Laser and plasma processing for advanced applications in material science

Resume : The talk will provide an overview of the use of fs time-resolved microscopy for studying the interaction of ultrashort laser pulses with dielectrics. This technique constitutes a powerful pump-probe tool for imaging ultrafast ablation and non-linear propagation, providing a means for optimization of fs-laser processing applications related to the fabrication of high precision micro-/nanostructures and integrated photonics devices. Applied to surface processing, fs-microscopy has the capability of imaging and quantifying laser-induced free-electron plasmas and their temporal evolution. Establishing a relation between local plasma densities and material modifications becomes especially important when searching for optimum temporal pulse shapes for tailored processing. In some dielectrics a transient ring pattern can be observed within the ablating region that changes for increasing pump-probe delays. These “transient Newton rings” point towards an ablation mechanism based on the expansion of a transparent thin shell, similar to that found in metals and semiconductors. When applied to bulk processing inside dielectrics, fs-microscopy unveils numerous complex interaction mechanisms, including self-focusing, beam filamentation and pre-focal energy depletion, strongly deteriorating the spatial distribution of the deposited laser energy. We show how these undesirable effects can be minimized by adjusting the processing parameters, enabling the fabrication of optimized structures.

Resume : Plasma plumes generated by femtosecond laser ablation of several metals (W, In, Te, Mn, Ni, Cu, Al) were investigated through Langmuir probe measurements. The aim of these experiments has been to establish a link between the plasma characteristics (temperatures, electron density, average charge state) and the physical properties of the targets (electrical and thermal conductivities, melting, boiling points etc.). The experiments were performed at various background pressures (10-2 -10-5 Torr), target biases and probe-target axial distances. The time-dependence of the probe current is studied assuming a shifted Maxwellian velocity distribution. By applying various probe biasing voltages and current time-integration, the probe volt-ampere characteristics were obtained. Two types of particles (hot and cold) are evidenced as having different temperatures and expansion velocities. An additional positive target biasing gives a residual ion current as consequence of center-of-mass velocity changing, and the probe characteristic is shifted with a constant value. At higher pressure (~10-2 Torr), an interesting behavior was observed in the electronic branch of the volt-ampere probe characteristics: periodic drops of the current for specific values of the probe bias. Some hypothesis on the origin of this peculiar behavior will be presented, along with a tentative correlation with the physical properties of the various metals investigated.

Resume : Thanks to recent advances in ultra-short pulsed laser manufacturing, reliable and high power Femto second lasers can now be used to process materials with a high degree of accuracy and resolution. Additionally, the non-linear absorption process taking place at the laser/material interface has widened the range of materials that can be processed. Diffractive Optical Element (DOE) manufacturing is a time consuming process involving many steps: coating, mask alignment and etching. Direct engraving of the DOE with a laser beam could be a very efficient means of rapid prototype manufacturing. Successful machining of a DOE in BK7 was obtained using an Amplitude Tangerine Femtosecond laser combined with a high-performance linear motor stage. The surface functionalisation was performed with a beam at a wavelength of 343 nm, a pulse width of 350 fs and a pulse energy of 20 ?J. By focussing the laser beam with a microscope objective, a binary phase grating with a period of 20 ?m, a groove depth and width of 1 ?m and 8 ?m respectively, was machined. The DOE profile was characterised by white light scanning interferometry and the diffractive efficiency measurements were corroborated by simulations performed by a Rigorous Electromagnetic Fourier Modal Method, taking into account the measurement profile. These encouraging results prove that high-speed femto second laser manufacturing of DOE in bulk glasses can be achieved, opening the way to rapid prototyping of multi-layered-DOEs.

Resume : In recent years, there has been a growing interest in ultrafast (femtosecond) laser processing of transparent materials and thin glasses for clean, efficient and high quality cutting and drilling. In this work, we study a concept that ultrashort laser pulses ensure laser ablation with lower heating of glass matrix at reduced thermal stresses as compared to longer pulses. Furthermore, avalanche ionization can be considerably suppressed by limiting number of free electron collisions via shortening the pulse duration and/or reducing laser fluence per pulse. The results will be presented on comparison of ultrafast laser ablation of fused silica and Willow glasses, which have different thermophysical and optical properties. Single- and multi-shot laser ablation was performed by Ti:sapphire laser operating at wavelength of 800 nm with pulse duration of 130 fs. A range of techniques such as optical profilometry, scanning electron microscopy, and space-and-time resolved spectroscopy were used to study crater profiles and quality as well as optical emission from laser ablated material and air plasma excited in front of the irradiation spot. The effect of varying fluence for femtosecond laser pulses was also studied. Damage thresholds for samples under study are compared. The excitation levels and glass temperature were evaluated based on the rate and energy equations.

Resume : Modeling of thermodynamic properties and phase transitions of materials is required at numerical simulation of processes of intense pulsed influences on condensed media. In the present work, an equation-of-state model for silica is proposed with taking into account the polymorphic transformations, melting and evaporation effects. As distinct from the previously obtained 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 silica over a wide range of densities and temperatures.

Resume : Medical grade polydimethylsiloxane (PDMS) elastomer is a widely used biomaterial in medicine and for production of high-tech devises – MEMS and NEMS. Up to now, samples of PDMS-elastomer are processed by UV or VIS fs- and ns-laser pulses. The tracks produced are successfully metalized by Pt or Ni via electroless plating. The metallization process is found to be not sensitive with respect to the time interval after the laser treatment. In this work we present much wide study of the PDMS-elastomer processed by IR, VIS and UV fs-laser pulses. Different processing parameters as laser wavelength, pulse duration, fluence, scanning speed and overlapping of the subsequent pulses are varied in order to activate and change of the surface morphology. High definition tracks are produced. Analyses by AFM, SEM and Raman scattering analyses are accomplished in order to get information about the alteration of the chemical composition and structural morphology of the ablated traces. All properties will be compared with those of the native material. Our results will confirm the promising expectation with respect to use such a laser-based method for micro- or nano-fabrication of hi-tech PDMS devices.

Resume : Several types of regular nanostructures were produced at the surface of an old, filled hard disk by irradiation with a femtosecond white light continuum. The 40-Gb disk consists of a glass substrate, covered by a 100 nm thick magnetic film and a 5 nm protecting cover layer. In most of the irradiated area, the film structure is replaced by a regular array of bubbles with average diameters of 250 nm. From the substantial extension of these spheres above the original virgin film surface we conclude that they are spheres of rearranged, aggregated film material. This assumption is further supported by the fact that, at the spot edge, regions of completely removed film are adjacent to even larger spheres with diameters up to 1 µm. Even further out at the spot edge, arrays of long (1.5 … 7 µm) parallel lines are found in regions where the protecting cover layer is removed, with a width of about 400 nm and a separation of about 500 nm. These lines are, again, higher than the surrounding surface by 20 nm, and are sub-structured in 200-nm long segments of 10-nm height. It is not yet clear whether these structures are remnants of the magnetic bit structures of the hard disk.

Resume : Multi-pulse femtosecond-laser irradiation of semiconductors in air leads to the formation of sub-wavelength periodic surface structures. The origin of laser-induced periodic surface structures (LIPSS) remains an open problem and still requires advanced theoretical studies. Recently, the role of Surface Electromagnetic Waves (SEW) was demonstrated theoretically and experimentally in several studies on temporal evolution of material surfaces after single-pulse excitation and under double-pulse irradiation with different separation time. However, theoretical predictions of LIPSS period remains imprecise. In this work, using 40 fs, 800-nm pulse irradiations, periodic structures perpendicular to the laser polarization were obtained on bulk silicon and silicon carbide films deposited on a Si substrates. Several SEW models were compared with the experimental measurements as a function of laser fluence. As a result, the structures on the bulk Si with near-wavelength period are quantitatively explained by the “Sipe-Drude” model, while on the SiC film the LIPSS with period of 100-150 nm are well described by laser coupling of Surface Plasmon Polaritons (“SPP-Drude” model) excited at the SiC-Si interface.

Resume : Laser-induced periodic surface structures (LIPSS) can be found on the surface of metals, dielectrics and semiconductor materials processed with single and multiple femtosecond laser pulses. The existing models of the femtosecond LIPSS formation try to describe periodic modulation of the electron and ion temperatures. However the mechanism how the temperature profile can result in a periodically-modulated surface profile in such a short time (less than 1 nanosecond) is still not clear. Estimations made on the basis of different hydrodynamic instabilities allow to sort out some mechanisms, which can bridge the gap between the temperature and the surface profile formation.

Resume : Sub-microstructured polymer films on solid substrates are used in many technological applications as optical elements, photonic crystals, high-density magnetic data storage devices and biosensors. In particular, semiconducting polymers like poly(3-hexyl thiophene) (P3HT) have been widely studied as active layers in organic thin film transistors and organic photovoltaic solar cells. Here we report on the formation of laser induced periodic surface structures (LIPSS) in P3HT thin films upon irradiation with the linearly polarized second and fourth harmonics of a Nd:YAG laser (532 and 266 nm, 8 ns pulses). By optimizing irradiation parameters (number of pulses and laser fluence) polymer gratings with different levels of order can be obtained. In particular, the high optical absorption of P3HT at 532 nm enables the formation of ordered nanostructures with periodicities around 460 nm. Raman spectroscopy at the excitation wavelengths of 785 and 442 nm was used in order to obtain information about both laser induced chemical and structural modifications, since molecular order and crystallinity in semiconducting polymers have a significant effect on their properties. As a matter of fact, conductive atomic force microscopy (C-AFM), which was used to measure the current through the film thickness, revealed differences in P3HT conductivity between valleys and ridges. Results are discussed in terms of the processes involved in LIPSS formation and related to potential applications.

Resume : The manufacturing of metal surfaces with highly controllable wetting properties is becoming a very active field in research and engineering. Based on nature examples like rose petals or lotus effect, an effective approach for this purpose is the combination of micro- and nano-structures into hierarchical structures. Traditionally these structures are manufactured by using different types of coatings. However, this can be achieved by only using femtosecond laser ablation in air atmosphere. The first part of this work is a study to determine the microscale modifications produced on a stainless steel alloy (AISI304) surface at high pulse energy, different velocities, and focal distance in order to obtain microstructures with a selected depth of 5 μm and line widths of 30-35 μm. The second part of the work is focused on finding the optima irradiation parameters to obtain the nanostructure pattern. Nanostructures have been defined by means of Laser Induced Periodical Surface Structures (LIPSS) of around 200nm high and a period of 500nm, which constitutes the nanostructure pattern. Finally, dual scale gratings of 50mm2 were fabricated for a range of irradiation parameters (line period, fluence, ablated depth or focal distance) and their effect on the measured contact angle. Combining the micro-pattern with the LIPSS nano-pattern, we have obtained almost superhydrophobic surfaces with measured static contact angles between 130 and 140º, from initial contact angles of 60º.

Resume : The vast majority of studies about the effects of radiation on the structure and properties of materials used in nuclear reactors or outer space applications have been performed on single crystals or pellets having large grain sizes. However, some specific applications require the use of thin films that are polycrystalline or even nanocrystalline. The effects of radiation on such thin films have only recently been studied, because it is quite difficult to obtain high quality samples. The Pulsed Laser Deposition (PLD) technique is very suitable for this task since it can grow some of the highest quality thin films of almost any materials starting from inexpensive targets. First, it allows the growth of high crystalline quality films at relatively lower substrate temperatures than other techniques. Secondly, by changing the deposition parameters, films possessing different chemical compositions and/or structures could be easily obtained. Thirdly, the surface morphology of the deposited films is very smooth, allowing for the use of characterization techniques such as X-ray reflectivity, grazing incidence X-ray diffraction, X-ray photoelectron spectroscopy, or nanoindentation that possess depth resolutions of the order of few nm. To illustrate these advantages, results obtained on ZrC, ZrN, and SiC thin films grown on Si substrates by the PLD technique that were ion-irradiated at room temperature by 800 keV Ar ions will be presented.

Resume : Al-doped ZnO (AZO) thin films with uncommon (110) orientation are obtained on amorphous substrates (glass and polysulfone) through Sequential Pulsed Laser Deposition technique from metallic targets at low substrate temperature (below 100°C). The structural, optical and electrical properties are investigated systematically depending on the oxygen deposition pressure (1 to 10 Pa) and doping concentration (≤ 4.4% at.). For AZO/glass samples we notice a change of the growing mode from (002) preferential orientation to an uncommon (110) preferential orientation through a combined effect of doping concentration and deposition pressure. This transition is accompanied by a change of the morphology (a granular structure with a decreasing density as the (110) peak become dominant), band gap widens (up to 3.88 eV) and electrical resistivity drops (~1x10^-3 Ωcm). As it is well known, for a ZnO material with a wurtzite structure spontaneous and strain induced polarization generate electric fields along the c axis causing a decrease of the quantum efficiency. Therefore, materials for which the c axis is in line with the films surface could be used for light emitting devices (OLEDs) with improved properties. For this reason, we performed AZO thin films deposition on polysulfone substrate to be used as anod for flexible OLEDs. We currently investigate the mechanism responsible for the (002) phase suppression and (110) phase growth for both AZO/glass and AZO/polymer deposited samples.

Resume : Europium oxide films have received large attraction for their use in the fields of microelectronics, spintronics, magnetism and photonics. The fabrication of crystalline high quality pure Eu-oxide thin films is challenging, and growth under oxide gas environment and high temperature processing are usually necessary. However, such processing can lead to the formation of Eu-silicides when Si substrates are used [1]. In this work, we report the preparation of Eu-oxide thin films (200 nm) in vacuum by pulsed laser deposition at room temperature on Si substrates. For deposition an ArF laser (193 nm) was focused on a pure sintered Europium oxide bulk target. In order to study the possible reaction of the Eu-oxide film with the Si substrate films with and without an amorphous Al2O3 buffer layer were deposited. Post-deposition annealing treatments where performed under different conditions. As result, according to the analysis of Raman and X-ray Diffraction (XRD) measurements, crystalline films are formed where both cubic and monoclinic phases can be identified. No silicide formations have been seen. Photoluminescence has been studied under laser excitation at 355 nm. All the films show intense and narrow peaks that are attributed to the intra 4f-transitions of Eu3+ ion in a crystalline host. However, clearly different emission spectra are observed as a function of the specific crystalline phases present. Changes in the magnetic hyperfine 5D0 – 7F0 transition at 612 nm confirms the crystal field effect and its influence over energy level splitting. The relationship of the photoluminescence emission spectra and the crystal structure will be discussed, as well as the possibility of the reduction of the Eu oxidation state. [1] G. Bellochi et al., Optics Express 20, 5501 (2012)

Resume : Ferrites are important magnetic materials with wide application area in current and emerging technologies. Within this class of materials, cobalt ferrite presents the highest magnetostrictive response due to which many sensors, actuators and magnetoelectric composites use this material as active component. Based on the large Faraday effect in the 700–800 and 400–500 nm spectral ranges, cobalt ferrite is considered as a possible alternative for magneto-optical (MO) devices. Among other effects, rare earth ions are reported to lower the Curie temperature and increase the MO response when present in ferrite structures. The RE substitution can also decrease the grain size, which is an important factor in low noise media. The aim of our study is to analyze the influence of rare earth substitution and deposition conditions on the structural, chemical, optical and magnetic properties of cobalt ferrite thin films. In this context CoFe1.8RE0.2O4 (RE=Gd, Dy, La) thin films were grown in different conditions by Pulsed Laser Deposition. The varied experimental parameters were target-substrate distance, laser fluence, deposition time and substrate type and temperature. The presence of the RE with large ionic radii determined a distortion of the spinel structure. The magnetic measurements revealed an increased magnetization for the CoFe1.8Gd0.2O4 thin film deposited at 400oC and while the La doped sample presented lower magnetization value.

Resume : New materials are required in order to meet upcoming technology nodes or to progress ‘beyond Moore’. It is well known that Pulsed Laser Deposition (PLD) is a very flexible and versatile technique allowing fast optimization of new thin film materials. Moreover PLD is superior above other deposition technologies for the stabilization of volatile elements and nucleation of complex oxide material systems. 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 new SolMateS’ R&D 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. The small footprint makes it very easy to attach it to an existing PLD beam path in the research facility. Since process recipes can be transferred directly to SolMateS’ PLD production equipment it is the ultimate valorization of thin film research. The PLD R&D platform is the missing link between lab and fab. The first SolMateS’ PLD production platform is installed in the field in 2013. This tool is the ultimate proof that PLD has now reached the maturity level of High Volume Manufacturing (HVM). This next generation deposition system is suitable for development and (pilot-) production purposes. It is designed for stability, reliability and low maintenance. Equipped with automated wafer handling it offers high run-to-run consistency at commercial throughput and yield. The PLD production platform accelerates the entry of new materials into commercial products. In this contribution the latest performance and specifications of the SolMateS’ PLD platforms are addressed. Data on stability and reproducibility of wafer scale deposition of piezoelectric Pb(Zr,Ti)O3 (PZT) thin films with excellent properties will be presented. Furthermore, performances and applications of Indium Tin Oxide and Aluminum Oxide thin films deposited with qualified processes will be shown.

Resume : Nanosized materials have attracted scientific and technological interest over the recent years due to the size dependent properties that can vary considerably from those of the bulk material. In particular, for semiconductor nanocrystals this allows adjustment of absorption and emission properties. GaAs is one of the most important III–V semiconductors that finds wide applications in electronic industry1. GaAs nanoparticles present large energy bandgap and a large exciton Bohr radius2 so that the quantum confinement effect is pronounced also for relatively big nanoparticles. This allows tuning of the band gap of the nanocrystals across the visible spectrum and makes nanocrystalline GaAs siutable for various applications. GaAs nanocrystals have been obtained both by chemical and physical techniques. We used the Laser Ablation in Liquid technique since it presents some advantages and can be applied for the preparation of colloidal semiconductor solutions. We have investigated the ablation of a GaAs crystalline target in acetone by two laser sources (Nd:glass 527nm, 250fs and 10 Hz and Nd:YAG 532nm, 7ns and 10Hz) with the aim of compare the effect of pulse duration on the physical and chemical processes involved during the ablation and, consequently, on the obtained nanoparticles properties. The ablation process has been studied both by shadowgraphic technique and optical emission spectroscopy and the obtained products have been characterized by transmission electron and scanning electron microscopies, by micro-Raman spectroscopy and X-ray diffraction. 1. A. Bar-Lev, Semiconductors and Electronic Devices, 2nd edn., Prentice Hall, New York (1984). 2. Y. Fu, M. Willander, E. L. Ivchenko, Superlattices Microstruct. 27, 255 (2000).

Resume : The processing of SiOx film with the typical thermal annealing is not localized process and can lead during annealing to the destruction of the electronic circuits components that are on the same substrate. Only recently, for the formation of nc-Si in SiOx film, the laser annealing was first used. For efficient use of nanostructures in silicon electronics it is necessary to perform the comprehensive theoretical and experimental study of the laser annealing process of non-stoichiometric SiOx films. In this paper, advancement of temperature profiles is analyzed in a non-stoichiometric film SiOx To simulate the temperature profile in the corresponding film used the following laser parameters: pulse duration 10 ns, the intensity of the laser beam is varied in the range of 14 ? 52 МW/сm2. The distribution of the temperature field in the film during its heated single laser beam described nonstationary heat equation, which is solved the numerical by finite element method.It is shown that the smaller the duration of the laser pulse, the greater the local temperature (temperature at the time of contact of pulse with the surface). Therefore, the pulse width is a parameter that can adjust the temperature on the surface of the sample and therefore further temperature distribution in the sample volume.

Resume : Laser-assisted atomic probe tomography is a versatile tool to analyze chemical composition of different materials (metals, semiconductors, dielectrics) with an atomic resolution. A solid tip is placed in a strong DC field and is subjected to rather weak ultra-short laser pulses. As a result, surface atoms are evaporated towards a detector one by one. For metals, evaporation is triggered by thermal heating of the tip apex. For oxides, additional high field effects explain the ultrafast contribution in Time Of Flight (TOF) observations. However, a second peak is usually obtained for semiconductors, and its origin remained unexplained. In this study, a three-temperature 3D model is applied to a silicon tip irradiated by femtosecond laser. Optical absorption of the laser pulse by the sub-wavelength tip reveals a strong enhancement of the laser field inside the tip, highly dependent to the tip geometry and to the laser wavelength. The numerical calculations demonstrate that inhomogeneous laser energy coupling with silicon lattice followed by energy diffusion result in a delayed heating of the apex, explaining the second peak observed in Time Of Flight measurements. The energy balance reveals that contribution of the Auger recombination to the heating depends on the laser wavelength and explains the experimental results.

Resume : The paper presents results on laser nanostructuring of Ag thin films. The thin films are deposited on glass substrates by pulsed laser deposition technology. Then the films are annealed by nanosecond laser pulses delivered by Nd:YAG laser system operated at λ = 355 nm. The film modification is studied as a function of the film thickness and the parameters of the laser irradiation as pulse number and laser fluence. In order to estimate the influence of the environment on the characteristics of the fabricated structures the Ag films are annealed in different surrounding media: water, air and vacuum. It is found that at certain conditions the laser treatment may lead to decomposition of the films into a monolayer of nanoparticles with narrow size distribution. The optical properties of the fabricated nanostructures are investigated on the basis of transmission spectra taken by optical spectrometer. In the measured spectra plasmon resonance band is observed as its shape and position vary depending on the processing conditions. The fabricated structures are covered with Rhodamine 6G and tested as active substrates for Surface Enhanced Raman Spectroscopy (SERS).

Resume : Medical grade polydimethylsiloxane (PDMS) elastomer is a widely used biomaterial in medicine and high-tech devises because of its remarkable properties: mechanical flexibility and stability; high dielectric constant and breakdown field; optical transparency in the ultraviolet (UV) – visible (VIS) spectral regions; high biocompatibility and biostability; simple and inexpensive fabrication. High definition tracks and electrodes can be accomplished by UV or VIS ns- or fs-laser pulse processing with subsequent metallization in order to get alterations of the chemical composition and structural morphology of the ablated traces. The importance of knowing the changes of the morphology, structure and chemical properties of the laser processed material will help to understand nature of the laser - matter interaction. In this work we present experimental results on change of the morphology, chemical composition and structure of UV, VIS and IR ns-laser processing. Laser processing of medical grade PDMS elastomer is accomplished using fundamental (λ = 1.06 µm), 2nd HG (λ = 532 nm) and 4th HG (λ = 266 nm) of Q-switched Nd:YAG laser (pulse duration τ=15 ns and rep rate of 10 Hz). The as-processed material is studied by XRD, SEM and µ-Raman analyses in order to get information for the influence of different processing parameters as laser wavelength, fluence and subsequent pulses on the surface morphology, crystallinity and chemical changing.

Resume : In this work results on laser processing of zinc oxide thin films deposited on different substrates are presented. ZnO films are deposited by classical PLD method in oxygen atmosphere on metal and quartz substrates. The produced films are then processed by nanosecond pulses delivered by Nd:YAG laser system. The laser processing parameters and the film thickness are varied and their influence on the fabricated structures is presented. The film morphology after the laser treatment strongly depends on the substrate. It is shown that at certain conditions the laser treatment of the film deposited on metal substrate leads to formation of a discrete nanostructure, composed of spherical like nanoparticles. The structure, morphology and optical properties of the fabricated samples are presented and discussed. The demonstrated method is an alternative way for fabrication of ZnO nanostructures with application in solar cell technology, sensor devise fabrication and optoelectronics.

Resume : The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of silicon by multiple linearly polarized 30 fs laser pulses (wavelength of 790 nm) is studied in air and water environment. The LIPSS surface morphologies are characterized by scanning electron microscopy and their spatial periods are quantified by two-dimensional Fourier analyses. It is demonstrated that the irradiation environment significantly influences the periodicity of the LIPSS. In air, low-spatial frequency LIPSS (LSFL) were found with periods somewhat smaller than the laser wavelength (70% of laser wavelength) and an orientation perpendicular to the laser polarization. In contrast, for laser processing in water, a reduced ablation threshold and LIPSS with approximately five times smaller periods (15% of laser wavelength) were observed in the same direction as in air. A thin-film based surface plasmon polariton model successfully describes the tremendously reduced LIPSS periods in water.

Resume : The quest for light absorption enhancement in future photovoltaics is relying on the surface plasmon resonance too. This can be realized by aluminium nanoparticles application. When placed close to the photoactive layer of bulk of the heterojunction, they scatter light heavily into the optically active layer, and thus enhance the efficiency of photovoltaic devices. For such an application, a good control of nanoparticles sizes and space distribution is a must. The control of sizes via thermal treatment sometimes calls for prohibitively high annealing temperatures, that tend to damage the heterojunction structure itself. Therefore, laser dewetting is an alternative mode of creating these plasmonic nanoparticles, while avoiding the need for excessive temperatures in the thermal treatment. Here we report on aluminium nanoparticle production by laser induced dewetting. Initially smooth Al films, produced by magnetron sputtering on monocrystalline silicon at room temperature were treated by nanosecond pulsed infra-red and ultra-violet laser. The nominal film thickness was ranged from 10 to 20nm, while the number of pulses varied from 1000 to 10 000, and single pulse energy fluence from 70 to 200mJ/cm2. Sharp size distribution, that is suitable for application, has been obtained for optimized combination of pulse number and fluence.

Resume : The nanostructures of porous ZnO are subject of research interest, due to their specific structure with high surface to volume ratio that may produce peculiar properties for use in sensing and optoelectronics applications. On the other hand, a large electromagnetic field enhancement originated from the localized surface plasmon resonance of noble metal nanostructures is employed in various applications. This research is focused on investigation of the coupled plasmonic-semiconducting nanomaterials for photoluminescence emission enhancement and SERS applications. The produced porous ZnO nanostructures with plasmonic Ag inclusions exhibit interesting and promising results. These heterostructured nanocomposites hold a great potential in applications such as a light emitting devices and SERS substrates. We demonstrate a two-step laser method for incorporating of plasmonic Ag nanoparticles into porous metal–oxide semiconductors. The synthesis is carried out by Nd:YAG laser and consisted of PLD from mosaic ZnO/Ag target and post deposition fragmentation by laser annealing. The produced porous ZnO nanostructures with plasmonic AgNPs exhibited interesting and promising results. The phase structure, chemical composition and morphology were analyzed by XRD, XPS and HRSEM. The plasmon resonance absorption was confirmed by optical transmission spectroscopy in the spectral range of 200-800 nm. The SERS activity and PL emission enhancement of the composites were studied.

Resume : In order to address the dynamics and physical mechanisms of LIPSS formation for three different classes of materials (metals, semiconductors, and dielectrics), two-color double-fs-pulse experiments were performed on titanium, silicon and fused silica. For that purpose a Mach-Zehnder interferometer generated polarization controlled (parallel or cross-polarized) double-pulse sequences at 400 and 800 nm wavelength, with inter-pulse delays up to a few picoseconds. Multiple of these two-color double-pulse sequences were collinearly focused by a spherical mirror to the sample surfaces. The fluence of each individual pulse (400 & 800 nm) was always kept below its respective ablation threshold and only the joint action of both pulses lead to the formation of LIPSS. Their resulting characteristics (periods, areas) were analyzed by scanning electron microscopy. The periods along with the LIPSS orientation allow a clear identification of the pulse which dominates the energy coupling to the material. For strong absorbing materials (silicon, titanium), a wavelength-dependent plasmonic mechanism can explain the delay-dependence of the LIPSS. In contrast, for dielectrics (fused silica) the first pulse always dominates the energy deposition and LIPSS orientation, supporting a non-plasmonic formation scenario. For all materials, these two-color experiments confirm the importance of the ultrafast energy deposition stage for LIPSS formation.

Resume : Laser-induced periodic surface structures (LIPSS) were generated on pure titanium and titanium alloy (Ti6Al4V) surfaces upon irradiation with multiple linear polarized femtosecond laser pulses in air (30 fs duration, 790 nm wavelength, 1 kHz pulse repetition rate, Gaussian beam shape). The conditions were optimized in a sample-scanning geometry for the processing of large surface areas covered homogeneously by two different types of nanostructures, i.e., low-spatial frequency LIPSS (LSFL) with periods around 600 nm and high-spatial frequency LIPSS (HSFL) having periods around 100 nm. For both types of nanostructures the tribological performance was characterized under reciprocating sliding condition against a ball of hardened steel at 1 Hz using different lubricants. After 1000 cycles, the corresponding wear tracks were characterized by optical and electron microscopy. For specific conditions, the wear was strongly reduced and the nanostructures (LSFL) endured the tribological treatment. Simultaneously, a significant reduction of the friction coefficient was observed, indicating the potential benefit of laser surface structuring for tribological applications. For optimization, the spatially Gaussian shaped beam used for the laser processing was transformed into a Top-Hat distribution by using a spatial light modulator (0.1 kHz). The tribological performance of samples processed with a Top-Hat beam is compared to that obtained with a Gaussian laser beam.

Resume : We present results on fabrication and characterization of Sr3Co2Fe24O41 nanostructures in colloid. Nanosecond laser ablation in liquid is used as a method for sample preparation. The target is fabricated from microparticles obtained by sol-gel auto-combustion. The powders synthesized are then pressed and annealed at a high temperature for a certain time and subsequently quenched rapidly to room temperature. The target is ablated in double distilled water using a Nd:YAG laser system. The laser wavelength (the fundamental, second and third harmonics) and fluence are varied in order to estimate their influence on the morphology of the nanostructures produced. The stability is also investigated of the colloids during their aging. To study the colloid’s optical properties, the optical transmission is measured in the near UV and visible regions. The shape of the nanostructures and their size distribution are visualized by using SEM and TEM analysis. XRD, SAED and HRTEM are utilized to examine the material phases of the nanostructures obtained. The results presented could be used for designing nanostructures fabrication technologies with parameters appropriate for application in the fields of spintronics and biomedicine.

Resume : Polydimethylsiloxane (PDMS) elastomer is a widely used material in medicine and high-tech devises 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 absorption of the native PDMS for UV, VIS and near IR wavelengths, the laser treatment is enhanced by an incubation process. The latter occurs as a result of the multipulse processing. In such a way, the initial absorbed laser fluence is valid only for the first laser pulse hitting the material. The next consecutive pulses interact with the material with changed optical properties. The importance of knowing the exact optical properties of the material will help to the description of the interaction between laser radiation and material as well as modeling of the process. In this work we present experimental results on gradual change of the optical properties during UV, VIS and IR ns-laser processing. Laser processing of medical grade PDMS elastomer is accomplished using fundamental (λ = 1006 nm), 2nd HG (λ = 532 nm) and 4th HG (λ = 266 nm) of Q-switched Nd:YAG laser (pulse duration τ=15 ns and rep rate of 10 Hz). The influence of different processing parameters as laser wavelength, fluence and number of the subsequent pulses on the optical absorption and surface morphology are studied.

Resume : Surface texturing by ultrashort laser pulses, in the range of hundreds of femtoseconds, is a simple and fast process that can be used to modify physicochemical properties of the irradiated area. A self-organization of the matter after laser irradiation results in micro- and nano-scaled structures on the sample surface. Surface specifications rely greatly on the control of key-parameters of the laser such as wavelength, laser fluence, polarization, spot overlap or number of impacts. According to the process parameters, structures at two scales are generated, allowing the changing of for instance the visual aspect of the surface or it’s wetting behaviour. This paper will focus on the generation of self-organized nanostructures known as ripples on a stainless steel sample, and on their characterization using the 2D Fast Fourier Transform technique. Ripples are periodic nanometric structures, assembled according to a preferential direction. In the case of a linear polarized laser beam, both these orientations are perpendicular. By inserting a half-wave plate into the optical path, it is easy to rotate the linear polarization around the optical axis and so modify the direction of the ripples. Characterization of these nanostructures by Scanning Electron Microscopy provides high resolution images, with the advantage that very high spatial frequencies can be reached for the calculation of the 2D Fast Fourier Transform of the periodicity of the ripples.

Resume : Pulsed laser ablation technique in liquids (PLAL) is one of the hot topics of contemporary research in the field of nanotechnology. In the most cases PLAL is used to produce particles of metals and their oxides, and there are relatively few works devoted to the synthesis of composite NPs. Composite systems are of great interest, because their properties generally differ from those of similar single-component structures. In addition, the physical properties of composite particles can be varied by changing their component ratio. In the present paper several approaches of PLAL, for example based on the sequential ablation of different targets in the same solution, simultaneous ablation of combined target, post irradiation method as well as a combination of different approaches have been developed to prepare bimetallic nanoparticles (Ag-Au, Ag-Cu) and particles of complex composition, such as Ag-ZnO nanocomposites and magnetic nanoscale compounds and alloys of gadolinium. By controlling laser irradiation time and laser energy different structures like core-shell, chain-like structure and hollow particles have been synthesized. The effect of several polymers like PVP, PVA and polysaccharides on the morphology and size stabilization of the generated nanostructures in the laser ablation and the secondary laser irradiation processes has been investigated. The possibility of application of the synthesized nanostructures in sensing, optics and biomedicine will be discussed.

Resume : Slate is a natural rock that has a very important presence in European buildings. It is usually employed in roofs, façades and for tiling. In spite of this broad use, production process of slate tiles is not optimized. An important quantity of slate from the quarry is wasted during the manufacturing of the final product. Therefore, companies are looking for new and improved methods capable of enhance their efficiency in order to increase productivity and reduce costs. Drilling is an important part of this manufacturing process. Conventional tools usually cause breaking of the slate tiles, so even a higher quantity of material is wasted. In this sense, laser is a very suitable tool to produce holes in this material since it does not generate any mechanical stresses on the workpiece. In this work we present a comprehensive experimental study on laser microdrilling of slate tiles. We employed a Design of Experiments (DoE) methodology to establish the influence of the most important processing parameters on the diameter of the holes. We also employed a Response Surface methodology to determine non-linear behaviors and the interdependence of these processing parameters on the geometry and quality of holes. Finally, we were able to produce holes with less than 100 microns in diameter, avoiding any fracture, and with a processing time of 45 ms per hole.

Resume : Long-range arrays of well-shaped metal nanostructures have been fabricated by a hybrid methodology, i.e. using Langmuir microsphere films and laser-assisted dewetting. As the initial step, we use colloidal lithography. Monolayers of 1-5 μm polystyrene microspheres are used as masks to pattern the surface of quartz or silicon substrates, typically in the order of cm², with a thermally evaporated Ag thin film of controlled thickness. When removing the spheres by physico-chemical means, the deposition directly leaves behind arrays of nanosize silver triangles / prisms that can be furthermore laser processed. Thus, by using two lasers (355-nm wavelength, 50-ps duration and 193-nm wavelength, 15-ns duration) for the metal dewetting, we aim to control the shape of the deposited nanostructures. A detailed study is presented here on the reshaping of these nanostructures by laser annealing. In previous work we prepared nanodot arrays, by using monolayers of spheres as microlenses, and by microsphere-assisted laser fabricated mesoporous membranes. Such hybrid methodology will enlarge the panel of available microsphere-assisted technologies to prepare surface nanomaterials.

Resume : The effects of surface topography are widely recognized as a key factor on the implant osseointegration. For example, hydrophilic surfaces seem to favour the interactions of an implant with cells as compared to hydrophobic surfaces. On the other hand, the increment of the roughness of an implant improves its mechanical fixation. Different techniques, such as sandblasting, plasma treatment, ion implantation, electrolytic coating, laser treatments, etc., have been studied to engineer the surface properties of biomaterials with the aim to improve their biological surface properties. The final objective of these treatments is the promotion of bone formation, confer better stability during the healing process, and in consequence allowing a faster loading of the implant. In this context, laser texturing offers a high versatility to tailor the surface properties of a biomaterial to improve their osseointegration. Laser treatments are highly localized, productive, flexible in materials and geometries, and can be performed at atmospheric pressure. In this work, we have studied the topographical modification of polypropylene (PP) which has been laser textured by Nd:YVO4 nanosecond lasers emitting at three different wavelengths of 1064, 532, and 355 nm. The influence of the laser processing parameters on the surface modification of PP has been investigated by means of statistically designed experiments. Processing parameters relevant to the process were identified and their influence on the surface texturing determined. Furthermore, most adequate processing conditions to increase the roughness and wettability, the main parameters affecting cell adhesion characteristics of implants, were also determined.

Resume : Information storage in organic materials is an essential aspect towards the development of organic electronic systems. Organic memory devices have focused attention on ferroelectric polymers as active storage components, where the poly(vinylidene fluoride) (PVDF) and its copolymer with trifluoro ethylene P(VDF-TrFE) are the most used. Nanopatterning can play an important role to enhance information density by controlling molecular orientation. Here, we report on the formation of laser induced periodic surface structures (LIPSS) on P(VDF-TrFE) thin films upon irradiation with the second harmonic of a Nd:YAG laser (532 nm, pulse duration 8 ns). Although P(VDF-TrFE) does not absorb light in the visible region, LIPSS can be obtained by the preparation of bilayer polymer thin films in which the bottom layer efficiently absorbs at the irradiation wavelength. In this case, poly(3-hexyl thiophene) (P3HT), which is a semiconducting polymer, was used. The ferroelectric nature of the structured bilayer was proven by piezoresponse force microscopy measurements. Ferroelectric hysteresis was found on both pristine and laser structured bilayer. Additionally, it is possible to write ferroelectric information at the nanoscale, and the laser structured bilayer showed an increase in the information storage density of an order of magnitude in comparison to the original bilayer. Results show the potential of laser nanostructuring procedure in order to develop non-volatile organic memory devices.

Resume : Conventional lithography techniques used for patterning of reasonable sized areas with sub 100 nm regular features requires expensive hardware or are time consuming. Holographic lithography is one of the most promising techniques for patterning regular structures. Pitch and pattern of the structures depends on the optical setup and laser wavelength where at least 2 laser beams are necessary. Complex pattern geometries can be obtained employing multiple beams or multiple exposures. It is practically the only way of producing 3D structures for visible range photonic applications via parallel exposure. In the current work sub-wavelength pitch structures were patterned in different positive and negative tone photoresist films on silicon employing automated Lloyd’s mirror interferometer setup and a long coherence length solid state UV laser. In the following step, thin silver films were deposited by electron beam evaporation on inclined samples with the regular structures. Specular reflection from the samples was investigated employing polarized white light angular reflection measurement system. Such structures demonstrated resonant optical response where sharp reflection peaks can be attributed to Wood’s anomalies, i.e. leaky modes excited in the regular structure, together with a broad absorption peak that can be attributed to the surface plasmon resonance in silver. The structures can be used as diffractive sensor chips in refractometry based in-situ refractive index sensors.

Resume : We show that highly conductive Cu films are obtainable from Cu complex ink by laser sintering. The Cu inks, synthesized using Cu formate as a precursor, were spin-coated onto polyimide substrate and scanned by an ultraviolet laser at 355 nm. The blowing of nitrogen gas into the irradiated area prevented the film from being oxidized and a minimum resistivity of 1.70 x 10^-5 ohm cm was obtained. The laser-sintered film, composed mainly of nanorods, exhibited a much tighter structure than the one achieved by the typical thermal process. While the film connectivity and surface coverage became very poor after thermal sintering, laser-sintered films exhibited tightly packed, compact microstructure maintaining a uniform thickness. This made it possible to achieve much lower sheet resistances by laser sintering, especially when the film thickness was less than 1 micrometer.

Resume : Femtosecond lasers are versatile tools to process transparent materials. Thanks to the non-linear interaction of ultrashort pulses with matter, tightly focused radiation can be absorbed even by materials transparent to the laser wavelength. This can be used in high-resolution bulk processing: the laser beam can penetrate and be absorbed just in a tiny region around the beam waist. However, this behavior poses a serious problem for surface modification. In this case, the radiation would not be absorbed at the surface unless the beam is just focused there. Otherwise, absorption would take place in the bulk leaving the surface unperturbed. Therefore, a strategy to position the laser beam waist on the material surface with high accuracy is essential. We investigate and compare two options to achieve the desired aim: the use of transmittance measurements across the sample and the use of reflectance data, both obtained during z-scans with pulses from a 1027 nm wavelength laser and 450 fs pulse duration. As the beam waist enters the material, a drop in the transmittance is observed while a reflectance peak is detected. With the combination of these observations, it is possible to control the position of the beam waist with respect to the sample surface with high resolution and, thus, attain pure surface modification. In the case of polymethyl-methacrylate (PMMA), this resolution is 1 µm. The results prove that these methods are feasible for submicrometric processing of the surface.

Resume : Nanosecond pulsed laser ablation of high purity zinc target immersed in double distilled water is used to fabricate different colloidal zinc oxide (ZnO) nanostructures. The influence of the laser wavelength on the properties of the synthesized ZnO nanostructures was examined. For this purpose three different wavelengths: second (532 nm), third (355 nm) and fourth (266 nm) harmonic of a Nd:YAG laser were used in the experiments. 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), X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-visible transmission measurements in order to evaluate their morphology, size distribution, crystalline structure, elemental composition 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 : We investigate the feasibility of using nanosecond laser pulses, at different wavelengths and energies, to remove metal particles having various sizes from different types of surfaces. Our study relates to the broader issues posed by the accumulation of large quantities of tritiated metal powders, due to wall erosion, in next-generation fusion reactors. Previously [1], we used laser-based methods to create surfaces contaminated with particles obtained from materials that are functionally related to those that will be used in such reactors. The present study capitalizes on our previous knowledge and represents another step forward towards the development of a solution for mobilization, transport and collection of metal powders from contaminated surfaces. We use laser-based techniques to obtain particle contaminated surfaces, which are subsequently treated by using nanosecond laser pulses. We investigate the influence of particle-surface bond strength and particle size on the removal efficiency and threshold. [1] F. Stokker-Cheregi et al., Digest Journal of Nanomaterials and Biostructures 7, 1569 (2012)

Resume : Recently, substantial interest is observed in utilizing of the plasmonic effect to enhance the electron transfer and electrode conductivity in biosensors based on transparent semiconductor materials such as Indium-Tin-Oxide (ITO). In this work we report the production and characterization of the ITO electrodes functionalized by Au nanoparticle (NP) arrays formed by pulsed laser nanostructuring of gold films. The SEM inspection of modified electrodes reveals the presence of spherical particles of diameters in the range of 40-100 nm and the NP-array geometry can be controlled by selection of the laser processing conditions. It is shown that particle size as well as packing density of the array are important factors which determine the electrode performance. The electrochemical characteristics of the ITO electrodes functionalized by Au NPs when studied in the presence of glucose solution show that the current registered at the oxidation peak rises with increasing glucose concentration markedly higher than in case of bare ITO. The detection limit reaches 20 µM and linear dependence is observed from 0.1 to 40 mM that covers the normal physiological range for the detection of blood sugar. Common interfering species naturally present in the physiological environment (e.g. ascorbic acid) do not reveal observable effects on the glucose detection. 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 : Direct laser scribing of solar cell has received considerable interest in recent years due to the non-contact, high resolution and high speed nature of the technique that make it suitable for industrial applications. This method is especially suitable for the patterning of thin film solar cells into modules by selective laser ablation of some layers of the stack. In this study, a femtosecond laser beam is focused at the surface of CIGS solar cell to achieve the selective ablation of the upper layers. We determine optimized process conditions for the selective ablation of the Transparent Conductive Oxide (TCO) layer for various thicknesses to perform a p3-type ablation with very limited degradation of the electrical properties of the solar cell. Similar experiments have been performed for the laser patterning of the CIGS film. The morphological and electrical characterization highlight the importance of using femtosecond laser pulses with minimized energy density to limit thermal effects on the ablation edges which lead to a reduction of the module efficiency. The different ablation mechanisms involved are discussed as a function of the layer properties. The results of this study demonstrate the ability of the laser process to selectively pattern the thin film solar cell with minimal loss of solar cell performance.

Resume : Ultra-short pulsed laser ablation of materials in liquid is a versatile technique for nanoparticles production. In the present work this approach has been used for producing in situ silver-silica core-shell nanoparticles during the process of silver ablation in stirred water suspensions of hexagonally ordered silica nanoporous (SBA-15 and MCM-41) materials. The nanocomposite suspensions obtained have been characterized by UV-vis spectroscopy and the observed features have been related to the components of the colloidal solution as well as to the laser ablation process parameters used. In order to obtain more detailed information about the nanocomposite generated materials TEM morphologic characterizations have been performed as well. Significant amount of small sized silver-core nanoparticles have been detected in both studied nanoporous silica structures and Ag-silica core-shell nanocomposites obtained within the nanoporous silica colloidal solutions have been also evidenced. The dispersion of the nanocomposites has been related to the extent of damage induced in the nanoporous silica structure during the ablation procedure here adopted. High stability of the produced silver-silica core-shell nanocomposites has been observed after a certain period from the production. We also evidenced that the choice of the ordered nanoporous silica material, SBA-15 or MCM-41, can affect the silica shell thickness as well as size distribution and their field of potential applications.

Resume : Laser-firing of metal on semiconductor layers is a well-known method to reduce the contact resistance of this layer system. Recently, it has been shown that liquid phase crystallized (LPC) solar cells on glass prepared with a laser-fired rear-side point contact scheme can gain significantly in efficiency. In order to develop a robust, scalable and cost-effective contacting technique, however, the laser process still needs to be optimized to the properties of the materials. We present a conductive atomic force microscopy (c-AFM) study on such laser-fired contacts that contains data acquired simultaneously on both the topography and the conductivity of the samples. A test structure consisting of an 100nm aluminum layer on a typical KOH structured p-type LPC polycrystalline silicon absorber on glass were fired with a 532nm Nd:VO laser using a pulse length of 16ns with stepwise increasing intensity. After analysing the influence of the laser intensity on the laser-fired contacts, the effect of different sample topographies corresponding to different grain orientations of the polycrystalline LPC sample, was investigated. The improvement of conductivity within the laser-fired spot was clearly confirmed. The crater diameter was found to increase independently of the grain orientation with increasing laser intensity. Surprisingly, it was found that the rim of the laser-fired spot at the transition to the unmodified silicon material has a much higher conductivity than the spot middle.

Resume : ZnO has a wide bandgap of about 3.4eV at room temperature and its luminescence has received considerable attention. In this study the manipulation of the luminescence of ZnO by laser annealing (LA) and/or by the influence of plasmonic metal nanoparticles in contact with the ZnO film are presented; the metal nanoparticles were produced by laser processes resulting in a wide size distributions ranging from 20 to 300 nm. For the purpose of this study, ZnO thin films were prepared using RF magnetron sputtering from a ZnO target and their microstructure was modified with single pulse LA process that affects their photoluminescence. In particular, the photoluminescence of the sputtered ZnO could be either in the UV, due to the Near-Band Emission (NBE), or in the visible range, due to the Deep-Level Emission (DLE) depending on the different microstructure as a result of different LA conditions. Secondly, the enhanced outcoupling of ZnO’s photoluminescence due to existence of plasmonic nanoparticles is also investigated. For this reason, plasmonic nanoparticles exhibiting localized surface plasmon resonance (LSPR) at different spectral positions were fabricated with the combination of RF magnetron sputtering (for ZnO and metal deposition) and LA (for ZnO refinement and metal nanoparticles formation). Different LA conditions were used in order to prepare plasmonic nanoparticles with different LSPR wavelength in order to enhance either the NBE or the DLE of the modified ZnO thin films.

Resume : The potential for nanosecond laser annealing (LA) to significantly enhance the electrical and optical characteristics of Aluminum doped ZnO (AZO) films deposited by RF-magnetron sputtering at low-temperature is demonstrated in our current work. Highly transparent and conductive AZO thin films were fabricated after optimizing both the deposition and the LA parameters. Under optimized deposition parameters, the 180 nm thick AZO thin films showed a resistivity of 1×10-3 Ω.cm, corresponding to a sheet resistance of 56 Ω/□, with carrier mobility 15.3 cm2/Vs, and carrier density 3.84×1020 cm-3. These electrical characteristics were enhanced after LA to a resistivity of 5×10-4 Ω.cm, corresponding to 28 Ω/□, 19.3 cm2/Vs, and 6.21×1020 cm-3 respectively. Moreover, the average visible transparency was enhanced from 85% to 90%. This combination of RF magnetron sputtering and ELA produces reliably AZO thin films with electro-optical characteristics that are very close to those of ITO, but crucially via low temperature and low thermal budget processing. Moreover, the adapted fabrication route could be applied to volume production, as the needed energy density for optimum ELA to half the resistivity is rather low (125 mJ/cm2).

Resume : On the laser facilities Kamerton-T and PHELIX, spallation phenomena were studied experimentally in graphite targets with nano- and picosecond shock-wave action. In the range of strain rates from 1/µs to 10/µs, data of dynamic tensile strength of this material were obtained. Spallation was observed not only on the backside of the targets, but also on their front surface. By using optical and scanning electron microscopy, the morphology of the front and back surfaces of the targets is studied. A comparison of the dynamic strength of graphite with the dynamic strength of synthetic diamond is done.

Resume : Laser-induced periodic surface structures (LIPSS) were formed on Si (c-Si) and porous Si (p-Si) surfaces irradiated by ultra-short pulsed laser beams at 266 nm central wavelength. Two utlra-short laser beams were used in this study: the first one is a Nd:YAG laser beam with 40 ps time duration and a repetition rate between 1-10 Hz, and the second is a Ti:Sapphire laser beam with a pulse duration close to 100 fs and a repetition rate in the range 1-1000 Hz. As reported in several papers, the shape and the spatial period of the obtained structures are strongly depending on the laser parameters: pulse duration, number of pulses and the beam fluence (dose). In this paper we aim to compare the dynamic of LIPSS formation on silicon substrates achieved at the femto and the pico time scale. Physics of interaction is obviously hugely different in those two regimes. Also, our methodology is to start our application with the c-Si substrate for comparing the LIPSS process formation to the literature. After this first step, we aim to study the p-Si case in order to compare the interference between the LIPSS and the nano-pores obtained in both regimes. We expect to evidence a huge change of the LIPSS structure in the case of the picosecond beam due to the presence of the liquid phase at the first stage (few laser doses) of laser interaction. Physico-chemical analyses (SEM, TEM, AFM and FFT images) are achieved to discuss the results on the LIPSS process formation in the p-Si case function of laser dose.

Resume : Laser-induced periodic surface structures (LIPSS) were formed on Cu/Si thin films using Nd:YAG laser beam (40 ps, 10 Hz, 30 mJ/cm2 (c-Si). The study of ablation threshold using linear and non-linear accumulation behaviour is leading to proof that LIPSS formation is always achieved over melting when varying the number of pulses from 1 to 10.000. Also, real time reflectivity signals exhibit typical behaviour to stress the formation of a liquid phase during the laser-processing regime. Atomic Force Microscopy (AFM) analyses have shown the topology of the micro-crater containing regular spikes with different amplitude. Those results are discussed with respect to the beam dose but also function of film thicknesses in the range 200 to 1000 nm. Transmission Electron Microscopy (TEM) technique allows finally to determine three distinguished zones in the close region of an isolated protrusion. The central zone is a typical crystalized area of few nanometers surrounded by a mixed poly-crystalline and amorphous area. In the region far from the protrusion zone Cu thin film structure is mainly amorphous. Real time reflectivity, AFM and TEM analyses evidence the formation of a liquid phase during the LIPSS formation in the picosecond regime. A two-temperature model (TTM) is also employed to check the lattice temperature level during the processing in the picosecond regime.

Resume : In the present study, laser surface texturing with line and dimple geometry has been developed using a ArF excimer laser operating at a wavelength of 193 nm with a pulse length of 5 ns. Following surface texturing, an extensive characterization of the textured surface has been carried out by scanning electron microscopy, electron back scattered diffraction (EBSD) technique and X-ray diffraction techniques. There is a significant refinement of microstructure along with a higher mass fraction of -titanium phase and oxides of titanium (rutile, anatase and few Ti2O3 phase) in the textured surface as compared to as-received one. The area fractions of linear texture and dimple texture measured by image analysis software were 45 % and 20 %, respectively. The surface energy (and hence, wettability) was decreased due to linear (29.6 mN/m ) texturing and increased due to dimple ( 67.6 mN/m) texturing as compared to as-received Ti-6Al-4V (37 mN/m ).

Resume : This paper reviews our recent work on the pulsed laser processing of graphene-based materials for organic photovoltaic applications. In particular we report on a rapid and facile method for the simultaneous reduction, doping[1] and functionalization[2] of GO. This technique is compatible with flexible, temperature sensitive substrates and was initially applied for the efficient production of highly transparent and conductive flexible graphene-based electrodes. It is based on the use of femtosecond laser irradiation for the in-situ, non-thermal, reduction of spin coated GO films on flexible substrates over a large area. Furthermore, we present a fast, non-destructive and roll to roll compatible photochemical method for the simultaneous partial reduction and doping of GO nanosheets through ultraviolet laser irradiation in the presence of reactive Cl2 precursor molecules [1]. By tuning the laser exposure time, it is possible to control the doping and reduction levels and therefore to tailor the work function (WF) of the GO-Cl derivatives from 4.9 eV to a maximum value of 5.23 eV, a WF value that matches the HOMO level of most polymer donors employed in OPV devices [3]. Moreover, we demonstrate the pulse UV laser - assisted photochemical functionalization of GO with small molecules as an efficient technique to realize polymer electron acceptors [2]. Potential applications of pulsed laser synthesized and modified materials in electronics, particular to bulk heterojunction organic solar cells are demonstrated and discussed. References 1 K. Savva, Y.H. Lin, C. Petridis, E. Kymakis, T.D. Anthopoulos, E. Stratakis, Journal of Materials Chemistry C, 2, 5931-5937 (2014). [2] M. M Stylianakis., M. Sygletou, K. Savva, G. Kakavelakis, E. Kymakis, E. Stratakis, Photochemical Synthesis of Solution-Processable Graphene Derivatives, Advanced Optical Materials , DOI: 10.1002/adom.201400450 (2015). 3 E. Stratakis, K. Savva, D. Konios, C. Petridis, E. Kymakis, Nanoscale, 6, 6925-6931(2014).

Resume : Over the past decade, Laser Ablation in Liquids (LAL) has become a popular method for the synthesis of colloidal nanoparticles. While the process is simple in execution, variation in particle size and polydispersity between product batches has been a problematic aspect of the method, even when great care in terms of experimental consistency is taken. In this regard, we investigated a relatively overlooked aspect that could be responsible for such variations in nanoparticle morphology. This aspect being the relative orientation between the laser polarization and linear features on the target surface that result from polishing. This effect was studied via shadowgraphy imaging of the induced cavitation bubble as a means of inferring the relative absorption of the incident pulse. The influence on particle size will also be presented. These results will be discussed in terms of reflectivity of the surface features, effective penetration depth, and thermal confinement within the ridges.

Resume : Fiber Bragg gratings (FBG) written in birefringent optical fibers can be used as advanced sensors for biomedical or mechanical applications. Here, FBG writing in an unique birefringent optical fiber by a single 20 ns KrF excimer laser (248 nm) pulse with a phase mask method and Point-by-point inscription by Ti:Sa femtosecond laser (800 nm) is demonstrated. This birefringent optical fiber has an elliptical stress cladding, in which a fiber core of high GeO2 doping is embedded in, and which has an additional isolating circular cladding. To enhance the photosensitivity of the fiber the concentration of GeO2 in its core was increased to 16 mol. A second method for the production of FBGs, the Point-by-point inscription of the refractive index changes has advantages over the conventional phase mask method. Due to the nonlinear interaction mechanism of the ultrashort laser pulses with the dielectric material, the grating structures can be created without stripping off the acrylate coating. This method allows to inscribe diffractive structures with or without codoping of GeO2 in the fiber core. FBGs with the reflectivity up to 10% have been written through the acrylate coating into the fiber core with 4 mol. % GeO2. Obtained FBGs can be used for new generations of measurement systems, such as fiber-optic hydrophone or monitoring system of extent objects (pipelines, railways, borders).

Resume : Iron carbides core with carbon shell nanoparticles have gained interest for biomedical applications, magnetic separations and as heat transfer agent. These nanoparticles with core/shell structure: Fe(C)@C were synthesized in a single step approach using the laser pyrolysis method. In order to diminish the carbon shell thickness, the iron pentacarbonyl vapors (Fe precursor) were mixed with an ethylene flow - diluted with Ar or H2 - used as carbon donor source. Elemental analysis performed by EDX reveals that the nature and proportion of diluted gas has an important effect on the as synthesized nanoparticles especially for their iron and oxygen content. Using optimized conditions, nanopowders with ~ 40 at.% Fe and less than 8 at. % O were synthesized. The morphology of such samples were investigated by TEM analysis and the particles has around 12 nm mean diameter and carbon shells with 3-4 onion-like graphene layers. The at XRD and SAED analysis of nanopowder samples with a protective carbon shell reveal only the presences of iron carbides (Fe7C3 or Fe3C) or αFe crystalline phases, whereas the Raman analysis showed the amorphous carbon peaks and the lack of iron oxides phases. Magnetic measurements performed at room temperature revealed values for the saturation magnetization up to 110 emu/g in a strong dependence with the iron proportion in nanopowders. Also, an in-situ surface functionalization was performed by supplementary introduction of acrylic acid vapors in the reactive precursors. The FT-IR analysis for these nanopowders show the presence of functional groups from acrylic acid derivatives. Such functionalized powders were easily dispersed in aqueous solutions when the CMCNa were used as stabilizer.

Resume : Nanoparticles and films of noble metals currently have attained wide popularity and aroused intense research interest in nanotechnology due to their well known properties, such as good conductivity, localized surface plasmon resonances, antibacterial and catalytic effects, etc. They are used in many different areas, such as medicine, solar cells, scientific investigation, etc. In this work we report a method consisting of a combination of laser ablation in liquids and electrophoretic deposition to produce Ag nanoparticles and deposit them at the same time on a substrate used as electrode. The obtained particles and films were characterized by means of transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and UV/VIS absorption spectroscopy. The coatings composed of Ag nanoparticles ranging from few to 60 nm were uniform and showed a clear localized surface Plasmon resonance.

Resume : An enhanced optical field generated around a nanostructure can concentrate optical energy into nanoscale space as a nanolens. Thanks to the nonthermal and intense processing by ultrashort pulsed laser, a merged method of the enhanced optical field and femtosecond laser processing enables high-precision processing on various kinds of materials. In this presentation, femtosecond laser processing with the enhanced optical field toward biomedical applications will be described. In our study, both the “material in the vicinity of nano-structure” and “nano-structure itself” can be a target of laser ablation. As for the former case, the focused optical field under polymer microspheres, which were conjugated to cell membrane, provides simultaneous cell membrane perforation of multiple cells by a single shot of 800 nm femtosecond laser illumination, enabling the introduction of exogenous molecules into cells. Owing to a little linear optical absorption and relatively low scattering coefficients at near-infrared wavelength, the interaction zone is localized in a focused spot on the cell membrane by nonlinear interaction, resulted in a little damage to the cell. As for the latter case, an enhanced optical field generated on a shell of hollow microcapsules contributes to localized disruption of the shell without doping with metals or dyes. This method has potential to realize light-triggered release of drug molecules embedded in the microcapsule. In the presentation, theoretical and experimental study on laser processing with enhanced-ultrafast optical field will be presented followed by recent works for biomedical applications.

Resume : A Photonic jet is known as a high concentrated low diverging beam which can be generated in the shadow side of a micrometric dielectric particle (sphere or cylinder). Its full-width at half maximum can be smaller than a half wavelength, beyond the diffraction limit. Thus, the incident power density of a laser source can be concentrated more than 200 times by a dielectric particle. It is a non-resonant phenomenon which takes place in the near-field of dielectric spheres even it concerns a propagative wave. A lot of possible applications have been imagined. However the 3D manipulation of microspheres is not obvious to control a potential photonic jet with matter interaction. Hence, be able to obtain photonic jet out of an optical fiber is a major issue. Namely if the same photonic jet can be achieved at the tip of an optical fiber, its control for material processing will be easier. Our study shows how to obtain photonic jet out of classical filled core optical fiber. The parameters dependences between optical fiber tip and photonic jet properties are more complexes and will be theoretically exposed. Methods to achieve such a needed optical fiber tip will be described. The ability to generate photonic jet out of the shaped optical fiber will be experimentally demonstrated and the potential applications for material processing exposed.

Resume : Laser interference is a versatile technique for producing patterned surfaces, the latter being very attractive due to their unique optical, electrical and chemical properties. When applied to metal films, the metal dewets from the substrate in the areas exposed to intensity maxima where formation of nanoparticles (NPs) and/or metal transport is generally reported. This work aims to show that the initial film nanostructure plays an essential role on the features of the patterns. We have produced silver layers with an effective thickness around 9 nm and having a quite different initial nanostructure, i.e. continuous or discontinuous film. Patterns with periods in the microscale have been produced by exposing a phase mask to a single pulse of an excimer laser operating at 193 nm. They are formed by regions of almost untrasformed film and regions where the film breaks up into isolated NPs due to laser induced melting. For the case of discontinuous sample, the temperature distribution across the pattern matches almost perfectly the intensity profile and thus the interface between the two regions of the pattern is sharp. For the case of continuous samples, the temperature distribution becomes smoothed due to lateral heat transfer and several different levels of transformation can be eventually found across the pattern. The mechanisms leading to these different levels are finally discussed as well as the importance of the pattern period.

Resume : We present innovative approaches for the fabrication of Dye Solar Cells (DSC) on glass substrates by processing all the main constituent materials with laser radiation, eliminating thus all the conventional thermal processes. We show that lasers can be successfully implemented for 1) patterning of the metal-oxide TiO2 film via ablation, 2) laser-assisted platinization of the counterelectrode, 3) encapsulation via laser-sealing of thermoplastic gaskets, and also 4) laser-sintering of the nanocrystalline TiO2 film. All the mentioned processes are optimized and utilised for the fabrication of the first efficient and durable all-laser-manufactured glass DSC. The power conversion efficiency of a fully laser-fabricated device was 5.3%, a value just over that of a cell fabricated with the same materials-set but processed with conventional procedures (5.2%). We also developed laser and lower power-density but broader UV-lamp sintering procedures for the TiO2 on thin flexible substrates delivering over 4% efficiency when incorporated in DSCs with transparent plastic counterlectrodes. These results pave the way for new scenario of an entire, laser-based, manufacturing line customized for dye solar cell technology with benefits related to its effective processing, automation, large area scalability and even embodied energy.

Resume : Advanced carbon coatings can be used for example as gas sensors, catalysts or for new design concepts for microfluidic elements or lab on chip applications. In this work, carbon nanotube carpets (CNT) are produced by PECVD technique (C2H4 - H2. RF plasma) assisted by a transition metal catalyst on many different substrates (metal, silicon, nitride/silicon). As a base for CNT growth, thin films of metal catalysts are deposited by PLD. To obtain nanoparticles, these thin films are subsequently heated to temperatures between 550 – 700 C° and treated in hydrogen plasma (within the same vacuum system). The CNT carpet structure (length, width, and diameter distribution) mainly depends on a variety of experimental parameters such as catalyst nanoparticle size and density, growth temperature, and various other conditions. The characterization of the various experimental parameters involved in the resulting quality of CNT is determined by different ex situ techniques as SEM, TEM, NEXAFS, XPS. In addition a portable and highly sensitive Raman setup was successfully coupled with the PECVD reactor enabling in situ growth monitoring of multi-wall carbon nanotubes despite plasma conditions. This new analysis tool can be interesting to monitor the growth under various experimental conditions and define easily the available range to obtain the best results.

Resume : High-k materials such HfO2 and ZrO2 have been extensively studied as alternative gate dielectrics of SiO2 due to its large direct tunneling currents when it is very thin. In in thin film transistors (TFTs), HfO2 and ZrO2 show more desirable properties than SiO2; low driving gate voltage of TFT, increased physical thickness to prevent electron tunneling with high capacitance value. To deposit high-k materials, plasma-enhanced atomic layer deposition (PE-ALD) is widely used but its low growth rate precludes its use for relatively thick structures. However, several papers about pulsed plasma-enhanced chemical vapor deposition (P-PE-CVD) were introduced as an alternative approach for ALD. They demonstrated self-limiting growth of Al2O3 and Ta2O5 with higher growth rate than PE-ALD. But fundamental studies for electrical properties of the P-PE-CVD films by fabricating TFTs and observation of device stability are rarely reported. In this paper, we observed self-limiting growth of HfO2 and ZrO2 using newly developed precursors ((C5H5)M[N(CH3)2]3, M = Hf, Zr) and O2 plasma with P-PE-CVD and PE-ALD. We compared electrical properties of films by fabricating MOSCAPs and IGZO TFTs. All films showed good dielectric properties (k value about 20~22 for HfO2 and 22~25 for ZrO2 with low leakage current<1x10^-8 A/cm^2) and excellent performance of TFTs (Ion/Ioff>10^8, μ>9 cm^2/Vs) with superior device stability in stability test (ΔVth<-0.5V after 3 hours of gate bias stress; VG=-20V).

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. Cast iron is a relatively inexpensive material, which presents a good castability, machinability and resistance, but it can be weakened by the oxidation. The surface properties of cast iron can be enhanced by a Ni-base alloy coating, a material with excellent performance under conditions of abrasion or corrosion at elevated temperatures. In this research work, a fiber laser is used to generate a NiCrBSi coating over flat substrates of gray cast iron (EN-GJL-250) and nodular cast iron (EN-GJS-400-15). The relationship between processing parameters (laser power and scanning speed) and geometry of a single laser track is 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 : Photosensitive elements based on layered semiconductor group A3B6 - In4Te3 and In4Se3 were obtained by liquid phase epitaxy and by vacuum sputtering Al, Ag, Au for obtaining of the metal thin films on the surface of single crystals for these compounds. To obtain epitaxial layers In4Te3 and In4Se3 was used method of isothermal liquid phase epitaxy with option of passing an electric current through the boundary melt-substrate. Density DC changed within 0,8- 2,5 A / cm2, while simultaneously take into account the effect on the crystallization layers of thermoelectric Peltier effect, thermal conductivity processes, diffusion and of charge transfer. Optimization of structural-phase state epitaxial layers In4Te3 and In4Se3 after LPE process was performed by laser annealing using YAG-laser (λ = 1,06 m, τ ~ 1 ÷ 4 ms) with a density of radiation I0 ~ 20 ÷ 30 kW / cm2. Perfection structure of epitaxial layers and homogeneity of phase composition was studied by methods SEM, AFM and of the X-ray electron probe microanalysis. Effect of laser radiation on optical and electrical characteristics of heterostructures In4Te3 - In4Se3 and structures with a Schottky barrier, such as (Al, Ag, Au) - In4(Se3)1-хТe3х studied by changing their spectral photosensitivity and IV and CV characteristics. The methods of SEM and AFM-microscopy were established optimum conditions for laser annealing in which improved epitaxial layer structure heteroboundary In4Te3 - lining, and which reduces the impact of recombination processes in this field. In the study in the AFM cross-layers found in nanostructured elements heteroboundary, that can exert influence on the processes of photosensitivity. Investigation C-V - characteristics of barrier structures Au - crystal In4(Se3)1-хТe3х showed that the nature of the curves corresponds to the presence of narrow-band as well as wide-band phases in the structure of the film after the PLI. Determined from the slope of the curves activation energy E0 given the chemical potential values for the above carrier concentrations are in good agreement with the values of the band gap of the possible phase compositions component.