3] B.-M. Kim, M.D. Feit, A.M. Rubenchik, E.J. Joslin, J. Eichler, P.C. Stoller, L.B. Da Silva, Applied Physics Letters 76, 4001-4003 (2000). [4] A. Naghilou, O. Armbruster, M. Kitzler, W. Kautek, The Journal of Physical Chemistry C 119, 22992-22998 (2015).

Resume : The laser modification threshold fluence was found to be a material constant for a given set of experimental parameters such as pulse duration, wavelength, number of pulses and repetition rate. The modification threshold fluence however shows a dependence on the beam diameter [1,2]. In the present study, the irradiation area dependence of the modification behaviour with femtosecond and nanosecond pulsed lasers were investigated not only for various spot sizes and repetition rates, but also for various surface defect densities. As model substances with high technological importance served steel, silicon, and polymethyl methacrylate. [1] S. Martin, A. Hertwig, M. Lenzner, J. Krüger, W. Kautek, Applied Physics A 77, 883-884 (2003). [2] G. Mann, S. Pentzien, J. Krüger, Applied Surface Science 276, 312-316 (2013).

Resume : Presence of contaminants on surfaces becomes a significant problem both in industry and at home. Small particles or bacteria adhered to surfaces of domestic kitchens are not easily removed by regular cleaning procedures. The effect of substratum wettability upon contaminants adhesion has been known for a long time. For instance, hydrophobic surfaces exhibit self-cleaning properties. These lead to the rolling and bouncing of liquid droplets which trap small particles from the surface. Also, some studies correlate the degree of hydrophobicity of a surface and the number of adhered bacteria. Therefore, the tailoring of the wetting characteristics of materials used in the kitchen or bathrooms is extremely relevant. Zimbabwe black granite is a middle-to-fine-grained natural stone commonly used in these living areas. In this study, the laser texturing of Zimbabwe black granite surfaces is investigated with the aim to enhance its hydrophobic character and to reduce the attachment of contaminants on the surface. Two laser sources (λ = 1064 and 532 nm) were used for this purpose. The influence of different laser processing parameters on surface characteristics (wettability, roughness, and chemistry) of granite was statistically assessed. Most suitable laser processing parameters required to obtain the highest hydrophobicity degree, reducing the attachment of contamination on granite surfaces,were identified.

Resume : For many nuclear applications, in particular in the ITER (international thermonuclear experimental reactor) tokamak, one of the main challenges is to avoid contaminations which can decrease the device capabilities. In the ITER reactor the fusion reaction gives rise to dust (micro and nanoparticles of carbon, tungsten, and beryllium) formation by etching of the vacuum vessel, mainly in the diverter region. In this work, the removal of tungsten nanoparticles with an excimer laser is investigated. The tungsten nanoparticles were synthesized by magnetron sputtering combined with gas aggregation and deposited on a silicon substrate. In order to simulate the ITER geometry different irradiation angles between the laser beam and sample were investigated (i.e. 30 º, 45 º, 60 º, and 90º). The samples were investigated before and after laser irradiation by scanning electron microscopy, Raman spectroscopy, X-ray diffraction, and profilometry to optimize the particle removal efficiency. Furthermore, in order to gain information in the ejection mechanism, plasma imaging was applied, and the speed and directionality of the ejected particles was determined. Our results indicate that laser – particle mobilization is a powerful technique, which could be successfully applied in the ITER tokamak for micro and nano-particle cleaning.

Resume : Low-temperature RF plasma treatment (RFPT) of surface and shallow layers of n- and p-type Ge amorphized by ion implantation correspondingly of BF2+ and P+ have been studied. The RFPT (13.6 MHz) was performed in forming gas, N2 and H2 gases with additional heating (up to 200°C). Thermal annealing (TA) and rapid thermal annealing (RTA) of the implanted samples in nitrogen atmosphere at temperature up to 500°C were performed for comparison. Amorphous phase recrystallization of the thin subsurface Ge layers and activation of implanted dopant were analyzed by Raman scattering spectroscopy (RSS); surface morphology – by AFM; distributions of implanted and activated dopant - by SIMS and ECV; electrical properties of the formed p-n junctions - by I-V indium probe methods. The RSS showed that the amorphous phase in the thin Ge layer was recrystallized by TA at considerably higher temperature than in case of RFPT. Direct experiments with RFPT of front and back sides of the samples demonstrated suppression of the amorphous phase recrystallization at such reduced temperatures. Comparison of RFPT in H2 and N2 atmospheres has shown considerable enhanced recrystallization process in first case. Distributions of implanted phosphorus after the treatments showed an absence of the dopant diffusion after used RFPT up to 1.5W/cm2 and peak concentration about 1x1020 cm-3. The nature of enhanced recrystallization of the amorphous implanted Ge layers and implanted dopant activation is discussed.

Resume : Europium monoxide (EuO) is a promising material for spintronics applications as it is one of the few natural ferromagnetic semiconductors[1], [2]. Moreover, EuO is epitaxial on silicon and therefore compatible with present electronics technology [3]. In order to increase the Curie temperature of EuO, before the incorporation of any dopants, it is important to establish more efficient methods to fabricate pure EuO films. A new enhanced methodology for preparing EuO thin films will be presented. The films have been obtained by pulsed laser deposition (PLD), the ablation of a Eu2O3 ceramic target[4] in vacuum a room temperature. A capping layer of Al2O3 was deposited on top of the films in order to prevent EuO films from ambient oxidation. The resulting films are amorphous and X-Ray Photoemission Spectroscopy (XPS) shows that the composition is EuO. The film structures EuO/Al2O3 exhibits a clear Eu2+ photoluminescence (PL), further confirming the reduction of the original Eu3+ in the target to Eu2+ in the films. The formation of crystalline phases upon post-annealing will be discussed. The results demonstrate that PLD in vacuum provides a suitable and efficient procedure to obtain EuO thin films of good quality. [1] B. T. Matthias, R. M. Bozorth, and J. H. Van Vleck, “Ferromagnetic Interaction in EuO,” Phys. Rev. Lett., vol. 7, no. 5, pp. 160–161, Sep. 1961. [2] T. S. Santos and J. S. Moodera, “Observation of spin filtering with a ferromagnetic EuO tunnel barrier,” Phys. Rev. B - Condens. Matter Mater. Phys., vol. 69, pp. 1–4, 2004. [3] J. Lettieri, V. Vaithyanathan, S. K. Eah, J. Stephens, V. Sih, D. D. Awschaiom, J. Levy, and D. G. Schlom, “Epitaxial growth and magnetic properties of EuO on (001) Si by molecular-beam epitaxy,” Appl. Phys. Lett., vol. 83, no. 5, pp. 975–977, 2003. [4] A. Quesada, A. del Campo, and J. F. Fernández, “Sintering behaviour and translucency of dense Eu2O3 ceramics,” J. Eur. Ceram. Soc., vol. 34, no. 7, pp. 1803–1808, 2014.

Resume : The influence of thermal effects on the structural transformations induced by femtosecond (fs) laser pulses is often overlooked due to the negligible thermal diffusion lengths involved during the absorption of the pulse. However, recent works [1,2] have shown that thermal effects in a heat affected layer below the surface of an ablation crater induced by a single fs pulse need to be given further consideration. In this work, we report for the first time the temporal evolution of this heat affected layer in a phosphate glass, by using an fs-resolved microscopy set-up with an optical fiber delay stage (delay up to 0.5 microseconds). In order to avoid screening effect by material ablation, a single pulse (120 fs) is focused at the sample surface with a fluence slightly below the ablation threshold. By image analysis and optical modelling we obtained the layer depth and the refractive index as a function of time, following an exponential law reaching a final depth of 720 nm at about 1 microsecond. This fundamental finding of thermal effects and their dynamics in fs-laser irradiated glasses is relevant for applications in material processing, to accordingly choose the processing pulse repetition rate, in order to excite either a still “liquid” (low viscosity material) or an already re-solidified surface. [1] A. Ben-Yakar et al., J. Phys. D. Appl. Phys. 40, 1447 (2007). [2] J. Hernandez-Rueda et al.,J. Opt. Soc. Am. B 31, 1676 (2014).

Resume : Using lasers to inscribe electrode designs directly onto substrates has been the latest trend in supercapacitor technology. Initial implementations employed affordable commercial DVD drives or laser engravers to reduce graphite oxide (GO) films into graphene; the latest advances have abandoned GO over polyimides (PI) as precursors for producing laser-induced graphene (LIG). However, research on laser pyrolysis and ablation of both precursors has long preceded supercapacitor applications, and it has yielded interesting results for pulsed and continuous lasers over a wide range of wavelengths. Attempting a thorough investigation of polyimide photopyrolysis via CO2 lasers, we revisit the LIG method to analyze the effect of laser operating parameters on the produced materials, and we determine the optimal operating windows for producing nanocarbons of various structures and surface morphologies .

Resume : This study is related to development of novel technologies for creation of advanced nanostructures of metals and oxides on different substrates, which are applied to high resolution analyses – surface enhanced Raman scattering (SERS) analyses. It is directly forwarded to human health and quality of the food - check of small amount or traces of no desired pollutants. Two types of nanostructured samples are produced. They are ion-beam deposited at glancing angle (GLAD) Ag or Si nanostructures on quartz substrate. GLAD technique is based on the control of the self-shadowing between the growing crystallites/nanostructures. Several samples are grown by rotation at different angles of incidence or without substrate rotation. The Si nanostructures are subsequently covered with Au by pulsed laser deposition technique. The as fabricated structures are coated with pesticide B58 (dimethoate) or Rhodamine 6G for testing of their activity as substrates for Surface Enhanced Raman Spectroscopy (SERS).

Resume : Production of surfaces with original and personalized visual color effects is one of the major challenges of our society. It has direct applications in the technologies requiring better methods of personal identification according with the quest of the enhanced police security. Laser interference by phase mask excimer irradiation is a versatile technique for the production of 1D and 2D patterned surfaces. When applied to metal films, the laser irradiation induces the periodic dewetting of the metal from the substrate resulting to the formation of nanoparticles. These nanostructures are optically characterized by their surface plasmon resonance that depends on the size, density and metal composition. Thus, optical contrast between the regions transformed into nanoparticles and non-transformed regions, and thus the diffraction efficiency of the surface, can be tuned. In this work we report the production of bimetallic, with different atomic ratio of Ag/Au, microstructured surfaces with different motives and periodicities in the range 6.3 microns to 1.7 microns. We will present experimental data showing that these regions have different diffraction patterns according with the periodic motive and the optical response of the nanoparticles. Thus, this technique allows a personalized optical signal to be encoded with a time-efficient and single-step laser technique.

Resume : As one of the most important physical properties of dilute ferromagnetic semiconductors (DFS), the magnetic anisotropy exhibits a complicated character and its origin is under continuous discussion [1, 2]. From the point of view of application, different magnetic anisotropies could meet various needs of spintronic devices. Due to different physical parameters (e.g. band gap, lattice constant) in various Mn doped III-V DMSs, various magnetic anisotropies are expected and could be tailored by Mn or hole concentrations [3-5]. To investigate this in greater detail, we prepare three typical III-Mn-V DFSs, InMnAs, GaMnAs, and GaMnP by ion implantation and pulsed laser annealing, which is a complementary approach to low-temperature molecular beam epitaxy. We report a systematic investigation on the magnetic anisotropy with the aim to understand its physical origin. [1]. T. Dietl et al., Rev. Mod. Phys. 86, 187-251 (2014) [2]. M. Birowska et al., Phys. Rev. Lett. 108, 237203 (2012) [3]. U. Welp et al., Phys. Rev. Lett. 90, 167206 (2003) [4]. M. Sawicki et al., Phys. Rev. B 70, 245325 (2004) [5]. C. Bihler et al., Phys. Rev. B 78, 045203 (2008)

Resume : We report a study on the biocompatibility vs. thickness in the case of titanium nitride (TiN) films synthesized on 410 medical grade stainless steel substrates by pulsed laser deposition. The films were grown in a nitrogen atmosphere, and their in vitro cytotoxicity was assessed according to ISO 10993-5 standard. Extensive physical-chemical analyses (profilometry, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction and surface energy measurements) have been carried out on the deposited structures with various thicknesses in order to explain the differences in biological behavior. XPS revealed the presence of titanium oxynitride beside TiN in amounts that vary with the film thickness. The cytocompatibility of films is influenced by their TiN surface content. The thinner TiN films (~60 nm) seem to be a more suitable option for medical applications, due to the combined high values of bonding strength and superior cytocompatibility.

Resume : We report on multi-stage pulsed laser deposition of Aluminum Nitride (AlN) on Si (100) wafers, at different temperatures. The first stage of deposition was carried out at 800 °C, the optimum temperature for AlN crystallization. In the second stage, the deposition was conducted at lower temperatures (room temperature, 350 °C or 450 °C), in ambient Nitrogen, at 0.1 Pa. The synthesized structures were analyzed by Grazing Incidence X-Ray Diffraction (GIXRD), Transmission Electron Microscopy (TEM), Atomic Force Microscopy and Spectroscopic Elipsometry (SE). GIXRD measurements indicated that the two-stage deposited AlN samples exhibited a randomly oriented wurtzite structure with nanosized crystallites. The peaks were shifted to larger angles, indicative for smaller inter-planar distances. Remarkably, TEM images demonstrated that the high-temperature AlN “seed” layers (800 °C) promoted the growth of poly-crystalline AlN structures at lower deposition temperatures. When increasing the deposition temperature, the surface roughness of the samples exhibited values in the range of (0.4 – 2.3) nm. SE analyses showed structures which yield band gap values within the range of (4.0 – 5.7) eV. A correlation between the results of single- and multi-stage AlN depositions was observed.

Resume : The fast, high -resolution and cost-effective machining of dielectric surfaces with laser radiation is a challenge for laser methods where self-organized processes like ns-laser induced metal droplet formation exhibit an outstanding potential. Further, laser etching methods like laser-induced front side etching (LIFE) allows a high-precision structuring of dielectrics. The combination of the self-organized melting transformation with the LIFE process allows the easy and large-area nanostructuring of dielectric surfaces. The structuring of different dielectric surfaces like SiO2 and Al2O3 assited by the laser-induced melting transformation of different metal layers like Mo, Cr and Ti was tested. As laser source a KrF excimer laser with a wavelength of 248 nm, a pulse duration of 25 ns and a top hat beam profile was used. The structuring process is split into a low (STEP 1) and high fluence treatment (STEP 2). STEP1: The low laser fluence irradiation of thin metal layers result in a nanostructring of the metal film due to the laser-induced melting and the surface tension induced mass transport in the liquid metal. STEP 2: The high laser fluence irradiation of the prestructured metal film on a dielectric substrate results in a removal of the metal and to a modification and nanostructuring of the dielectric surface. The resultant structures were investigated by atomic force (AFM) and scanning electron microscopy (SEM). The process was simulated using a heat equation to describe the laser solid interaction and a kind of Navier-Stokes equation to describe the mass transport in the liquid.

Resume : Development of new materials for electrolytes in Solid Oxide Fuel Cells (SOFC) applications are in demand for decreasing the operation temperature of such systems. Gd-doped ceria (GDC) and Gd, Sm co-doped ceria (GSDC) thin films were grown by Pulsed Laser Deposition for assessing them as electrolyte materials in low temperature SOFCs. An ArF laser working in oxygen atmosphere at a fluence of 4 J/cm2 and 30Hz repetition rate was used. SEM images showed that films deposited on Pt/Si substrate are dense, with homogeneous thickness of a few hundreds nm, with a tendency for columnar growth. The XRD patterns of the obtained materials revealed the formation of polycrystalline CGO and CGSO films exhibiting high crystallinity and a preferred (200) orientation growth. XPS analysis show a slight tendency of Gd segregation to the surface in CGO and CGSO thin films. Sm is found with its nominal bulk stoichiometry in quantitative analysis. The results on surface chemistry as well as the surface element relative concentrations clearly reveal similar surface properties of the targets and the corresponding thin films, opening perspectives for their use in SOFC systems.

Resume : We report the synthesis of Fe–doped TiO2-SiO2 nanoparticles using an injector endowed with three concentric nozzles. The Fe(CO)5 precursor was introduced through the central one together with the C2H4 laser sensitizer, whereas the [(CH3)3)Si]2O bubbled with Ar was either mixed with Fe precursor or introduced in the second annular nozzle, diluted with the bigger Ar confinement flow. The TiCl4 titania precursor (entrained also with Ar) was introduced after mixing with C2H4 and air through the first (median) annular nozzle. The flows were irradiated with a CO2 laser beam, resulting a suspended flame in the reaction zone which generated the oxide-based nanoparticles. By varying the injection geometry and/or the gas/vapor flows, the composition (Ti/Si atomic and anatase/rutile ratios) of the resulting nanoparticles changes, as demonstrated the EDS and XRD analyses, yet having the anatase (with crystallite mean size between 11 and 16 nm) as major phase. Moreover, the nanoparticles atomic Fe content was controlled (from 1 to 8.6%) by varying the amount of Fe(CO)5 flow. The nanopowders were also analyzed by TEM, SEM, SAED, Raman, UV and FTIR techniques.Some selected powders were characterized by magnetic measurements (Hysteresis, FC-ZFC curves and Mossbauer) showing weak magnetization, near superparamagnetic behavior and the presence of both Fe3 and Fe2 species.

Resume : The addition Sb2Se3 in Ge-Sb-Se based glasses has an effect on the structural and physical properties of the chalcogenide target. The effect of both structural and physical changes on the laser ablation plasma plume dynamics were studied by means of fast ICCD imaging and space-resolved optical emission spectroscopy. Systematic measurements have been carried out on plasma produced in vacuum chamber (10-6 Torr residual pressure) by Nd:YAG laser (10 ns, 532 nm) irradiation of (GeSe2)100-x(Sb2Se3)x (x = 0 ÷ 60) chalcogenide targets in PLD conditions. The ICCD sequential images of the global emission of the laser produced plasma plumes revealed the presence and evolution of three plasma structures having different formation mechanisms and expansion velocities. The velocities of various species and the corresponding excitation temperatures were determined through space – time spectral investigations. All the determined plasma parameters underline a specific dependence on the Sb2Se3 content. For concentration higher than 20% the expansion velocities of each species (Ge I 303.9 nm, Ge II 517.86 nm, Sb I 326.75nm and Sb II 600.5 nm) and the respective excitation temperature present a significant increase. The obtained results showcase the strong dependency between the physical and structural properties of the complex targets and those of the laser produced plasmas.

Resume : See-through solar cells show interest for building windows equipment due their potential of electrical power production associated to light transparency over a wide area. Our study is focused on laser scribing process on CIGS based solar cell to obtain a transparency level of the cells up to 50%. This parameter is controlled by tuning the density of holes performed by laser ablation in the solar cell thin film stack (3μm thick: Mo/MoSe2/CIGS/CdS/AZO) deposited on a glass substrate. In our experiment, a pulsed laser beam (nanosecond or femtosecond) is focused on the Molybdenum layer through the glass substrate and the complete stack is then removed by a single irradiation. The size and the density of the holes have been varied to control the transparency level while avoiding diffraction effects. The ablation mechanisms are discussed as the function of the irradiation parameters like pulse duration, fluence, spatial beam profile and spot size. The main issue of this backside ablation process is to avoid leakage current that could be induced by melted Molybdenum which is deposited on the edges of the holes and that would lead to a decrease of the cell electrical performances. Therefore, I vs V measurements under solar simulator are performed to evaluate the cell efficiency before and after the laser scribing process. Under some laser conditions, we find that the relative electrical performances of cells are preserved after laser holes scribing with a transparency rate of the CIGS solar cell up to 50%.

Resume : InxGa1-xAs/GaAs structures, grown by metalorganic vapor phase epitaxy (MOVPE) at 520°C, were investigated by in situ spectral reflectance (SR), high resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM). HRXRD curves are analyzed to determine the indium composition of different samples, denoted A, B, C, D and E. Reflectance three-dimensional plot as function of time and wavelength was recorded to quantify the evolution of reflectivity in the wavelength range from 400 to 1000 nm and to determine some growth parameters such us growth rates and thicknesses of InxGa1-xAs layers. Longitudinal cut through the 3D plot shows dissimilar behavior of reflectivity temporal evolution in three regions: region I (400-560 nm), region II (560-750 nm) and region III (750-1000 nm). Best simulations of reflectivity signals using the transfer matrix method (TMM) are developed to analysis the variation of optical constants spectra and the sensitivity (σSR) of incident wavelength to surface morphology of InxGa1-xAs layers. The obtained values of σSR were compared to RMS surface roughness given by AFM. A good agreement between the experimental results and the theoretical predictions was found. Keywords: InxGa1-xAs/GaAs structures; In situ spectral reflectance; refractive index; Atomic force microscopy; MOVPE. *Corresponding Author: mohamedmourad.habchi@fsm.rnu.tn

Resume : Molybdenum (Mo) - Aluminium (Al) - Molybdenum (MAM) multi-layered thin film is of interest to touch panel devices. In this study, selective structuring of MAM has been performed using 9ns short (1064nm) and 500fs ultra-short laser (1030nm) Gaussian laser sources with 2nd and 3rd harmonics. Different laser fluence regimes were identified both for femtosecond (FS) and nanosecond (NS) laser ablation. At very high fluence, total removal of MAM was observed with the delamination of the lower Mo surface. Reduction of fluence results in complete and partial removal of upper Mo and Al layers respectively. Further lowering of fluence results in a ‘volcano’ like structure, where the high expansion of Al compared with Mo builds up high pressure normally on Mo/Al interface. When this pressure exceeds the yield strength of Mo, Al flows out from a fragmented upper Mo layer, while a lower pressure generated micro and nano-bump on Mo surface. Below threshold fluence the molten Al results in a strained surface to Mo layer. We propose that the heating of Al and re-solidification causes a ‘flower-like’ strained pattern on the perturbed Mo surface. To understand these fluence regimes, a combined mechanical and thermal model is employed, based on finite element methods, to simulate NS and FS ablation process respectively. It has found that these fluences correspond to different ablation mechanisms. A full analysis and demonstration of MAM ablation by NS and FS laser will be presented.

Resume : Multilayer thin films hybrid structures with emission layer based on metal-organic phosphore tris(8-oxyquinoline) aluminum in inorganic matrices (boron oxide, lead fluoride, lead oxide) were fabricated by vacuum thermal deposition. The structure contains auxiliary (ITO, Al) layers and 15-20 hybrid luminescent layers with a total thickness less than 300 nm. The produced structures were subjected to heat treatment by laser radiation using semiconductor and gas laser systems: 785 nm, 973 nm (1W) semiconductor lasers and He-Ne (635 nm, 5 mW) and copper (510.6, 576.2 nm, 3 W) gas lasers. We observed the changes in luminescent characteristics (peak maximum and intensity) depending on a laser treatment which resulted from the exchange reaction between an element of inorganic matrix compound and a metal-organic coordination ion. At local heating with laser radiation it is possible to produce a structure with 2D controlled distribution of photoluminescence.

Resume : Indium islands on a molybdenum film on glass can be used as precursors for the preparation of copper-indium-gallium-diselenide (CIGSe) micro concentrator solar cells. Local arrangement of the islands is achieved by surface structuring using 30-fs laser pulses at 790 nm wavelength. Temperature and deposition rate used for the following physical vapor deposition (PVD) process of indium at a base pressure of 10-6 mbar are crucial for the production of perfect indium arrays. The deposition parameters have a significant influence on island density, volume and contact angle. The strongly favored nucleation at the laser irradiated spots can be explained by capillary condensation due to surface roughening upon femtosecond laser treatment. As shown by a comparison to nucleation experiments on smooth plasma-etched pits, this roughening is decisive for a reliable ordering of the islands rendering an improved control of the deposition process.

Resume : Laser-induced periodic surface structures (LIPSS) were generated on titanium nitride (TiN) hardcoating surfaces (deposited on metallic substrates) upon irradiation with multiple linearly polarized femtosecond laser pulses in air (30 fs duration, 790 nm wavelength, 1 kHz pulse repetition rate). The conditions were optimized in a sample-scanning geometry for the processing of large surface areas (5 mm x 5 mm) covered homogeneously by nanostructures with sub-wavelength periods ranging between ~200 nm and 700 nm. For these nanostructures the coefficient of friction was characterized under reciprocating sliding condition against a ball of hardened steel at 1 Hz using different lubricants (regime of mixed friction). After 1000 cycles, the corresponding wear tracks were characterized by optical and scanning electron microscopy. High-resolution energy dispersive X-ray analyzes (EDX) allowed the visualization of chemical alterations within the wear tracks. For specific conditions, the nanostructures endured the tribological treatment. Our experiments provide a qualification of the tribological performance of the fs-LIPSS on TiN surfaces.

Resume : The wetting behavior of material surfaces can be controlled by surface structures. We functionalized inorganic material surfaces, such as steel, titanium alloy and silicon, to modify the wetting behavior using ultrashort laser pulses (fs- to ps-range). The laser processing was performed by scanning the laser beam across the surface of initially polished flat sample material. A combined experimental and theoretical study of the laser processing parameters (peak fluence, scan velocity, line overlap) allowed the identification of different regimes associated with characteristic surface morphologies (laser-induced periodic surface structures, grooves, micro cones, dimples, etc.). Analyses of the surface using optical as well as scanning electron microscopy allowed the identification of morphologies providing the optimum similarity to the natural skin of lizards. For mimicking skin structures of moisture-harvesting lizards towards an optimization of the surface wetting behavior, additionally, a two-step laser processing strategy was established for realizing hierarchical micro- and nanostructures. In this approach, a laser-generated regular array of small dimples was superimposed (step 2) to the micron-scaled capillaries processed before (step 1). Optical focus variation imaging measurements finally revealed the three dimensional topography of the laser processed surfaces derived from lizard skin structures. The functionality of these surfaces was analyzed in view of wetting properties.

Resume : Laser induced periodic surfaces structures (LIPSS) have attracted extensive interest in recent years for their potential in surface nanostructuring process leading to enhance some surface properties of these materials such as wettability, color and reflectivity…. In this study, we aimed to investigate the LIPSS formation on large surfaces of titanium oxide thin films (25×25 mm²) for applications in thermoelectric field. Ti: Sapphire laser beam, with a pulse duration close to 100 fs and central wavelength λ=800 nm, is used in this work. A third harmonic generator is employed to generate the working wavelength λ=266 nm and the laser beam was focused into a circular spot of 400 μm diameter by a plan-convex lens. Our results showed the formation of three different kinds of LIPSS such as high spatial frequency LIPSS (HSFL) with period close to λ/2, low spatial frequency LIPSS with period close to λ (LSFL) and regular spikes. The formation of these nanostructures was mainly controlled by two parameters: the laser beam fluence (15

Resume : Surface texturing is an important aspect for enhanced light absorption in thin-film Si based solar cells. Here we demonstrate enhanced light-trapping in such fs-laser processed a-Si:H layers with a hydrogen content of 13% . Whereas multi-shot femtosecond (fs)-laser pulse processing is needed for black c-Si formation, we show here that single and double shot fs-pulse irradiation (790 nm, 30 fs) with peak fluences above the crystallization threshold generates nanotextured a-Si:H layers. Characterization was performed by optical microscopy, profilometry, Raman spectro-microscopy (473, 633 nm) and scanning electron microscopy. The enhanced light trapping in these layers is studied using scattered light spectroscopy in combination with spectral interferometry of fs laser pulses. For optimized fs laser processing parameters the nanotextured areas exhibit i) an up to 4-5 times higher Raman yield (λ=633 nm) in comparison to an untreated area and ii) the presence of long-living photonic modes spatially localized on the few µm scale. The intensity of the scattered light from these modes decreases with a lifetime of about 25fs which corresponds to a 7 times longer linear propagation length in comparison to the absorber layer thickness of 300nm. This explains the enhanced absorption and Raman yield.

Resume : Long-wavelength nanosecond lasers are highly pertinent for three-dimensional (3D) microfabrication applications in semiconductors. We investigate experimentally the energy delivery and deposition leading to laser-induced damage inside the bulk of n-type doped 100 oriented silicon crystals. Infrared nanosecond pulses (1550-nm and 3.5-ns duration) are tightly focused 1 mm under Si surface with a microscope objective (NA 0.3). To understand the physical processes leading to material damage, we perform integrated measurements of the transmitted laser pulses. To evaluate the energy deposition as a function of the incident pulse energy and material doping concentration (from 10^13 to 10^18 cm-3), we measure the depletion of the excitation beam with an integrating sphere. For low energy pulses (<1µJ), we find measurable nonlinear absorption (10%), but negligible dependence on the doping concentration. This result is similar to those obtained in a previous work in the femtosecond regime. It suggests that, for low energy pulses, two-photon ionization is the main nonlinear absorption mechanism. At higher energies, we find that the damage threshold decreases when the level of doping increases. This result suggests a negligible role of two-photon absorption and a predominant role of a mechanism related to doping for energy deposition leading to material modification.

Resume : This work is dealing with the use of a femtosecond laser beam for cutting multilayer substrate used in back-end energy harvesting applications, without shrinkage and or lateral damage. The beam parameters, as repetition rate, mean power, process speed and number of passes are investigated for optimizing the scribing in regard to the groove depth, the HAZ, and whole process time. The stacked materials are PET with adhesive deposited on alumina and fixed within a liner, used just a way to handle the stack without adhesive damage. Due to the ultra-short pulse duration (Ti:Sapphire beam, 800 nm,100 fs) the expected affected zone should be much less than thicknesses even increasing the beam energy dose. This last point is crucial to achieve a fully industrial process with high reliability. The best working point is achieved with a beam focus on the top of surface at the maximum frequency (1000 Hz). Systematic investigation of the groove depth versus laser beam parameters is finally discussed in this paper leading to the optimization of such industrial process.

Resume : Molecular dynamics simulation was used to investigate laser heating and ablation of aluminum into vacuum using nanosecond pulses. The target in the form of a parallelepiped with dimensions along x,y,z axes of 37x37x450 nm yelding 17.8M particles, was uniformly irradiated from the end. As an energy source we used top hat laser pulse with the intensity G=100-350 MW/cm2 and duration of 3 - 5 ns. With the given parameters of the simulation, the modeling made it possible to establish the 4 regimes of material removal: one slow regime - surface evaporation and three high-speed regimes - phase explosion (volumetric boiling), spinodal decomposition and supercritical expansion. Surface evaporation corresponds to G ~ 100 MW/cm2. The volume evaporation mechanism is realized in the region of 150 MW/cm2 where thin films are periodically detached at the side of the irradiated target with positive pressure in the subsurface region. As G rises in the same regime of phase separation, sets of nanoparticles of 5-7 nm size are observed. The ejection of nanoparticles is periodic throughout the nanosecond duration. Further growth of G to 300 MW/cm2 leads to a decrease of nanoparticle size and the gradual transition to the regime of spinodal decomposition, characterized by a lack of clear boundaries for all fragments in the sub-critical parameters. For G over 300 MW/cm2, the material removal takes place in supercritical expansion regime. Acknowledgements: This work was supported by RSF grant № 15-11-00032.

Resume : Molecular dynamics simulations performed on the basis of a hybrid continuum - atomistic model [1], was used to study the mechanisms of ablation of the metal (Al) film during unsteady pico - nanosecond laser irradiation. The temporal form of laser pulse was chosen to be a Gaussian curve. Among the studied mechanisms were surface evaporation, mechanical spallation, explosive boiling, spinodal decomposition and supercritical expansion. The boundaries for different mechanisms of ablation were determined in the variables (duration, fluence) and (duration, intensity). Such regimes of ablation of aluminum film under the influence of continuous laser radiation were considered in [2,3]. Account of the effects of unsteadiness showed the presence of several mechanisms of ablation changing into each other within a single pulse. Acknowledgements: This work was supported by RSF grant № 15-11-00032. Literature 1. C. Wu, L.V. Zhigilei Microscopic mechanisms of laser spallation and ablation of metal targets from large-scale molecular dynamics simulations Applied Physics A 114 (1), 11-32 (2014) 2. V.I.Mazhukin, A.A. Samokhin, M.M.Demin, A.V.Shapranov. Modeling of nanosecond laser vaporization and explosive boiling of metals. Mathem. Montisnigri. 29, 68 - 90, (2014) 3. V.I.Mazhukin, A.A. Samokhin, M.M.Demin, A.V.Shapranov “Explosive boiling of metals during nanosecond laser pulse action” Quantum electronics 44, p. 283 (2014)

Resume : The aim of this study was to obtain improved coatings for surfaces with increased biocompatibility and resistance to microbial colonization and biofilm formation. The prepared magnetite nanoparticles functionalized with gentamicin (Fe3O4@G) have been embedded into poly(lactic-co-glycolic acid) (PLGA) nanospheres by oil-in-water emulsion. The PLGA- Fe3O4@G nanospheres were deposited on the surface of glass and silicone samples by Matrix Assisted Pulsed Laser Evaporation (MAPLE). The thin films were analyzed by High Resolution Transmission Electron Microscopy (HR-TEM), Scanning Electron Microscopy (SEM) and Infrared Microscopy (IRM). The antimicrobial and antibiofilm efficiency of the thin films was tested on Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) clinical strains by viable cells counts assay performed at different time intervals. The obtained results proved that the thin films based on PLGA-Fe3O4@G nanospheres exhibited an efficient antimicrobial activity against both adherent and sessile bacterial cells. Besides their excellent anti-adherence and antibiofilm effect, the obtained MAPLE-deposited thin films were highly biocompatible, allowing the normal development and growth of cultured human endothelial cells. This approach could be successfully applied for the optimization of medical implants surfaces in order to control and prevent microbial colonization and further development of biofilm associated infections.

Resume : Au nanoparticles (NPs) exploit local surface plasmon resonance (SPR) response in the visible region, making them of great interest in different fields. Femtosecond (fs) pulsed laser deposition (PLD) is a powerful tool to synthesize NPs by direct ablation from bulk targets, which allows a uniform coverage of flat and patterned substrates with good adhesion. In this work, we aim at studying the influence of the laser fluence on the crystalline nature of the NPs as ejected from the target, using high resolution transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Moreover, the optical and morphological properties of the deposited samples have been analyzed by atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical spectroscopy. The Au NPs have been deposited by a KrF excimer laser (λ=248 nm, τ=500 fs, repetition rate 10 Hz) at different laser fluences, (from 0.1 to 3.0 J/cm2) and number of pulses (500-5000), on <100> Si, silica and Cu TEM grids. The analyses show a dense and uniform coverage of the substrate surface, and a dependence of the NPs size distribution, crystallinity and density on laser fluence and number of pulses. The optical characterization of the Au NPs on glass substrates shows the typical localized SPR peak. The experimental results demonstrate successful tuning of the SPR and are interpreted and related to the basic dynamics of the ejection process.

Resume : In the last years, using lead-free (Ba1−xCax)(ZryTi1−y)O3 (BCZT) piezoelectric materials became a key point strategy for replacing piezoelectric and ferroelectric materials containing toxic elements in different applications. Although there were envisaged various studies of lead-free BCZT for sensoristics domain, its specific characteristics such as superior piezoelectric properties makes it an interesting candidate for electrically stimulated implant designs. However, there are few data regarding interactions of various cells with BCZT coatings. Within this context, our approach is to explore the biocompatibility properties of BCTZ coatings using three different cells lines. The coatings were obtained using Matrix Assisted Pulsed Laser Evaporation method. This method allows the use of different types of substrates from flexible kapton to biocompatible metallic alloys due to low deposition temperature. Starting from a frozen target of nanopowders of BCTZ 45 composition and methanol, thin films of BCTZ 45 have been obtained on Pt-coated kapton substrates. The cell proliferation studies suggest that BCTZ 45 material led to an increase proliferation level compared to borosilicate glass coverslip irrespective of the cell line tested. The immunofluorescence study shows that the cell lines used in our experiment adhere on BCTZ45 material and display normal morphology on both glass coverslip and BCTZ45 material.

Resume : The epitaxial thin films of lead free (Ba1−xCax)(ZryTi1−y)O3 (BCZT) with compositions around morphotropic phase boundary (MPB) were deposited using pulsed laser deposition method (PLD). Single-crystalline substrates with different crystallographic characteristics have been used to promote different strain conditions into the films. The properties of the strained BCTZ thin films were investigated with various techniques such as XRD, AFM and HR-TEM for morphology and crystallinity characterization. The enhanced piezoelectric switching of the films was probed by piezoforce microscopy, by writting and reading domains during topography scanning. The dielectric spectroscopy measurements have shown very high in-plane dielectric permittivity (e’~3000) and low dielectric loss (tand<0.01) values for (Ba1-xCax)(ZryTi1-y)O3 strained thin films as compared with the relaxed ones.

Resume : We report on the optical and electrical properties of epitaxial strontium barium niobate (SrxBa1-xNb2O6- SBN) and Ca- doped SBN thin films obtained by pulsed laser deposition on different substrates. The microstructure, morphology and stoichiometry were studied by XRD, AFM, SIMS, SEM and TEM. The XRD and HR-TEM analysis evidenced the formation of c-oriented SBN and Ca-doped SBN thin films. As a function of Ca doping level, the pyroelectric and the birefringence behavior as well as the electro-optic coefficient (r33) of the thin films have been measured by reflection-type spectroscopic ellipsometry method, using coplanar electrodes. The maximum measured change of the refractive index is Δn = -0.00846 for Ez=25 kV/cm, leading to a value for the electro-optic coefficients r33 of about 40.5 pm/V.

Resume : Organic heterostructures with poly(3-hexylthiophene) (P3HT) and fullerene (C60) thin films were prepared by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) tehnique on AZO/glass substrate deposited by Pulsed Laser Deposition (PLD). Al:ZnO (AZO)/glass substrate was used in order to replace the indium tin oxide (ITO) in some kinds of applications as organic phtovoltaic cells (OPV) and organic light emitting devices (OLED). Optical (UV-VIS, FTIR and PL spectroscopy) and electrical properties of the obtained heterostructures were investigated in relation with the structural (X Ray Diffractions -XRD) and morphological (atomic force microscopy-AFM and scanning electron microscopy-SEM) properties. I-V characteristics of (AZO/P3HT/C60/Al and AZO/P3HT:C60/Al with P3HT:C60 in different proportions) structures were recorded in dark and under the illumination with a solar simulator (AM1.5) to establish which heterostructure is proper for the use in OPV. Was found that a dominant role in the electrical behavior of the investigated heterostructures has the roughness of the organic active layers obtained by MAPLE method.

Resume : The ability of processing through laser beams different kinds of metallic powders for direct production of 3D components with complex geometries has been gaining an impressive and growing attention for specific industrial applications. The process which can be distinguished as Selective Laser Sintering or Selective Laser Melting is even considered, more generally, as Additive Manufacturing where layer by layer material is built by the interaction between a laser beam and a powder bed. The rapid heating of the powder due to the laser beam energy transfer process followed by a rapid cooling rate induces within the manufactured material a cellular structure with fine sub-grains, which are in the range of few hundred of micrometers. These metastable structures, which are smaller than the grain size in conventionally manufactured 316L stainless steel components, can undertake towards a recrystallization process due to either heat or mechanical treatments. For instance when sub-grain boundaries of the cells are enriched with Mo and higher concentration of dislocation, dynamical processes occur generating local residual stresses. In these circumstances the segregation of Mo in cell boundaries is out of thermodynamic equilibrium conditions so that microstructures and phases are metastable. In the range of 1100°-1400°C heat treatments a complete dissolution of Mo in the Fe matrix with a gradual disappearance of sub-microns cell is observed feeding the growth of larger austenitic sub-grains formation. It follows a higher degree of Mo dissolution in the material matrix and a decrease of dislocation’s concentration [1]. In the work here presented we point out the occurrence of a similar behaviour where a microstructural evolution is caused after experiencing to fatigue of 80000 cycles some door joints stainless steel 316L produced by Additive Manufacturing. A decrease of dislocation’s number, an increase of twinning due to the growth of grains and to the release of local stresses has been observed for which an important role could be played by the presence of dislocations in cell boundaries as well as oxides nano-inclusion formed in-situ during the additive manufacturing process [2]. From these outcomes it is going to be presented how the 3D components produced by additive manufacturing could change and improve their features for potential industrial applications during life cycles and enhance such a behaviour by taking carefully into account the laser parameters and its scanning speed. [1] K. Saeidi, X. Gao, F. Lofaj, L. Kvetková, Z.J. Shen, Transformation of austenite to duplex austenite-ferrite assembly in annealed stainless steel 316L consolidated by laser melting, J. Alloys Comp., 633 (2015) 463-469 [2] K. Saeidi, X. Gao, Y. Zhong, Z.J. Shen, Hardened austenite steel with columnar sub-grain structure formed by laser melting, J. Mater. Sci. Eng. A 625 (2015) 221-229

Resume : We report the single step gas-phase continuous synthesis of tin and silicon nanometric mixed oxides using CO2 laser–induced pyrolysis in oxygen-deficient environments starting from organometallic volatile precursors Sn(CH3)4 and (CH3O)3SiCH3 in the presence of ethylene laser energy transfer agent. By varying the amount of molecular oxygen introduced in the reaction zone, the ratio between SnO and SnO2 can be controlled. Thus, for lower oxidant flows, the X-ray diffractograms of the resulted nanopowders reveal that the majority phase is the tin monoxide SnO (with mean cystallite size ~ 20 nm), whereas metallic Sn and SnO2 were the minority phases. By injecting higher O2 flows, the main resulted phase was SnO2, accompanied by the reducing of the atomic carbon content. Also, by changing the tin/silicon precursor ratio we were able to tune the atomic Sn/Si ratio in the resulted powders. The obtained nanoparticles were also analyzed using TEM, EDS, SAED, Raman and FT-IR techniques. Finally, they were tested in anodic compositions for Li-ion batteries based on the fact that both Sn oxides first react irreversibly with Li resulting metallic Sn, which can further reversibly intercalate Li atoms, acting thus as material for advanced energy storage.

Resume : Lysozyme embedded into blends of polyethylene glycol (PEG) and polycaprolactone (PCL) were developed via Matrix Assisted Pulsed Laser Evaporation (MAPLE) and Dip Coating techniques for long term delivery applications. Different polymer compositions were synthesized and evaluated to optimize drug release profile from fabricated coatings. The main surface features which affect and guide cellular and bacterial adhesion like roughness (AFM), and wettability measurements were investigated. The effect of lysozyme incorporation on crystallinity of polymers, chemical composition (FTIR) and antimicrobial properties of coatings against Escherichia coli and Staphylococcus aureus were also evaluated. In vitro cell culture tests on PCL-PEG-lysozyme coatings showed appropriate viability, good spreading and normal cell morphology. The release tests of lysozyme, along with all investigations essentially signify that these biodegradable composite coatings are potential promising candidates for local protein delivery applications.

Resume : Composite nanoparticles with Fe-C-Si-O composition may provide interesting magnetic and electric properties combined with biocompatibility and appetency to capture and carry bio-active molecules. The laser pyrolysis process using an inlet with three concentric tubes and a reactive mixture containing Fe(CO)5 vapors, C2H4 and SiH4 has been studied at different gas flows, pressures and laser power densities. In suitable conditions, the CO2 laser beam transfer its energy via C2H4 and SiH4 sensitizers mixture to the Fe(CO)5 vapors, triggering their decarbonylation with the formation of Fe based clusters. Then, by the SiH4 and/or C2H4 decomposition on their hot surfaces, nanoparticles with crystalline metallic/carbidic (Fe3C)/silicidic (FeSi2) Fe-based cores covered with disordered shells based on various combinations of C, Si and SiO2 (due to air exposure) resulted. The main crystalline phases and the mean crystallite size were determined by XRD. The nanoparticle sizes their elemental compositions were evaluated by electron microscopy analyses. The samples with a high Fe content (~30 at%) provide a high saturation magnetization (up to 60 emu/g) and they were subject for aqueous/PBS based dispersions. Stable dispersions with 75 to 150 nm hydrodynamic diameter were obtained using L-3,4-dihydroxyphenylalanine (L-Dopa) or sodium carboxymethylcellulose (CMCNa) as stabilizers. The nanoparticles cytoxicity and the effect on cells proliferation were investigated using different concentration of nanoparticles in PBS suspension uploaded into cellular media culture. Optical observation and hyperspectral characterization of nanoparticles in-situ were used to illustrate the nanoparticles incorporation in cells.

Resume : The refining of liquid steel composition in separate ladles under vacuum or a controlled atmosphere is referred to as secondary metallurgy. To fine-tune the final composition of the elaborated steel, current practice is to remove a sample of molten material for off line elemental analysis. There are two major problems: first, by sampling the material off-line, the process comes to a halt while the sample is analyzed. Secondly, if alloying materials were added and the melt was not sufficiently mixed, the composition may be inhomogeneous and changes decided on the basis of the analysis results of one particular sample may not bring the processed steel into desired specification. These issues could lead to excessive melting time, quality control problems, wasted feedstock, increased energy use and high CO2 emissions. The goal of this study is the testing and optimizing the performances of LIBS technique as a potential tool for implementing real time and in-situ analysis of steel composition. We propose the elemental analysis of the aerosols evacuated in the vacuum lines and filters, from a furnace running a vacuum degassing process. For the sake of simplicity, we analyzed the aerosols collected on solid substrates located at several positions on the vacuum line, as well as the filters of the vacuum pumps and compare the composition against steel samples elaborated in the same cycle. Based on the obtained results we identified the chemical elements that are presented in aerosols and steel. Based on this information it is expected to infer the chemical composition of the liquid steel from the measurement of aerosols evacuated through the vacuum pump lines. The LIBS results were compared with ex-situ complementary measurements by ICP-OES and -MS, and SEM-EDAX to infer the liquid steel composition.

Resume : Laser Induced Breakdown Spectroscopy (LIBS) technique has proven its ability to perform chemical maps on surfaces of numerous materials [1]. In addition, thick layered samples of different nature were characterized by LIBS using the conventional approach based on intensity profiles combined with the correlation method. The results revealed that, without using any normalization, the comparison of LIBS spectra through the linear correlation coefficient gave an improvement of the depth profile quality and the interface localization by minimizing the influence of fluctuations and decay of signals in the global intensity of spectra, caused by sources other than concentration variations. In this work, the capability of linear correlation for three dimensional mapping by LIBS has been studied. At this regard, a previous software that allowed the calculus of linear correlation coefficients and its representation in the format of depth profiles [2] has been improved to calculate these linear correlation coefficients and to display them in form of lateral distributions and depth-profiles. Furthermore, a new software has been developed in order to combine both, lateral distributions and depth-profiles, thus providing a representation of the linear correlation coefficients in the format of 3D maps. References: 1 V. Piñon, M.P. Mateo, G. Nicolas, Laser-Induced Breakdown Spectroscopy for Chemical Mapping of Materials, Appl. Spectrosc. Rev. 48 (2013) 357–383. 2 M.P. Mateo, G. Nicolas, V. Piñon, A. Yañez, Improvements in depth-profiling of thick samples by laser-induced breakdown spectroscopy using linear correlation, Surf. Interface Anal. 38 (2006) 941–948.

Resume : A successful functionalization of gold nanoparticles for in vivo applications implies the possibility of maintain its optical properties without affecting its cytotoxicity. Here we synthesized colloidal gold nanoparticles by using laser ablation in liquids. This is a technique that provides the possibility of one-step method for the production of functionalized nanoparticles. By using a Nd:YAG laser (1064 nm, 10 ns and 60 mJ) we synthesized Au NPs functionalized with POSS-thiol in biocompatible solvents like vegetable oils (Soybean oil, Olive Oil and Sunflower seed oil). The modification of the final plasmonic response as function of the solvent as well as the POSS-thiol concentration is presented. The morphology and the distribution of the functionalized NPs on the POSS-thiol chains were obtained from electron microscopy. Pulsed photoacoustic technique was used to study the synthesis process in-situ. Citotoxicity effects of our colloidal solutions were studied in buccal cell culture. The present work explore the viability of using POSS-thiol Au NPs functionalized fabricated through laser ablation with vegetal oils solvents for in vivo applications

Resume : The organic heterostructure with mixed active layer represents an alternative to bi-layer heterostructure showing improved exciton dissociation and charge carriers transport. The performances of this type of solar cells can be enhanced identifying new donor materials and optimizing the preparation method of the active layer. This paper presents some studies on the organic layers prepared from a mixture of an oligoazomethine (p type conduction) and a fullerene derivative, [6,6]-phenyl C61 butyric acid butyl ester/[C60]PCB-C4 (n type conduction), blended in 1:1 and 1:2 ratios. The new donors are characterized by a central unit of 2,5-diamino-3,4-dicyanothiophene and electron donating triphenylamine or carbazole groups at both ends and the selected acceptor [C60]PCB-C4 shows an increased solubility resulting in improved film morphology with effect on the properties. The mixed layers have been deposited on Si, glass, glass/ITO substrates by matrix-assisted pulsed laser evaporation (MAPLE) using chloroform and dimethyl sulfoxide as solvents, and the radiation =248 nm of KrF* excimer laser. Details about the structure and morphology have been obtained by XRD, AFM and SEM emphasizing the effect of the composition and solvent. Spectroscopic methods (UV-Vis, PL, FTIR) and I-V measurements in dark and under illumination have confirmed that these mixed layers prepared by MAPLE are adequate for solar cells applications. We have evaluated the parameters for solar cell structure realised with each type of mixed layer, identifying the structure showing the highest photovoltaic effect.

Resume : Models of thermodynamic properties and phase transformations of materials are required for numerical simulations of processes of intense pulsed influences on condensed media. In the present work, an equation of state for sodium chloride is proposed with taking into account the polymorphic transformations, melting and evaporation effects. As distinct from the previous multiphase equations of state, new expressions for the thermodynamic potentials are formulated. Those provide for a more correct thermal contribution of heavy particles in the liquid phase under rarefaction. A critical analysis of calculated results is made in comparison with available experimental data for sodium chloride over a wide range of densities and temperatures. Presented equation of state may be used efficiently at modeling of intense laser-material interactions.

Resume : The most encountered problems associated with Ti implants failure occurred at the metal-body interface. In order to reduce their number and improve the mechanical and chemical stability of this interface, the Ti surface is usually coated with a biocompatible thin film. We deposited mixtures of ZrN, ZrC, TiN, TiC and SiC films on highly polished Ti samples by a combinatorial pulsed laser deposition technique to investigate the role of the structure and composition on their properties. The mechanical properties of the films were characterized by nanoindentation, scratch and wear tests. The structural properties were investigated using the grazing incidence X-ray diffraction and X-ray reflectivity measurements. The chemical composition, density and thickness were extracted by modelling Rutherford backscattering spectra acquired with 2.2 MeV alpha particles. Electrochemical measurements involving corrosion and electrochemical impedance spectroscopy studies were carried out in physiological solutions at room temperature to evaluate the chemical stability of the titanium, bare or covered with the PLD grown films and to compare their performance. The results showed that the deposition of protective coatings resulted in more stable surfaces that were less affected by corrosion and exhibited better mechanical properties than bare Ti.

Resume : The laser impact induces the Raman scattering from the two film-components simultaneously with the conversion of PAcis into PAtrans. The total Raman-Stokes scattering from two pertinent bands (1248 cm-1 from PAcis and 1110 cm-1 from PAtrans), was measured simultaneously taking advantage of multichannel technique. The laser beam power P(?) is equivalent to the temperature T of isotherm i of isomerization reaction. The laser beam axis was normal to the PA- film surface and the retro- Raman scattering was collected. We elaborate a numerical model reproducing the Raman experiment within 5 % error. The rate constants, activation energy values, Arrhenius factors and linear regression coefficients are obtain with a small error. The kinetic results obtained, such as reaction orders values obtained, varying from 1/2 to 2/3, The isotherms in a time-scale of seconds were obtained for the first time and the initial rate constants k0(Pi) determined. The reaction order of 2/3 seems to be the most appropriate value in this case, since it refers to a solid state reaction propagation, where the reaction rate is controlled by a three dimensional development of active centers. The observed Raman scattering seems to obey some activated process. The temperatures of our isotherms were determined from the relationship: Ti = Eai / R/ ln (A / k0 (Pi)) , An estimate of N0 and then of fcis and ftrans was obtained. Key words: Polyacetylene, isomerization, laser, activation energies, Raman spectroscopy

Resume : Laser induced forward transfer (LIFT) constitutes an interesting alternative to conventional printing techniques in microfabrication applications. Originally developed to print inorganic materials from solid films, it was later proved that LIFT was feasible for printing liquids as well, which substantially broadened the range of printable materials. Any material which can be suspended or dissolved in an ink can be in principle printed through LIFT. The principle of operation of LIFT relies on the localized absorption of a focused laser pulse in a thin film of the ink containing the material to print (donor film). This results in the generation of a cavitation bubble which expansion displaces a fraction of the liquid around it, leading to the formation of a jet which propagates away the donor film and towards the acceptor substrate, placed at a short distance. The contact of the jet with this acceptor substrate results in the deposition of a sessile droplet. Thus, each droplet results from a single laser pulse, and the generation of micropatterns is achieved through the overlap of successive droplets. In this work we review our main achievements on the LIFT of inks, paying special attention to the analysis of the liquid transfer dynamics and to the most recent developments towards the optimization of the performance of the technique.

Resume : The organic and printed electronics field is currently motivated by the fruitful prospect of low- cost and large-area processing on flexible substrates for industrial applications such as sensor arrays or radio frequency identification (RFID) tags. Technologies compatible with solution processing which are also suitable for direct patterning of the critical layers can effectively fulfill the above requirements. In this work, we describe a versatile route based on the laser processing of both metallic and polymeric layers toward the fabrication of organic diodes on flexible foil. The patterning of the devices was performed by selective ablation using sub-ps laser operation at 1030 nm or 343 nm, while the top electrodes (Ag-ink) were formed by laser-induced forward transfer (LIFT) method. The active layer of the diodes consisted of a high mobility p-type polymer [diketopyrrolo-pyrrole-dithiophene-thienothiophene (DPP-DTT)], was deposited under ambient conditions via various solution processes. The morphological characterization of each layer along with the investigation of the effect of the device geometry and the film properties (i.e., thickness, roughness) of the semiconductor on the electrical behavior of the devices, are some critical aspects thoroughly discussed/studied herein. Remarkably, the resulting devices exhibited excellent electrical performance with high current density (10-3 to 10-2 A/cm2) and low threshold voltage (< -1 V). These results clearly demonstrate the potential of the proposed approach for its facile implementation to large-area processing toward the realization of low-cost organic RFID tags.

Resume : The recent proliferation of metal inks for inkjet and screen printing means that potential catalysts for electroless copper deposition are widely available. Laser printing of these catalysts could be a flexible, rapid and high-resolution method of patterned deposition for high-resolution additive manufacturing of highly-conductive metal tracks. Successful integration of laser-induced forward transfer (LIFT), for the deposition of metal catalysts, and subsequent electroless copper deposition is demonstrated here. Different catalyst precursors for LIFT have been used, both liquid and solid phase, and copper, silver and palladium. The adhesion of the different catalysts to glass and printed circuit board (PCB) composite fibreglass substrates is analysed, and copper has been deposited via electroless chemical deposition, and the speed of deposition examined closely. The possibility of integrating the LIFT process into an electronics manufacturing system is also analysed closely, and compared with competing technologies, including lithography, inkjet and screen printing.

Resume : Laser-induced transfer (LIT) covers a family of techniques for rapid prototyping of photonic, electronic and biomedical devices. These methods allow the fabrication of structures (voxels) involving sensitive materials, do not require a specialist environment and can even preserve the phase of a material in the final device. During LIT, the energy of a laser pulse is exploited to delaminate and eject a voxel, from of a thin film coated onto a carrier substrate, with the end goal of incidence and adhesion onto the desired receiver. Among these methods, laser-induced backward transfer (LIBT) is a process where a transparent receiver is traversed by the incident laser pulse, and an absorptive bulk material (here: silicon) acts as carrier. The choice of a bulk carrier facilitates structuring of the interface between donor and carrier before transfer. For intact solid transfer, these structures will then be imprinted onto the resulting voxel, and our initial results have shown that feature sizes down to ~150nm are capable of surviving the LIBT process. Here, we show our work on LIBT of transparent polymer layers via an image-projection based digital micromirror system for additional spatial structuring of voxels on the micron-scale. Experiments were carried out with the help of a 150fs pulse length, 800nm wavelength laser. We show our progress in defining the smallest surface feature sizes for carrier-imprinted voxels, leading to potential application in photonic devices.

Resume : The synergistic combination of optics and fluids offers interesting opportunities for enhanced laser fabrication at the micro and nanoscales. Here, I will present a key example of how fluids can help overcoming the traditional diffraction barrier of a laser-direct write system and enable deep sub-wavelength laser nanopatterning. This novel approach, termed droplet-assisted laser nanopatterning (DALP)1, is based on the LIFT printing of micro-droplets at userdefined positions on the surface to be patterned. By carefully controlling the wettability properties of the surface – it can be as simple as using an appropriate coating – a 90° contact angle between liquid and surface can be achieved. In this way, droplets can be used as hemispherical lenses, or in other words, as the liquid version of a solid immersion lens (SIL). In fact, contrary to the timeconsuming and difficult fabrication process characteristic of micro-SILs, surface tension provides these spontaneously formed droplet lenses with perfect optical quality. Notably, the focusing capabilities of the laser system used to print the droplets can be then further enhanced by using droplet lenses. Indeed, laser pulses focused through these lenses experience a reduction in spot size primarily limited by the refractive index of the liquid. This all-optics approach is demonstrated by writing arbitrary patterns with a feature size of about 280 nm, less than one fourth of the processing wavelength.

Resume : Spatial structuring of laser light radiation is crucial at the microscale and for laser micromachining applications. Common beam configurations are well suited for subsurface microprocessing of dielectric materials. However, they lack some distinctive features of non-diffracting beams. Non-diffracting beams and dispersion-less wavepackets possess abilities important for micromachining: resistance to diffractive and dispersive spread, self-healing. The ability of a superposition of non-diffracting beams to instantly self-focus at a given position and time moment is especially interesting when looking at structured light as a tool. Bessel, Mathieu and Airy beams are targeted by several groups worldwide as a flexible tool for microfabrication of glasses and other materials. Moving to the nanoscale, the polarization state of the light becomes an important variable for nanostructuring of the light. We report on a novel type of vector Bessel beam that has a spherical 3D doughnut embedded in its distinct focal line. We analyze possibilities to control the curvature of produced 3D doughnut and discuss the far-field structure of such vector beams. A discussion on possible experimental implementations is also presented.

Resume : There is increasing interest for patterns and structures on surfaces at the micro- and nano-scale. Femtosecond laser surface structuring with Gaussian beam s has already distinguished itself as a versatile method to fabricate surface structures on metals and semiconductors. In this communication, we report on femtosecond laser surface structuring with an optical vortex (OV) beam with different spatial distributions of the state of polarization (SoP) carrying an orbital angular momentum ℓ =± 1. The laser source is a Ti:Sa laser system delivering linearly polarized ≈35 fs pulses at 800 nm with a Gaussian beam spatial profile, at a repetition rate of 10 Hz. The OV beam is produced by a q-plate and focused onto the target, mounted on a computer-controlled XY-translation stage, at normal incidence. An electromechanical shutter controls the number of laser pulses, N, irradiated on the target surface. The morphological modifications of the irradiated surface are studied by using a field emission scanning electron microscope. Different SoP of the OV beam are used to demonstrate the fabrication of several regular surface patterns on silicon and copper targets. The spatial features of the surface structures are correlated with the SoP of the OV beam, addressing the similarities and differences observed for the two different targets. The threshold fluence for the generation of the regular structures (ripples and grooves) and its dependence on N is determined and discussed.

Resume : The phenomenon of surface wettability has a strong impact in a wide variety of sectors like chemistry, biomedicine, textile, naval or aerospace, where metallic corrosion, surface lubrication, or heat transmission, have important economic, functional and structural implications. In the last decades a great research effort has been done to develop new techniques or improving existing ones, in order to change the surface wettability of different materials. In particular, the study of the behavior of surfaces with water has a great interest due to the large number of processes where such liquid take part. The classical techniques, like stamping, EDM or micromachining, have limitations to satisfy the increasingly demanding requirements of wettability. In this work a laser based technique has been used to change the wettability of metallic materials (AISI 304 stainless steel and 2024 aluminum alloy). Experiments were conducted at three different irradiation wavelengths (λ=1064, 532, and 355 nm) using pulsed lasers in the nanosecond regime. A statistical factorial design of experiments was used to find the effects of main processing parameters apart from wavelength: laser power, pulse frequency and scanning speed. A systematic study was carried out through a set of laser micro-texturing experiments in order to apply different patterns over the surface of the samples. Suitable laser processing conditions were identified to produce superhydrofobic and superhydrofilic surfaces.

Resume : Advanced gas-turbine engines need new materials with enhanced properties in terms of protection against oxidation and decrease permitting their use at higher operating temperature. The excellent combination of light-weight and good mechanical properties makes the Ti alloys attractive for compressor section components in gas turbine engines [1]. Titanium offers the potential for component weight savings in the order of up to 50% compared to super alloys of Ni and steels. In last years, laser surface processing has been used in industry and in research laboratory for improving tribological properties of Ti alloys (corrosion, wear and/or fatigue resistance) [3-5]. Indeed large compressive stresses as well surface hardening induced by mechanical process as shock laser seem to play a positive role in the oxidation resistance of materials. This behaviour is observed on pure Zr [6]. In this study, an experimental campaign led on commercial pure Ti is carried out to understand the impact of laser shock as a protection against oxidation at high temperature. Laser-peened specimens are compared to untreated samples in terms of oxidation behaviour at high temperature (700°C) in dry air. Specimens were evaluated for their oxidation resistance by TGA and subsequently, by several techniques SEM/EDS, NRA, XRD (phase and residual stress) and Raman spectroscopy. We show that the laser peening substantially reduces the mass gain and prove the presence of N between oxide and alpha-case layers. [1] J-P. FERTE, Techniques de l'Ingénieur, doc. number BM7778 (2006) [2] J. STRINGER, Acta met. 8 (11) (1960) 758-766 [3] M.C. Marco de Lucas, L. Lavisse, G. Pillon, Tribol. Int. 41 (2008) 985–991 [4] R. Kaul, K. Ranganathan, O.S.M.L.M. Kukreja, Tribol. Trans. 55 (2012) 615–623 [5] R. Fabbro, P. Peyre, L. Berthe, X.J. Scherpereel, Laser Applications, 10(6) (1998) 265-279 [6] V. Optasanu, P. Jacquinot, T. Montesin, Adv. Mat. Res., 996 (2014) 912-917.

Resume : 3D structured Silicon (Si) has widely been used in many fields such as semiconductor industry, micro-fluidic systems, or Micro-electro-optical-mechanical-systems (MOEMS). Using recovered Si powder from wafering in selective laser melting as an additive manufacturing process, 3D functional Si systems can be built. Especially for the fabrication of small numbers of protrusions on Si wafers, long etching times and spoiling of crystalline silicon could be avoided. Therefore, the present study examines the possibility of consolidating micron-sized Si powder into macroscopic structures by laser irradiation. Morphology, crystallinity and impurities of the powders before irradiation are characterized by SEM, DTA, XRD, Raman spectroscopy, and ICP-OES. We investigate the interaction of laser beams with powder layers with thicknesses ranging from 1 to dozens of microns deposited by sedimentation on fused silica and silicon wafers. The optical properties of the powder layers are probed by UV-vis-NIR spectroscopy. These layers are then irradiated by varying several process parameters such as frequency and shape of temporally modulated laser intensities from pulsed lasers to continuous wave lasers, scan speed, laser wavelength, spot size, and overlay. The influence on structure, morphology and microstructure of the exposed areas are investigated with optical and confocal microscopy, as well as SEM. Their mechanical stresses and crystallinity are investigated.

Resume : The use of laser beam to joining dissimilar metal has been considered to applications in structural components of aircrafts. A common phenomenon involved Ti/Al joint is the presence of brittle intermetallic compound (IMC) in the interface region. The introduction of Si element in the junction region has shown significant influence on interfacial reaction mechanism, promoting the change of IMC type, depressing the growth of brittle IMC and improving the joint mechanical properties. In this work, Si was deposited on Ti-6Al-4V substrates by ionized magnetron sputtering powered by 300V/90mA DC and 50W RF sources with work pressure of 0.6 Pa and argon ambient, and deposition time between 1 h and 2 h. After, Ti-6Al-4V and AA6013 sheets were joined by a Yb:fiber laser welding system. Butt joint conditions were maintained constants (laser average power, 1200 W, process speed, 3.0 m/min, and laser offset toward Al alloy, 0.3 mm). EDS line scanning evaluated the elemental distribution at the joint interface with and without the introduction of Si. A decreasing of intermetallic layer is observed in joints with Si film deposited on the Ti-6Al-4V when compared to welded joint without Si. The thickness of interfacial IMC layer, formed by TiAl3, with Si film is about five times lower than the interfacial IMC layer of welded joint without the film, reaching the mean value of 2 µm. Further studies will associate the results to influence of IMC layer on the fracture behavior of the joint.

Resume : Layerwise laser cladding of the Fe and Al dissimilar alloys is important for the aerospace and automobile industries where serious difficulties are caused by the high brittleness of the intermetallide phases generated in the melting pool. On knowing the succession of the phase-structural transformations in the laser cladding (welding) joint, it is possible to attain the fabrication of such a barrier layer of the alloying elements, that is capable of wetting the joining alloys on the basis of iron and aluminium, protects them from the contact during the melting and prevents the formation of undesirable phases. The objective of the present study is to demonstrate the possibility to control physical properties and cracks formation of the graded structures in the iron and 2024 alloy powders (both TLS Co.) via laser cladding process. Element dissolution behavior, microstructure, phase constitution and mechanical properties of the aluminide reinforced iron matrix were investigated by SEM, XRD, TEM and microhardness measurement.

Resume : Mn doped III-V dilute ferromagnetic semiconductors (DFS) are of great interest in recent decades due to their potential for spintronics [1]. However, the low solid solubility of Mn in III-V semiconductors prohibits the common equilibrium preparation process. For long time, the low-temperature molecule beam epitaxy (LT-MBE) has been the only method to obtain DFS. The technical challenges in LT-MBE result in the fact that GaMnAs (and its alloys with low concentration of phosphorus or indium) is the only available DFS. In our work, making the full use of ion implantation combined with pulsed laser melting, we have extended the family of Mn doped III-V DFSs. All specimens exhibit the epitaxial structure and pronounced uniaxial magnetic anisotropy. Particularly, we have prepared InMnAs with both high Curie temperature and perpendicular magnetic anisotropy, which is difficult to prepare by LT-MBE due to many n-type defects [3], as well as GaMnP [4] and InMnP [5] which have only been prepared by ion implantation up to now. When compared with LT-MBE, this approach combining ion implantation and pulsed laser melting brightens the future of III-Mn-V DFS by two aspects: (1) Its efficiency and reproducibility make the possibility of the large-scale production in industry; (2) The introduction of new materials (GaMnP and InMnP) provides a more complete platform for understanding the DFS family. [1]. T. Dietl et al., Rev. Mod. Phys., 86, 187-251 (2014) [2]. D. Bürger et al., Phys. Rev. B, 81, 115202 (2010) [3]. Y. Yuan et al., J. Phys. D: Appl. Phys. 48, 235002 (2015) [4].Y. Yuan et al., IEEE Trans. Mag. 50, 2401304 (2014) [5]. M. Khalid et al., Phys. Rev. B, 89, 121301(R) (2014)

Resume : A reduction in size of magnets leads to an increase of the field gradient in the magnet's vicinity, while the magnetic flux density remains unchanged at a homothetically reduced distance. Recalling that the attractive magnetic force between a micro-magnet and magnetic particles is proportional to both the field and the field gradient, a micro-magnet is very well adapted to trap, position or selectively filter magnetic micro/nanoparticles. Nevertheless, the development of devices has been hindered by the difficulty of fabricating high quality magnets at the micro-scale and incorporating them into micro-systems. Based on the synthesis of high quality magnetic layer, we have reported on the development of arrays of high performance micro-magnets (NdFeB, SmCo, FePt) using a pulsed laser-based technique (Thermo-Magnetic Patterning, TMP [1]). Recently, development of specific masks using a collection of small UV-transparent particles as lens deposited by a Langmuir-Blodgett process, has allowed the realization of compact array of very small magnets (around µm). The extrinsic magnetic properties (remanence, coercivity) of the µ-magnets are comparable to high quality commercial bulk magnets. A combination of scanning µ-Hall probe microscopy and simulations indicate that these µ-magnets produce stray magnetic field gradients up to 10^6 T/m. Due to magnet quality, important applications like trapping/selection of magnetic particles [2] or cellular deformations [3] by flexible magnetic polymer tools [4, 5] are successfully demonstrated. -[1]- Dumas-Bouchiat, APL 96 (2010) -[2]- Zanini, APL 99 (2011) -[3]- Brunet, Nat. Comm. 4 (2013) -[4]- Dempsey & Dumas-Bouchiat, Patent US61/650,398 (2015) -[5]- Le Roy, Mat. Today Comm. (2015)

Resume : Small Angle X-Ray Scattering (SAXS) is a technique where a fine beam of intense x-rays from a synchrotron light source is passed through a target and the nanostructure of the target (in our case nanoparticles) is investigated by measuring the angular scattering of the x-rays. The information collected allows the particle size, state of aggregation, surface character and particle number density to be determined as a function of particle formation conditions such as surface material for ablated particles [1] and target environment [2]. The development of free electron laser sources (FELs) such as the LSLS in the US, X-FEL and FLASH in Germany, FERMI in Italy, and SACLA in Japan offers a billion times more X-Ray intensity than a 3rd Generation synchrotron (such as the ESRF or Soleil) and so one can imagine doing in-situ, single particle imaging with these machines. The application of this to the study of laser ablation plasmas will be discussed. References [1] Influence of the reactive atmosphere on the formation of nanoparticles in the plasma plume induced by nanosecond pulsed laser irradiation of metallic targets at atmospheric pressure and high repetition rate, M. Girault et al. Appl. Surface Sci. (In press 2016). [2] Oxidation-Induced Surface Roughening of Aluminum Nanoparticles Formed in an Ablation Plume, G.D Forster et al. Phys. Rev. Lett. 115 (2015) 246101

Resume : Laser materials processing of a-Si:H enables the realization of c-Si devices for display and PV applications. We have investigated the solid state crystallization process of a-Si:H applying single pulse irradiation of an amplified Ti:Sa laser (?=790nm, t=30 fs) or a XeCl excimer laser (?=308nm, t=65 ns). Although the pulse duration differs by more than six orders of magnitude and the light absorption process is based on one (ns-laser) and two (fs-laser) photons, similar results were observed. An increase of layer thickness is found for a fluence above the onset of crystallization. In contrast, thermal oven annealing results in a decrease of the layer thickness. At higher fluence surface texturing occurs. For both effects, onset of crystallisation and surface texturing the critical fluence value of the ns-laser is around 100% higher than the fs-laser value. This difference can be explained by the wavelength dependent reflection at the surface, penetration depth of the laser pulse and thermal diffusion. Depending on the fluence, Si-H dissociation, H-diffusion, local crystallization and material ablation play a significant role. The non-linear optical absorption of the fs-laser pulse leads to local absorbed energy densities for which also thermal processes dominate the crystallization. A detailed material characterisation by optical microscopy, surface profilometry, Raman spectroscopy (473, 633 nm) SEM and TEM will be presented and the crystallization behavior will be discussed.

Resume : Various excimer laser (KrF) spot sizes have been used for the production of carbon laser ablation plasma, and their effects on the plasma dynamics in vacuum (10^-6 mbar) were investigated. It was observed that at high fluences the plasma has an unusual shape, consisting in two arms with a sharp angle that remains constant during the expansion–an arrow like structure. The origin of this particular plume shape was found through the laser-created crater profile measurements and space-resolved optical emission spectroscopy (OES). Unlike for the low laser fluence regime, the laser created crater profile observed for high laser fluences presents two cavities: a first one close to the target surface, originating from a gently ablation, connected with a second narrower one, given by the focusing of the central part of the laser beam energy profile. This stepwise ablation is the first argument of the existence two colliding plasmas. From the OES measurements, it was revealed that this arrow plasma consists both in atomic and molecular species (C2). The existence of C2 molecules in high vacuum carbon plasma expansion confirms the existence of two colliding plasmas. We conclude that the energy distribution in excimer laser focalization spot plays a significant role on laser plasma dynamics.

Resume : Fast optical methods, mainly pulsed photothermal (PPT) and real time reflectometry (RTR) were successfully used for the thermo-physical characterization of numerous samples such as Ti embedded vertically aligned carbon nanotube (CNT) carpets and/or mesoporous silicon (MeSi) substrates. Those characterizations were achieved using a homemade optical device based on fast detectors. Contribution of real-time RTR to laser induced processes is highlighted through several applications with Excimer and Nd:YAG laser beams processing a high number of materials (sc-Si, sc-ZnO, Fe-C…) related either to sensor fabrication or surface properties enhancement. In addition to the surface temperature monitoring, the PPT technique, with less than 2ns response time, allows the evaluation of thermal properties of a wide range of thin film materials and typically those promising in microelectronic applications (packaging, connectic…). In this way thermo-physical properties of AlN, CNT and MeSi films will be discussed leading to predict the best materials fabrication process for a targeted application. As reducing the size of active surfaces, laser-based nanostructuration of copper thin films as well as MeSi was also successfully monitored using RTR at the picosecond scale. This last topic is also illustrated in correlation to thin films thermoelectric properties, particularly in the case of oxides and polymers films. Description of setups design will be finally detailed.

Resume : By focusing infrared ultrashort laser pulses (1.3 µm at 60 fs, FWHM) in the bulk of silicon (Si) with a microscope objective (NA 0.3), we create microplasmas by two photon absorption (TPA). We study the characteristics of energy deposition by imaging the focal volume and the free electron-hole plasma in 3D by pump-and probe experiments. Our integrated measurements highlight a severe limitation to the energy density that can be delivered in the bulk of Si at levels preventing any permanent modifications of the bulk material. At the energy of 27 nJ, we find that only 25% of the incoming pulse is delivered at the geometrical focus and the maximum achievable fluence of 40 mJ cm-2 is delivered. Any attempt to deliver more fluence by increasing the incoming energy has failed. When probing the focal volume with delayed probe pulses, we measure the space-time evolution of the free-carrier density distributions created by TPA. This relies on infrared transmission microscopy images and the Drude model to retrieve the density of free-carriers. According to the limitation of the delivered fluence, we find a clamping of the free-carrier density at 4 10^19 cm-3, that is significantly below the critical density of Si at 1.3 µm (6.6 10^21 cm-3). Interestingly, we observe on a nanosecond timescale a spatial spread of the produced microplasmas by electron diffusion. Numerical analyses of the images using the electron rate equation allow us to report the measurement of the ambipolar diffusion coefficient at high-injection levels that would be hardly possible by using other methods. We find a diffusion coefficient D_a of 2.5 cm^2 s^(-1) and an effective carrier lifetime τ_eff of 2.5 ns in bulk Si at room temperature.

Resume : Many modern industrial, medical, and conservation scientific applications require rapid qualitative and quantitative stratigraphic analyses of metal coatings. One promising option to achieve this is Laser-Induced Breakdown Spectroscopy (LIBS). In order to make such applications possible, detailed investigation of ablation and emission behaviour is a major task. This study used Nd:YAG lasers emitting at 1064, 532, 355 and 266 nm for the systematic ablation analysis of a galvanically deposited Ni-Co alloy layer (20% w/w Co, layer thickness 20 µm). The resulting plasma emission data were converted into stratigrams [1] employing the linear correlation coefficient method [2]. These were then used to determine the effective absorption coefficients [3], which were compared to theoretical estimations [4]. This approach allowed a systematic insight into both the influence of heat diffusion in the sample and laser-plasma interactions on the ablation rate. [1] T. O. Nagy, U. Pacher, H. Pöhl and W. Kautek, Appl. Surf. Sci. 302 (2014), 189-193 [2] M. P. Mateo, G. N. Costa, V. Piñon and A. Yañez, Surf. Interface Anal. 38 (2006), 941-948 [3] J. Krüger, W. Kautek, Adv. Poly. Sci. 168 (2004), 247-289 [4] E. Matthias, M. Reichling, J. Siegel, O. W. Kaeding, S. Petzoldt, H. Skurk, P. Bizenberger and E. Neske, Appl. Phys. A 58 (1994), 129-136

Resume : Laser Induced Breakdown Spectroscopy (LIBS) has been demonstrated to be a potential technology to detect materials at different depths from a multi layered sample. Femtosecond lasers along with suitable collection optics and spectrometer provide an efficient capability to distinguish emissions from thin layers with minimal damage to the sample. The present study deals with developing an optimized technique to characterize organic photovoltaic devices during selective laser scribing in stacks of layers with a thickness of 100's of nanometers. We have carried out LIBS measurements on a sample composed of top electrode (opaque or transparent), organic layer, bottom electrode, barrier layer and substrate layer situated from the top consecutively. A 40 fs Ti:Sapphire laser with very low pulse energy was used for excitation in combination with a spectrometer coupled with an ICCD for spectral detection of the laser induced plasma. Consecutive laser probing on a fixed location, acquiring spectral signatures from each individual laser ablation event was carried out during the process. The result established that different layers of the organic solar cell could be distinguished by their specific characteristic emission lines. Therefore spectroscopic detection and monitoring is possible along with selective ablation in real time. This project has received funding from the European Commission, Horizon 2020 Research and Innovation Action, in the framework of the ALABO project, Grant agreement No 644026 and under the scope of the International Associated Laboratory (LIA) MINOS between LP3 and IESL-FORTH.

Resume : Laser marking is a well-established technology in industry; however there are still issues where the marking process itself needs to be investigated. The passivation layer of stainless steel can be easily broken by laser treatment and in long time use of a marked component there can be problem with low material resistance to corrosion. For this reason we present a study of temperatures reached by different parameters of laser marking and their correlation with corrosion tests performed on marked samples. The marking was done using nanosecond pulsed fibre laser with variable pulse duration (from 9 to 200 ns), repetition frequency and pulse energy. Similar marking was obtained by different parameters but different corrosion resistance was observed and it correlates well with maximum temperatures reached in the laser spot, which varied from less than 1100°C to more than 1800°C. From the results it can be concluded that combination of longer pulse duration and higher repetition rate are the most suitable parameters for preserving of corrosion resistance of stainless steel after laser marking.

Resume : Cu2ZnSnS4 (CZTS) is a promising chalcogenide material for photovoltaic applications due to its band gap of around 1.5 eV, which is close to the optimum value for a single junction solar cell. Conventional vacuum-based techniques (including Pulsed Laser Deposition-PLD) for the growth of sulfur-containing materials often require the use of highly toxic H2S gas to compensate for losses of volatile elements, i.e., sulfur during film growth. Alternatively, one can use a thermal sulfur cracker source as an environmentally-friendly and non-toxic method of producing reactive sulfur species. A sulfur cracker source provides a large fraction of reactive sulfur species, such as S2, S3 and S4, that together with the ablated species of high kinetic energy arriving at the substrate can enhance the chemical reactivity during film growth by PLD. This combinatorial approach has not been explored before and we have assessed its feasibility for the deposition of Cu2ZnSnS4 to be used as absorber layer in thin film solar cells. The growth of CZTS films was achieved by laser ablation of a metallic target of Cu2ZnSn at 248 nm in combination with the reactive sulfur beam directed at the substrate. Our findings reveal non-stoichiometric metallic films at low fluence (<0.8 J/cm2) that merges into a stoichiometric transfer at high fluence. For a given laser fluence, we will discuss the role of the chemically active sulfur species on the composition and growth temperature of the sulfurized metallic films.

Resume : Heusler compounds have composition XYZ (so called half-Heuslers) or X2YZ (so called full-Heusler). Their tuneability originates from large number of elements. This provides the opportunity to adjust electronic structure and hence material properties in many desired directions, such as: half-metallic material for spintronic applications, zero-gap topological semiconductors. The properties of Heusler alloy are very sensitive to any non-stoichiometry and crystalline defect. Simple pulsed laser deposition from alloy targets is not very suitable in case of very interesting Heusler alloys like Rh2MnBi (ferromagnets for magnetooptical and spintronics applications). The deviation of composition from stoichiometry becomes a critical problem, especially due to Bi evaporation from surface of the growing films at high deposition temperature. In our work epitaxial Rh2MnBi thin films on MgO were fabricated by pulsed laser deposition by means of special designed alloy target. The centre of the target with Rh2MnBi composition was surrounded by pure Bi metal circle. During the laser ablation the plasma composition was monitored by mass spectroscopy. To fabricate the films with required composition the focusing lens was moved by two stepper motors along the sectors of the target always keeping the same focusing distance. During this ablation also the target holder was controlled moved to keep the substrate front of the laser spot. The spatial distribution of particular metals were characterised by means of EDX analyse. The epitaxial crystalline films were growth at substrate temperature 500 °C on the MgO substrates. The compositions as well as the valence band spectra and ARPES were analysed by NanoESCA system. The crystalline structure was examined by XRD. Magnetic properties of the film on substrate were measured by vibrating sample magnetometer.

Resume : Pulsed Electron Deposition (PED) is a method of creating thin films through ablation at low pressure that has many similarities to Pulsed Laser Deposition (PLD). Key advantages of PED include lower equipment cost and higher energy efficiency. We have investigated the use of PED as an alternative to PLD for production of the new solar cell material copper zinc tin sulfide (CZTS). Measurements of the electron energy distribution of the PED pulses at different discharge voltages are compared to the composition of the resulting films and to the influence of laser fluence on film composition with PLD. There is a similar deviation from the target stoichiometry depending on the electron energy/fluence with the two techniques. Additionally, droplets occur with both techniques with a strong reduction in droplet density at low energy/low fluence. Finally the desired lattice structure of crystalline CZTS is obtained at a relatively low temperature around 300 °C with both techniques and the deposition rate for PED is at least as fast as PLD with a 248 nm excimer laser or a 355 nm Nd:YAG laser. The beam-target interaction of PED versus PLD is discussed and our results for CZTS are compared with PED and PLD of the materials ZnS and CIGS. Overall, we find that PED is able to produce films in a similar manner to PLD with both techniques requiring fine tuning of the deposition parameters for good-quality films.

Resume : Transitional metals carbides and nitrides have been extensively investigated as hard and protective coatings for many applications from microelectronics to nuclear industry and space exploration. The pulsed laser deposition (PLD) technique is very useful to grow thin carbide and nitride films to investigate their optical, mechanical and electrical properties. A simple control of the deposition conditions (substrate temperature, nature and pressure of the gaseous atmosphere, laser fluence, repetition rate and wavelength) will results in the deposition of films having various metal to carbon or nitrogen atoms ratios, grain sizes, texture level and stress levels. However, it has been known for many years that, besides the non-uniform thickness of the PLD grown films, there might be lateral compositional variations, which will affect the film properties. Such lateral variations will depend on the mass of the ablated atoms. We investigated the lateral variations of the chemical and elemental composition of ZrC, TiC, ZrN, TiN and SiC as typical examples of compounds containing atoms with rather different masses. In addition, since these compounds are deposited under various reactive gases we also investigated the role of the deposition atmosphere on the film composition and properties.

Resume : Pulsed Laser Deposition (PLD) was used for depositing Zinc Antinomide (ZnSb) thin films. ArF laser (193 nm) allows the preparation of native nanostructured films, useful for enhancing their thermoelectric properties. Multi-target deposition has been performed, adding different amounts of dopants to ZnSb, to verify the effect of density of states variation on the thermoelectric properties A study of structural, compositional and electronic properties of thin films is reported as a function of laser parameters and temperature with the aim to evaluate the thermoelectric performance from the determination of the dimensionless figure of merit ZT. ZnSb, besides being a non-toxic, abundant and low-cost semiconductor, results a promising thermoelectric material for the temperature range 300 - 600 K.

Resume : Ferroelectric films are intensively studied for the design of tunable devices at microwaves since their dielectric permittivity can be tuned under an external DC electric field. KTa0.5Nb0.5O3 (KTN) ferroelectric oxide exhibits one of the highest dielectric constant, and thus permittivity agility under biasing. However practical applications are still restricted due to the intrinsic dielectric loss which strongly impacts the device insertion loss. In this study, KTN thin films are grown on sapphire substrates by Pulsed Laser Deposition at 248 nm. To reduce the insertion loss, a twofold solution is investigated. The first route consists in doping KTN material with MgO (3% and 6% in mol) in order to lower its intrinsic loss. By retrieving the KTN dielectric constant from measurements, our results show that loss tangent is reduced significantly (from 0.31 to 0.13), and that permittivity is also reduced from 860 to 390 at 10 GHz after MgO doping at 6%. To further enhance the loss reduction, a process based on the KTN film structuring by laser micro-etching at 248 nm has been implemented. The high absorption coefficient (alpha>200000/cm) of KTN under the 248 nm-laser beam promotes its removal in ‘non-critical’ areas, and thereby its confinement in active regions of the devices with micrometer accuracy. Experimental results demonstrate that doped KTN confinement enables a global loss reduction by a factor of 4 while keeping up 8% frequency tunability under 70 kV/cm in 10 GHz range.

Resume : Mesoporous carbon are versatile materials with a wide range of applications, from energy storage and conversion, to sensors and drug release systems. This broad application spectrum is related to their high surface area, controllable pore size, good electric conductivity, and chemical inertness. We report on UV light irradiation of a solution consisting of green phenolic resins (phloroglucinol/glyoxylic acid) and a surfactant agent (Pluronic F127) with the view to speed up (accelerate) the polymerization rate in order to obtain mesoporous carbon. The research was conducted, in comparison, with two UV light sources: a lamp (λ=254 nm) and a pulsed KrF* laser (λ=248 nm). The lamp irradiation in a dark room reduces the synthesis time to 3 hours, while the pulsed laser, to several minutes compared to one day for the classical method. Interestingly, by tailoring the laser irradiation conditions such as energy or pulse repetition rate one can easily increase the irradiation dose and consequently reduce considerably the exposure time allowing to obtain carbon materials with different textural and structural characteristics.

Resume : Composite layers with titanium silicide are of great interest for hardness increase. Magnetron sputtering and compression plasma flow treatment were used to synthesize modified layer containing Ti5Si3 in carbon steel (0.8 wt. % C). Synthesis was carried out in two stages. First titanium (0.5 μm), silicon (1 μm) and titanium (0.5 μm) coatings were deposited on carbon steel by means of magnetron sputtering. Then this system was treated by compression plasma flow (density of absorbed energy is 25 J/cm2). XRD investigations showed that silicide Ti5Si3 had formed. Modified layer also contained crystalline silicon and titanium carbide TiC. The hardness of modified layer increased more than 2 times (from 2.8 0.2 GPa to 6.1 0.7 GPa ).

Resume : In this paper we report formation of colloidal suspension of zinc oxide (ZnO) nanoparticles by nanosecond pulsed laser ablation of high purity zinc target immersed in double distilled water. The influence of the laser wavelength on the properties of the synthesized ZnO nanostructures was examined. For this purpose four different wavelengths: fundamental wavelength (1064 nm), second (532 nm), third (355 nm) and fourth (266 nm) harmonic of a Nd:YAG laser were used in the experiments. The influence of the laser fluence at a wavelength of 1064 nm is also studied. The optical spectra of the fabricated colloids were used to determine the optimal absorption of the zinc oxide nanostructures. This data is utilized to define an optimal laser wavelength that ensures maximal absorption by the already created nanostructures. Laser treatment of already fabricated colloids at this condition was applied to modify efficiently the size distribution of the colloidal nanoparticles. The produced colloidal nanostructure were analyzed by transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-Ray Diffraction (XRD) and UV-visible transmission measurements in order to evaluate their morphology, size distribution, crystalline structure, and optical properties. The presented method can be an efficient alternative for fabrication of metal oxide nanostructures with application in biomedicine, photonics and sensor devices.

Resume : Results on nanostructuring of Ag thin films by laser-assisted technique are presented. The thin films are deposited by on-axis pulsed laser deposition technology on dielectric and metal substrates. The as deposited films are then annealed by laser pulses delivered by nanosecond Nd:YAG laser system operated at λ=355 nm. At certain conditions, the laser processing can result in decomposition of the thin film into array of nanoparticles on the substrate. The characteristics of the obtained film modifications are studied as a function of the annealing conditions – number of the laser pulses and fluence of the laser pulses. The morphology of the samples surface is investigated by means of scanning electron microscopy. The optical properties study based on structure’s extinction spectra shows that film decomposition into nanoparticles results in clear peak in the spectra. This effect, called Surface Plasmon Resonance (SPR), is related to efficient excitation of plasmons in the nanostructures. The intensity and the position of the SPR peak are found to depend on both the processing parameters and the type of the substrate. The fabricated structures are covered with Rhodamine 6G and tested as active substrate for Surface Enhanced Raman Spectroscopy (SERS).

Resume : Al-doped ZnO thin films were successfully obtained at room temperature through sequential PLD (SPLD) from Zn and Al metallic targets in an oxygen/argon gas mixture. While keeping constant the total deposition pressure, we have investigated the effect of the progressive injection of the inert gas on the structural, electrical and optical properties. To compensate the charge carrier losses at higher deposition pressures, we have injected a supplementary argon gas flow, keeping a low partial pressure of oxygen. The electron concentration of the 1% of Al doped ZnO samples increases with oxygen depletion of the deposition environment due to the emergence of oxygen vacancies. Argon acts as an inhibitor for the defects related to the energetic species such as Zn and Al interstitials, leading to an increase of the Hall mobility as well. Thus, the highly (002) oriented samples have high optical transmittance (over 90%) and low electrical resistivity (down to 4 x 10^-4 Ω∙cm). In the same time, the internal stress in the films was found to decrease with argon injection. The obtained results demonstrate that the SPLD of AZO thin films in an oxygen/argon gas mixture leads to a considerable improvement of the electrical properties of the samples without affecting the optical ones and this method may be successfully used for transparent and flexible electronics.

Resume : Calcium fluoride (CaF2) nanoparticles (NPs), pure or doped by transition metals, among the large number of possible applications are receiving strong attention for their potential use in biomedical field as bioimaging probes [1] or for their roles as reservoirs of fluoride ions for cavities prevention in dentistry [2]. Various approaches have been used for the preparation of CaF2 NPs such as chemical co-precipitation method, reverse micro-emulsion method, combustion synthesis, microwave-assisted solvothermal method and so on. However, those methods need the use of chemical additives that can contaminate the CaF2 NPs. On the contrary, the Laser Ablation in Liquid (LAL) technique has been widely used to produce well dispersed Nps. This technique presents several advantages with respect to the most used chemical methods such as the possibility of a certain control of the Nps size, shape and crystallinity and the possibility to produce colloids free of chemical agents or stabilizers. In this paper we report the simple synthesis of CaF2 NPs obtained by ultra-short LAL of a CaF2 target in different solvents by a femtosecond laser source (Nd:glass laser 527nm, 250fs and 10 Hz). The NPS have been characterized in terms of crystallinity, composition and morphology by X-ray diffraction, transmission electron and scanning electron microscopies, micro-Raman spectroscopy, FTIR, UV-vis absorption and emission spectroscopy. [1] S.M. Lan, Y.N. Wu, P.C. Wu, C.K. Sun, D.B. Shieh, R.M. Lin, Acad. Radiol. 21, 281, 2014. [2] S. Kulshrestha, S. Khan, S. Hasan, M. E. Khan, L. Misba, A.U. Khan, Appl. Microbiol. Biotechnol. 2015 DOI 10.1007/s00253-015-7154-4.

Resume : Calcium copper titanate (CaCu3Ti4O12 - CCTO) is a perovskite-type material which has attracted considerable attention in the last 15 years for the very high value of its dielectric constant over a large range of temperatures [1,2]. Since thin films of this material are very promising for their potential application in microelectronics, several techniques have been used to deposit them. Among these techniques pulsed laser deposition (PLD), performed by ns laser sources, has been already used to deposit CCTO thin films but only in the presence of an oxygen atmosphere [3,4]. Since PLD performed by ultra-short laser sources has shown to be a god choice to avoid the loss of volatile elements during ablation, in this work a CCTO target has been ablated in vacuum by a Nd:glass laser with a pulse duration of 250 fs. The plasma produced by the laser-target interaction has been characterized by time and space resolved optical emission spectroscopy and ICCD fast imaging. The crystallinity and composition of the films, deposited on silicon substrates at different temperatures, have been analyzed by X-ray diffraction, energy dispersive x-ray spectroscopy and micro-Raman spectroscopy. The morphology of the films, formed by the coalescence of a large number of nanoparticles, has been studied by scanning and transmission electron microscopy and atomic force microscopy. The first steps of the films growth have been studied by transmission electron microscopy and dielectric measurements have been also performed. [1] M.A. Subramanian, D. Li, N. Duan, B.A. Reisner, A.W. Sleight, J. Solid State Chem. 151, 323, 2000. [2] S.Y. Chung, I.D. Kim, S.J.L. Kang, Nat. Mater. 3, 774, 2004. [3] Y. Lin, Y.B. Chen, T. Garret, S.W. Liu, C.L. Chen, L. Chen, R.P. Bontchev, A. Jacobson, J.C. Jiang, E.I. Meletis, J. Horwitz, H.-D. Wu, Appl. Phys. Lett. 81, 631, 2002. [4] A.G. Monteduro, Z. Ameera, M. Martino, A.P. Caricato, V. Tasco, I.C. Lekshmic, R. Rinaldi, A. Hazarika, D. Choudhury, D.D. Sarma, G. Maruccio, J. Mater. Chem. C 2015, DOI: 10.1039/C5TC03189C.

Resume : Organic-inorganic perovskites, which have led to much excitement in the photovoltaic community, have recently been shown to exhibit lasing when optically pumped. However, achieving single mode operation using a device architecture that is compatible with scalable low-cost manufacturing still remains an open challenge. Here, we present work to realise a perovskite distributed feedback (DFB) laser by nanoimprinting a large scale (up to 1.6 cm2) corrugated structure onto a polymer template, followed by the subsequent evaporation of a conformal perovskite layer. By varying the grating periodicity from Λ = 380 nm to 420 nm, we observe optically-pumped, surface emitting lasing at room temperature across a range of wavelengths. This method provides a general strategy to structure organic inorganic perovskites. This is a critical step towards all electrically pumped injection laser diodes. This approach opens the prospects of perovskite materials for much improved optical control in light emitting diodes, solar cells and also toward applications as optical devices[1]. [1] Saliba, M. et al. Structured Organic–Inorganic Perovskite toward a Distributed Feedback Laser. Advanced Materials, (2015)

Resume : The method of high-frequency cathode sputtering of CdSb single crystal target was used for obtainig of thin film CdSb-Cd1-xMnxTe and CdSb-In4(Se3)1-xTe3x heterojunctions. Since CdSb compound has significantly different partial vapor pressures of the components, there were set up technological modes that provide obtaining CdSb thin films of stoichiometric composition. The structure and phase composition of the films have been studied by AFM, SEM and electron probe microanalysis. X-ray diffraction topography was used for studying structure perfection of Cd1-xMnxTe and In4(Se3)1-Te3x crystal substrates of different composition (including x=0). Optimization of structural and phase state of CdS thin films was carried out by the action of millisecond YAG-laser (λ = 1,06 mkm, τ~1 ÷ 4 ms). The effect of laser treatment on electrical and spectral characteristics of CdSb-Cd1-xMnxTe and CdSb-In4(Se3)1-xTe3x heterojunctions was examined from the modification of I-V and C-V characteristics and photosensitivity spectra under laser radiation. It was found that coarsely granular texture and monocrystalline regions were formed in CdSb films at critical values of laser power. The changes in surface morphology of crystal substrates after laser treatment were also studied. It was shown that obtained for the first time CdSb-Cd1-xMnxTe and CdSb-In4(Se3)1-xTe3x heterojunctions shoud be promising as the sensors of electromagnetic radiation of different wavelength.

Resume : Ferromagnetic GaMnP layers were prepared by ion implantation and pulsed laser annealing (PLA). We present a systematic investigation on the evolution of microstructure and magnetic properties depending on the pulsed laser annealing energy. The sample microstructure was analyzed by high-resolution X-ray diffraction (HR-XRD), transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), ultraviolet Raman spectroscopy (UV-RS), and extended X-ray absorption fine structure (EXAFS) spectroscopy. The presence of X-ray Pendellösung fringes around GaP (004) and RBS channeling prove the epitaxial structure of the GaMnP layer annealed at the optimized laser energy density (0.40 J/cm2). However, a forbidden TO vibrational mode of GaP appears and increases with annealing energy, suggesting the formation of defective domains inside the layer. These domains mainly appear in the sample surface region and extend to almost the whole layer with increasing annealing energy. The reduction of the Curie temperature and of the uniaxial magnetic anisotropy gradually happens when more defects and the domains appear as increasing the annealing energy density. This fact univocally points to the decisive role of the PLA parameters on the resulting magnetic characteristics in the processed layers, which eventually determine the magnetic (or spintronics) figure of merit.

Resume : The aim of this work is to compare two nanopowders obtained with different methods deposited by a laser technique. Mixed oxide nanoparticles containing different Ti:Sn atomic ratio were synthesized  starting from sensitized mixtures of TiCl4 and Sn(CH3)4 precursors using laser pyrolysis technique. Tin oxide-based nanocomposites were obtained by glycine combustion technique starting from organometallic titanium tetraizoporpoxide and tetrabutyl-bis(acetyloxi) distanoxane. Structural and morphological properties of the obtained  nanoparticles have been characterized by XRD and TEM showing small particle sizes and structural homogeneity. Both anatase and rutile phases were identified in the resulted nanoparticles. The nanopowders were dispersed in aqueous media at different concentration using ultrasonication. Their hydrodynamic size distributions were evaluated before deposition by DLS (Dynamic Light Scattering). The water-based mixtures were frozen in liquid nitrogen and deposited using MAPLE (Matrix Assisted Pulsed Laser Evaporation) on Si substrates and interdigitated electrodes. The resulted thin films were analysed using TEM, XRD, SEM and EDX techniques and were successfully tested for low concentration hydrogen detection in synthetic air. The electrical measurements were performed during heating process (300-350°C , 3 hours) using different gas flows, starting  from 5000 ppm until 100 ppm.

Resume : Ultrafast laser selective removal of self-assembled Ag network electrode on PET substrate is investigated as an effective patterning method at high pulse repetition rate in heat accumulation regime. The Ag network was removed not only by direct laser ablation, but also by efficient delamination resulting from local heat accumulation at high repetition rate pulse irradiation. Temporal energy distribution of pulses was carefully controlled to induce proper heat accumulation at the interface between Ag and PET substrate. The laser process window reflecting the heat accumulation effect was found well below to the ablation threshold of PET, avoiding the damage of PET substrate during laser scanning. The flexible and transparent film heater (FTFH) fabricated by ultrafast laser patterned Ag network electrodes with different pattern shapes (linear pattern or zigzag pattern) showed the different saturation voltage to obtain 100 ºC because the saturation voltage are critically dependent on the series resistance of Ag network electrode. Successful operation of the FTFH indicates that ultrafast laser patterning is a simple yet promising technology for fabrication of patterned Ag network-based high quality FTFHs enabling high yield variant quantity production to meet various industrial requirements.

Resume : Large area periodic surface structures were generated on steel surfaces using 30-fs laser pulses at 790 nm wavelength. Two types of steel exhibiting a different corrosion resistance were used, i.e. a plain structural steel (corrodible) and a stainless steel (resistant to corrosion). Homogeneous fields of laser-induced periodic surface structures (LIPSS) were realized utilizing laser fluences close to the ablation threshold while scanning the sample under the focused laser beam in a multi-pulse regime. The nanostructures were characterized with optical and scanning electron microscopy. For each type of steel, more than ten identical samples were laser-processed. These samples were subjected to microbial adhesion tests, investigating bacterial adhesion behavior on the laser structures in comparison to polished reference surfaces. Short term experiments (<24h) were carried out to determine initial biofilm development. E. coli as a typical bacterium representing pathogenic bacteria and Shewanella putrefaciens as metal corrosive bacterium were used for biofilm development analyses. Bacterial cell adhesion was determined microscopically after DAPI cell staining (DNA staining). Comparison of the coverage areas between nanostructured and polished surfaces revealed differences in cell adhesion behavior and biofilm structure.

Resume : Topological insulators (TIs) are graphene-like two-dimensional materials, providing a broadband saturable absorption. Therefore, TI attracts a great amount of attention in the field of ultrafast photonics. Here, we demonstrated the femtosecond erbium-doped fiber laser mode-locked (ML) with reflectivity-type Bi2Te3 (BT) saturable absorbers (SAs), which were fabricated by pulse laser deposition (PLD) on Au/c-Al2O3. The highly c-axis oriented growth is evident from the X-ray diffraction peaks corresponding to the {003} family of Bi2Te3 and its thickness was measured to be about 20 nm. In order to check the quality and uniformity of BT-SAs, we measured the Raman spectrum at 15 different positions, sequentially from top to bottom and left to right. Three characteristic peaks of BT-SAs were observed at 59.9, 100.1, and 133.6 cm^−1, which are consistent with vibrational modes of Bi2Te3 crystal. Its absorbance of ~18.2% from 630 to 1800 nm was measured by UV-visible-NIR spectrophotometer. Self-starting ML pulses are readily obtained as pumping power increased to 72 mW, and sustained the ML state for pump powers up to 135 mW. The optical spectrum shows center wavelength of 1564.7 nm and a 3-dB bandwidth of 5.3 nm at pump power of 120 mW. The output power, pulse width, and pulse repetition rate are 3.56 mW, 525 fs, and 12 MHz, respectively, corresponding to peak power of ~525 W. In addition, the SAs can generate ML pulse by transversely moving over a large range of sample position. The ML fiber laser can operate stably and continuously over hours by using the BT-SAs.

Resume : In this work, novel biodegradable copolymer-Curcumin coatings were developed and evaluated in vitro as antitumoral systems. To facilitate sustained release of Curcumin, the bioactive element was embedded in the biodegradable Polyvinyl Alcohol-Polyethylene Glycol graft coatings obtained by Matrix assisted Pulsed Laser Evaporation (MAPLE). The strategy used in this study to obtain coatings with various roughness and porosity was to tailor target characteristics (solvent, composition, concentration of curcumin) and deposition parameters (fluence, number of pulses). The morphological characteristics of thin films were investigated by Atomic Force Microscopy and Scanning Electron Microscopy, while the structural characteristics of the thin films were characterized by Fourier Transform Infrared Spectroscopy (FTIR). The degradation behaviour was studied by ellipsometry (SE). Osteosarcoma cells interaction studies indicate that the developed hybrid coatings significantly decreased cells viability. The results of the physico-chemical characteristics of thin films along with in vitro studies preliminary analyses suggest that our polymeric hybrid coatings may be efficient for the design of antitumoral surfaces for biomedical applications. Acknowledgments: The research leading to these results has received funding from the Romanian Ministry of National Education, CNCS – UEFISCDI, under the projects PN-II-PT-PCCA-2013-4-199, PN-II-RU-TE-2014-4-2434 and PN09-39

Resume : Graphene have received increasing attention in the last years for biomedical applications for bone regeneration research. Nevertheless, by combining its specific characteristics with those of natural bioactive protein, enhanced biointerfaces can be obtained. In this work, we explore the feasibility of using the graphene sericin composites as potential coatings for testing in vitro osteoblast behavior. Matrix Assisted Pulsed Laser Evaporation technique was used for obtaining uniform coatings, with variable roughness depending on the deposition parameters and target composition. Characterization and evaluation of the coated substrates were carried out using different techniques (Fourier transform infrared spectroscopy, contact angle measurements, atomic force microscopy). The cellular model used to evaluate the in vitro biocompatibility of sericin, graphene and sericin/graphene composite films was represented by MC3T3-E1 pre-osteoblasts. The cell culture-based studies (phase contrast microscopy, LDH and MTT assays) have proved biocompatibility and the osteoblast behavior was correlated with both chemical composition and roughness. Our results give indications on the use of graphene based composites for tissue engineering applications. Acknowledgement Funding for this research was provided by the Romanian Ministry of National Education, CNCS – UEFISCDI, under the projects PN-II-PT-PCCA-213 and programme Nucleu PN09-39

Resume : The laser pyrolysis method was used to synthesize ZnO nanoparticles, starting from ZnSO4 as Zn precursor, from water or isopropyl alcohol solution as an aerosol, using ethylene as a sensitizer and N2O, or air, as oxygen source, with Ar for confinement. The Raman and XRD analysis of the reaction products indicates zinc oxide nanoparticles with an average diameter of 28 nm that lacks the E1LO vibrational mode of ZnO (583cm-1), which highlights a sufficient oxygen atmosphere for zinc oxidation, and a high content of turbostratic carbon. Laser pyrolysis is a convenient approach for ZnO nanoparticles synthesis, offering lower dimensional particles with good zinc/oxygen ratios that generate higher quality crystallization. The downside of this method is the low ZnO/C ratio, associated to high quantity of turbostratic carbon resulted from resonant ethylene dissociation in the pyrolytic flame. In our study we aim to increase the yield of the synthesis process varying experimental parameters, and also to map out the nanoparticles morphology dependence on such parameters, in order to combine the advantages of laser pyrolysis synthesis with a good process efficiency.

Resume : We propose tunable and selective areal chain alignment method is developed for spin-cast blend films of poly(3-hexylthiophene)(P3HT):[6,6]-phenyl-C61-butyric methyl ester (PCBM) system by a femtosecond laser process. Surface relief gratings were fabricated via laser direct writing using a femtosecond laser, which photo-expanded the P3HT:PCBM thin films. Photo-expansion was induced at a laser fluence below the ablation threshold of the thin film. The morphology (size and shape) of the photo-expanded region could be quantitatively controlled by the laser parameters, such as the focused beam width, repetition rate, laser fluence and so on. Grazing incidence x-ray scattering results revealed that the concentration of face-on P3HT crystals increased dramatically in the photo-expanded region relative to the concentration in the pristine region of the thin film. The alkyl chains of P3HT polymer in the photo-expanded region were highly aligned along the polarization direction of the laser. The micro-RAMAN spectra confirmed that neither the chemical composition nor the polymer chain length varied after femtosecond laser irradiation. This laser direct writing technique opens a new route to fabricating efficient organic semiconductor devices using a non-contacting non-toxic approach.

Resume : Medical grade polydimethylsiloxane (PDMS) elastomer is a widely used in medicine as implants, e.g. shunts and pacemakers, long term neural implants, micro-channeled tracks as electrodes for neural interfaces for monitoring and/or stimulation of neural activity, because of its remarkable properties: neutrality and chemical stability, very low electrical conductivity and transparency to visible and near infra-red light. The as prepared medical grade PDMS sheets with thickness of 190 μm are processed by a ns-Nd:YAG laser system comprises basic (λ = 1.064 μm), 2nd (λ = 532 nm), 3rd (λ = 355 nm) and 4th (λ = 266 nm) harmonic generations. It delivers pulses of 15 ns at repetition rate of 10 Hz. A special attention is paid on the comparison between the qualities of the trenches produced by focused none manipulated and homogenized laser beam at 355 nm. The processed tranches are viewed and analyzed by laser microscopy, μ-Raman and optical spectroscopy, and scaning electron microscope. Selective Pt or Ni metallization of the laser processed traces is produced successfully via electroless plating.

Resume : Optical devices based on rare earth (RE) ions have attracted significant research interest due to a variety of attractive applications, such as biosensors in the area of biomedical diagnostics, colored displays and photovoltaic spectral conversion layer. However for many application, the optical performance of such luminescent device can be limited by the intrinsic low absorption cross-section of the RE ions and/or the low level of light produced under illumination. To overcome these limitations, one key strategy is the use of metal nanostructures to enhance the fluorescence signal via localized surface plasmon resonance effects. In this study, the growth by pulsed laser deposition of ultrathin metallic films as well as nanoparticles is presented. Two kinds of metals, i.e Ag and Al, are investigated because of their plasmonic responses occurring in the blue and UV portion of the spectrum. We show that by tuning mainly the deposition rate and the background atmosphere, it is easily possible to obtain Ag nanoparticles exhibiting plasmonic resonances at wavelengths shorter than 500 nm. However for Al, we demonstrate that Al tends to perfectly wet the substrates (e.g., quartz and silicon), ant that appropriate surface is required in order to obtain Al nanostructures with plasmonic properties in the UV region. For each material, in situ electrical resistivity measurements are used to control the growth during the deposition, whereas conventional analysis technique (absorption spectroscopy, AFM, SEM, TEM and XRR) are used to control their properties.

Resume : Earth-abundant non-toxic materials Cu2SnS3 (CTS) and Cu2ZnSnS4 (CZTS) are very appealing for cheap, large-scale production of thin-film solar cells. Due to their complex stoichiometry it is very difficult to obtain a single phase material with evaporation or sputtering deposition. Here we discuss the fabrication of thin films of CTS and CZTS made with Pulsed Laser Deposition (248 nm, KrF laser) from sintered targets. Usually, e.g. in PLD of oxide materials, the loss of the most volatile component, i.e. oxygen, can be compensated with the introduction of reactive background gas in the chamber. In our case, however, the least volatile element, copper, is not transferred as expected. The stoichiometry of the deposited films strongly depends on the laser fluence: severe deficit (up to complete lack) of copper in the film is observed when the fluence is below 0.4 J/cm2, while a copper rich composition is observed at fluence values above 1 J/cm2. The stoichiometry of the deposited films can be understood in terms of the cohesive energy of the atoms composing the target; a cohesive energy which is very different among copper, zinc, tin and sulfur. A narrow range of fluence values that preserves the target stoichiometry is found. Furthermore, this method allows fabrication of very homogeneous, amorphous thin films of the Zn-Sn-S “alloy”, which is an immiscible ternary system that has no stable solid phase and thus cannot be made with standard film growth techniques.

Resume : Nano-sized materials i.e. carbon nanotubes (CNT) and decorated CNT (i.e. with nanoparticles), due to their unique mechanical and electrical properties, have immediate applications as building blocks for high-performance flexible/transparent electronics. For many applications within the microelectronics field, the challenge is now downsizing the devices, and integrating them onto large-area, flexible and low cost substrates. In this work, the direct writing of CNT and hybrid CNT materials onto nonconventional substrates, i.e. paper, plastics, tapes, glass, poly(dimethylsiloxane) (PDMS), Al foil, and ultrathin polymer substrates is reported. The direct writing technique is based on laser-induced forward transfer (LIFT), a simple process where a laser beam is focused through a transparent substrate onto a material film to be transferred. Every single pulse promotes the transfer of the thin film material onto a substrate that is usually placed parallel and facing the thin film at very short distances. With LIFT, CNT and hybrid CNT materials are transferred, with a transfer yield of nearly 100%, to fabricate chemical sensors. The chemical sensors maintain their original geometries and electronic properties with high fidelity. For example, the performance, i.e. the sensitivity, resolution, and response time of the laser-printed sensor devices was evaluated by exposure of the sensors to different toxic vapors. Different sensitivities and selectivity to the selected analytes i.e. acetone, ethanol, ammonia, etc. have been measured thus proving the feasibility of LIFT for applications in sensing devices. Acknowledgements This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CNCS – UEFISCDI, project number PN-II-RU-TE-2014-4-2311 and a grant from the Commission for Technology and Innovation CTI (project no. 16713.1 PFNM-NM).

Resume : Diamond-like carbon thin films can be used as protective coatings for tools and mechanical instruments exposed to friction and high temperatures, in view of increasing their life time. We synthesized by Pulsed Laser Deposition such coatings in various experimental conditions. Our objective was to determine the decisive parameters that modify the type of bonds between carbon atoms and consequently, the films structure and properties. Cross-sections of the DLC films were visualized by scanning electron microscopy, X-ray reflectivity (XRR) and optical ellipsometry were used to determine thickness and density differences, while Raman spectroscopy allowed identification of different types of bonds between carbon atoms. DLC films were mechanically studied by nanoindentation and scratching. Special precautions had to be taken for these analyses, because XRR and ellipsometry tests showed that the PLD carbon films consisted of two sub-layers: one denser and harder close to the substrate and a more porous one on top of it. It is the thickness of this upper layer that influences dramatically the mechanical properties of the films.

Resume : It is well known that Pulsed Laser Deposition (PLD) is a very flexible and versatile technique allowing fast optimization of new and complex material thin films. However, mainly because of the sample size, the developed materials and processes in PLD research tools only just make it into demonstrator devices. In order to make it into commercial applications, next generation PLD equipment is needed to bridge the gap between demonstrator and the prototype – pilot – production stages. The Solmates PLD platform is the next step beyond fundamental PLD research. The reliable hardware is flexible for fast process optimization and allows uniform thin film deposition up to 200 mm diameter with high reproducibility. The automated software ensures easy operation and stable performance. Thanks to those characteristics, integrating PLD thin films on devices becomes relevant for (pilot) production and commercialization. In this contribution the latest performance and specifications of Solmates PLD platform are addressed. Data on stability and reproducibility of wafer scale deposition of PZT thin films with excellent properties will be presented. Furthermore, two qualified processes Indium Tin Oxide and Aluminum Oxide thin films will be used to show some key capabilities of PLD such as damage free deposition on organic electronics or control of thin films density and microstructure for optical or sensing applications.

Resume : The optical properties of wide bandgap semiconductors such as AlN or AlGaN alloys make them useful for light generation in the deep UV spectral region. In addition, these materials possess large second order susceptibilities and thus can produce UV light by second harmonic generation. In order to make this process efficient, the pump and SH waves must be phase matched. The most efficient viable method is quasi phase matching, where the sign of the nonlinear coefficient in the material is periodically reversed after each coherence length. Another phase matching method is modal dispersion phase matching where the appropriate combination of interacting waveguide modes is selected. We present results on UV second harmonic generation in AlN waveguides grown on sapphire substrates following the two methods. The periodic AlN structures are fabricated by inverting the crystallographic c-axis, as determined by the substrate preparation prior to epitaxy. In this case, waveguide propagation efficiency is determined by the surface optical quality to reduce scattering. In addition, UV light is generated by using modal dispersion in single polarity waveguides. We observed three modal-phase-matched SH peaks in the UV region as described by modal phase matching. By measuring the SH signal in the UV region the extrapolated values of the UV refractive indices of AlN were confirmed.

Resume : Layered double hydroxides (LDHs), also known as hydrotalcites or anionic clays can be described with the general formula [M2+1-xM3+x(OH)2]x+(An-)x/n•mH2O, where M2+ and M3+ are divalent (Mg, Ni, Zn, Cu or Co) and trivalent (Al, Cr, Fe, or Ga) metal ions respectively. Here in we report on the deposition of thin films of LDH or LDHs derived mixed oxides by Pulsed Laser Deposition (PLD). Pressed targets of Mg-Al, Zn-Al, Ni-Al and Co-Al based LDH and their mixed oxides with different M2+/M3+ ratios were irradiated with a Nd:YAG laser (1064, 532 and 266 nm) in vacuum at room temperature. The Si substrates were placed in front of the target and parallel to it, at 4 cm distance. The as deposited LDH films were calcinated and treated in humid atmosphere. Reconstruction of the LDH lamellar structures occurs via “memory effect”. The effect of the calcination temperature and reconstruction time is investigated and discussed. X-Ray Diffraction, Atomic Force Microscopy, Scanning Electron Microscopy combined with energy dispersive X-ray analysis and Secondary Ions Mass Spectrometry were the techniques used to examine the structural and morphological properties of the deposited and treated films.

Resume : In this work the results on thermal nanostructuring of the Au films on Ti templates and structural properties of the obtained structures are presented. The bimetal nanostructures are prepared in a multi-step process. Initially, the titania nanotubes are produced on the surface of Ti foil by anodization in an organic solution containing fluoride ions. This is followed by chemical etching in oxalic acid and results in highly ordered dimpled foil surface. Subsequently, thin gold films (5-30 nm) are deposited onto prepared Ti substrates by magnetron sputtering. The as prepared layers are then dewetted by UV nanosecond laser pulses or in the furnace (temperature < 500°C). The SEM inspection reveals formation of honeycomb nanostructures (cavity diameter: 30-100 nm) covered with homogeneously distributed Au nanoparticles (NPs). It has been found that the laser annealing leads to creation of NPs inside Ti dimples whereas thermal treatment causes formation of NPs on the whole area of structured templates. The NPs size obtained via both dewetting processes does not exceed 100 nm and their shape and size can be tuned by the annealing time and working parameters of laser. The obtained results confirm that prepared material can be used as active substrate for Surface Enhanced Raman Spectroscopy (SERS). KG and KS acknowledge the National Science Centre of Poland for financial support via grants 2012/07/N/ST5/02139 and 2012/07/D/ST5/02269.

Resume : The laser-induced forward transfer (LIFT) technique is a versatile method that is adequate for the production of conductive lines, which are a key element in microelectronic devices. LIFT makes possible the printing of droplets of conductive inks from a donor film to a receptor substrate. The successive deposition of overlapping droplets results in the production of continuous lines. However, this simple approach presents two main drawbacks: scalloping and bulging. We have already overcome these issues by the use of fluidic guides that confine the possible expansion of the transferred droplets on the receptor substrate. This approach allows printing lines with excellent definition with widths down to about 50 µm, but improving line resolution requires the transfer of extremely small amounts of ink, which becomes challenging for the LIFT technique. The proposed solution to avoid this difficulty consists in printing ink into a well connected to a narrow fluidic guide. The ink fills the well and flows by capillarity into the fluidic guide, resulting in a conductive line with a substantially smaller width (down to 5 µm) than that of lines obtained through the conventional method.

Resume : TiO2/SnO2 nanocomposites have been prepared by laser pyrolysis of volatile TiCl4 and Sn(CH3)4 precursors in the presence of oxygen. Prior to the obtaining of TiO2/SnO2 nanocomposites with the different concentration of Sn (1.1-4.8 at %), the best experimental conditions were identified for preparing pure anatase phase TiO2 samples considered as photocatalytic reference sample. The TiO2/SnO2 composites were characterized using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and UV–vis diffuse reflectance spectroscopy (DRS) techniques. The structural results show the presence of anatase majority phase (65-82%) and mean crystallite dimensions in the 8-22 nm range. Laser synthesized TiO2/SnO2 samples have a lower band gap energy and higher photocatalytic efficiency in the process of methyl orange photodegradation than compared with the P25 Degussa commercial sample.

Resume : We report on the synthesis by pulsed laser deposition method of hydroxyapatite (HA) thin films from renewable biological sources for implantology applications. A comparative study on HA materials of synthetic or biological origin (ovine- or bovine-derived HA) was carried out. The calcination protocol applied to produce the biological HA powders was intended to simultaneously induce good crystallization and to prohibit the transmission of diseases. The morpho-structural and compositional properties of the films were evidenced by SEM-EDS, XRD, and FTIR spectroscopy, whilst their adherence to the Ti substrates was evaluated by pull-out tests. The micrographs of the synthesized structures showed a uniform distribution of spheroidal particulates with diameters in the range of (0.8‒4) µm. EDS analysis revealed the presence of Ca, P, Na, O, and Mg oligoelements. XRD and FTIR evidenced the monophasic HA structure of the PLD films, with their crystallinity degree being influenced by the biological origin. A slight carbonation of the biological HA films was also emphasized. The biological HA coatings exhibited excellent bonding strength values as compared to the synthetic ones. Based upon performances and low cost fabrication from renewable resources, we believe that these coatings could develop into a prospective competitor to synthetic HA, allowing to obtain new implants with better osseoconductive characteristics.

Resume : We report on the synthesis by pulsed laser deposition (PLD) of bioactive glass (BG) films onto ultra-high molecular weight polyethylene (UHMWPE) acetabular cups, and their preliminarily in vitro testing in simulated body fluids (ISO 23317:2014). Prior to and after the in vitro assays, the functionalized implants have been assessed multi-parametrically by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Fourier Transform Infrared (FTIR) spectroscopy. SEM analyses revealed the capability of PLD technique to uniformly cover the UHMWPE cups with BG films. EDS investigations demonstrated a congruent target-to-substrate atomic transfer. FTIR spectra evidenced the strong depolymerization of the as-deposited BG coatings. The series of morphological, compositional and structural analysis, performed after the in vitro testing in SBF for 30 days, indicated the high biomineralization capacity of PLD BG film, its surface being fully converted to a thick, rough, and continuous envelope consisting of carbonated hydroxyapatite acicular crystals. The functionalization of UHMWPE acetabular cups with BG films by PLD should allow for the fabrication of implant coatings with shorter osseointegration time and improved osseoinductive characteristics.

Resume : Nowadays, the market for high power lasers is rapidly growing. In the past, development of such powerful laser systems was held back by the lack of high-performance laser optics that exhibits elevated laser-induced damage threshold without sacrificing spectral or phase performance. In this paper we report the progress on the obtaining and characterization of antireflective coatings from dielectric oxides for high power laser optics. Starting from targets of Ta2O5, Al2O3, SiO2, and HfO2, thin layers were grown at different temperatures, in a controllable oxygen atmosphere, by radio-frequency plasma assisted pulsed laser deposition (RF-PLD) technique. The antireflection coatings with low roughness, uniform thickness, and high dielectric constant where obtained by selecting the best deposition parameters such as: wavelength, laser fluence, oxygen pressure, substrate temperature. The dielectric materials with low and high refractive index were combined for obtaining thin films and/or heterostructures with antireflection properties. Atomic force microscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and spectro-ellipsometry techniques were used to investigate the resulting heterostructures: HfO2/SiO2, Al2O3/SiO2, Ta2O5/SiO2, HfO2/Al2O3, Ta2O5/Al2O3. Acknowledgment: This work was supported by a grant from MEN-UEFISCDI, project PN-PCCA 38/2014 and project PN 09 39 (NUCLEU Program).

Resume : We report on the pulsed laser deposition of biological-origin hydroxyapatite (HA) thin films. The biological HA powders were calcinated according to a protocol which guarantees the full security against disease transmission and contamination. The role of reinforcement agents (Ti, MgO or Li2O) on the structure and bonding strength of the films was investigated. The morpho-structural, compositional, and mechanical properties of the films were evidenced by SEM-EDS, XRD, FTIR and pull-out tests, respectively. SEM micrographs revealed a granular morphology consisting of spheroidal particles with diameters in the micrometer range. EDS spectra indicated the purity of the films: apart from the healthy human bone main constituents and trace elements, no other elemental impurities were detected. XRD analyses demonstrated that the structures consisted remarkably of a pure HA phase, with different degrees of crystallinity mainly influenced by the reinforcement elements. The films’ bonding strength failure was of adhesive type, developing at the coating‒substrate interface at values of ~70 MPa. The adhesion strength represents a critical parameter for successful implantation and long term stability of these structures. Therefore, these excellent values of adherence need to be emphasized. Due to their improved performances and low cost fabrication from renewable resources, we think that these new coating materials could represent a valid candidate for implantology applications.

Resume : Particle removal by pulsed lasers is of fundamental importance in cleaning technologies and conservation science. In the case of mechanical desorption processes [1,2] adhesion forces have to be quantified. This was realized by scanning force microscopy (SFM). Polystyrene spheres attached to SFM cantilevers served as model particles. Pull-off forces on polymer and silicon substrates in the range of 50-200 nN were detected, which is about one order of magnitude lower than the predictions by theoretical models [3]. Therefore multiple contacts, asperities on the spheres, and humidity have to be considered [4]. These investigations are correlated with particle acceleration measurements induced by surface acoustic waves generated by laser pulses. Thus, an quantitative experimental comparison between the adhesion force and repulsive force caused by the surface acceleration become accessible. [1] S. Arif, O. Armbruster, W. Kautek, Appl. Phys. A 111 (2013) 309-317. [2] S. Arif, O. Armbruster, W. Kautek, Appl. Phys. A 111 (2013) 539-548. [3] R. Jones, H.M. Pollock, J. A. S. Cleave, C.S. Hodges, Langmuir 18 (2002) 8045-8055. [4] G.W. Tormoen, J. Drelich, E.R. Beach III, J. Adhesion Sci. Technol, 18 (2004) 1-17.

Resume : Laser light interaction with a matter enables such advanced material processing techniques like laser ablation, surface texturing, material cutting and drilling, and precise 3D-micromachining. In spite of its relatively long history, the laser micromachining has not achieved the desired flexibility as required by industrial applications such as silicon (Si)-photonics. Nanostructuring of silicon by lasers in its bulk is a difficult task, which has been targeted by several groups worldwide. The difficulties are conditioned by high refraction index of silicon, its indirect bandgap and efficient absorption of light in UV, visible and near-IR spectral ranges. Common beam configurations are not well suited for subsurface microprocessing of highly refractive materials, but Bessel beams increase the penetration depth. Thus, spatial structuring of laser light radiation at the microscale is crucial for microfabrication of semiconductors. We investigate a novel class of vectorial laser beams, which can overcome linear absorption and achieve intensity levels required for microprocessing of semiconductor materials. We demonstrate optical beams, having either a transverse or a longitudinal component of electric field, which controllably behaves on the beam axis inside the volume of a semiconductor material. Far field structure of such optical beams is also analyzed, and possible experimental implementations are also discussed in detail.

Resume : The laser-assisted microstructuring of thin films especially for electronic applications without damaging the layers or the substrates is a challenge for the laser methods. However, the solution of this technical problem exhibits an outstanding potential for pioneering development of flexible electronics. In many cases the thermal impact of the absorbed laser radiation causes the degradation of the functionality of the thin film. Besides reducing the thermal impact of laser pulse by shorting the pulse duration none thermal laser processes get more and more attended in the last year. In the following presentation a nanosecond pulse laser lift-off process at a wavelength of 1550 nm will be characterized and compared with a laser shock wave induced film delamination process. In order to compare the two different approaches regarding here damage free scribing capacity the laser scribing experiments were performed on thermally sensitive CIGS thin films. The resultant structures were investigated by optical microscopy and scanning electron microscopy (SEM). Additionally the experimental results were compared with the simulation using finite element method.

Resume : In the last years perovskite thin film solar cells attracted an increasing scientific attention due to the excellent perspectives for commercial application. In particular, both a high solar cell efficiency and low cost production can be achieved due to the unique properties of perovskites. The solar cell material has to be divided in small stripes for the production of large area modules. Laser scribing can be a promising method for scribing of the perovskite solar cell material to perform the integrated interconnection. In the present study laser scribing of perovskite solar cell material with different ultrashort laser sources is shown. The scribing of the perovskite material was performed by laser pulses with a duration of 10 ps and 150 fs. The modification of the scribed material in dependence on the laser parameters applied is analyzed in detail for both used lasers. Especially, the edge quality of the laser ablated structures is investigated in order to ensure the quality of the subsequent manufacturing steps for the interconnection. Therefore, the morphology of the ablated pits and scribes as well as the nearby material modifications after the laser scribing is analyzed by optical and scanning electron microscopy (SEM). Additional characterizations are performed by energy dispersive X-ray spectroscopy (EDX).

Resume : Suspensions of poly(bisphenol A carbonate) (PBAC) nanoparticles of varying size and shape have been produced by ablation of a PBAC target with the fourth harmonic of a Q-switched Nd:YAG laser (wavelength 266 nm, pulses of 4 ns, repetition rate 10 Hz). The target was placed at the bottom of a rotating glass vessel filled with around a 10 mm column of liquid. The size distribution and shape of the obtained nanoparticles were characterized by atomic force microscopy (AFM) in dried drops of the suspension cast on a silicon (100) substrate. Laser ablation in water at fluences close to 1 J/cm2 leads to the generation of spherical particles with diameters of several tens of nanometers. Ablation at lower fluences, around 0.1 J/cm2, results in the production of nanoparticles of smaller diameters and also of non-spherical nanoparticles. Additional irradiations, at the fluence of 0.1 J/cm2, were performed in several liquid media with different properties in terms of density, viscosity, thermal conductivity and linear absorption coefficient at the laser ablation wavelength. Inspection of the obtained nanoparticles by AFM reveals differences in their shape and size as a function of the liquid used for irradiation. The different size distributions were related to the thermal conductivity of the systems, while viscosity of the liquids seems to be responsible for the development of the different morphologies.

Resume : Depth profiling by laser-induced breakdown spectroscopy (LIBS) was applied to the investigation of galvanized steel sheets as a typical state-of-the-art multilayer coating system for environmental corrosion protection [1]. The samples were ablated stepwise by the use of two different wavelengths (266 and 532 nm) of a Nd:YAG-laser at various fluences. The plasma emission was registered as a function of both penetration depth and elemental composition in terms of linear correlation analysis [2]. Elemental depth profiles were calculated and compared to EDX cross-sections. A proven mathematical algorithm designed for the reconstruction of layer structures from distorted emission traces caused by the Gaussian beam profile can even resolve thin intermediate layers in terms of depth and thickness. Thereby light-plasma coupling is suggested to cause deviations in the ablation behaviour of Al and Ni, pointing towards a wavelength-dependent plasma shielding [3], which may influence the metal ablation with pulsed ns-lasers in addition to thermal heat transfer in the bulk metal. [1] T. O. Nagy, U. Pacher, H. Pöhl and W. Kautek, Appl. Surf. Sci. 302 (2014), 189-193 [2] M. P. Mateo, G. N. Costa, V. Piñon and A. Yañez, Surf. Interface Anal. 38 (2006), 941-948 [4] J. M. Vadillo, J. M. Fernandez Romero, C. Rodríguez and J. J. Laserna, Surf. Interface Anal. 27 (1999) 1009.

Resume : In pulsed laser deposition, the laser irradiation wavelength and the substrate nature and temperature crucially affect the composition, crystallinity, structure and magnetic properties of the grown deposits. In this work, cobalt ferrite (CoFe2O4) thin films were deposited on Si (100) and SrTi2O3 (100) single crystal substrates at room temperature and 770 K using laser wavelengths of 213, 532 and 1064 nm. The capability of modifying the characteristics of the films of CoFe2O4, the ferrite with the highest magnetocrystalline anisotropy, is of interest for applications involving the electrical control of magnetic properties. The deposited material was characterized by atomic force microscopy to determine the surface morphology, by X-ray diffraction to examine its crystallinity, and by micro-Raman, X-ray photoelectron and Mössbauer spectroscopies to investigate its composition and stoichiometry. The deposits were found stoichiometric for all laser wavelengths, type of substrate and temperature. At 770 K, the films were found crystalline and single-phase (100) with cubic spinel structure when grown on SrTi2O3, and polycrystalline when grown on Si. Differently, at room temperature the deposits although crystalline, also display amorphous domains.

Resume : Laser produced plasma plumes created by nanosecond laser ablation on metallic targets (Mn, Ni, Cu, Zn, Ti and Al) were investigated through simultaneous space- and time-resolved optical and electrical techniques. The aim of this work was to study the effect of the target physical properties (atomic mass, thermal and electrical conductivities, melting point, etc.) on the dynamics of the plasma plumes. The experiments were performed in similar conditions of laser fluence (10 J/cm2), background pressure (p = 10-5 Torr) and probe-target axial distances (d = 1 - 40 mm) for all the investigated targets. Plasma parameters (electron temperature, expansion velocities and excitation temperature) were found to depend on the target physical properties. In particular, a strong relationship was found between the electrical and thermal conductivities and the majority of plasma parameters. These preliminary results are a base for future studies that will allow us to understand the targets properties influence over the formation mechanisms and evolution of laser produced plasmas.

Resume : Recent advanced ambient ionization sources facilitate the study of native samples, without any preparation required for mass spectrometry analysis. In combination with sampling methods, they allow identification of biomolecules while retaining their histological localization. This has promoted the developments of various microsampling techniques like Laser Ablation/ Droplet Capture (LADC). LADC is characterized by the collection into solvent droplets of molecules removed from the sample by laser ablation. The ionization and the mass separation of the captured molecules can then be achieved using conventional MS techniques like Matrix-Assisted Laser Desoption/Ionization (MALDI) or electrospray ionization (ESI). We demonstrate that biomolecule analyses using 532 nm LADC are possible, despite the low absorbance of biomolecules at this wavelength. This is due to the preponderance of an indirect substrate-mediated laser ablation (SMLA) mechanism at low laser energy which contrasts with the conventional direct ablation driven by analyte absorption. Using our custom LADC system and taking advantage of this SMLA mechanism, we were able to perform large-scale proteomic analyses of micro-sampled tissue sections and demonstrated the possible identification of proteins with relevant biological functions.

Resume : Among ferrites, CoFe2O4 presents a high magnetostrictive response, large Faraday effect, high Curie temperature, mechanical hardness and chemical stability making this material a suitable alternative for the development of sensors, actuators, magneto-optic devices etc. Rare earth addition can allow a controlled modification of the structural and magnetic parameters. The aim of our study is to analyze the influence of rare earth substitution on the structural and magnetic properties of cobalt ferrite thin films. In this context CoFe1.97RE0.03O4 (RE= La, Ce, Sm, Gd, Dy, Ho, Er, Yb) thin films were grown in same conditions by Pulsed Laser Deposition (PLD) technique. The targets were obtained using the oxides of the main elements which were mixed in suitable proportions and then sintered at 1250oC, for 5 hours. The resulting disks were placed in a stainless steel vacuum chamber where a 10-3 Torr base pressure was ensured. The monocrystalline (100) Si substrate was placed at a distance of 55 mm in front of the target and heated at a temperature of 400oC during the 60 min deposition. The energy of the Nd-YAG laser (532 nm, 10 Hz, 10 ns) was kept at 30 mJ/pulse (2 J/cm2). Structural analysis results were obtained by profilometry, XRD, Raman spectroscopy and SEM/EDX technique. The magnetic character of the 100nm thick deposited samples was confirmed by VSM. The FMR measurements show an angular dependence of the resonance magnetic field suggesting the presence of anisotropic interactions.

Resume : During the last decades, the Pulsed Laser Deposition (PLD) technique has become a method of choice in producing films of unusual compositions. To optimize the deposition parameters and thin film growth process, knowledge of the plasma plume dynamics formed during laser ablation is necessary. We present some preliminary results on the dynamics of transient plasmas generated by femtosecond laser. The Langmuir probe technique was used to characterize the transient plasma from various metallic targets (Al, Mn, Ni, Cu, In, W) and the probe current being discussed in terms of a shifted Maxwell-Boltzmann distribution function. The time response was found similar for positive and negative polarizations as also the current oscillation frequency. When the target is positively biased, the collected charge – probe voltage characteristic is shifted by a constant value, and a peculiar effect results at low negative probe potentials. Consequently, unified distribution functions should exist for both types of charged particles. From total collected charge dependence vs. probe biasing, plasma temperature and averaged charge state were calculated by assuming an exponential growth. High correlation between these parameters exists, and other moderate correlations were found with thermal constants of metallic target materials.

Resume : For many applications in microelectronics the challenge is now the devices miniaturization, and integrating them onto large-area, flexible and low cost substrates. Ferrocene – Fe(C5H5)2 is a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central iron atom. It has very attractive properties as active membrane in sensors type devices. In this work we report on ferrocene printing as pixels at micro scale for sensor application.The direct writing technique is laser-induced forward transfer (LIFT), a simple process where a laser beam is focused through a transparent substrate onto a material (in form of thin film (ferrocene), deposited on substrate), to be transferred. Every single pulse promotes the transfer of the thin film material onto a receiver that is usually placed parallel and facing the thin film at very short distances. The ferrocene thin layers are grown by matrix-assisted pulsed laser evaporation on quartz. Spectroscopic-ellipsometry, Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy techniques were used to investigate the structure, morphology and optical properties of the films and transferred pixels on different receivers (PDMS, Si, IDT’s sensors structures). Acknowledgement: This work was supported by a Romanian National Authority for Scientific Research, CNCS - UEFISCDI, project PCCA 17/2012 and project PN 09 39 (NUCLEU PROGRAM).

Resume : In all experiments and models on Laser-induced periodic surface structures, the laser polarization is an important parameter, controlling pattern morphology and orientation. The present contribution presents the strictness of this polarization dependence on a polished surface of K890 tool steel. Our main focus is on the effect of superimposing pulses of different linear polarizations. We follow the pulse-to-pulse evolution of the ripples when changing the polarization in the course of picosecond-laser pulse trains, at a wavelength of 1064 nm: After an initial treatment by a series of horizontally polarized pulses, the surface was, then, treated by pulses with rotated polarization (45° resp. 90°). The secondary irradiation, from the first pulse on, starts to change the surface morphology by introducing a new ripples orientation according to the new polarization. A similar observation is found when writing a line scan with overlapping, individual pulses. The experiments strongly evidence that – at least for our target material – the orientation of LIPSS is dominated by the polarization of the last incident pulses, while the previously formed structures are overridden. This weak role of pre-formed structures makes the essential role of surface plasmons polaritons (SPPs) in LIPSS formation or other interference scenarios at least questionable. Instead, the experiments endorse the model of self-organized structure formation from a laser-induced thermal instability (dynamic melting).

Resume : Sodium bismuth titanate / Na(1/2)Bi(1/2)TiO3 (NBT) and barium strontium titanate / Ba(2/3)Sr(1/3)TiO3 (BST) exhibit ferroelectric properties at room-temperature, with permittivity (εr) in the range of 400‒500 and 700-1300, respectively. Both materials are suitable for integration in current radiofrequency (RF) and microwave devices (100 MHz - 24 GHz). However, the main drawback in their poling behaviour is associated to high leakage currents, due to structural and/or morphological aspects. Pulsed laser deposition (PLD) provides outstanding control of thin film growth, leading to accurately tailored morphology, stoichiometry, and therefore electrical properties. By adequately selecting the growth parameters (i.e. oxygen pressure, substrate temperature, and laser repetition rate), the NBT and BST thin films deposited in metal-insulator-metal planar architectures demonstrate accurate tunability, i.e. ~15% for NBT and up to 80% for BST (for film thickness in the range of 125 - 450 nm; 30 x 30 μm² electrode area; at 2.45 GHz and 10 V), with low resistance values and low dielectric losses. Finally, we discuss on potential RF applications and provide results on tunable antennae.

Resume : The nonlinear optical (NLO) response of some Co (II) and Ni (II) complexes is investigated by the static hyperpolarizability coefficients (β), calculated using the semi-empirical quantum chemistry algorithms (MOPAC software). The synthesized organic compounds are characterized by Fourier-transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance (1H NMR). The relationship between donor/acceptor moieties, the dihedral angles around the azo bridge (-N=N-) transmitter group, the pass length as well as the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), respectively, are also taken into account. Finally, thin films are grown by matrix-assisted pulsed lased evaporation (MAPLE) and their optical properties are emphasized. Our results highlight that the NLO response of such small, twisted molecules mainly depends on the dihedral angles of aromatic and heteroaromatic rings toward the transmitter group.

Resume : One of the main problems that cause fixation loosening in prosthesis and implants is the stress shielding due to bone reabsorption with time. This problem can be solved through the development of low Young-modulus alloys. Laser cladding technology is a technique that can melt and consolidate a powdered feedstock material to coat part of a substrate in order to improve its mechanical properties or corrosion and wear resistance. In this sense, this technique can be used to modify the surface of a titanium alloy with a different alloy or material with improves its properties in order to get an alloy with lower Young-modulus, like Ti-Nb alloys, to solve stress shielding problem in prosthesis fixation. In a recent paper1, we have demonstrated the capability of laser-induced breakdown spectroscopy (LIBS) technique for the chemical analysis of clad layers composed by mixtures of WC ceramics with NiCrBSi alloys and generated by laser cladding. In this work, LIBS technique will be evaluated to chemically characterize laser clads of Ti and Nb alloys in different proportions deposited on Ti and Ti6Al4V alloy substrates. The results will allow to compare the final and the theoretical composition of the clads estimated from the composition of the feedstock powdered material. For this analysis, pure Ti and Nb samples in addition to sintered samples with different proportion of Nb and Ti will be analyzed by LIBS and used as standards for the generation of calibration curves. References: 1 J.A. Varela, J.M. Amado, M.J. Tobar, M.P. Mateo, A. Yañez, G. Nicolas, Appl. Surf. Sci. 336 (2015) 396-400.

Resume : Laser production of noble metal nanoparticles is a rapidly expanding field due to its large applications and strong optical responses. The growth of noble metal nanoparticles (Au, Ag, Cu) and their optical features can vary significantly with the operative conditions used such as laser wavelength, fluence, target-substrate distance and position. The aim of the work here presented is to characterize the direct ejection of the nanoparticles induced by a Ti:S fs laser and relate this to the obtained deposits. With this aim the process was followed by snap shots acquired at different time delays using an Intensified Coupled Charge Device. At laser pulse regimes in the range of few up to tens of J/cm2, it is widely accepted that after the detection of a fast plasma plume component, which is characterized by high electron densities (ca. 10^18 cm-3) and electronic excited ions and atoms lasting about 1x10-6 s, even a secondary much slower emitting component takes place. The latter, whose emission is detectable in the range of 1-100x10-6 s, presents a continuum black-body like emission which is related to the evolution of the hot nanoparticles produced representing more than 80% of the ablated material [1-4]. In this work it is reported how the laser irradiation features together with the physical-chemical properties of the three noble metal used induce local changes in the characteristics of the obtained deposits such as: chemistry composition, 2) crystal structure and (3) morphology which have been evaluated by SEM, TEM, micro-XRD and XPS ex-situ techniques. It is going to be demonstrated how the fast imaging technique following the dynamics of the hot nanoparticles produced can be an useful in-situ diagnostic tool for predicting the process induced and relate this to the features of the obtained deposits. [1] N. Tsakiris, K. K. Anoop, G. Ausanio, M. Gill-Comeau, R. Bruzzese, S. Amoruso, L.J. Lewis, Ultrashort laser ablation of bulk copper targets: Dynamics and size distribution of the generated nanoparticles, J. Appl. Phys. 115 (2014) 243301. [2] R. Teghil, L. D'Alessio, A. De Bonis, D. Ferro, A. Galasso, G. Lanza, A. Santagata, P. Villani, D.J. Sordelet, Ultra-short pulse laser ablation of Al70Cu20Fe10 alloy: Nanoparticles generation and thin films deposition, Thin Solid Films 517 (2009) 1880-1886. [3] S. Amoruso, G. Ausanio, R. Bruzzese, M. Vitiello, X. Wang, Femtosecond laser pulse irradiation of solid targets as a general route to nanoparticle formation in a vacuum, Phys. Rev. B 71 (2005) 033406(1) 0331406(4). [4] R. Teghil, A. De Bonis, A. Galasso, A. Santagata, P. Villani, D.J. Sordelet, Role and importance of nanoparticles in femtosecond pulsed laser ablation deposition of Al-Cu-Fe quasicrystal, Chem. Phys. Lett. 438 (2007) 85-88.

Resume : Laser cladding is a method to deposit a coating on a substrate using laser as heating source. The interaction of the laser beam with the substrate generates a molten pool, in which the precursor material is fed. The relative movement between the beam and the workpiece makes possible to generate a layer with a thickness ranged from microns to millimeters. This technique can be applied to improve the surface properties of a new part and also in the restoration of worn or damaged components. Phosphor bronze is an alloy of copper, tin (3.5%-20%) and phosphorus (<1%). This material presents high fatigue resistance, corrosion resistance and low coefficient of friction. So, it is employed in applications like sleeve bearings or cam followers. Laser cladding technique can be employed to generate a bronze coating over steel to improve the surface properties of elements like drive shafts or bearings. In this research work, a high power near-infrared laser was employed to generate a bronze coating on AISI 4340 alloy steel (UNS G43400) substrates. The relationship between processing parameters (laser power and scanning speed) and geometry of a single laser track was examined. Microstructure and composition were studied by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS) and X-Ray Diffraction (XRD). The hardness and elastic modulus were analyzed by means of micro- and nanoindentation.

Resume : Plasma spray coating technology and deposition is one of the most important technologies available for producing the high-performance surfaces required by modern industry. In plasma spray coating process, particles are fed into a high- velocity, high- temperature gas jet where they melt or partially melt while being propelled at high velocity onto the surface to be coated. The flattening characteristics of the droplets impinging on a substrate are important determinants in governing the eventual quality of the plasma spray coating. Since plasma spray equipment is expensive to operate, the cost of developing new coatings can be very high. A computer model capable of predicting the coating properties as a function of process parameters will greatly reduce the development time and cost. Different codes have been developed in recent years to simulate the overall thermal spraying process, as well as the growth of the 3D coatings. The present investigation was carried out to have an approach to systematize the atmospheric plasma spraying process of two molten droplets in order to create a basis for numerically modeling the plasma dynamics, Keys words: Plasma spray process; molten ceramic; coating properties; fluid dynamic technique.

Resume : Medical grade polydimethyl siloxane (PDMS) elastomer is a widely used material in medicine and high-tech devises (especially like MEAs devices for neural and muscular surface interfacing) because of its mechanical flexibility and stability, high dielectric constant, optical transparency from the ultraviolet (UV) to near infrared (IR) spectral region, high biocompatibility and biostability, simple and inexpensive fabrication. Despite the low optical absorption of the native PDMS for UV, VIS and NIR wavelengths, successful laser treatment is accomplished due to the incubation process occurring below the polymer surface. With increasing of the fluence and the number of pulses chemical transformations have been revealed in the entire laser treated area. The incubation gets saturation after a certain number of pulses and the laser ablation of the material begins efficiently. This process is a complex function of the wavelength, fluence, number of pulses and the material properties as well. This work reports results on comprehensive characterization of the optical, structural and morphological properties of medical grade PDMS after surface modification by tunable fs-laser. The laser processing is accomplished using femtosecond laser system - Spitfire Ace Ti:Sapphire amplifier system (pulse width ~ 35 fs) with TOPAS Prime unit for wavelength extension from the deep UV range through the infrared (189–2000 nm). Systematic experiments are done to characterize how the laser beam parameters (wavelength (UV, VIS and IR range), fluence, and number of pulses) affect the optical absorption, surface morphology, structure and chemical composition in the laser treated areas. The material properties within the laser irradiated area are investigated by optical and laser microscope, micro-Raman spectrometry and scanning electron microscopy field emission gun.

Resume : Laser Induced Forward Transfer (LIFT) has recently proved its ability to print Organic Thin Films Transistors (OTFTs) [1,2]. In particular, pentacene could seem to be a promising organic semiconductor to design efficient OTFTs exhibiting hole mobilities up to 5-6 cm2V-1s-1 in presence of specific polymeric dielectrics [3]. However, the performances of LIFT-printed pentacene-based OTFTs remain few orders of magnitude lower than their counterparts manufactured by vacuum thermal evaporation. As the performances of such organic devices are strongly influenced by the growth and crystalline structure of the semiconducting film, as well as the quality of interfaces, it appears of prime importance to optimize the preparation of donor substrates from which LIFT-OTFTs are fabricated. In this work, we show that high-quality pentacene thin films (high crystallinity, ordered, and low surface roughness) can be produced by pulsed laser deposition without inducing any chemical degradation of pentacene molecules. Using Raman spectroscopy and x-ray reflectivity measurements, we also demonstrate that pentacene deposition on a gold layer results in highly disordered pentacene films. This observation may be one explanation for the low electrical performances of LIFT-printed pentacene-based OTFTs [1] L. Rapp, F. Serein-Spirau, J.-P. Lère-Porte, A.P. Alloncle, P. Delaporte, F. Fages, C. Videlot-Ackermann, Org. Electron. 13 (2012) 2035-2041 [2] L. Rapp, C. Constantinescu, P. Delaporte, A.P. Alloncle, Org. Electron. 15 (2014) 1868-1875. [3] S. Lee, B. Koo, J. Shin, E. Lee, H. Park, H. Kim, Appl. Phys. Lett. 88 (2006) 162109.

Resume : We report on the fabrication of adherent silver (Ag) doped carbon (C) layers deposited onto medical grade titanium substrates in order to provide to medical implants antimicrobial properties and the ability to accelerate the osseointegration process. In the search for optimal coatings capable to possess the desired mechanical and biological properties, the compositional and structural C to Ag libraries have been deposited by Combinatorial Pulsed Laser Deposition (C-PLD) technique. Thin films of Ag:C were grown onto medical grade titanium substrates by C-PLD methods using a KrF* excimer laser (λ = 248 nm, τFWHM = 25, ν = 10 Hz). Scanning electron microscopy, high resolution atomic force microscopy, energy dispersive X-Ray Spectroscopy, Rutherford backscattering spectrometry, X-ray diffraction, Raman spectroscopy, „pull-out” tests and surfaces energy measurements were employed to evaluate the morphological, structural, chemical and mechanical properties of the implant-type coatings. The biological response of the obtained thin films was assessed by in vitro investigations of the proliferation, adherence and cytotoxicity of cells cultivated on the surface.

Resume : CO2 laser pyrolsysis technique has been used for the synthesis of nanocrystalline powders as mixtures between the two tin oxides: SnO and SnO2. Cobalt-doped Sn oxides (SnO main phase) nanoparticles were also obtained at different ratios (1/40, 1/20, 1/10 and 1/5) between Co and Sn precursors. Sn(CH3)4 and CoNO(CO)3 vapors were used as the metal precursors, C2H4 as laser energy transfer agent and a N2 /O2 mixture as oxidizer. The key process parameters: system pressure, laser power and reactive gas flows were modified to obtain a nanoparticle-generating stable reaction zone (flame). Generally, the nanoparticles have spherical shapes with ~30 nm diameter. A weak particle size decreasing tendency was observed with increasing the dopant precursor flow. The elemental compositions and also the ratios between tin oxides were evaluated with EDX technique assuming the presence of Co only as CoO. XRD and SAED analyses show the presence of the two crystalline tin oxides, traces of metallic Sn and, at high Co doping level (more then 10 at.%), the presence of cobalt oxide. The tin oxides based nanocrystals have a high Li insertion capacity and thus these Cobalt-doped or undoped nanoparticles can be used as anode materials for Li-ion batteries. Therefore, some selected samples were tested using electrochemical measurements (cyclic voltammetry) using coin-type cells and the results show a relevant improvement for the samples with SnO as dominant phase.

Resume : In this work, we investigated the effect of laser annealing on the physical properties of sulfosalt Sn-Sb-S materials as promising candidates for thin films solar cells and phase change memory like Ge-Sb-Se/Te ternary system. SnSb4S7, Sn2Sb6S11, SnSb2S4, Sn4Sb6S13, Sn2Sb2S5 and Sn3Sb2S6 thin films were deposited by single source vacuum thermal evaporation onto unheated glass substrates.The as-deposited samples show polycristalline nature . The five compositions were annealed using ultravilolet laser under 100 mJ/cm² fluence. The structural, properties of thin films were studied using X-ray diffraction (XRD), Raman and FTIR spectroscopies. The surfaces morphologies were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The optical properties were carried out using UV-Vis spectroscopy. And the electrical measurements were focalised on the I-V and impedance spectroscopy. XRD results revealed that some samples lose their crystallinity by the laser annealing, which is conforted by the Raman measurement and the surface images of confocal microscopy. The surfaces images show that the samples having the highest Sn content are the most affected by the laser ablation. All films exhibit a high absorption coefficient (104-105 cm-1) in the visible region which is a good advantage for solar cells applications. The band gap energy decreases from 1.83 to 1.41 eV by increasing Sn content. We exploited the models of sellmeier and Wemple-DiDomenico for the analysis of the dispersion of the refractive index and the determination of the optical constants of the films.

Resume : During the last decades, femtosecond laser irradiation of materials has led to the emergence of various applications based on functionalization of surfaces at the nano- and microscale. Via inducing a periodic modification on material surfaces (band gap modification, nanostructure formation, crystallization or amorphization), optical and mechanical properties can be tailored, thus turning femtosecond laser to a key technology for development of nanophotonics, bionanoengineering, and nanomechanics. Although texturing semiconductor surfaces with femtosecond laser pulses has been studied for more than two decades, the dynamics of coupling of intense laser light with excited matter remains poorly understood. In particular, swift formation of a transient overdense electron-hole plasma dynamically modifies optical properties in the material surface layer and induces large gradients of hot charge carriers, resulting in ultrafast charge-transport phenomena. In this work, the dynamics of ultrafast laser excitation of a semiconductor material is studied theoretically on the example of silicon. A special attention is paid to the electron-hole pair dynamics, taking into account ambipolar diffusion effects and temperature-induced convection flows. The results have revealed that the charge carrier dynamics plays a key role in localization of material modification features. Modeling data on optical response are in agreement with pump-probe reflectivity measurements available in literature.

Resume : Laser ablation mechanisms of metallic targets leading to liquid nanodroplet ejection are of wide interest both from a fundamental point of view and for applications in various fields, especially when nanoparticles are involved. The phase explosion process was recognized as the driving mechanism of the expulsion of a mixture of vapor and liquid nanodroplets in the short pulse laser ablation of metals. A model based on thermodynamics that links the theory of homogeneous vapor bubble nucleation to the size distribution of the generated liquid nanoclusters has been recently proposed [Phys. Rev. E 92, 031301(R) (2015)]. The present work aims to take a step ahead to remove some assumptions made in previous work. Here an improved computational approach allows us to describe time-dependent nucleation in an homogeneous system with external heating. The simulation is designed for nanosecond laser ablation and the limits of its validity are discussed. Numerical results regarding the size distribution of formed liquid clusters and the time evolution of the process are shown for aluminum, iron, cobalt, nickel, copper, silver and gold. Connections with experimental data and molecular dynamics simulations, when available from literature, are reported and discussed.

Resume : Short pulse laser ablation of thin films is a promising technique that can produce uniformly spread non-agglomerated nanoparticles (NP) with a better size control as compared to the NPs generated in laser ablation of bulk targets. A series of large-scale atomistic simulations of femtosecond laser ablation of Ag and Pt films deposited on a transparent substrate is performed to obtain a detailed microscopic picture of the ablation phenomenon. The simulations are done for films of different thickness, from 5 to 20 nm, and a broad range of laser fluences. The dependences of the ablation mechanisms and nanoparticle size distributions on the thickness of the metal films and laser fluence are revealed in the simulations and several distinct physical regimes of the material ejection and NP formation are established. The conditions for the formation of unimodal and bimodal NP size distributions, often observed in experiments, are elucidated and the collapse of the bimodal NP size distribution into a unimodal one for film thicknesses decreasing down to 5 nm is predicted in the simulations. Moreover, the processes responsible for the surprising experimental observation of the formation of large NPs with diameters exceeding the film thickness by more than an order of magnitude are also discussed based on the simulation results. The results of the simulations are summarized in the form of a map of the physical regimes of the NP formation generated in the space of the film thickness and laser fluence.

Resume : The interaction of pulsed laser lights with amorphous semiconductor materials is applied to process thin layers of the device structures in several electronic technologies, especially when material modification is required within a few nanometers thick region near the sample surface. In melting conditions, the explosive crystallization phenomenon occurs ubiquitously during these processes due to the formation of a strongly under-cooled liquid layer. This phenomenon usually hinders the process control and, as a consequence, the material properties and quality after the irradiation are difficult to predict. This difficulty is also caused by the lack of a consistent model able to simulate the concurrent kinetics of the amorphous-liquid and liquid-crystal interfaces. Here we propose a multi-well phase-field model specifically suited for the simulation of explosive crystallization induced by pulsed laser irradiation in the nanosecond regime. The numerical implementation of the model is robust in spite of the discontinuous jump of the interface speed induced by the phenomenon. The predictive potential of the simulations is demonstrated by means of comparison of the modelling predictions with a plethora of experimental data in term of in situ reflectivity measurements and ex-situ structural, chemical and electrical characterizations.

Resume : Nanoscale periodic texturing on CVD polycrystalline diamond surface performed by femtosecond laser pointed out a relevant increase of optical absorbance and responsivity to visible and infrared radiation. The horizontal polarized laser beam has been focused perpendicularly to the diamond plate surface with a pulse energy 3.6 mJ focused on a small spot (100-200 mm in diameter) so that plates have been treated with an intensity higher than the diamond damage threshold. Fs-laser ultrashort pulses induced a controlled periodicity of ripples (in the order of 150-200 nm) and length of several μm, able to dramatically increase the diamond absorption, which is intrinsically visible-blind due the wide bandgap of 5.47 eV. The surface treatment has been performed in a high vacuum chamber (<10-7 mbar) with different laser wavelengths in order to investigate the effects on the laser induced periodic structures. Scanning Electron Microscopy (SEM) has been utilized in order to evidence the effects of the fs pulsed laser treatment on the polycrystalline structure of the diamond surface. SEM characterization shows that the surface modification is strongly dependent on both the laser wavelength and the crystallographic orientation of the single grain. As expected, different laser wavelengths induce changes in ripple periodicity: in this work we analize the experimental evidence of different induced structures due to the different grain crystallographic growth. Such study is relevant for the development and optimization of well controlled periodic structures on single crystal diamond, opening the path for novel applications.

Resume : Romania Diamond-like carbon thin films possess valuable mechanical properties that recommend them to be used in engineering fields, especially as protective coatings for metal machining tools, in view of increasing their lifetime. We have synthesized hard carbon thin films by pulsed laser deposition and further irradiated them with laser sources. The objective was to obtain on their surface periodical structures that will reduce their friction coefficient. As laser induced periodical surface structures on carbon films, generated with ps laser sources emitting in visible were not reported in literature, we conducted a thorough study of their morphology, structure and chemistry. Optical microscopy, scanning electron microscopy and atomic force microscopy investigations were conducted on films synthesized in various experimental conditions, in order to identify the energy and focusing regimes for producing surface structures on large areas. Peculiarities of surface structures such as dimensions, shapes, distances between structures and depths were investigated and 3d profiles of the irradiated surfaces were generated. Structural and chemical modifications induced by the laser radiation were studied by X-ray diffraction, micro-Raman and micro-FTIR, in order to identify cristalinity modifications or types of bonds between carbon atoms in the irradiated areas.

Resume : Formation of laser induced periodic surface structures (LIPSS) has been observed on polymers upon irradiation with a linearly polarized laser beam as the result of the interference between the incoming and the surface-scattered waves. Alternatively, irradiation through a mask induces the formation of a diffraction pattern which depends on the mask size and its distance to the sample. Poly(bisphenol A carbonate) (PBAC) films were irradiated through TEM grids using a Nd:YAG laser (266 nm, 8 ns pulses). The morphology of the polymer films was characterized by atomic force microscopy and surface properties were studied by water contact angle, colloidal probe technique and peak force quantitative nanomechanical mapping. The water contact angle of samples endowed with only LIPSS decreases in comparison to the pristine PBAC sample while for diffraction patterned films or with combination of diffraction pattern and LIPSS, the water contact angle increases. The adhesion force measured by the colloidal probe technique is very similar for pristine samples and for samples with only LIPSS. In the case of films with both kinds of structures, a significant increase of the adhesion force is observed close to the edge where micron size structure exists. When measured at the nanoscale, no significant differences are observed in the adhesion force. Our work indicates that changes of surface properties of polymer films can be controlled by this method at both the nano- and microscale.

Resume : We investigated LIPSS formation by ultra-short 800-nm laser pulses, both for single spots and for continuous line scans, on metallic targets (stainless steel, Ni, Ti) with emphasis on the effect of irradiation dose on morphology, homogeneity and periodicity of the ripples. For individual spots, we found very regular ripples of about 625-nm periodicity on all materials, perpendicular to the laser polarization. They are similar for all irradiation doses. Increasing the dose does not really change the ripples features but results in (a) a quadratic increase of the affected area, and (b) in a complex array of irregular grooves, dividing the central area in larger bullets. The latter structures slightly follow the Gaussian beam profile, with a shallow crater developing. For a continuous line scan in the direction of the electric field we do no longer find the dependence on the Gaussian beam profile, such as crater formation or the groove/bullet formation. Instead, the surface morphology is very regular over the whole trace. However, ripples orientation and wavelength are slightly scattered in a range of  15 %. This behavior is quite different from non-metallic targets, like silicon, where the beam profile is strongly visible across the trace. Thus, metal LIPSS-processing appears much more attractive for applications in tribology and wettability. For other materials, a promising strategy might be the structuring of a metal mold which is then transferred by plastic impression.

Resume : Laser induced periodic surfaces structures (LIPSS) formation is investigated on mesoporous silicon (MeP-Si) surface irradiated by ultra-short pulsed laser beams at 266 nm central wavelength. A comparative study is presented here on the dynamic of LIPSS formation on MeP-Si using two utlra-short laser beams. The first one is a Nd:YAG laser beam with 40 ps pulse duration, and the second is a Ti:Sapphire laser beam with a pulse duration close to 100 fs. Very low beam fluences were used in the range of 20 to 100 mJ/cm². Scanning electron microcopy (SEM) top view characterization displayed the formation of low spatial frequency LIPSS (LSFL) from nanoparticles by different mechanisms mainly coalescence and agglomeration at relatively low laser beam fluence but after a large number of laser pulse. However the cross section characterization have shown the formation of a liquid phase inside and below the LIPSS whatever was the used beam. In addition, transmission electron microscopy (TEM) experiments are conducted to investigate the molten silicon phase. It is found that after cooling of the liquid phase formed inside these LSFL a dominant amorphous phase is produced in the picosecond regime as well as in the femtosecond. However the mesoporous silicon between two ripples remains always well-crystallized. Finally a Micro-Raman spectroscopy analysis are performed to identify the chemical composition of the molten phase mainly on the close surface vicinity because all experiments were carried out in air ambient.

Resume : Concluding remarks. End of the Symposium.