Photon-assisted synthesis and processing of materials in nano-microscale

Resume : Direct laser writing is a very useful technique to process dielectrics for many applications, like micro-fluidics, photo-electronics or glass cutting for consumer electronics. Material processing requires accurate control on energy deposition profiles inside the transparent material, which strongly depends on irradiation conditions. Gauss-Bessel beams have been successfully used for ultra-high aspect ratio processing because of the enhanced stability of these beams in comparison with the unstable and complex filamentation regime of Gaussian beams . In this work, we temporally split the input 100 fs laser pulse in two equal pulses with a variable delay. We compare single and double pulse illumination as a function of delay on the drilling of high aspect ratio nanochannels in borosilicate glass. Our main result is that, with equal energy, splitting the pulse allows increasing the channel width and enables channel drilling for conditions when only index modification was created. The results strongly depend on the sub-nanosecond delay (ie at delays below the standard burst mode of lasers). We report measurements of energy absorption and interpret our results in terms of confinement of the energy deposition. Our results raise novel fundamental questions on laser-matter interaction and we anticipate a wide impact on technological applications to laser processing of transparent materials.

Resume : Beam profile engineering, where a desired optical intensity distribution can be generated by an array of phase shifting (or amplitude changing) elements is a promising approach in laser material processing. For example, a spatial light modulator (SLM) is a dynamic diffractive optical element allowing for experimental implementations of controllable beam profile. Scalar Mathieu beams have elliptical intensity distribution perceivable as “optical knives” in the transverse plane. On the other hand scalar Weber beams have a parabolic cross-section, which enables us to call them “optical showels”. Both families exhibit non-diffracting properties similar to Bessel beams, where a relatively long focal depth retains unchanging intensity distribution, which makes them a promising approach in laser processing. Here, we introduce vector versions of those beams with controllable polarization and investigate numerically their spatial spectra. We use vector Mathieu and Weber beams as a basis to construct controllable on-axis phase and amplitude distributions with polarization control. Further, we attempt to generate components of vector Mathieu beams experimentally using SLMs and report on our achievements in the control over the beam shape and dimensions along the propagation axis. Lastly, we discuss generation of femtosecond pulsed “knive” and “shovel” type beams using geometric phase elements, made with laser induced nanograting ripples in fused silica and produced by “Altechna R&D”.

Resume : The creation of a photonic jet at the tip of an optical fibre is an upcoming trend with various applications. The propagative, slightly diverging, light beam coming out of the fibre does not behave in accordance to the usual laws of wave optics. For example, the diffraction limit can be overcome, giving a FWHM smaller than a half wavelength. These unusual properties make the photonic jet an excellent tool for subwavelength micromachining. The shaping of optical fibre tips is commonly done by thermoforming. Nevertheless, this method has some shortcomings for single mode fibers: the curvature of the tip is harder to control and the effect on the size and shape of the core and its concentration in dopant is unknown. This study investigates an alternative fabrication process to obtain the desired tip shape: chemical etching. The simulation of the shape of the photonic jet out of single mode fibres was made by 2D FEM modelisation. The fibres were isotropically etched in 24% HF. The chemical etching process was studied both statically and dynamically, along with the effect of the vapours. By carefully controlling the experimental conditions, shapes in close accordance to the theoretical predictions were obtained. The tip shapes were observed by optical microscope and the size of the photonic nanojets measured through laser ablation on Si. Eight time less energy has been required for etching using a single mode fiber tip shaped combining both chemical etching and thermoforming. Intro : Fibre tip shaping, HF, chemical etching, photonic nanojet

Resume : Dr. Neretina’s laboratory has developed a new synthetic procedure for generating periodic arrays of metallic nanostructures shaped as hexagonal or triangular nanoplates using a room temperature light-activated growth mode. Such structures have the potential to act as the active components for the detection of biological and chemical analytes using various sensing modalities (e.g., Surface Enhanced Raman Scattering (SERS)). The synthesis is reliant on the formation of Au seeds exhibiting planar defects – without such defects the growth mode is deactivated. Through the engineering of defects, which have been extensively studied using Titan TEM imaging and electron diffraction, such structures have now been produced in high yield. Here, we will describe the techniques used to generate periodic array of seeds, demonstrate their utility in forming substrate-based metallic nanoplates and provide an understanding of the opportunities and challenges that lie ahead.

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 fabrication of metallic NPs in UHV conditions embedded in fluoride matrix prevent the oxidisation, which could degrade of plasmonic properties of NPs. In our work we demonstrated successfully fabrication of Ag, Al, Rh and Bi NPs embedded by CaF2 and Pr3+:CaF2 films fabricated by Pulsed Laser Deposition techniques (NPs) with auxiliary Electron Beam Evaporation (fluoride) at UHV conditions. The size of the NPs was controlled by the number of the laser pulses focused on the metallic target and varied between 5 and 20 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. Results were compared and discussed with the results of analysis structural properties performed by SEM, TEM, AFM and XRD. The calculated absorption cross absorption effective cross-section will be compared with experimental results. The plasmonic behaviour of metal NPs will be compared with those presented for metal oxides nanocomposites. The effect of NPs on luminescence and down conversion properties of Pr3+:CaF2 films will be presented as a function of their structural properties.

Resume : Considering the recent global interest in reducing energy consumption, SiC power electronics technology is now ready to enable the step to the next plateau for efficiency standards. In most case, SiC power modules are designed to work at operating temperatures around 250 oC. Therefore, comical available electronic components such as resistor, cannot use for the SiC modules because the electrode and resistor materials is deterioration in the temperature. In addition, we found that the trimming part is not good for the heat cycling properties (-40-250oC). To overcome this problem, we developed new thin film resistor by using a photo reaction of hybrid solution (PRHS) process. In this presentation, we will explain the PRHS process for the flexible oxide thin film resistor, capacitor and its electrical properties. First of all, we have developed the new hybrid solution for the thin film resistor. The hybrid solution was prepared by mixing the Ru organic solution and RuO2 particles without any glass and an organic vehicle. The hybrid solution was spin-coated on the Al2O3 or polyimide substrate. The coated hybrid solution was heated or irradiated by UV lamp. The film was characterized by XRD, SEM and electrical measurements. Flexible RuO2 film was successfully prepared by PRHS process at room temperature. Resistivity of the flexible RuO2 film was 4.8×10-4Ωcm. The resistance change was 2.4% at the temperature range from 300 to 25oC. In addition, at the time of implementation, flexible resistor would be expected to relax the crack that comes from the difference in the thermal mechanical properties. In addition, by using PRHS, patterned resistor film was formed by UV irradiation using the photomask after leaching the solvents. So PRP process is effective for not only crystallization but also patterning. Detail results will be presented in the conference. This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), "Next-generation power electronics/Consistent R&D of next-generation SiC power electronics" (funding agency: NEDO)

Resume : Irradiating plasmonic nanostructures with an ultrafast laser beam produces highly localized processes on the nanoscale in the surrounding medium. When these nanomaterials are imbedded in a biological media, their irradiation by a fs laser could results in a highly localized plasma, heat production and mechanical effects yielding to the production of nanobubbles and nanosurgery of cells. Recent developments of the fundamentals, modeling and applications of nanoplasmonics enhanced ultrafast laser nanosurgery of living cells will be presented. We will present a complete model that successfully describes all interactions occurring during the irradiation of plasmonics nanostructures by an ultrafast laser of various pulse widths and fluences. This model together with the help of the shadowgraphic imaging and scattering techniques, give valuable insight on the mechanisms of cavitation at the nanoscale, leading to the optimization of the nanostructure for bubble-based nanomedicine applications. We will also describe an in-silico rational design approach based on our theoretical modeling that optimizes cavitation without breaking the nanostructure. Using this framework, we demonstrate that nanoshells (NS) can significantly reduce the cavitation threshold in the near-infrared. Applications of laser optoporation and transfection of cells in various field of nanomedecine will be discussed. This technique has been successfully used to locally stimulate neurons.

Resume : Femtosecond ablation of metal thin films has been of vivid interest since decades [1,2]. Microbumps and nanojets have been observed on thin metal films [3-5]. The generation of microbumps has been attributed to two different mechanisms considering a loss of film strength without melting [5] and due to melting [3,4]. Metallic and non-metallic microbumps have the potential for various applications due to their unique properties such as wettability [6], superhydrophobicity [7] and self-cleaning [8]. In this study, the generation of microbumps on single and stacked copper/silver double layers has been investigated. The microbumps were characterized by SEM and EDX. Two temperature model calculations were employed to clarify the dynamics of microbump generation. [1] W. Kautek and J. Krüger, Proceedings of SPIE 2207, 600 (1994). [2] J. Krüger and W. Kautek, Proceedings of SPIE 2403, 436 (1995). [3] A. I. Kuznetsov, C. Unger, J. Koch, and B. N. Chichkov, Applied Physics A 106, 479 (2012). [4] D. S. Ivanov, Z. Lin, B. Rethfeld, G. M. O’Connor, T. J. Glynn, and L. V. Zhigilei, Journal of Applied Physics 107, 013519 (2010). [5] Y. P. Meshcheryakov and N. M. Bulgakova, Applied Physics A 82, 363 (2006). [6] B. J. Basu, V. Hariprakash, S. T. Aruna, R. V. Lakshmi, J. Manasa, and B. S. Shruthi, Journal of Sol-Gel Science and Technology 56, 278 (2010). [7] K. Rajavel, R. Gomathi, R. Pandian, and R. T. R. Kumar, Inorganic and Nano-Metal Chemistry 47, 1196 (2017). [8] H. Yu, J. Liu, X. Fan, W. Yan, L. Han, J. Han, X. Zhang, T. Hong, and Z. Liu, Materials Chemistry and Physics 170, 52 (2016).

Resume : When exposed to an ultrashort laser pulse, dielectric materials exhibit rapid changes in the optical properties induced by the strong-field excitation of electrons from the valence to the conduction band. The transient electron plasma can be seen experimentally in pump-probe experiments using, e.g., time-resolved reflectivity and spectral interferometry. The general trends, reflecting the increasing electron density, are captured by numerical simulations of the excitation process in a multiple-rate-equation model. However, for a thin sapphire sample, we recently observed the surprising occurrence of coherent optical amplification of a 400 nm probe pulse after excitation by an 800 nm pump pulse. The amplification factor depends non-linearly on the probe-pulse energy and is thus attributed to two-photon stimulated emission based on population inversion between the bottom of the conduction band and the top of the valence band. The gain occurs after a few hundred femtoseconds, consistent with a relaxation of the carriers to the band edge in combination with a carrier-induced band-gap shrinkage. The gain persists at pump-probe delays exceeding several tens of picoseconds [Nature Physics 14, 74?79 (2018); doi:10.1038/nphys4265].

Resume : Focus wave modes (FWM) are solutions of scalar Helmholtz equation, which are localized and can ideally propagate long distances without spreading due to diffraction and dispersion. This type of pulsed beams is understood in terms of superposition of individual monochromatic Bessel beams with a given angular dispersion. Here, we extend the concept of FWM's to another two classes of nondiffracting beams - parabolic Weber-type and elliptic Mathieu beams. We aim to construct a scalar analogues to the classic FWM's and investigate their propagation inside a dielectric material, when their temporal durations can be up to few cycles. Furthermore, due to the large spatial angles introduced by the angular dispersion required for those durations, vectorial theory is introduced. We overcome this problem by introducing vector parabolic and elliptic nondifracting beams with controllable axial polarization, which can be either linear, circular and radial or azimuthal. Those newly obtained vector monochromatic beams are substituted into expressions for nondiffracting and nondispersive pulsed beams and, as a result, spatio-temporal distortions are successfully compensated. Lastly, we dive into problems arising while applying these vectorial pulsed beams for laser-microprocessing applications. Finally, we briefly report here on generation and implementation of the considered pulsed beams in scenarios involving a laser-micromachining of transparent dielectric materials.

Resume : In the context of ultrashort laser-induced texturing of metals, the mechanisms involved in phase transformation determine the rapidity and the precision of the structuring process of the surface. The laser pulse produces an intense electronic excitation that transforms electronic and atomic structures to accommodate the energy of interaction between the electrons. A theoretical approach is proposed to predict the ultrafast processes on times shorter than electron-phonon dynamics, on the hundreds of femtosecond timescale. The lattice destabilization scenario is investigated theoretically from ab initio calculations relying on density functional theory (DFT) and time-dependent DFT simulations. First-principles calculations show that laser photo-excitation drives a charge distortion in the cold crystalline atomic arrangement. This induces high electronic stress and temperature along with an entropy increase on the subpicosecond timescale, with a potential for surface destructuring. In particular, electronic free energy dependence on interatomic distance as a function of the degree of ultrafast heating of metals establish nonequilibrium interatomic potentials revealing the disappearance of a free energy minimum. This shows that the electronic charge redistribution affects the lattice cohesion through non-thermal phenomena related to modified ion screening and high entropy effects.

Resume : Microfluidic biochips represent controllable environment platforms, offering the possibility to investigate biological reactions at a microscale level including intra-cellular reaction and single-molecule detection. Unlike the polymer-based bio-chips, the miniaturized microfluidic platforms fabricated usually by NIR femtosecond lasers in photosensitive-glass has additional advantages such as strength for easy handling and chemical resistance. In this work we propose a new approach for the fabrication of embedded 3D structures in photosensitive glasses by high-repetition-rate picosecond laser processing. Different shapes of micro-channels and reservoirs, generally used in the bio-chips design, are achieved in volume of the glass by picosecond laser irradiation followed by thermal treatment and wet chemical etching. The obtained results have revealed that picosecond laser offers several advantage such as a reduced processing time for large areas and low fabrication cost.

Resume : Engraving microstructures with highly smooth sidewalls is required for several applications. As examples, the roughness is a determinant factor to reduce liquid friction in microfluidic devices, to minimize scattering losses in ridge waveguides or to prepare clean cross sections for TEM and SEM analysis. Among elaboration techniques, ultrafast laser machining stands out from others by being contactless, maskless, fast and by minimizing thermal damage. As laser smoothing of sidewalls has been poorly reported in the literature, engraving have been studied with two picosecond lasers (8 and 50 ps) in silicon at atmospheric pressure by varying the laser wavelength (343 and 532 nm), the fluence and the beam scanning strategy, and characterized using SEM and confocal microscopy. This study shows that a fine tuning of the pulse overlap drastically enhances the smoothness of the flanks (less than 40 nm Ra). Moreover, it is found that laser engraving induces a structuration with a periodicity matching the pulse to pulse distance. The maximum profile height increases with this distance in accordance with a simple geometric model. Theoretically, less than 1 nm Ra should be obtained for pulse overlaps close to 100%. However, experiments show that the optimal surface quality is obtained at a much lower overlap (~80%) due to debris induced scattering on the edge. Acknowledgement: This work has been carried out in the frame of the European project SAM3 funded by EURIPIDES2 and CATRENE.

Resume : Laser-induced periodic surface structures (LIPSS) or ripples appear on different solid surfaces upon exposure to ultrashort laser pulses. We generate ripples in different liquids such as in water, methanol and ethanol. In contrast to the experiments in air or in vacuum, the LIPSS formation in liquids is in competition with additional effects influencing the pattern formation. They are: bubble formation due to the liquid boiling, self-focusing and frequency conversion due to relatively high nonlinear refractive index of the environment. Experimental parameters, at which the influence of these additional factors is diminished, are analysed and uniform ripples are obtained. Change in the ripples orientation with the incident pulse fluence is observed and discussed.

Resume : Surface nanostructuring using ultrashort laser beams has been shown to improve the thermoelectric properties of thin films through the formation of laser induced periodic surfaces structures (LIPSS). A good control of the formation of such structures could induce a better confinement of phonons in the material leading to the reduction of the thermal conductivity without destroying the electrical and Seebeck coefficients. In this work, we perform a comparative study of LIPSS formation on stoichiometric and sub-stoichiometric titanium oxide thin films (TiO2 and TiOx, with 1.6 ≤ x ≤1.8) that were grown using two different techniques, namely pulsed laser deposition (PLD) and magnetron sputtering (MS). Irradiation was performed using two femtosecond laser beams, with pulse width of 100 and 500 fs and wavelengths 266 and 1030 nm respectively. Other laser irradiation parameters such as beam scanning speed and laser fluence were varied and conditions for the formation of LIPSS were determined for both types of films, as observed by Scanning Electron Microscopy (SEM). A variety of nanostructures were thus detected and their shapes and sizes were found to strongly depend on initial growth technique, whether PLD or MS. The difference in the LIPSS patterns between both sets of films can be correlated to difference in their initial morphology and nanostructure. The mechanisms of LIPSS formation were mainly attributed to free-surface energy minimization, involving several forces (surface tension, thermo-capillarity instabilities) that contributed to move, agglomerate and organize the material in regular structures. Finally, laser nano-structuring of large and homogeneous surfaces up to 25 x 25 mm² show significant improvement of the films’ thermoelectric properties, and more particularly a huge increase of the Seebeck coefficient leading to a noticeable enhancement of the ZT figure of merit.

Resume : Planar arrays of nanoribbons are made with Pd nanoparticles obliquely deposited on PET substrates previously processed for Laser Induced Patterned Surface Structures (LIPSS). This new materials system is here studied as a candidate for anisotropic and flexible transparent conductor (TC). LIPSS on PET thin foils are first patterned with a linearly polarized nanosecond 266 nm laser scanned all over the substrates [1]. Dynamic mode Atomic Force Microscopy (topography and phase-contrast) is used to characterize the surface pattern. As-prepared specimens are comprised of large area, high coherence nanoripple pattern with a mean spacing 200 nm and average amplitude 46 nm. Separately, in a gas phase aggregation vacuum equipment, a beam of Pd nanoparticles (diameter 5 nm) is deposited on the LIPSS at an incidence angle 60-65º directed as to become partially shadowed by the ripple ridges. After the Pd deposition (estimate mean thickness 10 nm) the surface pattern preserves spacing and the phase-contrast AFM images show modulation across the ripples indicating formation of ribbons over the pattern. Optical transmittance in the visible and near UV range as well as four-probe electrical resistance measurements at room temperature are discussed and compared with requirements for next generation TC. [1] E. Rebollar, M. Castillejo, T. A. Ezquerra, “Laser Induced periodic surface structures on polymer films: From fundamentals to applications”. European Polymer Journal 73 (2015), 162-174

Resume : Defined as the tendency of a liquid to spread when in contact with a solid surface, wettability plays a major role in a variety of surface related phenomena as corrosion, heat transfer or tissue adhesion on implants. Consequently, great research effort is being devoted to address the wettability control of functional surfaces. Pulsed laser texturing at micro/nanometric level has been widely used for that purpose as a precision/time efficient technique. This work deals with the control of the wettability of AISI 304L stainless steel surfaces via laser texturing using three different pulsed laser sources working at the nanosecond regime. Samples wettability, measured via the contact angle θ (º), was systematically studied regarding to the processing parameters: wavelength, laser power, scanning speed, pulse frequency, track distance, and processing atmosphere. The exposure EX (J/mm2) has been identified as the key factor controlling the amount of change in θ (º), whereas the atmosphere has arisen as the one which drives that change towards more hydrophobic or hydrophilic values. The observed tendencies between wettability and the processing conditions have been related to the modifications in surface topography and chemistry induced by the laser treatment. Based on this knowledge, the processing parameters can be tuned to tailor the wettability of the untreated surfaces (θ = 88º) up to the desired value, ranging from superhydrophilicity (θ=0º) to superhydrophobicity (θ=152º).

Resume : Laser induced periodic surface structures (LIPSS) has been emerged as a reliable technology to improve and control Key functionalities on solids surfaces. We mention for instance, modification of tribological properties and surface wettability as well as selective bacterial adhesion. Recently, novel morphologies such as rhombic or triangular periodic, sub µm, structures have been introduced, opening the possibility to exploit LIPSS in novel applications like anti-icing, bactericidal and antireflection. Interestingly, surface texturing with double femtosecond pulses is a reliable technology to generate morphologies with no linear symmetry. Nevertheless, a significant part of the results reported only refers to inhomogeneous structures generated over area as small as a spot size. Here we show for the first time that by using a delay line based set-up (inter-pulse delay Δt varying from -100 ps up to 2 ns) is possible to generate a variety of homogeneous structures over large area. Our setup exploits almost ~100% of the power of an industrial femtosecond laser with pulse duration of 350 fs emitting at 1030 nm and operating with repetition rates up to 1 MHz. The surface morphology was characterized by SEM and FT. We illustrate the effect of the interplay between the process parameters and Δt on the induced morphology. We believe that our results provide ground-breaking data on material surface processing providing effective solutions for high demand industrial applications.

Resume : We study the structural modifications produced by irradiation of silica based glasses with femtosecond lasers. We have pointed out two new cases that are particularly interesting either from fundamental point of view that for the applications and showing the potential of this equipment in materials science: - Silica is an achiral glass. Nevertheless, for some values of the laser parameters and especially of its polarization direction versus the laser scanning, we can create rotatory power and circular dichroism. - The following glass 33Li2O-33Nb2O5-34SiO2 exhibits the potentiality to precipitate LiNbO3 crystals that are optically non-linear active (e.g. second harmonic generation), when the laser pulse repetition rate is above 100-200kHz. We have shown that when the crystal is nanosized, it is possible to orient them with the laser polarization. During the presentation, I will make a short review on published results on the two subjects. I will suggest mechanisms for the two findings that are quite different at first sight but both related to physico-chemical phase separation. The important fundamental aspect here is that light polarization appears to be a new “button” that we can adjust in solid phase in order to control and orient a transformation, in short the immaterial acts on the material. In the field of applications (integrated optics), the creation and control of the direction of the birefringence, of the circular properties and of the second order optical properties open unprecedented possibilities.

Resume : Interferometric ultra-fast laser interactions within thin dielectric films provide an emerging tool to generate novel surface and intra-film structures through confinement of non-linear optical phenomena on nano-scale dimensions of /2n fringe maxima. This paper extends our prior demonstration of intra-film cleaving of SiOx and Si3N4 dielectric thin-films on silicon substrates to unveil an expansive range of new nano/micro-scale morphologies in SiOx film. The intra-film structuring is driven from a multi-level stack of thin (≈ 40 nm) plasma disks, formed by a single laser pulse. A planar stack of micro-explosions present complex ablation and shock front physics. Morphology evolves with increasing laser pulse energy from formation of single to stacked micro- and nano-cavities, leading to quantized /2n intra-film ejections, and formation of nano/micro-blisters having complex multi-layered intra-film modification. Sequential quantized blistering and ejections open into ultra-thin glass “balloons” with ≈ 100 nm SiOx walls and near-spherical geometry from deep intra-film zones. Alternatively, such spheres may burst to create previously unreported topographies, such as cylindrical walls perpendicular to the transparent film surface. At high exposure, cross-sectional SEM of ion-milled films unveil multi-layered and inter-nested micro-chambers, whereby deepest film segments undergo laser cleaving and fusion by competition from upper layer shock fronts. Laser interferometric processing thus offers novel film morphologies not found in conventional surface processing methods, opening new application directions for micro-device manufacture, CMOS compatible microelectronics, nano-photonics and surface topology attractive for cellular/biological study.

Resume : Although the first demonstrations on the functionalization of glasses with laser pulses were provided more than two decades ago, no comparable technique exists inside silicon so far. Recently, nanosecond infrared pulses were employed for achieving permanent bulk modifications. In this study, we expand on the interaction regime which recently allowed us to demonstrate the first laser inscription of waveguides in the bulk of monolithic crystalline silicon. The writing procedure relies on 5 ns duration infrared laser pulses, tightly focused deep inside the bulk of silicon and longitudinally moved with respect to the sample. An in situ infrared phase-shift microscope has been specifically developed for accessing the refractive index change Δn. Depending on the writing speed, the channels exhibit either micro-cavities or nearly homogeneously densified volume. In this latter case where Δn≈5.3×10^(-3), the injection of light inside the structures proves their light-guiding properties. The modifications also exhibit different chemical etching rates. Etching using KOH not only enables to machine the silicon samples, but also to reveal the channels written in the bulk at different speeds for detailed material analyses. These analyses provide paramount information on the material science involved in this emerging regime of laser-matter interaction. The whole study is of broad interest for numerous applications including the growing field of silicon photonics as well as microfluidics.

Resume : Multiphoton Lithography is a laser-based additive manufacturing technique which allows fabrication with resolution down to a few tens of nanometres. Based on nonlinear absorption, Multiphoton Lithography has unique capabilities that no-other technique can provide. It has been implemented with a variety of materials and several components and devices have been fabricated such as metamaterials, biomedical devices, photocatalytic systems and mechanical models The unique capability of Multiphoton Lithography lies in that it allows the fabrication of computer-designed, fully functional 3D devices. In this talk, I summarize the principles of microfabrication, and present recent research in materials processing and functionalization of 3D structures. Finally, I discuss future applications and prospects for the technology.

Resume : The ability of plasmonic nanoparticles to greatly enhance the electric field of incident light in the near-field zone has many useful applications. One such application is enhancing upconversion of near-infrared light for improving solar cells [1]. Careful design of the nanoparticle geometry by numerical optimization can potentially lead to much improved results [2]. However, this approach requires, in particular, that the simulated near fields are very accurate. Electric near fields can be visualized experimentally by covering the nanoparticles with a polymer and subsequently polymerizing it with a laser in such a way that polymerization occurs only due to near-field enhancements [3]. By combining scanning electron microscopy and atomic force microscopy, surfaces of constant near-field enhancement can be traced out in 3D. Here, we present our results of using this technique on designed nanoparticles for validating near-field simulations. Multi-photon polymerization is carried out with a tunable, femtosecond laser source. By changing the irradiation wavelength, the spectral response of the nanoparticle is obtained, providing a broader basis on which to compare the simulated and measured plasmonic near fields. [1] H. Lakhotiya et al., Appl. Phys. Lett. 109(26), 263102 (2016) [2] J. Vester-Petersen, Appl. Phys. Lett. 111, 133102 (2017) [3] T. Geldhauser, Langmuir 28(24), 9041 (2012)

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 environmental monitoring or products of common use in everyday life. Plasma and 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 several different plasma (RF, MW, and HF-CVD) and laser (ns Nd:YAG and Excimer, fs Ti:Sa and OPA) sources in order to evidence differences in the obtained results induced by photo-chemical, photo-physical, and photo-thermal processes. The main parameters investigated for plasma sources were: applied power and (reactive or inert) gas pressure. Instead for laser sources were: pulse energy, spot dimension, beam travel speed, vacuum and (reactive or inert) gas pressure. Plasma-treated and laser-irradiated samples were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle measurement. Morphological results indicated that ripple-like structures of micrometer and sub-micrometer size formed after the laser and plasma irradiation, respectively.

Resume : The nano patterning of surfaces and thin films with pattern dimensions of less than 50 nm is challenging, in particular for large-area, low-cost fabrication. However, self-assembly processes provide a mechanism of pattern generation in this dimensional range, enabling an alternative fabrication route to the traditional lithographic road. The current work focuses on laser heating for high-temperature short-time annealing of DiBCP films to achieve self-assembly into vertical lamellas with periods in the range of 50 nm. To get vertical lamellas of the DiBCP neutral substrate were coated with a ~60 nm thick DiBCP film by spin-coating which were irradiated thereafter with a scanned CO2-laser beam. Depending on the laser power and the scanning speed different degrees of self-assembly were achieved across the laser irradiated line. The experimental results on laser-induced local self-assembly are combined with thermal simulations to explain the laser induced thermal annealing at irradiation times below 0.1 s. Combining local heating by laser beams can provide a tool for direct writing of hierarchical nano-microscale patterns and also for dry development of self-assembled DiBCP at the same time.

Resume : Ultrashort laser pulse micromachining features a high precision. By increasing the repetition rate of the applied laser to several 100 kHz, laser processing becomes quick and cost-effective and make this method attractive for industrial applications. Upon exceeding a critical laser intensity, hard X-ray radiation is generated as a side effect. Even if the emitted X-ray dose per pulse is low, the accumulated X-ray dose becomes significant for high-repetition-rate laser systems so that radiation safety must be considered. The X-ray emission during ultrashort laser processing was investigated for different pulse durations and materials in an intensity range up to 1e15 W/cm2. The investigations were performed with two laser systems (925 fs, 1030 nm, 400 kHz, 40 W, Trumpf TruMicro 5000 and 30 fs, 800 nm, 1 kHz, 1 W, Femtolasers Compact Pro) e.g. on steel, wolfram, and glass in ambient air. Corresponding X-ray spectra and X-ray dose measurements are presented and the mechanism of X-ray generation will be discussed. By using a laser-intensity dependent scaling law, the emitted X-ray radiation for respective processing conditions can be predicted. The latter enables to implement suitable radiation protection strategies for various laser systems and processing parameters.

Resume : Carbon fibre reinforced plastic (CFRP) is strong, lightweight and durable material with good corrosion and vibration resistance. It is a good candidate to replace metals in production of many parts, while an optimally designed CFRP part can be up to 70% lighter than steel and 30% lighter than aluminium as well as to have twice the strength, more than twice the fatigue resistance of steel and be twice time stiffer than aluminium. The benefit of CFRP for lightweight construction in automotive and airplane industries is widely accepted. Conventionally used techniques, such as shape-cutting and water-jet are connected with limitation related to quality and productivity. Therefore, laser processing, as a non-contact, flexible and easy to automated, was recently recognized as possible solution for large-volume production of CFRP parts. Unfortunately, this technology is also connected with two major chalanges: to machine the CFRP material with high speed and at the same time to minimize heat affected zone (HAZ). In this paper will be presented work on selecting processing strategies for two CFRP materials (C-PPS and C-PEEK) for various laser systems emitting in nIR and UV with pulse durations from ns to fs. Comparison of processing parameters (scanning speed, spot diameter, spot overlap) and laser parameters (pulse energy, repetition rate, pulse duration, wavelength) with respect to HAZ and cut quality for all processing strategies and optimal processing window for each laser system will be also presented.

Resume : Laser cleaning is a well stablished technique in different fields, among them conservation of Cultural Heritage. Currently laser cleaning systems are based on movement of the processing beam, or the workpiece positioning system, in two mutually perpendicular axes. Such systems are capable of cleaning flat (2D) surfaces placed perpendicularly to the processing beam. Our approach to process 3D surfaces is based on the prior knowledge of the workpiece surface by laser-triangulation profilometry. Using custom software, the profile data is transformed into a 3D model of the surface. From this model, the area to be cleaned is selected, as well as the laser processing parameters, i.e.; scanning speed, filling pattern and position of the beam focus in order to ensure an even cleaning treatment. Taking these parameters into account, the appropriate laser trajectories are calculated and, finally, orders are automatically generated for the controller of the sample positioning system. The results of the removal of paint from a granitic 3D stonework using the third harmonic of a Nd:YVO4 nanosecond laser are presented. Different analytical techniques used to evaluate the quality of the cleaning and possible damages in the stone surface confirmed the capacity of our system for the adequate laser processing of 3D surfaces. ACKNOWLEDGEMENTS This work was supported by BIA2014-54186-R Project; (Spanish Government, Ministry of Economy and Competitiveness). J.S. Pozo-Antonio was supported by a postdoctoral contract with the University of Vigo within the framework of the 2011–2015 Galician Plan for Research, Innovation and Growth (Plan I2C) for 2014.

Resume : As the development of biocompatible and/or biodegradable devices, such as implants and drug delivery systems, is constantly progressing, a wide range of bio-based and bio-inspired materials are becoming available. Further progress also requires the development of new methods focusing on the ease of preparation and processing. Microfluidic devices offer great opportunities in this context as a well-designed setup enabling the miniaturization of biological experiments by reducing the reagent volumes, shortening reaction times, and allowing for simultaneous complex operations by integrating laboratory protocols into a single chip device.1 In this work, we developed a straightforward 3D-printed microfluidic system that allows the preparation of microcapsules of uniform sizes through the formation of double emulsions. The presented system overcomes common limitations of microfluidic devices, such as high cost and lengthy procedures, while maintaining their reliability in producing microcapsules with interesting properties. Indeed, the successful formation of ethyl cellulose microcapsules is shown, while their potential applications in biological systems is discussed. 1. Dixit, C. K. & Kaushik, A. Microfuidics for Biologists. (2016).

Resume : This study deals with the use of laser techniques for preparation of advanced Au and Ag nanostructures on SiO2 (001) substrates to be applied for high-resolution analyses, namely, surface enhanced Raman spectroscopy (SERS) analyses. The activity was tested of the structures fabricated as substrates for SERS covered by small quantities (usually applied in agricultural medicine) of the fungicide Dithane DG (mancozeb). The study has a direct bearing on the human health and food quality by the way of assisting the detection of small amounts or residue of harmful pollutants.

Resume : Permanent, rigorous and efficient monitoring of the environmental pollution involves the use of efficient devices, namely sensors. The most important part of such a sensor is the active membrane that detects pollutants, based on chemical or physical phenomena. In the case of chemoresistive sensors, the use of new composite material by mixing organic and inorganic compounds appears to be a promising alternative. The aim of this work is to demonstrate the advantage of using nanostructured composites (WO3/polymer) as highly sensitive membranes to toxic gases, working also at low temperature. Matrix assisted pulsed laser evaporation was used to obtain these composites as thin films. The surface morphology was in detail studied by atomic force microscopy and scanning electron microscopy and the chemical structure was investigated by Fourier transformed infrared spectroscopy. The polymer/ WO3 ratio influence on the electrical properties was also evidenced. Acknowledgement: Financial support from the Romanian National Nucleu Program is gratefully acknowledged.

Resume : Design trend of electronic devices have been moved on smaller, thinner, lighter, and flexible and this trend will be pushed further to realize wearable and internet-on-thing devices. To keep pace with the flow in the electronics, micro-energy storage devices with high capacity and fast charge/discharge rate should be developed. Interdigitated microsupercapacitor (MSC) takes high potential for the micro power source due to its fast charge/discharge processes, long cycle life, and high power density compared to the microbatteries; however, fabrication of MSC with interdigitated electrodes selectively decorated with pseudo-capacitive materials such as transition metal oxides for increased capacitance are still challenging. Here, we developed simple fabrication of MSCs by in-situ formation of interdigitated graphene electrodes and ZnO nanorods by photothermal conversion of graphene oxides (GO) and Zn precursors using IR-laser scribing.

Resume : This work deals with the design, fabrication, and characterization of a fully integrated explosives detection platform based on a chemiresistive sensor array fabricated by laser-based methods. This detection platform is used for the detection of improvised explosives, as they are actually fabricated by terrorists due to the ease of access to unrestricted starting. The sensor array is fabricated by laser-induced forward transfer (LIFT) of nanomaterials, i.e. carbon nanotubes and hybrid carbon nanotubes decorated with semiconducting polymers. Conventional LIFT consists of the irradiation, using a pulsed laser, of a thin layer of an absorbing material (the donor) that has been deposited onto a transparent substrate. The layer is irradiated through the substrate and the light-matter interaction which takes place at the interface generates a strong increase of the local pressure. As a result, a small piece of the thin film located above the irradiated area is ejected (as a pixel) from the substrate surface and deposited onto a target substrate (the receiver) arranged in close proximity to the donor substrate. The size of the ejected material is controlled by the size of the incident laser spot. This work aims at 2 specific objectives: (1) The design and development of the integrated explosives detection platform, including explosives sensors / sensor arrays based on conductive polymers and single walled carbon nanotubes. (2) System integration, testing, and validation of integrated explosives detection platform. This corresponds to the development of a fully operational explosives detection system, able to perform sensitive and selective detection of the explosives of interest and consequently, a state of the art development in terms of sensors. Acknowledgement Financial support from i) NILPRP through the NUCLEU program and ii) UEFISCDI, though the “Fabrication, calibration, and testing of advanced integrated sensor systems aiming at applications in societal security (TESTES)” project are gratefully acknowledged.

Resume : Metal nanostructures have attracted a great deal of attention due to their unique properties and functionalities. In particular, noble metals at the nanometer scales exhibit distinct localized surface plasmon resonance (LSPR). The LSPR phenomenon can be effectively utilized for bio-sensors and noble optical devices such as color filters, polarizers and color printing. Although the spectral positions of LSPR peaks somewhat vary with particle size, the plasmonic behavior of these nanoparticles has a limited tuning range. Since Ag and Au particles exhibit resonance at different wavelengths, bimetallic particles will have a wider tuning range than the single-element paricles. We here show that bimetallic Ag-Au nanoparticles can be synthesized by irradiating commercial Ag nanowires coated with a thin Au film by a pulsed laser beam. This process is fundamentally based on Rayleigh instability. By adjusting the relative amounts of the two elements, we were able to tune the resonances peaks from 450 to 550 nm. More importantly, we could produce a few different plasmonic colors from a single sample simply by controlling the laser irradiance. This finding provides a possible way of implementing color laser printing without the need of using a pre-patterned template.

Resume : This work represents the response of noble metal composed borosilicate glass to laser radiation with femto- and nanosecond pulse duration. The sample material is gold or silver ion-doped borosilicate glass obtained by conventional melt quenching method. The produced glass samples are irradiated by laser pulses with femtosecond and nanosecond duration. The nature of the glass modifications as a function of the laser processing parameters is studied. For this purpose the laser fluence, laser wavelength and pulse number are varied in a wide range. Below the permanent modification threshold, defects associated with formation of color centers in the material are observed when femtosecond laser pulses are applied. The effect can be achieved for different wavelengths – in ultraviolet, visible and infrared spectral range. Irradiation with nanosecond laser pulses may also induce color change of the glass, but only at wavelength in the ultraviolet range. At conditions for permanent morphology modifications, different micro- and nanostructures are observed depending on the laser processing conditions. The annealing of the samples may result in formation of noble metal nanoparticles in the laser processed areas. Thus, the results can be used for fabrication of 3D complex composite systems in transparent materials that can be applied in the design of new optical components and lab on a chip devices.

Resume : Noble metal nanoparticle composed glasses attract significant attention due to the unique optical properties that they express in the near UV and visible spectral range. These are related to the high values of the extinction cross section and nonlinear optical characteristics. In this work we study the ability of laser induced modification of the optical properties of borosilicate glasses that contain gold and silver nanoparticles. The process is investigated by application of laser pulses with femtosecond and nanosecond duration. It is shown that at certain conditions the glass optical properties can be modified as a change of the nanoparticles plasmon resonance wavelength is observed. The influence of the laser fluence, laser wavelength and pulse number on this effect is studied. A theoretical model based on multiparticle Mie scattering theory is applied to explain the observed modifications. On its basis and performed analyses can be concluded that the induced optical properties variations are related to modification of the nanoparticles size and shape. The obtained results indicate an ability of nanoparticle size and shape modifications with a high spatial resolution in 3D and can be used for fabrication of integrated optical systems.

Resume : The fabrication of diffractive elements in ophthalmic polymers to induce refractive index changes is of great interest in the field of Optics and Ophthalmology for refractive correction. In this work, hydroxyethyl methacrylate and silicon-hydrogel contact lenses were structured with linear periodic patterns by means of Direct Laser Interference Patterning (DLIP). As laser sources, Q-switched laser systems emitting 10 ns pulses at a wavelength of 266 nm were used to produce periodic patterns on the surface of the polymer materials. The experiments were carried out employing a two-beam interference setup, studying the features of the laser processed areas as a function of both the laser fluence and the interference period. The topography of the structured areas was investigated using optical confocal microscopy. Compositional and structural modifications on the materials were studied by means of micro-Raman spectroscopy. Finally, periodic patterns were characterized through diffractive techniques to determine the diffractive properties of the DLIP periodic patterns.

Resume : Organic materials such as semiconducting polymers and fullerene derivatives have attracted much attention due to their potential applications in optics, electronics and photovoltaics among others. Nanostructuring by laser of semiconducting polymers has been recently accomplished rendering to functional surfaces of selective electrical conductivity, while micron size patterning by light of fullerene materials has been also described. However, at nanometer scale, ordering of fullerenes typically implies bottom-up strategies involving a template surface. Here, we report a one-step top-down laser-induced method to prepare [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) resist-free laser induced periodic surface structures (LIPSS) by illumination of spin-coated films with the second harmonic of a Nd:YAG laser. LIPSS selectively preserve the initial electrical conductivity of the PC71BM spin-coated films on the LIPSS valleys. The nanostructured sample can be solvent washed leaving in the laser illuminated zone an undissolved residue consisting of nanowires which were shown to be partially electrically conducting. It is proposed that laser irradiation induces an increase in the crystallinity of the bottom part of the hills and consequently enhances the electrical conductivity levels. These results point towards the potential use of the described technology for nanofabrication of organic electronic devices.

Resume : Laser pyrolysis technique was employed for the synthesis of three different magnetic iron-based nanopowders starting from Fe(CO)5 vapors and C2H4 sensitizer mixture. Iron oxide maghemite particles were obtained in the supplementary presence of oxygen, whereas Fe metal/carbide@C nanoparticles were prepared using an additional C2H4 coaxial flow. Fe-Si magnetic nanoparticles were also synthesized by adding a separate nearby parallel SiH4 flow. These nanopowders were dispersed in aqueous solutions (using also hydrophilic agents for the case of those Fe-C type with hydrophobic surface) containing mixtures of water-soluble acrylate monomers: acrylic acid, acrylamide, N-isopropylacrylamide, 2-hydroxyethylmethacrylate and/or poly(ethyleneglycol) methacrylate in the presence of small amounts of N, N’ methylenebisacrylamide and APS (NH4)2S2O8. The resulted suspensions were subsequently gelled under bath ultrasonication at 70°C. The composite hydrogels were characterized by XRD, FT-IR, Raman, SEM and their magnetic properties were recorded. Their swelling behavior was also tested, as well as their capacity for heat release under alternative magnetic field for local hyperthermia applications.

Resume : High temperare thermal treatment is a fundamental method to enhance the crystallinity of materials or to recover its instrinsic properties after processes. However, the thermal treatments has become an inacceceble technic since the treatment temperature is usually limited by such as transparent or flexible subtrates. Here, it is introduced the microwave ‘induction’ heating as a selective and fast heating method for conductive thin film. In different with the conventional microwave dielectric heating for electrically polarized molocules, the microwave induction heating has mechanism that strong current induced by oscillating magnetic field in giga-hertz frequency generates ohmic heat in conduction thin film. A 20nm-thick silver thin film sputtered on 5mm-thick glass substrate for low thermal emissivity coating has been selectively heated more than 550oC in 300ms without thermal damage by the microwave induction heating, while the temperature of glass substrate is maintained around room temperature. The surface resistance of the silver thin film is reduced to near 30% due to crystallinity enhancement.

Resume : Recently, our group discovered a unwanted real-time in situ nucleation and growth processes of metallic Ag nanoparticles on different silver-based semiconductors, such as: α-Ag2WO4, β-Ag2MoO4, Ag3PO4 and β-AgVO3, which were driven by accelerated electron beam irradiation from an electron microscope under high vacuum. Now, we present new data on effect of grow of the metallic Ag nanoparticles (NPs) on the surface and electrical properties of the 3D flower-like Ag4V2O7 crystals. The crystals were obtained by coprecipitation method and was structurally characterized by X-ray diffraction patterns, which were well indexed to the orthorhombic structure. The Ag4V2O7 crystals exhibit a uniform shape as 3D flower-like, with average diameter of 4.3 µm. By the slicing of the flower-like crystals, it was observed internal pores and channels. To verify the growth of metallic Ag NPs on Ag4V2O7 crystal surface, an EDXS (Energy-dispersive X-ray spectroscopy) spectrum system coupled with a transmission electron microscopy (TEM) was used for analyzing. After 2 minutes under electron beam irradiation, silver growth on the Ag4V2O7 surface. As expected, EDXS results confirmed that the electrons beam promoted the random growth of the metallic Ag NPs. To evaluate the effect of growth of metallic Ag NPs on the electrical resistance of the 3D flower-like Ag4V2O7, the electrical measurements were evaluated with the exposure time to eletron beam, so with the growth of these metallic Ag NPs. Initially, the resistance is governed by the bulk properties. After 5 min irradiation a slight increase in resistance is observed, which can be attributed to formation of silver vacancy (V'Ag) in the semiconductor bulk, since, the clusters of [AgOx] interact with the incoming electrons, resulting in Ag reduction and the migration of the Ag from the bulk to the surface and the formation V'Ag. The negative vacancies (V'Ag) along with the oxygen vacancies (V●O), previously present, make the semiconductor more resistive for irradiation times until 20 min. However, after 40 min irradiation, it is observed a decrease in resistance, due to the formation of a layer of metallic silver in the semiconductor surface. From this point on, bulk and surface contribute equally to semiconductor resistance. After 60 min irradiation, a huge decrease in the resistance is observed, due to high density of metallic Ag nanoparticles on Ag4V2O7 crystals surface, which makes the bulk highly resistive. However, in this case, the resistance measurement is governed by the metallic surface which presents lower resistance. In summary, we have observed, for the first time, that the external electron beam irradiation, by MET induces the formation and growth of metallic Ag NPs on the 3D flower-like Ag4V2O7 crystals surface. Therefore, the irradiation generated Ag NPs two important advantages are obtained: generation of Ag NPs in the crystal surface and control of semiconductor properties by electron irradiation

Resume : ZnO is one of the most investigated n-type semiconductor as transparent electrode for thin film solar cells and optoelectronic devices but the role of doping on the electrical and optical properties is not well understood. Here we report on the growth of Nd doped ZnO thin films by either pulsed laser deposition (PLD) or pulsed electron beam deposition (PED) on c-cut single crystal substrates at different substrate temperatures and gas pressures in an attempt to find the optimum doping concentration for minimal electrical resistivity. Although a structural disorder is induced by few % of Nd in the wurtzite ZnO network, epitaxial thin films are obtained even at relatively low substrate temperatures (300°C). Whatever the growth method, in-plane epitaxial relationships are observed and explained by the domain matching epitaxy model that matches integral multiples of planes across the film/surface interface. The doping is evidenced in both carrier concentration and structural disorder of the ZnO films leading to various optical and electrical film properties. The degenerate or non-degenerate semiconductor electrical properties of Nd:ZnO thin films are discussed in correlation with the strong influence of the growth conditions on the optical film properties in PLD and PED. This work demonstrates that Nd:ZnO thin films are promising transparent conductive oxides or optically active layers for photonic conversion in photovoltaic applications.

Resume : In the last decades, the organophosphate compounds have risen significant threatens and strains on environmental safety as well as on public health and homeland security. Within this context, the development of sensitive chemical sensors for the detection and measurements of contaminants is of high interest. In this work, we report on a laser method (i.e. Matrix assisted pulsed Laser Evaporation-MAPLE) for depositing an active polymeric based membrane for obtaining chemical sensors to be used for the analysis of organophosphate compounds. The deposition process of the polymer was carried out using an Nd:YAG pulsed laser, operating at different fluences (0.2–0.8 J/cm2 ) with a wavelength of 266 nm and a repetition rate of 10 Hz. It was found that for specific range of fluences the main functional groups in the MAPLE-deposited thin films determined by Fourier transform infrared spectroscopy revealed the similarity with the molecular structures of the initial material. However, there were significant changes depending on the deposition parameters in morphologies revealed by Atomic Force Microscopy and Scanning Electron Microscopy. The surface acoustic wave sensors have been tested using the Network Analyzer before and after polymer deposition. The polymer coated surface acoustic wave sensors responses have been measured upon exposure to various concentrations of organophosphate analyte. All sensors coated showed a clear response to the tested vapor. The materials deposited by MAPLE provided good premises for the development of a sensor with suitable stability, good reproducibility, and high sensitivity towards samples. Our results indicate that the sensor system can be used as a rapid, simple alternative in the analyses of organophosphate compounds. Acknowledgments: This work was supported by Romanian National Authority for Scientific Research (CNCS–UEFISCDI), under the projects PED 214 and Nucleus programme..

Resume : Silicon nanocrystals (SiNCs), or silicon quantum dots, defined as Si nanostructures with typical diameters below 10 nm, have recently attracted much attention due to a unique combination of their size-dependent optoelectronic properties and biocompatibility, which have great potential for use in biological imaging and diagnostic applications. In this work, we have developed and tested two laser-assisted approaches for controlled Si NCs synthesis: first is based on pulsed laser ablation of silicon in liquids, second – spark discharge between Si electrodes in liquid followed by laser irradiation of the formed colloid. Both approaches provide a possibility of synthesis control over the process and avoid use of reducing agents or chemical precursors. The focused beam of a Nd:YAG laser (1064 nm, 10 ns pulse width, 10 Hz repetition frequency) was used for ablation of Si target in distilled water, DMSO and 0.008 M aqueous DTPA solution. The phase composition, morphology, structure and optical properties of the synthesized nanoparticles have been investigated. The prepared ultrafine and well-dispersed SiNCs with an average diameter of about 5 nm exhibited blue luminescent emissions in the spectral range of 410-550 nm when excited at wavelengths near the direct band gap of the SiNCs. The luminescent emission band shifts to longer wavelengths with excitation wavelength increase. In the presentation, the potential of the prepared SiNCs for bio-imaging applications will be demonstrated.

Resume : Hydrogels have recently received considerable attention as smart materials in the fabrication of various biosensors, due to their unique properties which can be customized to the suit the needs of each individual application. Further to this, the shift to a 3D surface geometry increases their loading capacity and better preserves the protein function due to the hydrophilic environment in comparison to conventional 2D functionalization techniques. To date, various microfabrication techniques have been employed for fabricating micropatterns of protein-incorporating hydrogels on surfaces such as robot-controlled, pin-based, inkjet printing and photolithography. Herein, an elegant approach based on the use of the Laser Induced Forward Transfer (LIFT) as a laser direct-write printing technique for creating micropatterns of functional hydrogel networks onto receiving surfaces in a spatially controlled and contactless manner, where no masks or time-consuming procedures are required, is presented. The technique has been employed for transferring and photo-polymerizing acrylate monomers into hydrogel networks onto silane-modified silicon based surfaces. The proteins (antibodies) were either incorporated into the prepolymer solution or bound to the hydrogels upon their polymerization. More specifically, antibodies were covalently immobilized into the hydrogels with the use of NHS-acrylate, while the porosity or the hydrogel was adjusted by varying the ratios of the following three monomers: 2-hydroxyethyl acrylate, poly (ethylene glycol) diacrylate and trimethylolpropane triacrylate. The antibody loading efficiency and their ability to recognize and bind to their antigen has been evaluated for prepolymer solutions of different compositions (monomer functionalities and ratios in the mixture) as well as laser printing conditions and compared to both hydrogels that have been drop casted and then either photopolymerized or chemically polymerized.

Resume : Smart biointerfaces have played an important role in tissue enginnering or biomedical related areas and were based on the correlation between the chemical and morphological characteristics and the biological response. In this work, Matrix-Assisted Pulsed Laser Evaporation (MAPLE) was used to obtain poly(N-isopropylacrylamide) (pNIPAM) and pNIPAM derivative based functional and thermo-responsive thin films. The morphology, roughness and hydrophobic/hydrophilic character, and the thermoresponsive response were investigated by atomic force microscopy and contact angle measurements under two temperature conditions. The change in the contact angle and thickness values when the temperature was shifted from 37°C to 24°C for all the materials tested demonstrated clearly the thermoresponse of the laser processed coatings. In vitro tests confirmed the mesenchymal stem cell (MSC) growth dependence on the characteristics of the coatings, revealing no cytotoxic effect. Acknowledgments: This work was supported by Romanian National Authority for Scientific Research (CNCS–UEFISCDI), under the projects PNII- PT-PCCA-2013-4-199, PN-II-RU-TE-2014-4-2434 and Nucleus programme.

Resume : Graphene oxide is a promising precursor for the production of graphene. Photothermal and/or photochemical interactions using laser radiation may result in the photoreduction of graphene oxide [1]. In the present study, the reduction of graphene oxide is demonstrated by near-field femtosecond laser irradiation [2]. The laser beam was focused onto an atomic force microscope tip placed a few nanometers above the substrate. Near-field enhancement and/or thermal conduction below the tip induced the local reduction on graphene oxide nanosheets below the diffraction limit. [1] Y.-L. Zhang, L. Guo, H. Xia, Q.-D. Chen, J. Feng, and H.-B. Sun, Adv. Opt. Mater. 2 (2014) 10–28. [2] I. Falcón Casas and W. Kautek, „Apertureless scanning near-field optical lithography“, in „Laser micro-nano-nanomanufacturing and 3D microprinting“, (Ed.) A. Hu, Springer 2018.

Resume : Femtosecond pulse lasers provide a strongly growing field of applications in e.g. medicine, precision machining, photochemistry, and microscopy. Controlling the temporal shape of the pulse has been the subject of intensive research [1] and has led to important discoveries and applications [2]. One of the leading techniques in controlling the pulse shape utilizing liquid crystal spatial light modulators [3]. A complete manipulation of the phase and amplitude of each spectral component is possible [4]. A temporal pulse shaper in combination with a high power oscillator has been designed and implemented. This novel system was applied for pulse compression and material processing with an evolutionary algorithm employing the transmission signal as feedback. [1] A.M. Weiner, D.E. Leaird, J.S. Patel, J.R. Wullert, Optics Letters, 15 (1990) 326-328. [2] W. WS, R. H, D. M., Science, 259 (1993) 1581-1589. [3] T. Baumert, T. Brixner, V. Seyfried, M. Strehle, G. Gerber, Applied Physics B, 65 (1997) 779-782. [4] M.M. Wefers, K.A. Nelson, Optics Letters, 20 (1995) 1047-1049.

Resume : Oxidic nanocomposite powders were obtained in a single step from tetramethyltin (TMT) and methyltrimethoxysilane (TMS) mixed vapors carried by ethylene (which plays also the sensitizer role) or nitrogen irradiated with an infrared laser beam in the presence of insufficient molecular oxygen. The XRD difractograms revealed the presence of both tin oxide tetragonal phases: rutile-type cassiterite SnO2 and romarchite SnO, as well as the less reported Sn3O4 phase and low amount of metallic β-Sn. Their core-shell morphology was revealed by TEM images, some of the cores being composed from aggregated very small nanocrystals, whereas the shells seem to be amorphous. Using HR-TEM, crystalline planes ascribed to SnO2 and SnO phases were identified in nanopowders. The Si-O bonds were identified in FT-IR spectra around 1000 cm-1 together with those assigned to Sn-O bonds (around 500 cm-1). The Raman spectra presented a large and convoluted peak (between 300 and 700 cm-1 Raman shift) attributed to a superposition from tin oxides and silicon oxide signals. Selected powders were used to prepare anode materials (mixed with carboxymethylcellulose and carbon black) which were tested in half-cell lithium ion batteries. The discharge capacity decreases from the initial values ~ 700 and 650 mAh/g to lower values ~ 550 and 500 mAh/g, respectively after 50 cycles. The lithiation-delithiation redox processes, as well as the solid electrolyte interface (SEI) layer formation were evidenced using cyclic voltammograms.

Resume : Curcumin (CR) is a natural compound with a well known antioxidant and therapeutic activity. Recently it has been found that its stability may be enhanced when incorporated in LDH matrix . Curcumin intercalated layered double hydroxide nanohybrid as a potential drug delivery system for effective photodynamic therapy in human breast cancer or skin cancer. The synthesis of the hybrid LDH-CR powder implies the dissolution of CR in water or another organic solvent which is miscible with water. Since the solubility of CR in water is very weak, in this study we have aimed to investigate the effect of the solvent employed for its dissolution on the structural and physico-chemical properties of the resulting hybrid materials. Four powders of curcumin (CR)-containing Mg2.5Al-LDH hybrids (Mg/Al molar ratio of 2.5) were prepared by co-precipitation (P) and reconstruction (R) using two different solvents for the dissolution of curcumin: (i) an alkaline aqueous solution, and (ii) ethanol. The reconstruction used the calcinated (460oC for 18 h) form of the parent Mg2.5Al-LDH powder. All the solids were characterized by X-ray diffraction (XRD) , DR-UV-Vis and ATR FTIR spectrocopies and thermal analysis (TG-DTA) . The FTIR-ATR spectra of the all the powders except the powder prepared via reconstruction in ethanol exhibit LDH characteristics, consistent with the XRD results. Matrix Assisted Pulsed Laser Evaporation (MAPLE) was employed for the deposition of hybrid LDH-CR thin films. Aqueous solutions of the as prepared hybrid LDH-CR powders were frozen and used as targets for MAPLE depositions. The films were deposited at 266 nm. MAPLE is considered a "soft" deposition technique t suitable to conserve the CR stability. XRD, scanning electron microscopy, atomic force microscopy, FT-IR spectroscopy and photoluminescence measurements were used to characterize the deposited films in order to evindence the influence of the preparation methods on the structural and photophysical characteristics of the hybrid LDH-CR films. The controlled release of CR from the LDH-CR powders and films obtained by MAPLE in different pH buffers was also investigated.

Resume : The nano-TiO2 synthesis method tends to promote a certain crystalline phase formation, to the detriment of others. Laser pyrolysis of TiO2 previous studies [1] demonstrated the method’s ability to produce controlled mixed phase TiO2 nanoparticles, by experimental parameter modulation, presenting high thermal stability and a wide range of dimensions. This work proposes W/Ti oxide nanocomposites synthesis using resonant CO2 laser excitation of C2H4, for promoting simultaneous photo-excited processes of dissociation and nucleation for nanometric W and Ti oxides, with air as oxidizing agent. We follow the less studied W oxide crystalline phase predilection, within the pyrolytic process of nucleation, and its dependency of titania anatase/rutile ratio. The specific geometry of precursor injector and O2/sensitizer concentration produces distinctive nanocomposite morphologies and characteristics, as resulted from X-ray Diffraction, EDS, TEM and Raman spectroscopy analysis. TiO2 nanoparticles synthesized by laser pyrolysis have been proven to exhibit good photocatalytic activity [2], superior to those of commercial titania (P25 Degussa) or obtained by chemical synthesis methods. Several independent studies suggested that mixed phase anatase/rutile nano-TiO2 provides better photodegradation efficiency than pure anatase titania, especially in VIS light, while tungsten oxides enhances the semiconductor’s charge separation efficiency. Thus, our study aims to generate a nanocomposite that combines the advantages of both nanomaterials, with tunable crystalline phase percentages and W contents, for further photocatalytic purposes. [1] A.G. Ilie et al, Appl. Surf. Sci. 427 (2018) 798-806 [2] M. Scarisoreanu,et al, Appl. Surf. Sci. 418 (2017) 491-498

Resume : Aggregates of spherical Fe carbides-Si hybrid nanoparticles (Fe-Si NPs) with a controllable mean sizes from 4 to 20 nm were synthesized by laser pyrolysis into a single step procedure. The resulted powders were also post-treated using controlled oxidation combined with inert gas annealing up to 800°C. Structural, morphological, elemental composition, magnetic and luminescence investigations on as synthesized or thermal treated Fe-Si NPs were performed in order to optimize the synthesis and thermal treatment parameters. In optimized conditions Fe-Si NPs with luminescence in near-IR to red color region and saturation magnetization up to 50 emu/g were obtained. Stabilized PBS based suspensions with 0.5 to 5 mg/ml powder concentration and around 150-350 nm mean aggregate dimension were prepared from Fe-Si NPs using sodium carboxymethylcellulose (CMCNa ) as stabilizer. In vitro screening tests regarding the toxicity, cell uptake and hyperthermia effect in human lung fibroblasts (MRC-5) and colorectal (Caco2) cancer cells were performed on PBS based suspensions with as synthesized or thermal treated Fe-Si NPs and stabilized with CMC-Na.

Resume : This work presents the preparation of VO2/TiO2 composite nanoparticles using laser pyrolysis technique. The obtaining process was based on sensitized mixtures of TiCl4 and VOCl3 precursors in the presence of air. Nanocomposites with controlled V:Ti atomic ratios were produced at different synthesis parameters. Structural, morphological and optical properties of the obtained powders have been revealed by X-ray diffraction (XRD), scanning and high resolution transmission electron microscopy (SEM, HR-TEM), UV-VIS and ellipsometry spectroscopy techniques. The results indicate that the nanocomposite particles have a core-shell morphology contains a VO2 core and the TiO2 anatase shell. The variations of vanadium-titania phase led to the obtaining of a new photocatalyst with thermochromic properties for multifunctional smart coatings applications.

Resume : Copper and titanium thin films (with closely 200 nm thickness) are grown using magnetron-sputtering technique. Applying accumulative pulses with low and very low fluences (from 200 to 10 mJ/cm2), incubation curves were studied versus the beam wavelengths. The experiments are conducted under normal atmosphere, but using a heated holder with temperature ranging from room T° up to 200°C. The effect of temperature in increasing the incubation leading to film damage is investigated using SEM images ad also by combining surface dynamic reflectivity analysis with two laser probes at 633 and 478 nm wavelength. The heating laser used in this study is Nd:YAG laser (Continuum 1064 nm, 10 ns, 10 Hz) and the output beam is used from the fundamental wavelength to 266 nm using second, third, and quadruple harmonic generator. Even if the absorption of photons is slightly different in case of Cu and Ti films, first results returned different incubation behavior versus wavelength that are also sensitively affected by the substrate temperature. Additional physico-chemical analysis (Ellipsometry, AFM and contact angle) are proposed to help in the interpretation of the results at several stages of the beam accumulation.

Resume : In this work, the influence of laser fluence on the morphological and compositional characteristics of triblock copolymers (i.e. poly(lactide-co-caprolactone)- block-poly(ethylene-glycol)-block-poly(lactide-co-caprolactone) (PLCL-PEG- PLCL)) thin films obtained by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) is reported. The surface morphology of the deposited layers was investigated by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The surface chemistry was studied by Energy-Dispersive X-ray spectroscopy (EDX) and Fourier-Transform Infrared spectroscopy (FTIR). The layers obtained at fluences up 0.5 J/cm2 exhibit homogenous surfaces, while for fluences starting with 0.6J/cm2, "icosahedron" and cubic type structures were observed. The influence and the contribution of both fluence and Chlorine presence on the formation of the different types of structures with complex symmetry on the surface of the deposited layer is also discussed. Acknowledgements: This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CNCS/CCCDI - UEFISCDI, project number PN-III-P2-2.1-PED-2016-1715, within PNCDI III and Nucleus program.

Resume : Pseudo-nondiffracting beams are widely used for various applications like optical tweezers or laser microfabrication. Due to their high length to width ration they are usually called “optical needles”. In this work we with start with construction of an “optical needle”, which in contrary to a Bessel beam has an arbitrary intensity distribution. We analyze ways to change the spatial position of the “optical needle” either in focal region of a lens, or in the Fresnel region of a diffractive element. Next, we introduce a spatial array of independent “optical needles” and report on physical limitations due to mutual interference of individual beams. In order to verify our theoretical considerations and numerical simulations we employ a spatial light modulator and experimentally observe controllable spatial arrays with various numbers and spatial separations of individual beam. Lastly, we examine distortions caused by propagation through planar air-dielectric interface and attempt to compensate them.

Resume : BiFeO3 is one of the most promising multiferroic material exhibiting, however, drawbacks as low dielectric susceptibility, poor chemical stability and high dielectric loss. Recently, we have demonstrated that joining doping and epitaxial strain engineering a nanoscale stripe structure was induced, resulting in a significant improvement of the dielectric characteristics. By high resolution transmission electron microscopy (HR-TEM) we have evidenced nanostripe domains with alternating compressive and tensile strain in the Y-doped BiFeO3 epitaxial thin films. Small band gap values of bismuth ferrite (BFO) have triggered the interest due to the photovoltaic and photocatalytic potential, for pure or cation doped BFO. However, energy related properties of BiFeO3 can be improved by coupling the strong ferroelectricity of BFO with chemical stability and small band gap value of LaFeO3 within thickness graded heterostructures. Thin films of BFO on 5-20 nm thick epitaxial LFO films deposited on different strain-induced substrates, have been obtained by RHEED- assisted Pulsed Laser Deposition. Their functional dielectric, optical and photolytic behaviour has been unravelled in connexion with complex ensembles of nanoscale phase/nanodomain fluctuations within the epitaxial films.

Resume : The research is focused on fundamental study of processes and effects of interaction of short and ultra-short laser irradiation with optical transparent nanocomposite biocompatible polymers. Laser generation from ultraviolet to near infrared regions of the spectrum is applied. The high optical transparency of the biopolymers in this range and the requirements for precision and high quality processing demands for knowledge of the mechanisms and physical processes during interaction of laser irradiation with the material. Changes in physical and chemical properties due to laser surface modification are experimentally and theoretically studied. Various process parameters (laser wave length, pulse duration, fluence and number of pulses) are examined. Complex data of successful modification and activation of the surface of PDMS elastomer by using traditional laser processing and subsequent successful functionalization of the laser modified surface are provided. The preliminary results show promising prospects of implementation of such laser-based methods for micro- or nano-processing of optically transparent biopolymers for interface devices in bioengineering technologies such as neural implants.

Resume : The specific characteristics of tin dioxide (SnO2) i.e. high chemical and thermal stability make it suitable for a large area of applications such as displays, optical-electronic devices, and gas sensors. In this work, we report on the morphological and structural properties of SnO2 thin films grown by matrix assisted by pulsed laser evaporation (MAPLE). The thin film samples were obtained from a frozen target of SnO2 nanoparticles in different concentrations (1-5% w/w) and water as a solvent. A parametric study was carried out based on target composition, laser fluence and number of pulses in order to find the optimal deposition parameters for obtaining uniform and continuous layers. Investigations by atomic force microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy evidenced that the thin films deposited by MAPLE could be used as active materials in gas sensors, with a high sensitivity and response speed to various analyses. Acknowledgement: PED 65/2017 “Modular Aircraft Platform for Intelligent Atmospheric Monitoring (MAPIAM)” Keywords: SnO2, thin films, MAPLE, gas sensor

Resume : .

Resume : Solid Oxide Fuel Cells (SOFC) are ‘green’ electrochemical devices that transform hydrogen or other hydrocarbons into electricity with high efficiency and zero emission of pollutants. The cells are essentially formed by a dense solid oxide electrolyte and two porous electrodes. A typical cell configuration is an yttria-stabilised zirconia (YSZ) electrolyte, a Ni-YSZ fuel electrode and an YSZ-LSM (LSM: La1-xSrxMnO3) oxygen electrode. In this work we study the laser generation of patterned electrode-electrolyte interfaces in order to reduce cathode activation polarisation, which is one of the main contributions to the losses of a Solid Oxide Fuel Cell. A commercial computer-controlled Q-switched laser source emitting at λ=532 nm with 5 ns pulse width has been used to perform this patterning. Different micro-patterns, square and hexagonal arrays, on YSZ and Ni-YSZ plates have been tested. After that, symetrical cells have been prepared to determine their activation polarisation by Electrochemical Impedance Spectroscopy (EIS). Aspect ratio obtained by patterning is been also studied for the technological assessment of the future fabrication processes. Patterned cells show an improvement in the cathodic activation processes. The decrease in polarisation with respect to unprocessed ones is about 30%. Further studies are in progress to increase the contact surface and reduce the polarization.

Resume : Free-electron lasers (FELs) can generate ultrashort, coherent, X-ray flashes that are continuously tuneable and a billion times brighter than those from the best synchrotron X-ray sources. They require a photocathode capable of generating bright, low emittance bunches of electrons so atomic systems can be studied on their natural length and timescales. Overall FEL performance is dictated by the quality of the initial electron beam, meaning improvements require further understanding of the photocathode emission process. In this work, a predictive theoretical approach developed by the Harrison Group, building on the Spicer three-step model, will be employed to study new photocathode materials. Density Functional Theory calculations will be used to relate the surface electronic structure of AgBa and CuBa to the photoemission process. Alloys constituting stable, high work function metals (Ag, Cu) paired with an unstable, very low work function metal (Ba) can lead to stable intermediate phases with desirable photocathode properties versus pure metals. Increased quantum efficiency, low work function and low emittance are desired from the alloys to be studied. Achieving these goals will allow higher energy beams to be produced or a reduction in length and therefore cost of FEL facilities.

Resume : Dual-laser induced forward transfer process consists in irradiating a solid thin film deposited on a transparent donor substrate by a first long duration laser pulse, to locally melt the film, followed by a second irradiation with an ultrashort laser pulse to initiate material transfer in the liquid phase toward a receiver substrate. This method has been recently demonstrated as a versatile method to print high-resolution (<2 µm) patterns with a large working distance (>40 µm). However, the printing dynamics associated with these performances is only partially understood so far. In this paper, we focus the investigations on this aspect allowing further optimizations. Two key parameters that influences the ejection dynamics are discussed. First, the temperature evolution of the thin copper film within a quasi-continues wave (QCW) pulse heating process is calculated and visualizations of ejection events under different temperatures reveal the influence of Cu temperature on the ejection dynamics. Second, for a given Cu temperature, by increasing the fluences of the femtosecond pulse, the visualizations reveal a fluence threshold under which no ejection is observed, followed by the release of a single droplet, multi droplets and ultimately the formation of a jet. With both droplet and jet modes of ejection, we show clean microstructures (no debris) successfully printed onto a Si receiver placed as far as 60 µm away from the donor film.

Resume : Novel printing methods represent a class of emerging technologies, with applications in the field of microelectronics, which are cost-effective techniques with the ability to deposit highly resolved features. Typically, popular printing technologies, such as inkjet printing, deposit only low viscosity fluids. In a broad range of emerging applications, alternative printing techniques would enable the handling of materials with much higher viscosities. Laser-induced forward transfer technique (LIFT) meets these requirements and has already been applied for the direct printing of devices and components. However, in order to improve the process’ reproducibility and printing resolution, further research has to be conducted, regarding the rheological characteristics of the printable fluids and their jetting dynamics. In this work, we employ both time-resolved and high-speed imaging in order to investigate the formation and expansion of the liquid bubble, as well as the liquid jet’s propagation. The study is carried out both for Newtonian and non-Newtonian fluids, for a big range of viscosities. From the time-resolved experiments, it was observed that fluid ejections are initiated by the rapid expansion of a micrometer-sized vapor bubble that forms for both types of fluids. High-speed imaging illustrated all the different types of ejection regimes which are influenced by the fluid’s metal loading, the fluid’s viscosity, fluid thickness on donor and laser fluence on donor. Furthermore, a computational model is also utilized in order to gain more insight on the transfer mechanisms of the process. The simulation predictions are validated against experimental results, being in good accordance with the latter ones. Finally, we present an overall methodology for process parameters on Newtonian and non-Newtonian fluids to offer a criterion for stable operation with LIFT technique.

Resume : Networks of silver nanowires (Ag-NWs) can be electrical conductive and optically transparent at the same time. Thus, Ag-NWs are promising candidates to substitute transparent and conductive oxides like indium-tin-oxide. Furthermore, they can be deposited on flexible substrates without losing their functionality. Lasers have been previously used to perform a selective sintering or selective ablation of formerly deposited Ag-NWs by other means such as spraying, screen-printing or spin coating. However, direct-write methods for printing patterns can be suitable in order to reduce the amount of material used. Attempts of printing Ag-NWs by means of inkjet required a previous sonication step in order to avoid clogging issues. However, the reduction of the Ag-NWs length compromises their optical and electrical performance. In this work, we propose the use of laser induced forward transfer for printing Ag-NWs in a digital manner without altering their original properties. Inks with different concentrations of Ag-NWs have been evaluated. The effects of the laser pulse energy on the printed material has also been studied. It has been found that the optical and electrical properties of the printed patterns basically depend on the concentration of Ag-NWs after drying. Different patterns and electrodes have been printed by LIFT with good optical and electrical characteristics comparable to those deposited by traditional methods in large areas.

Resume : The question whether precise modeling of laser-produced plasmas can be achieved using simple statistical laws of equilibrium is a subject of controversial discussions since the early experiments of laser-matter interactions [1]. The successful description of spectral emission from laser plasmas by the model of local thermodynamic equilibrium observed in some cases [2] led to material analysis via so-called “calibration-free” laser-induced breakdown spectroscopy [3]. Since the first report, more than hundred papers have been dedicated to the subject with a rather poor outcome: calibration-free laser-induced material analysis is nowadays considered as quantitative for major elements while it is qualitative or semi-quantitative for minor and trace elements. The precise reasons for the low measurement accuracy are not yet well identified. Due to the large variability of experimental conditions and sample materials, multiple sources of measurement errors have been reported. Among them, the non-validity of the model is often inferred. In a recent paper, we have shown that the properties of laser-induced plasma can be tailored to allow for precise modeling by choosing appropriate experimental conditions [4]. Material ablation with ultraviolet nanosecond laser pulses in an argon atmosphere generates a plasma that is spatially uniform and in local thermodynamic equilibrium, two properties which are generally very difficult to achieve simultaneously. We took advantage of this “ideal” radiation source to investigate its use in analyses of complex materials via calibration-free laser-induced breakdown spectroscopy. A critical analysis of the measurement uncertainties is given and the perspectives of the application to materials such as glasses, alloys and organic materials (food) are discussed. [1] S. Elezier, A. D. Krumbein, D. Salzmann, J. Phys. D: Appl. Phys. 11, 1693 (1978). [2] J. Hermann, C. Boulmer-Leborgne, B. Dubreuil, I. N. Mihailescu, J. Appl. Phys. 74, 3071 (1993). [3] A. Ciucci, M. Corsi, V. Palleschi, S. Rastelli, A. Salvetti, E. Tognoni, Appl. Spectrosc. 53, 960 (1999). [4] J. Hermann, D. Grojo, E. Axente, C. Gerhard, M. Burger, V. Craciun, Phys. Rev. E 96, 053210 (2017).

Resume : Rapid and precise stratigraphic analyses of metal coatings are accessible by Laser-Induced Breakdown Spectroscopy (LIBS) where the plasma emission data are converted into stratigrams [1,2]. This is demonstrated for copper and nickel coating systems on steel. A ns-pulse Nd:YAG laser (1064 nm and 532 nm) was employed. The ablation rate depends strongly on the wavelength. This cannot be explained by the optical absorption of the substrates. The thermal diffusion length together with plasma shielding can explain the observed behaviour semi-quantitatively. Plasma shielding affects the ablation process with the near-infrared wavelength in contrast to the visible case where it is negligible. These results show that the beam-plasma interaction not only plays an important role in the quantification of the ablation rate, the depth resolution and the analysis depth, but also in the plasma heating which itself affects the plasma emission efficiency. [1] T. Nagy, U. Pacher, H. Pöhl, W. Kautek, Appl. Surf. Sci. 302 (2914) 189-193. [2] U. Pacher, M. Dinu, T.O. Nagy, R. Radvan, W. Kautek, Spectrochimica Acta (2017), in press.

Resume : The effort of automotive industry is the increasingly use of aluminum alloys to reduce the weight of the car. Regarding the lifetime of electrodes and the process reliability resistance, spot welding is not applied for joining of aluminum sheets. Instead, more expensive processes must be used, like riveting with supplementary component. This is caused by the electric isolating oxide layer at the sheet surface. This layer normally shows an irregular topography, causing a locale temperature increase and therefore high electrode wear. In this study, a new concept to increase the electrode lifetime and process reliability is reported. Using Direct Laser Interference Patterning, periodic surface patterns are produced at the contact area between the electrode and the sheet for influencing the contact resistance. By interfering two picosecond pulsed laser beams on the cupper electrode surfaces, line-like structures with a spatial period of 5 µm are produced. The resulting topography and morphology were analyzed by confocal microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. The electrical resistance between the contact partners copper and aluminum was measured during spot welding tests and contact resistance studies. A reduction up to 50 % of the electrical resistance by treating the electrodes could be achieved compared to an untreated reference.

Resume : Glass welding by ultrashort laser pulses is a method of glass bonding developed in laboratory and currently adapted as an industrial process. This method presents many advantages in term of resistance, process speed, hermeticity and biocompatibility compared to the classical glass bonding technics. The principle relies on the nonlinear absorption of the focused laser beam at the interface of the glass plates to weld. The demonstration of this method has been realized on glass plates having very high roughness and flatness quality, to obtain an optical contact between the samples. The industrialization of the method involves to overcome this quality requirement and process glass plates with ordinary surface quality. The study focuses on the analyses of the properties differences between welding seams realized on optically contacted and non-contacted samples. Welded seams have been created in borosilicate glass using 300 fs duration pulses with a tunable repetition rate up to 2 MHz. Welding area on optically contacted samples can be inscribed at low energy and are completely transparent, but are limited in dimension by the optical contact. Welding of ordinary glass plates without optical contact can be created by increasing the energy. This reduces the transparence of the welding seams and increases the residual stress, but allows to generate large welding area. The samples have been analyzed by Raman spectroscopy and third harmonic generation microscopy.

Resume : Bonding of glass on semiconductor is of great interest for the field of MEMS development, but classical methods like anodic junction are not suitable for every combinations of materials. The welding of glass on semiconductor by laser pulses could offer an alternative presenting advantages in term of mechanical resistance, hermeticity and biocompatibility. The use of nanosecond laser pulses has first been demonstrated, where the semi-conductor only is melted by the absorption of the laser pulses. The bonding of glass on semi-conductor has then been demonstrated by femtosecond laser pulses, which is known to reduce the heat affected zone and thus reduce the residual stress in the materials. The study focuses on the comparison on the welding formation process, by analyzing the welding seams by Raman spectroscopy. The shift and the broadening of the typical Raman peak of Silicon at 520 cm-1 can be linked to the residual stress in the material after processing. The experiments have been conducted on borosilicate glass and silicon, with a femtosecond laser generating 300 fs duration pulses at a tunable repetition rate up to 2 MHz, and a tunable wavelength between 515 and 1030 nm. The samples have been compared to those produced by a nanosecond laser generating 30 ns duration laser pulses at 1064 nm. The shift of the Raman spectra of the pristine materials and of the welded seams have been analyzed, highlighting the advantages of femtosecond laser welding over nanosecond.

Resume : Sub-µs Laser annealing (LA) is the preferred annealing technique in nano-electronics when strongly localized heating is needed in the manufacturing process flows. The application of such process in future electronic device generations is hindered by the difficulties in the process control and understanding. Accurate modelling is mandatory for process optimization and a seamless integration in the manufacturing flow.. Modelling development is a difficult task since devices are characterized by complex 3D structures with ~nm wide elements made of different materials/phases which may see their properties changing during the annealing process. We present a computational tool (LIAB: LASSE Innovation and Application Booster) for the simulation of LA process. This is a complex self-consistent problem, where the heating is evaluated by means of a self-consistent solution of the time harmonic solution of the Maxwell equations. The self-consistency derives from the dependence of the optical constant on the temperature, the phases (amorphous, crystal, liquid) and the alloy fraction. The main features of the package are: • Many materials calibration as a function of T and phases; • Coupling with Electromagnetic Simulations in 2D and 3D nano-structured topographies; • Multiple-dopant models simulating atoms diffusion solubility and segregation; • Alloy model (e.g. SiGe) and multiple phases; Some application cases will be discussed in order to demonstrate the potentiality of the package.