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Applied Surface Science (v.255, #10)

Laser ablation with short and ultrashort laser pulses: Basic mechanisms from molecular-dynamics simulations by Laurent J. Lewis; Danny Perez (pp. 5101-5106).

Laser ablation is a technology widely used in many applications. Understanding in detail the mechanisms that lead to ablation remains a formidable challenge because of the complexity of the processes taking place, the variety of species involved, and the range of length and time scales covered. Atomic-level experimental information is difficult to obtain and must be augmented by theory. In this article, we briefly review the progresses that we have accomplished using a simple two-dimensional molecular-dynamics model, insisting on the importance of considering the thermodynamics of the evolution of the systems in order to understand ablation. Through the identification of the thermodynamic pathways followed by the material after irradiation, our model has provided significant insights on the physical mechanisms leading to ablation. It has been demonstrated in particular that these depend strongly on the fluence, and are actually determined by the effective amount of energy received within different regions of the target. Further, internal or external factors, such as inertial confinement, play a key role in determining the route to ablation – and thus the types and sizes of particles ejected – by constraining the thermodynamical evolution of the system. We have established that, for ultrashort pulses in strongly absorbing materials, ablation proceeds by either spallation, phase explosion or fragmentation; the latter, we demonstrate, is the most important mechanism. For longer pulses, ablation may also proceed by trivial fragmentation.

Keywords: PACS; 79.20.Ds; 79.20.Ap; 61.80.AzLaser ablation; Molecular-dynamics simulations; Phase explosion; Fragmentation; Spallation

Molecular dynamics study of the role of material properties on nanoparticles formed by rapid expansion of a heated target by Tatiana E. Itina (pp. 5107-5111).

Rapid expansion of a heated target and its decomposition into fragments is investigated by using molecular dynamics simulations. Particular attention is focused on the void formation and nucleation that governs the target disintegration. The cluster formation process is investigated as a function of material properties (initial temperature, interaction potential and composition). Calculation results demonstrate the influence of these properties on void nucleation and growth and on the characteristic parameters of nanoparticles to be formed. In particular, larger initial temperature and expansion rate lead to the formation of smaller fragments. These effects are found to be similar for three different materials (silicon, nickel and metal alloy). In addition, the stoichiometrical cluster composition obtained in the expansion of a binary alloy is found to be fairly well preserved. The calculation results can be used for the interpretation of the experimental findings showing the formation of nanoparticles by short and ultra-short pulse laser ablation of both simple and more complex materials.

Keywords: PACS; 61.46.Df; 62.10+s; 64.75+gNanoparticles; Laser ablation; Fragmentation; Void nucleation; Molecular dynamics

Modeling of fast phase transitions dynamics in metal target irradiated by pico- and femtosecond pulsed laser by V.I. Mazhukin; M.G. Lobok; B. Chichkov (pp. 5112-5115).

We investigate laser pulse influence on aluminum target in irradiance range 10⁹ to 10¹⁶W/cm², pulse duration between 10⁻⁸ and 10⁻¹⁵s, Gaussian time profile with wavelength of 0.8μm. For all computations energy density was 10J/cm². Plasma in the evaporated material is generated at the energy density above 10J/cm²as the modeling showed.Long and short laser pulses distinguish by the mechanisms of energy transformation. For short laser pulses there is volumetric energy absorption, together with rapid phase transitions it lead to overheating in solid and liquid states, overheated solid temperature rises up to (6–8) T_m. Under influence of the energy saved in overheated solid, duration of the phase transitions becomes nanosecond, which is several orders of magnitude longer than laser pulse.

Keywords: Stephan problem; Rapid phase transitions; Overheating

Molecular dynamics study of nanoparticle evolution in a background gas under laser ablation conditions by K. Gouriet; L.V. Zhigilei; T.E. Itina (pp. 5116-5119).

Long-time evolution of nanoparticles produced by short laser interactions is investigated for different materials. To better understand the mechanisms of the nanoparticle formation at a microscopic level, we use molecular dynamics (MD) simulations to analyse the evolution of a cluster in the presence of a background gas with different parameters (density and temperature). In particular, we compare the simulation results obtained for materials with different interaction potentials (Morse, Lennard-Jones, and Embedded Atom Model). Attention is focused on the evaporation and condensation processes of a cluster with different size and initial temperature. As a result of the MD calculations, we determinate the influence of both cluster properties and background gas parameters on the nanoparticle evolution. The role of the interaction potential is discussed based on the results of the simulations.

Keywords: Molecular dynamics method; Cluster; Evaporation rate; Potential interaction

Phase transitions in femtosecond laser ablation by Mikhail E. Povarnitsyn; Konstantin V. Khishchenko; Pavel R. Levashov (pp. 5120-5124).

In this study we simulate an interaction of femtosecond laser pulses (100fs, 800nm, 0.1–10J/cm²) with metal targets of Al, Au, Cu, and Ni. For analysis of laser-induced phase transitions, melting and shock waves propagation as well as material decomposition we use an Eulerian hydrocode in conjunction with a thermodynamically complete two-temperature equation of state with stable and metastable phases. Isochoric heating, material evaporation from the free surface of the target and fast propagation of the melting and shock waves are observed. On rarefaction the liquid phase becomes metastable and its lifetime is estimated using the theory of homogeneous nucleation. Mechanical spallation of the target material at high strain rates is also possible as a result of void growth and confluence. In our simulation several ablation mechanisms are taken into account but the main issue of the material is found to originate from the metastable liquid state. It can be decomposed either into a liquid–gas mixture in the vicinity of the critical point, or into droplets at high strain rates and negative pressure. The simulation results are in agreement with available experimental findings.

Keywords: PACS; 61.80.Az; 79.20.Ds; 64.70.Dv; 64.70.FxLaser interactions; Laser ablation; Laser melting; Laser-induced spallation

Near field localization mediated by a single gold nanoparticle embedded in transparent matrix: Application for surface modification by N.N. Nedyalkov; S.E. Imamova; P.A. Atanasov; M. Obara (pp. 5125-5129).

In this work the near field properties of a single gold nanoparticle embedded in transparent host medium are investigated theoretically. The analysis of the electromagnetic field in the near field zone is obtained by finite difference time domain (FDTD) simulation technique. The nanoscale system consists of a transparent layer in which a gold particle with diameters of D=200 or 80nm is embedded, is situated on a substrate surface. Laser pulse at wavelength of 800nm irradiates normally this system. It is found that the field in the vicinity of the particle is enhanced, and at a certain condition the zone with the highest enhancement is localized on the substrate surface. Furthermore, the near field characteristics are found to be controllable by the dielectric properties of the host material, substrate, parameters of the incident irradiation and particle size. With the increase of the refractive index of the host medium, both the magnitude of the near field on the substrate and the characteristic size of the field enhanced zone decrease. The influence of the particle size and polarization of the incident laser irradiation on the near filed properties of the system are also presented. The proposed configuration can be applied for a multiple nanoprocessing and an integrated near field source with a spatial resolution of D/3.

Keywords: Nanoparticles; Plasmons; Nearfield; Nanoprocessing

Surface plasmon scattering on polymer–bimetal layer covered fused silica gratings generated by laser induced backside wet etching by H. Tóháti; Á. Sipos; G. Szekeres; A. Mathesz; A. Szalai; P. Jójárt; J. Budai; Cs. Vass; A. Kőházi-Kis; M. Csete; Zs. Bor (pp. 5130-5137).

Large amplitude fused silica gratings are prepared by combining the UV laser induced backside wet etching technique (LIBWE) and the two-beam interference method. The periodic patterning of fused silica surfaces is realized by s-polarized fourth harmonic beams of a Nd:YAG laser, applying saturated solution of naphthalene in methyl-methacrylate as liquid absorber. Atomic force microscopy is utilized to analyze how the modulation amplitude of the grating can be controlled by the fluence and number of laser pulses. Three types of plasmonic structures are prepared by a bottom-up method, post-evaporating the fused silica gratings by gold–silver bimetal layers, spin-coating the metal structures by thin polycarbonate films, and irradiating the multilayers by UV laser. The effect of the bimetal and polymer-coated bimetal gratings on the surface plasmon resonance is investigated in a modified Kretschmann arrangement allowing polar and azimuthal angle scans. It is demonstrated experimentally that scattering on rotated gratings results in additional minima on the resonance curves of plasmons excited by second harmonic beam of a continuous Nd:YAG laser. The azimuthal angle dependence proves that these additional minima originate from back-scattering. The analogous reflectivity minima were obtained by scattering matrix method calculations realized taking modulation depths measured on bimetal gratings into account.

Keywords: Laser induced backside wet etching (LIBWE); Interference lithography; SPR; AFM; Scattering; Grating

Plasmonic structure generation by laser illumination of silica colloid spheres deposited onto prepatterned polymer-bimetal films by Á. Sipos; H. Tóháti; A. Szalai; A. Mathesz; M. Görbe; T. Szabó; M. Szekeres; B. Hopp; M. Csete; I. Dékány (pp. 5138-5145).

Plasmonic structures are prepared on bimetal films evaporated onto glass substrates applying a multi-step process, and atomic force microscopy is utilized to study the structures after each step. Sub-micrometer gratings are generated on polycarbonate films spin-coated onto silver-gold bimetal layers by interference lithography (IL) applying the fourth harmonics of a Nd:YAG laser. These polymer gratings are used as prepatterned templates in order to deposit silica colloid spheres by spin-coating. It is shown that the conditions of periodic silica sphere-array formation along the template valleys are sufficiently large grating modulation depth, appropriate ratio of silica sphere diameter to grating period, and optimized speed of spinning. The periodic silica sphere arrays are illuminated by a homogeneous KrF excimer laser beam, and periodically arrayed sub-wavelength holes are drilled into bimetal films via colloid sphere lithography (CSL). The characteristic dimensions of the resulted plasmonic structures are defined by the polymer grating period and by the silica colloid sphere diameter. Attenuated total reflection spectroscopy is performed exciting plasmons on different metal-dielectric interfacial structures by the second harmonic of a continuous Nd:YAG laser. The polar and azimuthal angle dependent grating-coupling and scattering effects of the complex periodic structures on the resonance characteristic of plasmons is demonstrated.

Keywords: Interference lithography; Colloid sphere lithography; Plasmonic structure; Grating coupling/scattering

Application of Bessel beams to 2D microfabrication by X.-F. Li; R.J. Winfield; S. O’Brien; G.M. Crean (pp. 5146-5149).

Fs laser-based two-photon polymerisation (2PP) has been widely reported as a means of directly writing three-dimensional nanoscale structures. Usually the voxel of a high numerical aperture microscope objective is scanned through the resin to build up the required model. In the case of high aspect ratio two-dimensional structures, such as cell scaffolds, repeated scanning is required to build up the height.The voxel shape can be substantially elongated by the inclusion of an axicon lens in the laser beam line. In this report we describe the use of a Bessel beam produced in the region beyond the focus of an objective lens when the beam has been modified in this way.A Ti:sapphire laser was used to write a range of 2D square cell structures in a Zr-loaded sol–gel system. The process was characterised, in terms of the dimensions of the polymerised Bessel region, for different processing conditions. Examples of the structures are also described.

Keywords: Two-photon; Laser; Sol–gel; Axicon

Laser polymerization-based novel lift-off technique by B. Bhuian; R.J. Winfield; G.M. Crean (pp. 5150-5153).

The fabrication of microstructures by two-photon polymerization has been widely reported as a means of directly writing three-dimensional nanoscale structures. In the majority of cases a single point serial writing technique is used to form a polymer model. Single layer writing can also be used to fabricate two-dimensional patterns and we report an extension of this capability by using two-photon polymerization to form a template that can be used as a sacrificial layer for a novel lift-off process.A Ti:sapphire laser, with wavelength 795nm, 80MHz repetition rate, 100fs pulse duration and an average power of 700mW, was used to write 2D grid patterns with pitches of 0.8 and 1.0μm in a urethane acrylate resin that was spun on to a lift-off base layer. This was overcoated with gold and the grid lifted away to leave an array of gold islands.The optical transmission properties of the gold arrays were measured and found to be in agreement with a rigorous coupled-wave analysis simulation.

Keywords: Two-photon; Laser; Polymer; Lift-off

Ultrafast emission of ions during laser ablation of metal for 3D atom probe by A. Vella; J. Houard; F. Vurpillot; B. Deconihout (pp. 5154-5158).

The 3D atom probe(3DAP) is an imaging instrument based on the controlled field evaporation of single atoms from a sample having a tip shape with an end radius of 50nm. In the fs laser assisted 3DAP the evaporation is induced by the laser pulses so that the physical process involved in this 3DAP analysis might correspond to the very early stages of the ablation process. In this paper we present the principle of the 3DAP and we discuss the existing models of the fs assisted evaporation. At last, we test the relevance of these models with pump-probe experiments on tungsten tips in the tomographic atom probe.

Keywords: PACS; 68.43.Tj; 79.70.+9; 42.65.-k; 42.65.kyNon-linear; Optic optical rectification; Field emission; Atom probe

Emission spectra investigation of fs induced NPs probed by the ns laser pulse of a fs/ns DP-LIBS orthogonal configuration by A. Santagata; G. Albano; D. Spera; R. Teghil; P. Villani; G.P. Parisi; A. De Bonis; D.J. Sordelet (pp. 5159-5162).

A dual-pulse fs/ns laser induced breakdown spectroscopy configuration, where an initial 250fs ablating pulsed laser followed by a delayed ns laser beam placed at a fixed distance, orthogonally with the expanding plasma plume, has been used in air on a Al₆₅Cu₂₃Fe₁₂ quasicrystal. The obtained emission data were acquired with a set-up arrangement providing space detections, with a resolution up to 15μm, of the ns laser pulse generated signals. Assuming the fulfillment of local thermodynamic equilibrium conditions, the role played by the time lag between the two laser beams on the induced plasma excitation temperatures and electronic densities, as well as a space resolved process survey, has been followed. The spatial and time resolved spectra show, almost, steady values of the determined elementary plasma features with the development of nanoparticles occurring during the fs laser pulsed ablation process. The ns laser probe of the dual-pulse LIBS configuration here presented confirms that the nanoparticles induced can be largely widespread in both space and time whose compositions, overall, could retain the starting target stoichiometry. It is shown that these nanoparticles formation can actually take place at different times following the initial ultra-short laser beam incidence and that, especially at long inter-pulse delays (>100μs), modest compositional changes can be observed.

Keywords: PACS; 82.80.Dx; 32.30.Jc ;78.47.jc; 81.07.−bNs laser probe; Dual-pulse LIBS; Laser induced emission spectroscopy; Fs-pulsed laser ablation; Nanoparticles detection; Quasicrystal

Adaptive control of femtosecond laser ablation plasma emission by M. Guillermin; C. Liebig; F. Garrelie; R. Stoian; A.-S. Loir; E. Audouard (pp. 5163-5166).

The influence of temporal pulse shaping on plasma plume generated by ultrafast laser irradiation of aluminum is investigated. Time resolved plasma emission spectroscopy is coupled with a temporal shaping procedure in a closed loop. The ionic emission is enhanced relative to the neutral one via an adaptive optimization strategy. The plasma emission efficiency in case of optimized and ultrashort temporal shapes of the laser pulses are compared, evidencing an enhancement of the ionization degree of the plasma plume. Simplified temporal shapes of the femtosecond laser pulses are extracted from the optimized shape and their corresponding effect on laser induced plasma emission is discussed.

Keywords: Femtosecond laser; Plasma; Pulse Shaping; Thin film deposition

Time resolved Nomarski interferometery of laser produced plasma plumes by P. Hough; C. McLoughlin; T.J. Kelly; S.S. Harilal; J.P. Mosnier; J.T. Costello (pp. 5167-5171).

We report results from optical interferometric probing of a laser generated Zn plasma plume. The experiment was performed in a vacuum and O₂ rich environments where the background pressure of O₂ was maintained at 1000Pa and the results from both regimes are compared. The focus of our work is very much on the early stages in the life of the plasma plume which remains, to date, a largely unexplored area of study, at least in the pulsed laser deposition research domain. It was found that the electron density profile normal to the target is different in the background gas at early times (∼30ns) compared to that of the vacuum case. At later times (∼80ns) both profiles have a very similar shape. We also observe the formation of a shock wave at the plasma–gas interface shortly after plasma breakdown (<15ns).

Keywords: Laser; Plasma; Nomarski; Interferometery; Pulsed laser deposition; Electron density; Plasma scale length

Characterization of pigments used in painting by means of laser-induced plasma and attenuated total reflectance FTIR spectroscopy by M.P. Mateo; T. Ctvrtnickova; G. Nicolas (pp. 5172-5176).

The study of pigments which are found in the works of art is one of the most important tasks in the examination of historic, artistic and archaeological materials since it can provide information about their source, the pictorial technique used or the presence of restoration works.In some studies, the historical, artistic and technical characterization of the artefact is not the final goal but its restoration. In those cases, the knowledge about the chemical composition inferred from the analysis of the artwork is crucial for conservators and restorers in order to ensure that the same pigments that were used in the original work are employed for the restoration.In this work, the analytical characterization of a range of different pigments commonly used in art has been carried out using laser-induced plasma (LIBS) and attenuated total reflectance (ATR)-FTIR spectroscopy. The main purpose of this study is to provide a preliminary database of LIBS and ATR-FTIR spectra in order to supply both elemental and molecular information, respectively.

Keywords: Laser-induced breakdown spectroscopy (LIBS); ATR-FTIR; Pigments; Paintings

Gas phase kinetic and optical emission spectroscopy studies in plasma-enhanced hot filament catalytic CVD production of carbon nanotubes by M. Guláš; F. Le Normand; P. Veis (pp. 5177-5180).

Optical emission spectroscopy (OES) is used as the main experimental tool for comparison with simulations of the plasma and gas phase composition during plasma-enhanced hot filament catalytic chemical vapor deposition (PE HF CCVD) growth of carbon nanotubes (CNTs). Calculated concentration of more than 45 species in model of the CVD reactor is acquired by Chemkin™ software. Study of different conditions is performed and a close relationship can be found between the nature and the growth rate of carbon nanostructures and the concentration of the active gas phase species. Moreover it is shown that significant changes in the density and morphology of the CNTs grown in the presence of NH₃ could be mainly explained by the gas phase formation of CN and HCN.

Keywords: Plasma-enhanced CVD; Optical emission spectroscopy; Carbon nanotubes

Numerical simulation of plasma dynamics in laser shock processing experiments by M. Morales; J.A. Porro; M. Blasco; C. Molpeceres; J.L. Ocaña (pp. 5181-5185).

Laser shock processing (LSP) is based on the application of a high intensity pulsed laser beam ( I>1GW/cm²; τ<50ns) at the interface between the metallic target and the surrounding medium (a transparent confining material, normally water) forcing a sudden vaporization of the metallic surface into a high temperature and density plasma that immediately develops inducing a shock wave propagating into the material. The shock wave induces plastic deformation and a residual stress distribution in the target material.Laser shock processing is being considered as a competitive alternative technology to classical treatments for improving fatigue, corrosion cracking and wear resistance of metallic materials.The description of the relevant laser absorption phenomena becomes hardly complicated because of the non-linear effects appearing along the interaction process and which significantly alter the shocking dynamics.A simulation model (SHOCKLAS), dealing with the main aspects of LSP modelling in a coupled way, has been developed by the authors. In this paper the study will be centred on the simulation of the hydrodynamic phenomenology arising from plasma expansion between the confinement layer and the base material using HELIOS (1-D radiation-hydrodynamics lagrangean fluiddynamic code).This code is used to study plasma dynamics under laser shock processing conditions. The influence of the confining layer (medium and thickness) on plasma pressure is also studied.

Keywords: Plasma; Laser shock processing; Surface treatment; Shock waves; Residual stress; Numerical modelling

Influence of direct current plasma magnetron sputtering parameters on the material characteristics of polycrystalline copper films by Kah-Yoong Chan; Pei-Qing Luo; Zhi-Bin Zhou; Teck-Yong Tou; Bee-San Teo (pp. 5186-5190).

Physical vapor processes using glow plasma discharge are widely employed in microelectronic industry. In particular magnetron sputtering is a major technique employed for the coating of thin films. This paper addresses the influence of direct current (DC) plasma magnetron sputtering parameters on the material characteristics of polycrystalline copper (Cu) thin films coated on silicon substrates. The influence of the sputtering parameters including DC plasma power and argon working gas pressure on the electrical and structural properties of the thin Cu films was investigated by means of surface profilometer, four-point probe and atomic force microscopy.

Keywords: PACS; 68.55.−a; 81.15.CdCopper film; Cu; Magnetron sputtering; DC plasma power; Ar pressure

Physical aspects of the pulsed laser deposition technique: The stoichiometric transfer of material from target to film by J. Schou (pp. 5191-5198).

The physical processes of pulsed laser deposition (PLD) change strongly from the initial light absorption in a target to the final deposition and growth of a film. One of the primary advantages of PLD is the stoichiometric transfer of material from target to a film on a substrate. Even for a stoichiometric flow of material from a multicomponent target, the simultaneous arrival of the target atoms is not sufficient to ensure a stoichiometric film growth. The laser fluence has to be sufficiently high to induce ablation rather than pure evaporation from target, but a high fluence may lead to preferential (self)sputtering and possibly implantation of the light atoms in the film. A background gas of a sufficiently high pressure may reduce sputtering of the film, but may lead the preferential diffusion of the light component to the substrate. The importance of these processes during the entire PLD process will be discussed.

Keywords: Pulsed laser deposition; PLD; Stoichiometry; Laser plasma; Ion bombardment; Sputtering; Plume expansion

Current state-of-the-art of pulsed laser deposition of optical waveguide structures: Existing capabilities and future trends by R.W. Eason; T.C. May-Smith; C. Grivas; M.S.B. Darby; D.P. Shepherd; R. Gazia (pp. 5199-5205).

Pulsed laser deposition (PLD) has now reached a stage of maturity where the growth of thin films is routine. All that is required is a pulsed ultra-violet (UV) wavelength laser, a vacuum chamber, a target, and a substrate placed in near proximity to the plasma plume. Whether the film that you grow is the film that you need, and whether the thickness, uniformity, optical quality, stoichiometry, degree of crystallinity, orientation and much more is what is desired is another question entirely. PLD is both a science and an art and there are many tricks-of-the-trade that need to be considered to ensure that materials grown are the materials wanted. This paper discusses the practicalities of PLD systems, target geometries, heating regimes for successful epitaxial growth of crystalline films, the problem of particulates, laser sources to use, and in the context of our most recent PLD system, the number of independent lasers and targets used. We show that the use of multiple targets permits a combinatorial approach, whereby stoichiometry can be adjusted to grow designer materials, and in particular multilayer systems, ideally suited for active optical waveguides, a truly demanding end application where optical quality and in-plane losses must be reduced to an absolute minimum.

Keywords: PACS; 81.15.Fg; 68.55.at; 77.84.Bw; 78.20.−e; 78.67.ptPulsed laser deposition; Optical; Waveguide; Garnet crystal; Combinatorial; Multilayers

Femtosecond pulsed laser deposition of nanostructured TiO₂ films by Mikel Sanz; Malgorzata Walczak; Rebeca de Nalda; Mohamed Oujja; José F. Marco; Javier Rodriguez; Jesús G. Izquierdo; Luis Bañares; Marta Castillejo (pp. 5206-5210).

Nanostructured deposits of TiO₂ were grown on Si (100) substrates by laser ablating a TiO₂ sintered target in vacuum or in oxygen using a Ti:sapphire laser delivering 80fs pulses. The effect of the laser irradiation wavelength on the obtained nanostructures, was investigated using 800, 400 and 266nm at different substrate temperatures and pressures of oxygen. The composition of the deposits was characterized using X-ray photoelectron spectroscopy (XPS) and the surface morphology was studied by environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM). Deposits are absent of microscopic droplets in all conditions explored. The best deposits, constituted by nanoparticles of an average diameter of 30nm with a narrow size distribution, were obtained at the shorter laser wavelength of 266nm under vacuum at substrate room temperature.

Keywords: Femtosecond pulsed laser deposition; Nanoparticles; Nanostructured deposits; TiO; ₂

Temporally and spectrally resolved analysis of a copper plasma plume produced by ultrafast laser ablation by X. Wang; S. Amoruso; J. Xia (pp. 5211-5214).

We report an experimental analysis of the plasma plume produced during ultrafast laser ablation of a copper target, in high vacuum. The plasma plume optical emission is studied by using a hybrid time-gated imaging technique which allows obtaining simultaneous information on the spectral and spatial characteristics of the emitting species. We used both single and double pulse ablation scheme, observing their influence on the characteristics of the ablated atomic species.

Keywords: PACS; 52.38.Mf; 52.50.−b; 79.20.DsUltrafast laser ablation; Double pulse ablation; Plasma spectroscopy

Plasma plume photography and spectroscopy of Fe—Oxide materials by R. Viskup; B. Praher; T. Stehrer; J. Jasik; H. Wolfmeir; E. Arenholz; J.D. Pedarnig; J. Heitz (pp. 5215-5219).

Time-resolved photography was employed to study plasma dynamics and particle ejection of laser-irradiated iron oxide materials. Nano-particle powder, pressed powder pellets and sintered ceramics were ablated in air and Ar gas background by means of short laser pulses (Nd:YAG laser wavelength λ=1064nm and pulse duration τ_L≈6ns; KrF laser λ=248nm and τ_L≈20ns). Plasma plume dynamics significantly depended on sample morphology. The ejection of non-luminous particles up to several hundreds of microseconds after the laser pulse was observed for powder and pressed powder target materials. Laser-induced breakdown spectroscopy (LIBS) was employed for element analysis of iron oxide powders, pressed pellets and sintered ceramics. LIBS spectra of the different targets were comparable to each other and qualitatively independent of target morphology.

Keywords: Pulsed-laser ablation; Laser-induced breakdown spectroscopy; Plasma plume photography; Particle ejection; Nano-powder; Iron oxide

Nanostructured thin films obtained by ultra-short pulse laser deposition of vanadium carbide by R. Teghil; A. De Bonis; A. Galasso; P. Villani; A. Santagata; D. Ferro; S.M. Barinov (pp. 5220-5223).

In this paper we will report the results obtained by femtosecond Pulsed Laser Deposition on vanadium carbide. These results, compared with those obtained for another group 5 carbide, tantalum carbide, evidence large analogies between the two systems. Optical emission spectroscopy shows in both cases the presence of particles in the secondary plume and in both cases the films are formed by nanoparticles and present a stoichiometry corresponding to the hemicarbide.

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

Ultrafast pulsed laser deposition as a method for the synthesis of innovative magnetic films by V. Iannotti; S. Amoruso; G. Ausanio; A.C. Barone; C. Campana; X. Wang; L. Lanotte (pp. 5224-5227).

Exchange-coupled monocomponent magnetic films constituted of disk-shaped Ni and Fe nanoparticles were produced by ultrafast pulsed laser deposition, in vacuum. These films show a peculiar cauliflower-like structure, made of granular agglomerates of nanoparticles sticking to one another with a significant shape and orientation anisotropy. Both as-deposited Ni and Fe films present hysteresis loops with a high in-plane remanence ratio (0.61 and 0.81 at 250K, respectively), relatively low values of the saturation and coercive fields and a steep slope near coercivity. At temperature of 10K and 250K, the magnetization curves confirm the strong influence of the production technique on the topologic structure of these films, and consequently on their magnetic properties. In perspective, the striking and intriguing properties of these nanogranular films appear very promising for potential application as permanent magnets and in data storage technology.

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

Mg-based photocathodes prepared by ns, ps and fs PLD for the production of high brightness electron beams by P. Miglietta; L. Cultrera; C. Cojanu; E.L. Papadopoulou; A. Perrone (pp. 5228-5231).

Mg-based films have been prepared by pulsed laser deposition technique for photocathode applications. We have investigated the influence of pulse laser duration on morphology and photoemissive properties. Two laser sources have been used, generating pulses of 30ns at 308nm (XeCl excimer laser), 5ps and 500fs at 248nm (KrF excimer laser) to grow Mg films onto Si and Cu substrates in high vacuum (∼10⁻⁷Pa) and at room temperature. Morphological investigations carried out by scanning electron microscopy (SEM) have revealed that, in our experimental conditions, the number and the mean size of the droplets on the films surfaces decreases as the pulse laser duration shortens. The contamination level of Mg film surfaces have been studied by energy dispersive X-ray spectroscopy (EDX). The photoelectron performances in terms of quantum efficiency (QE) and emission stability have been tested in a UHV DC photodiode cell (10⁻⁷Pa). Measures of the QE of the samples surfaces have revealed a decrease on the initial value for Mg-based photocathodes prepared by fs laser (from 7.8×10⁻⁴ to 6.6×10⁻⁴) PLD with respect to ps (from 6.2×10⁻⁴ to 7.4×10⁻⁴) and ns lasers (from 5.0×10⁻⁴ to 1.6×10⁻³). A comparison among Mg-based photocathodes prepared by ns, ps and fs PLD for the production of high brightness electron beams has been presented and discussed.

Keywords: Photocathode; Pulsed laser deposition; Mg

On the growth of gadolinia-doped ceria by pulsed laser deposition by N. Pryds; K. Rodrigo; S. Linderoth; J. Schou (pp. 5232-5235).

In order to establish a new platform to manufacture micro-sized solid oxide fuel cells (SOFCs) with low operating temperatures, new design concepts, new preparation methods and new materials are being explored. Our studies in this paper are focused on the electrolyte material, and in particular gadolinia doped ceria (GDC), an electrolyte material, likely to replace the traditional yttria-stabilised zirconia (YSZ) for low temperature applications. GDC films were grown on a single crystal Si by pulsed laser deposition (PLD). The microstructure of the films as a function of growth time has been studied. We have found that the mean grain size increases with film thickness h as h^2/5, in agreement with theoretical results.

Keywords: PLD; Gadolinia doped ceria; Grain size

KrF pulsed laser deposition of La₅Ca₉Cu₂₄O₄₁ thin films on various substrates by M. Pervolaraki; G.I. Athanasopoulos; R. Saint-Martin; A. Revcolevschi; J. Giapintzakis (pp. 5236-5239).

Recent studies on single crystals of cuprate oxides containing spin chains and ladders have reported large anisotropic magnon-mediated thermal conductivity. A potential use of thin films of such materials could be in the thermal management of electronic devices for the guiding of unwanted heat to a heat sink. In this article, the pulsed laser deposition and characterization of La₅Ca₉Cu₂₄O₄₁ thin films on SrLaAlO₄, SrTiO₃, MgO, and Si substrates are reported for the first time. The films were grown using a pulsed UV laser (KrF, 248nm) and various substrate temperatures up to 650°C. The XRD spectra revealed successful target-film stoichiometric transfer and high texturing of the thin films with (0k0) preferred orientation.

Keywords: La; ₅; Ca; ₉; Cu; ₂₄; O; ₄₁; Thin films; Pulsed laser deposition

RHEED study of titanium dioxide with pulsed laser deposition by I.L. Rasmussen; N. Pryds; J. Schou (pp. 5240-5244).

Reflection high-energy electron diffraction (RHEED) operated at high pressure has been used to monitor the growth of thin films of titanium dioxide (TiO₂) on (100) magnesium oxide (MgO) substrates by pulsed laser deposition (PLD). The deposition is performed with a synthetic rutile TiO₂ target at low fluence. The topography and structure of the deposited layers are characterized using in situ high pressure RHEED and atomic force microscope (AFM). Based on these observations the growth mode of the films is discussed. The results will be compared to earlier results obtained for the growth of TiN films on (100) MgO.

Keywords: RHEED; PLD; TiO; ₂

Thin films of semiconducting lithium ferrite produced by pulsed laser deposition by R.D. Gunning; Karsten Rode; Sumesh R.G. Sofin; M. Venkatesan; J.M.D. Coey; Igor V. Shvets; James G. Lunney (pp. 5245-5247).

Thin films of lithium ferrite (Li_0.5Fe_2.5O₄) have been deposited on (001) Al₂O₃ by pulsed laser deposition, with substrate deposition temperatures ranging between 500 and 800°C, and oxygen pressures between 1×10⁻¹ and 4×10⁻⁷mbar. X-ray diffraction shows that films grow with a (111) orientation. Conversion electron Mössbauer spectra for the high-pressure films show a single sextet with a hyperfine field of 49T, while the low-pressure films show two sextets with hyperfine fields of 47 and 49T. The spectra also reveal paramagnetic ferric iron in both types of films. Magnetization measurements of the films show a saturation magnetization of between 1.7 and 3.1 μ_B per formula unit and a coercivity of between 10 and 44mT. The films prepared under the lower oxygen pressures are semiconducting with resistivities of 2×10⁻² to 8×10⁻²Ωcm. They exhibit an anomalous Hall effect with p-type conduction at 175K.

Keywords: Ferromagnetic; Semiconducting; Lithium ferrite; Mossbauer; Hall effect

Nanostructured high valence silver oxide produced by pulsed laser deposition by D. Dellasega; A. Facibeni; F. Di Fonzo; V. Russo; C. Conti; C. Ducati; C.S. Casari; A. Li Bassi; C.E. Bottani (pp. 5248-5251).

Among silver oxides, Ag₄O₄, i.e. high valence Ag(I)Ag(III) oxide, is interesting for applications in high energy batteries and for the development of antimicrobial coatings. We here show that ns UV pulsed laser deposition (PLD) in an oxygen containing atmosphere allows the synthesis of pure Ag₄O₄ nanocrystalline thin films, permitting at the same time to control the morphology of the material at the sub-micrometer scale. Ag₄O₄ films with a crystalline domain size of the order of tens of nm can be deposited provided the deposition pressure is above a threshold (roughly 4Pa pure O₂ or 20Pa synthetic air). The formation of this particular high valence silver oxide is explained in terms of the reactions occurring during the expansion of the ablated species in the reactive atmosphere. In particular, expansion of the PLD plasma plume is accompanied by formation of low stability Ag–O dimers and atomic oxygen, providing reactive species at the substrate where the film grows. Evidence of reactive collisions in the expanding ablation plume is obtained by analysis of the plume visible shape in inert and reactive atmospheres. In addition, we show how the dimensionless deposition parameter L, relating the target-to-substrate distance to the ablation plume maximum expansion length, can be used to classify different growth regimes. It is thus possible to vary the stoichiometry and the morphology of the films, from compact and columnar to foam-like, by controlling both the gas pressure and the target-to-substrate distance.

Keywords: PLD; Silver oxide; Thin films; Antibacterial; Nanostructured

Pulsed laser deposition and characterization of nitrogen-substituted SrTiO₃ thin films by I. Marozau; A. Shkabko; G. Dinescu; M. Döbeli; T. Lippert; D. Logvinovich; M. Mallepell; C.W. Schneider; A. Weidenkaff; A. Wokaun (pp. 5252-5255).

Nitrogen-substituted cubic perovskite-type SrTiO₃ thin films were deposited in a one-step process using pulsed reactive crossed beam laser ablation (PRCLA) and RF-plasma assisted pulsed laser deposition (RF-PLD). Both techniques yield preferentially oriented films on SrTiO₃(001), LaAlO₃(001) and MgO(001) substrates with the unit cell parameters within 0.390(5)< a<0.394(9)nm. The nitrogen content is higher in films deposited by PRCLA (0.84–2.40at.%) as compared to films deposited by RF-PLD with nitrogen plasma (0.10–0.66at.%). PRCLA with an ammonia gas pulse leads to a higher nitrogen content compared to the films grown with a nitrogen gas pulse, while films deposited by RF-PLD with ammonia plasma reveal only minor nitrogen contents (<0.10at.%). The amount of the incorporated nitrogen can be tuned by adjusting the deposition parameters. Films deposited by PRCLA have a lower roughness of 1–3nm compared to 12–18nm for the films grown by RF-PLD. PRCLA yields partially reduced films, which exhibit electronic conductivity, while films deposited by RF-PLD are insulating. There is also a pronounced influence of the substrate material on the resistivity of the films deposited by PRCLA: films grown on SrTiO₃ substrates exhibit a metallic-like behaviour, while the corresponding films grown on MgO and LaAlO₃ substrates reveal a metal-to-semiconductor/insulator transition. Nitrogen incorporation into the SrTiO₃ films results in an increased optical absorption at 370–500nm which is associated with N(2p) localized states with the energy about 0.7eV higher than the valence band energy in strontium titanate. The optical band gap energies in the studied N-substituted SrTiO₃ films are 3.35–3.40eV.

Keywords: Pulsed laser deposition; Thin film; Oxynitride; Strontium titanate; Optical properties; Electrical properties

Nanostructural pulse laser-deposited Ag(Tl)SbS semiconductor thin films: Growth dynamics, structural and electrical properties by L. Panchenko; H. Khlyap; V. Laptev (pp. 5256-5259).

Ag₃SbS₃ semiconductor material is an attractive substance for different optoelectronic and data storage applications [D. Adler, M.S. Shur, M. Silver, S.R. Ovchinsky, J. Appl. Phys. 51 (1979) 3289]. The most reliable way to get thin films with proper quality is the pulse laser deposition (PLD) technology. The paper reports data on growth dynamics (electron microscopic experiments (EME) performed in situ in order to clarify structural features of the films under PLD process), X-ray diffraction (XRD) investigations and room temperature current–voltage (IVC) characteristics. The sets of investigated samples were prepared by Nd:IAG laser. Films were deposited under substrate temperatures T=300K and T=400K and at different pulse repetition frequencies. EME studies revealed time-dependent changes of the grown films’ structure occurring under stationary pulse repetition frequency and the substrate temperature. The structure of the films was identified as an amorphous with nanoscale crystalline phase inclusions (there are results of the XRD studies). The IVCs investigations performed at the room temperature and under applied bias up to 10V in both directions showed a domination of tunneling current for all samples under study.

Keywords: Ag-containing thin films; Pulse laser deposition; XRD; Optical information storage

Chemical composition of ZrC thin films grown by pulsed laser deposition by D. Craciun; G. Socol; N. Stefan; G. Bourne; V. Craciun (pp. 5260-5263).

ZrC films were grown on (100) Si substrates by the pulsed laser deposition (PLD) technique using a KrF excimer laser working at 40Hz. The nominal substrate temperature during depositions was set at 300°C and the cooling rate was 5°C/min. X-ray diffraction investigations showed that films deposited under residual vacuum or under 2×10⁻³Pa of CH₄ atmosphere were crystalline, exhibiting a (200)-axis texture, while those deposited under 2×10⁻²Pa of CH₄ atmosphere were found to be equiaxed and with smaller grain size. The surface elemental composition of as-deposited films, analyzed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), showed the usual high oxygen contamination of carbides. Once the topmost 2–4nm region was removed, the oxygen concentration rapidly decreased, down to around 3–8% only in bulk. Simulations of the X-ray reflectivity (XRR) curves indicated a smooth surface morphology, with roughness values below 1nm (rms) and films density values of around 6.30–6.45g/cm³, very close to the bulk density. The growth rate, estimated from thickness measurements by XRR was around 8.25nm/min. Nanoindentation results showed for the best quality ZrC films a hardness of 27.6GPa and a reduced modulus of 228GPa.

Keywords: ZrC; Laser ablation; PLD; Thin films

Fabrication of Mg-doped ZnO thin films by laser ablation of Zn:Mg target by Tae Hyun Kim; Jin Jae Park; Sang Hwan Nam; Hye Sun Park; Nu Ri Cheong; Jae Kyu Song; Seung Min Park (pp. 5264-5266).

Mg-doped ZnO thin films were fabricated by laser ablation of Zn:Mg targets consisting of Mg metallic strips and Zn disk in oxygen atmosphere with a goal to facilitate convenient control of Mg contents in the films. The characteristics of the deposited films were examined by analyzing their photoluminescence (PL), X-ray diffraction and X-ray photoelectron spectroscopy (XPS) spectra. Mg contents as analyzed by XPS indicate that the target composition is fairly transferred to the deposited films. The wurtzite structure of ZnO was conserved even for the highly doped ZnO films and there was no Mg- or MgO-related XRD peaks. With increase in the Mg content, the bandgap and PL peak energy shifted to blue and the Stokes shift became larger.

Keywords: PACS; 79.20.Ds; 52.50.JmPulsed laser deposition; ZnO; Mg-doping

Structural and morphological characterization of TiO₂ nanostructured films grown by nanosecond pulsed laser deposition by M. Walczak; E.L. Papadopoulou; M. Sanz; A. Manousaki; J.F. Marco; M. Castillejo (pp. 5267-5270).

TiO₂ has attracted a lot of attention due to its photocatalytic properties and its potential applications in environmental purification and self cleaning coatings, as well as for its high optical transmittance in the visible–IR spectral range, high chemical stability and mechanical resistance. In this paper, we report on the growth of TiO₂ nanocrystalline films on Si (100) substrates by pulsed laser deposition (PLD). Rutile sintered targets were irradiated by KrF excimer laser ( λ=248nm, pulse duration ∼30ns) in a controlled oxygen environment and at constant substrate temperature of 650°C. The structural and morphological properties of the films have been studied for different deposition parameters, such as oxygen partial pressure (0.05–5Pa) and laser fluence (2– 4J/cm²). X-ray diffraction (XRD) shows the formation of both rutile and anatase phases; however, it is observed that the anatase phase is suppressed at the highest laser fluences. X-ray photoelectron spectroscopy (XPS) measurements were performed to determine the stoichiometry of the grown films. The surface morphology of the deposits, studied by scanning electron (SEM) and atomic force (AFM) microscopies, has revealed nanostructured films. The dimensions and density of the nanoparticles observed at the surface depend on the partial pressure of oxygen during growth. The smallest particles of about 40nm diameter were obtained for the highest pressures of inlet gas.

Keywords: PACS; 81.15.Fg; 68.55.−a; 61.82.FkTiO; ₂; Pulsed laser deposition; Nanostructures

AlN:Cr thin films synthesized by pulsed laser deposition: Studies by X-ray diffraction and spectroscopic ellipsometry by A. Szekeres; S. Bakalova; S. Grigorescu; A. Cziraki; G. Socol; C. Ristoscu; I.N. Mihailescu (pp. 5271-5274).

The structure and optical properties of AlN thin films doped with Cr atoms were studied by X-ray diffractometry, Fourier transform infrared spectroscopy and spectroscopic ellipsometry analyses. The films were synthesized by pulsed laser deposition from an AlN:Cr (10% Cr) target onto Si(100) wafers in vacuum at residual pressure of 10⁻³Pa or in nitrogen at a dynamic pressure of 0.1Pa. The study of the XRD patterns revealed that both phases co-existed in the synthesized films and that the amorphous one was prevalent. Two different amorphous matrices, i.e. two types of chemical bond arrangements, were found in films deposited at 0.1Pa N₂. By difference, deposition in vacuum resulted in the coexistence of hexagonal and cubic crystallites embedded into an amorphous matrix. The introduction of Cr atoms into the AlN lattice causes a broadening of the IR spectrum along with the shift toward higher wavenumbers of the characteristic Al–N bands at 2351cm⁻¹ and 665cm⁻¹, respectively. This was related to the generation of a compressive stress inside films. In comparison to the optical constants of pure AlN films, the synthesized AlN:Cr films exhibited a smaller refractive index and showed a weak absorption throughout the 300–800nm spectral region, characteristic to amorphous AlN structure.

Keywords: Cr-doped AlN films; Spectroscopic ellipsometry; Compressive stress in PLD films; Optical characteristics of AlN films

Structure and optical anisotropy of pulsed-laser deposited TiO₂ films for optical applications by Nadya E. Stankova; Ivan G. Dimitrov; Toshko R. Stoyanchov; Petar A. Atanasov; D. Kovacheva (pp. 5275-5279).

The evolution of the crystal, the microstructural and the optical properties of pulsed-laser deposited TiO₂ films, investigated by X-ray diffraction, atomic force microscopy, scanning electron microscopy, optical transmittance and m-line spectroscopy measurements are reported. The samples were grown on (001) SiO₂ substrates at temperatures from 250 to 600°C and oxygen pressures from 1 to 15Pa. Crystalline films consisting of single anatase or anatase and rutile phases, were obtained at temperatures higher than 400°C. A tendency toward columnar-like growth morphology was observed in the samples. Strong dependence of the optical properties on the surface roughness and the microstructure was determined. All films revealed single-mode waveguiding and optically anisotropic properties.

Keywords: Single-mode TiO; ₂; waveguiding films; Pulsed-laser deposition; Birefringence; Optical gas sensors

Optical study of BST films combining ellipsometry and reflectivity by V. Železný; D. Chvostová; L. Pajasová; M. Jelínek; T. Kocourek; S. Daniš; V. Valvoda (pp. 5280-5283).

Optical properties of plasma laser-deposited Ba_0.75Sr_0.25TiO₃ (BST) thin films have been investigated using variable angle spectroscopic ellipsometry (VASE) and near-normal spectroscopic reflectivity (NNSR) within a broad spectral range at room temperature. The samples prepared under various deposition conditions and the Si substrate coated with the structure SiO₂/TiO_x/Pt were measured. The X-ray diffraction, atomic force microscopy and alpha step measurement were used for characterization of the samples. A special attention was paid to study sample texture. Both sets of experimental data (VASE and NNSR) were fitted simultaneously to obtain the optical constants (e.g. complex refractive index) and thicknesses of the films. For modeling of the experimental data in the range of transparency the Cauchy and Urbach formulas were used. The direct fit procedure and the Cody–Lorentz model were applied around and below absorption edge. In the entire spectral range the reflectivity spectra were analyzed by Kramers–Kronig analysis. The data around the absorption edge were fitted using the single-wavelength method and the absorption edge features were found up about 3.5eV. The platinum-coated Si substrate data were fitted as a semi-infinite medium using the Drude and Lorentz oscillators model. The structure model for optical characterization of the sample included not only the BST layers and substrate but also the intermix and surface roughness layers to achieve good agreement with experimental data. The substrate structure was modeled by a simple bulk with surface roughness.

Keywords: BST thin films; Optical properties

Pulsed laser deposited Er³⁺,Yb³⁺:YVO₄ waveguiding films on MgO/Si substrates by D.R. Milev; P.A. Atanasov; A. Og. Dikovska; I.G. Dimitrov; K.P. Petrov; G.V. Avdeev (pp. 5284-5287).

Erbium, and erbium and ytterbium co-doped YVO₄ waveguiding films were deposited on MgO/Si substrates by PLD. The samples were post-annealed at two different temperatures in air atmosphere. The influence on the crystalline structure and waveguiding properties of the films at these annealing temperatures for two dopant concentrations was investigated. Layers annealed up to 900°C are polycrystalline. The dominant fraction of YVO₄ crystallites exhibited preferred orientation of the (001) zone axes parallel to the substrate surface. The polycrystalline samples show difference in the refractive indexes Δ n (Δ n= n_TE− n_TM) for TE and TM polarizations.

Keywords: Pulsed laser deposition; Rare-earth doped YVO; ₄; waveguides; Structural and optical properties; MgO buffer layer

Structural investigations of ITO-ZnO films grown by the combinatorial pulsed laser deposition technique by Doina Craciun; Gabriel Socol; Nicolaie Stefan; Marimona Miroiu; Ion N. Mihailescu; Aurelian-Catalin Galca; Valentin Craciun (pp. 5288-5291).

Mixtures of transparent and conductive oxides such as ITO-ZnO have been grown by a combinatorial pulsed laser deposition technique from two targets that were located 15mm apart. The films were deposited on (100)Si and quartz substrates that were heated at temperatures from 300 to 500°C. Measurements of the In to Zn ratios along the transversal axis of the substrates, which passes through the maximum thickness points corresponding to each target position were performed using energy dispersive X-ray spectroscopy and spectroscopic ellipsometry. From simulations of the X-ray reflectivity spectra, collected with a 2mm mask on different locations along the transversal axis of the samples, the density and thickness of the deposited films were calculated and then the In to Zn ratios. The crystalline structure and electrical properties of the deposited films were also investigated along the same axis. Changes in the ratio of In/Zn along this axis resulted in changes of the film lattice constant and texture.

Keywords: Pulsed laser deposition; Combinatorial; TCO; ITO; ZnO

Highly oriented crystalline Er:YAG and Er:YAP layers prepared by PLD and annealing by Jan Remsa; Miroslav Jelinek; Tomáš Kocourek; Jiří Oswald; Václav Studnička; Marian Čerňanský; František Uherek; Michal Jelínek (pp. 5292-5294).

High quality, thick, highly oriented crystalline thin films of Yttrium Aluminum Garnet (Y₃Al₅O₁₂) and Yttrium Aluminum Perovskite (YAlO₃) doped with Erbium were prepared by pulsed laser deposition. Samples were created in vacuum or oxygen environment. Depositions were arranged at room temperature, or at high substrate temperatures ranging from 800 to 1100°C. Amorphous layers were annealed by laser, or in oven (argon flow, temperatures in range from 1200 to 1400°C). Fused silica and sapphire (0001) were used as substrates. Properties of films were characterized by X-ray diffraction, atomic force microscopy, and by photoluminescence measurement. Size of crystalline grains was in the range 116–773nm. Thickness of layers was up to 17μm.

Keywords: Er:YAG; Thin films; Waveguides; PLD; Laser

Pulsed-laser deposition of smooth thin films of Er, Pr and Nd doped glasses by G. Epurescu; A. Vlad; M.A. Bodea; C. Vasiliu; O. Dumitrescu; H. Niciu; M. Elisa; K. Siraj; J.D. Pedarnig; D. Bäuerle; M. Filipescu; A. Nedelcea; A.C. Galca; C.E.A. Grigorescu; M. Dinescu (pp. 5295-5298).

Thin films of complex oxides have been obtained by pulsed-laser deposition (PLD) from glass targets belonging to the system Li₂O–Al₂O₃–P₂O₅–(RE)₂O₃, with RE=Nd, Pr, Er. The films were deposited on quartz, silicon and ITO/glass substrates using a F₂ laser ( λ=157nm, ι≈20ns) for ablation in vacuum. The structural, morphological and optical properties of the oxide films were investigated through IR and UV–VIS spectroscopy, Atomic Force Microscopy (AFM), Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Spectroscopic Ellipsometry. The laser wavelength was found to be the key parameter to obtain thin films with very smooth surface. In this way new possibilities are opened to grow multilayer structures for photonic applications.

Keywords: Phosphate glasses; PLD; Rare earth; Photonic structures

Morphological and optical properties of silicon thin films by PLD by R. Ayouchi; R. Schwarz; L.V. Melo; R. Ramalho; E. Alves; C.P. Marques; L. Santos; R. Almeida; O. Conde (pp. 5299-5302).

Silicon thin films have been prepared on sapphire substrates by pulsed laser deposition (PLD) technique. The films were deposited in vacuum from a silicon target at a base pressure of 10⁻⁶mbar in the temperature range from 400 to 800°C. A Q-switched Nd:YAG laser (1064nm, 5ns duration, 10Hz) at a constant energy density of 2J×cm⁻² has been used. The influence of the substrate temperature on the structural, morphological and optical properties of the Si thin films was investigated.Spectral ellipsometry and atomic force microscopy (AFM) were used to study the thickness and the surface roughness of the deposited films. Surface roughness values measured by AFM and ellipsometry show the same tendency of increasing roughness with increased deposition temperature.

Keywords: Pulsed laser deposition; Nano-crystalline silicon; Thin films

Influence of the substrate material on the properties of pulsed laser deposited thin Li1+_xMn₂O4−_δ films by F. Simmen; T. Lippert; P. Novák; B. Neuenschwander; M. Döbeli; M. Mallepell; A. Wokaun (pp. 5303-5306).

Thin Li1+_xMn₂O4−_δ films were deposited on several substrate materials (stainless steel, p-doped silicon and glassy carbon) by pulsed laser deposition. To obtain the correct thin film stoichiometries, targets with a different amount of excess lithium were required (Li_1.03Mn₂O₄+ xLi₂O; x=2.5 and 7.5mol%). The resulting polycrystalline thin films were characterized with respect to their morphology and electrochemical activity. It was found that only thin Li1+_xMn₂O4−_δ films deposited on stainless steel and glassy carbon showed the typical insertion and deinsertion peaks of Li⁺ during cycling.

Keywords: Pulsed laser deposition; Li; 1+; _x; Mn; ₂; O; 4−; _δ; Substrate; Film properties

Laser ablation of As_xSe100−_x chalcogenide glasses: Plume investigations by C. Focsa; P. Nemec; M. Ziskind; C. Ursu; S. Gurlui; V. Nazabal (pp. 5307-5311).

The use of amorphous chalcogenides offers advantages such as remarkable optical properties like a wide transmission window (∼1–20μm) depending upon composition, making them suitable for sensitive detection of clinical or environmental changes. They also present interesting high (non)linear refractive indices, photorefractive effects, and other properties interesting for wavelength conversion, all-optical switching or modulation, Raman and parametric amplification, laser sources for mid-IR, etc.Slab waveguides based on chalcogenide amorphous films with good adherence and controlled composition can be obtained using pulsed laser deposition allowing to design and to manufacture complex optical functions on waveguides within a small and compact chip. The aim of this work is to characterize the ejection plume obtained by laser ablation of As_xSe100−_x samples in order to get some insight on the process involved for optimizing the pulsed laser deposition process. The dynamics of the plume has been systematically investigated by ICCD camera fast imaging and space- and time-resolved optical emission spectroscopy for samples of various compositions.

Keywords: Laser ablation; Chalcogenides; Optical emission spectroscopy; Plasma plume dynamics

Shallow hydroxyapatite coatings pulsed laser deposited onto Al₂O₃ substrates with controlled porosity: correlation of morphological characteristics with in vitro testing results by F. Sima; C. Ristoscu; N. Stefan; G. Dorcioman; I.N. Mihailescu; L.E. Sima; S.M. Petrescu; E. Palcevskis; J. Krastins; I. Zalite (pp. 5312-5317).

We studied the influence of porous Al₂O₃ substrates on Ce-stabilized ZrO₂-doped hydroxyapatite thin films morphology pulsed laser deposited on their top. The porosities of substrates were monitored by changing sintering temperatures and measured with a high pressure Hg porosimeter.The depositions were conducted in 50Pa water vapors by multipulse ablation of the targets with an UV KrF* ( λ=248nm, τ∼25ns) excimer laser. The surface morphology of synthesized nanostructures was investigated by scanning electron microscopy and atomic force microcopy. Ca/P ratio within the range 1.67–1.70 was found for hydroxyapatite coatings by energy dispersive spectroscopy.The films were further seeded with mesenchymal stem cells for in vitro tests. The cells showed good attachment and spreading uniformly covering the entire surface of samples. The complexity of film morphology which is increasing with substrate porosity was shown to have a positive influence on cultivated cells density.

Keywords: Porous Al; ₂; O; ₃; substrates; Morphology of shallow HA coatings; In vitro; tests; PLD

Characterization of pulsed laser deposited chalcogenide thin layers by T. Petkova; C. Popov; T. Hineva; P. Petkov; G. Socol; E. Axente; C.N. Mihailescu; I.N. Mihailescu; J.P. Reithmaier (pp. 5318-5321).

In this work we report on pulsed laser deposition (PLD) of chalcogenide thin films from the systems (AsSe)100−_xAgI_x and (AsSe)100−_xAg_x for sensing applications. A KrF* excimer laser ( λ=248nm; τ_FWHM=25ns) was used to ablate the targets that had been prepared from the synthesised chalcogenide materials. The films were deposited in either vacuum (4×10⁻⁴Pa) or argon (5Pa) on silicon and glass substrates kept at room temperature. The basic properties of the films, including their morphology, topography, structure, and composition were characterised by complementary techniques. Investigations by X-ray diffraction (XRD) confirmed the amorphous nature of the films, as no strong diffraction reflections were found. The film composition was studied by energy dispersive X-ray (EDX) spectroscopy. The morphology of the films investigated by scanning electron microscopy (SEM), revealed a particulate-covered homogeneous surface, typical of PLD. Topographical analyses by atomic force microscopy (AFM) showed that the particulate size was slightly larger in Ar than in vacuum. The uniform surface areas were rather smooth, with root mean square (rms) roughness increasing up to several nanometers with the AgI or Ag doping. Based upon the results from the comprehensive investigation of the basic properties of the chalcogenide films prepared by PLD and their dependence on the process parameters, samples with appropriate sorption properties can be selected for possible applications in cantilever gas sensors.

Keywords: Chalcogenide thin films; Pulsed laser deposition; Morphology; Nanostructure

Foamy coating obtained by laser ablation of glass ceramic substrates at high temperature by D. Sola; J.I. Peña (pp. 5322-5328).

This paper presents a study of the effect of temperature in the machining of glass ceramic cooking plates by laser ablation. A Q-switched Nd:YAG laser at its fundamental wavelength of 1064nm with pulsewidths in the nanosecond range was used. The beam was focalized and scanned over the surface covering an area of several squared millimetres. With the same irradiance and process parameters the rise of the surface temperature some hundreds of degrees changes drastically the ablation conditions. As temperature is risen the amount of particles ejected from the interaction zone diminishes, recasting over the processed area generating a white and foamy self-layer.The size of the ejected particles and the morphology, composition and microstructure of the new layer is described. This layer could be used to change the thermal conductivity of the glass ceramic plate as well as for aesthetic purposes.

Keywords: Laser ablation; Glass ceramic; Foamy coating; High temperature

Laser ablation of powdered samples and analysis by means of laser-induced breakdown spectroscopy by T. Ctvrtnickova; L. Cabalin; J. Laserna; V. Kanicky; G. Nicolas (pp. 5329-5333).

The presented work proves the capacities of laser-induced breakdown spectroscopy (LIBS) as a fast, universal, and versatile technique for analysis of complex materials as ceramics. This paper reports on the analysis of ceramic raw materials (brick clays and kaolin) submitted to laser ablation in the form of pressed pellets. Spectrographic study was provided by standard single-pulse LIBS technique and orthogonal reheating double-pulse LIBS. It was found that both methods are comparable in terms of analytical performance, if adequate experimental parameters and signal detection systems are used.

Keywords: Powdered ceramics; Laser ablation; Laser-induced breakdown; Spectroscopy (LIBS); Calibration curve

Titanium oxide nanostructured films by reactive pulsed laser deposition by M. Fusi; V. Russo; C.S. Casari; A. Li Bassi; C.E. Bottani (pp. 5334-5337).

Nanostructured titanium oxide thin films have been grown by nanosecond UV pulsed laser deposition (PLD) performed in a reactive background atmosphere. We exploited laser ablation of a Ti target at different pressures of pure oxygen and Ar:O₂ mixtures to show that film growth can be tuned at the nanoscale from compact and dense to columnar and to porous, leading to different morphology, density and structure (oxidized fraction and degree of crystallinity). We observed that the position of the substrate relative to the time integrated visible plume front is fundamental in the determination of film structure and morphology. Film growth and film properties can be related to a non-dimensional parameter L which is the ratio between the target-to-substrate distance and the visible plume length. In particular, surface morphology and degree of structural order are strictly related to L irrespective of the oxygen content, while the latter mainly affects the oxidized fraction in the film.

Keywords: PLD; Nanostructured; Thin films; Titanium oxide; Anatase

Particle diagnostics of a ZnO laser ablation plume for nanostructured material deposition by Conor McLoughlin; Pádraig Hough; John Costello; Jean-Paul Mosnier (pp. 5338-5341).

We report results on the pulsed laser deposition of ZnO obtained with the help of a new apparatus that includes in situ reflectron time-of-flight mass spectrometry, with a view to progress the understanding of the role of clusters in the laser deposition of nanostructured materials. Experiments were carried out using a Nd-YAG laser at its fundamental frequency and frequency tripled, with a fluence on target of ∼7.7J/cm², in vacuum (10⁻⁴Pa) or oxygen (1Pa) atmospheres. The results show that under certain conditions there is preferential clusterisation of the material into certain mass numbers and finally that there exists a correlation between cluster presence in the plume and the deposition of nanostructures.

Keywords: Reflectron time-of-flight; Pulsed laser deposition; Zinc oxide; Cluster; Nanoparticle; Plasma diagnostic

Liquids microprinting through laser-induced forward transfer by P. Serra; M. Duocastella; J.M. Fernández-Pradas; J.L. Morenza (pp. 5342-5345).

Laser-induced forward transfer (LIFT) is a direct-writing technique which allows the deposition of tiny amounts of material from a donor thin film onto a receptor substrate. When LIFT is applied to liquid donor films, the laser radiation affects only a localized fraction of the liquid, thereby impelling the unaffected portion towards the receptor substrate. Thus, transfer takes place with no melting or vaporization of the deposited fraction and, in this way, LIFT can be used to successfully print complex materials like inorganic inks and pastes, biomolecules in solution, and even living cells and microorganisms. In addition, and for a wide range of liquid rheologies, the material can be deposited in the form of circular microdroplets; this provides LIFT with a high degree of spatial resolution leading to feature sizes below 10μm, and making it competitive in front of conventional printing techniques. In this work, a revision of the main achievements of the LIFT of liquids is carried out, correlating the morphological characteristics of the generated features with the results of the study of the transfer process. Special emphasis is put on the characterization of the dynamics of liquid ejection, which has provided valuable information for the understanding of microdroplets deposition. Thus, new time-resolved imaging analyses have shown a material release behavior which contrasts with most of the previously made assumptions, and that allows clarifying some of the questions open during the study of the LIFT technique.

Keywords: LIFT; Printing; Biosensors

Femtosecond laser writing of nanostructures on bulk Al via its ablation in air and liquids by E. Stratakis; V. Zorba; M. Barberoglou; C. Fotakis; G.A. Shafeev (pp. 5346-5350).

We report on the formation of self-organized nanostructures (NS) on bulk Al under its ablation in air and liquids with femtoseconds (fs) laser pulses. In case of exposure into liquids, NS are regularly formed on the Al surface with an average period of about 200nm, independent of the laser polarization. A dispersion of Al nanoparticles (NPs) into the liquid additionally occurs. Irregular nano-bumps are produced when the irradiation is performed in air. NP dispersions as well as NS formed on Al surface show a characteristic absorption peak in the near UV which has been attributed to plasmon oscillation of electrons. The wings of this peak extending to the visible, lead to a distinct yellow coloration of the processed Al surface and the liquid dispersions. Ultrafast laser processing of bulk Al in liquids may be potentially a promising technique for efficient production of nanosized aluminum.

Keywords: Laser ablation; Nanostructures; Nanoparticles; Aluminum; Liquid

Synthesis and characterization of TiO_x nanoparticles prepared by pulsed-laser ablation of Ti target in water by A.S. Nikolov; P.A. Atanasov; D.R. Milev; T.R. Stoyanchov; A.D. Deleva; Z.Y. Peshev (pp. 5351-5354).

Nanoparticles (NPs) creation by pulsed-laser ablation of targets in a liquid environment has recently become a promising technique, which has several relative advantages, such as simplicity and low cost. This technique was employed in the present work for preparation of TiO_x NPs suspension by ablation of metal Ti targets into twice-distilled water. A second harmonic generation (SHG) pulsed Nd:YAG laser was used in the experiments. Preferential formation of spherical NPs and their TiO_x nature was established. Aggregation of the created particles during aging was found. Transition of the NPs’ structure from amorphous to crystalline with increasing the laser energy was revealed. A difference was observed in the transmittance of the suspensions obtained depending on the laser intensity.

Keywords: Ti oxide nanoparticles; Pulsed-laser ablation in liquid; Optical properties and morphology; Chemical composition

Formation of ultrathin nanocomposite SiO₂:nc-Au structures by Pulsed Laser Deposition by A.V. Zenkevich; Yu.Yu. Lebedinskii; A.A. Timofeyev; I.A. Isayev; V.N. Tronin (pp. 5355-5358).

A method for the formation of Au nanocrystal (nc) arrays embedded in an ultrathin SiO₂ layer in one vacuum cycle is proposed. The method is based on the co-deposition in vacuum of ∼1nm thick uniform Si–Au amorphous layer at a specific composition ratio by Pulsed Laser Deposition on the pre-oxidized Si(100) substrate, followed by its oxidation in the glow discharge oxygen plasma at room temperature, resulting in the precipitation of Au ncs at the bottom interface and/or at the surface of the forming SiO₂ layer. The capping SiO₂ layer is formed by the glow discharge plasma oxidation of further deposited ultrathin Si layer. Au ncs 2–5nm in size and with the separation of ∼3–20nm from each other segregate during the oxidation of Au–Si mixture as evidenced by transmission electron microscopy (TEM). The evolution of Au and Si chemical state upon each step of the SiO₂:nc-Au nanocomposite structure formation is monitored in situ by X-ray photoelectron spectroscopy (XPS). The metrology of nanocomposite SiO₂:nc-Au structures describing the space distribution of Au ncs as a function of Au/Si ratio is presented.

Keywords: PACS; 61.46.w; 81.07.b; 64.75.StPulsed Laser Deposition; Au nanocrystals; Silicon dioxide; Nanocomposite; Au–Si; Glow discharge plasma

Fast synthesis of ZnO nanostructures by laser-induced chemical liquid deposition by Christian Fauteux; Riadh Smirani; Joseph Pegna; My Ali El Khakani; Daniel Therriault (pp. 5359-5362).

ZnO nanostructures were obtained by directly irradiating a small volume of a solution of precursor on a fused-quartz substrate using an unfocused continuous wave CO₂ laser for 2–30s at laser powers ranging from 20 to 40W. The laser-based thermochemistry approach allows rapid non-isothermal heating and convection enhanced mass transport which opens new growth mechanisms for the rapid deposition of nanomaterials at predetermined locations on a substrate. The deposits consist of a variety of ZnO nanostructure morphologies, including aggregated nanoparticles, nanorods, faceted nanocrystals and nanowires. The samples were characterized by scanning and transmission electron microscopy, X-ray diffraction and photoluminescence spectroscopy. They were found to exhibit an intense room-temperature photoluminescence, which is characterized by the presence of a strong UV peak around 390nm and no visible emission. The relationship between the PL signal characteristics and specific ZnO nanostructures was investigated in order to point up optimal nanostructures for possible luminescent devices.

Keywords: Laser chemical liquid deposition; ZnO; Nanostructures; Photoluminescence

Preparation of ZnO nanopowders by thermal plasma and characterization of photo-catalytic property by So-Jung Kim; Dong-Wha Park (pp. 5363-5367).

Nano-sized zinc oxide (ZnO) powders were prepared via a thermal plasma process from micro-sized zinc powder while oxygen was employed as a reaction gas. Two different carrier gases, oxygen and argon, were evaluated and the flow rate of the reaction gas was controlled. The photo-catalytic activities of ZnO powders were evaluated by measuring the degradation of methylene blue (MB) in water under the UV and visible region. The prevailing goal of this study is to improve the photo-catalytic activity of nano-sized ZnO powders for the removal of environmental pollutants. The ZnO nanopowders were characterized by XRD, SEM, BET, and UV–vis spectrometry. Their mean crystallites sizes ranged from 26.5nm to 48.6nm. It was confirmed by a XRD analysis that the ZnO nanopowders had a high quality wurtzite structure. SEM and XRD results show that the size of the particles synthesized increased with an increase of the flow rate of the oxygen reaction gas. The powder obtained using the argon carrier gas with higher oxygen reaction gas flow rate was more rod-shape. The MB decomposition rates of the obtained ZnO nanopowders were studied under the UV and visible region. In the UV region, synthesized ZnO could decompose MB as well as commercial ZnO. However, in the visible region, the MB decomposition rate obtained using ZnO was much higher than that by commercial ZnO.

Keywords: PACS; 52.77−j; 55.77.FvThermal plasma; Zinc oxide; Nanopowder; Photo-catalyst

Lamp-assisted CVD of carbon micro/nano-structures using metal catalysts and CH₂I₂ precursor by A. Rashid; L. Landström; D. Brodoceanu; K. Piglmayer (pp. 5368-5372).

Carbon micro/nanofibers and nanotubes were deposited via chemical vapor deposition (CVD) using CH₂I₂ precursor and different metal catalysts (Pd, Ni, Fe, Co and Mn) on Si (100) substrates. A versatile and low-cost IR lamp technique is employed to induce the deposition process. With this method carbon features could be obtained already at temperatures much lower than with common techniques. Palladium metal was deposited by laser-assisted CVD from a liquid solution of the ammine complex and the 3d metals by thermal evaporation. Large-scale periodicity of nano-sized metal catalysts, and subsequently of carbon deposits was obtained by using monolayers of polystyrene microspheres as mask. The carbon structures were analyzed by SEM and micro-Raman spectroscopy.

Keywords: CVD; Nano; Carbon

Preparation and characterization of nitrogen-doped TiO₂ nanoparticles by the laser pyrolysis of N₂O-containing gas mixtures by R. Alexandrescu; M. Scarisoreanu; I. Morjan; R. Birjega; C. Fleaca; C. Luculescu; I. Soare; O. Cretu; C.C. Negrila; N. Lazarescu; V. Ciupina (pp. 5373-5377).

Nitrogen-doped TiO₂ nanoparticles have been prepared by the IR laser pyrolysis technique. A sensitized mixture of TiCl₄ (vapors) and N₂O was used as titanium and nitrogen precursors, respectively. The structural properties of the resultant N-doped nanoparticles such as the phase formation and the average particle size and distributions were investigated by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The phase composition varied from almost pure anatase to mixtures of rutile and anatase. A decrease of the mean particle diameters from about 18nm in case of the almost pure anatase sample to about 13nm in case of the anatase–rutile mixture is observed. XPS analysis suggests and interstitial character of the doping process.

Keywords: Laser pyrolysis; Nanoparticles; TiO; ₂; Nitrogen-doping

Radiofrequency plasma beam deposition of various forms of carbon based thin films and their characterization by S. Vizireanu; S.D. Stoica; B. Mitu; M.A. Husanu; A. Galca; L. Nistor; G. Dinescu (pp. 5378-5381).

The characteristics of carbonic materials obtained by downstream deposition in a low pressure argon plasma beam injected with acetylene are reported. The influence of substrate temperature, presence of Ni catalyst and hydrogen in gas composition on the material properties is described. By increasing the substrate temperature, an enhanced order in the material is revealed by Raman spectroscopy, while FTIR measurements show a decreasing of the hydrogen content and the disappearing of sp¹ hybridized carbon in the deposit. The SEM and Raman investigation show a clear tendency of crystalline phases formation when hydrogen is assisting the deposition.

Keywords: PECVD; RF plasma beam; Amorphous hydrogenated carbon material; Nanostructured carbon

Hydroxylapatite nanoparticles obtained by fiber laser-induced fracture by M. Boutinguiza; F. Lusquiños; A. Riveiro; R. Comesaña; J. Pou (pp. 5382-5385).

This work presents the results of laser-induced fragmentation of hydroxylapatite microparticles in water dissolution. Calcined fish bones in form of powder, which were previously milled to achieve microsized particles, were used as precursor material. Two different laser sources were employed to reduce the size of the suspended particles: a pulsed Nd:YAG laser and a Ytterbium doped fiber laser working in continuous wave mode. The morphology as well as the composition of the obtained particles was characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and conventional and high resolution transmission electron microscopy (TEM, HRTEM). The results show that nanometric particles of hydroxylapatite and β-tricalcium phosphate as small as 10nm diameter can be obtained.

Keywords: Nanoparticles; Hydroxylapatite; β-TCP; Laser fragmentation

Magnetic properties of core-shell catalyst nanoparticles for carbon nanotube growth by C.T. Fleaca; I. Morjan; R. Alexandrescu; F. Dumitrache; I. Soare; L. Gavrila-Florescu; F. Le Normand; A. Derory (pp. 5386-5390).

Two types of core-shell nanoparticles have been prepared by laser pyrolysis using Fe(CO)₅ and C₂H₂ or [(CH₃)₃Si]₂O as precursors and C₂H₄ as sensitizer. The first type (about 4nm diameter) – produced by the decomposition of Fe(CO)₅ in the presence of C₂H₄ and C₂H₂ – consists of Fe cores protected by graphenic layers. The second type (mean particle size of about 14nm) consists also of Fe cores, yet covered by few nm thick γ-Fe₂O₃/porous polycarbosiloxane shells resulted from the [(CH₃)₃Si]₂O decomposition and superficial oxidation after air exposure. The hysteresis loops suggest a room temperature superparamagnetic behavior of the Fe-C nanopowder and a weak ferromagnetic one for larger particles in the Fe-Fe₂O₃-polymer sample. Both types of nanoparticles were finally used as a catalyst for the carbon nanotube growth by seeding Si(100) substrates via drop-casting method. CNTs were grown by Hot-Filament Direct.Current PE CVD technique from C₂H₂ and H₂ at 980K. It is suggested that the increased density and orientation degree observed for the multiwall nanotubes grown from Fe-Fe₂O₃-polymer nanoparticles could be due to their magnetic behavior and surface composition.

Keywords: PACS; 42.62−b; 61.46.Df; 75.60.−d; 52.77.Dq; 61.46.FgLaser pyrolysis; Core-shell nanoparticles; Superparamagnetism; Coercivity; HF PE CCVD; Oriented carbon nanotubes

Nanoscale characterization of single Au nanorods by confocal microscopy by Tina Züchner; Frank Wackenhut; Antonio Virgilio Failla; Alfred Johann Meixner (pp. 5391-5395).

We analyzed the scattering patterns of individual Au nanorods detected by means of confocal interference scattering microscopy in combination with a higher order laser mode. We placed the Au nanorods at the interface between two dielectric media and examined the influence of different interfaces on the signal amplitude, the signal-to-noise ratio as well as on the precision of topological measurements. Approaching the index matching regime allows for topological measurements with high accuracy minimizing the acquisition time. We were also able to track the position and the orientation of particles embedded in water even when they were not thoroughly sticking to the glass surface. These results underscore the potential of the presented technique for applications in life sciences.

Keywords: PACS; 78.67.Bf; 78.35.+c; 87.64.TtConfocal microscopy; Higher order laser modes; Nanophotonics; Particle plasmons; Single particle imaging

Role of plasma activation in tailoring the nanostructure of multifunctional oxides thin films by Maria M. Giangregorio; Maria Losurdo; Pio Capezzuto; Giovanni Bruno (pp. 5396-5400).

Potential of O₂ remote plasmas for improving structural, morphological and optical properties of various multifunctional oxides thin films both during plasma assisted growth as well as by post-growth treatments is discussed. In particular, an O₂ remote plasma metalorganic chemical vapor deposition (RP-MOCVD) route is presented for tailoring the structural, morphological and optical properties of Er₂O₃ and ZnO films. Furthermore, post-growth room-temperature remote O₂ plasma treatments of indium-tin-oxides (ITO) films are demonstrated to be effective in improving morphology of ITO films.

Keywords: Multifunctional oxides; ZnO; Er; ₂; O; ₃; ITO; O; ₂; plasma; Remote plasma-MOCVD

Pulsed plasma ion source to create Si nanocrystals in SiO₂ substrates by A. Lorusso; V. Nassisi; G. Congedo; N. Lovergine; L. Velardi; P. Prete (pp. 5401-5404).

A pulsed KrF excimer laser of irradiance of about 10⁸W/cm² was utilized to synthesize Si nanocrystals on SiO₂/Si substrates. The results were compared with that ones obtained by applying low bias voltage to Si(100) target in order to control the kinetic energy of plasma ions. Glancing incidence X-ray diffraction spectra indicate the presence of silicon crystalline phases, i.e. (111) and (220), on SiO₂/Si substrates. The average Si nanocrystal size was estimated to be about 45nm by using the Debye–Scherrer formula. Scanning electron microscopy and atomic force microscopy images showed the presence of nanoparticles of different size and shape. Their distribution exhibits a maximum concentration at 49nm and a fraction of 14% at 15nm.

Keywords: PACS; 52.38.Mf; 61.05.cp; 61.46.Hk; 68.37.Ps; 81.15.FgLaser ablation; Silicon nanocrystals; X-ray diffraction; Atomic force microscopy

Time-resolved transmission study of fused silica during laser-induced backside dry etching by T. Smausz; Z. Zalatnai; B. Papdi; T. Csákó; Zs. Bor; B. Hopp (pp. 5405-5408).

Laser-induced backside dry etching (LIBDE) is a promising technique for micro- and nanomachining of transparent materials. Although several experiments have already proved the suitability and effectiveness of the technique, there are several open questions concerning the etching mechanism and the concomitant processes. In this paper time-resolved light transmission investigations of etching process of fused silica are presented. 125nm thick silver coating was irradiated through the carrying 1mm thick fused silica plate by single pulses of a nanosecond KrF excimer laser. The applied fluences were 0.38, 0.71 and 1J/cm². During the etching process the irradiated spots were illuminated by an electronically delayed nitrogen laser pumped dye laser. The delay between the pump and probe pulses was varied in the range of 0ns and 20μs. It was found that the transmitted probe beam intensity strongly depends on the applied delays and fluences. Scanning electron microscopy and energy dispersive X-ray spectrometry of the etched surface showed the existence of silver droplets and fragments on the illuminated surfaces and silver atoms built into the treated surface layer influencing the transmission behavior of the studied samples.

Keywords: JEL classification; 78.68.+m; 81.65.Cf; 81.70.Fy; 68.37.HkLIBDE; Transmission; Time-resolved study; KrF; Laser etching

Synthesis of nano-sized antimony-doped tin oxide (ATO) particles using a DC arc plasma jet by Da-Woon Jung; Dong-Wha Park (pp. 5409-5413).

Nano-sized antimony-doped tin oxide (ATO) particles were synthesized using DC arc plasma jet. The precursors SnCl₄ and SbCl₅ were injected into the plasma flame in the vapor phase. ATO powder could conveniently be synthesized without any other post-treatment in this study. To control the doping amount of antimony in the ATO particles, the Sb/Sn molar ratio was used as an operating variable. To study the effect of carrier gas on the particle size, argon and oxygen gases were used. The results of XRD and TGA show that all Sb ions penetrated the SnO₂ lattice to substitute Sn ions. With the increased SbCl₅ concentration in source material, the Sb doping level was also increased. The size of the particles synthesized using the argon carrier gas was much smaller than that of the particles prepared using the oxygen carrier gas. For the argon gas, PSA results and SEM images reveal that the average particle size was 19nm. However, for the oxygen gas, the average particle size was 31nm.

Keywords: PACS; 52.77−j; 55.77.FvThermal plasma; Antimony-doped tin oxide (ATO); Nanopowder

Morphology control and electron field emission properties of high-ordered Si nanoarrays fabricated by modified nanosphere lithography by Ling Xu; Wei Li; Jun Xu; Jiang Zhou; Liangcai Wu; Xian-Gao Zhang; Zhongyuan Ma; Kunji Chen (pp. 5414-5417).

High-ordered silicon nanoarrays were prepared using direct nanosphere lithography combined with thermal oxidation. Atomic force microscope (AFM) images of the silicon arrays show that the patterns of polystyrene (PS) template are well transferred to the silicon surface. The size and morphology of the nanoarrays can be controlled effectively by varying the plasma-therm reactive ion etching (RIE) or thermal oxidation parameters. The field emission studies revealed that the typical turn-on field was about 7–8V/μm with emission current reached 1μA/cm². It is also found that the field emission current is highly dependent on the morphology of these Si nanoarrays.

Keywords: Silicon nanoarray; Nanosphere lithography; Electron field emission

Modification of semiconductor materials using laser-produced ion streams additionally accelerated in the electric fields by M. Rosinski; B. Badziak; P. Parys; J. Wołowski; M. Pisarek (pp. 5418-5420).

The laser-produced ion stream may be attractive for direct ultra-low-energy ion implantation in thin layer of semiconductor for modification of electrical and optical properties of semiconductor devices. Application of electrostatic fields for acceleration and formation of laser-generated ion stream enables to control the ion stream parameters in broad energy and current density ranges. It also permits to remove the useless laser-produced ions from the ion stream designed for implantation.For acceleration of ions produced with the use of a low fluence repetitive laser system (Nd:glass: 2Hz, pulse duration: 3.5ns, pulse energy:∼0.5J, power density: 10¹⁰W/cm²) in IPPLM the special electrostatic system has been prepared. The laser-produced ions passing through the diaphragm (a ring-shaped slit in the HV box) have been accelerated in the system of electrodes. The accelerating voltage up to 40kV, the distance of the diaphragm from the target, the diaphragm diameter and the gap width were changed for choosing the desired parameters (namely the energy band of the implanted ions) of the ion stream. The characteristics of laser-produced Ge ion streams were determined with the use of precise ion diagnostic methods, namely: electrostatic ion energy analyser and various ion collectors. The laser-produced and post-accelerated Ge ions have been used for implantation into semiconductor materials for nanocrystal fabrication. The characteristics of implanted samples were measured using AES.

Keywords: Laser–matter interaction; Laser ion source; Electrostatic fields for acceleration

Synthesis of carbon nanotubes and iron oxide nanoparticles in MW plasma torch with Fe(CO)₅ in gas feed by Lenka Zajíčková; Petr Synek; Ondřej Jašek; Marek Eliáš; Bohumil David; Jiří Buršík; Naděžda Pizúrová; Renáta Hanzlíková; Lukáš Lazar (pp. 5421-5424).

The MW plasma torch (2.45GHz) in the mixture of CH₄/H₂/Ar (42/430/1540sccm) with added Fe(CO)₅vapors was used for the synthesis of iron oxide nanoparticles and carbon nanotubes. The particles with well-defined facets consisting of Fe₃O₄ andγ-Fe₂O₃ and self-assembled into long chains were produced at the power of 360W. At higher power of 440–460W the deposit contained significant amount of multi-walled carbon nanotubes covered by iron oxide nanoparticles. The diameter of CNTs was 8–20nm. The particles had Fe₃O₄ and/orα-Fe₂O₃ cores of spherical shape covered by a thin layer of carbon.

Keywords: PACS; 52.80.Pi; 82.33.Xj; 81.07.Bc; 81.07.DeCarbon nanotube; Magnetite; Hematite; Iron pentacarbonyl

Bio-inspired water repellent surfaces produced by ultrafast laser structuring of silicon by M. Barberoglou; V. Zorba; E. Stratakis; E. Spanakis; P. Tzanetakis; S.H. Anastasiadis; C. Fotakis (pp. 5425-5429).

We report here an efficient method for preparing stable superhydrophobic and highly water repellent surfaces by irradiating silicon wafers with femtosecond laser pulses and subsequently coating them with chloroalkylsilane monolayers. By varying the laser pulse fluence on the surface one can successfully control its wetting properties via a systematic and reproducible variation of roughness at micro- and nano-scale, which mimics the topology of natural superhydrophobic surfaces. The self-cleaning and water repellent properties of these artificial surfaces are investigated. It is found that the processed surfaces are among the most water repellent surfaces ever reported. These results may pave the way for the implementation of laser surface microstructuring techniques for the fabrication of superhydrophobic and self-cleaning surfaces in different kinds of materials as well.

Keywords: Laser ablation; Silicon; Superhydrophobicity; Water repellence

Shadowgraphy investigation of laser-induced forward transfer: Front side and back side ablation of the triazene polymer sacrificial layer by Romain Fardel; Matthias Nagel; Frank Nüesch; Thomas Lippert; Alexander Wokaun (pp. 5430-5434).

Thin films of a photodecomposible triazene polymer are used as sacrificial layer for the micro-deposition of sensitive materials by laser-induced forward transfer. To understand the ablation process of this sacrificial layer, the ultraviolet laser ablation of triazene films was investigated by time-resolved shadowgraphy. Irradiation from the film side shows a complete decomposition into gaseous fragments, while ablation through the substrate causes ejection of a solid flyer of polymer. The occurence of the flyer depends on the film thickness as well as on the applied fluence, and a compact flyer is obtaind when these two parameters are optimized.

Keywords: Laser-induced forward transfer; Triazene polymer; Shadowgraphy imaging

In situ bioconjugation—Novel laser based approach to pure nanoparticle-conjugates by Svea Petersen; Jurij Jakobi; Stephan Barcikowski (pp. 5435-5438).

The generation and characterization of nanoparticulate carrier systems is important for drug delivery, biosensing and in vivo or in vitro diagnostics. Conventional nanoparticle generation is based on chemical synthesis methods requiring time intensive reaction and additive design for each material. Successive purification and surface functionalisation is often required after the nanoparticle generation to achieve pure nanoparticle-bioconjugates. We established a novel single step method, which allows the generation of pure nanoparticles and their in situ conjugation with biomolecules bearing electron donating moieties using pulsed laser ablation in liquids. For comparison between unspecific binding and binding through strong dative bonds (here: S-Au), we applied this preparation method to the conjugation of gold nanoparticles with unmodified and thiolated oligonucleotides. In order to determine optimal parameters (laser pulse energy, focus diameter), the influence on productivity of nanoparticle generation and their interaction with oligonucleotides is studied. We report quenching of nanoparticle growth and modification of the surface plasmon resonance as evidence of a successful functionalisation. Their stability in ionic solutions is evidenced with relevance to biological and medical assays. Negligible differences between the two model bioconjugations evidence the universality of the established in situ bioconjugation method.

Keywords: In situ bioconjugation; Gold nanoparticles; Ultrashort pulsed laser ablation

Characterization of organic material micro-structures transferred by laser in nanosecond and picosecond regimes by Ludovic Rapp; Christophe Cibert; Anne Patricia Alloncle; Philippe Delaporte (pp. 5439-5443).

The laser-induced forward transfer technique has been performed on thin layers of conducting organic materials for applications in plastic micro-electronics.This process is a promising alternative for fabrication of organic electronic components on flexible supports when usual techniques, such like ink-jet printing, cannot be considered. For example, when the organic material has no solubility properties or when complex architectures are needed.Experiments on the influence of pulse duration (nanosecond and picosecond) and wavelength on a large range of fluences have been proceeded using different lasers. An optimization of the process has been carried out by inserting a thin layer of absorbing metallic material between the substrate and the organic film. The advantage of this technique is to preserve organic layers from being damaged by thermal and photochemical effects during the interaction.The morphology and thickness of the deposit have been investigated by optical and scanning electronic microscopy. This experimental study is supplemented by electrical characterization of the deposits.

Keywords: Laser-induced forward transfer; Polymer; Nanosecond; Picosecond

Laser direct writing of combinatorial libraries of idealized cellular constructs: Biomedical applications by Nathan R. Schiele; Ryan A. Koppes; David T. Corr; Karen S. Ellison; Deanna M. Thompson; Lee A. Ligon; Thomas K.M. Lippert; Douglas B. Chrisey (pp. 5444-5447).

The ability to control cell placement and to produce idealized cellular constructs is essential for understanding and controlling intercellular processes and ultimately for producing engineered tissue replacements. We have utilized a novel intra-cavity variable aperture excimer laser operated at 193nm to reproducibly direct write mammalian cells with micrometer resolution to form a combinatorial array of idealized cellular constructs. We deposited patterns of human dermal fibroblasts, mouse myoblasts, rat neural stem cells, human breast cancer cells, and bovine pulmonary artery endothelial cells to study aspects of collagen network formation, breast cancer progression, and neural stem cell proliferation, respectively. Mammalian cells were deposited by matrix assisted pulsed laser evaporation direct write from ribbons comprised of a UV transparent quartz coated with either a thin layer of extracellular matrix or triazene as a dynamic release layer using CAD/CAM control. We demonstrate that through optical imaging and incorporation of a machine vision algorithm, specific cells on the ribbon can be laser deposited in spatial coherence with respect to geometrical arrays and existing cells on the receiving substrate. Having the ability to direct write cells into idealized cellular constructs can help to answer many biomedical questions and advance tissue engineering and cancer research.

Keywords: Laser processing; Matrix assisted pulsed laser evaporation direct write; Biomaterials; Patterning; Tissue engineering; Idealized cellular constructs; Combinatorial libraries

Small size plasma tools for material processing at atmospheric pressure by E.R. Ionita; M.D. Ionita; E.C. Stancu; M. Teodorescu; G. Dinescu (pp. 5448-5452).

A small size radiofrequency plasma jet source able to produce cold plasma jets at atmospheric pressure is presented. The surface modification of polyethylene terephtalate, polyethylene and polytetrafluorethylene foils is performed by using a scanning procedure. The contact angle measurements reveal that the treatment leads to hydrophilicity increase. The roughening of surface, specific to each material is noticed. A significant improvement of adhesion is obtained as result of atmospheric plasma treatments.

Keywords: Atmospheric plasma sources; Plasma treatment; Polymer modification; Hydrophilicity; Plasma roughening; Adhesion

Laser- and UV-assisted modification of polystyrene surfaces for control of protein adsorption and cell adhesion by Wilhelm Pfleging; Maika Torge; Michael Bruns; Vanessa Trouillet; Alexander Welle; Sandra Wilson (pp. 5453-5457).

An appropriate choice of laser and process parameters enables new approaches for the fabrication of polymeric lab-on-chip devices with integrated functionalities. We will present our current research results in laser-assisted modification of polystyrene (PS) with respect to the fabrication of polymer devices for cell culture applications. For this purpose laser micro-patterning of PS and subsequent surface functionalization was investigated as function of laser and process parameters. A high power ArF-excimer laser radiation source with a pulse length of 19ns as well as a high repetition ArF-excimer laser source with a pulse length of 5ns were used in order to study the influence of laser pulse length on laser-induced surface oxidation. The change in surface chemistry was characterized by X-ray photoelectron spectroscopy and contact angle measurements. The difference between laser-assisted modification versus UV-lamp assisted modification was investigated. A photolytic activation of specific areas of the polymer surface and subsequent oxidization in oxygen or ambient air leads to a chemically modified polymer surface bearing carboxylic acid groups well-suited for controlled competitive protein adsorption or protein immobilization. Finally, distinct areas for cell growth and adhesion are obtained.

Keywords: Laser; Ablation; Modification; Cell adhesion; Wetting; Polystyrene

Pulsed laser ablation of pepsin on an inorganic substrate by N. Cicco; T. Lopizzo; V. Marotta; A. Morone; M. Verrastro; V. Viggiano (pp. 5458-5460).

Pressed pepsin pellets used as targets were ablated with the pulses of the Nd-YAG laser. The activity of the pepsin thin layer, deposited on a glass substrate, was successfully detected by analyzing the proteolytic degradation areas on the polyacrylamide gel (PA-gel) copolymerized with albumin from the hen egg white (ovalbumin), used as an enzymatic substrate.

Keywords: Laser; Material

Fluorocarbon plasmas for nanotexturing of polymers: A route to water-repellent antireflective surfaces by Rosa Di Mundo; Vincenzo De Benedictis; Fabio Palumbo; Riccardo d’Agostino (pp. 5461-5465).

In this work the roughening of polystyrene by means of radiofrequency plasmas fed with CF₄ has been studied. The effect of the Ar addition to the feed, the input power and the treatment duration has been investigated in terms of etching and fluorination degree. Wettability and reflectance performances of selected textured surfaces, coated with a fluorocarbon film from a C₄F₈ fed plasma, have been characterized. All the considered surfaces, even those poorly structured, once coated, show slippery superhydrophobicity, while antireflective transparency appears to be limited to precise texturing characteristics.

Keywords: CF; ₄; plasma etching; Polystyrene; Super-hydrophobic; Water contact angle; C; ₄; F; ₈; deposition

The fabrication of polymer-based evanescent optical waveguide for biosensing by S.W. Kwon; W.S. Yang; H.M. Lee; W.K. Kim; G.S. Son; D.H. Yoon; S.-D. Lee; H.-Y. Lee (pp. 5466-5470).

A polymer waveguide was fabricated to amplify the evanescent optical field for biosensing. The structure of waveguide was designed to propagate a normal single mode at the input and output regions for low loss beam coupling and propagation. A sensing region was formed in the middle of the waveguide to activate the evanescent mode and to induce high birefringence by depositing a thin dielectric film with a high refractive index on a single mode waveguide. A polymer waveguide with the dimensions of 7μm-width and 2.5μm-thickness was fabricated by photolithography and dry-etching. The active region of the TiO₂ thin film was fabricated with the dimensions of 20mm-length, 20nm-thickness and 2mm-tapered tail. A polarimetric interference technique was used to evaluate the evanescent waveguide biosensor, and biomaterial such as glycerol was tested. The sensitivity of the sensor increased with increasing TiO₂ film thickness. For the fabricated waveguide with a 20nm-thick TiO₂ film, the measured index change to the lead phase variation of 2 π was 1.8×10⁻⁴.

Keywords: Polymer waveguide; Optical-biosensor; Titanium dioxide; Evanescent field; Refractive index; Birefringence

Micro-patterning for polymer electrolyte fuel cells: Single pulse laser ablation of aluminum films from glassy carbon by Bernhard C. Seyfang; Romain Fardel; Thomas Lippert; Guenther G. Scherer; Alexander Wokaun (pp. 5471-5475).

Microfuel cells are a possible replacement for batteries as energy sources in portable devices. At PSI a micropolymer electrolyte fuel cell was developed, whose flow fields consist of micro-structured glassy carbon plates. Micro-structuring of glassy carbon is carried out in a multi-step process. A sputtered aluminum mask is selectively removed by single pulse laser ablation from glassy carbon thereby defining micro-channels subsequently etched by reactive ion etching.A pulsed XeCl excimer laser (308nm) is used for the single pulse patterning of a metal mask on the glassy carbon. The influence of the excimer laser typical pulse to pulse energy fluctuations on the micro-structuring process must be known to minimize defects during RIE etching of the micro-channels. To obtain a better understanding of the processes occurring during ablation, ns-shadowgraphy was performed. The formation of a shockwave was observed, followed by a similar but much slower perturbation, and the subsequent release of fragments. The calculated velocities can be correlated with the energy release during ablation. The post-ablation examination of the samples by profilometry, optical microscopy, SEM and EDX is used to measure the amount of removed material, the quality of the aluminum mask edges and aluminum residues on the glassy carbon surface. Such criteria allow us to classify the laser irradiation as a function of laser fluence: no ablation, partial ablation, complete ablation, and over-ablation.

Keywords: Laser ablation; Aluminum film; Glassy carbon; ns-Shadowgraphy; Micropolymer electrolyte fuel cell

Bioglass thin films for biomimetic implants by C. Berbecaru; H.V. Alexandru; Adelina Ianculescu; A. Popescu; G. Socol; F. Sima; Ion Mihailescu (pp. 5476-5479).

Pulsed laser deposition (PLD) method was used to obtain bioglass (BG) thin film coatings on titanium substrates. An UV excimer laser KrF* ( λ=248nm, τ=25ns) was used for the multi-pulse irradiation of the BG targets with 57 or 61wt.% SiO₂ content (and Na₂O–K₂O–CaO–MgO–P₂O₅ oxides). The depositions were performed in oxygen atmosphere at 13Pa and for substrates temperature of 400°C. The PLD films displayed typical BG of 2–5μm particulates nucleated on the film surface or embedded in. The PLD films stoichiometry was found to be the same as the targets. XRD spectra have shown, the glass coatings obtained, had an amorphous structure. One set of samples, deposited in the same conditions, were dipped in simulated body fluids (SBFs) and subsequently extracted one by one after several time intervals 1, 3, 7, 14 and 21 days. After washing in deionized water and drying, the surface morphology of the samples and theirs composition were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), IR spectroscopy (FTIR) and energy dispersive X-ray analysis (EDX). After 3–7 days the Si content substantially decreases in the coatings and PO₄³⁻ maxima start to increase in FTIR spectra. The XRD spectra also confirm this evolution. After 14–21 days the XRD peaks show a crystallized fraction of the carbonated hydroxyapatite (HAP). The SEM micrographs show also significant changes of the films surface morphology. The coalescence of the BG droplets can be seen. The dissolution and growth processes could be assigned to the ionic exchange between BG and SBFs.

Keywords: PLD coatings; Bioglass thin films; SBFs experiments; Hydroxyapatite

Thin films of Cu(II)-o,o′-dihydroxy azobenzene nanoparticle-embedded polyacrylic acid (PAA) for nonlinear optical applications developed by matrix assisted pulsed laser evaporation (MAPLE) by Catalin Constantinescu; Ana Emandi; Cristina Vasiliu; Catalin Negrila; Constantin Logofatu; Costel Cotarlan; Mihail Lazarescu (pp. 5480-5485).

Thin films based on two different metal–organic systems are developed by MAPLE and their nonlinear optical applications are explored. A complex of o,o′-dihydroxy azobenzene with Cu²⁺ cation is found to organize as a non-central symmetric crystallite. A simple protocol is developed for the in situ fabrication of highly monodisperse copper-complex nanoparticles in a polymer film matrix of polyacrylic acid. The thin films were deposited on quartz substrates by MAPLE (matrix assisted pulsed laser evaporation) using a Nd:YAG laser working at 355nm. Atomic force microscopy (AFM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and optical second harmonic generation (SHG) were performed on the samples. The optical limiting capability of the nanoparticle-embedded polymer film is investigated.

Keywords: MAPLE; Thin film; Copper-complex nanoparticle; Polyacrylic acid

Biocompatible and bioactive nanostructured glass coatings synthesized by pulsed laser deposition: In vitro biological tests by A.C. Popescu; F. Sima; L. Duta; C. Popescu; I.N. Mihailescu; D. Capitanu; R. Mustata; L.E. Sima; S.M. Petrescu; D. Janackovic (pp. 5486-5490).

We report on the synthesis by pulsed laser deposition with a KrF* excimer laser source ( λ=248nm, τ=25ns) of bioglass thin films of 6P57 and 6P61 types. Physiology, viability, and proliferation of human osteoblast cells were determined by quantitative in vitro tests performed by flow cytometry on primary osteoblasts cultured on pulsed laser deposited bioglasses. Both types of glass films proved to be appropriate mediums for cell survival and proliferation. In a parallel investigation, cell morphology and adhesion to the surface was studied by fluorescence microscopy and scanning electron microscopy. Strong bonds between the materials and cells were found in both cases, as osteoblast pseudopodes penetrated deep into the material. According to our observations, the 6P57 glass films were superior with respect to viability and proliferation performances.

Keywords: Bioglass thin films; In vitro; biotests; Pulsed laser deposition

Multifunctional thin films of lactoferrin for biochemical use deposited by MAPLE technique by Catalin Constantinescu; Alexandra Palla-Papavlu; Andrei Rotaru; Paula Florian; Florica Chelu; Madalina Icriverzi; Anca Nedelcea; Valentina Dinca; Anca Roseanu; Maria Dinescu (pp. 5491-5495).

Lactoferrin (Lf) is an iron-binding glycoprotein present in almost all mammalian secretions which plays an important role in host defense against microbial and viral infections. The protein has been reported to also have anti-inflammatory activity and antitumoral effects in vitro and in vivo.Thin films of Lf were deposited on silicon, quartz and Thermanox plastic coverslip substrates by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique, using a Nd:YAG laser working at 266nm, at different laser fluences (0.1–0.8Jcm⁻²). The deposited layers have been characterized by Fourier Transformed Infra-Red spectroscopy (FTIR), and the morphology of the various substrates was investigated by Atomic Force Microscopy (AFM). The biocompatibility of lactoferrin thin films was evaluated for each substrate, by in vitro biochemical tests.

Keywords: MAPLE; Lactoferrin; Thin films; Proteins

Thin films of polymer mimics of cross-linking mussel adhesive proteins deposited by matrix assisted pulsed laser evaporation by R. Cristescu; I.N. Mihailescu; I. Stamatin; A. Doraiswamy; R.J. Narayan; G. Westwood; J.J. Wilker; S. Stafslien; B. Chisholm; D.B. Chrisey (pp. 5496-5498).

Mussels secrete specialized adhesives known as mussel adhesive proteins, which allow attachment of the organisms to underwater marine environments. Obtaining large quantities of naturally derived mussel adhesive proteins adhesives has proven to date rather problematic, thus, synthetic analogs of mussel adhesive proteins have recently been developed. We report deposition of 1:100 and 1:1000 poly[(3,4-dihydroxystyrene)-co-styrene)] mussel adhesive protein analogs by matrix assisted pulsed laser evaporation (MAPLE) using an ArF* excimer laser source. The deposited films have been evaluated for their antifouling behavior. The MAPLE-deposited synthetic mussel adhesive protein analog thin films are homogenous and adhesive, making the use of these materials in thin film form a viable option.

Keywords: Mussel adhesive protein; Thin films; Matrix assisted pulsed laser evaporation

Laser fabricated microchannels inside photostructurable glass-ceramic by J.M. Fernández-Pradas; D. Serrano; P. Serra; J.L. Morenza (pp. 5499-5502).

Microchannels have been fabricated by laser direct-write in photostructurable glass-ceramic (Foturan) for their application in 3D-microfluidic systems. A Nd:YAG laser delivering 10ns pulses at 355nm wavelength has been used for irradiation. Afterwards, thermal treatment and chemical etching have been required for channel formation. The kinetics of channel formation and the channel morphology have been studied by optical and electron microscopy. A minimum accumulated energy (pulse energy multiplied by the number of pulses in a same site) is required to induce channel formation. Channels with symmetric round apertures at both ends can be obtained when using low pulse energies. On the contrary, irradiation with too high energetic pulses produces direct material damage in Foturan and provokes the formation of non-symmetric channels. One millimetre long channels with a minimum radius of 15μm can be opened through Foturan slides after 15min of chemical etching.

Keywords: Laser direct-write; Photostructurable glass; Microfluidics

Radial inhomogeneities induced by fiber diameter in electrically assisted LFZ growth of Bi-2212 by M.F. Carrasco; R.A. Silva; N.J.O. Silva; R.F. Silva; J.M. Vieira; F.M. Costa (pp. 5503-5506).

Superconducting polycrystalline BSCCO fibers of 2:2:1:2 nominal composition were grown by the electrically assisted laser floating zone (EALFZ) technique. An electric current density of 2.1Acm⁻² was applied through the solid/liquid (S/L) interface. A net effect of the fiber diameter on the as-grown microstructure and on the final superconducting properties is observed. A higher critical current density (∼2520Acm⁻²) results for the thinner fibers ( ϕ=1.7mm) comparing to the value (∼1065Acm⁻²) found for the wider ones ( ϕ=2.5mm). The steep axial thermal gradient at the S/L interface in the thinner fibers is responsible for its superior texture degree, a crucial parameter for improved current transport properties. Moreover, a Cu-free Bi_x(Sr,Ca)_yO_z phase crystallizes preferentially from the melt in the wider fibers, acting as obstacles to the current flux.

Keywords: Electrically assisted laser floating zone process; Fibers; Superconductors

Investigation of thermo-mechanical behaviour of diffractive optical elements for CO₂ lasers by E. Neiss; M. Flury; J. Fontaine (pp. 5507-5510).

Phase diffractive optical elements are at present proposed for use with infrared high power lasers, for material surface treatment applications. However, the heating of the component exposed to several kilowatts per square centimetre can be a problem for practical implementation. The deformations due to thermal expansion of a gold binary diffraction grating under high power CO₂ laser exposure at 10.6μm are estimated by a Finite Element Method. They are compared to the geometrical tolerances obtained by a rigorous electromagnetic Fourier modal method which is used to calculate the optical performances. Several exposure parameters (duration, average laser power) and grating parameters (period, line space ratio) are investigated. The laser exposure should be limited to a few milliseconds with a power density on the grating of 10⁴W/cm², so that the amplitude of the deformations does not exceed the 75nm tolerance on the grating depth. One is thus assured that the diffraction efficiency in the first order remains superior to 38.5%.

Keywords: PACS; 42.79.DjDiffractive optical elements; CO; ₂; laser; Thermal and electromagnetic simulations

Heterogeneous atoms in laser-induced synthesis of carbon black by E. Popovici; L. Gavrila Florescu; I. Soare; M. Scarisoreanu; I. Sandu; G. Prodan; C.T. Fleaca; I. Morjan; I. Voicu (pp. 5511-5514).

Based on a high temperature hydrocarbon/heterogeneous atoms system of well-established composition, the formation of carbon nanostructures by laser-induced pyrolysis is related to the presence of heteroatoms in the reactants. In this paper, the goal is to underline the influence of some heteroatoms on the morphology and functionalizing nanostructured carbon materials by changing both gas composition and experimental parameters, with the focus to drive these materials into a regime where they can naturally interface with the surrounding matter. To investigate, in the versatile laser pyrolysis method, how to in situ modulate – through the presence of heterogeneous atoms – the characteristics of carbon nanopowders claimed by specific application is a challenge. Some preliminary results confirm experimentally their particular behavior during interaction with polymer matrices of some nanocomposites.

Keywords: Pyrolysis; Laser; Nanocarbon; Heteroatom

Growth of titanium oxynitride layers by short pulsed Nd:YAG laser treatment of Ti plates: Influence of the cumulated laser fluence by L. Lavisse; M.C. Sahour; J.M. Jouvard; G. Pillon; M.C. Marco de Lucas; S. Bourgeois; D. Grevey (pp. 5515-5518).

Titanium oxynitride layers were formed by surface laser treatment of Ti plates in air using a Nd:YAG laser source of short pulse duration about 5ns. The cumulated laser fluence was varied in the 100–1200Jcm⁻² range and its influence on the composition and the structure of the formed layers was studied by different characterization techniques providing physico-chemical and structural information. It was shown that the laser treatment induces the insertion of light elements as O, N and C in the formed layer with the amount increasing with the laser fluence. The in-depth composition of the layers and the co-existence of different phases were also studied.The way in which the laser parameters such as fluence affect the insertion of nitrogen and oxygen was discussed in connection with the effects of the plasma plume formed above the target.

Keywords: Titanium oxycarbides; Titanium oxynitrides; Laser treatment; Plasma

Breakdown limits of optical multimode fibers for the application of nanosecond laser pulses at 532nm and 1064nm wavelength by Guido Mann; Jens Vogel; Mohammadali Zoheidi; Markus Eberstein; Jörg Krüger (pp. 5519-5522).

For many applications, optical multimode fibers are used for the transmission of powerful laser radiation. High light throughput and damage resistance are desirable. Laser-induced breakdown at the end faces of fibers can limit their performance. Therefore, the determination of laser-induced damage thresholds (LIDT) at the surface of fibers is essential.Nanosecond (1064nm and 532nm wavelength) single-shot LIDT were measured according to the relevant standard on SiO₂ glass preforms (Suprasil F300) as basic materials of the corresponding fibers. For 10 kinds of fused silica fibers (FiberTech) with core diameters between 180μm and 600μm, an illumination approach utilizing a stepwise increase of the laser fluence on a single spot was used. For both wavelengths, the LIDT values (0% damage probability) obtained by means of the two methods were compared. The influence of surface preparation (polishing) on damage resistance was investigated. For equal surface finishing, a correlation between drawing speed of the fibers and their surface LIDT values was found. In addition to the surface measurements, bulk LIDT were determined for the preform material.

Keywords: Fiber waveguides (42.81.Qb); Physical radiation damage (61.80.−x); Laser-beam impact phenomena (79.20.Ds); Glasses (81.05.Kf); Radiation treatment (81.40.Wx)

Manufacturing of fine-structured 3D porous filter elements by selective laser melting by I. Yadroitsev; I. Shishkovsky; P. Bertrand; I. Smurov (pp. 5523-5527).

Selective laser melting (SLM) allows manufacturing porous 3D parts with customized near-net shape and internal geometry designed at the stage of their computer modeling. The relations between laser operational parameters, computer design of the manufacturing object, composition and microstructure of the obtained fine porous structures are discussed. A series of experiments are carried out on PHENIX PM-100 machine to analyze the influence of the manufacturing strategy on anisotropy and regularity of the internal structure of samples from stainless steel, nickel alloys and metal–polymer powders. The issues of accurate reproduction of the parts geometry, strategy of manufacturing thin-walled 3D filters and filters with customized pattern of the micron-sized channels are addressed. Effect of the porous structure on the material filtering performance is analyzed in order to optimize and diversify design of the porous materials for a given application and to improve their operational behavior.

Keywords: PACS; 42.62.−b; 64.70.dj; 81.05.Rm; 81.20.EvRapid manufacturing; Selective laser melting; Porous materials; Powders

Crystallization of hydrogenated amorphous silicon carbon films with laser and thermal annealing by D.K. Basa; G. Ambrosone; U. Coscia; A. Setaro (pp. 5528-5531).

The crystallization of silicon rich hydrogenated amorphous silicon carbon films prepared by Plasma Enhanced Chemical Vapor Deposition technique has been induced by excimer laser annealing as well as thermal annealing. The excimer laser energy density ( E_d) and the annealing temperature were varied from 123 to 242mJ/cm² and from 250 to 1200°C respectively. The effects of the two crystallization processes on the structural properties and bonding configurations of the films have been studied. The main results are that for the laser annealed samples, cubic SiC crystallites are formed for E_d≥188mJ/cm², while for the thermal annealed samples, micro-crystallites SiC and polycrystalline hexagonal SiC are observed for the annealing temperature of 800 and 1200°C respectively. The crystallinity degree has been found to improve with the increase in the laser energy density as well as with the increase in the annealing temperature.

Keywords: Silicon carbon alloys; Laser annealing; Thermal annealing; Crystallization

Optimization of a laser mitigation process in damaged fused silica by S. Palmier; L. Gallais; M. Commandré; P. Cormont; R. Courchinoux; L. Lamaignère; J.L. Rullier; P. Legros (pp. 5532-5536).

One of the major concerns encountered in high power laser is the laser-induced damage of optical components. This is a main issue of the development of the Europe's biggest laser, known as Laser Méga Joule (LMJ) especially in the section where the beam wavelength is 351nm. This study deals with the development of a laser treatment process to improve the laser damage resistance of silica optical components. First, by irradiating the component at 355nm in the nanosecond regime, defects of the silica optic are revealed and evolve as damage. Next, the damaged sites are irradiated with a CO₂ laser at a 10.6μm wavelength in order to melt and evaporate the silica in the damage neighborhood. In this study, we performed a variation of the CO₂ laser parameters to obtain the most efficient stabilization. To check this stabilization, damage resistance tests were performed with an UV laser representative of the LMJ (at 355nm/2.5ns). The results show that we can stabilize weak points and thereby make the component resistant to subsequent UV laser irradiation.

Keywords: PACS; 42.79.−e; 42.70.Ce; 81.65.−bLaser mitigation process; Silica; Laser-induced damage

High-power laser interference lithography process on photoresist: Effect of laser fluence and polarisation by M. Ellman; A. Rodríguez; N. Pérez; M. Echeverria; Y.K. Verevkin; C.S. Peng; T. Berthou; Z. Wang; S.M. Olaizola; I. Ayerdi (pp. 5537-5541).

High throughput and low cost fabrication techniques in the sub-micrometer scale are attractive for the industry. Laser interference lithography (LIL) is a promising technique that can produce one, two and three-dimensional periodical patterns over large areas. In this work, two- and four-beam laser interference lithography systems are implemented to produce respectively one- and two-dimensional periodical patterns. A high-power single pulse of ∼8ns is used as exposure process. The optimum exposure dose for a good feature patterning in a 600nm layer of AZ-1505 photoresist deposited on silicon wafers is studied. The best aspect ratio is found for a laser fluence of 20mJ/cm². A method to control the width of the sub-micrometer structures based on controlling the resist thickness and the laser fluence is proposed.

Keywords: Laser interference lithography; LIL; Photoresist; Surface nanostructuring; Pulsed lithography

Complementary use of the Raman and XRF techniques for non-destructive analysis of historical paint layers by M. Sawczak; A. Kamińska; G. Rabczuk; M. Ferretti; R. Jendrzejewski; G. Śliwiński (pp. 5542-5545).

The portable XRF spectrometer has been applied in situ for the non-destructive elemental mapping of the pigment components of the XV c. mural painting and frescos of the Little Christopher chamber in the Main Town Hall of Gdańsk, Poland. For a sufficiently large data collection the principal component analysis (PCA) was applied in order to associate the most intense lines of the elements Ca, Cu, Fe, Pb, and Hg in the XRF spectra with the palette of colors: white, brown, green, blue, red, yellow, and black observed in the painting. This allowed to limit the number of extractions of the micro-samples for the complementary Raman measurements thus assuring the practically non-destructive character of the entire analysis. The reliable identification of the pigment compositions was based on coincidence of the XRF, PCA and the Raman results which confirmed the presence of the chalk, malachite, azurite, red lead, mars red, mars yellow and candle black in the historical paints, except of the carbon-based black pigment being out of the XRF detection range. Different hues of the green paint were specified and the variety of the red and brown ones was ascribed to compositions of the Pb- and Fe-based red pigments (Fe₂O₃ and Pb₃O₄) with addition of the vermilion (HgS) and carbon black, in agreement with literature. The traces of elements: Ba and Sr, Sb and Mo, and also Cd, were ascribed to the impurities of Ca, those of some ochre pigments, and to the soluble Cd salts, respectively.

Keywords: PACS; 61.43.Gt; 61.66.Fn; 81.70.Fy; 82.80.EjX-ray spectrometry; Principal component analysis; Raman spectroscopy; Historical pigments

Micro-Raman investigation of stress distribution in laser drilled via structures by J. Wasyluk; D. Adley; T.S. Perova; A.M. Rodin; J. Callaghan; N. Brennan (pp. 5546-5548).

Through-wafer vertical electrical interconnects (vias) with diameters varied from 15 to 80μm were formed on Si substrates using a UV diode-pumped solid state laser (355nm). Micro-Raman spectroscopy was employed for the investigation of stress and structural changes induced in silicon within the heat-affected zone due to laser machining. A maximum stress of ∼300MPa, as a result of laser drilling, was observed close to the via edge. It was found that the stress decays within a distance of 1–3μm from the via’s side-wall and that the laser machining did not lead to the formation of amorphous silicon around the via structures.

Keywords: Laser micromachining; Vertical electrical interconnects; Micro-Raman spectroscopy; Stress in silicon; Heat-affected zone

Direct observation of phase transitions by time-resolved pyro/reflectometry of KrF laser-irradiated metal oxides and metals by N. Semmar; M. Tebib; J. Tesar; N.N. Puscas; E. Amin-Chalhoub (pp. 5549-5552).

New experimental results are obtained by coupling both time-resolved reflectivity and rapid infrared pyrometry under a hemispherical reactor. The heating source KrF laser beam (28ns, 248nm) is homogenized and as for probing, a CW He–Ne laser beam (10mW, 633nm) is used.Using both methods infrared pyrometry with an IR detector cooled with liquid nitrogen and sensitive in the spectral range 1–12μm, and time-resolved reflectivity with a rapid photodiode, we were able to study complex thermodynamic transitions with nanosecond time resolution. Three different materials are studied by varying the KrF fluence (energy/surface) from 100 to 2000mJ/cm²: thin films melting (Au/Ni), the threshold of plasma formation (Ti), and complex liquid phase segregation under semi-conductor state (ZnO). The formation of a liquid Zn film induced by temperature gradient is well evidenced by our signals. Also melting of thin films irradiated by low laser fluences (less than 500mJ/cm²) translates the typical thermodynamic behavior. Finally, wide fluence dynamic (400–2000mJ/cm²) is analyzed in the case of Ti surface, and results show two distinguished regimes: first one bellow 1000mJ/cm² corresponding to the early stage plasma initiation, and second one over 1000mJ/cm² to the dynamics of plasma expansion.

Keywords: Time-resolved pyro/reflectometry; Rapid thermodynamic transitions; KrF laser processing; Au/Ni thin film; Monocrystalline ZnO; Ti laser induced plasma

Laser cladding of tungsten carbides (Spherotene^®) hardfacing alloys for the mining and mineral industry by J.M. Amado; M.J. Tobar; J.C. Alvarez; J. Lamas; A. Yáñez (pp. 5553-5556).

The abrasive nature of the mechanical processes involved in mining and mineral industry often causes significant wear to the associated equipment and derives non-negligible economic costs. One of the possible strategies to improve the wear resistance of the various components is the deposition of hardfacing layers on the bulk parts. The use of high power lasers for hardfacing (laser cladding) has attracted a great attention in the last decade as an alternative to other more standard methods (arc welding, oxy-fuel gas welding, thermal spraying).In laser cladding the hardfacing material is used in powder form. For high hardness applications Ni-, Co- or Fe-based alloys containing hard phase carbides at different ratios are commonly used. Tungsten carbides (WC) can provide coating hardness well above 1000HV (Vickers). In this respect, commercially available WC powders normally contain spherical micro-particles consisting of crushed WC agglomerates. Some years ago, Spherotene^® powders consisting of spherical-fused monocrystaline WC particles, being extremely hard, between 1800 and 3000HV, were patented. Very recently, mixtures of Ni-based alloy with Spherotene powders optimized for laser processing were presented (Technolase^®). These mixtures have been used in our study. Laser cladding tests with these powders were performed on low carbon steel (C25) substrates, and results in terms of microstructure and hardness will be discussed.

Keywords: Laser cladding; Tungsten carbides

Micromachining of glass by the third harmonic of nanosecond Nd:YVO₄ laser by A. Ramil; J. Lamas; J.C. Álvarez; A.J. López; E. Saavedra; A. Yáñez (pp. 5557-5560).

The ablation processing of glass was performed by using the third harmonic of nanosecond Nd:YVO₄ laser. The objective of this work was the formation of deep holes with a high aspect ratio in soda lime glass; with this purpose different ways to raster the glass surface with the focused laser beam, i.e., single line, parallel lines and orthogonally crossing lines, have been tried and the effect of different parameters as the number of lines and number of scans in the depth and inclination of the sidewalls of the hole has been analyzed. Moreover, to reduce the time consumption in the laser processing of glass plates the relationship between penetration depths and overlapping factor has been studied and an optimum value of scan speed has been obtained for a particular case.

Keywords: PACS; 42.62.Cf; 52.38.Mf; 81.05.Kf; 81.65.Cf; 87.85.VaIndustrial applications; Laser ablation; Glasses (including metallic glasses); Patterning; Micromachining

Photo-thermal effects induced by KrF laser in complex oxides investigated by time resolved pyrometry: Cases of Er-doped ZnO and Y₂O₃ by E. Amin-Chalhoub; N. Semmar; J. Mathias (pp. 5561-5564).

To study the thermal/photon conversion of erbium-doped ZnO (ZnO:Er) substrates induced by UV pulsed laser, the rapid infrared pyrometry method is successfully used for monitoring the IR band (1–12μm) emission in a hemispherical chamber under vacuum. Samples are irradiated with a homogeneous laser beam KrF (248nm, 25ns) which induces surface temperature rise. The laser induced thermal radiations are detected by a liquid nitrogen cooled detector (2–3ns time rise).Semi-conductors doped erbium exhibit a complex behaviour under the KrF laser beam in the fluence range 200–400mJ/cm². Actually, the relaxation time of the induced IR signal is too wide (μs) compared to undoped samples (ns). For a better understanding, samples ZnO:Er and erbium-doped Yttrium oxide (Y₂O₃:Er) are studied. The fact that erbium (Er) spectra shows a photoluminescence in the band 1400–1600nm with a maximum at 1535nm, the pyrometry signals include the energetic contribution of the PL phenomenon and the pure thermal one. To confirm this statement, a germanium filter is used to cut off the IR radiations less than 2000nm. Finally, coherent results allowing thermal to photoemission conversion are discussed in the last part of this paper.

Keywords: Pulsed lasers; UV laser beam; Photoluminescence; ZnO:Er; Y; ₂; O; ₃; :Er; Complex oxides; Time resolved pyrometry

Nanostructural self-organization under selective laser sintering of exothermic powder mixtures by I. Shishkovsky; Yu. Morozov; I. Smurov (pp. 5565-5568).

Topology of the surface substructure induced by the synthesis of intermetallic compounds under selective laser sintering is studied by scanning electron microscopy. The data is then analysed by image processing software for identification and discussion of common features and peculiarities of the structure-formation process. A dependence between the fractal dimension D of low-dimensional nanostructures and laser energy input A is found. It is shown that particularities of the structural-phase transformations under intermetallic synthesis in the Ni–Al, Ti–Al, Fe–Ti and Ni–Ti systems determine the appearance of ordered nanosubstructures as honeycomb-like, dendritic or mosaic. The change of the fractal dimension of low-dimensional structures clearly correlates with the change of roughness, while the increase of the laser energy input influences the fractal dimension D in different ways. Sharp variations of the D orientation indicate a change of the phase-formation mechanism.

Keywords: Selective laser sintering (SLS); Self-propagating high-temperature synthesis (SHS); Laser-controlled intermetallic synthesis; Fractal dimension

Experimental investigation on laser removal of carbon and tungsten particles by A. Vatry; M. Naiim Habib; Ph. Delaporte; M. Sentis; D. Grojo; C. Grisolia; S. Rosanvallon (pp. 5569-5573).

During the operation of the ITER fusion facility, particles with size from 10nm to 100μm, mainly composed of carbon, beryllium, and tungsten, will be produced. Since dust could lead to safety issues, it must be periodically removed from the facility in order to keep their quantity below the safety limit requirements. In this context, laser cleaning appeared as a very promising technique, and investigations have to be done to understand the physical processes and optimize the procedure.Several experiments were carried out to improve the understanding of the phenomena involved during the laser-induced removal of Carbon particles. The ejection mechanisms have been experimentally studied for different irradiation conditions with nanosecond laser pulses. The removal efficiency and the fluence threshold were determined by optical microscopy. The influence of the substrate was studied for the dry laser cleaning configuration.This study presents scanning electronic microscopy pictures which show that the particle removal leads to a damage of the substrate. These damages give evidences on the ablation mechanism.The laser shock cleaning was also studied. In this configuration, the laser-induced shock wave can be used to push the particles away from the surface. This technique appears to be very useful to clean shadowed areas.

Keywords: Laser cleaning; Particle removal; Fusion reactor; Carbon; Tungsten

Study of surface layers and ejected powder formed by oxidation of titanium substrates with a pulsed Nd:YAG laser beam by I. Shupyk; L. Lavisse; J.-M. Jouvard; M.C. Marco de Lucas; S. Bourgeois; F. Herbst; J.-Y. Piquemal; F. Bozon-Verduraz; M. Pilloz (pp. 5574-5578).

Laser treatment of a titanium surface at certain conditions initiates the formation of titanium oxide layers as well as micro (nano) scale powder ejected from the surface of the substrate. The resultant morphology of the surface as well as the size and the structure of the particles are all strongly dependent on the treatment parameters (laser fluence, pulse frequency, overlap parameter, etc.). In this study, titanium substrates were treated with an industrial pulsed Nd:YAG laser in air, with varying parameters. Surface layers and ejected materials were compared using scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The rutile phase of TiO₂ dominates in the surface layers, while the ejected powder is mainly formed of anatase nanoparticles.

Keywords: Laser treatments; Plasma; Titanium dioxide; Nanoparticles

Laser cleaning of varnishes and contaminants on brass by M.P. Mateo; T. Ctvrtnickova; E. Fernandez; J.A. Ramos; A. Yáñez; G. Nicolas (pp. 5579-5583).

The capability of laser ablation to perform controlled cleaning of varnishes containing contaminants and paints used by restorers in artistic objects from brass samples while keeping unaltered the finish structure is demonstrated in this work. Adequate laser energy per pulse and number of laser shots required to perform a suitable cleaning by laser ablation have been optimized. The inspection of the samples before and after the cleaning process by optical microscopy and by Fourier transform infrared spectroscopy (FTIR) technique demonstrated that the finish structure of the surface was intact while the coatings were completely eliminated. Furthermore, a laser-induced plasma spectroscopy (LIBS)-based detection system was applied during the irradiation process for the analysis of the material removal and also for its monitoring.

Keywords: Laser ablation; Brass; Laser cleaning; Metal artefacts; Laser-induced breakdown spectroscopy (LIBS)

Metal matrix composite production by means of laser dispersing of SiC and WC powder in Al alloy by R. Jendrzejewski; K. Van Acker; D. Vanhoyweghen; G. Śliwiński (pp. 5584-5587).

The properties and processing parameters of the metal matrix composite (MMC) surface layers, obtained under conditions of the superposition of intense laser radiation with the kinetic effect due to gas-dynamically controlled particle injection, are investigated for the case of laser dispersing of the SiC and WC powders in the soft Al 6061 alloy. With substrate preheating above 600K the nearly homogeneous distribution of SiC particles up to depths of about 1mm, characterized by their content of about 35% by volume, is revealed by the scanning electron microscopes (SEM) inspection. In the microstructure the presence of the Al₄C₃ plates separated by the eutectic regions of Si–Al is observed and confirmed by the X-ray diffraction (XRD) and energy-dispersive spectrometer (XEDS) measurements. The surface layers (25cm²) consisting of parallel processing traces show the wear rate of about 3×10⁻⁴mm³/Nm which is markedly lower than that of the reference substrate. For WC under similar processing conditions the particle enriched layer of thickness of about 100μm is covered by the alloy material. The experimental data confirm that laser dispersing combines the advantages of the soft matrix with these of the wear and corrosion resistant material, and results in the improvement of the properties of composite material.

Keywords: Laser dispersing; Light alloys; Wear resistance

Hybrid laser-MIG welding of aluminum alloys: The influence of shielding gases by G. Campana; A. Ascari; A. Fortunato; G. Tani (pp. 5588-5590).

In this paper, laser-GMAW hybrid welding technologies of light metals are investigated by focusing particularly on shielding gas related problems such as distribution on the welding zone, mixtures and flow. In particular, a Computational Fluid Dynamics (CFD) software was used with the aim to investigate the effect on gas distribution and contamination of the adoption of an isolation chamber surrounding the welding zone. In particular, the turbulent flow model adopted was a standard k– ɛ one. A simple parallelepipedal geometry for the isolation chamber was adopted whose width and depth were fixed, while the height was set as a variable. A simulation activity was carried out in order to evaluate the relationship among chamber height, flow rates and inlet angle inclinations. The simulated welding environment was simplified without considering the presence and the effect of the laser induced plasma plume and of the electric arc.The main results concern the influence of isolation chamber height, gas flow rate and gas inlet inclination on the shielding gas contamination and distribution in a zone near the heat sources–material interaction zone. These results underline that there are particular values of the chosen variables which optimize the gas distribution around the welding zone allowing to achieve an even and reliable shielding effect.

Keywords: Hybrid welding; Shielding gas; Contamination; CFD

Laser structuring of metal surfaces: Micro-mechanical interlocking by J. Byskov-Nielsen; P. Balling (pp. 5591-5594).

Efficient micro-mechanical interlocking may be achieved on appropriately laser-structured surfaces. In this paper, we discuss the issues relevant for the laser-machining process, including the precision and the material removal rate. We investigate the surface morphology of stainless steel after irradiation by nanosecond laser pulses at different pulse energies and irradiation strategies. At the optimum operation parameters, we demonstrate that a high-average-power nanosecond laser provides a reasonable compromise between precision and production time.

Keywords: PACS; 61.80.Ba; 81.05.Bx; 81.40.Wx; 81.65.CfLaser ablation; Surface structuring; Micro-mechanical interlocking

Two-dimensional numerical modelling of radiation transfer in powder beds at selective laser melting by A.V. Gusarov; I. Smurov (pp. 5595-5599).

The radiation transfer equation is numerically solved in a layer of homogeneous absorbing scattering medium, which is equivalent to the powder bed, irradiated with a normally incident laser beam of an axially symmetric profile to estimate the spatial distribution of the deposited thermal energy. The scattering and lateral transport of laser radiation is shown to decrease the intensity of the heat source at the axis and to produce its weak tail around the laser spot. This decreases the maximum temperature in the powder bed. Narrowing the laser beam to increase the precision of selective laser melting becomes ineffective when the beam radius approaches the extinction length in the powder because it does not adequately narrow the zone of energy deposition.

Keywords: Selective laser melting; Powder bed; Radiation transfer equation; Radiative properties

Functionalized polyvinyl alcohol derivatives thin films for controlled drug release and targeting systems: MAPLE deposition and morphological, chemical and in vitro characterization by R. Cristescu; C. Popescu; A.C. Popescu; S. Grigorescu; L. Duta; I.N. Mihailescu; G. Caraene; R. Albulescu; L. Albulescu; A. Andronie; I. Stamatin; A. Ionescu; D. Mihaiescu; T. Buruiana; D.B. Chrisey (pp. 5600-5604).

We report thin film deposition of polyvinyl alcohol functionalized with carboxylic groups bound to aromatic nucleus (PVACOOH) by matrix-assisted pulsed laser evaporation (MAPLE). We used a KrF* excimer laser source ( λ=248nm, τ=25ns,ν= 5Hz). The obtained thin films have been investigated by FTIR, AFM, and in vitro tests. We identified the best compromise between the parameters of laser processing and characteristics of nanostructured thin films of PVACOOH in terms of porosity and similar composition with those of starting material.

Keywords: Controlled drug release; Porous polymers; Matrix-assisted pulsed laser evaporation; In vitro

Laser processing of polyethylene glycol derivative and block copolymer thin films by R. Cristescu; C. Popescu; A.C. Popescu; S. Grigorescu; L. Duta; I.N. Mihailescu; A. Andronie; I. Stamatin; O.S. Ionescu; D. Mihaiescu; T. Buruiana; D.B. Chrisey (pp. 5605-5610).

We report the deposition by MAPLE of: (i) a novel polyethylene glycol derivative with carboxyl functional groups and (ii) a block copolymer: poly(ethylene glycol)methyl ether- block-poly(caprolactone)- block-poly(ethylene glycol)methyl ether. We used a KrF* excimer laser source ( λ=248nm, τ=25ns, ν=5Hz). The laser fluence was set within the 200–700mJ/cm² range. The deposited thin films have been investigated by FTIR and AFM. We have concluded that the main functional groups of starting materials are present in the transferred film. We also examined the influence of laser fluence on both thin film structure and morphology.

Keywords: Controlled drug release; Porous polymers; Thin films; Matrix assisted pulsed laser evaporation

MAPLE prepared polymeric thin films for non-linear optic applications by Gabriel Socol; Ion N. Mihailescu; Ana-Maria Albu; Stefan Antohe; Florin Stanculescu; Anca Stanculescu; Lucian Mihut; Nicoleta Preda; Marcela Socol; Oana Rasoga (pp. 5611-5614).

This paper presents a study of some functionalised copolymers thin films prepared on silicon and quartz substrates by matrix assisted pulsed laser evaporation (MAPLE) method. Two polymeric structures have been synthesised by the copolymerisation of maleic anhydride and methyl methacrylate, respectively, maleic anhydride and vinyl benzyl chloride and their subsequent functionalisation with 2,4-dinitroaniline. UV–Vis, FTIR, Raman and photoluminescence spectroscopy have been used to investigate the influence on the properties of the films of different substrate temperature (150°C and 250°C), background N₂ pressure (5–30Pa) and polymer concentration in target (2% and 3%). We have evidenced that this deposition process does not damage the chemical structure of the polymers. SEM investigations revealed the droplets type morphology of the polymeric films with thickness between 41nm and 105nm calculated from ellipsometric measurements.

Keywords: PACS; 81.15.Fg; 78.66.Qn; 42.70.JkMAPLE; Polymer; Thin films; Optical properties

Optical properties of titanium oxycarbide thin films by L. Marques; H.M. Pinto; A.C. Fernandes; O. Banakh; F. Vaz; M.M.D. Ramos (pp. 5615-5619).

The optical properties of TiC_xO_y thin films, deposited by reactive dc magnetron sputtering at different oxygen flow, were investigated by spectroscopic ellipsometry in the energy range of 0.75–4.5eV. The dielectric functions measured in the energy range of intraband transitions were analyzed using the classical Drude theory. These results show that free plasma energy and the damping constant of the films depend strongly on film stoichiometry and on their oxygen content. The interband contribution to the optical conductivity of these films is in good agreement with the optical conductivity obtained from first principles calculations based on density functional theory. Both the experimental and the calculated results show that it is possible to significantly modify the optical properties of titanium oxycarbide by adjusting the oxygen content.

Keywords: Titanium oxycarbide; Optical properties; Ellipsometry; Magnetron sputtering; Density functional theory

Laser annealing of amorphous carbon films by E. Cappelli; C. Scilletta; S. Orlando; V. Valentini; M. Servidori (pp. 5620-5625).

Amorphous ( a-C) Carbon thin films were deposited, using pulsed laser deposition (PLD) with a Nd:YAG laser (1064nm, 7ns), from a pyrolytic graphite target, on 〈100〉 silicon and refractory metal (Mo) substrates to a film thickness of 55, 400 and 500nm. Samples were grown at RT and then annealed by a laser annealing technique, to reduce residual stress and induce a locally confined “graphitization” process.The films were exposed to irradiation, in vacuum, by a Nd:YAG pulsed laser, operating at different wavelengths (VIS, N-UV) and increasing values of energy from 6–100mJ/pulse. The thinner films were completely destroyed by N-UV laser treatment also at lower energies, owing to the almost direct propagation of heat to the Si substrate with melting and ruinous blistering effects.For thicker films the Raman micro-analysis evidenced the influence of laser treatments on the sp³/sp² content evolution, and established the formation of aromatic nano-structures of average dimension 4.1÷4.7nm (derived from the I_D/ I_G peak ratio), at fluence values round 50mJ/cm² for N-UV and 165mJ/cm² for VIS laser irradiation. Higher fluences were not suitable for a-Carbon “graphitization”, since a strong ablation process was the prominent effect of irradiation.Grazing incidence XRD (GI-XRD) used to evaluate the dimension and texturing of nano-particles confirmed the findings of Raman analysis. The effects of irradiation on surface morphology were studied by SEM analysis.

Keywords: Pulsed laser irradiation; Graphitizing process; a; -Carbon films; Carbon nano-structures; Raman analysis; GI-XRD analysis

Comparative study of grain sizes and orientation in microstructured Au, Pt and W thin films designed by laser interference metallurgy by Carsten Gachot; Rodolphe Catrin; Andrés Lasagni; Ulrich Schmid; Frank Mücklich (pp. 5626-5632).

The physical and chemical properties of materials are strongly correlated with their microstructure. Although size effects may lead to a more complex interpretation of the gained results, much effort is invested in the microstructural design of metallic thin films and the detailed understanding of dependencies, such as the impact of thermal annealing on the corresponding grain and micro-texture characteristics.The main focus of this work is the microstructural design of periodic arrays in Au, Pt and W thin films using laser interference patterns. Due to the high and localized periodic intensity profile of the nanosecond laser pulse, a precise redesign of the film microstructure in terms of recrystallization, phase arrangement, texture, residual stresses or topography is possible. We demonstrate the possibility of controlling the recrystallization process by adjusting the laser energy density. Furthermore, dynamic aspects of the induced recrystallization process such as temperature distribution were studied based on thermal simulations. The grain size distribution and the micro-texture were determined by electron backscatter diffraction. The size and scale of the tailored structures produced by this technique could be beneficial with regard to thermo-electrical as well as tribo-mechanical applications.

Keywords: Materials science; Metallic thin films; Tailored microstructures; Laser processing

Laser shock microforming of thin metal sheets by J.L. Ocaña; M. Morales; J.J. García-Ballesteros; J.A. Porro; O. García; C. Molpeceres (pp. 5633-5636).

Continuous and long-pulse lasers have been used for the forming of metal sheets in macroscopic mechanical applications. However, for the manufacturing of micro-electromechanical 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 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, particularly important according to its frequent use in such systems.In the present paper, a discussion is presented on the physics of laser shock microforming and the influence of the different effects on the net bending angle. The experimental setup used for the experiments, sample fabrication and experimental results of influence of number of laser pulses on the net bending angle are also presented.

Keywords: Laser microforming; Forming mechanisms; Numerical modeling; Experimental validation

Numerical study of melted particles crush metallic substrates and the interaction between particles and a plasma beam in the thermal projection process by Ilhem Kriba; A. Djebaili (pp. 5637-5640).

Plasma spray processes have been widely used to produce high performance coatings of a wide range of materials (metallic, non-metallic, and ceramics), offering protection from, e.g. wear, extreme temperature, chemical attack and environmental corrosion. To obtain good quality coatings, spray parameters must be carefully selected. Due to the large variety in process parameters, it is difficult to optimize the process for each specific coating and substrate combinations. Furthermore modelling the spray process allows a better understanding of the process sequences during thermal spraying. The simulation of coating formation to estimate the process parameters is an important tool to develop new coating structures with defined properties.In this work, the process of plasma sprayed coating has been analyzed by numerical simulation. Commercial code is used to predict the plasma jet characteristics, plasma–particle interaction, and coating formation. Using this model we can obtain coating microstructure and characteristics which form a foundation for further improvement of an advanced ceramic coating build up model.

Keywords: Thermal projection process; Plasma spray; Spray parameters; Specific coating; Numerical simulation

Fabrication of sub-wavelength surface ripples and in-volume nanostructures by fs-laser induced selective etching by Jens Gottmann; Dirk Wortmann; Maren Hörstmann-Jungemann (pp. 5641-5646).

Continuous sub-wavelength ripples on the surface of sapphire and fused silica have been produced not only in one dimension but also in two dimensions by scanning several tracks with an offset. This results in the formation of an extended grating. By investigation of cross-sections of sub-wavelength ripples a surprising high aspect ratio of larger than 10 is observed in the case of fused silica and a aspect ratio of about 2.5 in the case of sapphire.Using in-volume selective laser etching hollow nanoplanes (∼200nm in width, 1mm in length) and nano-channels (∼100nm in diameter) are obtained in sapphire.By scanning in the volume of sapphire and fused silica, structures very similar to the surface sub-wavelength ripples are observed in the volume. A common feed-back mechanism for both the formation of coherent sub-wavelength surface ripples and nanoplanes in the volume is discussed.

Keywords: Sub-wavelength ripples; Femtosecond laser radiation; In-volume laser-induced selective etching; Hollow nanoplanes

Laser activation of Ultra Shallow Junctions (USJ) doped by Plasma Immersion Ion Implantation (PIII) by Vanessa Vervisch; Yannick Larmande; Philippe Delaporte; Thierry Sarnet; Marc Sentis; Hasnaa Etienne; Frank Torregrosa; Fuccio Cristiano; Pier Francesco Fazzini (pp. 5647-5650).

Today, the main challenges for the realization of the source/drain extensions concern the ultra-low energy implantation and the activation of the maximum amount of dopants with a minimized diffusion. Among the different annealing processes, one solution is the laser thermal annealing. Many studies [F. Torregrosa, C. Laviron, F. Milesi, M. Hernandez, H. Faik, J. Venturini, Proc. 14th International Conference on Ion Implant Technology, 2004; M. Hernandez, J. Venturini, D. Zahorski, J. Boulmer, D. Débarre, G. Kerrien, T. Sarnet, C. Laviron, M.N Semeria, D. Camel, J.L Santailler, Appl. Surf. Sci. 208–209 (2003) 345–351] have shown that the association of Plasma Immersion Ion Implantation (PIII) and Laser Thermal Process (LTP) allows to obtain junctions of a few nanometers with a high electrical activation.All the wafers studied have been implanted by PULSION^® (PIII implanter developed by Ion Beam Services) with an acceleration voltage of 1kV and a dose of 6×10¹⁵at./cm². In this paper, we compare the annealing process achieved with three excimer lasers: ArF, KrF and XeCl with a wavelength of respectively 193, 248 and 308nm. We analyse the results in terms of boron activation and junction depth.To complete this study, we have observed the effect of pre-amorphization implantation (PAI) before PIII process on boron implantation and boron activation. We show that Ge PAI implanted by classical beam line allows a decrease of the junction depth from 20 down to 12nm in the as-implanted condition. Transmission Electron Microscopy (TEM) analyses were performed in order to study the structure of pre-amorphized silicon and to estimate the thickness of the amorphous layer. In order to determine the sheet resistance ( R_s) and the junction depth ( X_j), we have used the four-point probe technique (4PP) and secondary ion mass spectrometry (SIMS) analysis. To complete the electrical characterizations some samples have been analyzed by non-contact optical measurements. All the results are presented as a function of the laser fluence and the laser wavelength.

Keywords: Laser annealing; Plasma immersion ion implantation; Ultra shallow junctions

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Applied Surface Science (v.255, #10)

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Applied Surface Science (v.255, #10)