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Applied Surface Science (v.254, #4)

Laser Synthesis and Processing of Advanced Materials by Peter Schaaf; Rosalia Serna; James G. Lunney; Eric Fogarassy (pp. 789-789).

Substrate heating effects on the propagation dynamics of laser produced plume during pulsed laser deposition of oxides by A. Sambri; M. Radovic’; X. Wang; S. Amoruso; F. Miletto Granozio; R. Bruzzese (pp. 790-793).

We report on the expansion dynamics of laser-produced plasma plumes of complex oxides in an oxygen atmosphere. In particular, we have studied the combined effects of background gas pressure and substrate heating on the plume propagation in typical pressure and temperature regimes of oxides thin film deposition by pulsed laser deposition. Our results evidence a reduced resistance of the background gas to the plume propagation as the substrate temperature increases. The experimental data are analyzed in the frame of a model describing the plume propagation into the background gas. Our experimental findings clearly indicate that the deposition temperature might influence film growth, not only through its direct thermal effect on the surface kinetics of adatoms, but also by affecting the energetic properties of the precursors in the gas phase.

Keywords: Pulsed laser deposition; Oxides; Plasma plume dynamics

Localization of the electromagnetic field in the vicinity of gold nanoparticles: Surface modification of different substrates by Petar A. Atanasov; Nikolay N. Nedyalkov; Tetsuo Sakai; Minoru Obara (pp. 794-798).

Theoretical predictions and experimental results for nanosized modification of metal (Au), semiconductor (Si), or dielectric (soda lime glass) substrates using near-electromagnetic field enhancement in the vicinity of gold nanoparticles are presented. The near field properties for the system consisting of an isolated gold nanoparticle or nanoparticle aggregate deposited on the substrates, which is irradiated by electromagnetic wave, are investigated using Finite Difference Time Domain Simulation technique. The influence of the substrate material on the near field distribution characteristics is predicted. The results reveal that the field on the substrate surface is enhanced in the three investigated cases, but its spatial distribution and magnitude depend on the substrate material. In the case of the metal and semiconductor substrate the enhanced near field is strongly localized in the vicinity of the contact point with the particle, in an area with diameter smaller than the particle's one. The intensity of the enhanced field on the glass is more than an order of magnitude lower than the case of using silicon substrate. The properties of the near field on the substrate surface also depend on the particle arrangement. For a two-dimensional gold nanoparticle array, when the particles are closely arrayed, the intensity of the enhanced field on the substrate surface is minimal. With the increase of the interparticle distance the near field intensity increases. The validity of the obtained theoretical results is confirmed experimentally.

Keywords: PACS; 81.16.−c; 81.65.Cf; 52.38.MfPlasmons; Gold nanoparticles; Femtosecond laser nanostructuring

Laser-induced damage threshold of sapphire in nanosecond, picosecond and femtosecond regimes by O. Uteza; B. Bussière; F. Canova; J.-P. Chambaret; P. Delaporte; T. Itina; M. Sentis (pp. 799-803).

The surface laser-induced damage threshold fluence of sapphire is determined under various experimental conditions concerning the material irradiation (femtosecond, picosecond and nanosecond temporal regimes) and preparation (surface state). The results are of interest for optimising laser micromachining processes and for robust operation of high-peak power femtosecond Ti:sapphire laser chains.

Keywords: PACS; 42.70.Hj; 77.84.−sLaser-induced damage; Sapphire; Femtosecond; Picosecond; Nanosecond

VUV light induced surface interaction and accelerated diffusion of carbon, silicon, oxygen and other contaminants in LiF crystals by E. Sarantopoulou; C.P.E. Varsamis; Z. Kollia; A.C. Cefalas; J. Kovač; S. Kobe (pp. 804-810).

One hundred and fifty-seven nanometers irradiation of LiF crystals accelerates the penetration of C, O, N, Si and other contaminants within the crystal bulk. New bonding between the contaminant elements in both the irradiated and the non-irradiated areas of the crystal was identified. The chemical changes eventually form inhomogeneous nano/micro-islands, which further agglomerate to larger structures in the form of an interfacial layer. The concentration and diffusion (∼100nm) of contaminants in the irradiated part of the crystal is higher than for the non-irradiated one. The accelerated diffusion is due to a force perpendicular to the crystal surface. This force is generated by the laser's electric field gradient in the direction of beam propagation due to the inhomogeneous absorption at the interfacial layer. A theoretical diffusion model in the presence of the laser field allows rationalizing and interpreting the experimental results.

Keywords: PACS; 81.40.WX; 8140.TV; 81.40.−2Optics/surface contamination; Radiation damage; Light induced adsorption; Bulk diffusion; Silicon

Laser-produced plasma ion characteristics in laser ablation of lithium manganate by Donagh O’Mahony; James Lunney; Thomas Dumont; Stela Canulescu; Thomas Lippert; Alexander Wokaun (pp. 811-815).

Laser ablation is widely used to assist in the fabrication of prototype lithium manganate (LiMn₂O₄) thin film structures for Li-ion battery electrodes via the pulsed laser deposition technique. However, films can be considerably Li and/or O deficient, depending the deposition conditions used. Here we present data on the ionic component of laser-produced plasma in laser ablation of lithium manganate with ns excimer laser. Plasma was monitored using an electrical Langmuir ion probe, in time-of-flight mode in conjunction with mass spectrometry to identify the dominant ionic species. Ablation in vacuum at ∼2.5Jcm⁻² revealed the plasma's ionic component was composed primarily of singly charged Li and Mn ions. The time-of-flight data indicates significant deceleration of the plasma when ablation is carried out in an oxygen background gas pressure of the order of 10Pa. The implications for thin film growth are considered in terms of the possible gas phase interactions and/or thin film re-sputtering yield.

Keywords: PACS; 47.40.−x; 52.77.−j; 52.77DqLaser ablation; Ion dynamics; Langmuir probe; Lithium manganate; Resputtering

Influence of initial micro-porosity of target on material ejection under nanosecond laser pulses by Yu. Chivel; M. Petrushina; I. Smurov (pp. 816-820).

Heating and explosive destruction of the near surface volume of metal with initial micro-porosity under nanosecond laser pulse is simulated. It is shown that presence of initial micro-porosity may influence and modify the ejection mechanisms from melt and from solid phase. Thermal and gas dynamic processes in a gas bubble growing in laser irradiated melt are analysed. Experiments show rather different surface morphology defined by micro-explosions and melt ejection for different metals. Possible explosion of micro-pores and solid particles release under nanosecond laser irradiation is analysed for metals with high melting point. It is shown that the stress attains the values that are close to the damage threshold.

Keywords: PACS; 61.80.Az; 61.80.BaPore; Bubble; Droplets ejection; Laser ablation

Features of laser radiation interaction with metals having cryogenic temperature by Tatiana Khatko; Viacheslav Khatko (pp. 821-825).

In this paper we determine the features of the thermophysical processes involved in the interaction of laser radiation with metals that have cryogenic temperature. To do so, we use a one-dimensional model that involves heating a semi-infinite solid by a point thermal source with a constant flux density. Temperature fields, heating and cooling rates in the laser-irradiated zone for iron and titanium at the ambient temperatures of 77 (liquid nitrogen), 293 and 573K were calculated. The intensity of the laser irradiation enabled the melting temperatures of 1933K and 1812K on the Ti and Fe surface, respectively, to be reached. The duration of the laser pulse was 4.5ms. We show that a drop in ambient temperature from 573 to 77K leads to a rise in cooling rate from 3.25×10³ and 6.4×10⁶K/s to 4.25×10³ and 1.3×10⁷K/s in the Ti and Fe targets, respectively. Agreement was good between the calculated depths of melting and phase transformation isotherms and the experimental depths of the interfaces of melting and heat-affected zones.

Keywords: PACS; 52.50.Jm; 61Laser nitriding; Refractory metal; Liquid nitrogen; Microstructure

Investigation of tolerances of diffractive optical elements for the high power near infrared lasers by E. Neiss; M. Flury; J. Fontaine (pp. 826-829).

The deformations due to thermal expansion of a binary diffractive grating in fused silica under near infrared high power laser exposure are estimated by a Finite Element Method. They are compared to the geometrical tolerances obtained by a rigorous electromagnetic method which is used to calculate the optical performances. It is shown that the grating deformations remain below the geometrical tolerances for an average laser power of up to 1kW and an exposition of up to 100s.

Keywords: PACS; 42.79.DjDiffractive optical elements; High power laser; Thermal and electromagnetic simulations

3-D holographic lithography of organic–inorganic hybrids by M. Salaün; M. Audier; F. Delyon; M. Duneau (pp. 830-835).

Fabrications of ordered three-dimensional structures with submicron lattice constants were performed on organic–inorganic hybrids using a holographic lithography technique recently reported in the literature. The possibility of such a patterning has previously been demonstrated from single nanosecond laser pulse irradiation of thin films of epoxy photoresist and mixtures of methacrylate-alkoxy-silane with Zr or Ti alkoxides. In the present work, UV irradiation of similar hybrid resins were carried out through repeated laser pulses of low energy with a twofold objective: (i) to study the interference stability for future chemical gas phase decomposition experiments and (ii) to obtain patterning through large film thickness (e.g. 1mm). The influence of several parameters on the structuration was examined from observations by scanning electron microscopy and optical diffraction. Many interdependent parameters were considered in different steps of the process, namely (i) hybrid resin preparations with required properties of stability, transparency and viscosity, (ii) film coating on different substrates, (iii) UV irradiation (energy and number of laser pulses), (iv) ultrasonic dissolution of monomer, and (v) sample drying. As results, different structuration resolutions were observed as a function of these parameters. But if the influence of a few parameters was easily understood and controlled, it has also appeared that it was not the case of all of them.

Keywords: Holographic lithography; Organic–inorganic hybrid materials

Functional polymers by two-photon 3D lithography by Robert Infuehr; Niklas Pucher; Christian Heller; Helga Lichtenegger; Robert Liska; Volker Schmidt; Ladislav Kuna; Anja Haase; Jürgen Stampfl (pp. 836-840).

In the presented work, two-photon 3D lithography and selective single-photon photopolymerization in a prefabricated polydimethylsiloxane matrix is presented as an approach with potential applicability of waveguide writing in 3D by two-photon polymerization.Photopolymers based on acrylate chemistry were used in order to evaluate the optical capabilities of the available two-photon system. Several photoinitiators, tailored for two-photon absorption, were tested in a mixture of trimethylolpropane triacrylate and ethoxylated trimethylolpropane triacrylate. Best results were obtained with a recently synthesized diynone-based photoinitiator. Feature resolutions in the range of 300nm were achieved. Due to the cross-conjugated nature of that donor-π-acceptor-π-donor system a high two-photon absorption activity was achieved. Therefore, a resin mixture containing only 0.025wt% of photoinitiator was practical for structuring by two-photon polymerization. The required initiator content was therefore a factor of 100 lower than in traditional one-photon lithography.The aim of the second part of this work was to fabricate optical waveguides by selectively irradiating a polymer network, which was swollen by a monomer. The monomer was polymerized by conventional single-photon polymerization and the uncured monomer was removed by evaporation at elevated temperatures. This treatment leads to a local change in refractive index. Refractive index changes in the range of Δ n=0.01 (Δ n/ n=0.7%) were achieved, which is sufficient for structuring waveguides for optoelectronic applications.

Keywords: TPA; Two-photon polymerization (2PP); Photopolymerization; 3D lithography; Optical waveguide; Functional photopolymer

Pattern generation using axicon lens beam shaping in two-photon polymerisation by B. Bhuian; R.J. Winfield; S. O’Brien; G.M. Crean (pp. 841-844).

The fabrication of three-dimensional microstructures by two-photon polymerisation has been widely reported as a viable route to the development of photonic crystals, rotors, bridges and other complex artefacts requiring nanoscale resolution. Conventionally, single point serial writing is used to write the structures but recently multipoint beam delivery using beam division optics has been reported as a method of introducing parallel processing. In this paper we present an alternative and novel approach using an axicon lens to give profiled beam delivery. This enables complete three-dimensional annular structure fabrication without the use of scanning stages. In addition, the concept of axicon delivery is developed further to investigate three-dimensional structure as a function of axicon geometry.A Ti:sapphire laser, with wavelength 795nm, 80MHz repetition rate, 100fs pulse duration and an average power of 700mW, was used to initiate two-photon polymerisation. The axicon was used, in combination with a 100× microscope objective, to form representative three-dimensional structures based on the annular cell with varying diameter. The structures were written in a Zr-loaded resin prepared on a glass substrate using dip coating deposition of a Zr/PMMA hybrid prepared by the sol–gel method. Annuli with diameters up to 50μm were characterised in terms of topography and surface roughness using SEM and Zygo interferometer. The writing technique was also extended to fabrication of stacked structures.

Keywords: Two-photon polymerisation; Optics; Sol–gel

Controlled process for polymer micromachining using designed pulse trains of a UV solid state laser by Diana Ilie; Claire Mullan; Gerard M. O’Connor; Tony Flaherty; Thomas J. Glynn (pp. 845-849).

A flexible workstation equipped with a solid state laser operating at 266nm wavelength was used to machine holes in polyethylene terephthalate, polyimide and polycarbonate. An optical pulse picker was employed to reduce the high repetition rates of the laser, while a breakthrough sensor was used to avoid over-drilling of through holes. For each material, different repetition rates and designed pulse trains were tested to improve feature quality and process efficiency. Although the three polymers had very different reactions at this wavelength they all showed an improvement in feature quality with decreasing repetition rate due to a reduction in thermal effects. Up to 10kHz the average depth per pulse remained unchanged and afterwards a slight increase was observed but this was accompanied by large uncertainties. Bursts of pulses at 40kHz inserted inside the low repetition rate pulse train reduced the drilling time and the amount of debris redeposited without affecting the feature quality. It was found that a number of cleaning pulses after perforation eliminates the heat affected zone around exits. Holes with entrance diameters below 20μm and exit diameters as small as 2μm were obtained with high repeatability.

Keywords: Polymer; Micromachining; UV solid state laser; Pulse picker; Breakthrough sensor

Holographic lithography of a two-dimensional hexagonal structure: Effect of beam polarization by M. Salaün; M. Audier; M. Duneau; F. Delyon (pp. 850-854).

A comparison is made between the theoretical determination of the interference contrast function with fabricated two-dimensional hexagonal structures of submicron lattice constant. Experiments were performed using a siloxane based hybrid organic–inorganic material and a holographic lithography method.Thin hybrid structured layers were fabricated and characterized for different conditions of beam polarizations between 0° and 90°. As a result, the photo patterning appears to be strongly dependent on beam polarization in accordance with theoretical predictions.

Keywords: Holographic lithography; Hybrid organic–inorganic material

Excimer laser processing of ZnO thin films prepared by the sol–gel process by R.J. Winfield; L.H.K. Koh; Shane O’Brien; Gabriel M. Crean (pp. 855-858).

ZnO thin films were prepared on soda-lime glass from a single spin-coating deposition of a sol–gel prepared with anhydrous zinc acetate [Zn(C₂H₃O₂)₂], monoethanolamine [H₂NC₂H₄OH] and isopropanol. The deposited films were dried at 50 and 300°C. X-ray analysis showed that the films were amorphous. Laser annealing was performed using an excimer laser. The laser pulse repetition rate was 25Hz with a pulse energy of 5.9mJ, giving a fluence of 225mJcm⁻² on the ZnO film. Typically, five laser pulses per unit area of the film were used. After laser processing, the hexagonal wurtzite phase of zinc oxide was observed from X-ray diffraction pattern analysis. The thin films had a transparency of greater than 70% in the visible region. The optical band-gap energy was 3.454eV. Scanning electron microscopy and profilometry analysis highlighted the change in morphology that occurred as a result of laser processing. This comparative study shows that our sol–gel processing route differs significantly from ZnO sol–gel films prepared by conventional furnace annealing which requires temperatures above 450°C for the formation of crystalline ZnO.

Keywords: Zinc oxide; Laser annealing; Sol–gel

Time-resolved stimulated emission spectroscopy in the ultrashort domain through pump–probe experiments by S. Orlando; A. Paladini; L. Guidoni; A. Santagata; G.P. Parisi; P. Villani; R. Teghil; A. De Bonis; A. Galasso; A. Giardini (pp. 859-862).

The photoemission properties of fluorescent chromophores have a widespread application in many fields ranging from chemical-physics and biology to organic light emitting devices. These systems usually display high fluorescence conversion efficiency, which makes them suitable for transient/gain experiments also in liquid solutions, thin films and eventually in protein environments.Pump and probe methods have been widely employed for wavelength-resolved spectroscopy in the subpicosecond time scale. In our group, we have recently assembled a new experimental setup for pump and probe spectroscopy: preliminary tests on the Rhodamine B dye in ethanol have been performed in order to optimize the setup . The dynamic response of photoinduced changes of the chromophore dispersed into a suitable solvent has been studied with a subpicosecond time resolution.The optically prepared initial state of the Rhodamine B in ethanol solution appears to evolve on a timescale of few picoseconds into a successive state, which could be attributed to an intramolecular charge transfer state.

Keywords: Time-resolved laser spectroscopy; Ultrafast dynamics; Pump and probe; Rhodamine B

fs/ns dual-pulse LIBS analytic survey for copper-based alloys by A. Santagata; R. Teghil; G. Albano; D. Spera; P. Villani; A. De Bonis; G.P. Parisi; A. Galasso (pp. 863-867).

The quantitative analytic capability of a fs/ns dual-pulse Laser-Induced Breakdown Spectroscopy technique, based on the orthogonal reheating of a fs-laser ablation plume by a ns-laser pulse, is presented. In this work, it is shown how the effect played by the delay times between the two laser beams can vary the analytical response of this dual-pulse LIBS configuration. In order to address this task, the Sn, Pb and Zn calibration curves of five certified copper-based samples have been investigated. These calibration curves have been obtained, in air at atmospheric pressure, by integrating the emission data collected in two different inter-pulse delay zones, one in the delay interval of 1–41μs, the other within the range of 46–196μs. For drawing the species calibration curves, the emission intensities of the considered Pb(I), Sn(I) and Zn(I) electronic transitions have been normalized with a non-resonant Cu(I) emission line. The experimental results have shown that, by varying the inter-pulse delay between the two laser beams, complementary analytical results can be induced. By considering at once all data acquired within the inter-pulse delay time of 1–196μs, this hypothesis has been strengthened. The calibration curves obtained in this way are characterized by excellent linear regression coefficients (0.988–0.999) despite of the large Sn, Pb and Zn compositional variation of the targets employed. The results presented reveal, for the first time, that, by taking into account the role played by the inter-pulse delay time between the two laser beams, the fs/ns dual-pulse LIBS configuration here used can be improved and provide very good opportunities for performing quantitative analysis of copper-based alloys.

Keywords: PACS; 82.80.Dx; 79.20.Ds; 32.30.Jc; 32.30.−r; 39.30.+w; 78.47.+pLaser-induced emission spectroscopy; Dual-pulse LIBS; Laser-pulsed orthogonal reheating; fs laser-pulsed ablation; Copper-based alloys analysis

Characterization of inorganic species in coal by laser-induced breakdown spectroscopy using UV and IR radiations by M.P. Mateo; G. Nicolas; A. Yañez (pp. 868-872).

In this work, the capability of laser-induced breakdown spectroscopy for process control in a thermal power plant is presented through quantitative compositional characterization of the coal used for combustion. Laser-induced emission signal of seven samples with a range of concentrations was calibrated for quantification purposes. The eighth sample was subsequently analyzed five times as unknown in order to determine the precision and accuracy of the measurements. Two modes of operation, dynamic and static and two laser wavelengths, 1064nm and 355nm were employed in this study for comparison. The results revealed that UV wavelength provided better results than IR radiation in terms of accuracy for the quantification of inorganic species in coal after the comparison with conventional atomic absorption spectrometry characterization.

Keywords: Laser-induced breakdown spectroscopy (LIBS); Coal; Thermal power plant; Quantitative analysis; Calibration curves

The use of laser-induced plasma spectroscopy technique for the characterization of boiler tubes by G. Nicolas; M.P. Mateo; A. Yañez (pp. 873-878).

The present work focuses on the characterization of boiler tube walls using laser-induced plasma spectroscopy technique with visual inspection by optical and scanning electron microscopy of the cross-sections of these tubes. In a watertube boiler, water runs through tubes that are surrounded by a heating source. As a result, the water is heated to very high temperatures, causing accumulation of deposits on the inside surfaces of the tubes. These deposits play an important role in the efficiency of the boiler tube because they produce a reduction of the boiler heat rate and an increase in the number of tube failures. The objectives are to determine the thickness and arrangement of deposits located on the highest heat area of the boiler and compare them with tube parts where the heat flux is lower. The major deposits found were copper and magnetite. These deposits come mainly from the boiler feedwater and from the reaction between iron and water, and they do not form on the tube walls at a uniform rate over time. Their amount depends on the areas where they are collected. A Nd:YAG laser operating at 355nm has been used to perform laser-induced plasma spectra and depth profiles of the deposits.

Keywords: LIBS; Boiler tube; Chemical cleaning; Heat flux

Hybrid fuzzy logic control of laser surface heat treatments by José Antonio Pérez; José Luis Ocaña; Carlos Molpeceres (pp. 879-883).

This paper presents an advanced hybrid fuzzy logic control system for laser surface heat treatments, which allows to increase significantly the uniformity and final quality of the obtained product, reducing the rejection rate and increasing the productivity and efficiency of the treatment. Basically, the proposed hybrid control structure combines a fuzzy logic controller, with a pure integral action, both fully decoupled, improving the performances of the process with a reasonable design cost, since the system nonlinearities are fully compensated by the fuzzy component of the controller, while the integral action contributes to eliminate the steady-state error.

Keywords: Laser materials processing applications; Surface heat treatments; Process monitoring and control; Fuzzy logic

Substrate effect on excimer laser assisted crystal growth in phosphor Ca_0.997Pr_0.002TiO₃ polycrystalline thin films by Tomohiko Nakajima; Tetsuo Tsuchiya; Toshiya Kumagai (pp. 884-887).

Ca_0.997Pr_0.002TiO₃ thin films that show strong red luminescence were successfully prepared by means of an excimer laser assisted metal organic deposition process with a KrF laser at a fluence of 100mJ/cm² at 100°C. The CPTO films grew on the silica, borosilicate, and indium-tin-oxide coated glasses. The crystallinity of the Ca_0.997Pr_0.002TiO₃ films depended on the substrates; the borosilicate and indium-tin-oxide coated glasses with a large optical absorption of a KrF laser ( λ=248nm) were effective for the crystallization for the Ca_0.997Pr_0.002TiO₃. In addition, a high thermal conductivity of the indium-tin-oxide coated glass substrate could also improve the crystallinity due to an enhancement of thermal propagation to the film. Oxygen annealing at 500°C for 6h successfully eliminated the oxygen vacancy produced by the laser irradiation, and also remarkably improved the PL emission intensity. Thus, we have shown that substrate properties such as an optical absorbance and a thermal conductivity were quite important factors for the crystal growth and the PL emission for the Ca_0.997Pr_0.002TiO₃ in the excimer laser assisted metal organic deposition process.

Keywords: Excimer laser assisted metal organic deposition; Low-temperature fabrication; Thin film; Phosphor; Perovskite titanate; Laser anneal

FEM simulation of the laser plasma interaction during laser nitriding of titanium by Daniel Höche; Gerd Rapin; Peter Schaaf (pp. 888-892).

Laser nitriding of materials is based on the interaction of short pulsed laser radiation with the treated material and the hitherto formed laser plasma. The process is very promising for the fast formation of surface coatings with superior properties. Due to the short interaction times and the thin surface films an experimental observation of the underlying processes is very difficult. In order to access the basic mechanism, finite element method simulations of laser heating, evaporation, plasma formation and expansion, plasma composition and interaction with the materials surface have been performed. As a result, evaporation and expansion velocities, pressure balances and dissociation degrees have been derived. The results give a better insight into the physical processes and dependencies of the coating formation, in this case for the titanium–nitrogen system. This finally allows an optimization of the coating synthesis.

Keywords: Titanium; Plasma dynamics; FEM simulation

Analysis of surface and material modifications caused by laser drilling of AlN ceramics by N. Nedialkov; M. Sawczak; R. Jendrzejewski; P. Atanasov; M. Martin; G. Śliwiński (pp. 893-897).

For the laser drilling of aluminum nitride ceramic the processing results and the effects related to pulsed irradiation were investigated. Images of the drilled surface revealed regular, cylindrically shaped holes of about 100μm in diameter independently of the laser wavelength (1064/532/355 or 266nm). The holes were surrounded by circular heat-affected zones of larger diameter. A comparison of the elemental compositions of the original material and the processed one indicated a decrease of the nitrogen concentration in the affected area. The spectral analysis of the ablated material composition revealed the presence of ions and neutrals in dependence on the laser intensity applied. It was found that at intensity values close to the ablation threshold the ejected material consisted mainly of neutrals, while doubling of the intensity resulted in appearance of single-ionized Al species, which were also observed together with Al clusters in the mass spectra of the UV-excited plasma. Their prevailing content was revealed for drilling at higher intensities around 15GW/cm² at 532nm. Results of model calculations indicated, in agreement with the experiment, that at the threshold the ceramic decomposes into gaseous nitrogen and solid Al particulates, while at a higher fluence the material particles vaporize and influence the quality of drilling.

Keywords: PACS; 61.43.Gt; 61.82.Ms; 61.80.BaLaser drilling; AlN ceramics; Numerical simulations

Numerical analysis of Excimer laser assisted processing of multi-layers for the tailored dehydrogenation of amorphous and nano-crystalline silicon films by L. Fornarini; J.C. Conde; S. Chiussi; F. Gontad; B. Leon; S. Martelli (pp. 898-903).

The application of the striking electrical and optical properties of amorphous and nano-crystalline silicon in photovoltaic, photonic and nano-electronic devices is attracting increasing attention. In particular, its use both on polymeric substrates and in Integrated Circuit technology for the development of enhanced new devices has shown that processing techniques to produce amorphous hydrogenated and nano-crystalline silicon films avoiding high substrate temperatures are of great importance. A promising strategy to achieve this purpose is the combination of Hot-Wire Chemical Vapor Deposition at 150°C with Excimer Laser Annealing, thus maintaining the substrate at relatively low temperature during the complete process.In this work we present a numerical analysis of Excimer Laser Annealing, performed at room temperature, of a multilayer structure of thin alternating a-Si:H and nc-Si films deposited on glass and grown by Hot-Wire Chemical Vapor Deposition. A set of two different layer thicknesses a-Si:H (25nm)/nc-Si (100nm) and a-Si:H (30nm)/nc-Si (60nm) were analysed for a total structure dimension of 900nm. The aim is to determine the probable temperature profile to achieve controlled localized in depth dehydrogenation.Temperature distribution has been calculated inside the multilayer during the irradiation by a 193nm Excimer laser, 20ns pulse length, with energy densities ranging from 50 to 300mJ/cm². Calculations allowed us to estimate the dehydrogenation effect in the different layers as well as the structural modifications of the same layers as a function of the applied laser energy.The numerical results have been compared to the experimental ones obtained in similar multilayer structures that have been analysed through Raman spectroscopy and TOF-SIMS in depth profiling mode.

Keywords: PACS; 61.80.Ba; 81.40.Ef; 82.30.Rs; 73.61.JcExcimer laser annealing; a-Si:H; nc-Si; Dehydrogenation; Numerical model

A study on shielding gas contamination in laser welding of non-ferrous alloys by G. Tani; A. Ascari; G. Campana; A. Fortunato (pp. 904-907).

Laser welding of non-ferrous alloys is a high-productivity and cost-effective joining technology, which gained an undoubted interest especially in aerospace, chemical and medical industry, where high strength and corrosion resistant mechanical parts are required. Unfortunately some of the most used non-ferrous alloys are highly reactive with respect to the components of the environmental atmosphere: oxygen, nitrogen, hydrogen and humidity. This reactivity leads to the formation of porosities and to oxides and nitrides inclusion, which are responsible for a decrease of ductility and strength in welded joints.According to this a good shielding technique of the weld pool is of primary importance in order to obtain sound beads and reliable manufacturings. This paper deals with the opportunity of simulating the shielding gas behavior by means of Computational Fluid Dynamics software in order to understand the relationship among the outlet position, the shielding gas type and its flow rate.A simulation activity was carried out in order to evaluate the behavior of shielding gas concentration surrounding the weld pool. The simulated welding environment was simplified without considering the presence and the effect of the plasma plume. The main results concern the shielding gas contamination prediction with respect to the distance from the beam-material interaction zone.

Keywords: Laser welding; Shielding gas; Contamination; CFD

Crystalline patterning in Sm-doped sodium borate glass by CW Nd:YAG laser irradiation by Yusok Lim; Myeongkyu Lee (pp. 908-910).

Laser irradiation of glass materials has drawn much attention because this technique can offer a new processing method for spatially selected structural modification and/or crystallization in glass. Crystallized line and dot patterns at the micrometer scale were fabricated on the surface of Sm-doped sodium borate (Na₂O–B₂O₃) glass by irradiation of a continuous-wave Nd:YAG laser at λ=1064nm. The pattern sizes could be controlled by adjusting such parameters as scan rate, exposure time, and laser power. Analyses by Raman spectroscopy and X-ray diffraction revealed that the crystalline phase is Na₃Sm₂(BO₃)₃.

Keywords: Patterning; Glass; Laser

Micromachining of semiconductor by femtosecond laser for integrated circuit defect analysis by M. Halbwax; T. Sarnet; J. Hermann; Ph. Delaporte; M. Sentis; L. Fares; G. Haller (pp. 911-915).

The latest International Technology Roadmap for Semiconductors (ITRS) has highlighted the detection and analysis of defects in Integrated Circuits (IC) as a major challenge faced by the semiconductor industry.Advanced tools used today for defect cross sectioning include dual beams (focused ion- and electron-beam technologies) with resolution down to the sub-Angstrom level. However ion milling an IC with a FIB is time consuming because of the need to open wide cavities in front of the cross-sections that need to be analyzed. Therefore the use of a femtosecond laser as a tool for direct material removal is discussed in this paper. Experiments were performed on IC structures to reveal the different layers of fabrication: selective or total ablation can occur depending on the laser energy density, without delamination of the layers. Different laser irradiation conditions like pressure (air, vacuum), polarization, beam shaping, and scanning parameters have been used to produce different types of cavities. The femtosecond laser engraving of silicon-based structures could be useful for cross-sectioning devices but also for other applications like direct-write lithography, photomask repair, maskless implantation or reverse engineering/restructuring.

Keywords: Laser microcutting; Engraving; Femtosecond laser; Defect analysis

The influence of laser power and repetition rate on oxygen and nitrogen insertion into titanium using pulsed Nd:YAG laser irradiation by L. Lavisse; J.M. Jouvard; J.P. Gallien; P. Berger; D. Grevey; Ph. Naudy (pp. 916-920).

Oxygen and nitrogen insertion in a titanium substrate is performed in air using a Q-switched Nd-YAG laser. This process modifies the surface by the formation of specific layers on the substrate. These layers show different properties, largely influenced by the insertion of elements in the layers. The treatment conditions, especially the laser parameters (fluence and repetition rate), must be known and controlled. Using nuclear analysis, we demonstrate that oxygen insertion is mainly influenced by repetition rate, and that nitrogen insertion is controlled by laser fluence. The physical phenomena involved in the oxygen and nitrogen insertion are discussed.

Keywords: Laser surface treatments; Titanium oxides; Titanium nitrides; NRA

Investigation of temperature and stress fields in laser cladded coatings by Rafał Jendrzejewski; Gerard Śliwiński (pp. 921-925).

Temporal and spatial distributions of temperature and strain–stress have been modelled and investigated experimentally for the laser cladding process. The model corresponded to experimental conditions where the multilayer protective coatings were prepared by direct laser cladding of stellite SF6 powder on X10Cr13 chromium steel by means of a 1.2kW CO₂ laser. For calculations the effect of base preheating, temperature dependent material properties, and also influence of time-break between cladding of the consecutive layers were taken into account. The calculated temperature fields indicated good bonding of the substrate and coating, which was in agreement with the micro-analytical test results. A decrease of the number of microcracks in the coating with an increase of substrate preheating temperature was concluded from stress calculations and confirmed in the experiment. Moreover, an increase of the cracking susceptibility with an increase of the time delay between cladding of the consecutive layers was evidenced by modelling. The best technological results were obtained for the case of single-layer coatings prepared on a preheated substrate and for higher coating thickness required the processing of consecutive layers with a possibly short time delay is advisable due to effective usage of laser beam energy for preheating and lower temperature gradients.

Keywords: Strain–stress field; Laser cladding; Protective coating; Cracking

Supersonic laser spray of aluminium alloy on a ceramic substrate by A. Riveiro; F. Lusquiños; R. Comesaña; F. Quintero; J. Pou (pp. 926-929).

Applying a ceramic coating onto a metallic substrate to improve its wear resistance or corrosion resistance has attracted the interest of many researchers during decades. However, only few works explore the possibility to apply a metallic layer onto a ceramic material. This work presents a novel technique to coat ceramic materials with metals: the supersonic laser spraying.In this technique a laser beam is focused on the surface of the precursor metal in such a way that the metal is transformed to the liquid state in the beam–metal interaction zone. A supersonic jet expels the molten material and propels it to the surface of the ceramic substrate.In this study, we present the preliminary results obtained using the supersonic laser spray to coat a commercial cordierite ceramic plate with an Al–Cu alloy using a 3.5kW CO₂ laser and a supersonic jet of Argon.Coatings were characterized by scanning electron microscopy (SEM) and interferometric profilometry.

Keywords: Cellular solid; Aluminium; Laser

Advanced design of periodical architectures in bulk metals by means of Laser Interference Metallurgy by A. Lasagni; M. D’Alessandria; R. Giovanelli; F. Mücklich (pp. 930-936).

Patterning of high-resolution features on large-area metallic substrates has been performed by means of the Laser Interference Metallurgy method. Due to the intensity distribution of the interference pattern, this technique allows to locally and periodically heat the material surface to temperatures higher than the melting point with a long-range order. In this study, commercial stainless steel, copper and aluminum substrates were irradiated using single pulses of a nanosecond Nd:YAG laser with two and three laser-beam configurations operating at 355nm of wavelength. Thermal simulations have been performed by finite element method and compared to the experiments. The results indicate that the structuring is produced by a surface tension driven mechanism induced by the thermal gradient. Moreover, metals with short thermal diffusion lengths present very homogeneous structures and the structure depth that can be achieved at relatively high laser fluences during single-pulse experiments is on the order of the diffusion length.

Keywords: PACS; 64.70.Dv; 42.25.Hz; 81.65.CfLaser Interference Metallurgy; Metallurgical processes; Laser patterning

Physical aspects of laser nitriding of yttria stabilized t-zirconia by Y.P. Kathuria (pp. 937-941).

This manuscript describes the surface nitriding of yttria (Y₂O₃) stabilized tetragonal zirconia (t-ZrO₂) by using the pulsed Nd-YAG laser irradiation in the nitrogen atmosphere. The results show modification of the crystallographic structure between the original tetragonal zirconia and the treated one. Nitrogen atoms enter in zirconia substituting oxygen atoms in the network. X-ray diffraction and Raman spectra show an efficient transformation of the t-ZrO₂ at the surface that exhibit typical yellow-gold color of ZrN with high hardness and wear resistance. The X-ray diffraction results evidenced the new diffraction lines [c-ZrN(200)] that appear on the nitrided sample with alteration and shift in peaks as well as change in d-spacing or lattice parameter, whereas the Raman spectra revealed the two characteristics band related to acoustic part of low frequency in the 150–260cm⁻¹ region and optical part at high frequency in the 450–750cm⁻¹ region. Nitriding is accompanied by the formation of a few micron thick gradient layer of ZrN structure on the top via dissociative process: 2ZrO₂+N₂=2ZrN+2O₂ and a partial transformation of t-ZrO₂ into cubic zirconia (c-ZrO₂) beneath deep in the bulk due to nitrogen concentration gradient. Some new features on the physical characteristics such as hardness and roughness of the cut sections of t-ZrO₂ in the N₂ and O₂ atmosphere are discussed.

Keywords: Laser; t-ZrO; ₂; ZrN; XRD; Raman microscopy

Laser gettering of structural-impurity defects in the contacts of metal–intrinsic CdTe with a Schottky barrier by G.I. Vorobets; O.I. Vorobets; V.N. Strebegev; Yu.V. Tanasyuk (pp. 942-947).

The influence of surface laser treatment on structural properties of metal–intrinsic CdTe contacts was investigated by metallographic method and scanning electronic microscopy techniques. At critical intensities of pulse laser irradiation on the metal–CdTe boundary re-structuring of structurally impurity defects in a solid state occurs. A defect system of large grains of single crystalline CdTe is formed. Separate clusters were ordered over a long range and formed their own “crystalline sublattice”, probably, of trimetric configuration. A diameter of the cluster in nodes of such a lattice equalled 1–3μm, while distance between clusters was of about 10–15μm. As radiation dose was increased the clusters acted as getters of dot defects. At optimal modes of laser irradiation their sizes increased in 2–3 times, consequently leading to decrease in concentration of deep levels in the semiconductor. As has shown investigation of the I– V and C– V characteristics such processes caused reduction of GR component of a current, promoting field charge transfer mechanisms in contacts with a Schottky barrier.

Keywords: Surface laser treatment; Metal–intrinsic CdTe contacts; Defect system; Getters of dot defects; Generation–recombination current

Theoretical and experimental analysis of high power diode laser (HPDL) hardening of AISI 1045 steel by F. Lusquiños; J.C. Conde; S. Bonss; A. Riveiro; F. Quintero; R. Comesaña; J. Pou (pp. 948-954).

Laser surface hardening makes use of the rapid and cooling cycles produced on metals surfaces exposed to a scanning laser beam without affecting the bulk of the sample. Mechanical and chemical properties of the surface can be enhanced through the metallurgical transformations that take place during the mentioned thermal cycles. Steels and cast irons are the usual materials to be hardened by laser and recently the high power diode lasers (HPDL) became the appropriate tool to carry out this process. In this work, some systematic experiments have been carried out to harden AISI 1045 surface samples by a cw (HPDL) working at different power levels (470, 760W). The main processing parameters (scanning velocity and density power of the laser beam) were tuned from the prediction realized by the numerical (ANSYS) analysis of the heat conduction involved in the process. Such analysis allowed us to put in evidence the variation of the temperature and the cooling rate of the steel sample surface, affecting the uniformity of the demanding mechanical properties of the surface. In this way, a close-loop temperature control of the surface was justified in order to keep the hardness value within the range required. The formation of martensite phase in the laser treated superficial zone confirmed the hardening of the steel.

Keywords: HPDL laser hardening; AISI 1045 steel

Deposition and properties of high-carbon iron films by Salvatore Cusenza; Michael Seibt; Peter Schaaf (pp. 955-960).

Thin high-carbon iron films were deposited by pulsed laser deposition onto grids for transmission electron microscopy using pre-combined carbon/iron targets with equal area ratio. The deposited films of about 20nm in thickness were directly characterized by transmission electron microscopy. The films showed a variety of phases, surprisingly also including the NaCl-type FeC phase, which was theoretically predicted in the literature. For comparison, thin high-carbon stainless-steel films were deposited onto oxidized Si wafers with different carbon ratios in the targets (10, 20, 40 and 50at.%). These films were characterized by means of Mössbauer Spectroscopy, the magneto-optical Kerr-effect, grazing incidence X-ray diffraction and Rutherford backscattering spectrometry. With these methods clearly defined multilayer-structures were observed which could lead to interesting magneto-resistance phenomena if the thickness of the multilayers can be controlled by the processing parameters.

Keywords: FeC; Austenitic stainless steel; Mössbauer; Phase formation

Laser synthesis of nitrides on the surface of refractory metals immersed in liquid nitrogen by Tatiana Khatko; Viacheslav Khatko (pp. 961-965).

In this paper we describe an approach for the formation of composite layers on the surface of refractory metals. We show that laser radiation on refractory metals (Ti, V, Zr, Mo, Hf, Ta, and W) immersed in liquid nitrogen can provide a chemical synthesis of nitride phases on the surface of metals. The metals were subjected to pulsed laser radiation with a wavelength of 1.06μm. The power density ranged from 10⁴ to 10⁹Wcm⁻². The synthesis of nitrides began with the formation of Me_xN_y ( x> y) phases with low contents of nitrogen. When the melting point was reached at the metal surface, the quantity of MeN phases increased sharply. Study of the melting zone showed that it contained a non-uniform distribution of nitride phases. The quantity of nitrides was a maximum on the surface and decreased with the increase of the depth of melting zone. Due to the high-cooling rates, titanium nitride crystallized in the form of columns. Maximum microhardness in the Ti surface layer was up to 20,000MPa.

Keywords: PACS; 52.50.Jm; 61.10.Nz; 62.20Laser nitriding; Refractory metal; Liquid nitrogen; Microstructure; Hardness

Alumina–zirconium ceramics synthesis by selective laser sintering/melting by I. Shishkovsky; I. Yadroitsev; Ph. Bertrand; I. Smurov (pp. 966-970).

In the present paper, porous refractory ceramics synthesized by selective laser sintering/melting from a mixture of zirconium dioxide, aluminum and/or alumina powders are subjected to optical metallography and X-ray analysis to study their microstructure and phase composition depending on the laser processing parameters. It is shown that high-speed laser sintering in air yields ceramics with dense structure and a uniform distribution of the stabilizing phases. The obtained ceramic–matrix composites may be used as thermal and electrical insulators and wear resistant coating in solid oxide fuel cells, crucibles, heating elements, medical tools. The possibility to reinforce refractory ceramics by laser synthesis is shown on the example of tetragonal dioxide of zirconium with hardened micro-inclusion of Al₂O₃. By applying finely dispersed Y₂O₃ powder inclusions, the type of the ceramic structure is significantly changed.

Keywords: PACS; 42.62.−b; 64.70.−p; 28.52.−s; 81.05.JeRapid manufacturing; Selective laser melting; Ceramic powder

Crystallisation of TiO₂ thin films induced by excimer laser irradiation by O. Van Overschelde; R. Snyders; M. Wautelet (pp. 971-974).

Titanium dioxide thin films have been deposited by reactive magnetron sputtering on glass substrate and subsequently irradiated by UV radiation using a KrF excimer laser. In this work, we have study the influence of the laser fluence ( F) ranging between 0.05 and 0.40mJ/cm² on the constitution and microstructure of the deposited films. Irradiated thin films are characterized by profilometry, scanning electron microscopy and X-ray diffraction. As deposited films are amorphous, while irradiated films present an anatase structure. The crystallinity of the films strongly varies as a function of F with maximum for F=0.125J/cm². In addition to the modification of their constitution, the irradiated areas present a strongly modified microstructure with appearance of nanoscale features. The physico-chemical mechanisms of these structural modifications are discussed based on the theory of nucleation.

Keywords: Excimer; Anatase; TiO; ₂; Thin films

Heat transfer modelling and stability analysis of selective laser melting by A.V. Gusarov; I. Yadroitsev; Ph. Bertrand; I. Smurov (pp. 975-979).

The process of direct manufacturing by selective laser melting basically consists of laser beam scanning over a thin powder layer deposited on a dense substrate. Complete remelting of the powder in the scanned zone and its good adhesion to the substrate ensure obtaining functional parts with improved mechanical properties. Experiments with single-line scanning indicate, that an interval of scanning velocities exists where the remelted tracks are uniform. The tracks become broken if the scanning velocity is outside this interval. This is extremely undesirable and referred to as the “balling” effect. A numerical model of coupled radiation and heat transfer is proposed to analyse the observed instability. The “balling” effect at high scanning velocities (above ∼20cm/s for the present conditions) can be explained by the Plateau–Rayleigh capillary instability of the melt pool. Two factors stabilize the process with decreasing the scanning velocity: reducing the length-to-width ratio of the melt pool and increasing the width of its contact with the substrate.

Keywords: Selective laser melting; Radiation transfer; Heat transfer; Capillary instability

Strategy of manufacturing components with designed internal structure by selective laser melting of metallic powder by I. Yadroitsev; L. Thivillon; Ph. Bertrand; I. Smurov (pp. 980-983).

Application of selective laser melting for manufacturing three-dimensional objects represents one of the promising directions to solve challenging industrial problems. This approach permits to extend dramatically the freedom of design and manufacture by allowing, for example, to create an object with desired shape and internal structure in a single fabrication step. The design of the part can be tailored to meet specific functions and properties (e.g. physical, mechanical, chemical, biological, etc.) using different materials. Metallic objects were manufactured by Phenix PM 100 machine from Inconel 625 powder. The objective was to analyze the influence of the manufacturing strategy on the internal structure and mechanical properties of the components manufactured by selective laser melting technology. Anisotropy of the internal structure and mechanical properties of the fabricated objects were studied.

Keywords: PACS; 42.62.−b; 64.70.Dv; 28.52.−sRapid manufacturing; Selective laser melting; Powder

Laser annealing study of PECVD deposited hydrogenated amorphous silicon carbon alloy films by U. Coscia; G. Ambrosone; F. Gesuele; V. Grossi; V. Parisi; S. Schutzmann; D.K. Basa (pp. 984-988).

The influence of carbon content on the crystallization process has been investigated for the excimer laser annealed hydrogenated amorphous silicon carbon alloy films deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD) technique, using silane methane gas mixture diluted in helium, as well as for the hydrogenated microcrystalline silicon carbon alloy films prepared by PECVD from silane methane gas mixture highly diluted in hydrogen, for comparison. The study demonstrates clearly that the increase in the carbon content prevents the crystallization process in the hydrogen diluted samples while the crystallization process is enhanced in the laser annealing of amorphous samples because of the increase in the absorbed laser energy density that occurs for the amorphous films with the higher carbon content. This, in turn, facilitates the crystallization for the laser annealed samples with higher carbon content, resulting in the formation of SiC crystallites along with Si crystallites.

Keywords: Silicon–carbon alloys; Pulsed laser treatment; Crystallization

Ceramic components manufacturing by selective laser sintering by Ph. Bertrand; F. Bayle; C. Combe; P. Goeuriot; I. Smurov (pp. 989-992).

In the present paper, technology of selective laser sintering/melting is applied to manufacture net shaped objects from pure yttria–zirconia powders. Experiments are carried out on Phenix Systems PM100 machine with 50W fibre laser. Powder is spread by a roller over the surface of 100mm diameter alumina cylinder. Design of experiments is applied to identify influent process parameters (powder characteristics, powder layering and laser manufacturing strategy) to obtain high-quality ceramic components (density and micro-structure).The influence of the yttria–zirconia particle size and morphology onto powder layering process is analysed. The influence of the powder layer thickness on laser sintering/melting is studied for different laser beam velocity V ( V=1250–2000mm/s), defocalisation (−6 to 12mm), distance between two neighbour melted lines (so-called “vectors”) (20–40μm), vector length and temperature in the furnace. The powder bed density before laser sintering/melting also has significant influence on the manufactured samples density.Different manufacturing strategies are applied and compared: (a) different laser beam scanning paths to fill the sliced surfaces of the manufactured object, (b) variation of vector length (c) different strategies of powder layering, (d) temperature in the furnace and (e) post heat treatment in conventional furnace. Performance and limitations of different strategies are analysed applying the following criteria: geometrical accuracy of the manufactured samples, porosity. The process stability is proved by fabrication of 1cm³ volume cube.

Keywords: PACS; 42.62.−b; 61.43.Gt; 81.05.Je; 81.20.EvCeramic powder; Stabilized zirconia–yttria; Selective laser sintering

Modification of Cd1−_xMn_xTe crystal surface layers by nanopulsed laser irradiation by E.I. Gatskevich; G.D. Ivlev; A.I. Rarenko; A.I. Savchuk; V.N. Strebegev; Z.I. Zakharuk (pp. 993-996).

The surface modification of Cd1−_xMn_xTe ( x=0–0.3) crystal wafers under pulsed laser irradiation has been studied. The samples were irradiated by a Q-switched ruby laser with pulse duration of 80ns. Optical diagnostics of laser-induced thermal processes were carried out by means of time-resolved reflectivity measurements at wavelengths 0.53 and 1.06μm. Laser irradiation energy density, E varied in the range of 0.1–0.6J/cm². Morphology of irradiated surface was studied using scanning electron microscopy. The energy density whereby the sample surface starts to melt, depends on Mn content and is equal to 0.12–0.14J/cm² for x≤0.2, in the case of x=0.3 this value is about 0.35J/cm². The higher Mn content leads to higher melt duration. The morphology of laser irradiated surface changes from a weakly modified surface to a single crystal strained one, with an increase in E. Under irradiation with E in the range of 0.21–0.25J/cm², the oriented filamentary crystallization is observed. The Te inclusions on the surface are revealed after the irradiation of samples with small content of Mn.

Keywords: CdMnTe; Laser irradiation; Phase transformation; Reflectivity; Scanning electron microscopy

Short pulse laser microforming of thin metal sheets for MEMS manufacturing by J.L. Ocaña; M. Morales; C. Molpeceres; O. García; J.A. Porro; J.J. García-Ballesteros (pp. 997-1001).

Continuous and long-pulse lasers have been used for the forming of metal sheets for macroscopic mechanical applications. However, for the manufacturing of micro-electro-mechanical systems (MEMS), the applicability of such type of lasers is limited by the long-relaxation-time of the thermal fields responsible for the forming phenomena. As a consequence of such slow relaxation, the final sheet deformation state is attained only after a certain time, what makes the generated internal residual stress fields more dependent on ambient conditions and might make difficult the subsequent assembly process for MEMS manufacturing from the point of view of residual stresses due to adjustment.The use of ns laser pulses provides a suitable parameter matching for the laser forming of an important range of sheet components used in MEMS that, preserving the short interaction time scale required for the predominantly mechanic (shock) induction of deformation residual stresses, allows for the successful processing of components in a medium range of miniaturization but particularly important according to its frequent use in such systems.In the present paper, a discussion is presented on the specific features of laser interaction in the timescale and intensity range needed for thin sheet microforming with ns-pulse lasers along with relevant modelling and experimental results and a primary delimitation of the parametric space of the considered class of lasers for the referred processes.

Keywords: PACS; 62.50.+p; 81.20.Hy; 81.40.Vw; 85.85.+j; 87.80.MjLaser micro-scale peen forming; Forming mechanism; Numerical modelling

Laser synthesis of thin layers of In₄Se₃, In₄Te₃ and modification of their structure and characteristics by T.A. Melnychuk; V.M. Strebegev; G.I. Vorobets (pp. 1002-1006).

Trends of structural modifications and phase composition occurring in In₄Se₃ thin films and In₄Se₃–In₄Te₃ epitaxial heterojunctions under laser irradiations have been investigated. Dynamics of the layer structure modification, depending on laser modes, i.e. pulse duration τ=2–4ms, irradiation intensity I₀=10–50kW/cm², number of pulses N=5–50, was studied by electron microscopy. An increase in laser influence promotes enlargement of the layer grains and transformation of their polycrystalline structure towards higher degree of stoichiometry. As a result of laser solid restructuring heterojunctions of In₄Se₃–In₄Te₃, being photosensitive within 1.0–2.0μm and showing fast time of response, have been obtained. Laser modification of structure enables one to optimize electrical and optical properties of functional elements on the base of thin films and layers of In₄Se₃, In₄Te₃, widely used as infrared detectors and filters.

Keywords: Pulse laser irradiation; Epitaxial heterostructures n-In; ₄; Se; ₃; –p-In; ₄; (Se; ₃; ); 1−; _x; (Te; ₃; ); _x; Photosensitivity; Spectral characteristics

Laser synthesis of Au/Ag colloidal nano-alloys: Optical properties, structure and composition by Giuseppe Compagnini; Elena Messina; Orazio Puglisi; Valeria Nicolosi (pp. 1007-1011).

We have successfully synthesized Au/Ag colloidal nano-alloys with a wide range of compositions by laser ablation of single metal targets in water and a re-irradiation of mixed colloidal suspensions. The optical extinction spectra have been obtained in the plasmon resonance region and their analysis by using the Mie-Gans approach has lead to a quantitative estimation of a number of different structural features for the sols. Some of the obtained results are supported by X-ray photoelectron data and transmission electron microscopy, while others are used to investigate the kinetics of formation of the nano-alloys under laser irradiation.

Keywords: Laser ablation; Optical properties; Colloids; Nano-alloys; Plasmon resonance

Nanoparticles size modifications during femtosecond laser ablation of nickel in vacuum by S. Amoruso; G. Ausanio; A.C. Barone; R. Bruzzese; C. Campana; X. Wang (pp. 1012-1016).

Nanoparticles were synthesized by irradiating a nickel target with femtosecond laser pulses in high vacuum, and subsequently analyzed. The proof-of-principle experiments aim to modify the size characteristics of the produced nanoparticles. For nickel it is found that: (i) ultraviolet laser pulses lead to a remarkable change in the nanoparticles size distribution with respect to visible laser pulses; (ii) irradiation of the femtosecond pulses induced ablation plume with a second, delayed ultraviolet laser pulse can change the size characteristics of the produced nanoparticles.

Keywords: Ultrashort laser ablation; Nanoparticles

Au–Cu nanoparticles in silica glass as composite material for photonic applications by E. Cattaruzza; G. Battaglin; F. Gonella; R. Polloni; B.F. Scremin; G. Mattei; P. Mazzoldi; C. Sada (pp. 1017-1021).

In the framework of metal nanocluster composite glasses for photonic application, (gold+copper)-containing silica films were synthesized by radiofrequency co-sputtering deposition technique by varying the Au/Cu ratio. To obtain the formation of metallic (alloy) nanoclusters, the deposited samples were annealed in reducing atmosphere at 900°C. The linear and nonlinear optical properties of the composite glasses were investigated. In particular, the nonlinear ultrafast optical response was measured by means of the Z-scan technique at a wavelength of 527nm with single 6ps pulse configuration. Significant refractive and absorptive effects were observed in all the annealed samples. The two main figures of merit related to the performance of materials for optical switching device application were evaluated for all samples, showing interesting values for the Cu-rich composites.

Keywords: Composite glasses; Z-scan; Nanoparticles; Optical properties; Sputtering deposition

Excitation of high energy levels under laser exposure of suspensions of nanoparticles in liquids by G.A. Shafeev; A.V. Simakin; F. Bozon-Verduraz; M. Robert (pp. 1022-1026).

Laser exposure of suspensions of nanoparticles in liquids leads to excitation of high energy levels in both liquid and nanoparticle material. The emission spectrum of the colloidal solution under exposure of a suspension metallic nanoparticles in water to radiation of a Nd:YAG laser of a picosecond range of pulse duration is discussed. Excitation of nuclear energy levels and neutron release is experimentally studied on the model system of transmutation of Hg into Au that occurs under exposure of Hg nanodrops suspended in D₂O. The proposed mechanism involves: (i) emission of X-ray photons by Hg nanoparticles upon laser exposure, leading to neutron release from D₂O, (ii) initiation of Hg→Au transmutation by the capture of neutrons. The effect of transmutation is more pronounced using¹⁹⁶Hg isotope instead of Hg of natural isotope composition. The influence of laser pulse duration on the degree of transmutation (from fs through ns range) is discussed.

Keywords: Nanoparticles; Laser ablation; X-ray generation

Growth of crystalline/amorphous biphase Sm–Fe–Ta–N magnetic nanodroplets by S. Kobe; E. Sarantopoulou; G. Dražić; J. Kovač; M. Janeva; Z. Kollia; A.C. Cefalas (pp. 1027-1031).

Thin films of biphase (amorphous/crystalline) magnetic Sm–Fe–Ta–N nanodroplets were fabricated at room temperature with 157nm pulse laser deposition in nitrogen from a Sm_13.8Fe_82.2Ta_4.0 target. The 50–100nm biphase spherical nanodroplets consist of a 5–10nm internal crystal portion surrounded by the external amorphous phase. Nitrogen fixation in the nanodroplets occurred in the plume. The films exhibit a ferromagnetic response of 2.5kOe coercivity at room temperature. With further annealing and thermal treatment in nitrogen, the coercivity was increased to 5.0kOe. The surrounding amorphous layer prevents post-ablation oxidization of the crystalline magnetic nucleus of the nanodroplet.

Keywords: PACS; 75.70.i; 75.75.+aNanodroplets; Nanomagnetism; 157; nm; PLD; Sm–Fe–Ta–N; Magnetic interfaces

Hybrid polymer composites reinforced by layered silicate and laser synthesized nanocarbons by I. Dinca; A. Stefan; C. Serghie; A. Moga; L. Dumitrache; Z. Vuluga; D. Donescu; A. Dragomirescu; G. Prodan; V. Ciupina; L. Gavrila-Florescu; E. Popovici; I. Sandu (pp. 1032-1036).

The work presents some preliminary results obtained in the attempt to perform hybrid polymer-based nanocomposites with laser synthesized carbon nanostructures and layered silicate. The preliminary results suggest that there is a close relation between the improved characteristics of the obtained nanocomposite and filler's properties. Laser synthesized nanocarbons, from almost amorphous up to fullerenic-like structure were used. As layered silicate, a modified Cloisite-type montmorillonite is mentioned. Preliminary results suggest that some of these addition agents lead to samples of nanocomposites with significant improvement of their aimed properties.

Keywords: Nanocomposites; Polymer; Carbon; Laser pyrolysis; Layered silicate

Titanium dioxide nanoparticles prepared by laser pyrolysis: Synthesis and photocatalytic properties by E. Figgemeier; W. Kylberg; E. Constable; M. Scarisoreanu; R. Alexandrescu; I. Morjan; I. Soare; R. Birjega; E. Popovici; C. Fleaca; L. Gavrila-Florescu; G. Prodan (pp. 1037-1041).

TiO₂ nanoparticles were synthesized via the laser pyrolysis of titanium tetrachloride-based gas-phase mixtures. In the obtained nanopowders, a mixture of anatase and rutile phases with mean particle size of about 14nm was identified. Using the thermal heated laser nanopowders, mechanically stable films were produced by immobilizing titania nanopowders on glass substrates (the doctor blading method followed by compression). The photocatalytic activity of the prepared films was tested by the degradation of 4-chlorophenol in an aqueous solution under UV-illumination. By referring to known commercial samples (Degussa P25) similarly prepared, higher photocatalytic efficiency was found for the laser-prepared samples.

Keywords: TiO; ₂; nanoparticles; Laser pyrolysis; Fe-doped TiO; ₂; Anatase; Rutile

Experimental analysis of the production of micro- and nanofibres by Laser Spinning by F. Quintero; J. Pou; F. Lusquiños; A. Riveiro (pp. 1042-1047).

Laser Spinning is a new technique for the production of glass fibres with diameters in the nanometre to micrometre scale. It allows large quantities of nanofibres to be made with specific, controllable chemical compositions. Furthermore, the production of amorphous micro- and nanofibres of non-ready glass former materials was demonstrated. All these novel characteristics will potentially open up a whole new range of applications for the fibres.In this technique a high power laser is employed to melt the precursor solid material, while a supersonic gas jet is injected into the melt volume. The melt forms glass fibres as a result of its viscous elongation and cooling by the drag force and convective heat transfer produced by the gas jet. The influence of several operating conditions controlling the morphology, composition, and diameter distribution of the fibres is experimentally assessed by means of electron microscopy analysis, X-ray fluorescence and time-of-flight secondary ion mass spectrometry. The experimental results are discussed based on a theoretical explanation of the process of fibre formation. This leads ultimately to the deduction of a set of rules regarding the influence of the factors studied on the production of nanofibres by Laser Spinning.

Keywords: Laser Spinning; Nanofibres

Iron/iron oxides core–shell nanoparticles by laser pyrolysis: Structural characterization and enhanced particle dispersion by Ernest Popovici; Florian Dumitrache; Ion Morjan; Rodica Alexandrescu; Victor Ciupina; Gabi Prodan; Ladislau Vekas; Doina Bica; Oana Marinica; Eugeniu Vasile (pp. 1048-1052).

Well-dispersed nanoparticles with iron/iron carbide core and iron oxide shell structures may constitute an excellent magnetic material for different applications as magnetic nanofluids, contrast agents in magnetic resonance imaging, sensors and catalysts. Based on the ability of the CO₂ laser pyrolysis technique to synthesize nanoparticles of the Fe/Fe₂O₃ core–shell type, we further improve the powder dispersion by first collecting the nanoparticles in a toluene bubbler, positioned downstream and prior to the collection filter. Structural characterisation of the samples by electron microscopy and X-ray diffraction was performed. Conditions in which clusters contain a reduced number of nanoparticles (around 50) are evidenced. Mean core–shell particle sizes of 15nm were estimated. Finally, preliminary results on the morphology of iron/iron oxide core–shell nanoparticles as hydrocarbon-based magnetic nanofluids are presented.

Keywords: Laser pyrolysis; Iron nanoparticles; Core–shell structure; Particle dispersion; Magnetic nanofluid

Magnetic/non-magnetic nanoparticles films with peculiar properties produced by ultrashort pulsed laser deposition by V. Iannotti; S. Amoruso; G. Ausanio; A.C. Barone; C. Campana; C. Hison; X. Wang (pp. 1053-1057).

Films of magnetic nanoparticles uniformly mixed with non-magnetic nanoparticles have been produced by ultrashort pulsed laser deposition. These films present innovative characteristics with respect to their counterparts produced by standard techniques, as for example nanosecond laser ablation or sputtering, due to the peculiar shape and preferential distribution of their constituent nanoparticles. In the present investigation, the difficult coalescence among the deposited nanoparticles, specific characteristic of the ultrashort pulsed laser deposition, is particularly stressed for what concerns its effect on the collective magnetic behaviour. In particular, we observed that, even for a significant fraction of magnetic particles, the films exhibit an unusual high remanent magnetization, together with relatively low values of saturation and coercive fields, showing a strong squareness of the hysteresis loops. In perspective, these nanogranular films appear very promising for potential application as permanent magnets and in magnetic recording.

Keywords: Ultrashort pulsed laser deposition; Nanogranular magnetic films; High remanence ratio

Aligned carbon nanotubes catalytically grown on iron-based nanoparticles obtained by laser-induced CVD by F. Le Normand; C.S. Cojocaru; O. Ersen; P. Legagneux; L. Gangloff; C. Fleaca; R. Alexandrescu; F. Dumitrache; I. Morjan (pp. 1058-1066).

Iron-based nanoparticles are prepared by a laser-induced chemical vapor deposition (CVD) process. They are characterized as body-centered Fe and Fe₂O₃ (maghemite/magnetite) particles with sizes ≤5 and 10nm, respectively. The Fe particles are embedded in a protective carbon matrix. Both kind of particles are dispersed by spin-coating on SiO₂/Si(100) flat substrates. They are used as catalyst to grow carbon nanotubes by a plasma- and filaments-assisted catalytic CVD process (PE-HF-CCVD). Vertically oriented and thin carbon nanotubes (CNTs) were grown with few differences between the two samples, except the diameter in relation to the initial size of the iron particles, and the density. The electron field emission of these samples exhibit quite interesting behavior with a low turn-on voltage at around 1V/μm.

Keywords: CVD; Plasma-enhanced CVD; Laser-induced pyrolysis; Iron particles; Carbon nanotubes; Electron field emission

Laser synthesis of nanostructured ceramics from liquid precursors by Johannes Wilden; Georg Fischer (pp. 1067-1072).

The free-form net shape laser synthesis of nanostructured ceramics from liquid precursors enables a residual stress-free production of high temperature resistant ceramic units and components for the use in microsystem engineering. Due to the use of molecular compounded liquid, ceramic precursors the resulting ceramic components show outstanding properties, for example high purity and a nanostructured material design.The use of pulsed lasers enables a defined input of energy required to pyrolyse the precursor material into a crystalline ceramic, so the active volume can be reduced significantly compared to other processes, for example pyrolysis by furnace.In this paper several methods for a further minimization of the active volume are presented. The investigations determined different factors affecting the process. Realizing selective experiments allows a determination of their influencing level and the definition of a working area to produce three-dimensional components with high aspect ratio.By several studies, e.g., scanning electron microscopy, transmission electron microscopy as well as X-ray diffraction analysis, the atomic structure and composition of the created components were analyzed and valued, so the different reaction processes can be described extensively.

Keywords: Laser-assisted pyrolysis; Preceramic polymers; Nanostructured ceramic; Rapid manufacturing

Laser processing of micro-optical components in quartz by G. Kopitkovas; T. Lippert; N. Murazawa; C. David; A. Wokaun; J. Gobrecht; R. Winfield (pp. 1073-1078).

Laser induced backside wet etching combined with the diffractive gray tone phase mask has been used for the fabrication of a micro-lens array with a single lens diameter of 1mm and a micro-prism in quartz. The micro-lens array was tested as beam homogenizer for high power XeCl excimer laser yielding a clear improvement in the quality of the laser beam.The optimum fluence range for fabrication of micro-lenses by laser induced backside wet etching using 1.4M pyrene in THF solution and 308nm irradiation wavelength is 1–1.6J/cm². The etching mechanisms of LIBWE are based on a combination of pressure and temperature jumps at quartz–liquid interface.

Keywords: LIBWE; Micro-optics; Beam homogenizer; Quartz

Laser-assisted fabrication of new slab-coupled lithium niobate optical waveguide by Yalin Lu; R.J. Knize (pp. 1079-1082).

Recently a new type of lithium niobate waveguide was suggested for potential nonlinear optic applications. The waveguide consists of a uniform large core and a leaky coupled slab for realizing a lateral optical confinement to support the fundamental spatial mode propagation. Inside the waveguide, the slab layer is required to have a refractive index slightly lower than that of the core, but higher than that of the substrate. Lithium niobate doped with magnesium oxides shows an increased refractive index that is dependent on the dopant's concentration. Therefore, in order to fabricate such waveguides, the pulsed laser deposition approach was used to study the growth of such composition-modified lithium niobate as the slab layer. The as-grown films were characterized on its expitaxy, structure, and optical performance, via X-ray diffraction analysis, optical guiding experiment, etc.

Keywords: Slab-coupled waveguide; Pulsed laser deposition; Lithium niobate film

Effect of laser annealing on crystallinity of the Si layers in Si/SiO₂ multiple quantum wells by T. Arguirov; T. Mchedlidze; V.D. Akhmetov; S. Kouteva-Arguirova; M. Kittler; R. Rölver; B. Berghoff; M. Först; D.L. Bätzner; B. Spangenberg (pp. 1083-1086).

We report on continuous-wave laser induced crystallisation processes occurring in Si/SiO₂ multiple quantum wells (MQW), prepared by remote plasma enhanced chemical vapour deposition of amorphous Si and SiO₂ layers on quartz substrates. The size and the volume fraction of the Si nanocrystals in the layers were estimated employing micro-Raman spectroscopy. It was found that several processes occur in the Si/SiO₂ MQW system upon laser treatment, i.e. amorphous to nanocrystalline conversion, Si oxidation and dissolution of the nanocrystals. The speed of these processes depends on laser power density and the wavelength, as well as on the thickness of Si-rich layers. At optimal laser annealing conditions, it was possible to achieve ∼100% crystallinity for 3, 5 and 10nm thickness of deposited amorphous Si layers. Crystallization induced variation of the light absorption in the layers can explain the complicated process of Si nanocrystals formation during the laser treatment.

Keywords: Silicon nanocrystals; Si/SiO; ₂; multi-quantum wells; Laser annealing; Raman spectroscopy

ZnO thin film on side polished optical fiber for gas sensing applications by Anna.Og. Dikovska; P.A. Atanasov; A.Ts. Andreev; B.S. Zafirova; E.I. Karakoleva; T.R. Stoyanchov (pp. 1087-1090).

In this work, thin ZnO films have been produced by pulsed laser deposition on side-polished fiber for optical gas sensor applications. The influence was investigated of the processing parameters, such as substrate temperature and oxygen pressure applied during deposition, on the sensitivity to ammonia of the sensing element. A shift of the spectral position of the resonance minimum to the longer wavelengths was observed at room temperature for the sample prepared at 150°C substrate temperature and 20Pa oxygen pressure. Spectral changes in the range 0.16–1.13nm for NH₃ concentrations between 500 and 5000ppm were also observed.

Keywords: Side-polished fiber; ZnO thin films; Ammonia sensor; Optical fiber sensors

Influence on the laser induced backside dry etching of thickness and material of the absorber, laser spot size and multipulse irradiation by T. Smausz; T. Csizmadia; N. Kresz; Cs. Vass; Zs. Márton; B. Hopp (pp. 1091-1095).

Laser induced backside dry etching method (LIBDE) was developed – analogously to the well-known laser induced backside wet etching (LIBWE) technique – for the micromachining of transparent materials. In this procedure, the absorbing liquid applied during LIBWE was replaced with solid metal layers. Fused silica plates were used as transparent targets. These were coated with 15–120nm thick layers of different metals (silver, aluminium and copper). The absorbing films were irradiated by a nanosecond KrF excimer laser beam through the quartz plate. The applied fluence was varied in the 150–2000mJ/cm² range, while the irradiated area was between 0.35 and 3.6mm². At fluences above the threshold values, it was found that the metal layers were removed from the irradiated spots and the fused silica was etched at the same time. In our experiments, we investigated the dependence of the main parameters (etch rate and threshold) of LIBDE on the absorption of the different metal layers (silver, copper, aluminium), on the size of the irradiated area, on the film thickness and on the number of processing laser pulses.

Keywords: Dry etching; Excimer laser; Transparent material; Microprocessing; Thin film absorber; Fused silica

Nanosecond laser damage resistance of differently prepared semi-finished parts of optical multimode fibers by Guido Mann; Jens Vogel; Rüdiger Preuß; Pouya Vaziri; Mohammadali Zoheidi; Markus Eberstein; Jörg Krüger (pp. 1096-1100).

Optical multimode fibers are applied in materials processing (e.g. automotive industry), defense, aviation technology, medicine and biotechnology. One challenging task concerning the production of multimode fibers is the enhancement of laser-induced damage thresholds. A higher damage threshold enables a higher transmitted average power at a given fiber diameter or the same power inside a thinner fiber to obtain smaller focus spots.In principle, different material parameters affect the damage threshold. Besides the quality of the preform bulk material itself, the drawing process during the production of the fiber and the preparation of the fiber end surfaces influence the resistance. Therefore, the change of the laser-induced damage threshold of preform materials was investigated in dependence on a varying thermal treatment and preparation procedure.Single and multi-pulse laser-induced damage thresholds of preforms (F300, Heraeus) were measured using a Q-switched Nd:YAG laser at 1064nm wavelength emitting pulses with a duration of 15ns, a pulse energy of 12mJ and a repetition rate of 10Hz. The temporal and spatial shape of the laser pulses were controlled accurately.Laser-induced damage thresholds in a range from 150Jcm⁻² to 350Jcm⁻² were determined depending on the number of pulses applied to the same spot, the thermal history and the polishing quality of the samples, respectively.

Keywords: PACS; 52.38.Mf; 42.81.Cn; 61.80.−x; 81.40.Wx; 64.70.Pf; 81.05.KfLaser ablation; Optical fibers; Physical radiation damage; Radiation treatment; Glass transitions; Glasses

The ridge waveguide fabrication with periodically poled MgO-doped lithium niobate for green laser by S.W. Kwon; W.S. Yang; H.M. Lee; W.K. Kim; H.-Y. Lee; W.J. Jeong; M.K. Song; D.H. Yoon (pp. 1101-1104).

Ridge waveguides were fabricated using an external field, a precision lapping machine and neutron loop discharge (NLD) in magnesium-oxide-doped lithium niobate. The measured quasi-phase-matching (QPM) wavelength of the second-harmonic generation (SHG) in a 30mm long periodically poled magnesium-doped lithium niobate (PPMgLN) ridge waveguide which has a domain period of 6.8μm is about 532nm. A fabricated periodically poled magnesium-doped lithium niobate ridge waveguide was duty cycle of 51.9±2.83% and demonstrated second-harmonic generation. By using this periodically poled magnesium-doped lithium niobate ridge waveguide, highly effective, low-cost optical devices with high power or short wavelength can be achieved.

Keywords: Periodically poled magnesium lithium niobate; Ridge waveguide; Second-harmonic generation; Duty cycle

Manufacturing of Nd:Gd₃Ga₅O₁₂ ridge waveguide lasers by pulsed laser deposition and ultrafast laser micromachining by Jens Gottmann; Dirk Wortmann; Ion Vasilief; Leonid Moiseev; Dimitri Ganser (pp. 1105-1110).

Laser radiation is used both for the deposition of the laser active thin films and for the micro structuring to define wave guiding structures for the fabrication of waveguide lasers. Thin films of crystalline and amorphous neodymium doped Gd₃Ga₅O₁₂ are grown on single crystal yttrium aluminium garnet by pulsed laser deposition using excimer laser radiation.Manufacturing of the laser active waveguides by micro structuring is done using femtosecond laser ablation of the deposited films. The structural and optical properties of the films and the morphology of the structured waveguides are determined in view of the design and the fabrication of compact and efficient diode pumped waveguide lasers. The resulting waveguides are polished, provided with resonator mirrors, pumped using diode lasers and the waveguide lasers are characterized. The spectroscopic properties of the amorphous waveguide are investigated and an infrared waveguide laser is demonstrated. To our knowledge, there have been no reports by other groups of the successful operation of a structured waveguide laser fabricated by this technique or of a waveguide laser made from amorphous neodymium doped Gd₃Ga₅O₁₂.

Keywords: Pulsed laser deposition; Ultrafast laser micromachining; Ridge waveguide laser; Sub-wavelength ripples

Influence of surface effects on the performance of lead–niobium–germanate optical waveguides by D. Munoz-Martin; J. Gonzalo; J.M. Fernandez-Navarro; J. Siegel; C.N. Afonso (pp. 1111-1114).

Lead–niobium–germanate planar waveguides have been produced by pulsed laser deposition. The composition of the waveguides is found to be relatively weakly dependent on the laser fluence, while their surface morphology is affected dramatically. Smooth surfaces are obtained for a narrow fluence range centered at 2.0J/cm², while particulates having typical diameters of <0.5μm or droplets with typical diameters of <10μm are observed at lower and higher fluences, respectively. The refractive index of the waveguides increases with fluence up to 2.1 at 2.0J/cm², which is close to the value of the bulk glass, and remains constant at higher fluences. Propagation losses show instead a minimum (≈6.5dB/cm) at 2.0J/cm². The characteristics of the ablation process that leads to the ejection of solid particulates or molten droplets as well as the increase of the waveguides density on increasing the fluence are discussed to be responsible for the observed optical behavior.

Keywords: PACS; 81.15.Fg; 81.05.Kf; 42.82.Et; 78.20.−eLead–germanate glasses; Heavy metal oxide glasses; Optical waveguides; Optical properties; Pulsed laser deposition; Thin films

New techniques for laser microprocessing of photovoltaic devices based on thin-film a-Si:H by C. Molpeceres; S. Lauzurica; J.J. García-Ballesteros; M. Morales; S. Fernández-Robledo; J.L. Ocaña; J.J. Gandía; J. Cárabe; F. Villar; J. Escarré; J. Bertomeu; J. Andreu (pp. 1115-1120).

Laser-controlled ablation of individual layers in glass/TCO/thin-film silicon/metal structures is essential for cell isolation and monolithic interconnection in thin-film silicon photovoltaic technologies. More recently, the potential application of laser scribing techniques for the development of photovoltaic matrix position sensors based on a-Si:H has generated much activity, requiring an excellent control in laser-generated patterns obtained by direct material ablation.This work is aimed to determine process parametric windows for a-Si:H thin-film ablation processes using UV ns laser sources in thin-film a-Si:H-based devices. The study is focussed on direct writing techniques using UV sources. We present ablation threshold measurements and process quality assessment using advanced optical microscopy techniques. Moreover only fully commercial laser sources in the ns regime has been used, bearing in mind that thin film based photovoltaic technologies are still demanding further reduction in production costs and, nowadays, ultrafast sources are beyond their scope both for the investment and running cost of those equipments.

Keywords: Laser micromachining; Thin-film silicon; Thin-film laser ablation

Deep subsurface optical waveguides produced by direct writing with femtosecond laser pulses in fused silica and phosphate glass by A. Ferrer; V. Diez-Blanco; A. Ruiz; J. Siegel; J. Solis (pp. 1121-1125).

In the present work, we have analyzed the use of elliptical beam shaping along with low numerical aperture focusing optics in order to produce circular cross-section waveguides in different materials at large processing depths by direct femtosecond laser writing (100fs, 800nm, 1kHz). A variable slit located before the focusing optics allows to generate a nearly elliptical beam shape and also to reduce the effective numerical aperture of the beam along the shat axis of the ellipse. The focusing optics allows to focus the beam deep inside the sample, which is translated at a constant speed transversely to the writing beam direction. The influence of several experimental parameters (energy per pulse, slit width, processing depth) on the properties of the produced waveguides has been analyzed. The influence of the intrinsic properties of the material (refractive index, composition) has been analyzed by comparing results obtained in fused silica and Er:Yb co-doped phosphate glass. The results obtained show that this approach leads to the successful production of deep subsurface (up to 7mm) waveguides with circular cross-sections. Preliminary results using chirped pulses in the phosphate glass suggest that temporal pulse shaping can be used as an additional parameter to optimize the guided mode symmetry.

Keywords: Femtosecond; Waveguide; Glass; Micromachining; Chirp; Fused silica; Phosphate glass; Slit shaping; Spherical aberration

Using light to bioactivate surfaces: A new way of creating oriented, active immunobiosensors by Meg Duroux; Leonid Gurevich; Maria Teresa Neves-Petersen; Esben Skovsen; Laurent Duroux; Steffen B. Petersen (pp. 1126-1130).

Ultraviolet light can be used to immobilize biomolecules onto thiol reactive surfaces in order to, e.g., make biosensors. The mechanism involves light-induced formation of free, reactive thiol groups in disulphide containing molecules. This technology allows for the creation of arrays of biomolecules with a high degree of reproducibility, circumventing the need for often expensive nano/micro-dispensing technologies. The ultimate size of the immobilized spots is defined by the focal area of the UV beam. Light-induced immobilization has the added benefit that the immobilized molecules will be spatially oriented and covalently bound to the surface. In this paper, we demonstrate the utility of a sensor array created with the new sensor technology when integrated into a microfluidic system. Protein arrays made using light-induced immobilization showed successful antigen/antibody binding in a flow cell allowing the visualisation of real time binding and enzyme activity. This new technology is ideal for the creation of protein/DNA microarrays, can replace present micro-dispensing arraying technologies and is ideal as a molecular imprinting technology.

Keywords: Protein arrays; UV light; Biosensors; Microfluidics; Fluorescence microscopy; Light assisted protein immobilization; Fab fragments

3D-shaping of biodegradable photopolymers for hard tissue replacement by Monika Schuster; Claudia Turecek; Franz Varga; Helga Lichtenegger; Jürgen Stampfl; Robert Liska (pp. 1131-1134).

Continuously increasing life expectancy results in a rising number of bone diseases and fractures. Replacements from natural sources are not only limited in their availability, they also have some serious disadvantages such as possible immunological reactions or transmission of diseases. New synthetic biodegradable materials based on photopolymers could be an alternative solution. In these investigations an acrylate-based monomer formulation has been developed, consisting of a biodegradable basis monomer which is derived from gelatin, different reactive diluents, an appropriate photoinitiator and filler materials. For the three-dimensional shaping process stereolithography is the method of choice because of its capability to produce cellular structures with high resolutions.

Keywords: Photopolymerization; Bone replacement material; Stereolithography; Biodegradable

Femtosecond laser micromachining in the conjugated polymer MEH–PPV by C.R. Mendonca; S. Orlando; G. Cosendey; M. Winkler; E. Mazur (pp. 1135-1139).

Femtosecond-laser micromachining of poly[2-methoxy-5-(2′-ethylhexyloxy)- p-phenylene vinylene] films is investigated using 130fs pulses at 800nm from a laser oscillator operating at 76MHz repetition rate. We investigate the effect of pulse energy and translation speed on the depth and morphology of the micromachined regions. We quantified the MEH–PPV photobleaching induced by the fs-laser, and the conditions in which the emission of MEH–PPV is preserved after the micromaching.

Keywords: Micromachining; Femtosecond laser; Conjugated polymer

Photodegradation of PAMAM G5-stabilized aqueous suspensions of gold nanoparticles by Emilia Giorgetti; Anna Giusti; Francesco Giammanco; Simona Laza; Tommaso Del Rosso; Giovanna Dellepiane (pp. 1140-1144).

Gold nanoparticles are produced in the form of colloidal suspensions in water by ps laser ablation of a metallic target. The fifth generation of ethylenediamine-core poly(amidoamine) (PAMAM G5) is used as a capping agent. Thanks to the ability of PAMAM to encapsulate and stabilize gold cations within its inner cavities, it is possible to evidence, by simple UV–visible spectroscopy, a photo-fragmentation process induced by the 532nm radiation, which is resonant with the absorption plasmon band of gold nanoparticles. This effect, that can be also exploited to control the size and shape of gold nanoparticles obtained with different procedures, arises from electron photo-ejection and subsequent charging and disintegration of existing gold nanoparticles into smaller size products.

Keywords: Gold nanoparticles; Dendrimer; Photodegradation

Nanofractal surface structure under laser sintering of titanium and nitinol for bone tissue engineering by I. Shishkovsky; Yu. Morozov; I. Smurov (pp. 1145-1149).

Comparative microanalysis and histological studies of porous titanium and nitinol (NiTi) implants fabricated by selective laser sintering are carried out. Sintered Ti and NiTi nanoporous structures are developed with grain sizes ranging from dozens to several hundreds nanometer and their formation is discussed. Dependence of the surface morphology of the implant on laser processing parameters (laser power, scanning velocity and beam diameter) is observed by analyzing the fractal-type nanostructure and its self-organization from the nano- to the macro-passing through the microlevel.It is shown that functional characteristics of the synthesized medical implants depend on the pores size distribution and their relative location as well as on the nanostructural morphology of the sintered surface.

Keywords: Selective laser sintering; Medical implants; Nanostructural morphology

Study of the gradual interface between hydroxyapatite thin films PLD grown onto Ti-controlled sublayers by S. Grigorescu; A. Carradò; C. Ulhaq; J. Faerber; C. Ristoscu; G. Dorcioman; E. Axente; J. Werckmann; I.N. Mihailescu (pp. 1150-1154).

Hydroxyapatite thin films were grown on layered structures by Pulsed Laser Deposition with the goal of investigating the interface of the ceramic film with the substrate. The latter consisted of Si/TiN/Ti sandwich structures. This multilayer substrate was also prepared by laser ablation earlier in the same experimental session.This particular type of structure was chosen in order to induce the in situ growth of hydroxyapatite directly onto freshly deposited Ti. We tried this way to avoid previous direct Ti exposure to air, hence its oxidation. The subsequent depositions of multilayers were performed with the aid of a carousel multi-target system mounted inside the irradiation chamber. This allowed for selecting in order the respective TiN, Ti and HA targets without opening the chamber between individual depositions.X-ray diffractometry, transmission electron microscopy and selected area electron diffractometry studies revealed the formation at the interface of a transition complex phase, 2 to 25nm thick, consisting of a mixture of TiO₂ and CaP phase. The specific growth of TiN and Ti phases was also investigated.

Keywords: Nanostructured bioactive coatings; Hydroxyapatite; Gradual interfaces

Biocompatible and bioactive coatings of Mn²⁺-doped β-tricalcium phosphate synthesized by pulsed laser deposition by F. Sima; G. Socol; E. Axente; I.N. Mihailescu; L. Zdrentu; S.M. Petrescu; I. Mayer (pp. 1155-1159).

The extension of pulsed laser deposition to the synthesis on Ti substrates of β-tricalcium phosphate (β-TCP) coatings doped with manganese is reported. Targets sintered from two crystalline Mn-doped β-TCP powders (with the composition Ca_2.9Mn_0.1(PO₄)₂ and Ca_2.8Mn_0.2(PO₄)₂) were ablated with an UV KrF* ( λ=248nm, τ∼7ns) laser source. X-ray diffraction and energy dispersive X-ray spectroscopy investigations showed that the films, while prevalently amorphous, had a Ca/P ratio of about 1.50–1.52. Scanning electron microscopy analyses revealed a rather homogeneous aspect of the coatings which were molded to the relief of the chemically etched Ti substrate. Fluorescence microscopy was applied to test the proliferation of mesenchymal stem cells grown on the obtained biostructures. Our investigations found that, even 14 days after cultivation, the synthesized films were not cytotoxic. On the contrary, they showed excellent bioactivity, as demonstrated by the neat spread of the cells over the entire surface of Mn-doped β-TCP. When tested in osteoprogenitor cell culture, the Ca_2.8Mn_0.2(PO₄)₂ samples revealed a higher potential for proliferation and better viability compared with Ca_2.9Mn_0.1(PO₄)₂.

Keywords: Mn:β-TCP thin films; Biocompatible and bioactive coatings; In vitro; tests; PLD

Development of peptide-based patterns by laser transfer by V. Dinca; E. Kasotakis; J. Catherine; A. Mourka; A. Mitraki; A. Popescu; M. Dinescu; M. Farsari; C. Fotakis (pp. 1160-1163).

Peptide-based arrays and patterns have provided a powerful tool in the study of protein recognition and function. A variety of applications have been identified, including the interactions between peptides–enzymes, peptides–proteins, peptides–DNA, peptides–small molecules and peptides–cells. One of the main and most critical unresolved issues is the generation of high-density arrays which maintain the biological function of the peptides. In this study, we employ nanosecond laser-induced forward transfer for the generation of high-density peptide arrays and patterns on modified glass surfaces. We show that peptide-based microarrays can be fabricated on solid surfaces and specifically recognized by appropriate fluorescent tags, with the transfer not affecting the ability of the peptides to form fibrils. These initial results are poised to the construction of larger peptide patterns as scaffolds for the incorporation and display of ligands critical for cell attachment and growth, or for the templating of inorganic materials.

Keywords: Peptides; Microarray; LIFT

Parameters optimization for biological molecules patterning using 248-nm ultrafast lasers by V. Dinca; A. Ranella; A. Popescu; M. Dinescu; M. Farsari; C. Fotakis (pp. 1164-1168).

Laser-induced forward transfer has been used for the deposition of photoactive biotin in micron-scale patterns. The process uses a 500fs pulsed KrF laser beam to transfer small amounts of a liquid solution target as micron-size droplets to a substrate placed parallel and in close proximity to it. The biomolecules remain active after the transfer; this is demonstrated through fluorescence assays. In addition to the laser parameters, those regarding the target composition and the receiving surface for the miniaturization of the transferred patterns have been studied and optimized. Droplets as small as 5μm have been obtained by reducing the target thickness and transfer energy; by increasing the percentage of glycerol added in the biomolecules solution and by using hydrophobic surfaces as receiving substrates. The influence of the glycerol addition and the hydrophobicity of the receiving surfaces on the activity of the transferred biomolecules have also been studied.

Keywords: LIFT; Biomolecules patterns; Microarrays

Processing of poly(1,3-bis-( p-carboxyphenoxy propane)- co-(sebacic anhydride)) 20:80 (P(CPP:SA)20:80) by matrix-assisted pulsed laser evaporation for drug delivery systems by R. Cristescu; C. Cojanu; A. Popescu; S. Grigorescu; C. Nastase; F. Nastase; A. Doraiswamy; R.J. Narayan; I. Stamatin; I.N. Mihailescu; D.B. Chrisey (pp. 1169-1173).

We have demonstrated successful thin film growth of poly(1,3-bis-( p-carboxyphenoxy, propane)- co-(sebacic anhydride)) (20:80) by matrix-assisted pulsed laser evaporation using a KrF* excimer laser ( λ=248nm, τ=25ns, ν=10Hz). The deposited thin films have been investigated by Fourier transform infrared spectroscopy, and atomic force microscopy. We have demonstrated that the main functional groups of poly(1,3-bis-( p-carboxyphenoxy, propane)- co-(sebacic anhydride)) (20:80) are present in the deposited film. The effect of matrix on both thin film structure and surface morphology was also examined. The goal of this work is to explore laser processing of this material to create suitable constructs for drug delivery applications.

Keywords: Drug delivery systems; Copolymers; Thin films; Matrix-assisted pulsed laser evaporation

Fibre laser welding for packaging of disposable polymeric microfluidic-biochips by Andrei Boglea; Alexander Olowinsky; Arnold Gillner (pp. 1174-1178).

An essential step in the development of microfluidic-biochips is represented by the assembly process. Among the thermal bonding processes used for the assembly of such devices the laser transmission welding of polymers offers several advantages, especially when it comes about local deposition of energy and minimum thermal distortion in the joining components.The research presented in this paper proposes a new approach for the laser transmission welding developed for the packaging of disposable polymeric microfluidic-biochips. The new approach based on the use of a fibre laser and a tailored method for the laser energy deposition was tested on the sealing of polymeric biochips made from plexiglas and polypropylene with a covering foil. This method combines the characteristics of the polymer contour welding and quasi-simultaneous welding and allows the achievement of contamination-free, high quality weld seams as narrow as 100μm with a high dynamic making it suitable for the high volume production also.

Keywords: Laser transmission welding; Fibre laser; Microfluidic devices; Polymer welding

Nanofoaming in the surface of biopolymers by femtosecond pulsed laser irradiation by S. Gaspard; M. Oujja; R. de Nalda; C. Abrusci; F. Catalina; L. Bañares; S. Lazare; M. Castillejo (pp. 1179-1184).

In this work, the nanostructuring induced in femtosecond (fs) laser irradiation of biopolymers is examined in self-standing films of collagen and gelatine. Irradiation by single 90fs pulses at 800, 400 and 266nm is shown to result in the formation of a modified layer with submicrometric size structures. The size and uniformity of the observed features are strongly dependent on irradiation wavelength and on the characteristics of the biopolymer (water content and mechanical strength). Examination of the films by laser induced fluorescence serves to assess the chemical modifications induced by laser irradiation, revealing changes in the emission bands assigned to the aromatic amino acid tyrosine and its degradation products. The results are discussed in the framework of a mechanism involving the generation of large free-electron densities, through multiphoton and avalanche ionization, which determine the temperature and stress distribution in the irradiated volume.

Keywords: PACS; 52.38.Mf; 82.53.PsGelatine; Collagen; Biopolymers; Femtosecond laser processing; Nanostructuring

A multichannel Raman spectrometry study of polyacetylene isomerization induced by laser irradiation by Z. Skanderi; A. Djebaili; H. Benabid; M.J.M. Abadie (pp. 1185-1188).

The multichannel Raman spectrometry has been used in the study of the isomerization reaction of an 80% cis PA film into a trans PA, using a laser beam for a double purpose. It is employed simultaneously as an activation agent inducing the isomerization reaction and the Raman diffusion. In each experience, the power of the laser beam Pⁱ( λ) was equivalent to the temperature. Twelve spectra have been recorded at different time periods tj= j·d t. The integrations of the Raman intensities related to two selected bands were numerically calculated.We also proposed an original method for the determination of the isomeric composition. A quantitative relationship between the equilibrium temperature and the laser beam power (in the range of laser power: 30< Pⁱ( λ)<300mW) has been found. An estimate number of isomerized molecules N₀ and then a correction factors f_cis and f_trans were also obtained.

Keywords: Polyacetylene; Isomerization; Laser; Activation energies; Raman spectroscopy

Pulsed laser deposition of silicon substituted hydroxyapatite coatings from synthetical and biological sources by E.L. Solla; P. González; J. Serra; S. Chiussi; B. León; J. García López (pp. 1189-1193).

Silicon substituted hydroxyapatite (Si–HA) is a new material with an enhanced bioactibity and it can be produced by chemical synthesis. Nevertheless, the coating of metallic substrates with a bioactive material is a common method nowadays to improve its integration with the receptor bone.Si–HA films were deposited by pulsed laser deposition (PLD), using targets composed of mixtures of HA with different Si containing sources such as SiO₂ and diatomaceous earth. The Si–HA films were characterized in terms of structure and chemical composition by spectroscopic techniques (FTIR, XPS), and several ion beam techniques (RBS, PIXE). The analysis revealed that the Si is successfully incorporated into the HA structure, as well as traces of other elements such as Na, Fe or K.

Keywords: Pulsed laser deposition; Bioactive coatings; Silicon substituted hydroxyapatie

Comparative study of sub-micrometer polymeric structures: Dot-arrays, linear and crossed gratings generated by UV laser based two-beam interference, as surfaces for SPR and AFM based bio-sensing by M. Csete; Á. Sipos; A. Kőházi-Kis; A. Szalai; G. Szekeres; A. Mathesz; T. Csákó; K. Osvay; Zs. Bor; B. Penke; M.A. Deli; Sz. Veszelka; A. Schmatulla; O. Marti (pp. 1194-1205).

Two-dimensional gratings are generated on poly-carbonate films spin-coated onto thin gold–silver bimetallic layers by two-beam interference method. Sub-micrometer periodic polymer dots and stripes are produced illuminating the poly-carbonate surface by p- and s-polarized beams of a frequency quadrupled Nd:YAG laser, and crossed gratings are generated by rotating the substrates between two sequential treatments. It is shown by pulsed force mode atomic force microscopy that the mean value of the adhesion is enhanced on the dot-arrays and on the crossed gratings. The grating-coupling on the two-dimensional structures results in double peaks on the angle dependent resonance curves of the surface plasmons excited by frequency doubled Nd:YAG laser. The comparison of the resonance curves proves that a surface profile ensuring minimal undirected scattering is required to optimize the grating-coupling, in addition to the minimal modulation amplitude, and to the optimal azimuthal orientation. The secondary minima are the narrowest in presence of linear gratings on multi-layers having optimized composition, and on crossed structures consisting of appropriately oriented polymer stripes. The large coupling efficiency and adhesion result in high detection sensitivity on the crossed gratings. Bio-sensing is realized by monitoring the rotated-crossed grating-coupled surface plasmon resonance curves, and detecting the chemical heterogeneity by tapping-mode atomic force microscopy. The interaction of Amyloid-β peptide, a pathogenetic factor in Alzheimer disease, with therapeutical molecules is demonstrated.

Keywords: Abbreviations; LIPSS; laser induced periodic surface structure; SBI; scattered beam interference; SPR; surface plasmon resonance; LSPR; localized surface plasmon resonance; RGC; rotated grating-coupling/ed; AD; Alzheimer disease; TBI; two-beam interference; PC; poly-carbonate; DPFM; digital pulsed force mode; PPS; Pentosan polysulfate sodiumTwo-beam interference; Surface plasmon resonance; Rotated grating-coupling; Atomic force microscopy; Bio-sensing; Amyloid-β

Experimental investigations of laser-induced forward transfer process of organic thin films by Benjamin Thomas; Anne Patricia Alloncle; Philippe Delaporte; Marc Sentis; Sébastien Sanaur; Michael Barret; Philippe Collot (pp. 1206-1210).

This paper deals with transfer induced by laser of thin layers of a conducting polymer, the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), for applications in plastic electronics. This relatively simple technique of direct writing offers the ability to make surface micro-patterning by localized deposits of material. The study of the various mechanisms (ablation, transfer and deposit) has been carried out according to different conditions of irradiation: wavelength (from ultraviolet to infrared radiation), pulse duration (nanosecond and sub-nanosecond) and fluence. The morphology of the transferred patterns has been analyzed by optical microscopy and scanning electronic microscopy. Our objective is to understand the different mechanisms involved in the process in order to optimize it in terms of geometrical resolution while preserving the properties of the transferred material.

Keywords: LIFT; Polymer; Ablation; Transfer; Laser

Modified laser ablation process for nanostructured thermoelectric nanomaterial fabrication by Yalin Lu; R.J. Knize (pp. 1211-1214).

A modified pulsed laser deposition process was used to enhance the nanostructure generation inside Bi₂Te₃ nanocrystals. In this process, an additional femotosecond laser beam was used to add an energy shock on the ablated flume, which can result in rich nanostructures embedded inside Bi₂Te₃ nanocrystals. A large Si wafer was used to ‘freeze’ such nanostructures and to effectively collect such nanostructured nanocrystals for further processing. The generated nanocrystals were studied by X-ray diffraction and scanning transmission electron microscopy, and the results prove the existence of such embedded nanostructures. Such nanocrystals were also characterized electrically and thermally for the conductivity measurements.

Keywords: Thermoelectric effect; Bi; ₂; Te; ₃; nanocrystals; Nanostructured nanocrystals; Modified pulsed laser deposition process

Optical and electrical properties of PbTe films grown by laser induced evaporation of pressed PbTe pellets by Ali M. Mousa; J.P. Ponpon (pp. 1215-1219).

A simple and cheap method has been developed for the deposition of lead telluride thin films on glass substrates by pulsed Nd:YAG laser evaporation of lead telluride pellets made of high purity Pb and Te powders.Preliminary characterization of the crystallographic and optical properties of the films has been performed as a function of the substrate temperature.The influence of deposition conditions on the sheet resistance of these thin films has been studied. Both deposition temperature, nitrogen pressure during deposition, and addition of Ga and As impurities in the source pellets have been considered.

Keywords: PACS; 81.15.Fg; 61.10.Nz; 78.66.Li; 73.50.−h; 73.20.HbLead telluride; Laser ablation; Structural properties; Optical properties; Electrical properties

Femtosecond pulsed laser ablation deposition of tantalum carbide by R. Teghil; A. De Bonis; A. Galasso; P. Villani; A. Santagata (pp. 1220-1223).

In this work a frequency-doubled Nd:glass laser with a pulse duration of 250fs has been used to ablate a TaC target and to deposit thin films on silicon. The results have been compared with those previously obtained by nanosecond pulsed laser deposition and evidence of large differences in the plasma characteristics has been revealed. In particular, in the femtosecond and nanosecond plumes the energy and the velocity of neutral and ionized particles are very different. The features of femtosecond ablation include the delayed emission from the target of large and slow particles. The characteristics of the femtosecond plasma are clearly related to the morphology and composition of the deposited films and the results show a nanostructure consisting of a large number of spherical particles, with a mean diameter of about 50nm, with a stoichiometry corresponding to Ta₂C. To explain these features, an ablation–deposition mechanism, related to the ejection of hot particles from the target, is proposed.

Keywords: PACS; 79.20.Ds; 81.15.Fg; 52.70.KzTantalum carbide; Ultra-short pulse laser; Pulsed laser deposition; Nanoparticles

Morphological and structural characterizations of CrSi₂ nanometric films deposited by laser ablation by A.P. Caricato; G. Leggieri; A. Luches; F. Romano; G. Barucca; P. Mengucci; S.A. Mulenko (pp. 1224-1227).

The structure and morphology of chromium disilicide (CrSi₂) nanometric films grown on 〈100〉 silicon substrates both at room temperature (RT) and at 740K by pulsed laser ablation are reported. A pure CrSi₂ crystal target was ablated with a KrF excimer laser in vacuum (∼3×10⁻⁵Pa). Morphological and structural properties of the deposited films were investigated using Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffraction (GID), X-ray reflectivity (XRR), scanning (SEM) and transmission electron microscopy (TEM). From RBS analysis, the films’ thickness resulted of ∼40nm. This value is in agreement with the value obtained from XRR and TEM analysis (∼42 and ∼38nm, respectively). The films’ composition, as inferred from Rutherford Universal Manipulation Program simulation of experimental spectra, is close to stoichiometric CrSi₂. GID analysis showed that the film deposited at 740K is composed only by the CrSi₂ phase. The RT deposited sample is amorphous, while GID and TEM analyses evidenced that the film deposited at 740K is poorly crystallised. The RT deposited film exhibited a metallic behaviour, while that one deposited at 740K showed a semiconductor behaviour down to 227K.

Keywords: PACS; 61.10.Nz; 61.10.Kw; 81.15.Fg; 82.80.YcPulsed laser deposition; Thin film; Electron microscopy; X-ray diffraction; X-ray reflectivity

Role of vanadium content in ZnO thin films grown by pulsed laser deposition by M.E. Koleva; P.A. Atanasov; N.N. Nedialkov; H. Fukuoka; M. Obara (pp. 1228-1231).

Vanadium-doped ZnO films (Zn1−_xV_xO, where x=0.02, 0.03, 0.05 and 0.07), were formed from ceramic targets on c-cut sapphire substrates using pulsed laser deposition at substrate temperature of 600°C and oxygen pressure of 10Pa. In order to clarify how the vanadium concentration influences the films’ properties, structural and magnetic investigations were performed. All films crystallised in wurtzite phase and presented a c-axis preferred orientation at low concentrations of vanadium. The results implied that the doping concentration and crystalline microstructure influence strongly the system's magnetic characteristics. Weak ferromagnetism was registered for the film with the lowest doping concentration (2at.%), which exhibited a ferromagnetic behavior at Curie temperature higher than 300K. Increasing the vanadium content in the film caused degradation of the magnetic ordering.

Keywords: Pulsed laser deposition; Diluted magnetic semiconductors; Thin films

Towards the synthesis of MAX-phase functional coatings by pulsed laser deposition by Christian Lange; Michel W. Barsoum; Peter Schaaf (pp. 1232-1235).

Pulsed laser deposition with a Nd:YAG laser was used to grow thin films from a pre-synthesized Ti₃SiC₂ MAX-phase formulated ablation target on oxidized Si(100) and MgO(100) substrates. The depositions were carried out in a substrate temperature range from 300 to 900K, and the pressure in the deposition chamber ranged from vacuum (10⁻⁵Pa) to 0.05Pa Argon background pressure. The properties of the films have been investigated by Rutherford backscattering spectrometry for film thickness and stoichiometric composition and X-ray diffraction for the crystallinity of the films. The silicon content of the films varied with the energy density of the laser beam. To suppress especially the silicon re-sputtering from the substrate, the energy of the incoming particles must be below a threshold of 20eV. Therefore, the energy density of the laser beam must not be too high. At constant deposition energy density the film thickness depends strongly on the background pressure. The X-ray diffraction measurements show patterns that are typical of amorphous films, i.e. no Ti₃SiC₂ related reflections were found. Only a very weak TiC(200) reflection was seen, indicating the presence of a small amount of crystalline TiC.

Keywords: MAX phases; Pulsed laser deposition; Functional coatings; Functional ceramics

Generation of nanospikes via laser ablation of metals in liquid environment and their activity in surface-enhanced Raman scattering of organic molecules by S. Lau Truong; G. Levi; F. Bozon-Verduraz; A.V. Petrovskaya; A.V. Simakin; G.A. Shafeev (pp. 1236-1239).

The formation of dense arrays of nanospikes occurs under laser ablation of bulk targets (Ag, Au, Ta, Ti) immersed in liquids such as water or ethanol. The average height of spikes is 50nm and their density on the target amounts to 10¹⁰cm⁻². The effect is observed with sufficiently short laser pulses. In particular, either a 350ps or a 90ps Nd:YAG lasers are used in their fundamental harmonics. The nanospikes are characterized by UV-Visible reflection spectrometry and atomic force microscopy. The oscillations of electrons within nanospikes result in a permanent coloration of the surface and a modification of the optical reflection spectra of the metal. Scanning the laser beam along the metal surface allows its nanostructuring over extended areas (∼1cm²). The nanostructured Ag surface shows enhanced Raman scattering of acridine molecules at a concentration of 10⁻⁵M/l, whereas the initial Ag targets do not show any signal within the accuracy of measurements.

Keywords: PACS; 68.65.k; 64.70.Dv; 79.20.Ds; 42.62.CfPlasmon resonance; Laser ablation; Nanoparticles; Nanostructures; SERS

Thin layers of bovine serum albumin by matrix assisted pulsed laser evaporation by M. Jelinek; J. Remsa; E. Brynda; M. Houska; T. Kocourek (pp. 1240-1243).

Thin films of bovine serum albumin were prepared by cryogenic matrix assisted pulsed laser evaporation technique under various deposition conditions. Energy density of laser beam changed in the range 0.1–0.5Jcm⁻². Films were deposited in vacuum or in nitrogen ambient. Targets were prepared from bovine serum albumin solution in phosphate buffered physiological saline and with an addition of UV absorbers as dimethylsulphoxide, phthalic acid, or adenine. Polyethylene and silicon (111) were used as substrates. Film properties were studied with atomic force microscopy and Fourier transform infrared spectroscopy attenuated total reflection. The deposition changed native conformation of albumin, resulting in the formation of water-insoluble aggregates. Addition of laser light absorbers in target solutions did not prevent the damage of albumin structure.

Keywords: PACS; 52.38.Mf; 81.15.Fg; 87.14.EeThin films; Matrix assisted pulsed laser evaporation; Bovine serum albumin

Surface morphology of thin lysozyme films produced by matrix-assisted pulsed laser evaporation (MAPLE) by A. Purice; J. Schou; N. Pryds; M. Filipescu; M. Dinescu (pp. 1244-1248).

Thin films of the protein, lysozyme, have been deposited by the matrix-assisted pulsed laser evaporation (MAPLE) technique. Frozen targets of 0.3–1.0wt.% lysozyme dissolved in ultrapure water were irradiated by laser light at 355nm with a fluence of 2J/cm². The surface quality of the thin lysozyme films of different thickness deposited on 7mm×7mm Si-〈100〉-wafers was investigated with scanning electron microscopy and atomic force microscopy. Already at comparatively low thickness, ∼20nm, the substrate is covered by intact lysozyme molecules and fragments. The concentration of lysozyme in the ice matrix apparently does not play any significant role for the morphology of the film. The morphology obtained with MAPLE has been compared with results for direct laser irradiation of a pressed lysozyme sample (i.e. pulsed laser deposition (PLD)).

Keywords: Thin films; MAPLE; Lysozyme; SEM; AFM

Pulsed laser deposition of Bi₂Te₃ thermoelectric films by A. Bailini; F. Donati; M. Zamboni; V. Russo; M. Passoni; C.S. Casari; A. Li Bassi; C.E. Bottani (pp. 1249-1254).

Bi₂Te₃ is one of the most used materials for thermoelectric applications at ambient temperature. An improvement of thermoelectric performances through a suitable modification of electron and phonon transport mechanisms is predicted for low dimensional or nanostructured systems, but this requires a control of the material structure down to the nanoscale. We show that pulsed laser deposition provides control on film composition, phase and structure, necessary for a comprehension of the relationship between structure and thermoelectric properties. We have explored the role of deposition temperature, background inert gas type and pressure, laser fluence and target-to-substrate distance and we found the experimental condition ranges to obtain crystalline films containing the Bi₂Te₃ phase only, by comparing energy dispersive X-ray spectroscopy, Raman spectroscopy and X-ray diffraction analysis. Variations of substrate temperature and deposition gas pressure prove to be crucial also for the control of film morphology and crystallinity. Substrate type has no influence on film stoichiometry and crystallinity, but highly oriented growth can be achieved on mica due to van der Waals epitaxy.

Keywords: Bi; ₂; Te; ₃; Pulsed laser deposition (PLD); Thermoelectric thin films; Raman spectroscopy; X-ray diffraction

Magnetoresistance of magnetite thin films grown by pulsed laser deposition on GaAs(100) and Al₂O₃(0001) by M.L. Paramês; Z. Viskadourakis; J. Giapintzakis; M.S. Rogalski; O. Conde (pp. 1255-1259).

Magnetotransport properties of magnetite thin films deposited on gallium arsenide and sapphire substrates at growth temperatures between 473 and 673K are presented. The films were grown by UV pulsed laser ablation in reactive atmospheres of O₂ and Ar, at working pressure of 8×10⁻²Pa. Film stoichiometry was determined in the range from Fe_2.95O₄ to Fe_2.97O₄. Randomly oriented polycrystalline thin films were grown on GaAs(100) while for the Al₂O₃(0001) substrates the films developed a (111) preferred orientation. Interfacial Fe³⁺ diffusion was found for both substrates affecting the magnetic behaviour. The temperature dependence of the resistance and magnetoresistance of the films were measured for fields up to 6T. Negative magnetoresistance values of ∼5% at room temperature and ∼10% at 90K were obtained for the as-deposited magnetite films either on GaAs(100) or Al₂O₃(0001).

Keywords: PACS; 81.15.Fg; 76.80.+y; 75.50.Gg; 75.70.AkFe; ₃; O; ₄; thin films; Gallium arsenide; Sapphire; PLD; Magnetoresistance

Pulsed laser deposition of multiwalled carbon nanotubes thin films by F. Bonaccorso; C. Bongiorno; B. Fazio; P.G. Gucciardi; O.M. Maragò; A. Morone; C. Spinella (pp. 1260-1263).

The physical/chemical properties of multiwalled carbon nanotubes have attracted much interest for applications in different fields, from micro-electronic to coating technology due, in particular, to their peculiar conductivity properties, to their hardness and high resistance to thermal stress. The technology to produce carbon nanotubes thin films with the desired properties, however, is still under development. In this work, we report on multiwalled carbon nanotubes thin films deposited by pulsed laser deposition techniques ablating commercially polystyrene-nanotubes pellets on alumina substrates. MicroRaman spectroscopy and high resolution Transmission Electron Microscopy provide the experimental confirmation that carbon nanotubes-like structures are present on the alumina surface with both minimal morphological damage of the tubes and structural changes induced by laser beam.

Keywords: PACS; 81.16; 81.15.Fg; 81.16.Mk; 79.20.Ds; 78.30.J; 68.37.Lp; 68.49.Uv; 82.45.Mp; 78.67.ch; 61.46.FgIDORE; Laser deposition; Nanotubes

Production of microscale particles from fish bone by gas flow assisted laser ablation by M. Boutinguiza; F. Lusquiños; R. Comesaña; A. Riveiro; F. Quintero; J. Pou (pp. 1264-1267).

Recycled wastes from fish and seafood can constitute a source of precursor material for different applications in the biomedical field such as bone fillers or precursor material for bioceramic coatings to improve the osteointegration of metallic implants.In this work, fish bones have been used directly as target in a laser ablation system. A pulsed Nd:YAG laser was used to ablate the fish bone material and a transverse air flow was used to extract the ablated material out of the interaction zone. The particles collected at a filter were in the micro and nanoscale range. The morphology as well as the composition of the obtained particles were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The results reveal that the composition of the analyzed particles is similar to that of the inorganic part of the fish bone.

Keywords: Calcium phosphate; Nanoparticles; Microparticles; Laser heating

Optical and gas sensing properties of thick TiO₂ films grown by laser deposition by N.E. Stankova; I.G. Dimitrov; T.R. Stoyanchov; P.A. Atanasov (pp. 1268-1272).

In this work the optical and the gas sensing properties of thick TiO₂ waveguide films, produced by pulsed laser deposition, were investigated by m-line spectroscopy. The films were deposited on (001) SiO₂ substrates at temperature of 100°C. The thickness of the films was measured to be in the range from 650 to 1900nm and the roughness increases from 5 to 14.6nm. High quality mode spectra, consisted of thin and bright TE and TM modes, were observed in the films with thickness up to 1200nm. All the films revealed anisotropic optical properties. Gas sensitivity of the films to CO₂ was examined at room temperature on the basis of the variations of the refractive index. CO₂ concentration of 3×10⁴ppm was detected, which corresponds to a refractive index variation of about 1×10⁻⁴. The crystal structure and the optical transmittance of the films were also presented and discussed.

Keywords: Laser deposition; Thick TiO; ₂; films; Anisotropic optical properties; Gas sensing properties; CO; ₂

Nano-graphene structures deposited by N-IR pulsed laser ablation of graphite on Si by E. Cappelli; S. Orlando; M. Servidori; C. Scilletta (pp. 1273-1278).

Thin nano-structured carbon films have been deposited in vacuum by pulsed laser ablation, from a rotating polycrystalline graphite target, on Si 〈100〉 substrates, kept at temperatures ranging from RT to 800°C. The laser ablation was performed by a Nd:YAG laser, operating in the near IR ( λ=1064nm).X-ray diffraction analysis, performed at grazing incidence angle, both in-plane (ip-gid) and out-of-plane (op-gid), has shown the growth of oriented nano-sized graphene particles, characterised by high inter-planar stacking distance ( d_č∼0.39nm), compared to graphite. The film structure and texturing are strongly related both to laser wavelength and substrate temperature: the low energy associated to the IR laser radiation (1.17eV) generates activated carbon species of large dimensions that, also at low T (∼400°C), easy evolve toward more stable sp² aromatic bonds, in the plume direction. Increasing temperature the nano-structure formation increases, causing a further aggregation of aromatic planes, voids formation, and a related density (by X-ray reflectivity) drop to very low values. SEM and STM show for these samples a strongly increased macroscopic roughness. The whole process, mainly at higher temperatures, is characterised by a fast kinetic mode, far from equilibrium and without any structural or spatial rearrangement.

Keywords: PACS; 81.15.Fg; 81.07.−b; 81.05.Uw; 61.10.Eq; 68.37.Hk; 68.55.JkOriented nano-graphene growth; N-IR PLD; Carbon films; Grazing incidence XRD; Film density; X-ray reflectivity

Synthesis of functionally graded bioactive glass-apatite multistructures on Ti substrates by pulsed laser deposition by D. Tanaskovic; B. Jokic; G. Socol; A. Popescu; I.N. Mihailescu; R. Petrovic; Dj. Janackovic (pp. 1279-1282).

Functionally graded glass-apatite multistructures were synthesized by pulsed laser deposition on Ti substrates. We used sintered targets of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂, or bioglasses in the system SiO₂–Na₂O–K₂O–CaO–MgO–P₂O₅ with SiO₂ content of either 57wt.% (6P57) or 61wt.% (6P61). A UV KrF* ( λ=248nm, τ>7ns) excimer laser source was used for the multipulse laser ablation of the targets. The hydroxyapatite thin films were obtained in H₂O vapors, while the bioglass layers were deposited in O₂. Thin films of 6P61 were deposited in direct contact with Ti, because Ti and this glass have similar thermal expansion behaviors, which ensure good bioglass adhesion to the substrate. This glass, however, is not bioactive, so yet more depositions of 6P57 bioglass and/or hydroxyapatite thin films were performed. All structures with hydroxyapatite overcoating were post-treated in a flux of water vapors. The obtained multistructures were characterized by various techniques. X-ray investigations of the coatings found small amounts of crystalline hydroxyapatite in the outer layers. The scanning electron microscopy analyses revealed homogeneous coatings with good adhesion to the Ti substrate. Our studies showed that the multistructures we had obtained were compatible with further use in biomimetic metallic implants with glass-apatite coating applications.

Keywords: Biomimetic metallic implants; Bioglasses; Bioactive thin layers; Pulsed laser deposition

Preparation of epitaxial La_0.7Ba_0.3MnO₃ thin films on SrTiO₃ substrates by excimer laser-assisted metal organic deposition by K. Daoudi; T. Tsuchiya; T. Nakajima; T. Kumagai (pp. 1283-1287).

A KrF excimer laser irradiation was successfully used at 773K to crystallize and epitaxially grow La_0.7Ba_0.3MnO₃ (LBMO) thin films on SrTiO₃ substrates. The starting amorphous LBMO films were prepared by metal–organic deposition at 773K. The effects of the irradiation time, the laser fluence and the film thickness on the electrical properties and the microstructures of the films were investigated. Ten pulses of the KrF laser at a fluence of 80mJ/cm² were found to be sufficient to crystallize the 25nm thick LBMO film. Increasing the irradiation time was found to be useful for the densification of the films and efficient to improve their oxidation states. High qualities of LBM/STO interfaces were obtained by the excimer-laser irradiation in comparison with those films obtained by thermal annealing process. The temperature dependence of resistance R( T) of the LBMO thin films were investigated as function of the preparation conditions.

Keywords: PACS; 81.15−z; 81.15.Np; 73.61−r; 71.30+hLBMO; Excimer laser; MOD; TEM; TCR

Deposition of thin films for sensors by pulsed laser ablation of iron and chromium silicide targets by A.P. Caricato; A. Luches; F. Romano; S.A. Mulenko; Y.V. Kudryavtsev; N.T. Gorbachuk; C. Fotakis; E.L. Papadopoulou; R. Klini (pp. 1288-1291).

Thin films were deposited by KrF laser ablation of CrSi₂ and β-FeSi₂ targets with the aim to obtain silicide thin films and layers with narrow band gap for sensor applications. The CrSi₂-based films exhibit both semiconductor and metal properties, depending on the deposition conditions. Thus, the film of d≅40nm thick, deposited on Si at 740K, presents a band gap E_g≅0.18eV, and large thermo electromotive force (e.m.f.) coefficient α≅1.0–1.4mV/K at 300≤ T≤340K and a coefficient of tensosensitivity ( R– R₀)/ R₀ ɛ≅5. The film with the same thickness, but deposited on SiO₂ at 740K, presents a metal behavior at 125≤ T≤296K and a semiconductor one at 77≤ T≤125K. Its coefficient α varies in the range 5.0–7.5μV/K at 300≤ T≤340K. The 750nm thick film deposited on SiO₂ at 740K exhibits only semiconductor behavior in the range 296–77K with E_g≅0.013eV and α≅10–15μV/K at 293≤ T≤340K. The coefficient of tensosensitivity for these films is changing in the range 2–5. The β-FeSi₂-based films deposited on SiO₂ at 295≤ T≤740K show only semiconductor behavior. The thicker the film, the higher E_g: d≅150nm, E_g≅0.032eV; d≅70nm, E_g≅0.027eV; d≅60nm, E_g≅0.023eV. The higher E_g, the higher coefficient α. The coefficient of tensosensitivity for these films varies in the range 2.3–4.7. The more the semiconductor phase content in the deposited film, the higher are the values of α and ( R– R₀)/ R₀ ɛ.

Keywords: PACS; 81.16.Mk; 73.22−fLaser deposition; Thin films; Sensor

Structural and electrical characterization of lead-free ferroelectric Na_1/2Bi_1/2TiO₃–BaTiO₃ thin films obtained by PLD and RF-PLD by N. Scarisoreanu; F. Craciun; V. Ion; S.Birjega; M. Dinescu (pp. 1292-1297).

We report structural, dielectric and ferroelectric properties of sodium bismuth titanate–barium titanate, 0.94 Na_0.5Bi_0.5TiO₃–0.06 BaTiO₃, thin films grown on Pt(111)/Si by pulsed laser deposition and radiofrequency beam discharge assisted pulsed laser deposition. Structural investigations show that XRD spectra of the films grown by pulsed laser deposition correspond to single-phase pseudoperovskite and indicate coexistence of rhombohedral and tetragonal phases (morphotropic phase boundary), as for the target. These films are polycrystalline and randomly oriented. The spectra of films grown by radiofrequency beam discharge assisted pulsed laser deposition correspond to (001)-oriented single-phase pseudoperovskite with rhombohedral distortion, as if the morphotropic phase boundary would be displaced towards a slightly higher barium titanate content. Since the other deposition parameters have been the same, it seems that radiofrequency beam discharge assisted pulsed laser deposition induced a higher stress in the deposited films than the first growth technique and favoured the rhombohedral structure. Dielectric measurements show that the temperatures of the dielectric anomalies corresponding to ferroelectric–antiferroelectric–paraelectric transitions are higher that in target material for both sets of films. The relative dielectric constant was about 850 for PLD-grown films and about 1100 for RF-PLD grown films, while the loss tangent was about 0.05 for both sets of films. Polarization–electric field hysteresis loop shows small values of the remanent polarization (below 1μC/cm²) and coercive field (5kV/cm), since achieving of saturation values of remanent polarization was prevented by the low effective breakdown field of both sets of films.

Keywords: Lead-free ferroelectrics; Sodium bismuth titanate; NBT–BT thin films; Dielectric properties

Structural improvement of PLD grown KTa_0.65Nb_0.35O₃ films by the use of KNbO₃ seed layers by W. Peng; M. Guilloux-Viry; S. Députier; V. Bouquet; Q. Simon; A. Perrin; A. Dauscher; S. Weber (pp. 1298-1302).

Ferroelectric potassium tantalate niobate thin films with composition KTa_0.65Nb_0.35O₃ (KTN) were grown by pulsed laser deposition on(11¯02) α-Al₂O₃ (R-plane sapphire) substrate. The effect of a KNbO₃ (KN) seed layer on KTN thin film growth was investigated. The crystalline quality, ( h00) preferred orientation and in-plane epitaxial ordering of KTN thin films were greatly improved through the use of KN seed layers. KTN thin films with 14nm thick KN seed layer showed optimized crystallization (Δ ω=1.2°) and strong a-axis orientation. The microstructure investigation exhibited dense KTN thin films with a grain size of about 100nm. The refractive index measured by ellipsometry at 632.8nm was n₀=2.3 which is close to the bulk value of 2.34. Additionally, the presence of KN seed layer with nominal thickness (∼5nm) fully suppressed pyrochlore phase which competes with KTN perovskite growth. Secondary neutral mass spectroscopy analysis indicated that interfacial diffusion depth is decreased by the use of this seed layer. All of these results evidenced the strong improvement of KTN thin film grown on sapphire by using a KN seed layer in view of microwave application.

Keywords: Potassium tantalate niobate; PLD; Structural properties; SNMS; Pyrochlore phase

Pulsed laser deposition of nanoparticle films of Au by T. Donnelly; S. Krishnamurthy; K. Carney; N. McEvoy; J.G. Lunney (pp. 1303-1306).

Nanosecond pulsed laser deposition (PLD) has been used to grow nanoparticle films of Au on Si and sapphire substrates. The equivalent solid density thickness was measured with a quartz crystal monitor and the ion flux was measured with a time-of-flight Langmuir probe. The ion signal yields the ion energy distribution. The angular distribution of deposited material and the ablated mass per pulse were also measured. These values are incorporated into an isentropic plasma expansion model for a better description of the expansion of the ablated material. Atomic force microscopy and UV/vis optical spectroscopy were used to characterise the films. Atomic force microscopy shows that in the equivalent thickness range 0.5–5nm the deposited material is nanostructured and the surface coverage increases with increasing equivalent thickness. The optical absorption spectra show the expected surface plasmon resonance, which shifts to longer wavelengths and increases in magnitude as the equivalent thickness is increased.

Keywords: Gold nanoparticles; Pulsed laser deposition; Surface plasmon resonance; Ablation plume

Pulsed-laser deposition of nanostructured Pd/C thin films by N. Patel; R. Fernandes; G. Guella; A. Kale; A. Miotello; B. Patton; C. Zanchetta; P.M. Ossi; V. Russo (pp. 1307-1311).

Carbon-supported palladium thin films were synthesized at room temperature by KrF excimer pulsed laser deposition by using oriented pyrolytic graphite and Pd target. By changing the experimental conditions, a range of structures, from smooth to porous cluster-assembled carbon films were obtained prior to deposition of the Pd films. High amount of sp² coordinated graphitic carbon embedded with large degree of disorder is observed in these carbon films. Surface morphology was studied by using scanning electron microscopy, while compositional analysis was performed by using energy dispersive spectroscopy. Structural analysis was performed using Raman spectroscopy and Fourier transform infrared spectroscopy. The importance of morphology and chemical structure of carbon films on their catalytic activity was investigated by using the hydrolysis of aqueous NaBH₄ as a reference process. Pd/C film produced by pulsed laser deposition are here demonstrated to be a better catalyst than Pd/C powder because of the high content of sp² bonding carbon atoms arranged into the porous and irregular surface of the carbon film.

Keywords: Pulsed laser deposition; Carbon; Hydrogen generation; Catalyst; Sodium borohydride; Pd/C; Thin film

Pulsed laser deposition of smooth poly(methyl methacrylate) films at 248nm by Britta Lösekrug; Andreas Meschede; Hans-Ulrich Krebs (pp. 1312-1315).

Poly(methyl methacrylate) (PMMA) was pulsed laser deposited at a wavelength of 248nm using different laser fluences between 30 and 9000mJ/cm². While the composition of the films obtained after deposition at high laser fluences is close to that of the target, the molecular mass of the film material is reduced to about M_w=8000g/mol due to incubation processes independent on the high starting mass of the target. The microstructure of the films strongly depends on the laser fluence. After deposition at laser fluences above 500mJ/cm², the illuminated PMMA targets show a rough and molten surface with holes and bubbles resulting from strong subsurface heating. The corresponding PMMA films are very rough and exhibit a high number of droplets. In contrast, at laser fluences close to the deposition threshold of about 60mJ/cm² completely smooth films are obtained. Below the deposition threshold, the target performs incubation processes and colour changes occur, but it is only partially molten, and almost no ablation is observed. Only in a narrow fluence range above the deposition threshold (between about 80 and 160mJ/cm²) a crater with a smooth surface is formed at the target leading to a high ablation rate and to completely smooth films without any droplets.

Keywords: PACS; 68.55.−a; 81.15.FgPulsed laser deposition; Polymer

The role of the laser fluence on the Al₂O₃ target in the nanostructure and morphology of VO_x:Al₂O₃ thin films prepared by pulsed laser deposition by S. Núñez-Sánchez; R. Serna; A.K. Petford-Long; M. Tanase (pp. 1316-1321).

The role played by the laser fluence on the Al₂O₃ target when depositing VO_x:Al₂O₃ nanocomposite thin films by alternate ablation from ceramic alumina (Al₂O₃) and metallic vanadium (V) targets in vacuum has been studied. The fluence and number of pulses on the V target to prepare the nanoparticles has been maintained constant, while the fluence used to grow the Al₂O₃ host has been varied from 1.3 to 3.9Jcm⁻². The optical properties of the films, namely in-situ reflectivity during growth and extinction coefficient, evidence that the properties of the nanoparticles change as a function of the laser fluence on the Al₂O₃ host. Transmission electron microscopy analysis shows the formation of vanadium oxide nanoparticles with average diameters in the range of 4.6nm. Structural analysis of the nanoparticles shows that they are mainly crystalline. Phases of VO_x with average [O]/[V] ratios from 1.7 to 2.2 have been identified with the most commonly observed being V₃O₅. This is in agreement with low heat of formation of this oxide. It is shown that the oxidation of the nanoparticles induced during the deposition of Al₂O₃ is very efficient since no metallic V nanoparticles are formed even for the lowest fluence used.

Keywords: Pulsed laser deposition; PLD; Nanoparticles; Vanadium oxide

Laser forward transfer using a sacrificial layer: Influence of the material properties by Romain Fardel; Matthias Nagel; Frank Nüesch; Thomas Lippert; Alexander Wokaun (pp. 1322-1326).

The deposition of metal and polymer patterns was achieved with a laser forward transfer method involving a sacrificial release layer. Aluminum, gelatine and methylcellulose pixels were precisely transferred from a donor to a receiver substrate using the UV-laser decomposition of an intermediate triazene polymer layer. The roughness and edge sharpness of the pixels are found to be very dependent on the transfer material. For aluminum, a thick layer of triazene has to be used to get a clean transfer, which remains unclear yet. The applied fluence as well as the triazene thickness are strongly interdependent on the mechanical properties of the transfer layer. This work endeavours some important aspects of the transfer mechanism, and opens the way to further investigations, which are necessary to get a clear understanding of the process.

Keywords: Laser forward transfer; Triazene polymer

Micro structuring of LiNbO₃ by using nanosecond pulsed laser ablation by F. Meriche; E. Neiss-Clauss; R. Kremer; A. Boudrioua; E. Dogheche; E. Fogarassy; R. Mouras; A. Bouabellou (pp. 1327-1331).

In this work, we report on the fabrication and characterization of surface microstructures in lithium niobate thin films and single crystal by using KrF excimer laser ablation technique at 248nm with 6ns pulse width. Ablation is carried out through a mask projection set-up. Various experimental conditions are used in order to evaluate the potential of laser direct writing for photonic waveguides fabrication in lithium niobate. The surface morphology of the processed structures was studied by optical and atomic force microscopy. Laser processing mechanism is investigated by using micro-Raman spectroscopy.

Keywords: Laser micromachining; Laser ablation; Lithium niobate; Photonic structure

Laser ablation of aryltriazene photopolymer films: Effects of polymer structure on ablation properties by Romain Fardel; Pascal Feurer; Thomas Lippert; Matthias Nagel; Frank A. Nüesch; Alexander Wokaun (pp. 1332-1337).

Laser ablation of a homologous series of four tailor-made UV-sensitive aryltriazene polymers with an increasing content of photodecomposible chromophore units has been studied with a XeCl excimer laser (emission wavelength 308nm). Irradiation induces a photolytic cleavage of the aryltriazene chromophores which then leads to a fragmentation of the polymer main chain. Resulting effects of different chromophore densities on the ablation parameters of thin films were investigated by profilometry analysis of the ablated spots. No relevant influence of the chromophore density was found for the threshold fluence of laser ablation (∼25mJ/cm²) of the four polymers for single-pulse experiments. In the same way, ablation depths per pulse at a given laser fluence and with the same film thickness showed no significant differences. Remarkable differences were found for the resulting surface morphology of ablated spots at laser fluences near the ablation threshold. Homogeneous ablation resulting in a flat and smooth bottom surface of the ablated pits were observed mainly for laser fluences above the range of two times the ablation threshold (>∼50mJ/cm²). Investigating the ablation behaviour of such triazene-based photopolymers allows to derive photophysical key parameters necessary for the optimization of application processes where the designed polymers are used as sacrificial absorbing release layers in advanced laser-induced forward transfer (LIFT) applications.

Keywords: Laser ablation; Triazene photopolymers; Structure–property relations; Surface roughness; Thin films

Characterization of yttria-stabilized zirconia thin films grown by pulsed laser deposition (PLD) on various substrates by K. Rodrigo; J. Knudsen; N. Pryds; J. Schou; S. Linderoth (pp. 1338-1342).

Films of yttria-stabilized zirconia (YSZ) were deposited on substrates of various surface types by pulsed laser deposition (PLD). We have investigated formation of YSZ films by X-ray diffraction, focused ion beam and scanning electron microscopy. The deposited material grows with different morphologies such as columns or grains depending on the substrate used. We observed growth of grains only on the polycrystalline substrates, while on the single crystal columnar crystallites were seen. The YSZ coatings were porous, and nanochannels throughout film layers were observed in all YSZ deposits. Regardless of the type of substrate, all films exhibit a cubic phase of YSZ with the (111) crystallographic planes parallel to the surface as the major peak.

Keywords: Yttria-stabilized zirconia (YSZ); Pulse laser deposition (PLD); Thin films; Micro-solid oxide fuel cells (μ-SOFC)

Relationship between structure and deposition conditions for CuInO₂ thin films by C. Yaicle; A. Blacklocks; A.V. Chadwick; J. Perrière; A. Rougier (pp. 1343-1346).

CuInO₂ thin films were deposited using the Pulsed Laser Deposition technique. The influence of various deposition parameters and mainly the oxygen pressure on the texture, composition and structure of the films is discussed. Films deposited with an oxygen pressure in the 0.2–1Pa range exhibit the delafossite structure. Higher pressure introduces an increase in the oxygen content leading to a CuInO_2.10 composition for the film deposited at 5Pa and a progressive loss of the delafossite structure. As confirmed by an EXAFS study, the oxygen stoichiometry controls the Cu⁺/Cu²⁺ ratio.

Keywords: Thin films; Copper indium oxide; Delafossite; Stoichiometry; Oxygen pressure; Pulsed Laser Deposition; EXAFS

WO_x cluster formation in radio frequency assisted pulsed laser deposition by M. Filipescu; P.M. Ossi; M. Dinescu (pp. 1347-1351).

The influence of oxygen gas pressure and radio-frequency power on the characteristics of the WO_x films produced by laser ablation of a W target at room temperature in oxygen reactive atmosphere were investigated. Changing buffer gas pressure in the hundreds of Pa range affects the bond coordination, roughness and morphology of the deposited films, as investigated by micro-Raman spectroscopy, atomic force microscopy and scanning electron microscopy. The combination of radio-frequency discharge and buffer gas pressure on film nanostructure, as reflected by bond coordination, surface morphology and roughness is discussed.

Keywords: Pulsed laser deposition; Radio frequency; Clusters

Analysis of the electronic configuration of the pulsed laser deposited La_0.7Ca_0.3MnO₃ thin films by C.N. Borca; S. Canulescu; F. Loviat; T. Lippert; D. Grolimund; M. Döbeli; J. Wambach; A. Wokaun (pp. 1352-1355).

The electronic properties of La_0.7Ca_0.3MnO3−_δ thin films grown by the pulsed reactive crossed beam laser ablation method are investigated. The effects of post-deposition annealing of epitaxial La_0.7Ca_0.3MnO3−_δ thin films have been investigated using X-ray photoelectron spectroscopy (surface sensitive) and hard X-ray absorption spectroscopy (bulk sensitive). The films deposited in the high vacuum are oxygen deficient and contain mostly Mn³⁺. High temperature annealing in a flowing oxygen atmosphere partially changes the Mn oxidation state from +3 towards +3.4. These changes should favor a metal-like conduction and a ferromagnetic double exchange transport mechanism in the annealed thin films.

Keywords: Pulsed laser deposition; Thin films of manganates; X-ray photoemission spectroscopy; X-ray absorption spectroscopy

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Applied Surface Science (v.254, #4)