Laser interactions with materials: from fundamentals to applications

Resume : In recent years, it has been shown that novel functionalities can be achieved in oxide heterostructures in which the interfaces are atomically controlled, in terms of atomic stacking as well as in terms of the local symmetry. In transition metal perovskites ABO3, the physical properties are largely driven by the rotations of the BO6 octahedra, which can be tuned in thin films through strain and dimensionality control. However, both approaches have fundamental and practical limitations due to discrete and indirect variations in bond angles, bond lengths, and film symmetry by using commercially available substrates. We introduced modulation tilt control as an approach to tune the ground state of perovskite oxide thin films by acting explicitly on the oxygen octahedra rotation modes-that is, directly on the bond angles. By intercalating the prototype SmNiO3 target material with a tilt-control layer, we cause the system to change the natural amplitude of a given rotation mode without affecting the interactions. With this approach, we successfully adjusted the metal-insulator transition (MIT) to room temperature to fulfil the desired conditions for optical switching applications. In this contribution, I will highlight the recent developments in atomic controlled growth of epitaxial oxides by pulsed laser deposition and discuss recent new insights in the “physics” of pulsed laser deposition of complex oxides, focusing on the influence of oxygen pressure on the deposited species during growth as well as the large scale growth of epitaxial oxides on wafers up to 200 mm in diameter.

Resume : Cu(In,Ga)Se2 (CIGS) thin-film solar cells have been extensively studied by the research community and industry, motivated by the high conversion efficiencies, high radiation resistance, remarkable stability and the potential of lower cost production compared to crystaline silicon solar cells. The evolution of the efficiency reported through the years is notable, with record performances of 22.9%. The recent improvement in cell efficiency paves the way for module efficiencies up to 18% over the next few years. The typical CIGS solar cell with efficiency above 20% has the following configuration: soda-lime glass (SLG) as substrate, sputtered Mo as back contact, multi-stage co-evaporated CIGS as p-type absorber, chemical bath deposited CdS as n-type buffer layer and sputtered i-ZnO/ZnO:Al bilayer as the transparent front contact. Many deposition methods are being utilized to grow CIGS and CdS thin films; however, only few works on the pulsed laser deposition (PLD) technique have been reported. In this presentation, the growth of CdS/CuIn0.7Ga0.3Se2/Mo multi-layer structures on soda-lime glass (SLG) using PLD will be presented. The influence of PLD parameters on the properties of the CIGS and CdS layers and also the CdS/CIGS/Mo heterointerfaces will be discussed. Complete structural, compositional and morphological characterization, along with electrical and optical measurements, will be used to evaluate the quality of the CdS/CIGS diode and identify the optimum PLD growth conditions of the multi-layer structure.

Resume : The introduction of dopants, such as boron, into the graphene network, is essential for many applications (electrochemistry, sensors, photovoltaics, catalysis, etc.). Many preparation routes have been investigated for B-doped graphene (BG) films: CVD, chemical reactions between graphene or graphene oxide with boron precursors, hydrothermal and solvothermal processes, arc discharge, high temperature sublimation of highly B-doped SiC and B4C thermal decomposition. Another way consists in pulsed laser co-ablation of C and B solid sources followed by rapid thermal heating of the B-doped carbon film deposited on a metal catalyst, to obtain BG layers. The objective is to achieve a better control of boron concentration in the films. Here, we use for the first time pulsed laser co-ablation for the synthesis of B-doped graphene layers. Amorphous a-C:B films, containing 2%at. boron, 10 nm thick, are synthetized by nanosecond pulsed laser deposition on a Ni thin film (60 nm thick) previously deposited on a SiO2 substrate. Rapid Thermal Annealing is performed at 1100°C during 2’ with a heating rate of 15°C/s and a cooling rate of 1°C/s. Raman, XPS, FEG-SEM and AFM characterizations allow to determine the nature, composition and morphology of the BG films. The results confirm the fabrication of bi-trilayers boron doped graphene films with the same boron doping level (2%at) as the starting material. Our results pave a new way for boron doped graphene synthesis using laser processing.

Resume : A V-shape radiating carbon plasma, generated through excimer laser ablation of graphite, was characterized by complementary techniques. Fast ICCD imaging along with time- and space- resolved OES was used to sequentially record the evolution of plasma as a whole, or of specific excited species, while Faraday cup measurements provided the space-time distribution of the ions. To complete the picture, mechanical profilometry brought results on laser created craters features, that correlate with the plasma properties. When expanding in vacuum, the V-shape plasma consists in two radiating arms (so arranged that they form a sharp angle) and a low emission central region made of fast particles. Besides its unusual shape, a peculiar feature of the V-shape carbon plasma is the enhanced emitting area of visible radiation from C2 molecules. Moreover, along the plasma central axis, a minimum of emission intensity of the optically excited species was observed, while the ion distribution function reveals a maximum. Increasing the working pressure, the fast central plasma structure is better evidenced, through a re-heating effect of the ambient gas. In this context, the expansion velocities of the V-shape plasma structures and different parameters (electron density and plasma temperature) were determined.

Resume : In high power laser experiments where intensities lie in the range of 10^21-10^23 W/cm^2, having a high contrast ratio of the temporal profile and protecting the expensive laser optics from plasma debris and laser back reflections represent critical issues. The first is necessary in order to perform experiments with ultra-thin film targets and exploit advanced acceleration mechanisms while the second is required to ensure the safe operation of the laser system and increase optics lifetime. During the laser – matter interaction, the laser light intensity can deform and modulate the target, with the reflected light travelling back and potentially damaging the laser system and the transport optics. Typically, plasma mirrors are used to increase the temporal contrast of the laser with up to two orders of magnitude per mirror. The talk introduces the plasma mirrors physics and their use for contrast enhancement and protection from laser back – reflections.

Resume : Recently fluorescence-based techniques have gained great attention for detection of organic substances in small quantities for applications in environment control and health. Photonic technologies are in an excellent position to provide solutions in this context, since devices based on optical monitoring of light properties are very powerful tools for remote and non-invasive sensing applications. For these applications are necessary bright emitters that are clearly distinguishable and with a stable emission. In this respect rare-earth ions are very robust emitters with a very clean, narrow and robust emission. However, their emission tends to be less bright than that of traditional dyes due to their characteristic long-lifetime. A possible solution would be their combination with metallic nanostructures, particularly of Au and Ag, as they provide an enhanced emission due to plasmonic field absorption enhancement. In this work we investigate the modification of the emission luminescence properties of active thin films of europium oxide (Eu2O3) deposited on top of self-organized Au or Ag nanostructures prepared by Pulsed Laser Deposition (PLD). Au is investigated for its great stability for biological applications, while Ag is investigated due to the narrower band of its plasmon and its higher scattering efficiency. The potential enhancement of the emission efficiency is studied as a function of the deposition conditions, thickness and post-annealing treatments of Eu2O3 films.

Resume : Abstract Artificial intelligence (AI) has been heralded as the flagbearer of the fourth industrial revolution. But it comes with a cost and that is computing power. It is projected that by 2040, we will need more computing energy than the total terrestrial energy. Memory devices are responsible for a significant fraction of the energy consumed in electronic systems- typically 25% in a laptop and 50% in a server station. Reducing the energy consumption in memories is an important goal. For the evolving field of artificial intelligence the compatible devices must simulate a neuron in order to meet the low energy required for brain-like functions. We are working on three different approaches towards these problems- one involving an organic metal centred azo complex, the other involving oxide based ferroelectric tunnel junctions and the last involving real live neuronal circuits. Experimental Results Organic Approach: Our organic resistive memories built on oxide surfaces are robust, stable (operating from -40 to 80C for >10^6s) and enduring (>10^12 cycles) exceeding the ITRS roadmap specification significantly demonstrating the viability of this system for practical applications [1]. The molecule is a Ru centred Azo ligand based complex. The azo group can have three charged (redox) states and these molecules are spin coated on a PLD deposited atomically flat ITO film with metal electrodes on top. Besides meeting industrial metrices, this work implements in-situ spectroscopic platforms to detect molecular states of devices while in operation - an elusive goal in organic electronics. The mechanistic understanding thus developed leads to the realization of several hitherto unforeseen scientific paradigms such as voltage-controlled charge disproportionation, sequential layered redox mechanism leading to even 29-state devices. Such devices can offer a boon to the neuromorphic technology and brain inspired computing which are still in search of ideal material candidates for neuromorphic devices. Our devices are scalable from micron size to 50nm2 (measured with a c-AFM tip). With scaling the switching voltage drops from a maximum of 4 Volts (in a micron device) to 120mV (to a nano-device). The nano structures act as seeding points of locally enhanced fields significantly lowering the charge injection barrier. With these devices, we are now able to reach100aJ switching energy, at least 4 orders superior to any other resistive memory. Oxide Approach: On the oxide front the significant results are that ferroelectricity is seen even in PLD MBE grown one or two atomic layers of BaTiO3 or BiFeO3 resulting in ferroelectric tunnel junctions with usable On/Off ratios [2-5]. Oxygen vacancy motion can also play an important role in changing the device characteristics leading to synaptic characteristics and lead to multiple memory states. Live Neuronal circuits: Last but not the least, combinatorial PLD based oxide surfaces can be utilized to force neurons to grow at specific places on a surface giving the potential for fabricating live neuronal circuits. Using lithographically etched channels the axons could be guided to create a 2D matrix of neurons and if such circuits could be made reproducibly with live neurons this would lead to a significant understanding of neuronal communications and also understanding neurodegeneration process and also developing drugs to combat neurodegeneration. References 1. Sreetosh Goswami, et al., Nature Materials, 16, 1216 (2017) 2. C. J. Li, et al., Nano Letters 15 (4) 2568–2573 (2015) 3. Han Wanget al., Nature Comm. 9, 3319 (2018) 4. Weiming Lü, et al., Advanced Materials - In Print 5. Rui Guo, et al., ACS Applied Materials and Interfaces, 10, 12862 (2018)

Resume : Simple and doped biological-origin hydroxyapatite films were synthesized by Pulsed Laser Deposition onto medical grade Ti substrates. The role of doping reagents on physical-chemical, mechanical and biological properties of structures was studied. Morphological examination evidenced the fabrication of rough surfaces, ideal for the good adhesion of cells and anchorage of implants in situ. Structural investigations demonstrated a monophasic apatite-like nature of synthesized structures. Compositional analyses revealed the presence of typical natural doping elements of bone, along with a quasi-stoichiometric target-to-substrate transfer. Inferred bonding strength values were higher than the threshold imposed by ISO standard regulating load-bearing implant coatings. After only three days of immersion in simulated body fluid, FTIR spectra showed a remarkable growth of a biomimetic apatitic layer, indicative of a high biomineralization capacity of coatings. Synthesized layers exhibited low cytotoxicity on human osteosarcoma and skin cells and therefore, an excellent biocompatibility, corroborated with a long-lasting anti-staphylococcal and –fungal biofilm activity. Along with low fabrication costs, these combined characteristics could offer guidance towards the suitability of using biological-derived materials as viable alternatives to synthetic HA for the fabrication of a new generation of implant coatings. Acknowledgements: Contract PD 6/2018 and Core Programme 3N/2018.

Resume : The laser-induced microbubble technique (LIMBT) has been developed recently for micro-patterning of various materials. In this method, a laser beam is focused on a dispersion of nanoparticles (NPs), leading to the formation of a microbubble due to laser heating. Convection currents around the microbubble carry NPs that are then pinned to the bubble/substrate interface. Moving the focused beam results in migration of the microbubble and the deposition of material at the bubble/substrate contact area. We have recently found that controlling the construction and destruction of the microbubble, through modulation of the laser, enables the formation of continuous patterns by preventing the microbubble from being pinned to the deposited material.[1] Moreover, we show that a similar mechanism could explain microstructure formation from an ion solution. Photo-thermal reduction leads to formation of NPs that are then pinned to the bubble/substrate interface. By analyzing the nanostructure of the deposits by TEM, we show that the deposition on the substrate is a combination of amorphous and crystalline moieties. This innovative approach can be applicable for producing thin conductive patterns and allow fabrication of electronic devices and sensors. 1. Armon, N. et al. Continuous Nanoparticle Assembly by a Modulated Photo-Induced Microbubble for Fabrication of Micrometric Conductive Patterns. ACS Appl. Mater. Interfaces 9, 44214–44221 (2017).

Resume : There is still a widespread interest in conducting polymers due to their potential applicability in organic solar cells, organic field-effect transistors and organic light-emitting diodes just to cite a few examples. Among the conducting polymers, poly(3,4-ethylenedioxythiophene) complexed with poly(styrenesulfonate) (PEDOT:PSS) presents a series of interesting properties gaining importance since, besides its conductivity, it is transparent in the visible region, soluble in water, thermally stable and flexible. In this work, PEDOT:PSS thin films have been irradiated under ambient conditions with the 4th harmonic of a Nd:YAG laser resulting in Laser Induced Periodic Surface Structures (LIPSS) parallel to the laser polarization with a period close to the laser wavelength. Shape and size of LIPSS can be characterized by Atomic Force Microscopy (AFM). The nanoscopic structure of PEDOT:PSS films before and after irradiation have been studied by Grazing-Incidence Wide-Angle X-Ray Scattering (GIWAXS) using synchrotron radiation. In order to analyze the impact of laser treatment on the electrical properties of PEDOT:PSS, conductive AFM (C-AFM) measurements have been performed, showing that LIPSS preserve electrical conductivity of PEDOT:PSS. These results are important regarding the possibility of achieving functional polymer nanostructures by a quick and reproducible approach.

Resume : Submicron pattern fabrication by laser direct writing is still challenging due to the required resolution of the optics required for these pattern sizes. Therefore, various approaches of submicron pattern formation by bottom up processes such as laser-induced self-organizing processes, which allow submicron structure fabrication with dimensions equal or below the wavelength of the laser light, are under investigation. Here, the combination of two processing steps for the fabrication of hierarchical pattern is presented. Pre-patterned polymer substrates that feature polymer structures with micron dimensions are irradiated with pulsed UV laser radiation with a wavelength of 248 nm and a pulse duration of ~25 ns at low repetition rates. In consequence of this laser irradiation, laser-induced periodic surface structures (LIPSS) are formed at the surface of the pre-patterned polymer and allowing hierarchical pattern fabrication comprising micron and submicron features. Within the presentation the impact of the laser irradiation parameters such as laser fluence, repetition rate, spot size and confinement of the irradiation to the characteristics of the achievable LIPSS on top of the pre-patterned substrates are shown. In addition the geometry of the LIPSS for different dimensions and shapes of the pre-patterns is shown. The potential processes involved in the formation process of the hierarchical pattern will be discussed.

Resume : To realize next generation thin-film devices and/or 3D-LSIs, growth of polycrystalline Ge and/or GeSn thin films on insulating substrates is essential. Here, we have investigated CW laser annealing method to fulfill this demand. In the experiment, amorphous Ge (a-Ge) films or a-GeSn films with Sn concentration of 17% were firstly deposited on quartz substrates. Laser lights (diameter: ~10 um, wavelength: 532 nm) were irradiated on the samples with scanning speed of 6.67 m/s. Here, CW Nd:YVO4 diode-pumped-solid state laser was used as the laser source, and the laser power was changed from 350 to 1200 mW. Nomarski microscopy and Raman spectroscopy supported that both Ge and GeSn films were successfully crystallized after laser irradiation. Interestingly, crystallinity of GeSn film showed strong dependence on annealing laser power, while that of Ge film showed little dependence. We speculate that this is due to the difference of crystallization phenomena. The details will be discussed on site.

Resume : Silicon carbide (SiC) has attracted much attention in the last years due to its excellent physical and electrical properties, such as wide bandgap, high thermal conductivity, high breakdown electric field, high saturated electron drift velocity and resistance to chemical attack. These properties make SiC a promising material for high-temperature, high-power and high-frequency electronic devices as well as for optoelectronic such as solar cells, image sensors, gas sensors and photodiodes, just to cite a few. Thin films of SiC on Si (100) and SrTiO3 (100) substrates were grown by nanosecond pulsed laser deposition (PLD) at the wavelengths of 1064, 532 and 266 nm using a Q-switched Nd:YAG laser. Upon irradiation for two hours at a repetition rate of 10 Hz and a distance target-substrate of 4 cm, deposits consisted of smooth and uniform layers, holes and cracks free, with average roughness ≤ 1 nm and with 20 to 100 nm thicknesses as determined by atomic force microscopy in tapping mode. The effect of laser irradiation wavelength, laser fluence and the temperature of the substrate (300 K vs. 1025 K) on the morphology, composition and crystallinity of the deposits was determined. Deposits were analyzed by X-ray diffraction, micro-Raman spectroscopy and X-ray photoelectron spectroscopy to characterize their crystallinity and composition. Additionally, the nanomechanical properties of the deposited films and the photoluminescence were evaluated.

Resume : Herein, we report about an anomalous behavior of the photoelectrochemical (PEC) response of Eu-doped BiFeO3 (BEFO) thin films, as a function of the film’s thickness. The aim of the study was to reveal the water splitting potential of doped BFO with rare-earth Eu element. Heterojunction composed of Eu-BiFeO3 and Nb-SrTiO3 (STON) single crystal substrates were fabricated via pulsed laser deposition technique (PLD). By X-ray diffraction, the crystal structures of all deposited thin films were identified as rhombohedral one, with the out-of-plane axis value as a function of film’s thickness. Optical absorption measurements were carried out for the grown films, an indirect and direct band gaps being identified, with the values for both types of bend-gaps depending on the epitaxial strain. The photoelectrochemical behavior (PEC) was analyzed in respect with the thickness of the deposited BEFO layer. To investigate the PEC performance of the fabricated heterojunctions, the photocurrent density ( Jph ) versus bias potential characteristics in-electrolyte PEC setups has been measured. We have found that the photoelectrochemical response was higher for the BEFO samples as compare with the undoped BFO ones. Moreover, the photocurrent density ( Jph ) is almost independent by the film thickness is ranging from 20 nm to 200 nm, while a significant higher photoelectrochemical response is characterizing the heterojunction based on a 180-200 nm thick BEFO films. These anomalous photoelectrochemical response behavior were analyzed in conjunction with the HR-SEM and scanning electron microscopy (SEM) - room-temperature cathodoluminescence (CL) surface imaging analysis.

Resume : Laser ablation of metal-transition solid targets in organic solvents is a versatile strategy to synthesize metal carbide and carbon encapsulated metal nanoparticles that are obtained by mechano-chemical synthesis, requiring severe experimental conditions, usually. The formation of MxCy and core/shell MC/M@C nanostructures has been studied during the ablation of Ti, Ta and Mo metallic targets in organic solvents with different C/H and C/O ratio. Ablation experiments have been carried out by two laser sources (Nd:YAG, 532nm, 7nm, 10Hz and Nd: glass, 527nm, 250fs, 10Hz) to highlight the effect of laser pulse duration on properties and composition of the obtained nanostructures. The synthesized materials have been characterized by microscopic (SEM, TEM and AFM) and spectroscopic (FTIR, microRaman and XPS) techniques. The several reactions involved during the ablation process determine nanostructures composition, that has been related to the reactivity and physico-chemical properties both of the ablated targets both of the liquid media.

Resume : Iron-gold core-shell (CS) nanoparticles (NPs) are interesting as they allow the combination of properties such as nanomagnetism, plasmonics and thiol-based conjugation chemistry in one particle1. Laser ablation in liquids (LAL) is a versatile technique which allows generation of these CS NPs in a one step process directly from alloy bulk targets2. However, CS formation by LAL is still limited, due to a competitive process generating metastable solid solution (SS) NPs as by-products3. Therefore, the main focus of our work lies in a detailed understanding of the formation mechanism of the FeAu NPs by LAL and in this context deduce process parameters, which allow a maximum in CS yield. The internal phase structure of the resulting particles is analyzed by X-Ray diffraction (XRD) and High Resolution Transmission Electron Microscopy (HR-TEM). The results indicate that primarily the target composition as well as the nanoparticle size critically influence the CS/SS ratios, while high CS yields were found when iron molar fractions in the target exceed 65% and particle diameters are bigger than 10 nm. The experimentally found size effect was confirmed by theoretical calculations which revealed that the lowest free Gibbs Energy, indicating the thermodynamically most stable morphology, was found for a Fe@Au core shell-structure in case of particle sizes > 10 nm. These results can open the way towards high yield one step green Fe-Au CS NPs synthesis based on laser ablation in liquids. [1] T. A Larson, J. Bankson, J. Aaron, K. Sokolov, Nanotechnol., 2007, 18, 325101. [2] P. Wagener, J. Jakobi, C. Rehbock, V. S. K. Chakravadhanula, C Thede, U. Wiedwald, M. Bartsch, L. Kienle, S. Barcikowski, Sci. Rep., 2016, 6, 23352. [3] A. Tymoczko, M. Kamp, O. Prymak, C. Rehbock, J. Jakobi, U. Schürmann, L. Kienle, S. Barcikowski, Nanoscale, 2018, 10, 16434-16437.

Resume : Powder material development is crucial for laser-based additive manufacturing (LAM). Within the DFG Priority Program SPP2122 “Materials for Additive Manufacturing” we develop new composite materials with nanoparticles to overcome this limitation. These nanoparticles are generated by laser synthesis and processing of colloids (LSPC), a method that has been established as an economically feasible method to synthesize clean and surfactant-free colloidal nanoparticles in the gram-scale. To produce new compounds for powder-based LAM, laser-generated colloidal nanoparticles are adsorbed on metal or polymer powders through pH-variation under consideration of colloidal stability to avoid agglomeration. Due to the barrier-free surface of the small, highly dispersed colloidal nanoparticles, a high surface coverage and dispersion can be achieved even with mass loadings of 0.1 wt%, as will be shown in the contribution for silver nanoparticles supported on polyamide 12 powder or yttrium oxide nanoparticles supported on steel powder. Studies on LAM-built parts also show that the homogeneity of the surface coverage as well as the dispersion of the nanoparticles can be transferred to the final part. Within the additively manufactured metal component, we further show that the particle spacing of Y2O3 inclusion can be adjusted by the initial mass fraction of the adsorbed Y2O3 particles on the micropowder which finally leads to a significant increase in the compressibility at high temperatures.

Resume : We review nonlinear energy deposition by tightly focused laser pulses into water and the subsequent hydrodynamic events, with water representing large-band-gap materials. Tight focusing avoids nonlinear beam propagation effects and ensures spherical shock wave emission and bubble dynamics. The investigated parameter space encompasses pulse durations from fs to ns, wavelengths from UV to IR, and pulse energies from the bubble threshold to high-density plasmas far above threshold. We address the points: 1. Nonlinear energy deposition and plasma formation dynamics in the (pulse duration, wavelength, energy) parameter space. 2. Experimental results and model predictions on plasma energy density. 3. Modeling of plasma-induced hydrodynamic effects (breakdown - bubble formation and shock wave emission - bubble dynamics). 4. Partitioning of absorbed energy into a part necessary for the phase transition and parts going into bubble formation and shock wave emission. Partitioning is investigated as a function of volumetric plasma energy density, maximum bubble size (from macro to nano), and pulse duration (when is breakdown most “disruptive?). The comprehensive view on nonlinear energy deposition provides a framework for optimum laser parameter selection for different material processing tasks. Selection criteria are smooth onset and continuous tunability vs ‘big bang’, reproducability of energy deposition, and the disruptiveness of breakdown as a function of pulse duration.

Resume : Laser ablation in liquid (LAL) emerged as a powerful technique for the synthesis of multielement nanoparticles (NPs) such as metal alloys with thermodynamically forbidden composition. Consequently, there is a great interest in expanding the current knowledge about NPs formation during LAL, in order to improve the control on product structure and to extend the range of compositions accessible by this technique. Here we discuss about the results obtained so far with laser ablation synthesis in solution of nanoalloys with magnetic and plasmonic properties and metastable phase. In particular, we show how the systematic investigation carried out by laser ablation of thin metallic films by changing target structure, liquid environment and pulse length provided useful insight about the formation mechanism of homogeneous nanoalloys and about how to switch from homogeneous to core-shell nanoparticles. These results are of interest for the general understanding of the processes behind the LAL technique and for the production of multifunctional nanomaterials which are appealing in a wide range of applications from catalysis to photonics and nanomedicine.

Resume : One of the most intriguing challenges of modern nanotechnologies is the development of materials with physical/chemical properties favorable for highly efficient and color tunable lighting. To this purpose, pulsed laser ablation (PLA) is a versatile and environmentally friendly top-down strategy that is normally adopted to realize a large variety of luminescent nanomaterials. A key laser parameter is the pulse length (τ-laser) compared with the electron-phonon thermalization time, τ-therm, occurring in ps scale. In this work, we used two pulsed laser sources to irradiate a Zn target immersed in water, by which ZnO wurtzite nanocrystals (NCs) result from the Zn oxidation in water [1]: 1) Nd:YAG (1064 nm) emitting short pulses τ-laser≈ 5 ns >> τ-therm (thermal ablation); 2) Ti:Sapphire (800 nm) emitting ultra-short pulses τ-laser≈ 50 fs < τ-therm (non-thermal ablation). The different laser ablation settings strongly influence both the sizes and the optical properties of ZnO-NCs. Thermal ablation produces nanoparticles with sizes of ~30 nm that, under excitation above the direct bandgap (Eg ≈ 3.4 eV), emit two photoluminescence (PL) bands: the first, peaked at 3.3 eV (UV-band), is due to the excitonic recombination; the second, centered at 2.3 eV (green-band), is associated with oxygen vacancies [2]. In contrast, non-thermal ablation induces smaller nanoparticles with sizes <10 nm, that are comparable to the excitonic Bohr radius in ZnO-NCs, thus leading to quantum confinement effects. Indeed, both the optical gap and the UV and green PL bands shift towards higher energies on decreasing the ZnO-NCs sizes. Moreover, a third PL centered at 2.8 eV (blue-band), peculiar to fs PLA, is observed, its origin is still unclear. These results demonstrate that PLA is a successful method to synthesize ZnO nanosystems with controlled luminescence properties, thus increasing their application in lighting technologies. [1] P. Camarda, L. Vaccaro, F. Messina and M. Cannas, Appl. Phys. Lett. 107, (2015), 013103. [2] P. Camarda, F. Messina, L. Vaccaro, S. Agnello, G. Buscarino, R. Schneider, R. Popescu, D. Gerthsen, R. Lorenzi, F. M. Gelardi and M. Cannas, Phys. Chem. Chem. Phys. 18, (2016), 16237.

Resume : Laser ablation of metal in organic solvents (LAMOS) has been proven to be an efficient technique for one-step synthesis of carbon-encapsulated metal/metal carbide/metal oxide core−shell nanostructures. However, the correlation between the influential factors and the final products, such as composition of the core and structure of the carbon shell, is still unclear to date. In this talk, comparative experiments of 16 transition metals were performed to clarify the panorama of LAMOS, including metal atomization and liquid decomposition into carbon and reductive gases, subsequent metal carbonization, surface precipitation, and metal-catalyzed graphitization to form amorphous and graphitic carbon shells. Importantly, it is found that the carbon solubility in metals and the affinity of metals to oxygen are the critical factors in determining the core composition: (1) inert metals Cu, Ag, Au, Pt, Pd are directly transformed into pure metal cores; (2) active metals Ti, V, Nb, Cr, Mo, W, Ni, Zr evolve into metal carbide cores, but Mn, Fe, and Zn give birth to the mixture of metal and metal oxides cores. Such processing obtained core-shell structure presented excellent performances in electrochemical applications due to their outstanding catalytic activity and stability.

Resume : Metallic nanoparticles are receiving great attention as an alternative to overcome the continuous emergence of antibiotic-resistant bacteria. In this work Cu nanoparticles are prepared in liquid media by laser ablation to investigate their antibacterial activity. Colloidal solutions of Cu were prepared by ablating a copper metal foil submerged in distilled de-ionized water and methyl alcohol using a nanosecond Nd:YVO4 laser operating at 532 nm and a picosecond Nd:YVO4 operating at 1064 nm. Synthesized nanoparticles were characterized by X-ray diffraction (XRD), UV–Vis spectrophotometry, Scanning Electron Microscopy (SEM) and High Resolution Transmission Electron Microscopy (HRTEM). The antibacterial activity of the obtained nanoparticles by both laser sources and solvents was tested against Aggregatibacter actinomycetemcomitans, a gram negative bacteria which closely related to the dental implant failure. The kinetics of copper ion release was also tracked during the first 21 days by means of Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The obtained colloidal solutions resulted mainly in crystalline Cu nanoparticles ranging from few to 35 nm and rounded in shape. The nanoparticle size is more homogeneous when nanosecond laser is used as laser source and it decreases if methyl alcohol is used as solvent. Synthesized Cu nanoparticles exhibited inhibitory effect on bacteria strains with best results for those obtained by picosecond laser in water, which corresponds with a higher copper ion release. These results demonstrate not only the relation between copper nanoparticles size and their antibacterial activity, but also the influence of ion release on the biocidal process.

Resume : Electronic impurity doping of semiconductor nanocrystals (NCs) is a challenge in colloidal chemistry and holds promise in many photonic and spin-based nanotechnologies1. To date, our knowledge is limited to a few studies on a small number of compounds and dopants, with relevant electronic dopants still unexplored in nanoscale systems. Fine tuning of electronically doped NCs is also hampered by the statistical inhomogeneities of traditional approaches, restricting fundamental studies to statistical behaviours and complicating the realization of advanced devices. In our work2, we realize the first example of II-VI NCs electronically doped with an exact number of heterovalent gold atoms, a p-type impurity in bulk chalcogenides. Single-dopant accuracy across entire NC ensembles is obtained through a new non-injection synthesis employing Au clusters as ‘quantized’ dopant sources to seed the nucleation of CdSe NCs. Structural, spectroscopic and magneto-optical experiments trace a comprehensive picture of the physical processes due to the exact doping level of the NCs. Gold atoms are incorporated in CdSe NCs as nonmagnetic Au ions activating intragap photoluminescence. Fundamentally, the transient photoconversion of Au to Au2 artificially offsets the hole occupancy of the valence band states and results in diluted magnetic semiconductor behaviour revealing the contribution of individual paramagnetic centers to the magnetism of the NCs. 1Nat. Nano., 13 (2), 2018 2Nano Lett., In Press

Resume : Space-and time-resolved investigation techniques were implemented for the study of transient plasmas generated by laser ablation in various temporal regimes on a wide series of metallic and chalcogenide glass targets. The aim of this work was to implement two or three complementary investigation techniques in order to understand different aspects of the laser-produced plasmas. The experiments were performed on plasmas generated by ns, fs and ps laser ablation in similar irradiation (laser fluence: 5 - 20 J/cm2) and expansion conditions (p = 10-5 - 10-6 Torr). The optical investigations were performed by ICCD fast camera imaging and space- and time-resolved optical emission spectroscopy (OES), while for the analysis of the charged particles, the Langmuir probe (LP) method was implemented at various distances on the main expansion axis of the plasma plume. Despite the particularities of the laser-produced plasmas, the simultaneous use of both optical and electrical techniques was successfully implemented leading to quantitative comparisons between important plasma parameters extracted from each investigation technique. The global studies (ICCD imaging) revealed the splitting of laser plasma into two or three structures expanding with different center-of-mass velocities. The local investigations (OES and LP) allowed the determination of some key plasma parameters (temperatures, densities, collision rate or Debye length) related to the excited states from the plasma volume and the energy of the charged particles. The results are presented in a comparative manner discussing the effect of the pulse duration, laser fluence and target nature on the properties of the transient plasmas .

Resume : Surface nanostructuring is of great importance in technological applications. On a rough material surface ultrashort laser pulses can excite surface plasmon polaritons, i.e. surface plasmons coupled to a laser-electromagnetic wave. The interference of the plasmons wave and the incoming pulse leads to a periodic modulation of the deposited laser energy along the surface of a sample. The spatial and temporal evolution of the periodically modulated absorbed laser energy is studied after irradiation of gold in the framework of the two-temperature model (TTM). We present a new source term in the TTM, which takes into account the excited plasmon subsystem and therefore spatial periodicity. Our results show, that the electronic temperature follows the spatial profile of the source term. We investigate how these oscillations persist on large timescales when thermalization between electron and lattice subsystems is achieved, and we study their influence on the formation of surface structures. The developed method can be used to study the mechanisms of laser energy absorption under controlled conditions and the formation of the morphological effects. For example periodic surface structures, which could be of interest for medical applications, tribology, wetting, and others.

Resume : Ti6Al4V cranial prostheses in form of patterned meshes were laser 3D printed by Selective Laser Sintering in argon environment, using a CO2 laser source and micronic Ti6Al4V powder as starting material. The size and shape of prostheses were chosen based on actual computer tomography images of patient skull fractures supplied in the framework of a collaboration with a neurosurgery clinic. After optimizations of scanning speed and laser parameters, the printed material was defects free as shown by metallographic analyses and chemically it was uniform, without elemental segregation or depletion, as revealed by electron diffraction X-ray spectroscopy. The bulk had an ?? martensitic metallographic structure with randomly oriented acicular grains. The prostheses produced by 3D printing were further coated by Magnetron Sputtering with a bioactive thin layer of a natural animal origin hydroxyapatite, obtained from calcination of bovine bones. The X ray diffraction structural investigations of films revealed a monophasic hexagonal hydroxyapatite phase. Degradation tests demonstrated the biomineralization capacity of the films and resistance to degradation in biomimetic environments. In vitro tests were conducted in order to test the natural apatite bioactivity. Osteoblast cells proliferated from 1-7 days, they extended over the substrate in order to maximize surface contact and emitted pseudopodes, to the difference of cells grown on borosilicate control glass that kept a polyhedral shape.

Resume : This work aims at the fabrication and characterization of hernia repair mesh coatings as innovative solutions that facilitate optimal local integration of implants and prevent the risk of infection. The concept involves the application of a laser-based technique, i.e. matrix-assisted pulsed laser evaporation (MAPLE) for the deposition of polymer: carbon nanotube blends (with or without drug addition) as thin layers on monofilament, macroporous polypropylene and polyester meshes. Various polymer: carbon nanotube (with or without Gentamicin and Vancomycin drug) blends are chosen to be deposited as thin layers on the primary blanks (i.e. commercially available meshes). The chosen materials are single walled carbon nanotubes (CNTs) and poly(ethylene oxide) (PEO) polymer. Carrying out morphological investigation of the as-deposited coatings, i.e. by atomic force microscopy and scanning electron microscopy we found that the morphology and topography of the PEO: CNT coatings may be tuned by varying the concentration of CNT in the starting material. By increasing the concentration of CNTs in the as-deposited films they become smoother. In addition, by investigating the chemistry of the coatings surface we found that it is possible to deposit PEO: CNT (with or without Gentamicin and/or Vancomycin) coatings by MAPLE with an unaltered chemical structure. In addition, XPS investigation revealed that the films with the 20% CNT are CNT-like, whilst the films with 2% CNT are PEO-like.

Resume : Geometrical phase elements (GPE) and their applications are booming nowadays: from devices like high NA metalenses to special optics like top-hat elements, from wavelengths in the ultraviolet to the THz diapason. The reason behind such flexibility is due to variety of different production approaches – lithography based, sculptured coatings etc. and due to the varying orientation and individual properties of sub-elements of the GPE. Such elements can act as both scalar and vectorial diffractive optical elements (or as shapers of the spatial spectra of the input beam), but usually their vectorial properties are largely ignored due to the complexity of mastering phases and amplitudes of both transverse components. Here, we propose a new polarization independent approach, which enables us to encode information into the both x and y components of the geometrical phase element. We report on our numerical study on the efficiency and feasibility of such elements. Moreover, we use a femtosecond laser based setup to inscribe nanogratings in the bulk of the glass. By controlling the orientation and retardance of those nanogratings we effectively manufacture a GPE, where the amplitudes of the x and y components are encoded independently. Lastly, we present an experimental study on few selected GPE’s, which were fabricated using new encoding technique.

Resume : Therapeutic Drug Monitoring (TDM) is a clinical practice to assess the drug concentration in a biological fluid, usually blood plasma. TDM is critically important for Narrow Therapeutic Index (NTI) drugs, including Anti-Epileptic Drugs (AEDs), where small differences separate therapeutic from toxic doses. Blood concentration of AEDs is measured with the time consuming and costly Immunoassay tests, or High-Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS). Light scattering with ad hoc engineered plasmonic substrates made of noble metal (Au) nanoparticles (NPs) grown by pulsed laser ablation is a fast and comparatively inexpensive TDM approach for AEDs. Ablating in a transparent liquid a colloidal solution of Au NPs is obtained, while in a dense, inert, massive gas (Ar) NPs form in the expanding plasma plume and are deposited on an inert support (100-Si). Ambient gas pressure and laser pulse number in gas-phase synthesis and pulse duration and laser energy density in liquid-phase ablation affect the size, size distribution, shape and optical properties of the NPs and the NP arrays that self-assemble on the support, making possible to adjust the wavelength of the Surface Plasmon Resonance (SPR) peak. Thus, Surface Enhanced Raman Scattering (SERS) on samples of different origin, with various AEDs at concentrations of clinical interest become feasible. Our results on the SERS response of the AEDs Lamotrigine and Perampanel of relevant clinical interest are discussed.

Resume : The use of lasers to achieve transformations at interfaces, either on solids under air, controlled atmospheres or a diversity of liquid environments, is evolving at a fast pace and in-line with recent advances in photonic technologies. The singular properties of lasers, which provide a choice of emission parameters, such as emission wavelength, pulsed or cw mode and pulse width, together with the use of optomechanical means to scan in beam or line fashion, are ideal in order to trigger physico-chemical phenomena which are not available with alternative methods and are, at large, based on thermally activated processes. In this communication we will introduce the Laser Ablation Backwriting (LAB) method and we will show how it can be used to perform dry chemical reactions with spatial control and at room temperature. This research is supported by the project SPRINT (EU H2020-FETOPEN 801464).

Resume : When an intense ultrashort light pulse – in the visible domain- interacts with a wide band gap dielectric, a plasma can be generated by non-linear photoexcitation of carrier from the valence band to the initially empty conduction band. These carriers can be further excited in the conduction band, leading to an increase of their energy distribution, and thus of the amount of energy transferred to the material. If this deposited energy exceeds some critical threshold, permanent modification like damage or ablation may take place. The two key parameters determining the energy deposition are the density and the temperature of the plasma. In this presentation, we wish to demonstrate that a sequence of double pulse can be used to better control these two parameters, and thus to optimize energy deposition and facilitate for instance ablation of insulators and semi-conductors in the VUV domain. First, in the visible domain, using the second harmonic and the fundamental of a Ti-Sa laser, we show that time resolved double pump- and probe experiment allows to directly observe the sequence of events carrier excitation/ carrier heating, provided the parameters (energy, duration, delay) are appropriately chosen. Then, the ablation threshold (due to the first pulse) is dramatically reduced by the presence of the second pulse, while the characteristic of ablation are still determined by the first pulse [1]. Finally, new information regarding the excitation mechanisms, in particular impact ionization and avalanche are obtained [2]. In the second part, we show that this double pulse technique can be extended in the VUV domain. Using high order harmonics of a Ti-Sa laser (harmonic 25, ie. wavelength of 32 nm), whose intensity of far too low to damage any material, we could observe direct ablation of a dielectric, namely quartz, -SiO2, when the VUV pulse if followed by an IR pulse, whereas no effect is observed with each of these pulses alone. [1] Guizard, S.; Klimentov S.; Mouskeftaras A. ; Fedorov N., Geoffroy G.; Vilmart G., Applied Surface Science 336, p. 206, 2015. [2] A Mouskeftaras, S Guizard, N Fedorov, S Klimentov Applied Physics A 110 (3), 709-715, 2013.

Resume : Advanced gas-turbine engines need new materials with excellent mechanical properties and resistance to high temperature oxidation. The combination of light-weight and good mechanical properties makes the titanium alloys very attractive for compressor section components [1]. Titanium offers the potential for component weight savings in the order of up to 50% compared to super alloys of Ni and steels. However, the mechanical properties of titanium deteriorate beyond 500 °C. Mechanical surface treatments such as shot-peening (SP) have shown their ability to improve the high temperature oxidation resistance of pure zirconium and titanium [2], but SP may be accompanied by surface pollution. Laser shock peening (LSP) appears as a good alternative to avoid this problem as it has been reported for pure titanium [3]. Here, we have investigated the effect of LSP treatments on the high temperature oxidation behavior of Ti-beta21S (TIMET, Ti-15Mo-3Nb-3Al-.2Si). LSP treated samples have been compared to untreated ones for oxidation times going from 5 to 3000 h at 700 °C in dry air. The mass gain variation was recorded by TGA for short durations. For long durations, the samples placed in a furnace set at 700 °C were periodically extracted to be weighed. Oxidized samples were studied by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), x-ray photo-electron spectroscopy, nuclear reaction analysis, x-ray diffraction, micro-Raman spectroscopy and hardness measurements. A higher resistance of LSP treated samples against oxidation at 700 °C has been observed. The contribution of different mechanisms such as the changes in the microstructure due to the LS treatment and the eventual diffusion of nitrogen will be discussed.

Resume : Metal oxide semiconductors are gaining more and more importance due to the many applications in fields as different as optoelectronics and photocatalysis, among many other. One of the most extensively studied materials in the group of MOS is ZnO. Nevertheless, many aspects of its use for the production functional nanostructures are still open. Probably the most challenging issues regarding this material, is to attain an efficient doping (in particular p-type). The tailoring of the material properties through the introduction of dopants is one of the most active fields in the ZnO research. However, the rise of severe environmental problems has brought to front different applications for which not only composition and defect structure is important. Photocatalys or sensing applications require surface conditions that can be achieved by laser treatment. Different patterning approaches in MOS substrates will be reviewed. As an example, polycrystalline substrates were structured by ultrafast laser pulses to induce the formation of Laser Induced Periodic Surface Structures (LIPSS). The performance of the irradiated areas as growth patterns for the production of highly ordered nanostructures was then analysed. Three main types of periodic structures were induced upon fs-laser structuring depending on the irradiation conditions: LSF (Low Spatial Frequency) and HSF (High Spatial Frequency) LIPSS and pseudo-spikes (PS). It has been found that the growth of micro- and nanostructures in the irradiated regions is much faster than in the non-irradiated ones. Our results indicate that using LIPSS as growth patterns can reduce the growth time to periods much shorter than those normally used from Vapor-Solid (VS) or Vapor- Liquid-Solid) VLS growth processes. Strong differences in morphology and luminescent properties are appreciated, not only between irradiated and non-irradiated areas, but also between areas irradiated under different conditions. The best regions to be used as growth templates for VS processes are found to be those irradiated in the highest energy deposition regime, featuring pseudospikes. This widens largely the current possibilities to tailor the characteristics of the grown structures

Resume : Direct-write (DW) techniques stand out from other more conventional approaches for their ability to print inks in a digital manner, which is desirable for short production runs or in defect repair. Laser-induced forward transfer (LIFT) is a DW technique capable of transferring user-defined patterns by means of laser irradiation. In LIFT a layer of ink is spread on a transparent donor substrate and faced down, at a convenient gap, above a receiver substrate where the pattern will be printed. Then, a laser pulse is focused on the donor film and a portion of the ink is ejected towards the receiver, where it is deposited as a voxel. By printing multiple voxels in a sequential way any pattern can be reproduced. Unlike its major competitor, inkjet printing, LIFT allows depositing a wider range of ink rheologies, since it is nozzle-free and therefore not prone to clogging issues. This is especially relevant in printed electronics, where high solid content inks are usually required. In this study we investigate the LIFT of silver inks with high solid content for the fabrication of highly conductive pads. Through the variation of the main process parameters, such as laser pulse energy or donor-receiver gap, we determine the optimum working conditions that allow obtaining continuous conductive lines with the lowest sheet resistance. As a proof-of-concept of the feasibility of the technique, we print an RF inductor and show that it performs according to the design specifications.

Resume : Chalcogenide Phase-Change Materials (PCMs), mainly GeSbTe-based alloys, have already been widely used for optical data storage (DVD-RAM or CD-RW). Thanks to their unique reversible and very fast amorphous to crystalline phase transition which is characterized by an uncommon huge change in optical and electrical properties. PCMs are now extensively studied to produce phase-change memory or aiming at developing further innovative non-volatile memories such as or storage class memories (SCM). The interaction of PCMs with a femtosecond light pulse has attracted significant attention since the possible non-thermal amorphous↔crystal phase transition could be used to drive the phase-change above the thermal “speed limits”. We used frequency domain interferometry (FDI), a pump-probe technique to investigate femtosecond dynamics in highly excited amorphous GeTe films. A pump pulse (25 fs, 800 nm, 1kHz) is used to trigger the phase transition. The interference patterns of the two probe pulses (120 fs, 532 nm) are measured simultaneously along S and P polarization to give access to complex refractive index as well as the surface hydrodynamics. In the sub-ps time scale a very rapid switch to a metallic state mainly attributed to the real part of the refractive index is observed while the surface is clearly moving within few hundreds of femtoseconds. Ab-initio simulations show that the change of chemical bonding of GeTe amorphous structure explains the trends observed in the experimental results.

Resume : In the context of ultra-short pulse machining of transparent materials important progresses in terms of resolution, accuracy and quality of the induced modification have been realized. However, the experimental studies exploring the spectral domain have been rare, mainly due to the difficulties of obtaining sufficiently powered pulses at multiple wavelengths. In this work, we report on ablation thresholds of fused silica at 257 nm, 515 nm, 1030 nm, 1550 nm and 1900 nm; all obtained through non-linear optical processes by making use of the same femtosecond amplifier laser system (1030 nm wavelength and 180 fs pulse duration). Experiments have been carefully carried out ensuring similar irradiation conditions, making the comparison possible. Among the results, we observe the increase of the single-shot fluence ablation threshold from the ultraviolet to the near-infrared, followed by a saturation from 1030 to 1900 nm. Also, on the interest of exploring possible benefits on laser micromachining a morphological analysis of the craters is performed. We observed that once the energy threshold is exceeded, larger ablated depth and higher depth tuneability can be accessed with short-wave infrared pulses. As perspective, the values presented in this work can help for validation of theoretical models, as well as to suggest ablation strategies with longer wavelengths for extending the range of aspect ratio that can be accessed with femtosecond Gaussian beams.

Resume : We take advantage of the remarkable properties of graphene to combine it for the first time with 3D plasmonic nanostructured Si substrates for SERS. Large-area arrays of Si nanopillars were developed by femtosecond laser processing of Si in water. Coating the structured Si surface by a thin Au layer results in the spontaneous formation of Au nanoparticles. The whole process is scalable. Monolayer graphene was grown on a Cu foil by CVD and transferred on the substrates. Raman spectra were acquired with a Raman microscope (488, 514, 633, and 785 nm excitation). We also employed 3 reference substrates: a) nano-Si without Au, b) flat Si with 50-nm Au layer, c) pristine Si. We complement Raman measurements with FDTD simulations. The Raman signal of graphene on the plasmonic 3D substrate is enhanced by 2-3 orders of magnitude, which is comparable to the highest enhancements of graphene measured to date. For the first time, this enhancement is observed for all excitation wavelengths, across the entire visible spectrum. Numerical simulations elucidate the advantages of the substrate 3D topography. When the Si nanopillars are decorated with Au nanoparticles, graphene conforms around them as it bends between nanopillars, emitting a strong Raman signal. Due to synergistic effects with the Si nanopillars, the Au nanoparticles are no longer indistinguishable, as on a flat substrate. Instead, different nanoparticles become more active for different wavelengths and locations on the pillars. The Raman signal is calculated to increase monotonically with the depth of graphene bending, demonstrating the advantages of exploiting a 3D topography. These results pave the way for future real-world applications of large-area hybrid nanomaterials.

Resume : Elemental analyses of thin films with complex composition are challenging as the standard analytical techniques based on measurement calibration are difficult to apply. We show that calibration-free laser-induced breakdown spectroscopy (LIBS) presents a powerful solution, enabling quantitative analyses of multielemental thin films with analytical performances better than those obtained with other techniques. The demonstration is given for a nickel-chromium-molybdenum alloy film of 150 nm thickness that was produced by pulsed laser deposition. The LIBS spectra were recorded in experimental conditions that enable simple and accurate modeling of plasma emission [1]. Thus, a calibration-free approach based on the calculation of the spectral radiance of a uniform plasma in local thermodynamic equilibrium was applied to deduce the elemental composition. Supported by analyses via Rutherford backscattering spectrometry and energy-dispersive Xray spectroscopy, the LIBS measurements evidence nonstoichiometric mass transfer of the alloy during the thin film deposition process [2]. [1] Hermann J., Grojo D., Axente E., Gerhard C., Burger M., Craciun V., Phys. Rev. E 96, 053210 1-6 (2017) [2] Hermann J., Axente E., Pelascini F., Craciun V., Anal. Chem. //doi.org/10.1021/acs.analchem.8b05780, online published (2019)

Resume : In the present work, we demonstrated how powder bed fusion (PBF) technology can contribute to a better understanding of functional and structural properties of shape memory alloys (SMAs) in Ni-Ti systems. Correlation of specific resistance and phase structure in porous nickel-titanium intermetallic phases after the PBF was experimentally observed. The electrical resistivity of the phases studied (austenite, R-phase, martensite) was shown to increase with temperature but the slopes are quite different. The intermediate R-phase in nitinol (NiTi – intermetallic phase) shows generally higher electrical resistivity than the austenite phase, but its value grows with a decrease of temperature for the laser fused samples. We explained this fact by the accumulation of dislocation with the continuous increase of the R-phase with the temperature decrease. Hysteresis loop of the electrical resistivity is more remarkable in the laser sintered samples than in the laser melted ones due to different 3D part’s porosity and is a lot higher than that of solid material having a similar composition.

Resume : The ongoing development of nanofabrication capabilities ever increases our ability to exploit the light-matter interactions occurring at the nanoscale, promising breakthroughs in many technological sectors. To translate these capabilities into practical optical devices, we require materials which can expand the window of low-loss plasmonic responses into the IR. Transparent conductive oxides are appealing candidates due to their high DC conductivity, refractory character, durability and CMOS compatibility. An additional asset is their non-stoichiometric character which allows for modulating their opto-electronic properties. In this work we utilize excimer laser annealing on room temperature sputtered indium tin oxide, aluminium-doped zinc oxide and gallium-doped zinc oxide thin films in oxidising and reducing environments. We investigate the role of laser fluence, number of pulses and ambient composition in altering the crystal structure, composition and opto-electronic properties. We perform extensive characterization via Hall-effect, x-ray diffractometry, atomic force microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy and spectroscopic ellipsometry in the wide spectral range from 0.3-40 μm. We report a modulation of the carrier mobility and concentration while preserving the amorphous nature of the thin films, providing a route to selectively tune the plasmonic response of TCO based nanostructures by controlling the laser annealing parameters.

Resume : Transition metal carbides are well known for their tribological properties, such as high hardness, high wear resistance, and chemical stability. TiC, a faced-centred cubic (fcc) crystal structure, has a high melting point of around 3 000 °C, and an exceptional hardness of 28 GPa. TiC is also well known for its good electrical and thermal conductivities and is commonly used in applications such as cutting tools, wear resistant coatings, heat exchangers, and electrical devices. Electrochemical properties, such as hydrogen absorption and storage, have already been thoroughly studied, and it has been demonstrated that such properties change with the amount of carbon. In this context, the aim of this study is to compare the electrochemical properties of stoichiometric and substoichiometric titanium carbides, TiC and TiC~0,6, with respect to their crystallographic orientation. Thus, thin films are synthetized on various substrates (MgOs, c-cut sapphire, and BK7 glass slides) by pulsed laser deposition (PLD). First, their morphology and structure are investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high resolution X-ray diffraction (XRD). Thin films, between 20 and 200 nm, exhibit subnanometric roughness. Hetero-epitaxial growth is observed in the films grown on mono-oriented substrates, following the (100), (110) and/or (111) atomic plans. On glass substrates, TiC~1 and TiC~0,6 films are preferentially orientated following the (111) and (200) plans. It appears that TiC~1 films are more difficult to be grown on glass than TiC~0.6 films, as delamination is consistently observed. At the opposite, thin films of substoichiometric TiC~0,6 are surprisingly of high quality on BK7 glass. To the best of our knowledge, this is the first report on TiC thin films grown on such simple and inexpensive substrates. Finally, electrochemical investigations are also performed, and the results reveal that the films behaviour is identical to the bulk material, indicating the high quality of the PLD grown thin films.

Resume : In the last decades, numerous and intensive studies have been focused on the interaction between ultrashort laser pulses and solid surfaces to create micro- and nanostructures in metals to change their surface properties. In particular, Laser Induced Periodic Surface Structures (LIPSS) have been widely explored to produce surface corrugations for this purpose. Apart from the aforementioned topographical micro- and/or nano-modifications, most of the available studies report a laser induced modification of the material composition, together with an associated effect on the surface functionalities -either by increasing the wettability or by improving cell adhesion among others-. However, little efforts have been made in order to establish a correlation between the laser processing conditions and the resulting chemical modifications in the ultrashort pulse regime. In this work, we present an exhaustive EDX and XRD analysis of the oxide formation on Ti6Al4V surfaces as a function of laser irradiation parameters. Two different regimes were found: Low Spatial Frequency LIPSS with no oxide formation for low accumulated fluences and High Spatial Frequency LIPSS with an increasing oxygen content for higher accumulated fluences. The effect of the repetition rate of the laser source on the oxidation process is also studied and a discussion on the formation mechanism is presented.

Resume : The laser-induced microbubble technique (LIMBT) has been recently developed for micro- patterning of various materials. My research is focused on improving this bottom-up approach and discovering ways to use it for applying various materials. The principle of LIMBT is that a microbubble formed by laser heating results in convective flows, leading to material deposition at the bubble/substrate interface. Moving the focused beam relative to the sample results in the migration of the microbubble and constant deposition of additional material. Up till now, the LIMBT was used to form continuous patterns only from very few types of nanoparticles (NPs) such as soft oxometalates. For other types of NPs, instability of the micro-bubble led to inconsistent material deposition. Additionally, it couldn't reach a resolution below ?4 ?m. I have recently demonstrated [1] that modulation of the laser enables the formation of thin continuous patterns due to improved control over the microbubbles. We have coined this method: M-LIMBT (modulated-LIMBT). I have applied this technique on various NPs such as Ag and Cu NPs. I found that after deposition of the NPs the formed structures had a resistivity of ~5.10-7 ?m, which shows that the NPs have sintered due to the laser heating. The minimum line width using modulation has improved to ~1 ?m. Finally, I have shown how this concept could be extended for one-step synthesis and patterning of metal organic frameworks (MOFs). [1] Armon, N. et al. Continuous Nanoparticle Assembly by a Modulated Photo-Induced Microbubble for Fabrication of Micrometric Conductive Patterns. ACS Appl. Mater. Interfaces 9, 44214?44221 (2017).

Resume : Laser ablation in liquid is a versatile method for the production of nanoparticle colloids. However, due to the high purchasing price of laser systems this method is perceived to be expensive. In this contribution, we compare lasers of different price categories with regard to their maximal ablated mass per time (productivity), maximal ablated mass per time and power input (efficiency), and the resulting price per volume of colloid (economic efficiency). Moreover, the difference in laser ablation in air and in water is examined. Lasers with pulse durations of 3 ps, 1 ns and 5 ns are chosen and their fluence-dependent productivity is determined in a continuous flow experiment. From this data, the threshold fluence and the efficiency are extracted. For one, the ablation threshold fluence increases between 1.7 to 3.0 times, when changing from ablation in water to air. On the other side, the maximal productivity and the efficiency is higher in air. The latter can be correlated to beam shielding by the NP and redepositing of ablation material in the liquid environment. Comparing the ablation efficiency for the different laser systems in water, the 1 ns laser reached the highest value. Due to the low purchasing price of this system, a colloid can be produced the most efficient way with this system. We further find that compared with a commercially available colloid, the production of colloids via laser ablation in liquids is economically feasible for amounts larger than 4 mL per day.

Resume : High levels of atmospheric pollutants have a negative impact on human health and the environment. The sensitive sensors have great interest for an accurately measuring of pollutants. In this paper we present results regarding the active membrane of sensors based on metal oxide nanoparticles (NPs) (SnO2, WO3, CeO2 - materials with a wide band-gap semiconductor and remarkable chemical stability and electrical properties). These membranes were fabricated as thin films by MAPLE deposition technique on different type of substrates. In order, to obtain thin films with morphological, structural (AFM, SEM, XRD analyses) and electrical properties suitable for a qualitative response of the sensors, the deposition parameters (NPs concentration in the liquid, laser fluence, the solvent type) were varied. In particular, the CeO2-NPs (1% concentration in water) were uniformly distributed over the surface of the layer; the high roughness (RMS) around 107 nm indicates a large specific area required for sensors. In order, to achieve a uniform surface and high RMS, the concentration of WO3-NPs in the liquid and the laser fluence were varied. For SnO2, the sample obtained at lower laser fluence has a more uniform, denser surface than that obtained at higher fluence. „This work was supported by a grant of the Romanian Ministery of Research and Innovation, project number 33PCCDI/ 2018, within PNCDI III”.

Resume : Fluoride doped by rare-earth (RE) makes them excellent for optoelectronics and photonics applications. However, due to the low absorption cross-section of the RE ions, the efficiency of the converting layer needs to be increased. One of concept to overcome this drawback is to combine RE with metallic nano-particles (NPs) which exhibit local surface plasmon resonance (LSPR) in UV and visible spectral range. The presentation reports on fabrication of metal-fluoride nanostructured thin films by pulsed laser deposition and evaporation supported by auxiliary plasma. This method operates under new physical conditions. Therefore, it makes possible to fabricate new advanced nanostructured films with unique functional properties such as the metal fluoride films with a unique plasmonic and luminescence properties. In our work we demonstrated successfully fabrication of Ag, Al and Bi NPs embedded by LiF , CaF2 and Pr3+:CaF2 films. The fabrication of metallic NPs in UHV conditions embedded in fluoride matrix prevent the oxidation, which could degrade of plasmonic properties of NPs. The effect of additional laser annealing on crystalline structure of the metals nanoparticles will be presented. The prepared layers were analysed by spectral ellipsometers in the spectral range from 145 nm to 5000 nm. The analysis of the measured date revealed an absorption band in the range from 200nm up to 450 nm corresponds to LSPR of incorporated metallic NPs depending on the metals and size, respectively. The calculated absorption cross absorption effective cross-section will be compared with experimental results.

Resume : Tin antimony sulfide (SnSb4S7) is one of the most promising compounds for the next generation of optoelectronic and thin film photovoltaic devices. SnSb4S7 material was synthesized by a solid-state reaction using earth-abundant tin, antimony and sulfur elements. The effects of excimer laser annealing (ELA) at different pulse energies on the structural, morphological and optical properties of thermally evaporated SnSb4S7 films were investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy measurements showed that the films annealed by an excimer laser of 248 nm were amorphous for weak energy densities whereas the sample irradiated with 111 mJ/cm-2 was polycrystalline with a preferential orientation. The ELA effects on the optical properties were also studied in the wavelength range 300-1800 nm by using UV-Vis-NIR spectroscopy. The absorption coefficient of all samples in the fundamental absorption region is higher than 104 cm-1. We also found that the optical band gap decreases from 2.04 to 1.84 eV after irradiating the thin films under different laser energy densities.

Resume : The use of ultrashort superpower pulses in modern laser technologies is accompanied by the appearance of new physical phenomena. Their study leads to the need to make appropriate adjustments to the mathematical models used. One of these effects is the effect of pressure of collectivized electrons in a metal under conditions of strong thermodynamic nonequilibrium. The correct formulation of the mathematical model in the continual approximation is carried out within the framework of the single-speed two-temperature hydrodynamic model. In the atomistic model, by analogy with the continual model, an additional force arises in the equations of motion (the so-called blast force) from the electronic subsystem in the form of a gradient of the “non-equilibrium” part of the electronic pressure. The effect of electron pressure was studied in a series of computational experiments based on the molecular dynamics simulation of femtosecond action on an Al target. A large gradient of electron pressure at the surface at an early stage of development leads to the breakaway of a thin subsurface subnanometer layer of matter flying away at high speed. At the stage of a slower process of unloading ionic pressure, a rarefaction wave with negative pressure is formed, leading to the separation of melt films with a thickness of 10-20 nm. The speed of dispersion of liquid fragments is significantly lower than the speed of the first split layer. This work was supported by RSF, project 18-11-00318.

Resume : In this paper, we demonstrate the capabilities of liquid assisted laser ablation technique in combination with laser-induced modification for synthesis of binary SiSn and GeSn nanocrystals (NCs). Nanostructures based on the GexSn1-x and SixSn1-x alloys are interesting due to the possibility of adjusting the lattice parameters and the width of the band gap, changing the mobility of charge carriers that makes them promising for the applications in optoelectronics and photovoltaics. For the alloyed NCs synthesis a two-step technique was developed based on the laser ablation of a germanium (silicon) target immersed in a cell filled with the preliminarily prepared Sn suspension in ethanol with the subsequent laser irradiation of the formed colloid. For the ablation and additional irradiation the Nd3+: YAG laser (1064 nm, energy 80 mJ/pulse, repetition rate 10 Hz, pulse duration 10 ns) and its second harmonic (532 nm) were used, respectively. The phase composition, morphology, structure and optical properties of the synthesized NCs have been investigated. Laser induced rapid heating, subsequent co-melting, and re-solidification processes at high cooling rates have been considered to be experimentally achieved at the optimized laser processing parameters. The prepared NCs with an average diameter of about 5 nm exhibited a shift of the Raman peaks attributable to Ge and Si (to the lower wavenumbers) that can indicate the incorporation of Sn into the lattice and alloy formation. The potential of the prepared alloyed NCs as a photovoltaic material will be demonstrated.

Resume : Polymers are replacing progressively metals and metallic alloys in technological applications over the past few decades and there is great interest in physico-chemical treatments for modifying polymeric surfaces. The aim of our studies is to change physical and chemical properties of the polymeric surfaces in order to enhance performances in some specific applications such as automotive. Laser treatments are of particular interest in morphological and chemical modifications of the polymer for nano-particles coating and surface functionalization in general. We employed a fs Ti:Sa laser source in order to evidence differences in the obtained results induced by photo-chemical, photo-physical, and photo-thermal processes by means the change of the main laser parameters such as: pulse energy, spot dimension according to the distance of the focused laser beam to the sample surface. Laser-irradiated samples were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray diffraction (XRD), m-Raman spectroscopy, FT-IR spectroscopy and contact angle measurement. Morphological results indicated that ripple-like structures of micrometer and sub-micrometer size were formed after the laser irradiation keeping the main chemical features of polymer surface.

Resume : In the last decades, there is an increased interest in developing strategies for improving bio-interfaces in the field of orthopedic implants. Understanding interaction of cells with bio-interfaces is essential to the design of scaffolds that can control cell adhesion, proliferation and differentiation in regenerative medicine. Ceria nanostructures may not only improve the biointerface mechanical properties, but also stimulate the regenerating tissue biochemical activity. It is well-known that formation of compounds derived from molecular oxygen (i.e. hydroxyl radicals, hydrogen peroxide) during cellular growth hinders cell proliferation, which can be prevented by nanostructured CeO2 that neutralize the oxidative stress. Based on the unique benefits of ceria on cells, the aim of this work was to prepare specific micro and nanostructured CeO2 films, and to determine their in vitro biological performance as correlated to the coating architecture. Pulsed Laser Deposition (PLD) method was used for obtaining CeO2 thin films. The resulting morphologies and the main features were characterized using scanning electron microscope (SEM). The wetting behavior and surface free energy of CeO2 films were studied using the contact angle measurement. The initial adhesion of the MG-63 osteosarcoma cell and the effect of the micro and nanostructured coatings on their morphology and adhesion was analyzed by fluorescence and SEM microscopy. It was observed that the different structured ceria films obtained by PLD influenced especially the early response of MG-63 cells, but with little influence on viability, therefore being promising candidates for improved orthopedic implants. In perspective, different cells lines response will be analyzed toward establishing an osteogenic response.

Resume : The process of laser radiation induced formation and decomposition of Ag nanoparticles in glass is studied. Glass samples with composition of 50 wt% SiO2, 20 wt% Al2O3, 20 wt% B2O3, 5 wt% CaO, 2 wt% Li2O, 3 wt% MgO are fabricated by melt quenching method. AgNO3 is added in the fabrication stage in amount to form final glass samples with compositions of 0.1 and 1 wt% Ag. The fabricated samples are irradiated by laser pulses delivered by Nd:YAG nanosecond and Ti:sapphire femtosecond laser systems. The laser parameters as wavelength, fluence and the applied pulse number are varied in a broad range in order to estimate the glass response. It is found that at certain conditions laser radiation can induce direct formation of silver nanoparticles in the irradiated zones. The process is different from the already presented in the literature that requires annealing after the laser processing. Based on XPS, TEM, and optical transmission and luminescence analyses the mechanism of nanoparticles formation is discussed. It is also found that the laser radiation of the formed nanoparticles can result in their decomposition. The efficiency of the process is studied for a wide range of laser parameters for both nanosecond and femtosecond laser pulses. In this process a complete recovery of the native glass optical properties can be achieved. The obtained results can be used in a technology for modification of the optical properties of composite glasses and design of complex photonic and data storage devises.

Resume : II-VI semiconducting chalcogenides have become a great part of research interest due to their possibility to use in a wide range of device applications with their remarkable optoelectronic properties as ideal direct band gap, high absorption coefficient and photosensitive behavior in the visible region of spectrum. Based on these optical and electrical properties, these compounds have been investigated as an alternative material system in the fabrication of low cost optoelectronic devices and used as promising materials for the development of current technological devices. Among these compounds, cadmium selenide (CdSe) thin film has long been popular in the field of optoelectronics due to their high transparency in visible region, direct and wide band gap value, photoconductivity, high electron affinity and n-type semiconducting behavior. Although this type of films have potential applications in fabrication of light emitting diodes, thin film transistors, gas sensors, photodetectors and solar cells, in recent years, attention has been directed to alternative methods as variations in chemical constituents, doping, formation of ternary analogues, surface patterning in order to manipulate the material characteristics of thin films to improve the performance of the devices. In this study, CdSe thin films were deposited on a soda-lime bare glass and indium tin oxide (ITO) coated glass substrates using direct evaporation of high purity and stoichiometric CdSe powder at room temperature. Bare glass substrates were used in thin film characterization processes and ITO coated glass substrates was employed to create transparent conducting oxide layer for possible device applications. For the deposited CdSe thin films, energy dispersive X-ray (EDS) analysis showed an average atomic percentage of CdSe is near to stoichiometric composition of the source material as Cd:Se ratio (50:50). The X-ray diffraction profile of the samples was indexed according to JCPDS files and the characteristics diffraction peaks were observed in a good agreement with the literature without any formation of secondary phase in the structure. The surface imaging using scanning electron microscopy (SEM) and detailed surface morphology analysis by using atomic force microscope (AFM) showed that the deposited CdSe thin films are dense and compact in nature. From the optical transmission studies, films were found in direct optical transition characteristics and the band gap values of the samples were calculated using Tauc plots. In addition to the film analysis on different substrates, substrate-assisted laser patterning was investigated as an alternative technique to create functional structures for possible optoelectronic applications. The straight and continuous line patterns on bare and ITO coated glass substrates were optimized in terms of pulse repetition rate, laser power, pulse energy and the feeding speed of the nanosecond pulsed Nd:YAG laser system. Uniform periodic pattern without any damage to the glass substrates were achieved with a wavelength in the infrared region. It was observed from EDS spectrum of the films that the stoichiometric transfer of material from source powder to the deposited films on different substrates with different line patterns was achieved. In the case of surface morphology, the effects of laser patterning on characteristics of the CdSe thin films deposited on bare and coated glass substrates were investigated by SEM and AFM images. UV/Vis spectrophotometer was used to discuss the transmittance and reflectance characteristics of these patterned samples. Acknowledgement: This work was partially supported by the Scientific and Technological Research Council of Turkey (TUBITAK) Project No: 118F317

Resume : The increase of aeronautical transport with environmental constraint needs to make planes as fuel-efficient as possible. One of the solutions is to make aircrafts lighter. Some materials, especially the dense nickel alloys, should be substituted with lighter materials. To improve some of the materials properties mechanical treatments could be efficient, like shot peening [1] or laser shock peening [2]. In this last case, laser irradiance must be very high, above 10 GW/cm², which needs powerful specially designed laser sources. Laser irradiance effects on the composition modification of the extreme surface of pure titanium was studied during the first stage of high temperature oxidation, at 700 °C. Laser shock-peening treatments with irradiance in the range of 2 to 11 GW/cm² were performed. Direct surface analysis of laser-shocked and oxidized samples were conducted by SEM/EDS microprobe and completed by Ion Beam Analysis (IBA) to observe the evolution of light elements like nitrogen and oxygen during the different steps of oxidation. A furnace coupled with XPS analysis allowed us to investigate the superficial layers of laser-shocked samples after short oxidations. Raman spectroscopy shows rutile formation. Analyses underline that the oxidation of pure titanium leads to nitrogen insertions under the native rutile oxide. For longer exposures, up to 100 h, the concentration of large quantities of nitrogen was revealed at the oxide/-case interface for the laser-shocked samples. This accumulation could be the main reason of the improved oxidation resistance of laser-shocked pure titanium in air at 700°C. References [1] A. Kanjer et al., Surf. Coat. Technol. 326 (2017), 146–155. [2] A. Kanjer et al., Surf. Coat. Technol. 343, (2018) 93-100.

Resume : Titanium is a metallic material with good mechanical properties, very interesting in aeronautic applications for its low-weight characteristic. Unfortunately, the oxidation resistance of this material drastically decreases over 550°C. To improve the oxidation resistance some mechanical treatments as shot peening and laser-shock peening can be applied. Nevertheless, the origin of the improvement of this oxidation resistance is not yet clearly understood. Previous studies underlined the importance of some parameters of the treatments on the mechanical efficiency of LSP. In this study, we explore the influence of two parameters (the number of impact per area and the laser irradiance value) on the microstructural modifications. The number of superposed impacts varies from one to three. The laser irradiance was in the range of 8 and 9 GW/cm2. The higher value is suggested by previous studies. The impact zones were observed by 3D optical microscopy and interferometric analysis. Cross-section observations were made by SEM (in BSE mode) and EBSD. The microstructure evolution as a function of the number of impact and laser irradiance was highlighted. The type and density of twinning seem to be the most affected features. These evolutions give some explanations on the effect of the shock wave on the local modifications inside the material. Compressive twins are directly induced during direct shock wave, while tensile twins are produced by interference between the main and secondary reflected waves. Previous works showed that the LSP treatment led on the whole sample surface induces thinner oxide layers than on untreated samples. In this work samples with single impact zone of few mm of diameter were oxidized under air at 700°C. The oxide layer in the laser-impacted zones was similar with those of non-impacted areas. This suggests that, for protection against oxidation purposes, the laser-shock penning treatment needs a large surface recovery.

Resume : Titanium oxide, Copper and titanium thin films (with closely 200 nm thickness) are grown on Si substrate using magnetron-sputtering technique. The first objective is to establish the incubation curves for ultrashort beams (fs and ps) at 266 nm. The working fluences are in the range 10 to 500 mJ/cm2 and the number of pulses is varied from 10 to 105. The induced micro-craters are analyzed by Scanning electron microscopy (SEM) and interferometric optical microscopy (IOM). The last technique allows to scan the micro/nano craters in order to evaluate the anisotropy of the ablation mechanisms in correlation to the laser ablation regime. Two kind of incubation curves (by SEM and IOM are compared and discussed and the corresponding incubation curves are proposed. The LIPSS formation conditions (regular LIPSS, spikes and dots) under both laser beams (fs and ps) are also investigated and discussed versus the incubation phenomena in each thin film case.

Resume : Owing to its high carrier mobility as well as compatibility with silicon-based technology, germanium recently attracted a renewed interest for its high performances in various technological area such as photonics, nano- and opto-electronics. Nevertheless, Ge-based devices often require both very high (>1e20 cm^-3) and ultra-shallow doping, which are challenging for most of dopants due to their low solubility and high diffusivity. For this purpose, pulsed laser melting (PLM) is the most promising technique, being able to promote ultra-fast liquid phase epitaxial regrowth allowing both enhancement of incorporation together with diffusion confinement, at the same time. Our latest experimental results on p- and n-type doping of Ge or Ge-on-Si as obtained by performing PLM in different conditions will be presented. In particular, the talk will be focused on possible issues (like contaminations, clustering and thermal stability) along with different strategies employed to improve electrical activation and to meet different applications: for example, PLM combined with ion-implantation or in-situ doping. Fundamental information about non-equilibrium diffusion or strain evolution will be discussed thanks to advanced chemical (1D and 3D), electrical and structural characterizations with nanometer resolution.

Resume : The laser treatment is widely used to control the wettability properties of material surfaces. In present work we propose a novel approach for obtaining of silicon surfaces ensuring an arbitrary apparent contact angle within the range from 0° to 170° for water. We found a narrow range of regimes of infrared laser irradiation leading to formation of a unique self-organized structure on the silicon surface – microcolumn grid with spacing about tens microns. Formation of the structure within the laser spot is due to a combination of ablation, oxidation, product ablation redeposition and cracking along the crystal lattice. A study of degradation of the self-organized structure for overlapping laser spots was carried out. It is demonstrated that scanning of the laser beam in the regimes of self-organized structure formation on the silicon substrate allows to obtain an extended surface area with superhydrophilic properties. The extreme wettability retains preserved when the samples are stored in air for six months. Hot-wire CVD of fluoropolymer coating onto the superhydrophilc silicon was used to further control the silicon wettability properties. An increase in the fluoropolymer film thickness up to 100 nm allows to change gradually the surface from superhydrophilic to superhydrophobic. The wettability properties of the produced fluoropolymer–silicon system were analyzed using the Wenzel and Cassie theories. The work was supported by the Russian Science Foundation (grant number 18-79-10119).

Resume : Laser treatment of silicon with short pulses has been rapidly developing over the past few decades. The ability to deposit large amounts of energy in a densely localized area has found use in pico- and femtosecond laser processing and nanostructuring of semiconductors. Nevertheless, the fundamental mechanisms underlying such processes as ultrafast melting, layering and removal of matter, caused by laser radiation are still the subject of scientific debate. A theoretical study of these mechanisms, based on mathematical modeling, is faced with the problem of determining material properties in a wide range of temperature and pressure. Polymorphic transformations in silicon, arising from the transition of a substance from one crystalline state to another, affect its properties. In the vicinity of the phase transition, all properties undergo qualitative changes and significantly differ from similar characteristics of metals. The report presents the properties of silicon in a wide range of temperature and pressure including the critical region, obtained using molecular dynamics modeling. Such important characteristics of Si as the pressure dependences of the temperature and heat of melting, temperature dependences of the heat of evaporation, the coefficient of linear expansion, heat capacity, and density are determined. Results are compared with experimental data. This work was supported by RSF, project 18-11-00318.

Resume : The second harmonic (λSH = 532 nm) of a Nd:YAG system is utilized to produce nanowire networks by pulsed laser ablation of a silver target immersed in double-distilled water. A static electrical field is applied perpendicularly to the direction of the laser beam propagation to investigate its impact on the nanowires formation. The intensity of the electric field and the fluence of the laser beam are varied. The profile of the optical transmission spectrum is used to indirectly assess the morphology of the material being ablated. The nanostructures obtained are visualized by transmission electron microscopy and their microstructure is studied by selected area electron diffraction (SAED). The nanowire networks are of importance for biomedical application and in surface-enhanced Raman spectroscopy.

Resume : Recent advances in ultra-high power fs-laser physics and technology materialized in the construction of several operational PW-level installations worldwide. Beam steering and focalization at such high intensities is performed using high quality mirrors, which are using either dielectric layers/multilayers or metallic layers. We used the pulsed laser deposition technique (PLD) to obtain thin HfO2 and ZrO2 dielectric layers that were investigated as coatings for fs-lasers mirrors. The PLD installation uses an ArF excimer laser, since its 193 nm radiation is better absorbed in oxide targets than the 248 nmwavelength of KrF lasers. Films were deposited on Si and quartz substrates under various oxygen pressures to optimize their optical properties. The single and multiple pulses fs laser damage threshold (LDT) of deposited films were tested using two laser installations. One installation is a CPA 2101 (Clark - MXR) system who delivers pulses at 2 KHz with 200 femtosecond pulse duration at 775 nm wavelength. The other fs-laser installation is the ASUR system in the University of Marseille delivering 25 fs pulses at a repetition rate of 10 Hz. The irradiated spots were investigated using optical and scanning electronic microscopy to obtain the damage threshold of the deposited films versus the PLD growth conditions. The obtained results are compared to those reported in the literature and open the way to obtain optical layers for fs-laser mirrors possessing good LDT values by using the PLD technique. Acknowledgements The work presented was funded by Nucleu –INFLPR program and ELI 17/2017 project.

Resume : Thin films of pentacene, i.e. a polycyclic hydrocarbon consisting of five linearly-fused benzene rings, are grown on silicon and quartz (SiO2) substrates by matrix assisted pulsed laser evaporation (MAPLE) and by using toluene as a frozen matrix (melting point: −95 °C). The thin film samples are subsequently investigated for their optical, morphological and chemical structure, i.e. by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM), and spectroscopic-ellipsometry (SE). Due to its highly conjugated aromatic behaviour, pentacene exhibits semiconductor properties and has been shown to generate excitons upon absorption of ultra-violet (UV) or visible light. Here, we studied the ultrafast excited state dynamics of pentacene, in bulk and as thin films, after optical excitation by using femtosecond (fs) time-resolved second harmonic generation (SHG). A pulsed femtosecond Ti:sapphire laser (80 MHz repetition rate, 800 nm, 100 fs) was employed to demonstrate SHG potential of such polycyclic aromatic hydrocarbon simple molecule. The substrates used in studying the films are inert and non-interacting, known to deliver no noteworthy contribution to the SHG-signal. Therefore, the pure response of pentacene to the electronic excitation can be resolved in contrast to the measurements on SiO2. This study provides important insights on the excited states dynamics of pentacene, an essential step for understanding the photophysics of simple, linearly-fused arenes.

Resume : This study presents a methodology for the synthesis of one-dimensional colloidal nanostructures. The method consists of laser ablation of a ferromagnetic target (Fe) in a liquid medium carried out in the presence of an external magnetic field. Direct deposition of the ablated material is realized as a substrate was placed in the liquid. At certain experimental condition deposition of nanoparticle chains on the substrate can be realized. The ablation experiments were performed in two different liquids – ethanol and distilled water, as their role on the characteristics of the ablated material is clarified. The influence of different laser processing parameters and ablation geometry on the features of the nanostructures deposited on the substrate and these dispersed in the liquid were also investigated. On a basis of detailed analyses using Scanning Electron Microscopy, X-ray Photoelectron Spectroscopy, and Transmission Electron Microscopy the morphology, composition, and size distribution of the fabricated nanostructures were studied. The optical properties of the produced colloids were also evaluated by optical transmittance measurements in the UV–VIS spectral range. The presented method allows fabrication of contamination-free nanostructures with potential application in biotechnology, catalysis, sensorics and magneto-optics devices.

Resume : With platinum established as the most commonly used electrocatalyst for the sluggish oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEM-FCs), its high demand and limited supply present an obstacle for the full commercialization of FC technology by raising the overall costs at non-competitive levels. Thus, considerable research efforts have been dedicated to doping nanocarbons with low-cost heteroatoms (e.g. N, B, P, S) proven to enhance catalytic activity, with less attention having been directed to iodine as a dopant. However, the volatility of iodine renders it an appropriate heteroatom donor in elemental or compound form as hydroiodic acid for laser pyrolysis: the application of high-powered lasers to homogeneous gas-phase media based on the resonance between the laser radiation and a gaseous photosensitizer. Laser pyrolysis constitutes a versatile method for the bulk production of fine powders with uniform and controllable particle size distribution and morphology. Using typical carbon donors, such as acetylene, and introducing iodine fumes into the precursor mixture leads to the production of iodine-doped core-shell nanocarbons. These are extensively characterized via spectrometric (Raman, XRD, XPS), thermogravimetric/adsorption (TGA, BET), and microscopy (SEM, HRTEM) techniques; their electrocatalytic performance is evaluated on dedicated PEM-FC testing stations.

Resume : Functionalizing physical or chemical properties of surfaces is nowadays routinely achieved by means of light-matter interaction using laser beams. We present a way to generate random fingerprint-like patterns resulting from the surface melting of 500 nm-thick amorphous thin films of Ge-Sb-Te chalcogenide alloys covered by a 10-nm thick SiN capping layer after exposition to different laser pulses (30 fs 800 nm Ti:Saph, 400 fs and 400 ps Yb fiber 1030 nm) in the µJ range energy. The patterns were investigated by AFM and optical phase contrast microscopy. The spatial frequency of the obtained wrinkles is determined to be on the μm-1 scale. The latter is related to the thickness of the melted layer of material which depends on the laser fluence (in the tenth of mJ/cm2 range); the higher the intensity, the thicker the layer and the smaller the spatial frequency. The origin of the physical mechanism at play here is clearly different from so called laser induced periodic surface structure (LIPSS) patterns. Further HR-TEM measurements indicate that the irradiated layer of material is still amorphous, but seems to be made of a different amorphous phase than the pristine underlying one. A straightforward application of these patterns is to use them as anti-counterfeiting tags. We show as well how a neuron based algorithm is able to unambiguously retrieve a pattern among a test samples to 100.

Resume : Nowadays stimuli-responsive materials have received increasing interest due to their potential applications in smart systems, sensors, printed or stamped elements. Here, we report on the fabrication of a photochromic thin films using Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique. Two types of photochromic dyes were used: an organic pigment with a spirooxazine structure encapsulated in an appropriated organic resin and an AZO organic dye intercalated in an inorganic layered double hydroxide (LDH). The nanocomposites were transferred by UV laser (266 nm) on different substrates: Si (001), polyamide and flexible transparent polymers. Water, ethanol were used as solvents for the preparation of the targets for MAPLE experiments. The optical, structural, morphological and photochromic properties of the as deposited films revealed the role guest chromophores and of the host matrix either resin or LDH.

Resume : The fabrication of highly doped and high quality Ge layers is currently a challenging hot topic in nanoelectronics, photonics and radiation detectors, particularly regarding n-type doping. In this matter, dopant deposition followed by pulsed laser melting (PLM) has demonstrated to be a simple and cheap doping method, with a thermal budget lower than other methods commonly used and, at the same time, able to achieve record activation levels with no residual damage and excellent electrical and optical properties relevant for Ge future advanced devices. Ge samples with a n-type dopant Sb sputtered on the surface have been treated with PLM using a 7 ns, 355 nm Nd:YAG solid status laser or a 25 ns, 248 nm KrF excimer laser. A broad characterization has been performed, based on secondary ion mass spectrometry, channeling-Rutherford backscattering spectrometry, single and differential Van der Pauw-Hall, high resolution x-ray diffraction, infrared reflectivity. We show that PLM promotes an efficient diffusion of high Sb concentrations in the Ge melted subsurface layer followed by fast epitaxial regrowth, leading to samples with exceptional crystalline quality and active concentrations well above 1e20 cm^-3. Key properties such as substitutional fraction, electron mobility, residual strain, infrared reflectivity and plasma frequency are also characterized and discussed.

Resume : Laser as a source of radiation is a versatile form of energy with a various range of application. In this research, liquid-phase pulse laser ablation (LP-PLA) was used to produce graphene nano-sheets. For this purpose flexible graphite have been exfoliated in four different solvents by employing 1064 nm laser wavelength using 70 mJ/pulse energy. They were then characterized using X-Ray Diffraction Pattern (XRD), acetone was selected as a desired liquid medium, and afterward, the morphological and structural studies of graphene nano-sheets prepared by LP-PLA method in acetone medium was done by Field Emission Scanning Electron microscopy (FESEM), UV-Vis-NIR and Raman spectroscopy. In addition, it is found that increasing the energy of laser pulses to 120 mJ/pulse in acetone as the liquid environment, leads to the formation of undesired nanoparticles remained on the surface of the graphene nano-sheets. Also, pinned graphene-nano-sheets on the surface target was demonstrated by FESEM analysis.

Resume : The field of flexible and stretchable electronics has evolved very rapidly over the past 10 years, enabling unprecedented innovations in consumer electronics and sensors. As the demand for miniaturization and power of flexible devices increases, so does the need for novel manufacturing processes and materials, but also for technologies addressing the fabrication of reliable and durable interconnections under large mechanical stress and small bending radii. Laser Induced Forward Transfer (LIFT) of metal nanoparticle and nanowire inks, has emerged as a key-enabling technology for flexible electronics. In this paper, we demonstrate how this technology can also be applied for achieving high resolution flexible interconnections, with form factors in the order of 10 micrometers. In particular, we have employed different Ag nano-inks in terms of nanoparticle size and various flexible substrates such as PEN and PDMS for the validation of the performance of these interconnections: an all-laser fabricated flexible platform comprising Ag microelectrodes has been developed for test cycles of bending at radius < 1cm and stretching. Moreover, emphasis has been given on the study of electro-migration of Ag, a phenomenon occurring when Ag atoms diffuse under high current densities. For test structures comprising Ag nanoparticles, we have conducted acceleration stress tests in order to shed light on the effect of nanoparticle size and substrate (joule heating) on the electro-migration process.

Resume : Silicon wafers with a passivation layer of silicon dioxide are a commonly used substrate in micro technology especially in microelectronic. Besides lithography, laser processing obtains an increasing role in the processing of such microelectronic devices. The laser is used to separate functional structures or partially remove the passivation layer. Ultra-short pulse laser increase the processing quality, precision and can achieve a higher selectivity compared to longer pulse durations. The knowledge of the ablation behaviour of the SiO2 layer is essential to avoid damage to functional structures by the laser processing of microelectronic devices. Therefore, the selective ablation of a 100 nm thin silicon dioxide layer on silicon substrate was investigated using an ultra-short pulse laser with a wavelength of 1028 nm. The influence of the pulse duration, in the range between 200 fs and 10 ps, on the ablation process was examined. Single and multiple pulses ablation thresholds of the SiO2 layer were determined and the corresponding incubation coefficients calculated. Optical, scanning electron and atomic force microscopy were used to characterize the irradiation area. As a result, different ablation morphologies were observed, dependent on the processing parameters. These results were applied to realize simple structures by selective ablation of the SiO2 layer.

Resume : In this work we prepared carbon nanostructures doped with halogen by laser pyrolysis method, starting from tin precursor - SnCl4 and ethylene / DMDS. The inert gas (Ar) was used to confine and cool the nanoparticle species from reaction. The study of the effect of the synthesis parameters on the resulting nanoparticles morphology and structure was made by X-ray diffraction (XRD), electronic transmission microscopy (TEM), electronic scanning microscopy (SEM), spectroscopy (EDS) and optical spectrometry (UV-Vis). The results of these studies will be useful in optimizing the synthesis of halogen doped carbon nanostructures and determine the parameters appropriate to the desired result, regarding efficient energy generation.

Resume : The design and processing of instructive surfaces with synergic mechanical, chemical or topographical properties capable of directing cell behaviour represents both the main challenge and the main strategy to guarantee the long-term success of a biomedical device or implant. Nevertheless, the design must take in consideration the correlation between cell type, material characteristics and the specific function to be accomplished for the aimed application. In this work, laser processing of micro-structured biomaterials ( i.e ceramics) with convex and concave topographies for evaluating the role of materials surface topography on Mesenchymal Stem Cells-MSCs responses are presented. Ti Saphire fs laser was used to obtain optimized architectures of zirconia ceramics. All the surfaces were analysed by Atomic Force Microscopy and Scanning Electron Microscopy and the contact angle measurements revealed a direct correlation between the material type and morphology with Mesenchymal stem cells response. The physico-chemical characteristics of the microstructured surfaces, along with the in vitro analyses, suggest that our designed biointerfaces represent an efficient way to tackle the design of implant surfaces or smart interfaces for wide range of biomedical applications. Acknowledgment: Financial support from Nucleu Program 2019 is acknowledged.

Resume : Chemical sensors and biosensors are the main components in products designed for healthcare monitoring systems as they are attractive competitors of the bulky, expensive, and complex analytical instruments currently used in medical applications. However, recent estimates show that the biosensor and electrochemical sensor market are dominated by glucose sensors. Therefore, there is a great need to expand the application of biosensors beyond glucose. Even more, taking into account the rapid development of the society’s needs, concepts such as intelligent clothing and wearable devices receive increasing attention. In addition, new features such as portable, flexible, and real-time monitoring become more and more important. In the last years, recent approaches are focused on wearable electrochemical sensors, which can detect target analytes (i.e. a variety of heavy metals) in saliva, tears, sweat, and interstitial fluid. The aim of this work is the development of an original flexible and wearable biosensor based on nanocomposite materials (polymers and graphene) fabricated by laser-induced forward transfer. In particular we focus on the synthesis of donor materials and the optimization of the LIFT process for obtaining reproducible pixels which are used as electrodes for the electrochemical biosensors. We printed different polymer:graphene nanocomposites onto flexible substrates (coated with an insulating layer, for ex. Parylene C, which prevents electrical contact with the body fluids). The biosensors fabricated by LIFT are used for the detection of heavy metals in human body fluids. Promising results i.e. high sensitivity and detection limits were obtained, which proves LIFT as an alternative method for printing nanoscale materials aiming at the fabrication of wearable sensors. Acknowledgement Financial support from i) NILPRP through the NUCLEU program and ii) UEFISCDI, though the “Smart flexible biosensor via laser transfer for body fluids monitoring (iFLEX)” project are gratefully acknowledged.

Resume : Lasers are currently indispensable for many civilian and military applications and there is a considerable need to develop optical limiting materials for laser damage prevention of optoelectronic devices and for people protection. Specific to an optical limiting material is the linear increase of the transmitted power/fluence of the laser beam when the incident one is increasing, below a threshold, while above the threshold the transmitted power/fluence remains constant, independently of the power/fluence of the incident laser beam. The optical limiting capability of several synthesized reduced graphene oxide (rGO) based materials, as films, organic/inorganic solutions, and silico-phosphate composite materials have been investigated by intensity scan at different wavelengths and temporal regimes of excitation: fs pulses at 1550 and 775 nm, ns pulses at 1064 nm. The experimental transmittance has been determined in all performed experiments. The value of the optical transmittance, in the linear regime, and the saturation intensity of the nonlinear transmittance curves, where applied, have been determined. The laser induced damage in the synthesized materials, under the action of laser beams, was also investigated. Our results evidenced the influence of the ?matrix? that embed the rGO. The influence of rGO concentration and of P2O5, in silico-phosphate matrix, on optical limiting potential was discussed. Acknowledgements: MANUNET Program, Project MNET17/NMCS-0114, OLIDIGRAPH

Resume : Hybrid organic-inorganic thin films based on zinc phthalocyanine (ZnPc) and ZnO nanoparticles were deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE). Synthesized by a simple wet chemical precipitation method, the ZnO nanoparticles were featured by hexagonal wurtzite structure, band-gap value at ~3.3 eV and emission bands typical for this semiconductor. The organic (ZnPc) - inorganic (ZnO) hybrid films were obtained by MAPLE involving the following experimental conditions: dimethylsulphoxide (DMSO) as solvent, 350 mJ/cm2 laser fluence, 40 000 number of laser pulses and 5 cm target-substrate distance. The properties of the hybrid films containing ZnO nanoparticles in various amounts were evaluated by a complex characterization. Thus, scanning electron microscopy confirms the presence of the ZnO in the prepared hybrid films. No chemical decomposition of the pristine organic and inorganic compounds was observed in the FTIR spectra. The optical spectra recorded on MAPLE films disclose the signature of the raw materials (ZnPc and ZnO). The current-voltage (I-V) measurements carried out in dark and under illumination reveal the influence of the ZnO nanoparticles amount on the electrical properties of the hybrid films. Our study provides new insight in the MAPLE deposition of the organic-inorganic hybrid films which can find applications in the photovoltaic cells area.

Resume : The main limitations of the organic devices’ performances come from the low mobility of the charge carriers, reduced diffusion length of exciton and reduced interfacial contact area between the donor and the acceptor compound. The synthesis of new organic semiconductors and development of new device configurations represent alternatives for obtaining an efficient charge carriers transport and devices with improved performances. This paper presents some studies of the organic heterostructures realized in both bi-layer and mixed layer configurations on flat and patterned glass covered by ITO substrates by Matrix assisted pulsed laser evaporation/MAPLE (solvent=chloroform, fluence=300 mJ/cm2, number of pulses=15000). A start-shaped arylenevinylene compound was used as donor and perylene tetracarboxidiimide, a non-fullerene compound, as acceptor. The glass substrate was covered by a grating of nanostructures developed by UV-Nanoimprint Lithography characterized by a cylindrical shape, periodicity=1.1 m, diameter=400 nm, depth~300 nm. The ITO electrode has been subsequently deposited on this nanostructured surface by Pulsed Laser Deposition (fluence=1.2 J/cm2, number of pulses=7000, p_oxygen=1.5 Pa). SEM and AFM measurements have evidenced the influence of the ITO electrode nano-patterning on the morphology of the organic layer deposited by MAPLE. The effect of the periodically array of (nano)structures on the optical and electrical properties of the heterostructures with bi-layer compared to the heterostructure with mixed layer has also been analyzed.

Resume : Bioceramic scaffolds have been widely used as templates for cell adhesion, proliferation, and differentiation thus promoting tissue regeneration. However, their brittleness, constrains application in tissue engineering. The most common bioactive materials that are used in bone and dental tissue engineering are zirconia (Zr), hydroxyapatite (HAp) and calcium phosphates ceramics (CaP). Zirconium possess suitable mechanical properties, but its inertness is a big challenge to develop a scaffold with excellent bioactive characteristics. On the other hand, polymers can be easily fabricated into complex shapes and porous structures. Thus, a combination of bioceramics with biodegradable polymers is employed to achieve better biological features. In this study we have employed femtosecond laser texturing for surface processing of zirconia ceramics and its blends with biopolymers. Altering morphology and roughness of Zirconium based ceramics is an effective way of improving its adhesive properties. In this study, femtosecond Ti: sapphire laser was selected to provide treatment of chitosan/hydroxyapatite thin films reinforced by nano ZrO2 (CH/HAp/ZrO2) at different ratios and Alumina Toughened Zirconia (ATZ) ceramics. SEM analysis of produced microstructures demonstrated creation of surface modification in the form of stripes, evenly distributed with well-defined boundaries resulting in increased effective surface area of the sample. EDX analysis revealed that the typical elements for CH/ HAp/ZrO2 and ATZ were preserved after laser treatment. The ability of the patterns to enhance adhesion and orientation of MC3T3 osteoblasts and adipose derived (ADSC) stem cells, as measured by fluorescence microscopy imaging, due to changes in surface morphology, were assessed. The obtained results suggest that femtosecond laser treatment offers a fast and promising approach to introduce controlled topography at the micrometric scale by creating a path for optimization of ceramic scaffold surface properties.

Resume : Montmorillonite (MMT) is lamellar clay material, part of smectite group of phyllosilicate mineral species. Montmorillonite has an interesting lamellar structure allowing guest absorption between the lamellas. The absorption can take place at the surface, or interlayer. The aim of this work is to produce lamellar montmorillonite (MMT) thin films as active surfaces for the absorption of organic and inorganic pollutants from residual waters. Pulsed laser deposition (PLD) and matrix assisted pulsed laser evaporation MAPLE are the techniques employed for the deposition of montmorillonite thin films. The deposition parameters, especially the laser wavelength, substrate temperature and background deposition pressure, play an important role in the composition and morphology of the films. The chemical composition, crystalline structure, surface morphology of the MMT thin films were thoroughly investigated and crystalline films with good adhesion to the substrate and controllable thickness were obtained. The possible applications of the as deposited films, especially in electrochemical sensors, are presented and discussed.

Resume : Composites consisting of metallic nanoparticles (NPs) embedded in dielectric matrices have attracted considerable interest due to their possible applications in nonlinear optical devices such as optical computing, switching, real time holography, and phase conjugators. These composites may present large nonlinear optical response due to electronic transitions in the NPs. In this work, ordered arrays of plasmonic gold nanoparticles embedded in fused silica plates were produced by 2 MeV Au ion implantation at normal incidence through a lithographic mask, followed by a post-implantation annealing treatment. As lithographic masks we used monolayers of silica microspheres with three different sizes (590, 650 and 900 nm in diameter) onto quartz substrates and the implantation fluences ranged from 1E16 to 1E17 ions/cm2. A strong optical absorption band associated with the Localized Surface Plasmon Resonance (LSPR) was observed at 520 nm. The third-order nonlinear optical response of the samples was characterized by using the Z-Scan technique with a wavelength of 532 nm and a pulse duration of 26 ps.

Resume : We demonstrate a possibility of a controlled laser writing of well-organized arrays of silver nanoparticles (AgNPs) with a size of 10 nm in initially mesoporous SiO2 films (180 nm thickness). The films were fabricated by the sol-gel method and pre-doped with silver nitrate. The obtained metasurfaces consist of the ordered 2D structures with a period of Λ = 410 and 520 nm and a track width of ~150 μm. These structures were formed by a progressive laser scanning. Picosecond laser pulses (λ=355nm, τ=30ps, f=10Hz) were used. The beam profile was linearly polarized and transformed into a two-beam interference pattern. To obtain an interference pattern, a confocal optical system was used, where the function of a diffraction spreader was performed by a phase grating made on fused quartz using the laser-induced black-body heating method. The mechanisms of laser recording of the obtained structures are then examined. The processes, such as photochemical synthesis of AgNPs and formation of a film nanorelief, are shown to be involved. The optical properties of the plasmonic 2D metasurface were also investigated at different angles and directions of the incidence of natural light, as well as for both TE and TM polarized light. As a result, we observed and explained an increase in the plasmon resonance at λ = 486 and 520 nm and a change in the diffuse reflection depending on the direction of the incident light with respect to the periodic structure. These results are promising for photonics applications.

Resume : The non-lead piezoelectric materials with strong piezoelectric response are regarded as key materials for replacing Pb-based materials in functional devices. Lead-free (Ba1−xCax)(ZryTi1−y)O3 is a perovskite material which exhibits values of the piezoelectric coefficients similar or even superior to the hard PZT materials. Doping with Ca and Zr allows flexibility in the stoichiometry to be obtained, the tunability of the functional properties by varying the level or doping ratio being the main advantage. By incorporating the piezoelectric ceramic material BCTZ into the PVDF matrix, high-piezoelectric and flexible heterostructures can be obtained, which will allow incorporation of the pressure sensor device in various applications. Thin film of BCZT45 and PVDF/BCZT45 were deposited on Pt-kapton substrate by MAPLE technique. Thin films of BCZT45 on different substrates have been deposited by PLD for comparison purposes. Piezoforce microscopy measurements on PVDF/BCZT/Pt/Kapton films revealed high values of the d33 effective piezoelectric coefficient and good switching behavior, as shown by phase variation under electric field. The out-of-plane PFM response shows strong domain contrast, indicating that the material is polar with a polarization vector oriented mainly along the c-axis. The good piezoelectric properties of the PVDF/BCZT films indicate the possibility to employ these structures as piezoactive elements.

Resume : Organic photovoltaic cells (OPV) present big interest due to their specific properties as mechanical flexibility, light weight, ease to process and low cost fabrication. The organic semiconductors are very good absorbers (absorption coefficients>105cm-1) and their photogeneration mechanism is an excitonic one. Taking into account that the diffusion length of exciton in organic materials is smaller than 80 nm, the bulk heterojunction configuration resulting from the blend of a Donor and an Acceptor molecules, such as P3HT:PCBM, seems to be a promising way to obtain performant OPVs. Unfortunately, the P3HT:PCBM polymeric blend is unstable in light interaction and exhibits a different behavior when mixed and deposited layer-by-layer, so solvents should be carefully chosen. For this reason we use for deposition of polymers two techniques: MAPLE (Matrix Assisted Pulsed Laser Evaporation) and spin-coating. First technique allows the polymer to be deposited regardless of the chosen solvent. The proposed configuration of our structures is IZO-5nm/Ti/SnO2 nanoparticles/PEDOT:PSS/P3HT-PCBM-Si:PCPDTBT/ZnO/Ag, in which a low band gap polymer, e.g. poly[2,1,3-benzothiadiazole-4,7-diyl[(4,40-bis(2ethylhexyl)dithieno[3,2-b:20,30-d]silole)-2,6-diylalt-(2,1,3-benzothiadiazole)-4,7-diyl], (Si-PCPDTBT), is added to increase the number of photons harvested from solar spectrum and also to improve the stability. Acknowledgements: The study was supported by project 40PCCDI/2018, funded by UEFISCDI.

Resume : The composite Ag/ZnO nanostructures are fabricated by combining the laser and ion implantation techniques. The ZnO thin films are grown by pulsed laser deposition (PLD). The Ag+-ion implantation technique is used for surface embedding the silver nanoparticles in the ZnO thin film matrix. The implanted samples are also laser annealed by Nd:YAG laser at 355 nm and 532 nm at different laser fluences and number of laser pulses. The proposed structures are examined as SERS substrates, and the results are considered with respect to their microstructure, composition and optical properties. The heterostructures of optical transparent semiconductors and noble metal nanoparticles attract grate attention, as a higher SERS effect could be achieved due to contributions from both the electromagnetic enhancement, excited by the LSPR (localized surface plasmon resonance) of noble metal nanostrustures and the semiconductor supporting chemical enhancement, caused by the charge transfer between the noble metal and semiconductor. The effect of surface topography on SERS response is investigated. The properties of implanted nanostructures before and after the laser annealing are studied by SEM (scanning electron microscopy), AFM (atomic force microscopy), XPS (X-ray photoelectron spectroscopy) and UV-VIS spectroscopy. This paper provides a relation between the nanoscopic features of the prepared Ag/ZnO nanocomposites and their effectiveness as SERS active substrates. Acknowledgements: This work is financially supported by the Bulgarian National Science Fund under the Russian-Bulgarian bilateral project DNTS/Russia 02/3 – 14.06.2018 “Combined laser and ion implantation techniques for nanostructuring of Ag/ZnO composites for SERS applications”; in Russia - RFBR grant No. 18-58-18001.

Resume : The incorporation of trivalent rare-earth ions in a glass matrix allows developing active optical devices such as laser, IR-to-visible up-converters, optical amplifiers, phosphors, thermometry, etc. Among the large variety of matrix composition studied, the most noteworthy are calcium silicate, calcium alumino-silicate and magnesium alumino-silicate glasses due to their excellent physical properties, which beside their ability to incorporate high concentration of rare-earth active ions, have led to various applications in solid state lasers, optical waveguides, luminescence probes, and even in medicine as in vivo radiation delivery vehicles for cancer treatment of internal organs. In this work, the energy transfer processes between Er3+ and Yb3+ ions in Ca3Al2Si3O12 and Mg3Al2Si3O12 glasses have been characterized by using several samples containing a fixed Er3+ concentration (0.5 mol%) and variable Yb3+ concentration (0.1, 0.5, 1 and 2 mol%). A relationship between the energy transfer parameters was established under selective Er3+ excitation at 800 nm (4I15/2 -> 4I11/2 absorption band) by using a Ti:Sapphire laser. Additionally, the dynamics of the resonant infrared levels (4I13/2 (Er3+):2F5/2 (Yb3+)) together with the dominant erbium emitting manifolds (2H11/2:4S3/2 and 4I13/2) have been investigated under pulsed excitation at 532 nm (4I15/2 -> 2H11/2 absorption band) using the second harmonic of a pulsed Nd:YAG laser. The use of both Er3+-pumping schemes, CW and pulse excitation, has allowed the full quantification of the macroscopic transfer and back transfer coefficients Finally, these macroscopic parameters have been used to establish a rate-equation model that allows to describe the dynamics of Er3+/Yb3+ co-doped alumino-silicate glasses.

Resume : In this work the fabrication of diffraction gratings by femtosecond laser inscription in poly-hydroxyethyl-methacrylate and silicone hydrogel polymers used as soft contact lenses is reported. Linear diffraction gratings were inscribed by focusing the laser radiation 100 µm underneath the surface of the samples. As laser sources low- and high-repetition-rate Ti:sapphire laser with a pulsewidth of 120 fs working at 1 kHz and 80 MHz were used. Periodic patterns were produced by the variation of the pulse energy as well as the distance between tracks and scanning speed. Compositional and structural modifications on the materials were studied by means of micro-Raman spectroscopy. Far-field diffraction pattern was characterized under illumination of a continuous-wave He-Ne laser at 632.8 nm. First- and second-order efficiency as well as total efficiency were assessed. Finally, refractive index changes induced in the processed areas were evaluated to determine the processing conditions at which the modification was the optimal.

Resume : Sodium doped CuInS2 materials (CIS:Na) was synthesized by a solid-state reaction using ‎earth-abundant copper, indium and sulfur elements. Sodium was used as dopant element (0.1, ‎‎1 and 3 wt %). The thermal evaporation technique was used to prepare CIS:Na thin films. ‎Then, the films were irradiated at room temperature in ambient air using a KrF excimer laser ‎with ‎a wavelength 248 nm. The irradiation was performed under laser energy density of 50 ‎mJ/cm2. ‎The Raman and XRD characterization revealed the amorphous character of the films ‎due to the porous behavior shown by the confocal microscopy. A strong change of the surface ‎morphology of the films was observed and it depends on the Na weight percent doping. ‎Optical constant were calculated from transmittance T and reflectance R spectra using a ‎special MATLAB program. CIS:Na thin films exhibit high absorption coefficients (104 - 2×105 ‎cm-1) in the visible range and the higher values were obtained for 3 wt % and it has the highest ‎Surface Energy Loss Function (SELF) values. The direct band gap (Eg dir) was in the range ‎‎1.61-2.06 eV. The refractive indices show an anomalous behavior in the optical gap region. ‎The CIS:Na 3 wt % sample exhibits a lower refractive index. All the dispersion curves of ‎refractive index were analyzed using Wemple-DiDomenico model. The real dielectric constant ‎and relaxation time were calculated.‎

Resume : Ba0.6Sr0.4TiO3 (BST) ferroelectric thick films were grown on single-crystal MgO substrates by using pulsed laser deposition (PLD) method. A KrF excimer laser, emitting at 248 nm wavelength with a fluence of 2 J/cm2 and repetition rate of 5 Hz, has been used. Structural, morphological, optical, and terahertz characterization of the BST films were performed by X-ray Diffraction, Scanning Electron Microscopy, Atomic Force Microscopy, Spectroscopic Ellipsometry (SE), and Terahertz Time-Domain Spectroscopy (THz-TDS). As a result of a parametric study, single-phase samples with appropriate microstructure were achieved. SE was employed to extract the thickness and optical properties by using a 3-layer optical model (substrate / thin film / roughness). The inferred refractive index @630nm is approximately 2.07, while the optical interference is visible until 3.3 eV. The THz-TDS measurements in transmission set-up were carried out one after the other on substrates before and after the BST film deposition. The standard THz-TDS analysis of double-layer samples proved difficult to complete in the cases in which a thin or thick film is deposited on a much thicker substrate of known dielectric properties. The effect of the film on the propagation of the electromagnetic wave is usually weak and often obfuscated by spurious effects, with the result of inconsistent values for the dielectric quantities. Nevertheless, we have been able to extract the complex dielectric permittivity in THz domain for BST samples with thicknesses higher than 2 micrometers, by developing a specific procedure of data analysis. Acknowledgments: This work was supported by a grant of Ministry of Research and Innovation, CNCS - UEFISCDI, project number PN-III-P1-1.1-TE-2016-1711, within PNCDI III”.

Resume : Microwave antenna developed for space industry must be able to operate in harsh environments where the radiation dose and temperature gradients are high. In order to protect these electronic devices, various coating techniques and materials were developed. Pulsed laser deposition (PLD) coatings allow the deposition of different materials on the microwave antenna for shielding it from the outer space harsh conditions. In this work we report the obtaining of multilayer structures for electronic devices protection in space environments. For this purpose, the heterostructures of Al2O3/Y:ZrO2 were deposited by PLD on microstrip coplanar antenna. The frequency response of microwave antenna was measured before and after deposition of heterostructure. The crystalline and morphologic properties of the coatings were studied by X-ray diffraction and atomic force microscopy (AFM) techniques. The optical properties and the thicknesses of layers were investigated by spectroscopic ellipsometry (SE). The dependence of optical constant with temperature was determined by SE in the 23-3000 C range of temperature. Acknowledgements: This work was supported by a grant of the Ministry of National Education and Scientific Research, RDI Programe for Space Technology and Avanced Research - STAR, project number 168/20.07.2017

Resume : Film is a widely used material in all kinds of fields. In weapon research field, it is used as ablation layer of the laser slapper detonator which has attracted attention due to high anti-electromagnetic interference, high-resolution timestamp and high safety. The energy transformation of the laser slapper detonator is “laser energy-heat energy-flyer kinetic energy”. In the process, the ablation layer play an important role in absorbing laser energy and transforming laser energy to heat energy. Several kinds of materials are used as ablation layer, among which reactive multilayers are new and has the potential to improve plasma performance induced by pulsed laser. In this study, Al/NI based reactive multilayers with two different modulation periods were integrated into ablation layer using magnetron sputtering technology. The structure and chemical composition of Al/Ni multilayers were confirmed by transmission electron microscopy. The effects of the Al/Ni multilayers on the plasma properties induced by pulsed laser were systematically investigated in terms of the electron temperature and density using laser-induced breakdown spectroscopy. Measurements of the plasma expansion velocity were performed using ICCD systems. It is found that the electron temperature and density has a relative to modulation period of Al/Ni multilayers, which is much higher than Al or Ni layer alone. The laser induced plasma expansion velocity is consistent with that found using electron temperature. Thus the conclusion that the ablation layer of Al/Ni reactive multilayers exhibited a high level of plasma and promoted laser induced plasma energy efficiency.

Resume : Boron and potassium nitrate composites (B/KNO3) is one of the most widely used pyrotechnics for laser ignition applications. As main components of B/KNO3, boron and potassium nitrate serve as fuel and oxidizer, respectively, with trace additives mostly function as binder. Compared with other fuels, boron owns the highest volumetric energy density. However, the oxide layer (B2O3) on its surface will hinders its combustion and ignition, which have limited the application of boron in practical utilizations. Therefore, enhancing the combustion and ignition performance of B/KNO3 powders is valuable and significant. In this study. Carbon nano-tube aerogel loaded with boron and potassium nitrate (CABPN) energetic composite was prepared by ice template method. SEM images proved the micro structure of CABPN to be porous and nearly laminar. The Brunauer–Emmett–Teller (BET) specific areas of CABPN and BPN were 57.9 m2/g and 28.8 m2/g, respectively, indicating that the porous structure doubled the surface area, which is helpful for the reaction of combustion. Thermal-decomposition behavior of CABPN was studied by TG/DSC, and two consecutive exothermic peaks at around 410 ℃ and 460 ℃ were observed. Finally, a series laser ignition experiments were conducted and it was found that the boron content could regulate the laser ignition threshold of CABPN. Additionally, by loading Carbon nano-tube aerogel into B/KNO3, the ignition performance can be significantly enhanced.

Resume : Iridium thin films with a thickness varied between 20 and 100 nm are grown on MgO substrates with various crystallographic orientations by using by two different techniques, i.e. direct-current magnetron sputtering (DC-MS) and pulsed laser deposition (PLD). First, we present and discuss results on high resolution X-ray diffraction (XRD) and atomic force microscopy (AFM). Both types of analysis reveal that substrate temperature / annealing of up to 1200°C has significant effects on their structure and morphology, yet no effects are observed upon the electrical resistivity (~12 µΩ⋅cm) of the films, and no traces of iridium oxide are identified. High resolution transmission electron microscopy (HR-TEM) of the substrate-thin film interface show that iridium exhibits epitaxial growth with no diffusion effects. This aspect is challenging in electrode applications due to the difficulty in controlling phenomena occurring at the interfaces. Finally, we compare the advantages and disadvantages of each deposition technique, and present results with respect to their use as highly thermally resistant electrodes in tunable micro-capacitive components.

Resume : For the application related to tissue engineering, implants, the controlled interfacial properties of materials and modulated behaviours of cells and biomolecules on their surface are important requirements. Roughness, chemistry and mechanics of biomaterials are all sensed by cells. Organization of the environment at the nano- and the microscale, as well as chemical signals, triggers specific responses with further impact on cell fate. Producing smart bio-interfaces with targeted functionalities represents the key point in effective use of hierarchically topographical and chemical bioplatforms. In this work, we present laser-based approaches (e.g. Matrix-Assisted Pulsed Laser Evaporation (MAPLE) and laser texturing used for the design of bio-interfaces aimed at controlling cell behaviour in vitro. Keywords: Bio-interfaces, laser processing, topography, protein-based coatings, stem cells

Resume : Nanolasers play an important role in transmitting messages with high speed, low energy loss and without interruption to each other when propagating in the same path. In this work, we report a semiconductor-insulator-metal (SIM) structure of ultraviolet nanolaser based on surface plasmon polariton (SPP) breaking through the diffraction limit. A gain medium of the single high crystallinity zinc oxide nanowire fabricating by chemical vapor deposition is crucial for laser operating at room temperature. The two-dimensional material, hexagonal boron nitride (hBN), which acts as the plasmonic nanocavity is prepared by mechanical exfoliation and is placed between a nanowire and the single crystal aluminum film. The SIM structure was found to exhibit higher optical intensity than the single nanowire without SPP effect. The high crystallinity of the hBN and the aluminum film are both the key factors to decrease the plasmonic losses when the light propagating at the interface between the dielectric layer and the metal substrate.

Resume : Nonlinear optical materials with functions of generating second harmonic generation (SHG) or/and two photon photoluminescence (TPPL) have attracted great interest because of their applications in extending coherent light frequencies from the given lasers[1], biological imaging and photodynamic therapy[2]. Here we report on two metal–organic frameworks, namely, Bis{4-[2-(4-pyridyl)ethenyl]benzoato}-zinc(II) and -copper(II) with 7-fold diamondoid network structures, which are capable of generating SHG, and TPPL depending on an excitation wavelength in the range from 680 nm to 1400 nm. The second order optical nonlinearity, |deff|, of the single crystals has been determined to be 20.05 pm/V (zinc(II) at 900 nm) and 114pm/V (copper(II) at 1000 nm). The two photon absorption cross-section, σ2, is measured to be ~17.86 GM at 680nm for zinc(II). 1. Liu M, Quah H S, Wen S, et al. J. Mater. Chem., 2017, 5(11): 2936-2941. 2. Quah H S, Chen W, Schreyer M K, et al. Nat. Commun., 2015, 6: 7954.

Resume : Trigonal rare-earth borates RM3(BO3)4 (where R = Y, Eu, La-Lu; M = Al, Ga, Fe, Cr) belong to a new class of multiferroics, in which magnetic, electrical, and order parameters coexist. Rare-earth aluminum borates and gallium borates combine good luminescent and pronounced nonlinear optical properties. They belong to the new generation of materials for lasers. Magnetic properties of the YGa3(BO3)4: x% Cr samples (where x = 0.1, 0.2) were studied using electron paramagnetic resonance (EPR) and X-ray diffraction analysis. Received a new data about the state of doping ions of Cr3 in a single crystal of YGa3(BO3)4 have been obtained when studying the spectra of electron paramagnetic resonance. It is demonstrated that the ions of Cr3 substitute for the trivalent gallium ions. The spectra of three magnetically equivalent ions rotated through 120 degrees are registered. The obtained parameters of spin Hamiltonian of the Cr3 ions in the YGa3(BO3)4 single crystal have been analyzed. The absorption lines associated with the transitions between the levels characterized by unlike quantum numbers differ in width. At the frequency of 9,3 GHz (X band), the width of transition ( -1/2) is 83 Gs, the width of the interdoublet transition is 270 Gs. At the frequency of 33.458 GHz (Q band), the width of transition( -1/2) is 100 Gs, the width of the interdoublet transition is 360 Gs. The width of an absorption line is determined by a number of factors: spin-spin interaction between the chromium ions, electron-nuclear interaction of the Cr3 ions with the nuclear moments of the neighbors, inhomogeneity of the crystal field. Spin-spin interaction between the chromium ions is insignificant because of small concentration of the doping ions. Additionally, the crystallographic structures of the Cr-doped YGa3(BO3)4 in ambient conditions and structure temperature stability in high temperature range were established by in-situ X-ray diffraction. High-temperature XRD measurements demonstrate structure stability of Cr-doped borates in the high temperature range from 300 to 1073 K. Also we have found the unit cell thermal expansion anisotropy for Ga-based borates is 1.26 times higher than for Al-based one.

Resume : Laser-induced graphene (LIG) is a porous graphene-like material created on commercial polyimide foil with a strong IR laser. By varying the parameters - i.e. laser duty cycle, scanning speed and laser pulse density – one obtains LIG of different morphologies and likely different electrochemical properties. LIG has proven interesting as electrode material for bioanalysis. However, to make reliable electrochemical sensors, a thorough understanding of electrochemical properties as a result of varying LIG process parameters is direly needed. Electrical sheet resistance and peak-to-peak separation in CVs were hence studied and parameters varied systematically on a 30 W CO2 laser system. As the duty cycle is proportional and the scanning speed inversely proportional to the resulting energy density (fluence), it was found that low duty cycles at high speed have no effect while high duty cycles at low speed result in disintegration. However, a broad array of workable settings in between result in highly reproducible and durable electrodes. Furthermore, low pulse density of 500 PPI (pulses per inch) caused anisotropic electrical sheet resistance which changed to isotropic at 2000 PPI. Higher PPI resulted in higher conductivity and lower peak-to-peak separation values with the lowest sheet resistance of approx. 15 Ohm/sq, which is similar to best values reported for screen printed carbon. These electrodes enable fast electron transfer kinetics for a broad range of bioanalytically relevant molecules such as dopamine and acetaminophen. The simple and fast fabrication using low-cost equipment makes these LIG-electrodes a powerful electrode material in point-of-care sensors where otherwise screen-printed electrodes are used.

Resume : Electrospun polyimide (PI) nanofibers are a potential carbon precursor for generating high performance carbon nanofiber (CNF) electrodes integrated in miniaturized electrochemical sensors where the 3D-structure offers benefits to the system. Using a laser to carbonize electrospun nanofibers is attractive as CNF electrodes can be in situ created with favorable designs and mass production capability. However, unlike lasing PI film their non-uniform and delicate 3D structure can lead to the difficulty in maintaining the nanofibrous features after lasing. In the present work, we aim to unravel crucial factors that facilitate the laser-induced CNFs (LCNFs) with intact morphology and desirable electroanalytical performance. Here, PI nanofibers contained iron and were spun onto an ITO electrode prior to writing the LCNF electrodes by CO2 laser. Control over electrode morphology and electroanalytical performance via electrospinning conditions, iron content, and lasing strategy were thoroughly investigated. Moreover, the effect of these findings on design constraints for electrode fabrication was studied. The as-prepared LCNF electrodes exhibit favorable morphologies and remarkable electron transfer kinetic for both outer- and inner-sphere redox species that are highly comparable to thermal treated CNFs. This work will strengthen the application of 3D-LCNFs in point-of-care diagnostic devices where high sensitivity, short response time, high reproducibility, and low cost are required.

Resume : Nano-composites materials based on reduced Graphene Oxide (rGO) and metal oxide semiconductors (MOS) have been attracting the attention of the scientific community due to its great variety of physical properties and potential applications as solar cell materials, supercapacitors, photocatalytic materials, and chemical sensors. Different synthesis procedures have been employed in order to produce materials with tunable properties and microstructural homogeneity. Within this context, several laser-based methods have been pointed out as a greener and more efficient manner to reduce graphene oxide. Here, we report the reduction of a graphene oxide solution when a nanosecond Nd:YAG pulsed laser is directly focused in the solution under agitation. The rGO solution was then deposited in a substrate with Pt interdigitated electrodes and ZnO nanoparticles were deposited over the rGO layer via RF magnetron sputtering. Our results demonstrate a greener and cheaper path to produce thin films of this nanocomposite based on rGO and ZnO. Also, the gas-sensing performance of this nanocomposite was evaluated regarding ozone detection.

Resume : We have developed successfully the synchrotron based time-resolved X-ray excited optical luminescence (TR-XEOL) and X-ray excited optical luminescence (XEOL) at the TPS 23A X-ray Nanoprobe (XNP) beamline at Taiwan Photon Source (TPS). Not only the TR-XEOL and XEOL, the multifunctional XNP with hard X-ray energy range (4-15 keV) but also includes other featured methods, such as X-ray absorption spectroscopy (XAS), X-ray fluorescence (XRF), cathodoluminescence (CL), X-ray diffraction (XRD) and Bragg ptychography. Based the temporal and high spatial resolution, so that the XNP in a single probe can simultaneously obtain the compositional, optical and structural information. Advanced by energy-tunable hard X-rays, the XNP at TPS provides 40nm spatially resolving means for investigating the optical properties of specific elements in the novel luminescent materials, such as 2D materials, trihalide perovskite and wide bandgap semiconductors. An ultrafast streak camera is synchronized with the pulse structure of the synchrotron ring to investigate the dynamics of luminescence of the materials with temporal resolution 30 ps ~ 1.72 μs in the single bunch mode. In parallel to the construction of the XNP endstation, demonstrative XEOL experiments were studied by unfocused X-ray beam at Taiwan Light Source (TLS). Temperature dependent XEOL and polarization-dependent XEOL were used to study the peculiar near-band-edge (NBE) emission of c-plane and a-plane ZnO wafers, respectively. The detail design of the TR-XEOL and XEOL at XNP, and the demonstrative experimental results of trihalide perovskite CH3NH3PbBr3, 2D materials and a single ZnO microrod will be reported.

Resume : Magnesium/Magnesium alloys layers stand for a hot topic in recent research devoted to the development of biodegradable metallic implants which are safely dissolved, in time, with a controlled rate. This is due to an accumulation of positive circumstance such as: degradability, excellent biocompatibility, low density and relatively low costs. Once in the body, Mg is progressively resorbed, and no secondary surgery is required to remove implant remains after healing. Mg/Mg alloys are prone to rapid corrosion in physiological environment resulting in the synthesis of magnesium oxide/hydroxide layers and release of hydrogen gas. Bioactive glasses are recognized as “intelligent” materials, which convert inside human body to hydroxyl-carbonated apatite layers, very similar to the inorganic part of the bone. We report herewith on deposition of Bioactive Glass films by PLD onto biodegradable metallic (Mg/Mg alloy) substrates. The deposition was conducted with a KrF* excimer laser source. The coatings well reproduce the initial composition in targets, as demonstrated by complementary physical-chemical analyses via: IR spectroscopy, SEM, EDS and XPS. In vitro tests after immersion in physiological fluids were conducted to evaluate the corrosion resistance of uncovered vs covered biodegradable metallic implants. The results support the idea of fabrication of efficient shield barriers against corrosion on Mg/Mg alloys for use in a new generation of biodegradable metallic implants.

Resume : It is well known that the use of ultrashort (fs) pulsed lasers can induce the generation of (quasi-) periodic nanostructures (LIPSS, ripples) on the surface of metallic samples[1]. Such nanostructures have also been observed in sample’s surfaces that have been irradiated with UV lasers with a pulse duration of 300 ps. In this work, we compare the characteristics of these nanostructures on 25-micrometer thick Nb sheets induced by different pulsed lasers, and we analyze the influence of the different parameter conditions that were selected for the laser processing. In addition to conventional continuous or burst mode processing configurations, a meandering laser line scanning has also been investigated. This configuration allows the processing of large areas with a more uniform distribution of nanostructures at the surface. The influence of these nanostructures on the superconducting properties of Nb has also been investigated. With this aim, magnetic hysteresis loops have been measured at different temperatures to analyze how these laser treatments can affect the flux pinning behavior and, in consequence, their critical current values. This research is partially supported by projects ENE2017-83669-C4-1-R (Agencia Estatal de Investigación & Programa FEDER), Gobierno de Aragón (Research group T54_17R). References [1] J. Bonse, S. Höhm, S. V. Kirner, A. Rosenfeld, and J. Krüger, “Laser-induced periodic surface structures – a scientific evergreen,” IEEE J. Sel. Top. Quantum Electron., vol. 23, no. 3, p. 9000615, 2017.

Resume : Conventional optical components like lenses undergo dispersion leading to chromatic aberrations resulting in poor imaging. The most popular technique in practice to correct it is to use series of cascading lenses, which results in bulky devices. Metasurfaces, an array of nanoantennas of sub-wavelength thickness can be employed to achieve this as they are compact and effective. Through our work, we demonstrate dispersion compensation using metasurface in a simpler case of a prism and show the design of a dispersion compensator metasurface for a plano-convex lens with ray tracing results. Metasurfaces are known to cause abrupt phase and polarization shift in the outgoing light. For a desired functionality, one can fabricate the metasurface with corresponding phase profile using nanoantennas. For our study, we use constant phase gradient metasurface made of TiO2 nanopillars (dielectric material) on SiO2 substrate. This can be obtained by placing 0 to 2π phase elements in the increasing order along one particular direction and periodically repeating the same arrangement. One can see that this mimics the conventional blazed gratings in design and also functionality. All in all, the motivation of this work is to combine refractive and diffractive components to mitigate dispersion as both have opposite sense of dispersion. The generalized laws of refraction at the metasurface-air interface are used for the calculations. The phase gradient is a parameter to design the metasurface given the angle of transmission, incidence and the wavelength of incident light. The technique of Fourier plane imaging and spectroscopy is utilized to study minute angles of dispersion in the prism’s case. The results obtained are for broadband visible region of 550-700 nm.

Resume : Ultra-fast laser processes are among the key technologies for the manufacturing of flexible organic electronic devices. These are alternative techniques to photolithographic methods and they have the advantage for im-plementation to roll-to-roll (R2R) manufacturing processes for the low-cost and large area production of numer-ous flexible Organic Electronic devices, such as Organic Photovoltaics (OPVs). The optimization of the laser pro-cess parameters for the selective removal of the different nanomaterials for OPVs (transparent electrodes, pho-toactive blends, buffer layers, cathode electrode) with high precision and without affecting the underlying nanolayers is of paramount importance. In this work, we present a robust process for the precise laser patterning (P1, P2 and P3) of OPV nanolayers in inverted device structure onto flexible polymer substrates using ps laser system. These include state-of-the-art inorganic nanomaterials (e.g. Indium Tin Oxide, Ag Nws, IMI, AZO, WOx), as well as transparent polymers (e.g. PEDOT:PSS) and photoactive polymers as electron donors (e.g. polythiophenes) and acceptors (e.g. fullerene derivatives, PCBM, etc.) or state of the art ready to use photoactive inks (e.g. PI-5, OETD1A1) in single and multilayer structures. Also, we investigate the effect of the laser process parameters (e.g. fluence, speed) on the patterning shape and quality, in order to obtain high quality patterned shapes with minimum amount of debris and sharp interfaces. Finally, we present the implementation of the ultra-fast laser patterning process in the manufacturing of OPV modules and we demonstrate the potentiality of low cost ultra-fast laser processes to be used as a standard pro-cess step for r2r manufacturing processes for Organic and Printed Electronics devices.

Resume : Single-molecule electrochemical sensors are currently used in DNA and protein sequencing and for analysis of protein-protein interaction. Nanopore-based sensors would potentially benefit from higher spatial and temporal resolution when achieving more accurate sequencing. We will report the initial results of the project that aims to combine tunnelling nanojunctions based on device reported by Nadappuram1 with ultrafast spectroscopy approaches. Ultrafast spectroscopy developed to reveal electronic dynamic at a picosecond level can potentially increase the time resolution of electrochemical sensors. A sequence of ultrafast optical pulses will illuminate the devices. First, ‘pump’ pulse can bring molecular to excited states, and then ‘push’ pulse can modify the excited state in an extremely short time and give rise to changes of tunnelling current. We believe the combination of ultrafast spectroscopy with nanoscale tunnelling current detection will lead to a new single-molecule characterisation method with high spatial and temporal resolution. 1 B. P. Nadappuram, P. Cadinu, A. Barik, A. J. Ainscough, M. J. Devine, M. Kang, J. Gonzalez-Garcia, J. T. Kittler, K. R. Willison, R. Vilar, P. Actis, B. Wojciak-Stothard, S.-H. Oh, A. P. Ivanov and J. B. Edel, Nat. Nanotechnol., , DOI:10.1038/s41565-018-0315-8.

Resume : A promising method for producing surface patterns in the micro- and sub-microscale is direct laser interference lithography (DLIL). In this technique two or more laser beams interfere each other and generate a periodic pattern on the surface. Especially important feature, when it comes to functionalization of implantable elements with original roughness, such as passive middle ear implants, is possibility of local modification of the surface after two commonly used surface treatments ? shot peening and acid etching. Therefore, in this study DLIL was used to produce periodic grooved and island pattern on titanium surfaces after shot peening and acid etching. In this study Nd:YAG laser operating 1064 nm wavelength, with the pulse duration 10 ns, energy density 400 mJ cm-2 and 7 laser pulses was applied. In order to characterized biological response the bioactivity and cell adhesion tests were performed. The bioactivity of the surface was investigated using SBF immersion tests, in different soaking times (0.5 h to 168 h). The deposited apatite layers on titanium surface were deeply evaluated using SEM, XPS, EDS and FTIR. For the cell (MG 63) adhesion tests similar short incubation times were applied. The adhered cells were analyzed using confocal microscopy and SEM observations. The obtained results of biological response were analyzed by correlating with the results of the physicochemical properties of the modified titanium surfaces. Our results showed that DLIL modified surfaces exhibit better biological activity compared to shot peened and acid etched one. Presented methodology can be used as an effective tool for manufacturing controlled surface structures improving the bone?implants interactions. This research was financially supported by The National Science Centre Poland under Grant no. 2016/23/N/ST8/02044.

Resume : Metal matrix nanocomposites are materials with enhanced mechanical resistance, tensile strength, wear resistance or thermal conductivity as compared to bare metals or alloys, with the added benefit of reduced weight. They could be the materials of the future and replace at large scale the metallic alloys of today in automotive, military or aeronautic fields. However, these are materials that allow for limited machining. In case of laser processing of nanocomposites, there are difficulties caused by melting that can induce dispersed phase segregation and thus possible mechanical properties downgrade. Moreover intense ablation during laser irradiation and generation of intense spatter are also severe drawbacks in machining. We tried to overcome this last aspect by tuning the laser parameters under high speed monitoring during processing of an aluminium alloy reinforced with alumina nanoparticles. Imaging via an optical microscope allowed for recording at millimeter level, providing new information on liquid-metal dynamics during laser irradiation as well as plausible explanations for spatter occurrence and pores formation. Droplets trajectory and speed were assessed by computerized image analysis. It was found that the velocity of visible droplets expulsed laterally or at the end of the plume emission from the metal surface was not dependent on the plasma plume speed. It was observed that the number of droplets on surface was 1.5–3 times higher when the laser beam was focused in depth as compared to focused beams, even though the populations average diameter were comparable. Three methods were tested for removing droplets in situ, during plume expansion: an argon gas jet crossing the plasma plume, a fused silica plate collector transparent to the laser wavelength placed parallel to the irradiated surface and a mask placed onto the aluminium composite surface.

Resume : Cholesteric liquid crystal (CLC) phase exhibits a helical structure with a twist axis perpendicular to the local molecular director. When light propagates in the Bragg regime through a CLC slab with a planar texture, the medium gives rise to Bragg reflection. As shown previously, CLCs are involved in ultrafast optical applications (e.g., slow light and temporal laser pulse shaping). In particular, they can be used to compress laser pulses due to their 1-D photonic nature, and a combination of high birefringence and nonlinearity. Here we propose to use a femtosecond source and an advanced statistical experimental approach for detailed characterization of the ultrafast temporal changes undergone when a pulse propagates through the bandgap edges of CLC. Home-made CLC samples with a thickness ranging from 14 to 56 µm present a variable spectral bandgap so that the laser spectrum overlaps partly with the blue or red edge Fourier-transform spectral interferometry analysis then enables to recover the changes of spectral intensity and phase of pulses transmitted through. Furthermore, a cluster analysis technic of collected from 1000 to 2000 data points allowed us to estimate the microscopic homogeneity of the samples. As a result, we estimate the temporal changes undergone by the laser pulse, depending on the relative position of the laser spectrum and bandgap edges.

Resume : Pulsed laser annealing is one of the promising low thermal budget approaches to overcome process limitations and develop alternative schemes to achieve better device performance and enable 3D architectures. Its applications range from the Front End Of Line (doping, contacts, strain engineering) to Back End Of Line (Cu grain engineering) in logic and memory. One key enabler for integrating this disruptive technology in the coming highly challenging technology nodes is an accurate time-resolved modeling of laser matter interaction, thermal diffusion, phase change and species diffusion at the nanosecond timescale, all to be solved self-consistently. In this paper, we will present the 3D TCAD simulation package of the Laser Annealing process (Laser Annealing Innovation Application Booster or LIAB), with a specific focus on the enthalpy and phase field models and calibration of relevant materials. The coupled partial differential equation system is described and a methodology for materials calibration, especially challenging in the melting regime, is detailed with results shown for group-IV and Back End Of Line materials.