Laser interaction with advanced materials: fundamentals and applications

Resume : Although a large variety of antimicrobial agents are currently available, they are often rendered ineffective by the ability of many types of microorganisms to develop genetic resistance and to grow in multicellular structures known as biofilms. Of the various strategies to inhibit microbial biofilms, use of bioactive surfaces that are resistant to microbial colonization is the most promising approach. In this respect, we have prepared thin composite biopolymeric films containing either natural (flavonoid) or synthetic (antibiotic) bioactive substances by means of a matrix assisted pulsed laser evaporation (MAPLE) approach that involves use of a pulsed KrF* excimer laser source (λ = 248 nm, τ = 25 ns, ν = 10 Hz). Chemical bonding in the films was evaluated using Fourier transform infrared (FTIR) spectroscopy. An assay to assess the antimicrobial performance of MAPLE-modified surfaces was performed by spectrophotometric counting of viable cells. As revealed by scanning electron microscopy, the MAPLE technique did not affect the surface properties of the deposited materials for biomedical applications. The flavonoid-containing thin films showed increased resistance to microbial colonization, highlighting their potential to be used for the design of anti-biofilm surfaces. Since these bioactive substance-containing composites do not contain antimicrobial agents, there is lower risk of the development of microbial resistance.

Resume : We report the Laser Induced Forward Transfer (LIFT) of antibodies from a liquid donor film onto paper receivers for application as point-of-care (POC) diagnostic sensors. Paper was chosen as the ideal receiver due to its inherent biocompatibility, wicking properties, wide availability and price, all of which make it an efficient and suitable platform for POC diagnostic sensors. A modified LIFT procedure, referred to as Dynamic Release Layer (DRL-LIFT), has been employed to ensure the viability of the biomolecules post-transfer. The laser used was a KrF excimer operating at 248 nm with a repetition rate of 1 Hz, pulse duration of ~10 ns, and delivering a maximum energy of ~400 mJ per pulse. Both enzyme-tagged and untagged IgG antibodies were LIFT-printed. The functionality and immunological reactivity of the LIFT-printed antibodies was confirmed by developing and demonstrating an Enzyme Linked Immunosorbent Assay and establishing the standard calibration curve for the LIFT-printed pixels. Additionally, it was shown that the localisation of the LIFT-printed pixels and immobilisation of the antibodies, a pre-requisite for paper-based diagnostic devices, was maintained throughout the wet-bench process which further justifies the spatial patterning ability of LIFT. This work demonstrates that LIFT is a technique capable of transferring antibodies onto a paper substrate accurately, reproducibly and with minimal loss of biochemical viability.

Resume : Amorphous chalcogenide thin films are of high current interest for technological applications as optical storage media or waveguides for photonic integrated circuits. During the last decades, the Pulsed Laser Deposition (PLD) technique has become a method of choice in producing such films in laboratory. Using bulk targets of pure and rare-earth (Er, Pr) doped Gallium Lanthanum Sulphide (GLS) we have deposited chalcogenide thin films on Si and SiO2 substrates in a vacuum chamber using nanosecond, picosecond and femtosecond ablation. Several tens of samples have been deposited in different conditions, in order to study the influence of various parameters, as laser wavelength and pulse width, fluence, target – substrate distance, background pressure etc. The produced samples have been characterized by contact profilometry, Raman spectroscopy, time-of-flight secondary ion mass spectrometry (TOF-SIMS), variable-angle spectroscopic ellipsometry (VASE), optical transmission, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). We will present the main conclusions of this systematic study, with special focus on some peculiar effects observed in the morphology, structure, composition and optical properties of the deposited thin films.

Resume : Recently, low dimensional piezo- and ferroelectric nanomaterials have attracted much attention because of their potential application in nanodevices such as nanosensors and actuators, nanogenerators and nanopiezotronics. Among them, Potassium Sodium Niobate (KNN) ceramics have received increasing attention because of their good piezoelectric and ferroelectric properties. KNN is made from volatile alkali metal compounds, which require carefully controlled manufacturing conditions and low reaction temperatures. In this study, KNN nanorods were prepared by PLD on sapphire and platinized silicon substrates at relatively low deposition temperature. Sintered targets with nominal composition of Na0.5K0.5NbO3 were ablated in 0.2 mbar oxygen atmosphere by the ultraviolet line of a Nd:YAG laser system (λ=266 nm, pulse duration of 5 ns, repetition rate of 10 Hz, and energy density of 0.1 J/cm2). The deposition temperature was varied between 400 and 600 ºC. The films were then analyzed by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), optical transmittance and reflectance spectroscopy, capacitance-voltage characteristics and Piezo-electric Force Microscopy (PFM). SEM micrographs and XRD measurements showed that well crystallysed KNN rods could be obtained at 550ºC with good structural, dielectric, and ferroelectric properties. The measured dielectric constant was 300 and the remanent polarization and coercive field values were 7 kV/cm and 24 kV/cm, respectively. The nanoscale piezoelectric data obtained with piezoresponse force microscopy provide a direct evidence of strong piezoelectricity in as-prepared KNN rods.

Resume : We report on the deposition of polycaprolactone (PCL)-polyethylene glycol (PEG) composite coatings on titanium and <100> double side polished silicon substrates by both matrix assisted pulsed laser evaporation (MAPLE) and dip coating (DC) techniques using chloroform as a matrix solvent. PCL is known for its excellent tensile properties, flexibility and biodegradability, but a slow degradation rate. Therefore, PCL has been blended with the more soluble PEG in order to obtain biodegradable polymeric composite coatings. PEG and PCL were mixed in 1:3, 1:1 and 3:1 ratios. In order to find the optimal MAPLE deposition parameters, we conducted a study of laser fluence (0.2 - 0.5 J/cm2). On the other hand, in the case of DC method, we varied the withdrawal velocity to analyze the variation of the thickness and the uniformity of the thin films. FTIR spectra showed that the films are stoichiometric with no polymer decomposition. For composite coatings, PEG-PCL diffraction peaks have indicated that both polymers can crystallize when they are mixed. Surface morphology of composite coatings depends on the chemical composition, polymeric mixture ratio and deposition method while the wettability studies proved that the composite coatings exhibit highly hydrophilic surfaces. As such, the fabricated biodegradable PEG-PCL composite coatings can constitute a versatile biomaterial for tissue engineering applications.

Resume : We report on the deposition by Matrix Assisted Pulsed Laser Evaporation technique of biomimetic nanocrystalline apatite coatings on titanium substrates. The targets were prepared from metastable, poorly crystalline apatite powders, synthesized by a biomimetic approach. For the deposition of thin films, a KrF* excimer laser source was used . The analyses revealed the existence, in synthesized powders, of labile non-apatitic mineral ions, which form a hydrated layer at the surface of the nanocrystals. The thin film investigations showed that the structural and chemical nature of the nanocrystalline apatite was prevalently preserved. The perpetuation of the non-apatitic environments was confirmed. Our study demonstrated that MAPLE is a suitable technique for the congruent transfer of a delicate material, such as the biomimetic hydrated nanohydroxyapatite

Resume : The treatment of bone defects remains the major challenge of reconstructive surgery. In order to repair the defects caused by tumors or other disease, one can improve the properties of implants surface by adding organic or inorganic materials (polymers, bioglass). Simple and mixtures of poly(ε-caprolactone) (PCL) and poly(lactic acid-co-glycolic acid) (PLGA) in different ratios (1:3, 1:1, 3:1) have been deposited by matrix assisted pulsed laser evaporation (MAPLE) and dip-coating to produce thin films on titanium, glass and silicon substrates. We identify the optimum deposition conditions with respect to the structural, morphological, and wettability properties of films. In the case of MAPLE technique, PCL/PLGA composite films were deposited at different laser fluences, in the range (300-500)mJ/cm2, while the withdrawal speed was varied for dip-coating. Fourier transform infrared (FTIR) spectrometry evidenced that the chemical composition of coatings deposited by the two methods was preserved whereas the X-ray diffraction (XRD) studies revealed the presence of diffraction peaks of PCL only. SEM investigations exhibited a dependence of surface morphology on the chemical composition, polymeric mixture ratio and deposition method. Depending on the polymeric mixture ratio and deposition method, wettability tests performed on the polymeric coatings showed a either hydrophobic or hydrophilic behaviour.

Resume : The latest research and advances in bio-nanotechnologies allows us to combine many of the available biocompatible polymers for tissue engineering applications. In this study, polyethylene glycol (PEG)/Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) composite coatings were deposited on grade 4 CP titanium and silicon substrates by Matrix Assisted Pulsed Laser Evaporation (MAPLE) and dip-coating (DC) techniques. These two polymers were chosen for their biocompatible properties, but also for their solubility or degradation properties. Three polymeric weight ratios were considered for thin films depositions (1:1, 1:3, 3:1). PEG/PHBV composite films were deposited by MAPLE at different laser fluences, in the range (300-500)mJ/cm2, while for dip-coating the withdrawal speed was varied between 60-100mm/min. Fourier transform infrared (FTIR) spectra evidenced the preservation of chemical composition for both deposition methods whereas the X-ray diffractograms recorded on the composite films revealed the presence of diffraction peaks typical for PEG and PHBV polymers. SEM images showed a dependence of surface morphology on the chemical composition, polymeric mixture ratio and deposition method. Also, the surface wettability investigations showed different hydrophilic behavior, depending on the polymeric mixture ratio and deposition conditions.

Resume : To simulate the temperature profile in the corresponding film used the following laser parameters: pulse duration 10 ns, the intensity of the laser beam is varied in the range of 14-52 MW/cm2. The distribution of the temperature field in the film during its heated single laser beam described nonstationary heat equation, which is solved the numerical by finite element method. During the laser pulse of 10 ns with intensity of 52 MW/cm2 the temperature up to 1800 K can be reached on the sample surface. The temperature at the surface grows for some time after the laser pulse (t = 10 ns) finished. Further cooling of the film is due to the flow of heat from the film surface, and also due to heat transfer in the silicon substrate. After 30 ns from the beginning of irradiation the annealing temperature on the surface of the film is stabilized. The stabilized temperature depends on the laser intensity: the higher intensities, the higher temperature. The temperatures of the sample at higher intensities of laser irradiation are enough to stimulate the phase transition of SiOx film into nanocomposite SiO2(Si) film with Si nanocrystals.

Resume : Pyrene is a polycyclic aromatic hydrocarbon made of four fused benzene rings. Usually used in dyes and dye precursors, its derivatives are also valuable molecular probes via fluorescence spectroscopy: having high quantum yield and lifetime, its derivatives have been used to determine specific environments, e.g. photodegradation effects related to laser processing. We present here results on a newly synthesized bis-pyrene compound that, besides the typical fluorescence, also exhibit semiconducting properties. Thin films have been grown by vacuum thermal evaporation on oxidized silicon, and on transparent suprasil substrates. The influence of the temperature on the thin film's morphology, optical, and electrical properties, are discussed. Micrometric-sized pixels have subsequently been printed by laser-induced forward transfer (LIFT) using a Nd:YAG laser source (355 nm, 50 ps pulse duration), to produce functional organic thin film transistors (o-TFTs). Top-contact vs. bottom-contact configurations are presented, and the influence of the ambient pressure during LIFT procedure is discussed.

Resume : Carbon coatings have been reviewed in terms of its advantages on the newly developed electrode materials for rechargeable lithium-ion battery, in addition to various metals and metal oxides. In this frame, this paper reports the use of laser pyrolysis method for preparing carbon-coated MoS2 (C-MoS2) nanoparticles from solid precursor. To obtain C-MoS2 nanoparticles, molybdenum hexacarbonyl Mo(CO)6 (Mo donor) hydrogen sulphide H2S (S donor) and ethylene C2H4 (C donor) were used as reactant gases. Also, sulphur hexafluorine SF6 has been used as energy transfer agent. To obtain a reasonable vapor pressure, the Mo(CO)6 solid precursor was heated between the melting and boiling temperatures (150 0C-156 0C). The synthesized C-MoS2 nanopowders were investigated by scanning electron microscopy equipped with an energy dispersive X-ray analyzer, Raman spectroscopy and X-ray diffraction techniques. The results demonstrated that the C-MoS2 have a well-developed crystalline structure.

Resume : Nanofoams are permeable, nanostructured materials, which have applications in many areas, including electronics, biological sciences and aerospace engineering [1-4]. Nanofoam fabrication using an ultrafast laser enables control over the precise location as well as the fabrication rate, leading to the possibility of applications such as evanescent sensors and energy harvesting devices. Here, we extend our initial work on glass nanofoam fabrication [5] by demonstrating the production of metal, ceramic, polymer and novel chalcogenide glass nanofoam at atmospheric pressure, with dimensions of ~hundred microns in height and millimetre-square in area. Our investigation showed that both the volume and density of the nanofoam was a function of both the material as well as the exposure protocol (number of pulses and their energy density). [1] Brock S L (2007), Science (New York, N.Y.) 317 460–1. [2] Fischer A E et al. (2007), Nano Letters 7 281–6. [3] Viswanathan P et al. (2012), J. Amer. Chem. Soc. 134 20103–9. [4] Burchell M J et al. (2006), Ann. Rev. Earth and Plan. Sciences 34 385–418. [5] Grant-Jacob J A et al. (2014), J. Phys. D: Appl. Phys. 47 055105.

Resume : We report on the synthesis by PLD of bioactive glass (BG) thin films of SiO2–Na2O–K2O–CaO–MgO–P2O5 compositional system onto ultra-high molecular weight polyethylene (UHMWPE) acetabular cups, and their characterization by immersion in simulated body fluid (SBF). After 42 days of immersion in SBF under homeostatic conditions, a partial dissolution of the BG film was observed, followed by the chemical growth of a carbonated hydroxyapatite layer. This behavior of the PLD glass coatings is the result of ion exchanges between BG and SBF solution, and is in accordance with the bioactivity mechanism proposed by Hench. Fourier Transform Infrared Spectroscopy evidenced the strong depolymerization of the deposited BG coatings, favorable to a high bioreactivity and rapid osteointegration. The top-view Environmental Scanning Electron Microscopy showed significant morphological changes, the typical PLD film surface being converted after 42 days of soaking in SBF to a rough one consisting of acicular crystals. Energy Dispersive Spectroscopy analysis demonstrated the conservation of the targets stoichiometry after transfer. Moreover, the parent BG films showed an excellent purity, without any traces of contamination. We consider that the functionalization of UHMWPE acetabular cups with BG films by PLD opens good prospective for the fabrication of implants with improved osteoinductive characteristics.

Resume : We report on biological hydroxyapatite (HA) thin films (1.29 – 3.3 µm thick) of human (dentine, DHA) and animal (bovine, BHA and ovine, OHA) origin synthesized by PLD. X-Ray Diffraction studies evidenced a monophasic HA structure of the films, with a crystallinity degree influenced by the biological origin. Scanning Electron Microscopy investigations showed film surfaces with moderate roughness consisting of particulates with a mean size of ~2μm. Energy Dispersive Spectroscopy analysis revealed the presence of traces of Mg, Na, Cl, F and C besides the prevalent Ca and P. This composition is similar to that of the genuine human healthy bone. The OHA thin films exhibited the highest adherence (~69 MPa) to titanium substrate as compared to the DHA (50 MPa) and BHA (42 MPa) structures. Based upon their improved performances and low cost manufacturing, these renewable biomaterials could develop into valuable competitors to commercial HA for implantology applications.

Resume : Azo-dyes and organometallic compounds have been studied lately, in bulk or as thin films, due to their particular optical properties for potential applications in optoelectronics and sensors. Such particular properties include non-linear interactions, e.g. two-photon absorption, second harmonic generation, optical limiting and all-optical poling. We present here a study on the LIFT printing of micrometric-sized pixels, using MAPLE deposited thin film donors. Details about the influence of the pixel’s morphology, structure, interface, and thickness, on their optical behaviour, are presented and discussed.

Resume : The overall aim of this work is to build a new kind of micro-system for the detection of toxic metals, emerging pollutants and pathogens in both sewer overflow and river water which responds to a strong societal demand in public health and environmental safety. New multi-sensor networks are based on carbon materials such as graphene, Diamond-Like Carbon (DLC), boron-doped DLC and nitrogenated DLC. Thin films have been synthesized on standard silicon or silicon nitride substrates by either nanosecond or femtosecond pulsed laser deposition. The doped coatings have been deposited at room temperature by ablating graphite targets with an ultrashort laser (800 nm, 35 fs, 1 kHz). Doping with boron has been performed by ablating alternatively graphite and boron targets whereas doping with nitrogen has been obtained by ablating graphite in a nitrogen atmosphere with and without plasma assistance. A KrF excimer laser (248 nm, 20 ns, 10Hz) has been also used for the synthesis of few-layer graphene. The carbon materials were used as working electrodes by using cyclic voltammetry to detect electroactive pollutants (heavy metals, phenols, …). The structural and morphological film characteristics have been correlated with the electrochemical performances. The femtosecond laser technology was also used to design flexible analytical microsystems.

Resume : The ability to form oxygen vacancies associated with the easy change of valence between Ce(IV) and Ce(III) confers to cerium oxide properties that have attracted great interest. Such properties are very attractive for the realisation of devices based on ceria (CeO2) nanoparticles in many fields. It has also an important role in promoting noble metal activity, such as Au, Pt and Ag. Recently, CeO2 was also investigated as a catalyst support for electrochemical biosensors, because it is chemically inert, biocompatible and a good electrical conductor. In this work, CeOx thin films are prepared by ablating a metallic cerium target under reducing atmosphere to minimize the cerium oxidation during the deposition. A systematic study has been made regarding the influence of various parameters both on the surface composition and on the structure of the deposited films. The effects of the background pressure, the composition of the gas, the target-substrate and the radial distance have been studied. A correlation between the deposition parameters and the valence states of cerium in the deposited films is established. We demonstrate that PLD is a powerful method that allows control of the crystallinity, morphology (grain size) and the composition (Ce3+ and Ce4+ ions contents, oxygen vacancies) of the deposited films. We also demonstrate that it is possible to produce films containing high surface concentrations of Ce3+, up to 70% of the total cerium content. The possible core-shell structure of the nanoparticles is discussed.

Resume : Low energy Ar+ ion irradiation has been applied to an Au/BiFeO3/Pt capacitor structure before deposition of the Au top electrode. The irradiated thin film exhibits multilevel resistive switching without detrimental resistance degradation, which makes the intermediate resistance states more distinguishable as compared to the non-irradiated thin film. The stabilization of resistance states after irradiation was discussed based on the analysis of conduction mechanism [1] during the resistive switching, which was investigated by means of temperature-dependent current-voltage measurement from room temperature to 423 K. The retention of the LRSs was improved in a controllable manner by Ar+ ion irradiation. Stabilization of the LRSs is attributed to the reduced randomicity of the defect states induced by manipulation of the oxygen vacancy concentration via irradiation. The present work shows that low-energy ion irradiation is an efficient tool for tuning of the resistive switching properties Au/BiFeO3/Pt capacitor structures [2]. [1] Y. Shuai, X. Ou, W. Luo, N. Du, C. Wu, W. Zhang, D. Bürger, C. Mayr, R. Schüffny, S. Zhou, M. Helm, and H. Schmidt, Nonvolatile Multilevel Resistive Switching in Ar+ Irradiated BiFeO3 Thin Films, IEEE Electr. Dev. Lett. 34, 54-56 (2013) [2] X. Ou, Y. Shuai, W. Luo, P.F. Siles, R. Kögler, J. Fiedler, H. Reuther, S. Zhou, R. Hübner, S. Facsko, M. Helm, T. Mikolajick, O.G. Schmidt, and H. Schmidt, Forming-Free Resistive Switching in Multiferroic BiFeO3 thin Films with Enhanced Nanoscale Shunts, ACS Appl. Mater. Interfaces 5, 12764-12771 (2013)

Resume : Tin based nanoparticles have been synthesized by laser pyrolysis using thetrametyl tin as reactive precursors and ethylene as energy transfer agent. Regarding their application, as electrode for rechargeable battery, the dimensions of the tin based nanoparticles are required to be minimum. Considering this requirement, the experimental parameters have been varied and the mean diameter of the tin nanoparticles has been decreases from 120 nm to 45 nm, as deduced from XRD and TEM analysis. The synthesis of small nanoparticle dimension has performed obtained by decreasing the residence time and the reactive zone, and varying the temperature of pyrolysis flame between 520 to 560 0C. The inlet nozzle diameter, dedicated for reactive gas mixtures, and the thetrametyl tin vapor flow strongly influences the reactive mechanism and consequently the nanoparticle dimensions. Furthermore, when the flame reactive temperature exceed 600 0C a minor ethylene decomposition is generated. The EDX elemental evaluation and Raman Spectroscopy revealed that Sn- nanoparticles with high C content (around 20 at.%) have been synthesized.

Resume : The aim of the study is to critically compare hydroxyapatite thin films deposited on Ti substrates by two different laser techniques: pulsed laser deposition (PLD) and matrix assisted pulsed laser evaporation (MAPLE). An enhanced chemical and biological activity is expected for the films deposited by MAPLE from nanopowders due to the extended surface area in contact with the reactive media. The experiments were carried out in a reaction chamber using the same KrF* excimer laser source (λ=248nm, τ(FWHM)≈25ns). All films were post-deposition treated in a flux of water vapors in order to improve morphology and crystallinity. Specific coating surface features were evidenced by optical, scanning electron and atomic force microscopy investigations. They were shown to depend on deposition technique. The crystalline structure of the coatings was monitored by X-ray diffraction before and after thermal treatment. To evaluate the biocompatibility of coatings, cellular adhesion, proliferation and differentiation tests were conducted.

Resume : Some of our previous works which have made an analysis of the combustion process in the laser synthesis of nanopowders delineated two combustion processes; a volume and an ignition combustion one. Both of them appear in the pyrophoric synthesis, in which some gases are decomposed in a strongly exothermic process produced by a focused laser beam with high power density, up to 50 kW/cm2. These types of combustion processes enable a good control of the flame temperature in the synthesis zone. By studying the SiH4/C2H2 combustion process we intend present two precursor's preparing pathways: the dilution of reactant gases into a mixing chamber by keeping the stoichiometric ratio of the active precursors and, preheating the precursors with and without their partial and / or complete decomposition. As results we present an imaging study of the flame. The dependences between different synthesis parameters and characteristics of nanoparticles are presented basing on the measurements performed through various methods such as TEM, SEM, EDAX, XRD, etc

Resume : Gamma Fe2O3 or Fe2O3/Fe3C nanoparticles were synthesized by laser pyrolysis using various optimized Fe(CO)5, O2 and C2H4 flow ratios in the reactive mixture and different laser power. Based on particular conditions two different iron oxide based nanoparticles were synthesized with a hydrophilic or hydrophobic behavior, both having a good magnetization saturation value (around 90 emu/g). TEM EDX, XRD and magnetic analysis were performed for a comprehensive characterization. The raw powders were successfully dispersed in an aqueous solution, using L- Dopa or TMAOH as stabilizing agents. Dispersed samples having concentrations of grams or tens of grams per liter, with or without stabilization agents, have been tested and DLS measurements proved their good stability, with hydrodynamic diameter varying between 70 to 150 nm when stabilizing agents were used. Thermal conductivity and viscosity tests on L-Dopa and TMAOH based on magnetic nanofluids (tens grams/l powder concentration)reveal an increasing up to 40% in thermal conductivity and no more than 5% increasing in viscosity validating them as thermal transfer fluids. Water-based nanoparticle dispersions and also those stabilized with L-Dopa proved good biocompatibility, as demonstrate by an in vitro study in which cellular uptake, cytotoxicity, and intracellular H2O2 production were assessed in primary leukocytes and a breast carcinoma cell line (MCF7).

Resume : We report the deposition of organic structures based on maleic anhydride–aniline derivatives (maleic anhydride-cyano aniline-A3 or maleic anhydride-2,4 dinitroaniline-A6) by matrix assisted pulsed laser evaporation (MAPLE) method on In doped ZnO (IZO) electrode. IZO films were obtained by pulsed laser deposition (PLD) on polymeric flexible substrates like polyethylene terephtalate (PET) and biaxially-oriented polyethylene terephthalate (Mylar). After the deposition, the IZO films were annealed up to 150oC for 1h or oxygen plasma treated at 0.6 mbar for 60 s. The MAPLE films were characterized by UV-VIS, Photoluminescence and FTIR spectroscopy. Atomic Force Microscopy was used to investigate the morphological features of the obtained layers. I-V characteristics of (metal/organic/IZO/flexible substrate) structures were recorded in dark and under the illumination with solar simulator (AM1.5). We found a good transparency of the organic film/IZO structures and the preservation of the PL properties after the laser transfer of the monomers. An improvement of electrical and optical performances was observed after the post-deposition treatments of IZO films. The correlation between the morphology and the electrical properties of the thin films was also investigated. I-V measurements revealed a diode behavior for metal/A6/IZO(annealed)/Mylar structure.

Resume : Over the last few years comprehensive research has been carried out for finding new approaches for transdermal drug delivery systems (TDS). In this study TDSs of Captopril employing thin polymer multilayers (i.e. polyisobutylene, ethylcellulose and hydroxypropyl (methyl)cellulose in different ratios) were fabricated by matrix-assisted pulsed laser evaporation (MAPLE). The TDSs were characterized in terms of their appearance, thickness, Captopril content, in vitro release rate and diffusion profiles. Atomic force microscopy and scanning electron microscopy have been applied to investigate the surface morphology of the TDSs. More insight on surface morphology, Captopril distribution and content in the deposited thin films has been achieved by contact angle measurements, Fourier transformed infrared spectroscopy and spectrophotometry measurements. In vitro release studies demonstrated controlled release for each TDS developed. The dissolution data suggested that the TDSs followed Higuchi kinetics i.e. cumulative amount of drug was proportional to the square root of time. These results indicate that MAPLE could be an alternative technique for the fabrication of Captopril transdermal patches.

Resume : In this work nanocomposites obtained by combining Ag nanoparticles with oligothiophenes have been investigated via optical and structural characterizations. The versatile Laser Ablation in Liquid method, for producing colloidal stable and defined Ag nanoparticle solutions has been adopted. UV-vis absorption spectra of the colloidal solutions of Ag nanoparticles obtained by ablating an Ag target in water using 100 fs laser pulses have provided the Ag nanoparticles evaluation mean size in the range of 50±20 nm. The Ag nanoparticle-oligothiophene nanocomposites solutions have been characterized by fluorescence and absorption techniques. For this purpose steady-state photoluminescence and absorption (350-800nm) together with time-resolved photoinduced absorption and emission spectroscopies have provided insights on the electronic structure, as well as the excitation and de-excitation mechanisms involved. The hybrid nanocomposites used have shown a blue shift with the increase of the concentration of metal nanoparticles. A study on their optical, electronic and structural characterizations has been drawn.

Resume : Polymers like polymethyl-methacrylate (PMMA) are gaining interest for the design of microfluidic and lab-on-a-chip devices due to its transparency and chemical stability. Since laser beams can be focused to deliver energy with high spatial resolution, laser ablation can be used for the micromachining of a variety of materials. However, thermal effects, which for polymers are particularly critical, limit the resolution. Use of femtosecond laser pulses reduces these effects and allows the activation of non-linear absorption mechanisms on the beam waist for producing ablation even if polymers are transparent to the laser radiation. Ablation of PMMA was performed with a laser of 450 fs and 1027 nm. Series of laser pulses were fired on PMMA samples at different energies and focusing conditions (z-scans). In-situ measurement of the transmittance is evaluated as a high-precision method for controlling the z position of the sample surface. Ablated surfaces were inspected through optical and scanning electron microscopies. The morphology of the surface is related with the different energies and focusing conditions. The results show how under proper focusing conditions and pulse energies near the ablation threshold, PMMA surface can be machined with sub-micrometric resolution. At 200 nJ of incident energy, there is a range of 2 µm in the z position where the ablation produced on the surface is similar.

Resume : The development of thermoelectric thin films has brought a new perspective to the integration of thermoelectric cooling devices into microelectronic systems for thermal management purposes. Bulk Bi0.5Sb1.5Te3 exhibits the highest room-temperature power factor among p-type materials and is considered a state-of-the-art thermoelectric material. Bi0.5Sb1.5Te3 thin films with thermoelectric properties similar to or even better than bulk are desired. We used pulsed laser deposition at 248 nm to deposit thin films of the title compound from dense targets of Bi0.5Sb1.5Te3 with an excess of 1 wt% Te. Targets with excess of Te were used in order to avoid Te deficiency during synthesis. Fused silica substrates were employed for the deposition of the thin films at various temperatures in the range of RT and 350°C. We investigated the effect of deposition temperature, film thickness, fluence and annealing temperature on the thermoelectric properties of the films. We will present our recent results on the Seebeck coefficient, electrical resistivity and Hall carrier concentration as a function of temperature (2-400K) for Bi0.5Sb1.5Te3 thin films grown at different temperatures and of different thickness. Also we will present the annealing effects to the topology and electrical properties of the films. We will compare the thermoelectric properties of the Bi0.5Sb1.5Te3 films to those of the bulk material. Acknowledgement: The work was supported in part by the Cyprus Research Promotion Foundation (Project ANAVATHMISI/ 0609/06).

Resume : Hydroxyapatite (HA) is a well consecrated biomaterial for bone substitution. In form of thin films deposited by advanced pulsed laser technologies, it can be used for coating of metallic implants with good mechanical strength. We used for deposition HA of animal (bovine, BHA) doped with (2%) MgF2 or (5%) MgO and human (dentine, DHA) doped with (5%) Ti origin to improve the hardness, fracture toughness, thermal stability, densification and to enhance the biocompatibility and bioactivity. In PLD experiments, a KrF* (λ = 248 nm, τFWHM ≤ 25 ns) excimer laser source was used. The deposited thin films were characterized by XRD, FTIR, SEM, EDS and Pull-out adherence tests. The cytotoxic activity was tested using human fibroblasts and the vital staining assay. The specimens proved to be not cytotoxic in contact with human fibroblasts. The film microbiological assay was performed on three strains isolated from patients with dental implants failure, i.e. Candida albicans, Enterobacter sp. and Microccocus sp. The tested materials behaved differently in the three cases. The best antimicrobial activity was proved in case of Enterobacter sp. when the tested specimens strongly inhibited the bacterial adherence, the most significant effect being obtained in the presence of BHA:MgO thin film, followed by DHA:Ti and BHA:MgF2. The improved antibacterial performance recommend these biomaterials as an alternative to commercial HA for implants coating.

Resume : Medical grade polydimethyl siloxane (PDMS) elastomer is a widely used biomaterial as encapsulation and/or as substrate insulator carrier for long term neural implants because of its remarkable properties. Femptosecond and nanosecond laser irradiation of PDMS-elastomer surface under ambient conditions is investigated. Different processing parameters including pulse duration, wavelength (266, 355 and 532 nm), fluence and scanning speed have been investigated to optimize the surface activation without altering the polymer bulk properties and to fabricate high definition tracks and electrodes. Remarkable alterations of the morphological and the structural characteristics as well as of the chemical composition of the ablated traces in comparison with the native material are observed. Comparison of the Raman spectroscopic results illustrates well defined dependence of the chemical composition on the pulse duration. A local chemical transformation is occurred in the nanosecond laser fabricated tracks. An extra peak at about 516 cm-1 is observed in the spectrum which is ascribed to crystalline silicon. Obvious ablative decomposition in the Raman spectra of the femptosecond laser treated surface is not observed. Femptosecond and nanosecond laser activated tracks are metallized selectively with Ni or Pt. It is observed the time interval between the laser irradiation and the electroless deposition is not critical parameter for successful metallization to occur.

Resume : Laser processing for thin-film applications requires the fabrication of high resolution and well-defined patterns written by laser but also addresses the electrical functionality of the laser written patterns. Due to the high energy impact on laser irradiation and subsequent laser-induced processes laser modifications of the film materials or the substrate can change the electrical properties in consequence of the laser processing. Hence, an application-oriented optimization of laser processing requires both the evaluation of geometrical as well as electrical characteristics of the laser process. In this presentation a recently developed approach of in process evaluation of the laser impact on the electrical characteristics of thin-film samples is presented. The experimental set-up, the methodology of the measurements, and the evaluation of the measurements will be presented and discussed. The presented technique will be applied to the P3 scribing process of thin film solar cells to allow the minimization of the electrical losses due to laser scribing.

Resume : Molybdenum is widely used in solar cell industry, OLED devices and as an element in 2D dichalcogenide materials. Selective laser patterning of such structures offers a potential route to high volume production. Laser molybdenum interactions are very interesting due to its partly-filled d band electronic configuration. The objective of this study is to explore to laser ablation of Molybdenum with different parameters of a femtosecond laser. A repetitively pulsed femtosecond laser source with wavelengths 1030 nm, 515 nm and 343 nm, each of pulse duration 500 fs, was used to ablate Molybdenum with thickness of 0.125 mm. A beam scanning system was used to direct beam over surfaces. The threshold fluence was determined for different wavelengths, spot sizes and repetition rates. The spectral emission from the ablated Molybdenum plume was also investigated. Experiments were performed on rough and polished Molybdenum samples. Results show the damage threshold of Molybdenum at 1030 nm is characterised by single absorbed threshold fluence (0.09 ± 0.01 Jcm-2) for the range of experimental parameters used. Laser ablation at 515nm is described by two threshold values. Gentle and strong ablation was measured to be 0.05 ± 0.002 Jcm-2 and 0.2 ± 0.03 Jcm-2 respectively. Initial results confirm the threshold fluence for UV to be 0.12 ± 0.004 Jcm-2. A full parametric study on femtosecond laser ablation of molybdenum will be presented.

Resume : Models of thermodynamic properties and transformations of materials are required for simulations of processes in condensed media under intense laser pulsed influences. In the present work, an equation-of-state model for organic compounds is proposed with taking into account the physical-chemical transformations at high pressures and temperatures. These transformations are connected with decomposition of initial molecules and formation of diamond-like carbon and other components under intense loading conditions. Multiphase equations of state for polystyrene, polymethylmethacrylate and epoxy composition are developed. As distinct from the previously obtained equations of state [1], new expressions for the thermodynamic potentials are formulated. Those provide for a more correct accounting for physical-chemical transformations of the substances under ultrafast heating and rarefaction [2]. A critical analysis of calculated results is made in comparison with available experimental data for the organic compounds over a wide range of densities and temperatures. [1] K. V. Khishchenko, I. V. Lomonosov and V. E. Fortov, Int. J. Thermophys. 23, 211–219 (2002). [2] M. E. Povarnitsyn, N. E. Andreev, P. R. Levashov, K. V. Khishchenko, D. A. Kim, V. G. Novikov and O. N. Rosmej, Laser Part. Beams 31, 663–671 (2013).

Resume : Lipase is an enzyme catalyzing reactions borne by triglycerides such as transesterification for biodiesel production and has been used in biosensors for detection of β-hydroxyacid esters [1] and triglycerides in blood serum [2]. Immobilization of the enzymes is essential for their industrial application, since it allows the development of continuous processes, easier separation of products, the reuse of the catalyst and, in some cases, it enhances enzyme properties such as pH and temperature stability and their catalytic activity in non-aqueous media [3]. MAPLE is a thin film deposition technique derived from Pulsed Laser Deposition (PLD) for deposition of delicate materials (biomolecules, polymers, etc.) in undamaged form. The main difference in comparison to classical PLD is the use of a frozen (usually by means of a liquid nitrogen flux) target obtained from a solution or a suspension of the guest material (to be deposited) in a matrix (a volatile solvent). In this way, the laser beam energy is mainly absorbed by the matrix while only the guest material reaches the substrate, since the solvent is pumped away by the vacuum system. By MAPLE technique it can be possible to “freeze” the conformation of the lipase as it is in solution, in such a way to tailor lipase properties in solution. In this way the lipase conformation, essential for its catalytic activity, would be independent on the support properties. Here we show that Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique can be used to deposit lipase. 1. T. Kullick, R. Ulber, H.H. Meyer, T. Scheper, K. Schlügerl. Anal. Chim. Acta. 239 (1994) 271 2. Mohanasundaram Sulur Veeramani, Karuppiah Prakash Shyam, Noel Prashant Ratchagar, Anju Chadhabc and Enakshi Bhattacharya, Miniaturised silicon biosensors for the detection of triglyceride in blood serum, Anal. Methods, 2014, Advance Article; DOI: 10.1039/C3AY42274G. 3. P.M. Nielsen, J. Brask, L. Fjerbaek. Eur. J. Lipid Sci. Technol. 110 (2008) 692-700.

Resume : Silver nanoparticles have attracted much attention as a subject of investigation due to their well known properties, such as good conductivity, antibacterial and catalytic effects, etc. They are used in many different areas, such as medicine, industrial applications, scientific investigation, etc. There are different techniques for producing Ag nanoparticles, chemical, electrochemical, sonochemical, etc. These methods often lead to impurities together with nanoparticles or colloidal solutions. In this work laser ablation under ambient conditions (LAAC) is used not only to produce silver nanoparticles but also to deposit them on a substrate. Production and deposition of silver nanoparticles are integrated in the same step to reduce the process. The obtained particles are analysed and the nanoparticles formation mechanism is discussed. The obtained nanoparticles were characterized by means of transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and UV/VIS absorption spectroscopy. The obtained nanoparticles consisted of Ag nanoparticles showing spherical shape with diameters ranging from few to 70 nm. The ablated Ag nanoparticles were deposited directly on a glass to form a coating whose composition was confirmed by the use of Glancing incidence X-ray diffraction (GXRD).

Resume : Direct Laser Writing (DLW) based on the multi-photon polymerization of photosensitive materials is a technique that allows the fabrication of three-dimensional structures with sub-micron resolution. The polymerization is based on multi-photon absorption; when the beam of an ultra-fast laser is tightly focused into the volume of a transparent, photosensitive material, the polymerization process can be initiated by non-linear absorption within the focal volume. By moving the laser focus three-dimensionally through the material, 3D structures can be fabricated. The technique has been implemented with a variety of materials and several components and devices have been fabricated such as photonic crystal templates, mechanical devices and microscopic models. The unique capability of DLW lies in that it allows the fabrication of computer-designed, fully In this seminar we summarize the principles of microfabrication by DLW. We discuss the fundamental principles of multi-photon absorption and describe a typical DLW experimental set-up. Then we concentrate on the materials used for DLW microfabrication, and on our recent work in the functionalization of the surface and the bulk of the 3D fabricated structures. Finally, we discuss the future applications and prospects for the technology.

Resume : ZnO is a promising material for UV photonic devices such light-emitting diodes (LED) or laser diodes. UV LEDs and laser diodes require high quality films for which the composition and morphostructure have to be perfectly controlled. Random lasing due to light amplification can occurs in cavities self formed by these film microstructure. This effect has already been observed in ZnO material in various states : powders, polycrystalline and highly textured materials(nanowires)or epitaxial thin films. In this work, PLD was used to grow ZnO thin films onto c-cut sapphire substrates under different oxygen pressures (from vacuum to 0.1 mbar) and substrate temperatures (from room temperature to 700°C). The stimulated emission photoluminescence spectra were recorded under excitation by a frequency tripled pulsed NdYAG laser (355 nm ; 10 ns pulse duration) at different pump powers. The PL emission in the UV-visible range was collected using a UV-visible (300-800 nm) USB spectrometer. The lasing effect is evidenced in these PLD ZnO films and the wavelength and the peak intensities are demonstrated to be depending upon the composition and structural properties of films.

Resume : Abstract withdrawn

Resume : Laser assisted method for fabrication of nanoparticles on the surface of ceramic substrate is presented. The method is based on laser nanostructuring of thin metal film deposited on the substrate. Using this technique, gold nanoparticles on alumina ceramic surface are fabricated. The influence of the laser fluence and pulse number on the characteristics of the produced nanoparticles is studied and discussed. The obtained structures are tested as substrates in Surface Enhanced Raman Spectroscopy of standard dyes. The efficiency of the substrates is estimated by the ability of detection of the smallest dye concentration compared to that of bare ceramic substrate, thin gold film on ceramic substrate, and nanoparticles on polished crystalline alumina. The strongest enhancement is observed for the ceramic substrate covered by nanoparticles. This could be attributed to the highest density of the areas with strong near field intensity enhancement in the vicinity of gold nanoparticles in the porous material, and the specific spatial distribution of the near field intensity. These effects are studied and discussed on the basis of Finite Difference Time Domain simulations. The proposed method could be a base of a simple fabrication technique for cheap and reliable substrates for Raman spectroscopy analysis with ultra-high sensitivity.

Resume : Cu2ZnSnS4 (CZTS) has recently emerged as a promising thin film absorbing material for the low-cost thin-film solar cells. Cu2ZnSnS4 (CZTS) thin films can be grown by reactive pulsed laser deposition in a sulfur containing atmosphere using a multi-metallic target of Cu2ZnSn. However, the ablation of a target alloy containing highly volatile elements, such as Sn is still poorly explored. Here we present an experimental study of laser ablation of a multi-metallic target of Cu2ZnSn in vacuum using a KrF excimer laser operating at a wavelength of 248 nm. The thin films were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The morphology and composition of the thin metallic alloys grown at room temperature was studied as a function of laser fluence. Ablation of the metallic target at high fluence results in deposition of large irregular features on the substrate, and thus growth of highly non-uniform thin metallic films. The distribution of the metallic droplets for an on- or off-axis geometry will be discussed.

Resume : Laser ablation plasmas are capable to sustain efficient generation of short wavelength coherent radiation by frequency up-conversion to low- and high-order harmonics. Complex plasmas possess compositional and dynamical properties that allow for some degree of tuning in the selection of nonlinear optical (NLO) species and phase matching conditions, and reversely in some cases harmonic generation (HG) can be employed as a diagnosis tool for such plasmas. In this work we investigate low-order, two-colour pump HG in nanosecond laser ablation plasmas of boron carbide (B4C), a material that generates ceramic microstructures of various geometries by pulsed laser deposition. Frequency tripling of a fundamental driving beam at 1064 nm (Nd:YAG laser pulses of 15 ns) resulted in 3rd HG at 355 nm, while sum-frequency mixing of two driving beams at 532 and 1064 nm resulted in 4th HG at 266 nm. In both cases, the ablation plume of B4C was created with a different Nd:YAG laser with controllable delay with respect to the driving source, and monitored by optical emission spectroscopy to help elucidate the species responsible for the NLO processes studied. We characterized the even and odd harmonic intensities as a function of the polarizations and pulse energies of ablation and driving lasers. This, together with the spatiotemporal mapping of the plasma by the driving beams, has provided clues about the nature and distribution of the NLO generated by ablation of the B4C target.

Resume : New contact-free measurement technique for thermoelectric power is developed. The technique allows of determination of the thermoelectric power value by analyzing the differential tunnel volt-ampere characteristics obtained by scanning tunneling microscopy. By the use of this technique the thermoelectric power of Au nanoclusters pulsed laser deposited on highly oriented pyrolytic graphite HOPG(0001) was studied. It was found out that thermoelectric power of nanocluster decreases with its size. The results obtained might be used for the development of nanoelectronics, for example, the development of nanocoolers and temperature sensors of integrated circuits.

Resume : Laser Induced Forward Transfer (LIFT) proved its ability to print Organics Thin Films Transistors. This process allows the transfer from a donor substrate of pixels with micrometer sizes of organic and inorganic materials with a submicronic resolution. However, the properties of each layers and the quality of the interfaces are key factors for the performances of the devices. It is then necessary to optimize the preparation of donor substrates. The focus is put here on the growth of pentacene layers by PLD, a well-known organic semiconductor chosen for its high charge carrier mobility. The main objectives are to control its molecular degradation that can occur during the deposition and its structural and morphological properties which influence the device performance. We show that by tuning the laser fluence, the background atmosphere and the substrate temperature, it is possible to obtain high-quality (high crystallinity and low surface roughness) pentacene thin films without chemical degradation. For each experimental condition, both the thickness and the refractive index were in-situ monitored by means of ellipsometry, whereas conventional analysis technique (absorption, microRaman and FTIR spectroscopy, AFM, XRR and GIXD) were used to control the film quality and their properties. Moreover, varying the substrate (Suprasil, PMMA or Triazene which is used as a sacrificial layer on the LIFT process) the influence of surface properties on pentacene thin films structure and morphology is also investigated. Finally, optimized pentacene layers have been characterized by current-voltage measurements

Resume : Magnetic nanomaterials with controlled magnetic structure are good candidates for spintronic applications. In this work, nanocomposites of cobalt ferrite (CoFe2O4) and magnetite (Fe3O4) were grown as thin films on SrTiO3 (100) substrates by nanosecond pulsed laser deposition. Self-prepared sintered targets of cobalt ferrite were irradiated under vacuum (10-6 mbar) with Nd:YAG laser pulses of 1064 nm and 15 ns. The composition, crystallinity, surface structure and magnetic properties of the films were determined by atomic force microscopy (AFM), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction (XRD), micro-Raman and Mössbauer spectroscopies and magneto-optic Kerr effect (MOKE) measurements. Deposits consist of a mixture of nanostructures of rectangular and cubic prisms having alignment directions offset by 45º. The former, of sizes around 20x30 nm, appear with high superficial density, while the latter of larger sizes, side of 50-100 nm, appear scattered at lower density. XRD patterns supply evidence of monocrystalline deposits, whereas Mössbauer and micro-Raman spectra show that their composition differs from that of the target and consist of a mixture of cobalt ferrite and magnetite. SEM/EDX measurements suggest that rectangular prisms would be made of cobalt ferrite and cubic prisms by magnetite. These results, together with MOKE analysis, give clues on the control of magnetic properties at the nanoscale of the grown films.

Resume : Staphylococcus aureus represents one of the major infectious threats for hospital environment, because of its wide spread and increasing antibiotic resistance. This study reports on the deposition of γ-cyclodextrine/usnic acid thin film by Matrix Assisted Pulsed Laser Evaporation (MAPLE) as anti-adherent coating on medical surfaces, in order to improve their resistance to microbial colonization. The prepared surfaces were characterized by Transmision Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Infrared Microscopy (IRM). Microbial biofilm formation was established from SEM images and culture-based assays for up to 3 days of incubation at 37oC, while biocompatibility was evaluated by analyzing the qualitative and quantitative phenotypic changes of the treated eukaryotic cells up to 5 days. SEM micrographs revealed uniform morphologies of the prepared films, while IRM proved the functional groups integrity and the homogeneity of the γ-cyclodextrine/usnic acid thin film. Microbiologic results showed that the obtained thin films efficiently inhibited S. aureus adherence and biofilm formation potentials for all tested time points. These results demonstrated that the functionalized surfaces with γ-cyclodextrine and usnic acid deposited by MAPLE can successfully prevent the microbial cells adhesion and biofilm development on the medical surfaces.

Resume : The purpose of this study was the fabrication, characterization and bioevaluation of -aminobutiric acid-silica network thin film prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE) as a matrix for controlled local delivery of tetracycline, with practical applications in developing of improved medical surfaces for the prevention or reduction of surface-associated infections. Thin films were characterized by Infrared Microscopy (IRM), X-Ray Diffraction (XRD), Brunauer?Emmett?Teller Analysis (BET), and High Resolution Transmision Electron Microscopy (HR-TEM). Microbial colonization was investigated by quantitative and qualitative biofilm formation assays, while the biocompatibility of the prepared materials was evaluated by microscopy and biochemical assays. TEM analysis reveals a good homogeneity and an average size of particles lower than 10 nm. The prepared thin films significantly improved the resistance to microbial colonization, inhibiting the biofilm formation on both Gram positive and Gram negative tested strains, when peliculised on the tested medical surfaces. These results, correlated with the high biocompatibility of these thin films, highlight the possibility of using the γ-aminobutiric acid-silica network films for the controlled local delivery of the therapeutic agents in lower active doses, thus reducing the occurrence of rejection for implanted prosthetic devices.

Resume : Laser irradiation of nanoparticles (NPs) can result in the particles size and shape changes through the fragmentation and aggregation processes, can lead to the defects removal and crystallinity improvement, as well as to the phase transitions, that change the composition and inner structure of the particles. In this paper the effect of laser irradiation on the changes in the morphology and structure of the iron oxide NPs has been studied. The colloidal and powder iron oxide NPs were subjected to laser irradiation by the second harmonic of the Nd:YAG laser (wavelength 532 nm, pulse duration 10 ns) with fluence 400 mJ/cm2 for 15 min. It has been shown that the result of laser modification of NPs is mostly determined by the temperature that is reached during the irradiation. Laser irradiation resulted in the ordering of crystal structure and partial removal of adsorbed and structural hydroxyl groups from the particle surface. The morphology of NPs changed from the irregularly shaped particles to spherical ones with diameters close to the initial particle sizes (50-90 nm). Besides, a fraction of small NPs with sizes in the range of 5-8 nm has been observed after laser modification. It has been found that laser heating of α-Fe2O3 phase in non-equilibrium conditions result in the formation of spinel phases of iron oxide (γ-Fe2O3, Fe3O4) while single-phase γ-Fe2O3 sample undergoes a partial thermo stimulated phase transition to the thermodynamically stable α-Fe2O3 phase.

Resume : Research and development of new nanostructuring materials for engineering of nanoplasmonic and nanophotjnic structures is perspective direction of material science. Low-temperature solid-phase interaction in a simple eutectic pairs of metal- semiconductor thin films is one of the ways to create such materials. Such materials are used for recording media and could be used for criation of photonic crystals. Two-component systems of semiconductors and metals forming simple eutectic pairs was investigated. The solid-state interactions on the interface of systems metal-metal or metal-semiconductor are discussed. The results of the laser and thermal annealing are represented. Transmission spectra of binary mixtures Ge-metals measured in situ during the annealing demonstrate changes as a function of the annealing temperature. Change in reflection index spectra and dimensional photonic crystals is demonstrated. The advantage of these materials (low-energy interactions, long lifetime and environmental) make them promising for neoteric tecnology.

Resume : We discuss the properties of thin films obtained following the pulsed laser ablation (PLD) of a silica xerogel that is normally used to synthesize Er/Yb doped LiYF4 by the sol-gel technique. Although PLD is a particularly suited growth technique for such multi-component glass ceramics that are unstable at high temperatures, classical PLD growth of thin films starting from doped LiYF4 sintered ceramic targets has been shown to yield thin films with large roughness values, of the order of hundreds of nanometers [1]. Similar roughness values have also been reported by other groups following laser ablation of a doped LiYF4 single crystal target [2, 3]. This is an issue when considering possible practical applications of doped LiYF4 thin films. These materials are generally obtained using the sol-gel technique, which however does not enable a precise control over the thickness of the resulting films. In our study we explore the viability of using laser ablation of a silica xerogel, followed by substrate annealing, in view of achieving composite thin films of Er/Yb doped LiYF4 crystals embedded in a SiO2 matrix. Such thin films may be considered for the realization of coatings meant to improve the quantum efficiency of solar cells by up-conversion. [1] F. Stokker-Cheregi et al., J. Phys. D: Appl. Phys. 47 (2014) 045304. [2] C. Garaponet al., Appl. Phys. A 91(2008) 493. [3] S. Barsanti et al., Thin Solid Films 516 (2008) 2009; S. Barsanti et al., Thin Solid Films 517 (2009) 2029.

Resume : There is currently a lack of experimental evidence concerning thin films grown by ultra fast pulsed laser deposition (UFPLD) using picosecond laser sources. To this end, Au thin films have been grown on glass substrates by UFPLD using a 10-ps high-repetition-rate laser source. A systematic parametric study has been carried out with variation of laser fluence, substrate temperature, deposition time and target-substrate separation distance. The investigations has focused on surface characterization (SEM), depth profiling, structural (XRD) and optical properties (spectrophotometry) of the obtained thin films. Maps with morphological (thickness, roughness, porosity, uniformity) and structural (planes orientation, crystallites sizes, compactness) parameters for each film were made and used in conjunction with optical spectra to determine the decisive parameters in changing the optical properties. Due to the large number of particles present on the films surface, there has been a need to understand the dependence of the surface plasmon resonance shift on the particles shape and/or particles interactions with other particles and the substrate. For this, the model proposed by Yamauchi et al. and Fedotov et al. [1, 2] has been employed. In addition, we will describe the possible sensing strategy which employs Au nanoparticles as individual sensing elements. [1] T. Yamaguchi, S. Yoshida, A. Kinbara 1974 Thin Solid Films, 21 173 [2] V.A. Fedotov, V.I. Emelyanov, K.F. Macdonald, N.Zheludev, J. Opt. A: Pure Appl. Opt. 6 (2004) 155–160

Resume : TiO2/Fe/HMDSO nanoparticles presenting core?shell structures were simultaneously manufactured by the single-step laser pyrolysis. The present study is a continuation of our previous investigations on the TiO2/Fe and TiO2/HMDSO systems. The aim of this work is to study the synthesis by IR laser pyrolysis of magnetic TiO2 based nanocomposites which implies many concurrent processes induced in the gas phase by the laser radiation. The dependence between characteristic properties and the synthesis parameters was determinated by many analytical and complementary methods: crystallographic analysis (X-ray diffraction), UV-Vis and IR spectroscopy, EDAX, SEM, TEM and HRTEM analysis, magnetic measurements and photocatalytic degradation of specific water pollutants. Magnetic TiO2 - based nanopowders with carbosilane polymer shells contains particle with mean dimensions (about 13-23 nm diameter) and narrow diameter distributions. Photocatalytic properties of novel multifunctional TiO2-based magnetic nanocomposite were tested as compare with the reference P25 Degussa sample.

Resume : We present results obtained following a multi-stage study, in which: i) Ti supports are irradiated and patterned using a femtosecond laser source; ii) the obtained structures are covered with various types of polymers using the matrix assisted pulsed laser evaporation (MAPLE) technique, which has proven to be particularly suitable for such coatings [1]; iii) lastly, different cell types are cultured in order to check the functionality of the obtained coating/substrate systems. Our study is motivated by the possibility of achieving a type of medium in which electrical stimulation can be used to generate preferential growth and/or cells differentiation. In order to achieve this, the patterned Ti supports will be covered, by MAPLE, with three types of polymers meant to provide electrical stimulation [polypyrrole (PPy)] and increased biocompatibility [poly(lactic-co-glycolic) acid (PLGA) and polyurethane (PU)]. The functionality of the obtained polymer coatings/patterned Ti substrate systems will be tested by osteoblasts and fibroblasts cell cultures. Our study reports on cells proliferation, viability and morphology analyses. [1] A. Matei, J. Schou, S. Canulescu, M. Zamfirescu, C. Albu, B. Mitu, E.C. Buruiana, T. Buruiana, C. Mustaciosu, I. Petcu, M. Dinescu, Appl. Surf. Sci. 278, 357 (2013).

Resume : We have previously reported on the ability of the laser techniques to produce thin films of layered double hydroxides (LDHs) and composite films organic/LDH. The aim of this work is to produce and characterize composite films of fatty acids/ LDH as hydrophobic surfaces. LDH based on Mg-Al and Zn-Al with different ratio were investigated and acetic acid, stearic and lauric acid have been considered as short, medium and long -chain fatty acid. Standard matrix assisted pulsed laser evaporation (MAPLE) and combined matrix assisted pulsed laser evaporation/ pulsed laser deposition have been employed for the growth of the composite layers. The morphological, structural and chemical characterization of the films is presented; the intercalation of the selected fatty acids in the LDH structure has been correlated with the Mg2+/Al3+, Zn2+ /Al3+ ratio and it was found to strongly influence the film wettability.

Resume : Recent discovery in ZnO nanogenarator has spurred tremendous interest in micro sensor power application. The fundamental principle of ZnO nanogenarator is to utilize the environmental mechanical energy, which is available everywhere from irregular vibrations, light airflow, noise and human activity with a wide spectrum of frequencies and time-dependent amplitudes. The first prototyping of a nanogenarator by means of ZnO piezoelectric nanowire (NW) arrays, piezoelectric nanostructured materials have demonstrated to able to drive micro-sensor and sensor network nods in micro-power range. However so far the power output from NW nanogenarator is still in the power range micro watt, which is still far way from milli-power output source requested by most applications of individual sensor and sensor network system. The lacking of high power output in current ZnO NW generator is partially attribute to non-well c-axis oriented crystalline of ZnO NW material and low yield in NW device, both are synthesized by chemical method. In this paper, the piezoelectric properties of ZnO film grown by pulsed-laser deposited (PLD) in the temperatures range of 400 to 600 degree are investigated. Structurally, special emphasis is placed on XRD grain size characterizations of the grown films. Additional characterizations using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) will be detailed at a later date. The piezoelectric properties of these films are characterized by Piezoelectric Force Microscopy (PFM). It is found that the piezoelectric properties of the films are strongly dependent on grain size of the films. The observed corresponds of piezoelectric (PE) property to grain size is also theoretically explained. *Corresponding author, zhangw@njut.edu.cn

Resume : Thin SiC films were grown on (100) Si substrates at temperatures from 400 to 1000 oC under various CH4 pressures by the pulsed laser deposition (PLD) technique using a KrF excimer laser. After deposition, films were in situ annealed at their deposition temperature under 500 mbar of CH4 for 1 hr. X-ray reflectivity investigations showed that films exhibited mass densities similar to SiC single crystal samples, while symmetrical and grazing incidence X-ray diffraction investigations found that films deposited at 800 °C or higher substrate temperatures were nanocristalline. X-ray photoelectron spectroscopy investigations found that films contained in bulk a relatively low oxygen concentration of around 1.0 at. %, while nanoindentation results showed that the deposited SiC films were very hard, with hardness values above 40 GPa for films deposited at temperatures higher than 800 °C. Modeling of spectroscopic ellipsometry data was used to extract the refractive index and extinction coefficient values of these films.

Resume : Layered double hydroxides (LDHs) with Mg-Al and Zn-Al were deposited using pulsed laser deposition (PLD). We studied the ability of our films to detect copper cations in aqueous solutions. Copper is known as a common pollutant in water from urban and industrial waste. Clay minerals, including layered double hydroxides reduce the toxicity of copper by adsorbing it. The obtained films were characterized using X-Ray Diffraction, Atomic Force Microscopy, Scanning Electron Microscopy with energy dispersive X-ray analysis, Fourier Transform Infra-Red Spectroscopy and Secondary Ions Mass Spectrometry. Adsorption of copper solution was carried out using Atomic Absorption Spectrometer. The effects of various parameters such as contact times, concentration were investigated. The results in this study indicate that LDHs thin films obtained by PLD have potential as an effective adsorbent for removing copper from aqueous solution.

Resume : The laser-assisted microstructuring of thin films especially for electronic applications without damaging the layers or the substrates is a challenge for the laser micromachining techniques. The thin-film patterning by ablation of the polymer substrate at the rear side has been demonstrated recently and is called ‘SWIFD’ – shock-wave-induced film delamination patterning. However, the realising of high speed, low damage, and high resolution patterning processes with lasers has a great potential for applications in, e.g., flexible electronics. This study focusses on the temporal sequence of processes that characterize the mechanism of this SWIFD process. For this purpose high-speed shadowgraph experiments were performed in a pump probe experimental set-up using a KrF excimer laser for ablating the rear side of the polyimide substrate and measuring the shock wave generation at laser ablation of the polymer substrate as well as the thin-film delamination in dependence on the laser irradiation parameters. In addition, the SWIFD process was studied on different thin layers on polyimide substrates. The morphology and size of the ablation pit as well as of the thin-film structures were studied by SEM and AFM for various laser irradiation parameters (laser fluence, number of laser pulses, laser beam diameter). The shadowgraph experiments allow the time-dependent identification and evaluation of the shock wave formation, substrate bend, and delamination of the thin film.

Resume : The introduced laser method demonstrates a novel concept of complex nanostructuring of dielectric surfaces assisted by a laser-induced molten metal layer deformation process where the structuring process is defined by the deformation process of the thin metal layer [1, 2]. The method allows the fast, large-scale, and cost-effective production of randomly distributed surface nanostructures with a lateral dimension down to 10 nm. The dynamics of the metal layer deformation process was studied by time-dependent reflection and transmission measurements. The resultant structures were investigated by atomic force (AFM), optical microscopy, and scanning electron microscopy (SEM). The experimental results were compared with the simulation findings that take into account the heat equation (laser-solid interaction including melting and evaporation) and the Navier-Stokes equations (deformation process of the molten phase). The simulation allows a very good description of the experimental results and will allow the optimization of the structuring results. [1] P. Lorenz et al., Appl. Surf. Sci. 280 (2013) 933. [2] P. Lorenz et al., Appl. Phys. A 111 (2013) 1025.

Resume : Significant advances in non-volatile solid state memory devices were driven by the discovery of Ge-Sb-Te alloys found along the GeTe?Sb2Te3 tie-line. The rapid laser-induced crystallization with large property changes represented the grounds for many research studies. To ensure an ns transition from amorphous to metastable structure, the structural characteristics and other optical properties of the deposited films need to be carefully adjusted. Our work was focused on comparing the structural, chemical and optical properties of Ge-Sb-Te thin films obtained by laser ablation using pulsed lasers which operate in different conditions (pulse duration: ns, fs, ps; repetition rate: 10Hz, 1kHz). In each temporal regime, other experimental parameters were varied such as target-substrate distance, deposition time, laser fluence, wavelength etc. The structural characteristics were studied using profilometry, SEM, EDX, ToF-SIMS, Raman spectroscopy and XRD, while for optical properties we considered the VASE and spectrophotometry techniques. The main observed characteristics were the improved surface morphology and chemical composition of the samples deposited by ps- and fs-PLD.

Resume : Silicon oxynitride (SiON) materials have been object of research as they offer a suitable technological platform for the development of integrated optoelectronic devices such as light emitting devices (LEDs) or high speed silicon optical modulators. This is due to their excellent properties that include a large refractive index that can be tuned from that of SiO2 (1.45) to that of Si3N4 (2.01), high transparency in the visible-near infrared range, good electrical properties and compatibility with the current Si-technology. More recently, in the search for efficient light emitting materials with superior performance and large integration capability has motivated the study of more complex matrices such as aluminum-doped silicon oxynitrides. Among the several advantages provided by this quaternary host, the possibility of tuning the electrical and optical properties, the enhanced light emission from luminescent species and the decrease in the maximum phonon energy become major key points that stimulate the ongoing research of these materials. In this work, we report on the photoluminescence (PL) response from thin films produced by pulsed laser deposition (PLD) in vacuum (400 mPa) at room temperature, by focusing an ArF excimer laser on two separate targets: a ceramic SiAlON (Si 25.2 - Al 19.5 - O 10 - N 43.5 - Y 1.7 at %) and a metallic Er target. During the process, the Er is distributed in the films forming doping layers with different interlayer spacing. The composition of the films is different compared to that of the target, showing a remarkable decrease in the Al content (up to 3 at %) that varies depending on the deposition conditions. The as grown films show Er-related emission peaking at 1533 nm. This PL emission is further enhanced by post-deposition annealing treatments up to 850ºC. The PL excitation spectra analysis evidences that the Er ions are excited via energy transfer from the matrix. The role of the PLD conditions on the emission properties will be investigated in order to achieve maximized PL emission.

Resume : The use of Ni-YSZ thin films as anode system in Solid Oxide Fuel Cells is ultimately depending on its capability to modify its electrical properties in the presence of oxydizing or reducing atmosphere, at the operation temperature. This is mainly connected to the amount of nickel in the material, as well as to its uniform distribution in the dielectric host. In this work, the laser ablation technique was utilized for obtaining Ni-YSZ thin films with various amount of nickel. The depositions were perfomed by using an ArF excimer laser at 193 nm which irradiated a commercial YSZ target partially covered with Ni sectors (up to 50%). Oxygen atmosphere was used for avoiding substochiometric compound formation, and for better reactivity on the substrate level, an additional RF discharge was assisting the deposition, as well. Si and Si/Pt substrates, placed at 5 cm in front of the target, were heated up to 600 degreesC during PLD process. A thorough investigation regarding material morphology, structure and chemical composition was performed by means of AFM, SEM, XRD and SNMS techniques. The oxidation states of Y, Zr and Ni were determined by XPS analysis. The electrical conductivity of the materials in the temperature range from RT to 800 degrees C both in oxidizing and reducing atmospheres are reported.

Resume : In the last decade, the biogene amines have catched the researchers’ interest due to their direct relation to the meat freshness and thus, the rapid detection of volatile organic compounds (VOC). In the present study, we report on the deposition of novel meso-phenyl unsymmetrical substituted porphyrin, 5-(4-carboxyphenyl)-10,15,20-triphenylporphyrin (CPTPP) thin films by matrix assisted pulsed laser evaporation (MAPLE) onto silicon substrates with screen-printed transparent conducting oxide electrodes, aiming to design a fluorecent-chemosensor for biogene amines detection. FTIR spectroscopy and Raman spectrometry have confirmed that the chemical structure of MAPLE-deposited thin films was preserved for fluences within the range 200-400 mJ/cm2. AFM examination has shown that the thin films had a uniform and continuous morphology for 300 mJ/cm2 laser fluence. Cyclic voltammograms on screen printed electrodes have demonstrated that CPTPP is appropriate as a single mediator for various biogene amines (histamine, cadaverine, putresceine) with high yield in fluorescence and electrochemical signal. We have shown that MAPLE deposition of CPTPP thin films can replicate both the bulk structure and serve as a soft technique in deposition of porphyrin thin films and patterns.

Resume : This study aimed for the evaluation of anti-microbial effect and biocompatibility of newly fabricated antibiotics functionalized magnetite nanostructures, of 5 nanometers average diameter, prepared as bulk material by Matrix Assisted Pulsed Laser Evaporation (MAPLE). Prepared thin films were characterized by High-Resolution Transmision Electron Microscopy, Scanning Electron Microscopy, Infrared Microscopy and X-ray Diffraction. In vitro biological assays have been performed in order to evaluate the influence of fabricated thin film on the Gram positive and Gram negative biofilm development as well as their in vitro biocompatibility for up to five days of incubation (qualitative and quantitative methods) with eukaryotic cells. The in vivo biocompatibility experiments were performed on holoxenic mice. The obtained 5 antibiotics functionalized magnetite nanostructures-based thin film have proved to be efficient to prevent microbial development and contamination of implanted prothesis, as demonstrated by the inhibitory activity on mature biofilm development. Furthermore, these thin film nanostructured surfaces proved a good biocompatibility both in vivo and in vitro, demonstrating their potential to be used for clinical purpose. Taken together, these results have a great impact, opening new perspectives for the anti-infective therapy.

Resume : The electronic properties of semiconductor thin films are closely related to their structure. Semiconductors that exhibit room-temperature ferromagnetism are central to the development of semiconductor spintronics. This work concerns the deposition and subsequent characterization of films in the system MnGeSb: (Fe, Co). The films have been simultaneously deposited on Si, GaAs, InAs and Al2O3 substrates at moderate substrate temperatures (Tmax= 200oC) using a PLD 2000 Workstation (PVD Products Ltd.). The targets were home-made bulk alloys grown by the vertical gradient freeze technique.. Films of 50-400nm thickness have been obtained. The morphology, carrier type and concentration are investigated in relation with the films thickness and substrate material. Structural and optical characterizations were done by XRD, SEM, EDX, micro-Raman spectroscopy, spectroscopic ellipsometry and small-angle X-ray scattering (SAXS). AFM measurements show a clear influence of the substrate material on the morphology of the films. The Hall effect measurements were carried out at room temperature using an Ecopia HMS-3000 Hall Measurement System. showing that PLD Co-doped films are n-type, with a carrier concentration of the order1021 cm-3 and mobilities of the order 102 cm2/Vs.

Resume : This work presents a numerical resolution of heat distribution equation of pulsed laser beam impact on a sample of polyacetylene characterized by multichannal Raman spectroscopy. The method is based on finite elements theory which allowed the determination of: (i) The temperature of laser impact zone , (ii) The propagation zone of isomerization of a polyacetylene sample. A computer program was been developed for this purpose. Concerning the D.S.C study: Different PA was used, we report the results of two polyacetylene samples prepared successively ( i ) at the surface of the catalytic solution, called horizontal PA, and ( ii ) on the surface of wet wall by catalytic solution , called vertical PA . The samples were studied in the temperature range from 30 °C to 280 °C and subjected respectively to heating rates of 5, 10, 20, 40 and 80 °C / min. We recorded the temperatures corresponding to the maximum of the exothermic peak (T max) of the isomerization reaction. It is observed that the points related to the two samples are placed on the same Arrhenius line. The study allowed the determination of the activation energy and the collision factor of the isomerization reaction, these are Ea = (31.00  0.18) Kcal / mole and A = (2.24  0.45 *1013 ) /s. These results are found to be close to those obtained in literature by Ito and Bernier. Key Words: Polyacetylene - isomerization - DSC - kinetics - multichannal Raman spectroscopy

Resume : Multiferroic BFO-based materials are intensively studied for their wide range of applications, from spintronics and multistate memories to photocatalysis. We have synthesized BFO nanoparticles by laser ablation in different liquids (deionized water, alcohols) using an Nd-YAG laser working at different wavelengths (266 and 355 nm) and fluences (1.4- 3 J/cm2). The average particle size was estimated by transmission electron microscopy (TEM) and the optical properties by spectroscopic ellipsometry (SE) and UV-Vis spectrometry (ultraviolet?visible). To evaluate their functional multiferroic and photocatalytic properties, the BFO nanoparticles have been deposited as thin films by MAPLE (Matrix Assisted Pulsed Laser Evaporation). The influence of experimental parameters such as the solvent type, laser wavelength or thickness of the MAPLE deposited BFO thin films on the local piezoelectric response, optical, multiferoic and photocatalytic properties has been studied using techniques such as XRD, HRTEM, SE, UV-VIS, PFM or dielectric/ferroelectric spectroscopy. A comparison with PLD deposited layers properties is also performed.

Resume : Titanium and titanium alloys have been used in a number of applications in industry ranging from aircraft components, chemical processing facilities to gas turbine engines due to their high strength to weight ratio, high corrosion resistance and relatively high melting temperature. However, further application of titanium and titanium alloys is considerably restricted by their low surface hardness, high friction coefficient and poor wear resistance. Therefore, the surface characteristics of titanium and titanium alloys need to be improved. Thermal spray coating is one of the most common ways to improve the surface characteristics of materials. The plasma-sprayed Al2O3 and Al2O3–TiO2 ceramic coatings have been extensively used in many applications as surface coating to protect components against wear and corrosion due to their thermal, chemical and mechanical stability. Recently, nanostructured Al2O3–13 wt.%TiO2 coating demonstrate novel and attractive properties such as bond strength, toughness, abrasive wear and thermal shock resistance. In this paper, numerical model is developed using the finite volume method, based on Navier-Stokes equations and (VOF) method to simulate the impact, spreading and flattening of the Al2O3–13 wt.%TiO2 droplets impacting onto a solid surface . The model simultaneously takes into account the fluid flow and heat transfer in the liquid particle and the surrounding gas, and the heat transfer in the substrate. To understand the effect of solidification on the droplet impact dynamics and splat morphology, the simulations were run with smoothed and roughened surfaces considering different roughness magnitude. The results show a substantial build up of temperature at the surface and large temperature gradients throughout the thickness, which are due to the differences in the melting point, specific heat and latent heat of fusion of alumina and titania, as well as the difference in their particle sizes. Also, the increase in magnitude of the mean substrate roughness promotes splat instability (jetting and/or satellite break-up) and formation of radial fingers. It was also observed that the increase in general surface roughness may result in the lower spreading ratio (Dfinal / Dinitial) of thermally sprayed ceramic particles. The spreading process of a droplet is governed not only by the inertia and viscous forces, but also by the thermal contact resistance in the substrate surface.

Resume : Wurtzite ZnO possesses a wide band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature. ZnO has been extensively studied because of its potential applications in various fields, such as gas sensor, solar cells, photodetectors, light emitting diodes and laser systems. Rare earth doped ZnO has attracted much attention as a luminescent material for both fundamental research and applications. Cerium and europium doped ZnO thin films were grown by Pulsed Laser Deposition (Nd:YAG, λ= 266 nm, τ = 6 ns) from Ce2O3:ZnO (1% Ce) and Eu2O3:ZnO targets, respectively, in oxygen or nitrogen ambient. ZnO films were deposited on fused silica and Si (100) substrates at substrate temperature of 300°C and at room temperature. Optical properties were analyzed by optical spectroscopy, spectrophotometric measurement and spectral ellipsometry. Structural properties were characterized by XRD. The corresponding variations in the morphology and microstructural properties were measured using AFM. Chemical composition and structural properties were examined by XPS.

Resume : Pulsed energy beam deposition methods like pulsed laser deposition (PLD) or pulsed electron beam deposition (PED) are very anisotropic processes leading to non-homogeneities in the deposited thin films. Indeed, film thickness, composition and structure are function of the precise position on the substrate with respect to the normal to the target. In this work we have investigated the composition, structure, optical and electrical properties of ZnO thin films grown by PLD and PED as a function of position on the substrate by means of Rutherford Backscattering Spectrometry, X-ray diffraction analyses, optical transmittance and electrical measurements. The energy of ablated species having an important role on the thin film growth, time-resolved angular distribution of plume ions measurements have also been performed with ion probes mounted at various angles with respect to the normal. These results will be presented comparatively for PLD and PED methods as well as the influence of the composition, structure and energy of ablated species on the optical and electrical properties of ZnO films.

Resume : This work is dealing with the use of a femtosecond laser beam to process various insulating substrates employed in microelectronic packaging such as flexible polymers, composite mica multilayers and glass. Typical thickness of these substrates is in the range of few hundred micrometers (100 to 500 µm) and exhibit unsuitable properties by mechanical scribing. Due to the ultra-short pulse duration (less than 110 fs), the expected affected zone (HAZ) should be much less than thicknesses. This last point is crucial to achieve a fully industrial process. Mica, PET 125, PEN and Kapton are also mostly transparent, and the fs laser beam is modulated from 800 to 266 nm to optimize the scribing process. The laser parameters as frequency (up to 1000 Hz), mean powers (up to 3.5 W) and number of passes are investigated for optimizing the scribing in regard to the grooves depth, the HAZ, and speed of process. scanning electronic microscopy and optical microscopy are employed for analyses the local structure after laser scribing. UV-Visible ellypsometry is also used to obtain the optical properties (reflectivity and optical indexes) namely in the wavelength of interest (800, 400 and 266 nm). Non linear absorption is finally considered to understand the physical mechanisms behind fs laser beam interaction with those substrates responsible of depth scribing limitation.

Resume : Laser-based technology used in transferring micrometer sized pixels, from donor to receiving substrates, has been previously demonstrated for organic and inorganic materials by laser-induced forward transfer. Here, we report on the one-step laser printing of multilayered organic-based field effect transistors, using thin films of diPhAc-3T as semiconductor, parylene-C as dielectric and Ag as gate electrode, respectively. The laser, a 50 ps pulsed Nd:YAG device operating at 355 nm, was used to print transistor pixels arrays at ambient temperature. The pixels (350 µm sized-squares, and 500-700 nm in thickness), fabricated in top gate-bottom contact configuration, were investigated for their current-voltage characteristics immediately after printing. The morphology and structure were investigated by optical, electronic, and atomic force microscopy. Electrical characterizations demonstrated that the transistor is fully functional with hole mobilities to 4 x 10^-4 cm^2/V.s, threshold voltage Vt near -10 V and Ion/Ioff ratio near to 10^4 - 10^5. The efficient cohesion between the three different layers offers an exceptionally high physical resistance to laser pulses, while maintaining the electrical properties.

Resume : Pulsed laser deposition (PLD) is a versatile technique which allows the production of thin films with tailored properties. We studied the effect of laser fluence on the morphology, composition, structure and electric conductivity of deposits generated by pulsed laser ablation of a metallic aluminum target in vacuum using a Q-switched Nd:YAG laser (1064 nm, 15 ns). Upon irradiation for one hour at a repetition rate of 10 Hz, deposits on glass consisted of smooth layers of several tens of nanometers, as revealed by atomic force microscopy. Crystallinity, surface chemical composition and conductivity of deposits were determined by X-ray diffraction, X-ray photoelectron spectroscopy and broadband dielectric spectroscopy respectively. Irradiation at fluences around 2 J/cm2, resulted in deposition of amorphous aluminum oxide films. Differently, at higher fluences above 7 J/cm2, the deposits are constituted by metallic aluminum films. Monitoring of the composition and dynamics of the ablation plume was carried out by optical emission spectroscopy which revealed differences in composition under the two fluence regimes. In particular, highly ionized species are more abundant in the plumes generated at higher fluences. The results are discussed by invoking the relations between composition and dynamics of the ablation plume and the properties of deposits, and demonstrate the possibility of control by PLD of the properties of deposits and their either metal or dielectric character.

Resume : The laser-induced forward transfer (LIFT) process can become competitive with other industrial deposition techniques only if its throughput is drastically increased. To this end, we use a galvanometric mirrors system which scans the beam of a fast UV picosecond laser, focusing successive pulses on a silver nanoparticles ink-coated donor substrate. Laser pulses interact with the liquid film and generate adjacent cavitation bubbles that push the ink away from the substrate and form jets. We visualize the ejections with a time-resolved imaging system to study the dynamics of multi-jets regime. Pulses far away from each other produce unperturbed jets. But when the pulses are brought closer, the cavitation bubbles start to interact, which modifies the ejection dynamics and results in significant change of the bubble shape. The ink is ejected faster and in different directions depending on the spacing between pulses. Each bubble modifies the previous one and displaces it away. We present all these effects and discuss them, considering how a cavitation bubble expands in an ink film modified by a previous bubble.

Resume : Alumina has singular properties which make it a quite important material in many fields of the modern industry: electronics, medicine, car manufacturing, communications, etc. In most of its applications, elements made of alumina should be identified by some characters or symbols printed directly on them; however, there is still a lack of a reliable and efficient method to print on alumina. In this sense, laser marking is a promising process to solve this problem. In this paper, we present an extensive experimental study on the conditions to induce coloration on alumina by visible (532 nm) and near-infrared (1064 nm) laser radiation. Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) equipment were employed to analyze the results. The physical processes involved on laser induced coloration were determined in order to make the marks in alumina more legible. The most suitable laser operating conditions were also defined and are reported here. Finally, we propose an explanation for the differences of the coloration induced under different atmospheres and laser parameters. As a practical outcome, we have improved the current laser marking results so the identification of alumina elements becomes clearer since a higher coloration contrast was achieved.

Resume : Overcoming the drawbacks given by conventional methods, we designed and demonstrated a highly efficient synthesis of graphene employing intensely pulsed white light (IPWL) that photoinduces depth-controlled heating rapidly to avoid the substrate damage. The approach provided the synthesis at the interface of Ni-catalyst layer and the substrate, thereby forming the graphene layer directly on a targeted substrate after etching the catalyst without deleterious transfer process. Moreover, since the carbon atoms can be supplied from polymer layer and/or impurities hosted into the catalyst, any external carbon source was not required. In realizing a nonlinear saturable absorber that functioned as mode-locker to form short laser pulses, graphene synthesized by IPWL was incorporated in a fiber-optic component. Ni-catalyst of 50 nm was deposited onto the end surface of a fiber ferrule, and IPWL was irradiated during <60 s with the fluence of ~ 30 J/cm2 under ambient condition. After etching out the catalyst layer, the crystallinity of graphene was checked by Raman. The graphene deposited ferrule was sandwiched by an additional one for laser-graphene interaction. By managing the intracavity power level, chromatic dispersion, and polarization state, we successfully obtained short pulse laser output that has operating center wavelength, repetition rate, and estimated pulse duration of 1571.7 nm, 14.03 MHz, and 3.4 ps, respectively. Higher harmonic pulsation was also achieved.

Resume : This paper will present our recent work on the pulsed laser processing of two-dimensional (2D) materials. In particular, we report on the morphological effects induced upon the interaction of ultrashort laser pulses with various layered crystals. Experiments show that for fluences slightly above the damage threshold, a rippled morphology is attained. Besides this, rapid and facile methodologies for the laser assisted generation of graphene, molybdenum disulfide and boron nitride nanosheets, as well as their decoration with metallic nanoparticles (NPs), will be demonstrated. The former can be attributed to a femtosecond laser assisted exfoliation process, while the fairly good dispersion of nanosheets suggests that large surface areas are available for chemical reactivity. On the other hand, decoration of nanosheets with NPs can be realised through excimer laser irradiation of colloidal dispersions of 2D flakes in the presence of NPs dispersed in solution. Potential applications of pulsed laser synthesized and modified materials in electronics, particular to bulk heterojunction organic solar cells are demonstrated and discussed.

Resume : Several previous studies have demonstrated controlled (size and shape) fabrication of metal nanoparticles (NPs) by laser annealing (LA) of an uncapped metal thin film. In this work we LA stacks of bilayers of metal/dielectric thin films with 193nm and 248nm, producing nano-structures with plasmonic behavior, whereby the metal nanoparticles remain embedded in the dielectric. Therefore we present a novel engineering approach that is capable of subsurface modification, transforming metal layers capped by dielectrics into durable coatings with tunable plasmonic response. Multilayers consisting of alternate layers of AlN and Ag were fabricated by RF magnetron sputtering on Si wafers and on flexible biaxially oriented polypropylene (BOPP) substrates. The bilayer thickness was kept constant at 15 nm and we varied the individual layer thicknesses of Ag and AlN. Upon LA and by varying the processing parameters, we delivered Ag nano-spheres of various size distribution embedded in a hard, inert and durable ceramic material; suitable for applications under harsh environment. We quantitatively analyze the effects of LA (number of pulses, laser wavelength and fluence) and simulate the temperature profile of the structures. Our findings qualify these metal nanostructure arrays as potential candidates for core nanostructures in plasmonic devices.

Resume : Laser-based excitation and detection of one-dimensional (1D) guided wedge waves propagating along the apex of a solid wedge were performed. The characteristic features of guided wedge waves were determined for several anisotropic silicon wedges with different symmetry properties. The pump-probe laser setup allowed the selective excitation of localized and of leaky or pseudo-wedge waves and of two-dimensional (2D) surface acoustic waves. Leaky or pseudo-wedge waves could be discovered for the first time in anisotropic silicon wedges. The strongly localized wedge waves are the slowest elastic waves, whereas the phase velocity of the supersonic pseudo-wedge waves is higher than that of the surface and slow shear bulk waves. Numerical calculations of the phase velocities were performed on the basis of the Laguerre function method. The theoretical results are in very good agreement with the measured velocity values. With the laser experiments it was possible to observe directly the decay of the wedge waves into the bulk material and to see the coupling of the pseudo-wedge wave with the surface acoustic wave on the wedge faces by laser-probe-beam deflection. Wedge waves are expected to open new possibilities for nondestructive evaluation (NDE) of solid edge systems owing to the dispersion effect, observed for imperfect edge geometries, and nonlinear effects due to the high concentration of stress and strain near the apex of the wedge. While surface and pseudo-surface acoustic waves already have found important industrial applications for linear wedge waves several feasibility studies have been performed in recent years, practical applications, however, are still missing.

Resume : A photonic nanojet is an extremely narrow local field that spurts from the rear surface of a transparent sphere with size exceeding the wavelength. With sphere downscaling to the sub-wavelength level, the effect progressively vanishes and the intense field becomes highly localized. Our experiments show that there are two ways in which photonic nanojets can be obtained with sub-micrometer diameter spheres. The first and obvious option is to decrease the wavelength. Using a 193-nm wavelength nanosecond laser, we illuminate spheres with well-controlled diameters from 260 nm. The spheres are assembled into monolayers at the surface of oxidized silicon substrates so that ablation with the nanojets produces periodically-porous silica membranes. The second way relies on nanosphere engineering. Using a modified Stöber method, we synthesize core-shell gold-silica nanospheres. What is essential in our sphere design is to use a light-blocking core to increase the apparent length of the scattered field. We produce and image photonic nanojets at 400-nm wavelength. We show that photonic nanojets similar to those observed with micrometer scale conventional dielectric spheres can be obtained with engineered spheres of only 320-nm diameter. Photonic nanojets from nanoscale spheres must allow ultra-high-density periodic light matter interactions opening routes for new laser nanofabrication and optical diagnostic technologies.

Resume : Raman laser-light polarization dependence have been observed with micro-Raman on so called “D disorder” Raman peak which is characteristic of graphene A type edge structure. This laser light polarization dependence is not observed on the “G “and “2D” peaks of graphene bulk material. Only a reduced laser light polarization dependence is observed for the so-called “D disorder” peak (or band) of DLC composite material containing sp2 clusters (which can be assimilated to imbedded graphene nano-flakes). We suggest explaining this effect in considering the local aspects of our newly discussed extension of the double resonance Raman scattering theory and with the coupling between in-plane and out-of-plane graphene phonon modes which exist in the bulk of graphene material. This coupling of phonon modes can also exist on sp2 clusters edges when those are interlinked to some surrounding matrix material, meanwhile it cannot exist on free graphene edges, and with which we suggest the so called “D disorder” peak possible to provide information on how sp2 cluster edge atoms are bonded to their surrounding matrix. Further on considering the binary and ternary symmetry of corresponding phonon vibration modes, we suggest also some possible resonance between out-of-plane vibration modes and harmonic overtone of in-plane mode, with which the 2D peak to be laser light polarization independent and to give account for the Raman peak observed at 1250 cm-1 which is also characterizing graphene and we propose the iLOLA Raman designation.

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

Resume : We report infrared laser annealing of the silicon surface damaged by Ar plasma irradiation. The surface of n-type 500-micrometer-thick silicon substrates with surfaces coated with 100 nm-thick thermally grown SiO2 layers were irradiated with 13.56 MHz capacitance coupled Ar plasma at 50 W for 120 s. Ar plasma irradiation markedly decreased the light induced minority carrier effective lifetime from 1.7x10^-3 (initial) to 1.7x10^-5 s. Moreover, the capacitance response at 1 MHz alternative voltage as a function of the bias voltage (C-V) measurement reveled that Ar plasma irradiation caused a density of interface traps of 8.0x10^11 cm^-2eV^-1 and a large hysteresis of voltage of 2.0 V in C-V characteristics. Those results mean that Ar plasma caused substantial carrier recombination and carrier trap defect states at the silicon surfaces. The top surface of the samples were subsequently heated with contentious wave 940-nm-semiconductor laser irradiation at 3.6x10^4 W/cm^2 for 4 ms at room temperature in air. The light induced minority carrier effective lifetime was markedly increased to 1.7x10^-3 s, which was the same as the initial value. The density of interface traps was decreased to 8.1x10^9 cm^-2eV^-1. Moreover, the hysteresis of voltage was also decreased to 0.1 V in C-V characteristics. Laser heating effectively decreased the densities of plasma induced carrier recombination and trap states. Those experimental demonstrations suggest that laser rapid heating is useful for decrease damage induced by plasma irradiation, whose process is inevitable for semiconductor device fabrication.

Resume : We report for the first time on the redox multiphoton polymerization of an organic-inorganic composite material, in which one of the components, a vanadium organometallic complex, also acts as a photoinitiator [1]. The composite employs multiphoton absorption to self-generate radicals by photo-induced reduction of the metal species from Vanadium (V) to Vanadium (IV). We exploit this material for the fabrication of fully 3D structures by multiphoton polymerization with 200 nm resolution, employing a femtosecond laser operating at 800 nm, in the absence of a photoinitiator. Nonlinear absorption measurements indicate that, the use of an 800 nm laser initiates the photopolymerization due to three-photon absorption of the vanadium alkoxide. The laser power required to induce this three-photon polymerization is comparable to what is required for inducing two-photon polymerization in materials using standard two-photon absorbers, most likely due to the high content of vanadium in the final composite (up to 50% mole). [1]Kabouraki, E., A. N. Giakoumaki, et al. (2013). "Redox Multiphoton Polymerization for 3D Nanofabrication." Nano Letters 13(8): 3831-3835.

Resume : Holographic lithography (HL) is emerging as a high throughput technique for structuring full wafer scale surface areas with regular patterns from sub-micrometer to nanometer scale periodicities in a single exposure. The biggest limitation of HL is that only periodic patterns can be produced. Despite this drawback HL has been shown to be applicable for structuring photonic crystals, nanowires, porous membranes, magnetic dots, etc. In this work 1D and 2D periodic microstructures in thin positive and negative tone photoresist (on float glass and silicon substrates) were fabricated employing original two-beam multiple exposure HL setup (442 and 405 nm CW lasers). Applying different angles of rotation in between two or three sequential exposures enabled obtaining higher contrast of fringes compared to multiple beam HL approach. Produced patterns were analysed employing optical and scanning electron microscopes (SEM) and compared with the simulated optical field distributions. Intensities of the diffraction maxima of the produced structures were measured and their spatial distributions were compared with fast Fourier transforms of optical microscope dark field micrographs. SEM micrographs were used to determine point lattice types and rotational symmetry of the fabricated structures. Regular structures with periodicities of 1.1-1.2 um and 2D point lattices of rhombus, triangular and square point lattices with different rotational symmetries were fabricated.

Resume : Typical LIPSS structures were produced on silicon (periods between 500 … 650 nm), brass, copper, and stainless steel (period around 400 nm) by irradiation with pulses from an ultra fast (100 fs) white light continuum, spreading in wavelength from 400 … 750 nm. The ripples periods depend, clearly, on both, the material and the irradiation dose (number of pulses), increasing with increasing dose on silicon, decreasing on stainless steel. Given the CONTINUOUS excitation spectrum with very moderate power in narrow spectral intervals, it appears unlikely to attribute the structure formation to any interference effect. Instead, the results are in full agreement with our dynamic model of self-organized structure formation.

Resume : We propose two microsphere-laser joint methods to produce long-range arrays of well-shaped metal nanostructures. First method is a microsphere monolayer assisted laser-induced forward transfer (LIFT) method that allows the parallel printing of metal nanodroplets. The second one is a hybrid methodology: microsphere lithography as initial step, and excimer laser metal dewetting to control the shape of the deposited nanostructures. In our experiments, transparent microsphere monolayers on high-purity suprasil substrates are covered with thermally evaporated Ag films of controlled thickness. When back-illuminated using laser pulses (355-nm wavelength, 50-ps duration) the laser interaction with the microsphere near-field mask produces periodic local detachments of the films that can be collected on a receiving substrate. The results allow discussing the challenges associated with downsizing of the LIFT technique to the nanoscale. When removing the spheres by physico-chemical means, the deposition directly leaves behind arrays of nanosize silver triangles that can be furthermore laser processed. A specific study is presented here on the reshaping of these nanostructures by annealing with an excimer laser (193-nm wavelength, 15-ns duration). In previous work, we prepared nanodot arrays using microsphere-assisted laser fabricated mesoporous membranes. These two alternative methods will add to the panel of available microsphere-assisted technologies to prepare surface nanomaterials.

Resume : Laser-induced periodic surface structures (LIPSS, ripples) were generated on stainless steel and titanium alloy surfaces upon irradiation with multiple linear polarized femtosecond laser pulses (pulse duration 30 fs, central wavelength 790 nm). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning geometry for the processing of large surface areas covered homogeneously by the nanostructures. The irradiated surface regions were subjected to optical microscopy (OM), white light interference microscopy (WLIM) and scanning electron microscopy (SEM) revealing sub-wavelength spatial periods. The nanostructured surfaces were tribologically tested under reciprocal sliding conditions against a sphere of hardened 100Cr6 steel at 1 Hz using paraffin oil and engine oil as lubricants. After 1000 sliding cycles at a load of 1.0 N, the corresponding wear tracks were characterized by OM and SEM. For specific conditions the laser-generated nanostructures endured the tribological treatment. Simultaneously, a significant reduction of the friction coefficient was observed in the laser-irradiated (LIPSS-covered) areas when compared to the non-irradiated surface, indicating the potential benefit of laser surface structuring for tribological applications.

Resume : The formation of laser-induced periodic surface structures (LIPSS, ripples) upon irradiation of silicon with multiple irradiation sequences consisting of femtosecond laser pulse pairs (pulse duration 150 fs, central wavelength 800 nm) is studied numerically using a rate equation system along with a two-temperature model accounting for one- and two-photon absorption and subsequent carrier diffusion and recombination processes [1]. The temporal delay between the individual equal energy fs-laser pulses was varied between 0 and 5 ps for quantification of the transient carrier densities in the conduction band of the laser-excited silicon. Additionally, cumulative effects were considered to account for multiple irradiation sequences. The results of the numerical analyses reveal the importance of carrier generation and relaxation processes in fs-LIPSS formation and quantitatively explain the two time constants of the delay dependent decrease of the rippled area observed experimentally [2]. Evidence is presented that (i) a threshold carrier density must be exceeded transiently turning the semiconductor to a metallic state and that (ii) interference between a surface plasmon polariton and the laser radiation is required to trigger the fs-LIPSS formation. [1] T.J.-Y. Derrien, J. Krüger, T.E. Itina, S. Höhm, A. Rosenfeld, J. Bonse, Opt. Express 21, 29643-29655 (2013). [2] S. Höhm, A. Rosenfeld, J. Krüger, J. Bonse, Appl. Surf. Sci. 278, 7-12 (2013) .

Resume : We report the direct synthesis of titania nanoparticles covered /embedded in carbon/silica layers/matrix using oxidative laser pyrolysis technique. The vapors of TiCl4 and [(CH3)3Si]2O (HMDS) were used as precursors while C2H4 was employed as laser energy transfer agent (sensitizer) and air as oxidant. In the first experimental series, the Ti precursor was introduced through the inner nozzle, whereas the Si precursor was separately injected by an annular coflow. For the second experimental series, the HMDS and TiCl4 flows were interchanged simultaneously with the progressively diminishing of the Ti precursor flow. The color of the powders resulted from the first configuration was grey, whereas from the second configuration was dark blue. XRD reveals the presence of anatase/rutile crystalline phases. In the first series the anatase percent in the mixture with rutile increases from 39 to 78% with the increasing of supplementary air flow introduced through the 2nd nozzle. The second series powers show a higher anatase content (85-90%) simultaneously with an increasing of the Si atomic percent (from ~ 8 to 18%). The presence of carbon revealed by the EDS can be visualised in HR-TEM images (as turbostratic shells surrounding the TiO2 nanoparticles). The raw powders were annealed in air at 450°C followed by the preliminary testing of their photocatalytic properties.

Resume : The increasing demand for transparent conductive electrodes (TCE) in optoelectronic devices, flat-panel displays, organic light emitting diodes and photovoltaic cells has pushed to find new structures and materials to this aim. Dielectric-metal-dielectric (DMD) multilayer structures [1, 2] are good candidates compared to standard TCEs electrodes because of the enhanced conductivity, high optical transmission, lower temperature process, reduced thickness and, consequently, significant cost reduction and improved mechanical flexibility. However, DMD multilayers are still far from being implemented on thin film photovoltaic device technology. A crucial aspect is the TCE film patterning (scribing) for electrical isolation. This is done by a laser ablation removing the thick, typically 0.7 to 1 μm, TCE front contact deposited on glass. In this work we show how the energy density threshold for laser scribing is significantly reduced when the standard AZO single layer is replaced with a 10 times thinner AZO/Ag/AZO multilayer structure, still having good electrical and optical properties [3]. Thin films of 40/10/40 nm of AZO/Ag/AZO were grown on soda lime substrates by RF magnetron sputtering at RT. Nd:YAG laser treatments were done by a single pulse (12 ns) at 1064 nm. The fluence was varied in the range 1.15 to 4.6 J/cm2. Our experimental results, supported by computer simulation, provide clear evidences of the key role played by the silver interlayer in lowering the laser power to obtain electrical isolation within the laser spot. [1] Kim S. et al. J. Photon Energy 2:021215 (2012). [2] Crupi I. et al. Thin Solid Films 520, 4432 (2012). [3] Crupi I. et al. Nanoscale Res Lett 8:392 (2013).

Resume : Carbon monoxide (CO), in its quality of a major toxic air pollutant usually emitted by products of combustion processes from industrial, transportation and domestic activities, has always been among the central issues in the environmental protection field. Gold (Au) is a metal with no reactivity in bulk; however, in the form of nanoparticles it exhibits high activity for several reactions. It has already been shown that gold nanoparticles supported on oxides can assist oxidation of CO. It has further been shown that the reactivity of gold depends on both the nanoparticle size and on the support used. The progress in synthesizing porous, nanosized, and nanostructured oxide materials allows one to use such structures as a support medium in catalytic reaction. The aim of this work is to fabricate zirconium oxide (ZrO2) nanostructures on steel substrates by pulsed laser deposition (PLD). The morphology of the ZrO2 nanostructures is related to the morphology of the layer (metal or oxide) pre-deposited on the steel substrates. Subsequently, Au nanoparticles are deposited on the ZrO2 nanostructures. The catalytic behavior of Au supported on ZrO2 is investigated with a view of low-temperature CO oxidation. The catalytic activity of the Au/ZrO2 system is related to the gold particle size and the zirconium oxide support’s porosity.

Resume : We report on the formation of laser induced periodic surface structures (LIPSS) upon irradiation with the fourth harmonic of a Nd:YAG laser (266 nm, pulse duration 7 ns) followed online by synchrotron Grazing Incidence Small Angle X-ray Scattering (GISAXS). Spin coated films 100-200 nm thick of different polymers were irradiated at repetition rates between 1 and 10 Hz employing laser fluences below the corresponding ablation threshold. In situ measurements were performed at the BM26B at the ESRF in order to study the evolution of the structural features online upon repetitive irradiation and to obtain information about the mechanisms involved in LIPSS formation. Laser irradiation was performed at normal incidence with the laser polarization parallel to the propagation of the X-ray beam. LIPSS parallel to the polarization direction and with final periods close to the laser wavelength were obtained, as confirmed by atomic force microscopy. The number of pulses needed for the onset of LIPSS formation and for achieving the optimal order of the structures varies for the different polymers. It has been verified that both absorption coefficient and the glass transition temperature of the polymer are crucial magnitudes for the onset of LIPSS formation. The real time monitoring allows online optimization of both laser fluence and repetition rate for LIPSS formation.

Resume : Ultrashort laser-induced modification of silicon is a process of great interest for future three-dimensional microelectronics, photodetectors and photovoltaics. Within the study of laser-induced nanostructures, sub-surface modifications of silicon have been observed by several authors. It has been proposed that the crystalline silicon is transformed into metastable polymorphic phases that could be attributed to stresses or high pressure waves [1]. Recently, it has been demonstrated that the surface morphology along with the femtosecond laser excitation of charge carriers plays an important role in the spatial modulation of the laser deposited energy [2]. In this work, we present a new possible explanation for this sub-surface modification based on an inhomogeneous absorption energy profile described by Mie scattering theory along with the free-carrier excitation. Finite Difference Time Domain (FDTD) simulations and Transmission Electron Microscopy (TEM) analysis suggest that the fs-laser-irradiated pre-structured surface acts as an assembly of microlenses which enhances the laser energy density at a micrometric range below the surface level and thus induce the local change of phase. The possibility of sub-surface modifications along with the transient change of the optical properties is thus demonstrated below the surface of nanostructured silicon. [1] M.J. Smith, E. Mazur et al, J. Appl. Phys. 110, 053524 (2011) [2] T. J.-Y. Derrien. Ph.D. thesis, Aix Marseille Université (Feb. 2012)

Resume : The fundamental principle of ZnO nanogenarator is to utilize the environmental mechanical energy, which is available from irregular vibrations and human activity with a wide spectrum of frequencies and time-dependent amplitudes. The prototyping of a recent nanogenarator by means of ZnO piezoelectric nanowire (NW) arrays have demonstrated to able to drive micro-sensor and in micro-power range. However so far the power output from NW nanogenarator is still below micro watt, which is far away from milli-power output source requested by most applications of individual sensor. The mechanism understanding of piezo-electric conversional in ZnO material and device is crucial to further boost power output. In this paper, the Pd-dopied ZnO films grown by pulsed-laser deposited (PLD) in the Pd doping range of 0.01-0.05% are investigated. The grown films are structurally characterized by XRD, SEM and AFM. The piezoelectric properties of these films are characterized by Piezoelectric Force Microscopy (PFM). The free-carrier density is characterized by CV and Hall-effect station. It is found that the piezoelectric properties of the films are strongly dependent on free-carrier density. The observed corresponds of piezoelectric (PE) property to grain size is also theoretically explained by the combination mechanism of free-carrier and static-charge.. *Corresponding author, zhangw@njut.edu.cn

Resume : An important step in optimizing the growth process of Pr and Er doped GaLaS (GLS) thin films by laser ablation is to study the properties of the plasma formed after the interaction of laser radiation-bulk material. The induced plasma expansion was investigated through time- and space-resolved optical emission spectroscopy and fast gate ICCD imaging. For target ablation we used two types of lasers with different pulse durations (ns and fs) and repetition rates (10Hz and 1kHz). The ICCD sequential snapshots of the spectrally unresolved plasma of Er and Pr doped GLS revealed the formation of a single plasma structure but with different dynamics as the temporal regime is changed. From the space–time evolution of spectral lines intensities we determined the velocities of various species and also the variation of the excitation temperature and electronic density. In some cases, the unusual higher velocities of atoms compared to ions suggest the presence of different recombination, excitation and ionization mechanisms or radiative processes during plasma expansion. Periodic oscillations of both excitation temperature and electronic density were observed with periods of 130ns and 100ns for the Er:GSL and Pr:GLS respectively.

Resume : The formation of laser-induced periodic surface structures (LIPSS) has been widely observed following solid target irradiation with ultrashort laser pulses. The interference between incident laser and a surface scattered/diffracted wave leads to inhomogeneous energy deposition at the illuminated surface. The material response also contributes to LIPSS formation through relaxation and self-organization. Surface planes with different crystal orientations possess different densities of surface atoms, surface energies and potential bonding sites, therefore these planes respond differently to the energy absorption, which may consequently play a role during LIPSS formation. The present study shows the influence of crystal orientation on LIPSS formation. Electron Backscatter Diffraction (EBSD) characterization has been exploited to provide structural information within the laser spot on irradiated samples to determine the dependence of LIPSS formation upon the crystal orientation. The results provide experimental evidence that laser-induced lattice damage, the formation of LIPSS and crystal orientation are highly correlated. Significant differences on crystal planes with different orientations are observed at low-to-medium number of laser pulses at low fluence regime, outstandingly for (111)-oriented surface which favors dislocation storage rather than LIPSS formation.

Resume : Nanosecond pulsed laser ablation of Au and Ag targets in water was utilized to prepare noble metal nanostructures – nanoparticles and nanowire networks. The fundamental (λ = 1064 nm), the second (λ = 532 nm) and the third (λ = 355 nm) harmonics of a Nd-YAG laser system were used for their fabrication. The duration of the ablation process was varied to optimize the fabrication conditions for both materials. It was interrupted after 5, 10, 15, 20, 25 min respectively and the mass concentration of the nanostructures in the colloid were measured. This enabled us to establish the dependence of the ablation rate on the concentration. The effect of the liquid pressure on the characteristics of the different nanostructures was investigated by changing the liquid level over the corresponding target. Five different values were utilized of the water level above the target surface (5, 10, 15, 20, 25 mm) at a constant liquid volume and duration of the ablation process (10 min) and different laser fluencies. Images obtained by transmission electron microscopy were used to visualize the morphology of the nanostructures produced. The profile of the optical extinction spectra of the colloids was helpful in assessing the state of the solid phase and the morphology of the material. To explain the differences in the spectra profiles, theoretical simulations were used of the extinction cross-sections for free nanoparticles and for aggregates of interacting nanoparticles.

Resume : Colloids of noble metal nanostructures were produced by pulsed laser ablation of solid targets in water. The fundamental (λ = 1064 nm), the second (λ = 532 nm) and the third (λ = 355 nm) harmonics of a Nd:YAG laser system were utilized in the ablation process. Sedimentation and aggregation of the nanoparticles produced were studied by measuring the optical extinction spectrum of the colloids, which were stored in a cuvette at a constant temperature for this purpose. The optical extinction spectra were taken at different heights of the cuvette and their changes at different time periods after fabrication were traced. They were used to assess the aging process of the colloids expressed in sedimentation and aggregation of the nanostructures. To visualize these two processes, transmission electron microscopy was used. The influence of the aggregation on the optical properties of the colloids was evaluated by theoretical simulations of their optical extinction spectra. Ultrasonic treatment of the colloids was applied to achieve modification of the already created clusters and recover the optical properties of the colloids as closely as possible similar to these on the day of preparation. As a result, some of the aggregates were completely disintegrated while others fragmented into smaller ones. The aim was to establish the optimal storage conditions of the colloids in view of preserving their characteristics.

Resume : Laser ablation of materials in Liquid has been demonstrated to be a versatile technique for nanoparticles production. The ablation of metal plates in solution has shown this peculiar ability whose scientific interest has been widely growing up during the last years. In this work the Laser Ablation in Liquid technique has been used for producing silver nanoparticles confined in hexagonally ordered mesoporous SBA-15 and MCM-41 silica materials. The goal of inserting Ag nanoparticles within the silica structure has been pursued recently for enhancing the catalytic suitability of such materials. With this aim silver nanoparticles have been generated by using a 100 fs, 800 nm Ti:Sa pulsed laser beam in confined nanoporous silica MCM-41 and SBA-15 water solutions. Polidispersion nanoparticle distributions were characterized by UV-Vis spectroscopy and the features were related to the preparation method of the colloidal solution as well as the laser beam parameters used. Furthermore, the obtained Ag nanoparticles dispersed within the nanoporous silica network was accomplished by XRD, SEM and TEM characterizations. A significant amount of 5 nm size silver nanoparticles, in the form of metallic silver (Ag0) can be obtained by a suitable selection of the laser ablation in liquid condition used. The work performed shows that the choice of the experimental parameters employed for laser ablation in aqueous silica suspension can affect dimension distributions of the obtained nanoparticle.

Resume : Protective coatings with a high abrasive wear resistance can be obtained from powders by laser cladding technique, in order to extend the service life of some industrial components. So this work was devoted on one hand, to produce laser clad layers of self-fluxing NiCrBSi alloy powder mixed with WC powder on stainless steel substrates of austenitic type (AISI 304) and on the other hand, to employ the laser-induced breakdown spectroscopy (LIBS) technique to chemically characterize these clad layers. With the suitable laser processing parameters (mainly output power, beam scan speed and flow rate) and powders mixture proportions between WC ceramics and NiCrBSi alloys, dense pore free layers have been obtained on single tracks, on large areas with overlapped tracks and on multiple layers. In this last case, a material with concentration gradient has been produced applying different proportions of WC particles through the coating. The results achieved by LIBS technique allowed us to determine the chemical composition of these coatings and was particularly interesting for multiple layers with different concentrations where the LIBS rasters performed on cross-sections allowed to discriminate the thicknesses of the different layers. Moreover the LIBS signals were correlated with the hardness measurements on these materials showing their dependence.

Resume : In this work Ag and Au thin films (5-10 nm in thickness), grown by RF Magnetron Sputtering were subjected to Laser Annealing (LA), using pulsed UV laser sources; thus transforming the as grown layers to nanoparticles of various sizes and shapes. A systematic study over the applied laser wavelength, fluence and sample environment pressure is presented for a single pulse process. A key feature for a potential future large scale processing is simplicity and speed for high capacity and low fabrication costs; thus our motivation to study LA effects with only one single pulse. We used two laser sources, ArF (193 nm) and KrF (248 nm), and varying fluences (up to 1 J/cm2). A pressure cell was used to study the effect of LA whilst the sample is pressurized with an inert gas (up to 10 bar) and comparisons with experiments conducted under ambient atmosphere were made. The derived nanostructures were evaluated in terms of their topography employing Atomic Force Microscopy and their plasmonic behavior employing Optical Reflectance Spectroscopy (ORS). In summary we report the influence of the laser annealing parameters on tailoring the structural and optical properties of the NPs that are derived by nanostructuring thin metal films of Ag and Au. Acknowledgements: The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement n° PIEF-GA-2012-330444.

Resume : In the present investigation, epitaxial growth of silicon films was carried out on poly-Si seed layers, which were grown by aluminium induced crystallization (AIC) on glass, using CW infrared laser annealing. The seed layers were RCA cleaned before the deposition of a-Si precursor using electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD) at 250oC. The films were characterized by elastic recoil detection analysis (ERDA) to evaluate the hydrogen content, and the analysis showed that the films contain a high concentration of hydrogen (~10 at. %). The laser crystallization process in solid phase regime resulted in crack free films while the surface is cracked in liquid phase regime. The microstructural quality and grain size distribution of laser annealed epitaxial layers showed a strong dependence on the gas mixtures (SiH4/Ar/H2) used to deposit a-Si precursor used for epitaxy. However, the layers showed a strong (100) orientation similar to the seed layer as observed from electron backscatter diffraction (EBSD) analysis. The average grain size of the epitaxial layers is found to be superior to 7 μm with a wide range of distribution from 1 μm to 30 μm. The texture of the epitaxial films was not affected by the film thickness but merely the average grain size. The laser scanning speed and its power are shown to have significant effects on the silicon crystallized fraction.

Resume : Nanostructuring features under ultrafast laser excitation of metallic surfaces are strongly influenced by light coupling and the associated material response under conditions of electron-phonon nonequilibrium. This is nowadays imperfectly described with uncertainties on the transient variation of optical and electronic properties during irradiation. In that context, dedicated ab initio calculations were carried out in the framework of the Density Functional Theory to elucidate some of the primary aspects of material response. Ground-state calculations and molecular dynamic simulations have been thus conducted to derive electronic structure and associated transport properties under nonequilibrium conditions. We observe that electronic temperature leads to strong modifications of the electronic screening. This displaces in turn the electronic structure, affecting transient electronic properties such as free electron number, specific heat and thermal pressure. Finally, we evaluate the optical index under different electronic temperatures based on the Kubo-Greenwood formalism. In addition to providing insights into the dynamics of optical response of a metallic surface, these transport properties also shines a new light on a recurring problem concerning periodicity variations of LIPSS (ripples) under ultrashort excitation. Accordingly, the consequences of thermal nonequilibrium on inhomogeneous electric field distribution on a rough metallic surface will be also addressed.

Resume : One of the ablated morphologies of interaction laser – matter, which have attracted particular attention, is the appearance of surface LIPSS (Laser Induced Periodic Surface Structure). LIPSS formation on copper thin films was investigated in this present work by applying accumulative pulses with 42 ps and 10 ns pulse duration at 266 nm wavelength and 1Hz repetition rate. Copper and Cobalt thin films were deposited on silicon and glass substrates by magnetron sputtering. Both laser beams have the same spatial energy distribution (Gaussian) but different pulse duration. This allows the study of this last parameter effect on LIPSS formation. Namely, a comparison of the ablation threshold and the incubation coefficient on copper and cobalt thin films varies with respect to the pulse duration and the shot number. Morphologies changes of ablated regions were studied as a function of pulse duration, fluence and shot number. Moreover, the change of reflectivity on copper thin film is also identified during the LIPSS formation by Time Resolved Reflectivity (TRR) method. This method was widely used due to their non-destructive advantage namely in the nanosecond regime; it is also fast and sensitive with a high spectral/spatial resolution. In this study several beams were used (cw Cd-He (325 nm), Blue DPSS (473 nm) and He-Ne (633 nm)) as probing lasers directed onto the same UV heating laser spot. The reflected signals are measured using very fast photodiodes (less than 35 ps time rise) and correlated to the MEB images during the LIPSS formation.

Resume : The phenomenon of large areas coherent covering with LIPPS produced by multiple, adjacent spots is investigated by varying spot overlap and irradiation dose per spot. In contrast to the typical experimental arrangement, the linear traces of spots were produced by discontinuously advancing the sample between the individual spots. We show that even with almost no overlap the LIPSS patterns appear to be coherently connected. Further, we study the effect pre-structuring the sample surface by impressing lines, narrower than one spot diameter on stainless steel and silicon.

Resume : The dynamics of the formation of laser-induced periodic surface structures (LIPSS) on fused silica upon irradiation with linearly polarized fs-laser pulses (50 fs pulse duration) is studied using two complementary experimental setups. For analyzing the relevance of temporally distributed energy deposition in the early stage of LIPSS formation, a Mach-Zehnder interferometer generated multiple double-pulse sequences at two different wavelengths (400 & 800 nm) and with varying inter-pulse delays up to a few ps. These two-color experiments confirm the importance of the ultrafast energy deposition to the silica surface for LIPSS formation, particularly by the first laser pulse of each sequence. The second laser pulse subsequently reinforces the previously seeded spatial LIPSS frequencies. Additional fs-pump-probe diffraction measurements were performed in trans-illumination geometry to investigate the influence of transient excitation stages in the early LIPSS development. In this (second) setup, the temporal delay between the pump-pulse (800 nm wavelength; inducing the LIPSS) and the probe-pulse (a frequency-doubled fraction of the pump-beam) can be varied between 0 and 1 ns with a temporal resolution of ~0.1 ps. The results prove that the ultrafast energy deposition of the first few laser pulses to the materials surface is essential for the formation of LIPSS. In silica, it triggers specific subsequent physical mechanisms such as the formation of self-trapped excitons.