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Applied Surface Science (v.253, #19)

Photon-assisted synthesis and processing of functional materials by Maria Dinescu; Hiroshi Fukumura; Henry Helvajian; Eric Millon; Tamas Szörenyi (pp. 7645-7645).

Polymers as fuel for laser-based microthrusters: An investigation of thrust, material, plasma and shockwave properties by L. Urech; T. Lippert; C.R. Phipps; A. Wokaun (pp. 7646-7650).

The micro-laser plasma thruster (μ-LPT) is a micropropulsion device, designed for steering and propelling of small satellites (1–10kg). A laser is focused onto a polymer layer on a substrate to form a plasma, which produces the thrust that is used to control the satellite motion. Three different polymers were tested to understand the influence of their specific properties on the thrust performance: poly(vinyl chloride) (PVC) as a low-energetic material, a glycidyl azide polymer (GAP), and poly(vinyl nitrate) (PVN) as high-energetic polymers. Different absorbers (carbon nanoparticles or an IR dye) were added to the polymer to achieve absorption at the irradiation wavelength (1064nm). The influence of the material and dopant properties on the decomposition characteristics and the energy release were investigated by thrust measurements and ns-shadowgraphy. Mass spectrometry and time- and space-resolved plasma emission spectroscopy in air and vacuum were used to analyze the degree of fragmentation as function of the material properties. The kinetic energies of selected fragments were calculated from the spectra. GAP+C showed the best performance in all measurements at high fluences, while at low fluences PVN+C revealed the best performance.

Keywords: Polymer; Micro-laser plasma thruster; Laser ablation

Plasma characterization and room temperature growth of carbon nanotubes and nano-onions by excimer laser ablation by G. Radhakrishnan; P.M. Adams; L.S. Bernstein (pp. 7651-7655).

The deposition of carbon nanotubes and carbon nano-onions at room temperature using excimer laser radiation to ablate mixed graphite–metal targets is described. Our deposition conditions are in contrast to other investigations on the pulsed laser deposition of carbon nanotubes that have employed high temperatures and high pressures. We find that the formation of these carbon nanostructures is dependent on the ambient gas employed during ablation. In the presence of O₂ gas, carbon nanotubes and nano-onions are produced, while inert atmospheres such as Ar yield amorphous carbon. High-resolution, in situ, time-resolved emission spectroscopy has been used to track the evolution of species (C₂, C₃, Ni/Co) in the ablation plume. Spectral fits on low and high-resolution spectra reveal that the vibrational-rotational temperatures for C₂ produced in O₂ remain at ∼5000K for nearly 20μs but drop rapidly in Ar. Details of the formation of carbon nanotubes and nano-onions, and in situ time-resolved optical emission spectroscopy are described.

Keywords: Carbon nanotubes; Carbon nano-onions; Room-temperature deposition; Excimer laser ablation; Emission spectroscopy; Plume diagnostics

Mechanisms of small clusters production by short and ultra-short laser ablation by Tatiana E. Itina; Karine Gouriet; Leonid V. Zhigilei; Sylvie Noël; Jörg Hermann; Marc Sentis (pp. 7656-7661).

The mechanisms involved into the formation of clusters by pulsed laser ablation are studied both numerically and experimentally. To facilitate the model validation by comparison with experimental results, the time and length scales of the simulation are considerably increased. This increase is achieved by using a combination of molecular dynamics (MD) and the direct simulation Monte Carlo (DSMC) methods. The combined MD–DSMC model is then used to compare the relative contribution of the two channels of the cluster production by laser ablation: (i) direct cluster ejection upon the laser-material interaction, and (ii) collisional sticking and aggregation in the ablated gas flow. Calculation results demonstrate that both of these mechanisms play a role. The initial cluster ejection provides cluster precursors thus eliminating the three-body collision bottleneck in the cluster growth process. The presence of clusters thus facilitates the following collisional condensation and evaporation processes. The rates of these processes become considerable, leading to the modification of not only the plume cluster composition, but also the dynamics of the plume expansion. Calculation results explain several recent experimental findings.

Keywords: PACS; 52.38Mf; 02.60.CbNanoparticles; Laser ablation; Simulation; Clusters

Atomic force microscopical and surface plasmon resonance spectroscopical investigation of sub-micrometer metal gratings generated by UV laser-based two-beam interference in Au–Ag bimetallic layers by M. Csete; A. Kőházi-Kis; Cs. Vass; Á. Sipos; G. Szekeres; M. Deli; K. Osvay; Zs. Bor (pp. 7662-7671).

Metal films containing silver and gold layers having different thicknesses were evaporated on glass substrates. Two-beam interference technique was applied to irradiate the surfaces by the fourth harmonic of a pulsed mode Nd:YAG laser. The atomic force microscopical study showed that surface relief grating having a period of 900nm corresponding to the interference pattern was developed on the metallic films. The modulation amplitude of the laser-induced gratings was increasable by enhancing the number of laser pulses at constant fluence, and a groove depth commensurable with the film thicknesses was generated at the average fluence of 39.5mJ/cm² on bimetallic layers. The surface structure was more regular, and the modulation amplitude was larger in case of bimetallic films containing thicker gold layers. The threshold fluences of the phase transitions were determined by numerical temperature model calculations for different metal layer compositions, and a good agreement was found between the calculated and experimentally observed threshold values. The division of the metal stripes into droplets and the development of holes were explained by the melting of the entire metal layers and by the vaporization of silver at higher fluences. The angle-dependent surface plasmon resonance spectroscopy realized in Kretschmann arrangement proved that the laser-induced grating formation was accompanied by the change in the optical thickness and by the modification of the structure of the bimetallic films. Broad side wings appeared on the resonance curves caused by grating–coupling in case of appropriate rotation angle and sufficiently large modulation depth of the grating's grooves, according to our calculations. The coupling on deep gratings developed on bimetallic films containing the thinnest gold layer and on monometallic silver films resulted in separated secondary resonance minimum development. The periodic adherence of native streptavidin on the metallic gratings was detected by tapping mode AFM, and based on the shift of the secondary resonance peak.

Keywords: Atomic force microscopy; Surface plasmon resonance spectroscopy; Rotated grating–coupling; Bimetallic films

Modelling chemical kinetics of small clusters after nanosecond laser ablation by A.V. Gusarov; V.I. Titov; I. Smurov (pp. 7672-7676).

Nanoclusters of various materials have recently been obtained by laser ablation. Strong evaporation of a condensed phase caused by laser irradiation is well known to generate an overcooled vapour. Further expansion thereof increases the oversaturation degree and facilitates homogeneous nucleation and cluster growth. To investigate homogeneous nucleation at very high expansion rates attained at nanosecond laser ablation, kinetic equations are applied describing all the possible gas-phase chemical reactions of dissociation and coalescing between small clusters. Additional cooling due to thermal emission by clusters is taken into account. Twenty smallest carbon molecules are considered. The model is applied to nanosecond laser ablation of graphite in vacuum. The resulted vapour molecular composition is characterised by dominating molecules C₃ and C₅ and an exponential drop of heavier clusters concentrations with their mass. The growth of heavier clusters is controlled by the balance between liberating the latent heat of their formation and the energy losses by expansion and thermal emission.

Keywords: PACS; 42.62.b; 47.45.nNanosecond laser ablation; Carbon clusters; Chemical kinetics

ns- and fs-LIBS of copper-based-alloys: A different approach by A. De Giacomo; M. Dell’Aglio; O. De Pascale; R. Gaudiuso; R. Teghil; A. Santagata; G.P. Parisi (pp. 7677-7681).

A self-calibrated analytical technique, based on plasmas induced by either 250fs or 7ns laser pulses, is presented. This approach is comparable to other calibration-free methods based on LTE assumption. In order to apply this method to very different laser pulse durations, the partial-local thermodynamic equilibrium (p-LTE) has been considered within the energy range of 30,000–50,000cm⁻¹. In order to obtain the neutral species densities, the detected plasma species emission lines intensities have been treated together with the experimental evaluated background black-body Planck-like emission distribution. For validating the followed method, three certified copper-based-alloys standards were employed and their minor components (Ni, Pb and Sn) amounts were determined. As a result, it arises, that this standardless method, independently from the laser source pulse durations, provides good quantitative analysis, and, consequently, that the composition of the plasma plume emitting species induced is not affected by the laser pulse time width.

Keywords: PACS; 82.80.Dx; 39.30.+w; 79.20.Ds; 32.30.Jc; 78.47.+pSelf-calibrated LIBS; Copper-based-alloys analysis; Laser induced optical emission spectroscopy; fs-LIBS; ns-LIBS

Plume propagation through a buffer gas and cluster size prediction by A. Bailini; P.M. Ossi; A. Rivolta (pp. 7682-7685).

A mixed-propagation picture for the expansion of an ablation plume through a buffer gas at different pressures is proposed after a brief discussion of the available analytical expansion models. Using parameter values deduced by the model the size of carbon clusters formed during plume propagation in helium is evaluated and compared with experimental data. Starting from experiments on silver plume propagation through molecular oxygen the size of silver clusters is predicted.

Keywords: PACS; 79.20.Ds; 52.38.Mf; 81.16.MkPulsed laser deposition; Plume expansion; Cluster synthesis; Carbon; Silver

Modeling of plasma-controlled surface evaporation and condensation of Al target under pulsed laser irradiation in the nanosecond regime by V.I. Mazhukin; V.V. Nossov; I. Smurov (pp. 7686-7691).

Phase transition on the surface of an aluminium target and vapour plasma induced by laser irradiation in the nanosecond regime at the wavelengths of 1.06 and 0.248μm with an intensity of 10⁸–10⁹W/cm² in vacuum are analysed. Particular attention is paid to the wavelength dependence of the observed phenomena and the non-one-dimensional effect caused by the Gaussian laser intensity distribution. A transient two-dimensional model is used which includes conductive heat transfer in the condensed phase, radiative gas dynamics and laser radiation transfer in the plasma as well as surface evaporation and back condensation at the phase interface. It is shown that distinctions in phase transition dynamics for the 1.06 and 0.248μm radiation result from essentially different characteristics of the laser-induced plasmas. For the 1.06μm radiation, evaporation stops after the formation of hot optically thick plasma, can occasionally resume at a later stage of the pulse, proceeds non-uniformly in the spot area, and the major contribution to the mass removal occurs in the outer part of the irradiated region. Plasma induced by the 0.248μm laser is much more transparent therefore evaporation does not stop but continues in the subsonic regime with the Mach number of about 0.1.

Keywords: Surface phase transitions; Laser-plasma interaction; Knudsen layer

Two color laser ablation: Enhanced yield, improved machining by Sandra Zoppel; Johann Zehetner; Georg A. Reider (pp. 7692-7695).

Laser ablation of semiconductors with nano- and picosecond lasers can be significantly improved, both in terms of yield and surface quality, by simultaneous irradiation of the sample with the fundamental beam ( λ=1064nm) and a small amount of its second harmonic (SH) produced in a thin nonlinear crystal. While the total energy fluence is conserved, the small fraction of the second harmonic serves to excite electrons into the conduction band to get the ablation process started. For femtosecond laser pulses, the effect becomes insignificant, since sufficient conduction band population is provided by multiphoton absorption.

Keywords: Laser ablation; Two-photon absorption

Plume expansion dynamics during laser ablation of manganates in oxygen atmosphere by S. Amoruso; A. Sambri; X. Wang (pp. 7696-7701).

The effect of ambient gas on the expansion dynamics of the plasma plume generated by excimer laser ablation of a LaMnO₃ target is investigated by using fast photography and optical emission spectroscopy. The plume propagation in an oxygen environment is examined with pressure ranging from vacuum to few hundreds Pa. Imaging analysis of the plume emission has allowed following the changes in the plume front dynamics as a function of time and pressure. The expansion dynamics of the plume front is examined by means of a theoretical description of plume evolution and shock-wave propagation in dimensionless variables. Optical emission spectroscopy analysis showed that the oxides are mainly formed in the gas-phase through reaction of the ablated atomic species with ambient oxygen. Moreover, we observed that the formation of oxides is strongly favoured at a pressure level where the formation of a shock-wave occurs.

Keywords: PACS; 52.38.Mf; 79.20.Ds; 81.15.Fg; 52.50JmShock-wave propagation; Pulsed laser deposition; Manganates

Matrix assisted pulsed laser evaporation of poly(d,l-lactide) thin films for controlled-release drug systems by R. Cristescu; A. Doraiswamy; T. Patz; G. Socol; S. Grigorescu; E. Axente; F. Sima; R.J. Narayan; D. Mihaiescu; A. Moldovan; I. Stamatin; I.N. Mihailescu; B. Chisholm; D.B. Chrisey (pp. 7702-7706).

We report the successful deposition of the porous polymer poly(d,l-lactide) by matrix assisted pulsed laser evaporation (MAPLE) using a KrF* excimer laser (248nm, τ=7ns) operated at 2Hz repetition rate. The chemical structure of the starting materials was preserved in the resulting thin films. Fluence played a key role in optimizing our depositions of the polymer. We demonstrated MAPLE was able to improve current approaches to grow high quality thin films of poly(d,l-lactide), including a porosity control highly required in targeted drug delivery.

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

Stimulation of the local growth of aligned carbon nanotubes by pulse laser exposure of the substrate by K. Zimmer; R. Böhme; D. Ruthe; B. Rauschenbach (pp. 7707-7710).

The local stimulation of carbon nanotubes (CNT) growth at the laser-modified sites that have been obtained by excimer laser irradiation at 248nm causing a local surface modification has been investigated by two different processing methods. The influence of the laser processing parameters on the CNT growth is compared for the irradiation of thin spin-coated iron nitrate films on silicon substrates and the backside irradiation of a fused silica substrate being in contact with an iron nitrate solution. Both techniques cause the formation of catalytic surface sites either by decomposition of the film or by deposition from the solution. For both laser modification approaches the local growth of vertical aligned nanotubes has been observed. In the case of spin-coated film the laser irradiation conditions have only a small influence on the CNT growth whereas at backside modification by means of a solution a strong dependence on the laser processing parameters has been found.

Keywords: Excimer laser; Surface modification; Carbon nanotubes; Local growth

Thin films of polyaniline deposited by MAPLE technique by C. Constantinescu; N. Scarisoreanu; A. Moldovan; M. Dinescu; C. Vasiliu (pp. 7711-7714).

Polyaniline (PAni) has important electro-conductive properties, high absorbance in microwave range and it is also frequently used in gas sensors because of its capability to convert chemical interactions into electrical signals. The methods of obtaining polyaniline in the form of thin films and/or nanostructures are complicated and request special physical and chemical treatments, both on the substrate surface and for the polymer itself.In this paper we applied matrix assisted pulsed lased evaporation (MAPLE) for obtaining thin films and nanostructures of polyaniline. In MAPLE, the target consisting of the material (usually 0.2–3wt%) dissolved in a solvent is frozen and it is evaporated using a laser. In our case polyaniline–emeraldine salt (PAni–ES) was dissolved in xylene or toluene, frozen in liquid nitrogen and was used as target. The third and the fourth harmonics of a Nd–YAG laser ( λ=355nm and 266nm) were used as laser sources. The obtained films have been characterized by atomic force microscopy, dielectric spectroscopy and Fourier transform infrared spectroscopy. The influence of the solvent type and of the laser parameters (wavelengths and fluence) on the polyaniline structures composition and properties has been investigated.

Keywords: Polyaniline; MAPLE technique; FT-IR spectroscopy

Laser cleaning of gilded wood: A comparative study of colour variations induced by irradiation at different wavelengths by S. Acquaviva; E. D’Anna; M.L. De Giorgi; A. Della Patria; L. Pezzati; D. Pasca; L. Vicari; F. Bloisi; V. Califano (pp. 7715-7718).

There is a growing interest by art conservators for laser cleaning of wood artworks, since traditional cleaning with chemical solvents can be a source of decay, due to the prolonged action of chemicals after the restoration. In this experiment we used excimer and Nd:YAG lasers, emitting radiation in the ultraviolet (248nm), visible (532nm) and near infrared (1064nm), to investigate the effect of laser interaction on gilded wood samples at different wavelengths. Increasing fluence levels were tested to assess threshold values both for surface damage and colour changes. Detailed colorimetric analyses of the irradiated samples show that cleaning effectiveness is related to the emission wavelength, the fluence and the number of pulses.

Keywords: Laser cleaning; Gilded wood; Nd:YAG lasers

Monitorizing nitinol alloy surface reactions for biofouling studies by C.Z. Dinu; V.C. Dinca; S. Soare; A. Moldovan; D. Smarandache; N. Scarisoareanu; A. Barbalat; R. Birjega; M. Dinescu; V. Ferrari DiStefano (pp. 7719-7723).

Growth and deposition of unwanted bacteria on implant metal alloys affect their use as biomedical samples. Monitoring any bacterial biofilm accumulation will provide early countermeasures. For a reliable antifouling strategy we prepared nitinol (NiTi) thin films on Ti-derived substrates by using a pulsed laser deposition (PLD) method. As the microstructure of Ti-alloy is dictated by the tensile strength, fatigue and the fracture toughness we tested the use of hydrogen as an alloying element. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) investigated the crystalline structure, chemical composition and respectively the surface morphology of the nitinol hydrogen and hydrogen-free samples. Moreover, the alloys were integrated and tested using a cellular metric and their responses were systematic evaluated and quantified. Our attractive approach is meant to select the suitable components for an effective and trustworthy anti-fouling strategy. A greater understanding of such processes should lead to novel and effective control methods that would improve in the future implant stability and capabilities.

Keywords: NiTi thin films; Hydrogen temporary alloying element; Surface analyses; Biofilms; Biofouling

Phase diagrams of laser-processed nanoparticles of brass by P.V. Kazakevich; A.V. Simakin; G.A. Shafeev; F. Monteverde; M. Wautelet (pp. 7724-7728).

Nanoparticles of brass are prepared by ablation of a brass target in ethanol using radiation of a copper-vapor laser at various laser fluences. The nanoparticles are characterized by TEM and optical spectroscopy. The multipulse laser irradiation leads to formation both the nanoparticles in liquid and well-ordered micro-structures on a surface of a target. It is revealed that both the morphology and absorption spectra of brass nanoparticles depend on presence of the micro-structures. Nanoparticles with the various phase diagrams are formed from a flat brass surface and from the same surface with micro-structures. The results are compared with a model of phase diagrams, in which size and composition effects are taken into account.

Keywords: Laser ablation; Nanoparticles; Plasmon resonance; Colloidal solutions; Phase diagram

The effect of the nanocarbon structures from laser pyrolysis on microorganisms evolution by L. Gavrila Florescu; C. Fleaca; I. Voicu; I. Morjan; L. Stamatin; Ioan Stamatin (pp. 7729-7732).

The carbon nanoparticles existing in environment are an important factor on healthy either by their toxicity or by interaction with pathogen microorganisms, which can make them more resistant or induce a specific mutagenesis. To understand the role of the nanocarbon particles, a series of carbon nanopowders was synthesized by gas-phase laser pyrolysis from different hydrocarbon-based mixture and used to design cell culture media for Escherichia coli and Staphylococcus aureus. The microorganisms, grown in a given incubation time, were investigated by fluorescent markers (water soluble quantum dots). We report that structure and properties of the nanocarbons influence the behaviour of the aerobic microorganisms. We show that carbon nanopowders are oxygen supplier for microorganisms and, at the same time, due to the presence of polyaromatics or heterogeneous atoms existent in the reactive gas mixture, could have an inhibition/poisoning effect.

Keywords: Laser pyrolysis; Nanocarbons; Microbiology; Toxicology

Laser printing of enamels on tiles by J.M. Fernández-Pradas; J.W. Restrepo; M.A. Gómez; P. Serra; J.L. Morenza (pp. 7733-7737).

A Nd:YAG laser beam is used as a tool to print patterns of coloured enamels on tile substrates. For this, the laser beam is scanned over a layer of raw enamel previously sprayed on the tile surface. The possibility to focus the laser energy to heat a small zone without affecting the rest of the piece presents some advantages in front of traditional furnace techniques in which the whole piece has to be heated; among them, energy saving and the possibility to apply enamels with higher melting temperatures than those of the substrate. In this work, we study the effects of laser irradiation of a green enamel, based in chromium oxide pigment and lead frit, deposited on a white tile substrate. Lines obtained with different combinations of laser beam power and scan speeds were investigated with the aim to optimize the process from the point of view of the quality of the patterns. For this purpose, the morphology of the lines and their cross-sections is studied. The results show that lines with good visual properties can be printed with the laser. The characteristics of the marked lines were found to be directly related with the accumulated energy density delivered. Moreover, there is a linear relationship between the accumulated energy density and the volume of melted material. A minimum accumulated energy density is required to melt a shallow zone of the glazed substrate to allow the adhesion of the enamelled lines.

Keywords: Laser print; Enamel; Tile

Laser surface micro-texturing of Ti–6Al–4V substrates for improved cell integration by N. Mirhosseini; P.L. Crouse; M.J.J. Schmidth; L. Li; D. Garrod (pp. 7738-7743).

Biological behaviour of an implant, such as osseointegration, depends on both the chemical composition and the morphology of the surface of the implant. This paper reports the surface modification of Ti–6Al–4V – which is widely used in implantation – by Nd:YAG ( λ=1064nm, τ=100ns) laser irradiation in order to enhance biointegration. Surface parameters are evaluated in terms contact angle measurement and surface roughness. Biocompatibility of the samples is investigated in vitro by monitoring 2T3 osteoblast cell growth on the samples through MTT assay.

Keywords: Laser surface treatment; Nd:YAG; biocompatibility; Wettability; Cell growth; 2T3 osteoblast cells

Transient effects in pulsed laser irradiation by V.I. Mazhukin; M.G. Lobok; I. Smurov (pp. 7744-7748).

Theoretical analysis of the influence of the temporal profile (rectangular, triangular, Gaussian) of the laser pulse on heating/cooling and phase transition velocities and quantity of ablated material was performed on the basis of a multifront Stephan problem. Modeling showed that material removal under stationary conditions (that correspond to long pulses) is entirely controlled by specific heat and material density, while in the case of transient regimes (short pulses) thermal conductivity and heat capacity play a predominant role. Interaction of the melting and evaporation fronts characterized by an evaporation front velocity far exceeding the melting front one is one of the examples of the transient nature of the phenomena influenced by the laser pulse parameters.

Keywords: PACS; 79.20.Ds; 64.70.Dv; 42.62.−bLaser melting; Laser evaporation; Laser pulse shape

Laser-induced thermal desorption mass spectrometry of functionalized silicon surfaces by Dominic Lingenfelser; Peter Hess (pp. 7749-7754).

Functionalization of materials and laser patterning of chemisorbed layers play an increasing role in tailoring and structuring surface properties on the nanoscale. An attractive method of investigating organic functionalizations is laser-induced thermal desorption (LITD). The analysis of well-defined H- and D-terminated Si(111)-(1×1):H(D) surfaces was used to quantify the LITD technique. Moreover, oxidized silicon surfaces were functionalized with trimethylsilyl (TMS) and (3,3,3-trifluoropropyl)-dimethylsilyl (TFP) hydrophobic end groups. The samples were irradiated normal to the surface with focused XeCl laser pulses. The desorbed species were monitored at an oblique angle and their time-of-flight (TOF) distributions were measured with a quadrupole mass analyzer. The TOF temperatures of silicon were calibrated for different laser pulse energies by desorption of H₂ and D₂. In the LITD experiments, the desorption of trimethylsilanol groups was observed for TMS terminations, indicating that essentially the whole molecule desorbs from the surface. The TOF data could be fitted to Maxwellian distributions, providing the desorption yield of the emitted species, their mass, and temperature. On the other hand, several characteristic fragments were found for the TFP-terminated surface. The TOF distributions indicate that the fragments detected with the analyzer derived from different desorbed species.

Keywords: PACS; 68.43.Tj; 81.07.Pr; 82.80.RtLaser-induced thermal desorption; Functionalized silicon; Mass spectrometry

Matrix assisted pulsed laser evaporation of cinnamate-pullulan and tosylate-pullulan polysaccharide derivative thin films for pharmaceutical applications by M. Jelinek; R. Cristescu; E. Axente; T. Kocourek; J. Dybal; J. Remsa; J. Plestil; D. Mihaiescu; M. Albulescu; T. Buruiana; I. Stamatin; I.N. Mihailescu; D.B. Chrisey (pp. 7755-7760).

We have demonstrated the successful thin film growth of two pullulan derivatives (cinnamate-pullulan and tosylate-pullulan) using matrix assisted pulsed laser evaporation (MAPLE). Our MAPLE system consisted of a KrF* laser, a vacuum chamber, and a rotating target holder cooled with liquid nitrogen. Fused silica and silicon (111) wafers were used as substrates. The MAPLE-deposited thin films were characterized by transmission spectrometry, profilometry, atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The deposited layers ranged from 250nm to 16.5μm in thickness, depending on the laser fluence (0.065–0.5Jcm⁻²) and number of pulses applied for the deposition of one structure (1500–13,300). Our results confirmed that MAPLE was well-suited for the transfer of cinnamate-pullulan and tosylate-pullulan.

Keywords: Drug delivery; Polysaccharide; Pullulan derivatives; Thin films; Matrix assisted pulsed laser evaporation

Laser ablation of metals by femtosecond pulses: Theoretical and experimental study by N.N. Nedialkov; P.A. Atanasov; S. Amoruso; R. Bruzzese; X. Wang (pp. 7761-7766).

We have investigated ultrashort laser micromachining of metals, both from the point of view of the basic physical processes, and the technological implications. The process of hole drilling of Ni with ≈300fs SHG ( λ=527nm) Nd-glass and Al samples with 100fs Ti:sapphire ( λ=800nm) laser pulses, respectively, has been experimentally addressed by using time-gated optical emission spectroscopy of the ablated material and SEM analysis of the targets. The ablation process has also been analyzed by classical, molecular dynamics (MD) simulations, by using a Morse potential to describe the interaction between the atoms, and taking into account the electron heat diffusion contribution. The dependence of the ablation depth on laser fluence, as measured by SEM analysis, is in good agreement with the numerical simulations and is also well correlated with the optical emission yield of the expanding plume.

Keywords: MD simulations; SEM analysis; Optical emission yield

Laser R2PI spectroscopic and mass spectrometric studies of chiral neurotransmitters by A. Giardini; V. Marotta; A. Paladini; S. Piccirillo; F. Rondino; M. Satta; M. Speranza (pp. 7767-7772).

One color, mass selected resonant two-photon ionization (1cR2PI) spectra of supersonically expanded bare neurotransmitter, (1 S,2 S)-(+)- N-methyl pseudoephedrine (MPE), and its complexes with chiral and achiral molecules have been investigated. The excitation spectrum of bare MPE has been analyzed and discussed on the basis of theoretical predictions at the B3LYP/6-31G** level of theory. The results allowed to get information on the possible conformers of MPE molecule and on the intermolecular forces on its cluster formed with a variety of solvent molecules, including chiral alcohols, lactates and water. Further information on intermolecular interactions have been obtained with ESI-CID-MS² technique, applied to chiral biomolecules linked through a metal ion to the neurotransmitter. The experimental results are compared with theoretical predictions.

Keywords: Laser; Mass spectrometry; Clusters; Supersonic beam; Chirality

Laser ablation of aluminosilicates: Comparison between allophane and mixed alumina/silicas by Fourier Transform-Ion Cyclotron Resonance-Mass Spectrometry by J. Castello; J.J. Gaumet; J.F. Muller; S. Derousseaux; J. Guilment; O. Poncelet (pp. 7773-7778).

Laser ablation coupled to Fourier Transform-Ion Cyclotron Resonance-Mass Spectrometry [FT-ICR-MS] was used for analysing allophane aluminosilicates and mixtures of Al₂O₃/SiO₂. We show that both positive and negative ionization modes in FT-ICR-MS allows direct analysis of the various Al/Si ratios in allophanes and mixed alumina/silica samples. FT-ICR-MS technique provides a routine analytical methodology providing insight into the Al/Si molar composition and the origin of any aluminosilicate materials.

Keywords: Aluminosilicates; Allophanes; LA-MS

Ablation with femtosecond pulses: The effect of temporal contrast by J. Bohus; T. Csákó; T. Szörényi; S. Szatmári (pp. 7779-7782).

An inherent property of the ultrashort pulse lasers used presently for materials processing is that the main pulse is accompanied by an amplified spontaneous emission background. The temporal quality of the pulses is characterized by the temporal contrast. Due to the 5–6 orders of magnitude difference in the duration of the main pulse and the pedestal, high intensity contrast does not mean necessarily high enough difference in the respective energies. In materials processing applications consideration of the energy contrast is advisable. The importance of the contrast in determining the ablation process is exemplified by the dependence of the ablation rate of boron carbide on the cleanness of the pulses of a high brightness hybrid dye/excimer laser system. It is shown that serious consideration of the effects of the nanosecond background is mandatory when evaluating the results.

Keywords: PLD; PLA; Ultrashort pulse processing; Intensity contrast; Energy contrast; Ablation yield

Nanosecond and femtosecond laser spectroscopy of molecules of biological interest by P. Villani; S. Orlando; A. Santagata; A. De Bonis; S. Veronesi; A. Giardini (pp. 7783-7786).

This paper mainly concerns on nanosecond and femtosecond laser spectroscopy of aromatic organic compounds as neurotransmitters, and plume diagnostics of the ablated species, in order to characterize the plasma dynamics, i.e. the temporal and spatial evolution of the plume. Optical emission spectroscopy has been applied to characterize the transient species produced in the femtosecond (fs) and nanosecond (ns) regimes. The laser sources employed for optical emission spectroscopy are a frequency-doubled Nd:YAG Handy ( λ=532nm, τ=5ns) and a frequency-doubled Nd:glass ( λ=527nm, τ=250fs). These studies aim to detect and give information on the photoexcitation and photodissociation of these biological molecules and to compare the plasma characteristics in the two ablation regimes.

Keywords: Photoexcitation; Photodissociation; Laser ablation

Femtosecond and nanosecond laser damage thresholds of doped and undoped triazenepolymer thin films by J. Bonse; J. Solis; L. Urech; T. Lippert; A. Wokaun (pp. 7787-7791).

The influence of pulse duration on the laser-induced damage in undoped or infrared-absorbing-dye doped thin triazenepolymer films on glass substrates has been investigated for single, near-infrared (800nm) Ti:sapphire laser pulses with durations ranging from 130fs up to 540fs and complementarily for infrared (1064nm) Nd:YAG ns-laser single-pulse irradiation. The triazenepolymer material has been developed for high resolution ablation with irradiation at 308nm. Post-irradiation optical microscopy observations have been used to determine quantitatively the threshold fluence for permanent laser damage. In contrast to our previous studies on a triazenepolymer with different composition [J. Bonse, S.M. Wiggins, J. Solis, T. Lippert, Appl. Surf. Sci. 247 (2005) 440], a significant dependence of the damage threshold on the pulse duration is found in the sub-picosecond regime with values ranging from ∼500mJ/cm² (130fs) up to ∼1500mJ/cm² (540fs). Other parameters such as the film thickness (50nm and 1.1μm samples) or the doping level show no significant influence on the material behavior upon irradiation. The results for fs- and ns-laser pulse irradiation are compared and analyzed in terms of existent ablation models.

Keywords: Femtosecond laser damage; Triazenepolymer films; Optical microscopy; Polymethylmethacrylate

Optical emission spectroscopy investigation of an ultra-short laser induced titanium plasma reheated by a ns laser pulse by A. Santagata; R. Teghil; A. De Giacomo; M. Dell’Aglio; G.P. Parisi; A. De Bonis; A. Galasso (pp. 7792-7797).

The dynamics of a titanium plasma species, induced in air by coupling a fs-ablating laser pulse with an orthogonal ns-reheating laser source placed at the fixed distance of 1.0mm from the target surface, has been followed by temporally resolved emission spectroscopy. The temporal evolutions of plasma features such as excitation temperatures and electron densities have been evaluated by using two different laser energies of the first fs-ablating laser pulse (0.8mJ and 3.0mJ). Optimum inter-pulse delay times, experimentally determined, of 250μs and 500μs were used for the fs laser energy of 3.0mJ and 0.8mJ, respectively. By experimental inspections of the main plasma species electronic transitions so obtained, a strong enhancement was evaluated up to one and two orders of magnitude for Ti(I) and Ti(II), respectively. Independently from the fs laser energy employed, the plasma features showed the same temporal behaviour implying that the ns-reheating characteristics of this process belong to the reheating mechanism itself. The experimental results have been discussed and the excited species evolutions and elementary processes involved, as well as, the local thermodynamic equilibrium departures, have been outlined.

Keywords: PACS; 32.30.Jc; 32.30.−r; 33.55.Be; 39.30.+w; 78.47.+p; 79.20.DsLaser induced emission spectroscopy; Dual pulse LIBS; Laser pulsed orthogonal reheating; Emission enhancement; LTE departure; Fs laser pulsed ablation; Titanium

Correction of small imperfections on white glazed china surfaces by laser radiation by I. Képíró; K. Osvay; M. Divall (pp. 7798-7805).

A laser-assisted technique has been developed for correction of small diameter (1mm) and shallow (0.5mm) imperfections on the surface of gloss fired porcelain. To study the physics and establish the important parameters, artificially made holes in a porcelain sample have been first filled with correction material, then covered with raw glaze and treated by a pulsed, 7kHz repetition rate CO₂ laser at 10.6μm. The modification of the surface and the surrounding area have been quantified and studied with a large range of parameters of incident laser power (1–10W), width of the laser pulses (10–125μs) and duration of laser heating (60–480s). Although the shine of the treated area, defined as the distribution of micro-droplets on the surface, is very similar to the untreated surfaces, the surroundings of the treated area usually show cracks. The measurement of both the spatial temperature distribution and the temporal cooling rate of the treated surface has revealed that a simple melting process always results in high gradient temperature distribution within the irradiated zone. Its inhomogeneous and fast cooling always generate at least micro-cracks on the surface within a few seconds after the laser was turned off. The duration and intensity of the laser irradiation have been then optimized in order to achieve the fastest possible melting of the surface, but without producing such high temperature gradients. To eliminate the cracks, more elaborated pre-heating and slowed-cooling-rate processes have been tried with prosperous results. These achievements complete our previous study, making possible to repair the most common surface imperfections and holes of gloss fired china samples.

Keywords: PACS; 81.05.Je (ceramics); 81.65.Ps (polishing); 81.65.−b (surface treatments); 82.80.Ch (infrared spectroscopy)Porcelain; Spatial temperature distribution; Micro-cracks

Femtosecond pulsed laser deposition of biological and biocompatible thin layers by B. Hopp; T. Smausz; G. Kecskeméti; A. Klini; Zs. Bor (pp. 7806-7809).

In our study we investigate and report the femtosecond pulsed laser deposition of biological and biocompatible materials. Teflon, polyhydroxybutyrate, polyglycolic-acid, pepsin and tooth in the form of pressed pellets were used as target materials. Thin layers were deposited using pulses from a femtosecond KrF excimer laser system (FWHM=450fs, λ=248nm, f=10Hz) at different fluences: 0.6, 0.9, 1.6, 2.2, 2.8 and 3.5J/cm², respectively. Potassium bromide were used as substrates for diagnostic measurements of the films on a FTIR spectrometer. The pressure in the PLD chamber was 1×10⁻³Pa, and in the case of tooth and Teflon the substrates were heated at 250°C. Under the optimized conditions the chemical structure of the deposited materials seemed to be largely preserved as evidenced by the corresponding IR spectra. The polyglycolic-acid films showed new spectral features indicating considerable morphological changes during PLD. Surface structure and thickness of the layers deposited on Si substrates were examined by an atomic force microscopy (AFM) and a surface profilometer. An empirical model has been elaborated for the description of the femtosecond PLD process. According to this the laser photons are absorbed in the surface layer of target resulting in chemical dissociation of molecules. The fast decomposition causes explosion-like gas expansion generating recoil forces which can tear off and accelerate solid particles. These grains containing target molecules without any chemical damages are ejected from the target and deposited onto the substrate forming a thin layer.

Keywords: AFM; FTIR; PLD, Thin films

Finite element simulation of pulsed laser ablation of titanium carbide by V. Oliveira; R. Vilar (pp. 7810-7814).

In the present paper, a 2D finite element model based on the heat-conduction equation and on the Hertz-Knudsen equation for vaporization was developed and used to simulate the ablation of TiC by Nd:YAG and KrF pulsed laser radiation. The calculations were performed for fluences of 8 and 10J/cm², which according to experimental results obtained previously, correspond to large increases of the ablation rate. The calculated maximum surface temperature of the target for both lasers is higher than the estimated value of TiC critical temperature, corroborating the hypothesis that the increase of the ablation rate is explained by the explosive boiling mechanism.

Keywords: PACS; 61.80.Ba; 81.05.Je; 81.15.FgLaser ablation; Finite element simulation; Titanium carbide

Femtosecond laser-induced damage of gold films by Jörg Krüger; Daniela Dufft; Robert Koter; Andreas Hertwig (pp. 7815-7819).

Single- and multi-shot ablation thresholds of gold films in the thickness range of 31–1400nm were determined employing a Ti:sapphire laser delivering pulses of 28fs duration, 793nm center wavelength at 1kHz repetition rate. The gold layers were deposited on BK7 glass by an electron beam evaporation process and characterized by atomic force microscopy and ellipsometry. A linear dependence of the ablation threshold fluence F_th on the layer thickness d was found for d≤180nm. If a film thickness of about 180nm was reached, the damage threshold remained constant at its bulk value. For different numbers of pulses per spot ( N-on-1), bulk damage thresholds of ∼0.7Jcm⁻² (1-on-1), 0.5Jcm⁻² (10-on-1), 0.4Jcm⁻² (100-on-1), 0.25Jcm⁻² (1000-on-1), and 0.2Jcm⁻² (10000-on-1) were obtained experimentally indicating an incubation behavior. A characteristic layer thickness of L_c≈180nm can be defined which is a measure for the heat penetration depth within the electron gas before electron–phonon relaxation occurs. L_c is by more than an order of magnitude larger than the optical absorption length of α⁻¹≈12nm at 793nm wavelength.

Keywords: PACS; 79.20.D; 42.62.C; 44.10; 78.66.BSingle- and multi-shot ablation; Ti:sapphire laser; Gold films

Morphological and chemical modifications and plume ejection following UV laser ablation of doped polymers: Dependence on polymer molecular weight by E. Rebollar; G. Bounos; M. Oujja; S. Georgiou; M. Castillejo (pp. 7820-7825).

This work investigates the effect of polymer molecular weight ( M_W) on the morphological and chemical modifications and on the plume ejection of doped polymethyl methacrylate (PMMA), and polystyrene (PS) films following irradiation at 248nm. Micro-bubbles develop in the irradiated films of the low absorbing PMMA-based substrates. The extent and kinetics of the observed morphological changes are respectively larger and last longer in the low M_W polymer, as evidenced by optical microscopy and real-time monitoring of transmission of a CW laser. The changes observed in the Raman spectra upon irradiation indicate that degradation occurs to a higher extent in larger M_W polymers. Laser induced fluorescence (LIF) probing of the plume reveals the presence of NapH and PhenH products from, respectively, NapI- and PhenI-doped films and a slower ejection process in the plume of low M_W polymer. For highly absorbing PS, a less dramatic dependence on M_W is observed. Results are discussed in the framework of the bulk photothermal model, according to which ejection requires a critical number of bonds to be broken.

Keywords: Polymer molecular weight; Laser ablation; Optical microscopy; Raman spectroscopy; Ablation plume

Frequency selective IR-filter produced by using EB-lithography by Y.P. Kathuria (pp. 7826-7830).

This paper reports on the fabrication of Jerusalem cross diplexer by direct write electron beam (EB) lithography followed by reactive ion etching (RIE) on a phosphorus doped polished silicon wafer substrate. Such structures can be used as frequency selective components in visible, microwave and near infra-red wavelength region. Replication of the patterns is accomplished by micron or sub-micron order mould fabricated from the silicon (Si) master. Fourier transform infra-red reflectance (FT-IR) measurements were performed to characterize the structured patterns. The spectral reflectance from these patterns clearly show a reflection dip due to surface plasmon excitation in the near infra-red wavelength at about 1.42 and 2.5μm, respectively. Potential applications such as antireflection surface (ARS) can be realized.

Keywords: Lithography; Infra-red; Cross diplexer

Laser-assisted shape selective fragmentation of nanoparticles by P.V. Kazakevich; A.V. Simakin; G.A. Shafeev; G. Viau; Y. Soumaré; F. Bozon-Verduraz (pp. 7831-7834).

Experimental results are presented on laser-assisted fragmentation of gold-containing nanoparticles suspended in liquids (either ethanol or water). Two kinds of nanoparticles are considered: (i) elongated Au nanorods synthesized by laser ablation of a gold target immersed in liquid phase; (ii) gold-covered NiCo nanorods with high aspect ratio ( θ∼10) synthesized by wet chemistry processes. The shape selectivity induced by laser fragmentation of these nanorods is gained via tuning the wavelength of laser radiation into different parts of the spectrum of their plasmon resonance corresponding to different aspect ratios θ. Fragmentation is performed using three laser wavelengths, involving a Cu vapour laser (510 and 578nm) and a Nd:YAG (1064nm). Nanoparticles are characterized by UV–vis spectrometry, Transmission Electron Microscopy (TEM). The effect of laser pulse duration (nanosecond against picosecond range) is also studied in the case of fragmentation with an IR laser radiation.

Keywords: Laser ablation; Gold; Nanorods; Plasmon resonance

Organic nanoparticles suspensions preparation by underwater excimer laser ablation of polycarbonate by I. Elaboudi; S. Lazare; C. Belin; J.L. Bruneel; L. Servant (pp. 7835-7839).

Ablation with excimer laser pulses on polycarbonate (PC) film has been performed in ultrapure water. It is demonstrated that it is a new efficient method for organic nanoparticles (ONP) suspensions synthesis. Proof of the formation of ONP is given by analysis of the water phase with AFM and UV–vis spectroscopy. The obtained transmission measurements are approached with the aid of Mie theory to estimate composition of suspensions. Results indicate that the polycarbonate film is partly ablated into nanometric particles with size ranging from 8 up to 180nm. This is also supported by force atomic microscopy. Confocal Raman microspectroscopy was done directly on water suspensions. Thanks to the optical trapping phenomenon of the nanoparticles, their vibrational Raman spectrum was more easily obtained. Original polycarbonate is lost although some polymeric structures are detected along with graphitic carbon.

Keywords: Laser ablation; Organic nanoparticle; Underwater; Polycarbonate; Mie theory; Confocal Raman microspectroscopy; Optical trapping; Graphitic carbon; Aqueous suspension

Synthesis of nano-structured materials by laser-ablation and their application to sensors by T. Okada; J. Suehiro (pp. 7840-7847).

We describe the synthesis of nano-structured materials of ZnO and Pd by laser ablation and their applications to sensors. The synthesis of ZnO nano-wires was performed by nano-particle assisted deposition (NPAD) where nano-crystals were grown with nano-particles generated by laser-ablating a ZnO sintered target in an Ar background gas. The synthesized ZnO nano-wires were characterized with a scanning electron microscopy and the photoluminescent characteristics were examined under an excitation with the third harmonics of a Nd:YAG laser. The nano-wires with a diameter in the range from 50 to 150nm and a length of up to 5μm were taken out of the substrate by laser blow-off technique and/or sonication. It was confirmed that the nano-wires showed the stimulated emission under optical pumping, indicating a high quality of the crystalinity. Pd nano-particles were generated by laser-ablating a Pd plate in pure water. The transmission electron microscope observation revealed that Pd nano-particles with a diameter in the range from 3nm to several tens of nanometers were produced. Using these nano-structured materials, we successfully fabricated sensors by the dielectrophoresis techniques. In the case of the ultraviolet photosensor, a detection sensitivity of 10nW/cm² was achieved and in the case of hydrogen sensing, the response time of less than 10s has been demonstrated with Pd nano-particles.

Keywords: Nano-structure; Laser-ablation; Nd:YAG laser

Synthesis of ZnO nanowires by pulsed laser deposition in furnace by Hyo Jeong Son; Kyung Ah Jeon; Chang Eun Kim; Jong Hoon Kim; Kyung Hwa Yoo; Sang Yeol Lee (pp. 7848-7850).

ZnO nanowires were fabricated on Au coated (0001) sapphire substrates by using a pulsed Nd:YAG laser with a ZnO target in furnace. ZnO nanowires have various sizes and shapes with a different substrate position inside a furnace. The length and the diameter of these ZnO nanowires were around 3–4μm and 120–200nm, respectively, confirmed by scanning electron microscopy (SEM). The diameter control of the nanowires was achieved by varying the position of substrates. The ultraviolet emission of nanowires from the near band-edge emission (NBE) was observed at room temperature. The formation mechanism and the effect of different position of substrates on the structural and optical properties of ZnO nanowires are discussed.

Keywords: PACS; 52.38. Mf; 78.67. −n; 81.07. −bZnO nanowire; Laser ablation; Vapor–liquid–solid; Au; UV emission

Ultrafast laser assisted fabrication of ZnO nanorod arrays for photon detection applications by Yalin Lu; Iyad Dajani; R.J. Knize (pp. 7851-7854).

Orderly aligned ZnO nanorod arrays were grown by the ultrafast laser assisted ablation deposition method. These nanorod arrays were further used to make efficient p–n heterojunction photodetector arrays, which have the potential to have nanoscale spatial resolution for imaging, unique incident polarization discrimination capability, and much improved quantum efficiency as well as detection sensitivity. Both front- and back-illumination photodetection schemes were demonstrated by growing those ZnO nanorod arrays on p-type silicon and p-type Zn_0.9Mg_0.1O-coated Al₂O₃ (0001) substrates, respectively. Typical diode rectification behavior and photosensitivity were observed in both designs through I– V and photocurrent measurements.

Keywords: ZnO nanorod array; UV photodetector; Pulsed laser deposition; p–n heterojunction

Study of the laser-induced forward transfer of liquids for laser bioprinting by M. Duocastella; M. Colina; J.M. Fernández-Pradas; P. Serra; J.L. Morenza (pp. 7855-7859).

Laser-induced forward transfer (LIFT) is a direct-writing technique that allows printing patterns of diverse materials with a high degree of spatial resolution. In conventional LIFT a small fraction of a solid thin film is vaporized by means of a laser pulse focused on the film through its transparent holder, and the resulting material recondenses on the receptor substrate. It has been recently shown that LIFT can also be used to transfer materials from liquid films. This widened its field of application to biosensors manufacturing, where small amounts of biomolecules-containing solutions have to be deposited with high precision on the sensing elements. However, there is still little knowledge on the physical processes and parameters determining the characteristics of the transfers.In this work, different parameters and their effects upon the transferred material were studied. It was found that the deposited material corresponds to liquid droplets which volume depends linearly on the laser pulse energy, and that a minimum threshold energy has to be overcome for transfer to occur. The liquid film thickness was varied and droplets as small as 10μm in diameter were obtained. Finally, the effects of the variation of the film to substrate distance were also studied and it was found that there exists a wide range of distances where the morphology of the transferred droplets is independent of this parameter, what provides LIFT with a high degree of flexibility.

Keywords: Laser direct writing; LIFT; Biosensors; Microarrays

Application of the laser ablation for conservation of historical paper documents by A. Kaminska; M. Sawczak; K. Komar; G. Śliwiński (pp. 7860-7864).

Laser ablation was applied for surface cleaning and spectroscopic diagnostics of historical paper documents and model samples in the framework of the conservation projects. During cleaning the spectra of ablation products were recorded by means of the LIBS technique which allowed for nearly non-destructive identification of surface layers such as contaminants, substrate and pigments. For consecutive laser pulses a strong decrease of band intensities of the emission lines of Ca, Na, K, Al and Fe ascribed to contaminants were observed. The effect was used for monitoring of the cleaning progress of stained paper. For surface cleaning and spectra excitation the Q-switched Nd:YAG laser of 6ns pulsewidth operating at wavelengths of 266, 355, 532, and 1064nm and of fluence selected from the range 0.3–0.9J/cm² was applied. The ablation parameters were optimized in agreement with the literature and the results were confirmed by surface studies and testing of the mechanical and chemical properties, and also by the response to the ageing process of the paper substrate. In case of the model paper irradiated in the UV range at 266 and 355nm a visual inspection revealed local damages of the cellulose fibers accompanied by a decrease of the mechanical strength of the substrate. The effect was more pronounced after artificial ageing. The best results were obtained for samples irradiated at 532nm and at laser fluence below the damage threshold of 0.6J/cm², which is in agreement with literature.

Keywords: Laser ablation; Spectroscopic analysis; Paper conservation

Structural modifications in fused silica induced by ultraviolet fs laser filaments by I. Zergioti; K.D. Kyrkis; D.G. Papazoglou; S. Tzortzakis (pp. 7865-7868).

It is shown that the tight focusing of short ultraviolet laser pulses (248nm, 450fs) in the bulk of high bandgap transparent solids (fused silica) can result in structural modifications in the material. These can vary from small changes of the refractive index to birefringence, cracks and voids. This restructuring of the medium is due to the high laser intensities attained, and the plasma that is generated through multi-photon processes. The restructuring comes in the form of a string, which is the result of the nonlinear propagation of the laser beam in the medium as a self-trapped filament. We resume the conditions for the generation of the different types of modifications and comment on the temporal evolution and the role of the plasma strings at the trail of the light filaments.

Keywords: Fused silica; Laser; Filamentation

Hf1−_xSi_xO_y dielectric films deposited by UV-photo-induced chemical vapour deposition (UV-CVD) by M. Liu; L.Q. Zhu; G. He; Z.M. Wang; J.X. Wu; J.-Y. Zhang; I. Liaw; Q. Fang; Ian W. Boyd (pp. 7869-7873).

Hf1−_xSi_xO_y is an attractive candidate material for high- k dielectrics. We report in this work the deposition of ultra-thin Hf1−_xSi_xO_y films (0.1≤ x≥0.6) on silicon substrate at 450°C by UV-photo-induced chemical vapour deposition (UV-CVD) using 222nm excimer lamps. Silicon(IV) and hafnium(IV) organic compounds were used as the precursors. Films from around 5 to 40nm in thickness with refractive indices from 1.782 to 1.870 were grown. The deposition rate was found to be of 6nm/min at a temperature of 450°C. The physical, interfacial and electrical properties of hafnium silicate (Hf1−_xSi_xO_y) thin films were investigated by using X-ray photoelectron spectroscopy, ellipsometry, FT-IR, C– V and I– V measurements. XRD showed that they were basically amorphous, while Fourier transform infrared spectroscopy (FT-IR), clearly revealed Hf–O–Si absorption in the photo-CVD deposited Hf1−_xSi_xO_y films. Surface and interfacial properties were analysed by TEM and XPS. It is found that carbon content in the films deposited by UV-CVD is very low and it also decreases with increasing Si/(Si+Hf) ratio, as low as about 1at.% at the Si/(Si+Hf) ratio of 60at.%.

Keywords: High-k dielectrics; Hf; _1-x; Si; _x; O; _y; films; HfO; ₂; /Si interface; CMOS technology; UV photo induced chemical vapour deposition (UV-CVD)

Color center formation in KCl and KBr single crystals with femtosecond laser pulses by J.T. Dickinson; S.C. Langford; S.M. Avanesyan; S. Orlando (pp. 7874-7878).

Because of their extremely high instantaneous powers, femtosecond lasers can color many nominally transparent materials. Although the excitations responsible for this defect formation occur on subpicosecond time scales, subsequent interactions between the resulting electronic and lattice defects complicate the evolution of color center formation and decay. These interactions must be understood in order to account for the long-term behavior of coloration. In this work, we probe the evolution of color centers generated by femtosecond laser radiation in potassium chloride and potassium bromide single crystals on time scales from microseconds to hundreds of seconds. By using an appropriately chosen probe laser focused through the femtosecond laser spot, we follow the changes in coloration due to individual or multiple femtosecond pulses and the evolution of that coloration for long times after femtosecond laser radiation is terminated.

Keywords: Femtosecond laser; Alkali halides; F-center

Strong luminescence emission enhancement by wet oxidation of pyrolytic silicon nanopowders by R. D’Amato; M. Falconieri; M. Carpanese; F. Fabbri; E. Borsella (pp. 7879-7883).

A strong luminescence enhancement of several orders of magnitude was obtained using a wet chemical oxidation process on silicon nanopowders (Si-np) produced by laser-assisted pyrolysis of silane. IR absorption spectroscopy, X-ray diffraction analysis and Raman characterization of the as-prepared and processed Si-np show that the oxidation process acts on the oxide layer surrounding the particles by improving its stoichiometry, without affecting the inner crystalline silicon core. Accordingly, the luminescence emission band was centered at about 780nm and was not shifted after the oxidation process. These results point out the importance of the quality of the oxide capping layer for the passivation of defects which can otherwise quench the luminescence emission.

Keywords: Si-np; XRD; DLS

Polymer self-assembled nano-structures and surface relief gratings induced with laser at 157nm by E. Sarantopoulou; Z. Kollia; A.C. Cefalas; A.M. Douvas; M. Chatzichristidi; P. Argitis; S. Kobe (pp. 7884-7889).

Surface relief gratings (SRG) and self-organized nano-structures induced by laser light at 157nm on the fluoropolymer poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA), films were obtained under well-controlled light exposure conditions. Regular and semi-regular spaced self-organized grating-like structures were created on polymeric films for ∼7.5–100mJ/cm² laser energy fluence. For lower laser fluence, the surface morphology of light exposed/non-exposed areas exhibited irregular-like structure morphologies, while polymer surface irradiation with energy fluence higher than 150mJ/cm² causes progressively fading out of the regular patterns. Under the specific experimental conditions, the SRG and self-organization patterning have their origin in the development of a surface thermal instability (Rayleigh's instability), which is resolved itself into regular patterns on the surface of the fluoropolymer film. The thermal instability is due to the explosive polymer surface photo-dissociation at 157nm and the build up of longitudinal and periodic surface stress, which eventually create the SRG and the self-assembled structures on the polymer.

Keywords: Surface relief gratings; Light-induced structures; Nano-structures; Self-assembly; Fluoropolymers; VUV; 157; nm

Micro-structuring of TiO₂ thin films by laser-assisted diffraction processing by O. Van Overschelde; G. Guisbiers; M. Wautelet (pp. 7890-7894).

Thin films of TiO₂ are deposited by magnetron sputtering on glass substrate and are irradiated by UV radiation using a KrF excimer laser (248nm). These thin films are patterned with a razor blade placed on the way of the radiation just in front of the TiO₂ thin film. Just near the edge of the razor blade on the thin film, diffraction lines are observed, resulting in the ablation of the film. These patterns are characterized by optical microscopy, mechanical profilometry. Diffraction up to the 35th order is observed. The results are shown to be compatible with a model in which electronic excitation plays the major role.

Keywords: Titanium dioxide films; Laser processing; Thin films; Microstructuring; Diffraction

Structure and properties of the bronze laser alloyed with titanium by S. Kac; A. Radziszewska; J. Kusinski (pp. 7895-7898).

The paper describes the microstructure and properties (microhardness and wear resistance) of the bronze laser alloyed with titanium. The laser alloying was done using a pulsed Nd:YAG laser with a generated beam energy of 25–35J. A very fine microstructure was formed under such rapid solidification conditions like laser treatment. The high chemical homogeneity and fine structure of the melted zone were attributed to high cooling rates due to the short interaction time with Nd:YAG pulsed laser radiation and relatively small volume of the melted material. The structure obtained in the surface layer after laser alloying permits to get a high level of hardness and an improved wear resistance.

Keywords: Microstructure; Properties; Bronze laser

Waveguides in lithium niobate fabricated by focused ultrashort laser pulses by Jonas Burghoff; Christian Grebing; Stefan Nolte; Andreas Tünnermann (pp. 7899-7902).

We report on investigations of the bulk microstructuring of lithium niobate crystals with intense femtosecond laser pulses. In different crystal cuts, optical waveguides were produced whose properties depend strongly on the processing parameters. To explore the origin of the refractive index changes, we subjected the crystals to different conditions (like temperature, illumination, etc.) while monitoring the waveguide output. This way several mechanisms for the change in refractive index could be singled out. These include the photorefractive effect, inhomogeneous ion concentrations and stress in the crystalline lattice. As an application, we demonstrate frequency doubling of 1064nm laser radiation in a microstructured phase-matched waveguide.

Keywords: Femtosecond laser machining; Lithium niobate; Optical waveguides

Synthesis of TiN thin films by a new combined laser/sol–gel processing technique by Tamer Ezz; Philip Crouse; Lin Li; Zhu Liu (pp. 7903-7907).

In this work a novel method for synthesising TiN coatings is reported. A high-power diode laser at different powers and traverse speeds was applied to a mild steel substrate, coated with a slurry of titania sol–gel, urea and graphite. The reaction chemical thermodynamics was investigated to estimate the compositions, temperature range, and the required reaction enthalpy for producing TiN. A one-dimensional heat transfer model was used to optimise the processing parameters. Surface morphology and microstructure of the deposited coatings and substrate surface layers were examined using optical microscopy, scanning electron microscope, and field emission gun scanning electron microscope which reveals deposition of very thin layer about 0.3μm of pure TiN and the presence of sub-micron crystalline structure of TiN forming a metal matrix composite inter-layer with the substrate below the film which suggest a good metallurgically bonding with the substrate. Chemical composition was determined by energy dispersive X-ray analysis. The phases were identified by X-ray diffraction which confirms the synthesis of TiN film for all the samples. Results of nano-hardness measurements revealed a hardness value of the order of 22–27GPa.

Keywords: Laser processing; Sol–gel; Titanium nitride

Effects of some synthesis parameters on the structure of titania nanoparticles obtained by laser pyrolysis by M. Scarisoreanu; Morjan; R. Alexandrescu; R. Birjega; I. Voicu; C. Fleaca; E. Popovici; I. Soare; L. Gavrila-Florescu; O. Cretu; G. Prodan; V. Ciupina; E. Figgemeier (pp. 7908-7911).

The preparation of TiO₂ nanoparticles by CO₂ laser pyrolysis of TiCl₄ (vapor)-based gas mixtures was investigated as a function of laser power and influence of the oxidizer. Increased crystallinity and crystallite dimensions as well as increase of the rutile fraction are observed at moderate flow increase in the flow rate of the oxidizing agent.

Keywords: TiO; ₂; nanoparticles; CO; ₂; laser pyrolysis; Nanostructure

Laser annealing of Al implanted silicon carbide: Structural and optical characterization by C. Boutopoulos; P. Terzis; I. Zergioti; A.G. Kontos; K. Zekentes; K. Giannakopoulos; Y.S. Raptis (pp. 7912-7916).

Pulsed-laser-based methods have been applied for post-implant annealing of p-type Al-doped 4H–SiC wafers in order to restore the crystal structure and to electrically activate the doping species. The annealing was performed with the third harmonic (355nm) of a Nd:YAG laser at 4ns pulse duration. The epilayers were characterized by micro-Raman spectroscopy under surface and cross-sectional backscattering. Changes in the phonon mode-intensity were related to the laser annealing induced recrystallization of the implanted material. The results were compared with changes in the infrared reflectivity across the Reststrahlen band. Transmission electron microscopy analysis showed the formation of columnar polycrystalline structure after the laser annealing process.

Keywords: Nd:YAG laser; Al-doped 4H–SiC surface; XeCl excimer laser; Electronic and optoelectronic devices; UV laser irradiation

In situ STM of pulsed laser nanostructured deposits: First stages of film formation by D. Cattaneo; N. Righetti; C.S. Casari; A. Li Bassi; C.E. Bottani (pp. 7917-7921).

In the synthesis of nanostructured thin films the characterization of the growth processes plays a fundamental role for the control of the film and surface properties. Moreover when the deposition technique is based on the production and the assembling of nanoparticles/clusters the characterization of the precursor size distribution is of fundamental importance.We have designed a pulsed laser deposition (PLD) apparatus for the production of nanostructured thin films and surfaces, connected to a UHV variable temperature scanning tunneling microscope (STM). The whole system is devoted to the synthesis and in situ study of nanostructured and nanoporous functional metal and metal oxide films and surfaces. We have deposited W nanoparticles produced by a few hundreds laser pulses in order to investigate the initial mechanisms of the film growth. Different deposition conditions have been explored by controlling the laser generated plasma expansion through a background gas in the PLD chamber. STM measurements have been performed on W thin films deposited on different substrates to study both the size distribution and the aggregation of the precursors on the surface. Although substrate effects must be taken into account, the control of the background gas pressure and of the target-to-substrate distance allows to produce surfaces with different morphologies. This opens the possibility to tailor the material properties through the control of the size and deposition energy of the building nano-units.

Keywords: STM-Scanning tunneling microscopy; Nanostructured thin films; Pulsed laser deposition; Tungsten

Laser induced backside dry etching of transparent materials by B. Hopp; Cs. Vass; T. Smausz (pp. 7922-7925).

Laser induced backside wet etching (LIBWE) is a well-known procedure in the micromachining of transparent materials. We developed a modified technique in which the absorbing liquid of LIBWE was substituted by an absorbing solid thin film (laser induced backside dry etching, LIBDE). Fused silica plate having 1mm thickness was coated by a 100nm thick silver layer. The metal film was irradiated through the quartz plate by single pulses of a nanosecond KrF excimer laser. The applied fluence was varied in the range of 90–4030mJ/cm², the illuminated area was 1.05mm². At the appropriate fluences it was found that the silver was removed from the irradiated spots and here the fused silica was etched, simultaneously. The dependence of the etch rate (which corresponds to the etched depth, since this is a single-pulse technology) on the fluence was investigated. The results showed a linear relation between etching depth (0–600nm/pulse) and applied fluence in the range of 0.2 (the etching threshold fluence) to 4J/cm². With its higher etching rate, the LIBDE procedure is much more effective than LIBWE. The morphology of the etched holes was studied by an atomic force microscope. A thermal model was developed for the description of the etching mechanism which was in a good agreement with the experimental results.

Keywords: LIBWE; Quartz; KrF

Single-step laser deposition of functionally graded coating by dual ‘wire–powder’ or ‘powder–powder’ feeding—A comparative study by Waheed Ul Haq Syed; Andrew J. Pinkerton; Zhu Liu; Lin Li (pp. 7926-7931).

The creation of iron–copper (Fe–Cu) alloys has practical application in improving the surface heat conduction and corrosion resistance of, for example, conformal cooling channels in steel moulds, but is difficult to achieve because the elements have got low inter-solubility and are prone to solidification cracking. Previous work by these authors has reported a method to produce a graded iron–nickel–copper coating in a single-step by direct diode laser deposition (DLD) of nickel wire and copper powder as a combined feedstock. This work investigates whether dual powder feeds can be used in that process to afford greater geometric flexibility and compares attributes of the ‘nickel wire and copper powder’ and ‘nickel powder and copper powder’ processes for deposition on a H13 tool steel substrate.In wire–powder deposition, a higher temperature developed in the melt pool causing a clad with a smooth gradient structure. The nickel powder in powder–powder deposition did not impart much heat into the melt pool so the melt pool solidified with sharp composition boundaries due to single metal melting in some parts. In wire–powder experiments, a graded structure was obtained by varying the flow rates of wire and powder. However, a graded structure was not realised in powder–powder experiments by varying either the feed or the directions. Reasons for the differences and flow patterns in the melt pools and their effect on final part properties of parts produced are discussed.

Keywords: Diode laser; Deposition; Wire; Powder; Functionally graded

Control parameters in pattern formation upon femtosecond laser ablation by Olga Varlamova; Florenta Costache; Markus Ratzke; Jürgen Reif (pp. 7932-7936).

Femtosecond laser ablation experiments on different materials have revealed a great diversity of self-organized nano-structures on the bottom of the ablated area. They range from arrays of nano-spheres to bifurcating longer lines, with size and shape depending on the irradiation dose and number of laser pulses. In this contribution, laser beam polarization and surface charge distribution, following surface relaxation, are investigated as control parameters for this nano-structures formation. Experiments with linear, circular and, for the first time, elliptical polarized light indicate that the laser polarization has a great influence on the orientation of the ripples. Investigations with laser beams of elliptical polarization show that, whereas the ripples orientation is defined by the major axis of the polarization ellipse, the ripple morphology is sensitive to the ellipticity. For silicon samples electrical measurements with a scanning-probe microscope on the ablated area reveal a spatial variation of the surface potential, possibly generated by a local change in dopant density, correlated with the patterns’ modulation on the crater bottom.

Keywords: Femtosecond laser ablation; CaF; ₂; Silicon; Self-organized nano-structures; Elliptical polarization; Electrical properties

TiO₂ nanoparticle thin film deposition by matrix assisted pulsed laser evaporation for sensing applications by A.P. Caricato; S. Capone; G. Ciccarella; M. Martino; R. Rella; F. Romano; J. Spadavecchia; A. Taurino; T. Tunno; D. Valerini (pp. 7937-7941).

The MAPLE technique has been used for the deposition of nanostructured titania (TiO₂) nanoparticles thin films to be used for gas sensors applications. An aqueous solution of TiO₂ nanoparticles, synthesised by a novel chemical route, was frozen at liquid nitrogen temperature and irradiated with a pulsed ArF excimer laser in a vacuum chamber. A uniform distribution of TiO₂ nanoparticles with an average size of about 10nm was deposited on Si and interdigitated Al₂O₃ substrates as demonstrated by high resolution scanning electron microscopy-field emission gun inspection (SEM-FEG). Energy dispersive X-ray (EDX) analysis revealed the presence of only the titanium and oxygen signals and FTIR (Fourier transform infra-red) revealed the TiO₂ characteristic composition and bond. A comparison with a spin coated thin film obtained from the same solution of TiO₂ nanoparticles is reported. The sensing properties of the films deposited on interdigitated substrates were investigated, too.

Keywords: TiO; ₂; nanoparticles; SEM-FEG; EDX; Sensor

Deposition and growth kinetics studies of thin zirconium dioxide films by UVILS-CVD by Mingliang Chen; Xinyu Zhang; Qi Fang; Junying Zhang; Zijing Lin; Ian W. Boyd (pp. 7942-7946).

We report the deposition of thin zirconium dioxide films on Si(100) by a technique of ultraviolet-assisted injection liquid source chemical vapor deposition (UVILS-CVD) by using ultraviolet with 222nm radiation. The alkoxide zirconium(IV) tert-butoxide (Zr[OC(CH₃)₃]₄) was used as precursor while nitrous oxide was driven into the reaction chamber as an oxidizing agent. The ZrO₂ films were deposited under various conditions and characterized by ellipsometry, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. The growth rate decreased with the increasing of substrate temperatures from 200 to 400°C. Deposition rate of 20nm/min was observed at a substrate temperature of 350°C. There was a liner relation between the thicknesses of the films and deposition times. As a result the thicknesses can be accurately controlled by changing the number of drops of precursor introduced by the injection liquid source. The growth rate increased with the increasing concentrations of the precursor, nevertheless the trend stopped when the concentration exceeded 8.5%. The growth kinetics were also studied and the results were fit to a three-step kinetic model involving a photo chemical reaction, a reversible precursor absorption process and a following irreversible deposition reaction.

Keywords: Metal oxide semiconductor field effect transistor; UVILS-CVD; Microelectronic industry

Periodic sub-micrometric structures using a 3D laser interference pattern by M. Salaün; A.-L. Joudrier; M. Audier; S. Pignard (pp. 7947-7951).

A method to obtain three-dimensional sub-micrometric periodic structures is presented. The experimental set-up consists in a pulsed UV laser beam source ( λ=355nm) coming into an interferometer in order to generate four beams converging inside a chamber. According to the directions, to the relative intensities and to the polarizations of these four beams, a 3D interference pattern can be obtained inside the overlapping volume of these four beams; the characteristics of the four laser beams have been optimized in order to obtain a maximal contrast of intensity. In order to visualize the interference pattern, its contrast and its stability at each laser pulse, a video camera coupled to an oil immersion microscope objective has been installed above the interferometer. By suppressing the central beam, it is also possible to generate a bidimensional interference pattern which defines an hexagonal structure in the (111) plane with a period of 377nm.This optical set-up has been used to obtain 3D sub-micrometric periodic structures in negative photoresists. Experiments consist in a one- or multi-pulse irradiation of the photoresist followed by a development procedure which leads to a sub-micrometric face-centred cubic structure cut in a (111) plane with a cell parameter of 650nm. The optimization of the experimental conditions is presented for two kinds of photoresists; the role of the substrate according to its reflectivity at the laser wavelength and its influence on the interference pattern is also discussed.

Keywords: PACS; 42.25.Hz; 42.70.Gi; 42.82.Cr; 78.30.Jw; 82.35.+tSub-micrometric periodic structures; Photonic band gap; Photoresist

High fluence deposition of polyethylene glycol films at 1064nm by matrix assisted pulsed laser evaporation (MAPLE) by A. Purice; J. Schou; P. Kingshott; N. Pryds; M. Dinescu (pp. 7952-7956).

Matrix assisted pulsed laser evaporation (MAPLE) has been applied for deposition of thin polyethylene glycol (PEG) films with infrared laser light at 1064nm. We have irradiated frozen targets (of 1wt.% PEG dissolved in water) and measured the deposition rate in situ with a quartz crystal microbalance. The laser fluence needed to produce PEG films turned out to be unexpectedly high with a threshold of 9J/cm², and the deposition rate was much lower than that with laser light at 355nm. Results from matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis demonstrate that the chemistry, molecular weight and polydispersity of the PEG films were identical to the starting material. Studies of the film surface with scanning electron microscopy (SEM) indicate that the Si-substrate is covered by a relatively homogenous PEG film with few bare spots.

Keywords: High fluence deposition; Polyethylene glycol films; Matrix assisted pulsed laser evaporation (MAPLE)

Analysis of excimer laser annealing of amorphous SiGe on La₂O₃//Si structures by L. Fornarini; J.C. Conde; S.Chiussi; P. Gonzalez; B. Leon; S. Martelli (pp. 7957-7963).

The reduction of complementary metal oxide semiconductor dimensions through transistor scaling is in part limited by the SiO₂ dielectric layer thickness. Among the materials evaluated as alternative gate dielectrics one of the leading candidate is La₂O₃ due to its high permittivity and thermodynamic stability. However, during device processing, thermal annealing can promote deleterious interactions between the silicon substrate and the high- k dielectric degrading the desired oxide insulating properties.The possibility to grow poly-SiGe on top of La₂O₃//Si by laser assisted techniques therefore seems to be very attractive. Low thermal budget techniques such as pulsed laser deposition and crystallization can be a good choice to reduce possible interface modifications due to their localized and limited thermal effect.In this work the laser annealing by ArF excimer laser irradiation of amorphous SiGe grown on La₂O₃//Si has been analysed theoretically by a numerical model based on the heat conduction differential equation with the aim to control possible modifications at the La₂O₃//Si interface. Simulations have been carried out using different laser energy densities (0.26–0.58J/cm²), different La₂O₃ film thickness (5–20nm) and a 50nm, 30nm thick amorphous SiGe layer. The temperature distributions have been studied in both the two films and substrate, the melting depth and interfaces temperature have been evaluated. The fluences ranges for which the interfaces start to melt have been calculated for the different configurations.Thermal profiles and interfaces melting point have shown to be sensitive to the thickness of the La₂O₃ film, the thicker the film the lower the temperature at Si interface.Good agreement between theoretical and preliminary experimental data has been found.According to our results the oxide degradation is not expected during the laser crystallization of amorphous Si_0.7Ge_0.3 for the examined ranges of film thickness and fluences.

Keywords: Poly SiGe; La; ₂; O; ₃; Excimer laser annealing; Crystallization

Study of porous carbon thin films produced by pulsed laser deposition by R. Janmohamed; J.J. Steele; C. Scurtescu; Y.Y. Tsui (pp. 7964-7968).

Amorphous carbon is an interesting material and its properties can be varied by tuning its diamond-like (sp³) fractions. The diamond-like fractions in an amorphous carbon films depends on the kinetic energy of the deposited carbon ions. Porous amorphous carbon thin films were deposited onto silicon substrates at room temperature in a vacuum chamber by Glancing Angle Pulsed Laser Deposition (GAPLD). Krypton fluoride (248nm) laser pulses with duration of 15ns and intensities of 1–20GW/cm² were used. In GAPLD, the angles between the substrate normal and the trajectory of the incident deposition flux are set to be almost 90°. Porous thin films consisting of carbon nanowires with diameters less than 100nm were formed due to a self-shadowing effect. The kinetic energies of the deposited ions, the deposition rate of the films and the size of the nanowires were investigated. The sp³ fraction of the porous carbon films produced at intensity around 20GW/cm² were estimated from their Raman spectra.

Keywords: Porous thin films; Nanowires; Glancing Angle Pulsed Laser Deposition (GAPLD); Diamond-like Carbon (DLC); Amorphous carbone

Effects of refractive index modifiers and UV light on an epoxy-functional inorganic–organic hybrid sol–gel derived thin film system by Shane O’Brien; Mehmet Çopuroğlu; Gabriel M. Crean (pp. 7969-7972).

Thin film systems consisting of (3-glycidyloxypropyl)trimethoxysilane (GDPTMS), dimethyldimethoxysilane (DMDMOS) and, either zirconium(IV) n-propoxide (Zr(OPrⁿ)₄) or diphenyldimethoxysilane (DPDMS) were synthesised via the sol–gel method. GDPTMS and DMDMOS were employed as the main network formers, whereas Zr(OPrⁿ)₄ or DPDMS was both a network former and a refractive index modifier. The comparative effects of Zr and DPDMS content, and UV light on the optical and thermal properties of the system were evaluated. Refractive index measurements and cross-sectional scanning electron microscopy of the resultant thin films were performed. The thermal stability of each system, in terms of temperature at 10% mass loss, was characterised by dynamic thermogravimetry. It was demonstrated that the selection of refractive index modifier along with UV irradiation plays an important role in tuning the optical and thermal properties of an epoxy-functional inorganic-organic hybrid sol–gel derived thin film system.

Keywords: Organically modified silane; Sol–gel method; UV light; Refractive index; Thermal stability

Laser synthesis of semiconductor nanostructures with narrow band gap by S.A. Mulenko; Y.V. Kudryavtsev; V.P. Mygashko (pp. 7973-7976).

Semiconductor nanostructures with narrow band gap were synthesized by means of laser chemical vapor deposition (LCVD) of elements from iron carbonyl vapors [Fe(CO)₅] under the action of Ar⁺ laser radiation ( λ_L=488nm) on the Si substrate surface. The temperature dependence of the specific conductivity of these nanostructures in the form of thin films demonstrated typical semiconductor tendency and gave the possibility to calculate the band gap for intrinsic conductivity ( E_g) and the band gap assigned for impurities ( E_i), which were depended upon film thickness and applied electrical field. Analysis of deposited films with scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrated their cluster structure with average size not more than 100nm. Semiconductor properties of deposited nanostructures were stipulated with iron oxides in different oxidized phases according to X-ray photoelectron spectroscopy (XPS) analysis.These deposited nanostructures were irradiated with Q-switched YAG laser ( λ_L=1064nm) at power density about 6×10⁷W/cm². This irradiation resulted in the crystallization process of deposited films on the Si substrate surface. The crystallization process resulted in the synthesis of iron carbide–silicide (FeSi2−_xC_x) layer with semiconductor properties too. The width of the band gap E_g of the synthesized layer of iron carbide–silicide was less than for deposited films based on iron oxides Fe₂O3−_x (0≤ x≤1).

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

Photon-assisted synthesis of C₆₀ polymers by laser irradiation by Hiroshi Yamamoto; Nobuyuki Iwata; Ryoji Hashimoto; Shingo Ando (pp. 7977-7980).

The harmonics of a free electron laser (FEL) were irradiated in vacuum to surfaces of compressed C₆₀ and a mixture of C₆₀ and I₂. The power and frequency of the fundamental FEL macro-pulse were ca. 0.5mJ/pulse and 2Hz, respectively. The irradiation time was 120–180min. After irradiation of FEL with a typical wavelength of 450 or 345nm, the Raman peak of Ag(2)-derived vibration mode of C₆₀ shifted to the lower-energy side. The Raman peak shift of the mixture powder sample was greater than that of pure C₆₀. Furthermore, changes of the crystalline structure indicated that various intermolecular combinations occurred by irradiation. These results strongly suggest that three-dimensional polymerization of C₆₀ was promoted by laser irradiation and the effect of photon-assisted hole-doping from iodine atoms to C₆₀ molecules.

Keywords: C; ₆₀; Polymerization; Free electron laser (FEL); Hole-doping; Raman spectroscopy

Bioactive glass and hydroxyapatite thin films obtained by pulsed laser deposition by E. Gyorgy; S. Grigorescu; G. Socol; I.N. Mihailescu; D. Janackovic; A. Dindune; Z. Kanepe; E. Palcevskis; E.L. Zdrentu; S.M. Petrescu (pp. 7981-7986).

Bioactive glass (BG), calcium hydroxyapatite (HA), and ZrO₂ doped HA thin films were grown by pulsed laser deposition on Ti substrates. An UV KrF^* ( λ=248nm, τ≥7ns) excimer laser was used for the multi-pulse irradiation of the targets. The substrates were kept at room temperature or heated during the film deposition at values within the (400–550°C) range. The depositions were performed in oxygen and water vapor atmospheres, at pressure values in the range (5–40Pa). The HA coatings were heat post-treated for 6h in a flux of hot water vapors at the same temperature as applied during deposition. The surface morphology, chemical composition, and crystalline quality of the obtained thin films were studied by scanning electron microscopy, atomic force microscopy, and X-ray diffractometry. The films were seeded for in vitro tests with Hek293 (human embryonic kidney) cells that revealed a good adherence on the deposited layers. Biocompatibility tests showed that cell growth was better on HA than on BG thin films.

Keywords: Bioactive glass; Calcium hydroxyapatite; Pulsed laser deposition

Laser-assisted growth of microstructures on spatially confined substrates by S.I. Dolgaev; N.A. Kirichenko; A.V. Simakin; G.A. Shafeev (pp. 7987-7991).

Laser-assisted growth of microstructures on spatially confined substrates is experimentally studied. The experiments are performed using a copper-vapor laser with pulse duration of 20ns, and repetition rate of 7.5kHz. Ropes made of Ni–Cr wires with diameter of 50–100μm, as well as the edge of 50μm thick Ni foils were exposed to multiple laser pulses. The morphology of structures that grow on these targets drastically differs from periodic array of micro-cones observed on semi-infinite targets made of the same materials. In case of wires the structures have radial symmetry and do not show any periodicity, while in case of a foil the periodic structures are aligned along its edges. The model of micro-structures formation in spatially confined conditions is elaborated based on the numerical solution of the heat conduction and hydrodynamics equations. It is shown that boundary conditions imposed by confined target onto melt flow strongly affect the structure morphology. The micro-structure formation is related to the confinement of melt flow under combined action of both capillary forces and gradients of surface tension.

Keywords: Ni–Cr; Micro-cones; SEM

Comparative interaction mechanisms for different laser systems with selected materials on titanium alloys by M.W. Turner; P.L. Crouse; L. Li (pp. 7992-7997).

This paper describes further research into, and modelling of, the interaction mechanisms of various laser types with materials, including synthetic oil and silicone grease. A Q-switched Nd:YAG pulsed laser, a CW CO₂ laser, and a pulsed KrF excimer laser ( λ=248nm) were used in the study. In general, the materials studied were very absorptive in the ultraviolet, less absorptive in the infrared, and least absorptive in the near-infrared. For the excimer, photo-ablation takes place, while for the other two wavelengths thermal vapourization dominates. In the case of silicone grease, full volatilization is only obtained using the excimer. For the other two wavelengths, this is not the case, with a sticky residue remaining after treatment. Interaction with synthetic oil with its lower boiling point can be obtained for all three laser types. With the Nd:YAG the dominant heating mechanism is conduction from the substrate and a baking effect is observed with strong interaction between the contaminant and the substrate. For the two pulsed lasers, oxidation is substantially less, while for the continuous wave CO₂, the interaction time is sufficiently long for oxidation and secondary reactions to take place if care is not taken to work below the reaction threshold.

Keywords: Laser; Titanium; Surface interaction mechanisms

Combined laser/sol–gel synthesis of calcium silicate coating on Ti–6Al–4V substrates for improved cell integration by N. Mirhosseini; P.L. Crouse; L. Li; D. Garrod (pp. 7998-8002).

New studies have shown that tricalcium silicate powder is a bioactive material and can encourage bone–implant integration. This paper reports the synthesis of Ca₂SiO₄ coating on Ti–6Al–4V samples by laser irradiation under submerged conditions. The results of using a 160–1500 LDL 1.5kW diode laser (rectangular spot=2.5mm×3.5mm, λ=808 and 940nm with equal intensities) is reported. A number of experiments were carried out varying laser parameters, such as scanning speed and laser power. Coatings are evaluated in terms of microstructure, elemental composition (XRD), SEM and wettability. The in vitro biocompatibility of the samples is investigated by monitoring 2T3 osteoblast cell growth on the samples.

Keywords: Laser surface treatment; High power diode laser; Tricalcium silicate; Bioglass; Biocompatibility; SEM; XRD; Wettability; Cell growth; 2T3 Osteoblast cell

Effect of boron concentration on the UV photosensitivity of silica glass film for planar lightwave circuit by Dongwook Shin (pp. 8003-8007).

The photosensitivity dynamics in SiO₂ glass with a composition similar to that of silica planar lightwave circuit (PLC) devices was investigated as a fundamental study prior to device fabrication. Silica bulk glasses with similar composition to the core layer of PLC devices were prepared with various concentrations of B₂O₃. The photosensitivity in boron and germanium co-doped amorphous SiO₂ yields a refractive index change Δ n as high as 10⁻³ after irradiation with a KrF UV laser beam. The index modulation disappeared after thermal annealing. The result of annealing experiment and UV absorption/Raman spectra revealed that the molar volume change by UV irradiation is responsible for the index variation in the material.

Keywords: Silica glass; Photosensitivity; Bragg grating; PLC; Boron co-doping

Analysis of materials modifications caused by UV laser micro drilling of via holes in AlGaN/GaN transistors on SiC by Tim Wernicke; Olaf Krüger; Martin Herms; Joachim Würfl; Holm Kirmse; Wolfgang Neumann; Thomas Behm; Gert Irmer; Günther Tränkle (pp. 8008-8014).

Pulsed UV laser drilling can be applied to fabricate vertical electrical interconnects (vias) for AlGaN/GaN high electron mobility transistor devices on single-crystalline silicon carbide (SiC) substrate. Through-wafer micro holes with a diameter of 50–100μm were formed in 400μm thick bulk 4H–SiC by a frequency-tripled solid-state laser (355nm) with a pulse width of ≤30ns and a focal spot size of ∼15μm. The impact of laser machining on the material system in the vicinity of micro holes was investigated by means of micro-Raman spectroscopy and transmission electron microscopy. After removing the loosely deposited debris by etching in buffered hydrofluoric acid, a layer of <4μm resolidified material remains at the side walls of the holes. The thickness of the resolidified layer depends on the vertical distance to the hole entry as observed by scanning electron microscopy. Micro-Raman spectra indicate a change of internal strain due to laser drilling and evidence the formation of nanocrystalline silicon (Si). Microstructure analysis of the vias’ side walls using cross sectional TEM reveals altered degree of crystallinity in SiC. Layers of heavily disturbed SiC, and nanocrystalline Si are formed by laser irradiation. The layers are separated by 50–100nm thick interface regions. No evidence of extended defects, micro cracking or crystal damage was found beneath the resolidified layer. The precision of UV laser micro ablation of SiC using nanosecond pulses is not limited by laser-induced extended crystal defects.

Keywords: Pulsed UV laser; Laser micro processing; Laser-induced material modifications; AlGaN/GaN; High-electron mobility transistors; Silicon carbide; Via holes; Micro-Raman spectroscopy; Transmission electron microscopy

Tailoring light pulse amplitudes for optimal laser processing and material modification by F.E. Livingston; L.F. Steffeney; H. Helvajian (pp. 8015-8021).

A laser processing technique has been developed for laser direct-write patterning tools that enable site-selective material modification processes on the scale of the laser spot size. The technique controls the delivery of laser energy for optimal laser processing by the dynamic regulation of individual laser pulses to form a prescribed sequence of amplitude-modulated laser pulses. This sequence of amplitude-modulated pulses, called a pulse-script, is then administered to each laser spot size area along a tool path regardless of the stage motion velocity. In our current configuration, up to 32 different pulse-scripts can be independently selected and applied during direct-write patterning at motion velocities exceeding 400mm/s. The novel processing technique seamlessly merges information that depicts the tool path pattern in Cartesian space with the type of material modification and transformation processes that are desired at each laser spot location. This paper describes the fundamental and functional aspects of this new technique. As a demonstration of the technique, a series of variable wavelength attenuators and embedded cutoff filters have been fabricated in a photo-structurable glass ceramic material.

Keywords: Laser processing techniques; Pulse-script; Photo-activation; Laser pulse modulation

SEM/TEM characterization of periodical novel amorphous/nano-crystalline micro-composites obtained by laser interference structuring: The system HAlO–Al·Al₂O₃ by C. Petersen; A. Lasagni; C. Holzapfel; C. Daniel; F. Mücklich; M. Veith (pp. 8022-8027).

Layers of the metastable, amorphous HAlO are synthesized by chemical vapor deposition from the molecular compound tert-butoxyalane ([^tBu–O–AlH₂]₂). At temperatures above 500°C, these layers transform to biphasic Al·Al₂O₃ due to the elimination of di-hydrogen. The interaction of HAlO films with short laser pulses causes partial transformation of amorphous HAlO into nano-crystalline Al·Al₂O₃. Using an interference pattern of two coherent high-power Nd:YAG laser beams produces local and periodic heating, inducing crystallization at equally distant lines in the HAlO layer. Depending on the laser fluence, different morphologies and different amounts of crystalline phases are obtained. In this study, the surface morphology and the distribution of crystalline phases of the structured samples are analyzed using SEM, FIB and TEM. The two-dimensional structures consist of periodic variations of morphology, chemical composition, and phase identity with a well-defined long-range order. When bio-functionalized, the structured samples may be used as carriers for structurally controlled cell-cultivation.

Keywords: Characterization; Nano-crystalline; HAlO film; Nd:YAG laser; Interference; CVD

Polymer films filled with organic molecules by CO₂ laser evaporation in vacuum by K. Grytsenko; O. Lytvyn; L.F. Ivanov; P.N. Grakovich; M. Sonntag; S. Schrader (pp. 8028-8031).

A new p-type of material for organic field-effect transistors (OFETs) is 5,5′-di(9,9′-di-(butyl)-fluorene′)-2,2′-bithiophene (DBFBT). DBFBT films have been prepared by casting, by thermal evaporation in vacuum, and by means of CO₂ laser evaporation. The photon energy from a CO₂ laser is too small to break chemical bonds of the DBFBT molecule, but the heating rate is extremely high. Pressed pellets of powders composed of DBFBT and polychlorotrifluoroethylene (PCTFE) were used as targets for the fabrication of films. These targets were irradiated by a laser beam of 40W cw-power and 0.5cm diameter. The deposition rate was 30–50nm/s. The films have been characterised by optical spectroscopy and by AFM. The structure of DBFBT films produced by casting from solution and thermal deposition is composed of elongated crystals, while the laser deposited layers show cluster structure. By FTIR the films show the absorption band of pure DBFBT, with intensity proportional to the DBFBT concentration in the PCTFE matrix. The absorption bands for a pure DBFBT film, for a film with 22vol.% and with 34vol.% of DBFBT in the PCTFE matrix are situated at 274, 298 and 402nm, where the latter is the most intense one. No significant difference in the band positions of all samples has been found. We concluded that no interaction between chromophore and matrix occurs. The DBFBT molecules in the PCTFE matrix did not oxidize during storage under ambient condition over a period of a year.

Keywords: CO; ₂; laser evaporation; Thin organic film; Fluoropolymer; Cluster; Composite

Organic–inorganic materials for fabrication of integrated optical circuits by J. Jabbour; S. Calas-Etienne; M. Smaïhi; S. Gatti; R. Kribich; G. Pille; Y. Moreau; P. Etienne (pp. 8032-8036).

In the last few years, ORganically MOdified SIlicates (ORMOSILS) [R_xSi(OR)4−_x] prepared by sol–gel process were particularly attractive for integrated optics fabrication. A composition based on 3-(trimethoxysilyl)propylmethacrylate (MAPTMS) has already allowed the industrial fabrication of optical integrated devices. For this kind of materials, the polymerization of the organic network is typical of free radical curing.In this work, we try to obtain waveguides with another hybrid precursor [2-(3,4-epoxycyclohexylethyltrimethoxysilane)] using cationic polymerization. The main advantage of cationic polymerization is its ability to allow spontaneous cure reaction in presence of oxygen, in contrast with radical polymerization. We choose cycloaliphatic compounds because of their well-known high polymerization rates. The polymerization of the organic network of this hybrid material requires a cationic photoinitiator.The purpose of this paper is dedicated to the inorganic part of the material. Hydrolysis and polycondensation are followed by²⁹Si NMR. The main objective is to obtain the highest reactive multifunctional oligomer with the lowest OH groups content.Based on our results, we obtained 3D waveguides with a cross-section of 5μm×5μm.

Keywords: Organic–inorganic; Epoxides; Sol–gel; Waveguides; ²⁹; Si NMR spectroscopy

Reactive pulsed laser deposition of gold nitride thin films by A.P. Caricato; M. Fernàndez; G. Leggieri; A. Luches; M. Martino; F. Romano; T. Tunno; D. Valerini; A. Verdyan; Y.M. Soifer; J. Azoulay; L. Meda (pp. 8037-8040).

We report on the growth and characterization of gold nitride thin films on Si 〈100〉 substrates at room temperature by reactive pulsed laser ablation. A pure (99.95%) Au target was ablated with KrF excimer laser pulses in nitrogen containing atmosphere (N₂ or NH₃). The gas ambient pressure was varied in the range 0.1–100Pa. The morphology of the films was studied by using optical, scanning electron and atomic force microscopy, evidencing compact films with RMS roughness in the range 3.6–35.1nm, depending on the deposition pressure. Rutherford backscattering spectrometry and energy dispersion spectroscopy (EDS) were used to detect the nitrogen concentration into the films. The EDS nitrogen peak does not decrease in intensity after 2h annealing at 250°C. Film resistivity was measured using a four-point probe and resulted in the (4–20)×10⁻⁸Ωm range, depending on the ambient pressure, to be compared with the value 2.6×10⁻⁸Ωm of a pure gold film. Indentation and scratch measurements gave microhardness values of 2–3GPa and the Young's modulus close to 100GPa. X-ray photoemission spectra clearly showed the N 1s peak around 400eV and displaced with respect to N₂ phase. All these measurements point to the formation of the gold nitride phase.

Keywords: Young's modulus; Gold nitride thin films; X-ray photoemission spectroscopy; Reactive laser ablation

Free electron laser nitriding of metals: From basis physics to industrial applications by D. Höche; G. Rapin; J. Kaspar; M. Shinn; P. Schaaf (pp. 8041-8044).

Titanium was laser nitrided by means of free-electron laser irradiation in pure nitrogen atmosphere. The variation of pulse frequency and macropulse duration of the free electron laser resulted in δ-TiN_x coatings with different thickness and different micro- and macroscopic morphologies. The coatings revealed, characteristic values for hardness, roughness and crystallographic texture, which originate from the growth mechanism, the solid–liquid interface energy and the strain. Further investigations showed that the dendritic growth is beginning at the surface and that the alignment of dendrites is normal to the surface. A correlation of the texture with the time structure of the laser pulses was found. Numerical simulations were performed and compared with the experimental results. The simulations can explain the experimental results.

Keywords: PACS; 81.65.Lp; 52.50.Jm; 61.80.Ba; 76.80.+yLaser surface treatment; Nitrides; Laser plasma; Reactive laser treatment; Laser nitriding; Titanium

Synthesis of nanoparticles and suspensions by pulsed laser ablation of microparticles in liquid by Dongsik Kim; Deoksuk Jang (pp. 8045-8049).

Recent studies demonstrated that the process to produce metal and oxide nanoparticles by laser ablation of consolidated microparticles is a convenient and energy-efficient way to prepare nanoparticles. In this work, the novel process is applied to nanoparticle synthesis in the liquid environment and the results are compared with those by the gas-phase process. Metal and oxide nanoparticles are synthesized by pulsed laser ablation of the compacted metal microparticles using a Q-switched Nd:YAG laser in water. It is shown that the process is effective for preparing nanoparticle suspensions having relatively uniform size distributions. While the laser fluence and the degree of compaction strongly influence the size of the produced nanoparticle in air, the sedimentation time is shown to be the most critical factor to determine the mean size of the suspended particles.

Keywords: Liquid-phase synthesis; Nanoparticle synthesis; Metal microparticles; Pulsed laser ablation

The influence of shielding gas in hybrid LASER–MIG welding by Giovanni Tani; Giampaolo Campana; Alessandro Fortunato; Alessandro Ascari (pp. 8050-8053).

Hybrid LASER-GMAW welding technique has been recently studied and developed in order to meet the needs of modern welding industries. The two sources involved in this process play, in fact, a complementary role: fast welding speed, deep bead penetration and high energy concentration can be achieved through the LASER beam, while gap bridgeability and cost-effectiveness are typical of the GMAW process.Particularly interesting, in this context, is the CO₂ LASER–MIG welding which differs from the Nd:YAG LASER–MIG technique for the high powers that can be exploited and for the good power/cost ratio of the process.This paper is a part of a wide study on the hybrid CO₂ LASER–MIG welding and investigates the influence of the shielding gas both on the stability of the process and on the dimensional characteristics of the weld bead. Two different parameters have been taken into consideration in order to develop this analysis: the shielding gas composition and the shielding gas flow.The experiment, performed on AISI 304 stainless steel plates, has been planned exploiting design of experiment techniques. The results have been analyzed through a statistical approach in order to determine the real influence of each parameter on the overall process.

Keywords: Hybrid welding; Shielding gas; GMAW; Laser; Stainless steel welding

Effects of transverse magnetic field on a laser-produced Zn plasma plume and ZnO films grown by pulsed laser deposition by Tae Hyun Kim; Sang Hwan Nam; Hye Sun Park; Jae Kyu Song; Seung Min Park (pp. 8054-8058).

By adopting a fast photography and time-resolved optical emission spectrometry, we have investigated the effects of transverse magnetic field on the expansion dynamics and enrichment of Zn atoms and Zn⁺ ions in a plume produced by laser ablation of a Zn target in oxygen atmosphere. Plume splitting due to the magnetic field was apparent but the splitting patterns of Zn and Zn⁺ were totally different. The surface morphology and photoluminescence characteristics also changed significantly. In particular, the growth rate increased by as much as 2.4–4.3 times compared to the conventional PLD method.

Keywords: PACS; 79.20.Ds; 52.50.JmLaser ablation; Laser-induced plasma; Magnetic field

Fabrication of 550nm gratings in fused silica by laser induced backside wet etching technique by Cs. Vass; K. Osvay; M. Csete; B. Hopp (pp. 8059-8063).

A series of 550nm spacing gratings were fabricated in fused silica by laser induced backside wet etching (LIBWE) method using the fourth harmonic of a Q-switched Nd:YAG laser (wavelength: λ=266nm; pulse duration: FWHM=10ns). During these experiments we used a traditional two-beam interference method: the spatially filtered laser beam was split into two parts, which were interfered at a certain incident angle (2 θ=28°) on the backside surface of the fused silica plate contacting with the liquid absorber (saturated solution of naphthalene-methyl-methacrylate c=1.85mol/dm³). We studied the dependence of the quality and the modulation depth of the prepared gratings on the applied laser fluence and the number of laser pulses. The surface of the etched gratings was characterized by atomic force microscope (AFM). The maximum modulation depth was found to be 180–200nm. Our results proved that the LIBWE procedure is suitable for production of submicrometer sized structures in transparent materials.

Keywords: Laser induced backside wet etching; Two-beam interference; Grating fabrication

Parametric analysis of the selective laser melting process by I. Yadroitsev; Ph. Bertrand; I. Smurov (pp. 8064-8069).

Selective laser sintering/melting (SLS/SLM) technology is used for manufacturing net-shaped objects from commercial Inox 904L powder with ≤20μm particle size. Experiments were carried out on PHENIX-PM100 machine equipped with a 50W cw fiber laser. Powder is layered by a roller over the surface of a 100mm-diameter build cylinder. Optimal parameters of layer thickness and power input per unit speed for SLM were determined. It was shown that the greater the value of P/ V ratio is, the larger is the remelted line (called as “vector”). Influence of the shifting of consecutive single vectors on the process of forming the first layer was studied. Different strategies for forming objects with less than 1mm-sized inner structures were tested, as, for example, forming a 20mm×20mm×5mm box with 140μm-thick inner compartment walls.

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

Laser interference metallurgy: A new method for periodic surface microstructure design on multilayered metallic thin films by A. Lasagni; C. Holzapfel; T. Weirich; F. Mücklich (pp. 8070-8074).

Methods for micro- and nanostructuring are essential for functionalization of materials surfaces. In particular, photon-assisted methods for synthesis of functional surfaces have been intensively investigated in the last years. In this study, a new method for surface modification and production of long-range order periodical structures called “laser interference metallurgy” is explored. A metallic thin film sample consisting of three layers composed of Fe, Cu and Al (from top to bottom) on a glass substrate was irradiated with an interference pattern using a Nd:YAG laser (wavelength of 355nm, 10ns of pulse duration). For the interference pattern, a configuration producing a line-type energy distribution was chosen. The laser fluence was high enough to melt the aluminium and copper layers at the interference maxima but the iron layer remained in the solid state. Thus, diffusive and convective exchange occurred between aluminium and copper at the energy maxima positions leading to periodical alloy formation with a long-range order. Because it remained in solid state, the iron layer at the top acted as a protective layer effectively preventing removal of the molten layers. The interaction of the different layers was characterized using FIB, TEM and EDX in STEM mode.

Keywords: Laser interference metallurgy; Alloying; Metallic thin films

Single- and multi-pulse formation of surface structures under static femtosecond irradiation by M. Guillermin; F. Garrelie; N. Sanner; E. Audouard; H. Soder (pp. 8075-8079).

Femtosecond surface structure modifications are investigated under irradiation with laser pulses of 150fs at 800nm, on copper and silicon. We report sub-wavelength periodic structures formation (ripples) with a periodicity of 500nm for both materials. These ripples are perpendicular to the laser polarization and can be obtained with only one pulse. The formation of these ripples corresponds to a fluence threshold of 1J/cm² for copper and 0.15J/cm² for silicon. We find several morphologies when more pulses are applied: larger ripples parallel to the polarization are formed with a periodicity of 1μm and degenerate into a worm-like morphology with a higher number of pulses. In addition, walls of deep holes also show sub-wavelength and large ripples.

Keywords: Ripples; Morphology; Laser

Metal nanoparticle production by pulsed laser nanostructuring of thin metal films by S.J. Henley; J.D. Carey; S.R.P. Silva (pp. 8080-8085).

The controllable nanostructuring of thin metal films by nanosecond UV laser pulses is introduced as a novel technique for the production of metal nanoparticles supported on a range of different oxide substrates, including indium tin oxide. This processing is performed at low macroscopic temperatures. The physical mechanisms underlying the nanostructuring are discussed and applications for these nanoparticle films, including as catalysts for nanotube/nanowire growth and in surface enhanced Raman spectroscopy measurements, are introduced.

Keywords: Metal nanoparticles; Laser processing; Catalyst film; Surface enhanced Raman

Fabrication of grating structures by simultaneous multi-spot fs laser writing by R.J. Winfield; B. Bhuian; S. O’Brien; G.M. Crean (pp. 8086-8090).

Two-photon polymerisation is an established technique for the fabrication of three-dimensional microstructures. To date structures have mostly been developed using single beam serial writing. A novel approach to simultaneous multi-spot two-photon polymerisation, that uses a SiO₂ on glass Fraunhofer diffractive optical element to generate an array of beamlets, is described. A Ti:sapphire laser, with wavelength 790nm, 80MHz repetition rate, 100fs pulse duration and an average power of 25mW, was used to initiate two-photon polymerisation. The DOE, in combination with a high power microscope objective, efficiently transforms the laser beam into a linear array of four spots of equal intensity. The fabrication of a periodic transmission grating, using parallel processing with these four spots, is shown. The grating was written in a Zr-loaded resin prepared on a glass substrate using dip coating deposition of a Zr/PMMA hybrid prepared by the sol–gel method. The operation of the diffractive element and the performance of the diffraction grating are also discussed.

Keywords: Two-photon polymerisation; Diffractive optics; Sol–gel

Indirect laser etching of fused silica: Towards high etching rate processing by R. Böhme; K. Zimmer (pp. 8091-8096).

The indirect laser processing approach (LIBWE) laser-induced backside wet etching allows defined microstructuring of transparent materials at low laser fluences with high quality. The optical and the thermal properties of the solid/liquid interface determine the temperatures and therefore the etching mechanism in conjunction with the dynamic processes at the interface due to the fast heating/cooling rates. The exploration of organic liquid solvents and solutions such as 0.5M pyrene/toluene results in low etch rates (∼20nm/pulse). By means of liquid metals as absorber here, demonstrated for gallium (Ga), etch rates up to 600nm/pulse can be achieved. Regardless of the high etch rates a still smooth surface similar to etching with organic liquid solutions can be observed. A comparative study of the two kinds of absorbing liquids, organic and metallic, investigates the etch rates regarding the fluence and pulse quantity. Thereby, the effect of incubation processes as result of surface modification on the etching is discussed. In contrast to pyrene/toluene solution the metallic absorber cannot decompose and consequently no decomposition products can alter the solid/liquid interface to enhance the absorption for the laser radiation. Hence, incubation can be neglected in the case of the silica/gallium interface so that this system is a suitable model to investigate the primary processes of LIBWE. To prove the proposed thermal etch mechanism an analytical temperature model based on a solution of the heat equation is derived for laser absorption at the silica/gallium interface.

Keywords: Laser; Fused silica; LIBWE; Etching; Transparent material; Gallium; Organic liquid; Etch mechanism; Surface modification; Solid/liquid interface

Pulsed laser deposition of doped skutterudite thin films by D. Colceag; A. Dauscher; B. Lenoir; V. Da Ros; R. Birjega; A. Moldovan; M. Dinescu (pp. 8097-8101).

Ca_xCo₄Sb₁₂ skutterudite thin films have been prepared by pulsed laser deposition using a Nd:YAG laser working at 532 or 266nm of wavelength. Characterization has been carried out by X-ray diffraction, atomic force microscopy and scanning electron microscopy. Emphasis has been put on the difficulty to obtain the skutterudite phase. Influence of the deposition temperature, the way of sticking the substrate, the laser fluence, the base pressure prior to deposition and the laser wavelength has been studied. All parameters revealed to have a drastic effect, and the skutterudite could only be achieved in a very narrow range of temperature and laser fluence, for a given wavelength, showing the importance on how these parameters are measured to ensure reproducible results.

Keywords: Skutterudite thin films; Pulsed laser deposition; XRD; AFM

Pulsed laser deposition of Co-based Tailored-Heusler alloys by C.E.A. Grigorescu; E. Valerio; O. Monnereau; L. Tortet; L. Argeme; G. Pavelescu; S.A. Manea; C. Ducu; A. Malinovski; H.J. Trodahl; A. Bittar; N. Strickland; R. Notonier; W.R. Branford; M. Autric (pp. 8102-8106).

Thin films of nonstoichiometric Heusler alloys Co₂MnSb_xSn1−_x ( x=0.2; 0.4; 0.6; 0.8) have been grown by pulsed laser deposition (double-target/double beam configuration) on Si (100) substrates using a KrF excimer laser ( λ=248nm, τ=20ns). The substrate temperature was held at 300K in all experiments to prevent interface interdiffusion of the species. A comparison between the compositions of films and corresponding targets has been done through energy dispersive X-ray spectroscopy (EDS) analysis showing a very satisfactory match. Scanning electron microscopy (SEM) imaging served to investigate the morphology of the films in order to determine the size and density of droplets which may influence the optical data. Optical conductivity derived from reflectivity measurements shows absorption onsets close to 1eV, which corresponds to the onset of valence-to-conduction transitions in the minority spin bands theoretically predicted. The values of the saturation magnetisation measured at 300K on the quaternary alloys are very close to those of ternary ones for which either half-metallic properties or high spin polarisation were theoretically predicted.

Keywords: Quaternary; Alloys; Ternary

Structure and anisotropy of epitaxial fcc FePt films by P. Schaaf www.schaaf.physik.uni-goettingen.de; K. Zhang; C. Lange; A. Holz; M. Weisheit; S. Fähler (pp. 8107-8110).

Pulsed laser deposition (PLD) was used to deposit FePt films onto single crystalline MgO substrates. When deposited at room temperature, films grow epitaxial within the A1 phase. Structure and magnetic properties were examined by X-ray diffraction, Rutherford Backscattering Spectrometry (RBS), magneto-optic Kerr effect, Mössbauer spectroscopy, and Magnetic Orientation Mössbauer Spectroscopy (MOMS). These measurements allow to exclude local ordering and reveal the anisotropic intrinsic and extrinsic magnetic properties. These results are discussed with respect to the texture and microstructure of these films.

Keywords: PACS; 81.65.Lp; 52.50.Jm; 61.80.Ba; 76.80.+yPulsed laser deposition (PLD); Iron platinum (FePt); Magnetic anisotropy; Atomic ordering; L; 1; ₀; ordering; Magnetic anisotropy; Epitaxy; Magnetic Orientation Mössbauer Spectroscopy (MOMS)

Femtosecond laser synthesized nanohybrid materials for bioapplications by Cs.L. Sajti; S. Giorgio; V. Khodorkovsky; W. Marine (pp. 8111-8114).

Hybrid nanomaterials were synthesized by adopting femtosecond laser ablation of a ZnO target in pure ethanol. Dye molecules were grafted onto the ZnO nanoparticles by mixing colloidal ZnO–ethanol solution prepared by laser ablation to Tetramethylrhodamine B isothiocyante, or to Rhodamine B solutions. Strongly facetted nanohybrid particles were observed with an average size of 15nm, by HRTEM measurements. From photoluminescence spectroscopy of the nanohybrids after single and multiphoton excitations, we observed energy transfer from the ZnO nanoparticles towards the attached dye molecules. Moreover, IR excitation spectra of the hybrid nanomaterials reveal the emission of the grafted dye via two photon absorption of the ZnO.

Keywords: Hybrid nanomaterials; IR excitation spectra; Absorption

Three-dimensional biomolecule patterning by Maria Farsari; George Filippidis; Theodore S. Drakakis; Kyriaki Sambani; Savas Georgiou; George Papadakis; Electra Gizeli; Costas Fotakis (pp. 8115-8118).

A new method is demonstrated, where three-dimensional protein structures are made by employing multi-photon polymerization and photobiotin photolysis. The technique enables the construction of arbitrary two- and three-dimensional shapes with submicron resolution. The integrity of the immobilized biotin is confirmed by derivatization with fluorescently labeled streptavidin. Fluorescence microscopy is used in order to visualize the distribution of fluorescent streptavidin on the 3D structure.

Keywords: Photopolymerization; Biotin; Nonlinear stereolithography

Printing technologies for fabrication of bioactive and regular microarrays of streptavidin by C.Z. Dinu; V. Dinca; J. Howard; D.B. Chrisey (pp. 8119-8124).

In this study, we report and compare two methods for fabricating patterns of streptavidin protein using soft litography microprinting technique (μCP) and laser-based method termed ‘matrix assisted pulsed laser evaporation direct write’ (MAPLE DW). The μCP approach is a parallel deposition technique capable of X depositions per stamper. The technique is limited in more sophisticated multicomponent deposition by the size of patterns that can be produced and the features obtained during the transfer process. The computer-aided design/computer-aided manufacturing (CAD/CAM) ability of MAPLE DW overcomes the limitations of the μCP approach. (i) We establish the science and engineering principles behind the effective transfer of microarrays and (ii) we explore issues regarding the direct immobilization, morphology and function of the deposited protein at the interface with an aqueous environment and in the precision of controlled ligand-receptor reactions. In summary, our objective was to develop simple, robust microfabrication techniques for the construction of model 2D and 3D bioscaffolds to be used in fundamental bioengineering studies.

Keywords: Bioengineering studies; Ligand-receptor; Microfabrication

Novel photonic technique creates micrometer resolution protein arrays and provides a new approach to coupling of genes, peptide hormones and drugs to nanoparticle carriers by M. Duroux; L. Duroux; M.T. Neves-Petersen; E. Skovsen; S.B. Petersen www.bionanophotonics.com (pp. 8125-8129).

We demonstrate that ultraviolet light can be used to make sterically oriented covalent immobilization of a large variety of protein molecules onto either thiolated quartz, gold or silicon. The reaction mechanism behind the reported new technology involves light-induced breakage of disulphide bridges in proteins upon UV illumination of nearby aromatic amino acids, resulting in the formation of free, reactive thiol groups that will form covalent bonds with thiol reactive surfaces. In general, the protein molecules retain their function. The size of the immobilization spot is limited to the focal point of illumination being as small as a few micrometers. This new technology allows for dense packing of different bio-molecules on a surface, allowing the creation of multi-potent functionalised new materials, such as nano-biosensors. We have developed the necessary technology for preparing large protein arrays of enzymes and fragments of monoclonal antibodies. Dedicated image processing software has been developed for making quality assessment of the protein arrays. This novel technology is ideal to couple drugs and other bio-molecules to nanoparticles which can be used as carriers into cells for therapeutic purposes.

Keywords: Light-assisted protein immobilization; UV light; Disulphide bridges; Micro-arrays; Micro-dispensing; Nanoparticles

Pulsed laser deposition of tungsten and tungsten oxide thin films with tailored structure at the nano- and mesoscale by A. Bailini; F. Di Fonzo; M. Fusi; C.S. Casari; A. Li Bassi; V. Russo; A. Baserga; C.E. Bottani (pp. 8130-8135).

Nanostructured thin films synthesized by assembling atoms or clusters present a structure characterized by a modulation at the nanoscale and by a large effective area, which can be exploited for the tailoring of specific structural or electronic properties. These systems are appealing for functional applications, e.g. in sensing and catalysis. We have investigated the deposition of tungsten and tungsten oxide thin films with a wide range of morphologies by exploiting nanosecond pulsed laser deposition (PLD) in an inert background atmosphere (He, Ar and Kr). We show that the non-dimensional ratio of the target-to-substrate distance to the time integrated visible plume length, which depends on the gas mass and pressure and on the substrate position, permits to select morphologies ranging from a compact structure with a density similar to bulk, to a film with an open, low density foam-like mesostructure and a high fraction of voids.

Keywords: PLD; Nanostructured thin films; Tungsten; Tungsten oxide

Vanadium–Al₂O₃ nanostructured thin films prepared by pulsed laser deposition: Optical switching by S. Núñez-Sánchez; R. Serna; M. Jiménez de Castro; J. García López; A.K. Petford-Long; J.F. Morhange (pp. 8136-8140).

The formation and optical response of VO_x nanoparticles embedded in amorphous aluminium oxide (Al₂O₃) thin films by pulsed laser deposition is studied. The thin films have been grown by alternate laser ablation of V and Al₂O₃ targets, which has resulted in a multilayer structure with embedded nanoparticles. The V content has been varied by changing the number of pulses on the V target. It is found that VO_x nanoparticles with dimensions around 5nm have been formed. The structural analysis shows that the vanadium nanoparticles are oxidized, although probably there is not a unique oxide phase for each sample. The films show a different optical response depending on their vanadium content. Optical switching as a function of temperature has been observed for the two films with the highest vanadium content, at transition temperatures of about −20°C and 315°C thus suggesting the presence of nanoparticles with compositions V₄O₇ and V₂O₅, respectively.

Keywords: Nanoparticles; Vanadium; Pulsed laser deposition; Optical switching

Substrate temperature influence on the properties of nanostructured ZnO transparent ultrathin films grown by PLD by M. Suchea; S. Christoulakis; M. Katharakis; G. Kiriakidis; N. Katsarakis; E. Koudoumas (pp. 8141-8145).

Zinc oxide films of 40nm thickness have been deposited on glass substrates by pulsed laser deposition using an excimer XeCl laser (308nm) at different substrate temperatures ranging from room temperature to 650°C. Surface investigations carried out by using atomic force microscopy have shown a strong influence of temperature on the films surface topography. UV–VIS transmittance measurements have shown that our ZnO films are highly transparent in the visible wavelength region, having an average transmittance of ∼90%. The optical band gap of the films was found to be 3.26eV, which is lower than the theoretical value of 3.37eV. Besides the normal absorption edge related to the transition between the valence and the conduction band, an additional absorption band was also recorded in the wavelength region around 364nm (∼3.4eV). This additional absorption band may be due to excitonic, impurity, and/or quantum size effects. Photoreduction/oxidation in ozone of the ZnO films lead to larger conductivity changes for higher deposition temperature. In conclusion, the ozone sensing characteristics as well as the optical properties of the ZnO thin films deposited by pulsed laser deposition are strongly influenced by the substrate temperature during growth. The sensitivity of the films towards ozone might be enhanced significantly by the control of the films deposition parameters and surface characteristics.

Keywords: PACS; 81.15.Fg; 68.55.−a; 68.55.Ac; 68.60.−p; 68.37.Ps; 73.50.−h; 78.20.−ePulsed laser deposition; Thin films; Zinc oxide; Surface properties; Conductivity

Enhanced luminescent characteristics of laser-ablated GdVO₄:Eu³⁺ thin films by Li-doping by Kyoo Sung Shim; Hyun Kyung Yang; Ye Ran Jeong; Byung Kee Moon; Byung Chun Choi; Jung Hyun Jeong; Jong Seong Bae; Soung Soo Yi; Jung Hwan Kim (pp. 8146-8150).

Li-doping has been used to improve luminescent characteristics of thin films. Influence of Li-doping on the crystallization, surface morphology and luminescent properties of GdVO₄:Eu³⁺ films have been investigated. Crystallinity and surface morphology of thin films have been very important factors to determine luminescent characteristics and depended on the deposition conditions. The GdVO₄:Eu³⁺ and Li-doped GdVO₄:Eu³⁺ thin films have been grown using pulsed laser deposition method on Al₂O₃ (0001) substrates at a substrate temperature of 600°C under an oxygen pressure of 13.33–53.33Pa. The crystallinity and surface morphology of the films were investigated using X-ray diffraction (XRD) and atomic force microscope (AFM), respectively. A broadband incoherent ultraviolet light source with a dominant excitation wavelength of 310nm and a luminescence spectrometer have been used to measure photoluminescence spectra at room temperature. The emitted radiation was dominated by the red emission peak at 619nm radiated from the transition of⁵D₀–⁷F₂ of Eu³⁺ ions. Particularly, the peak intensity of Li-doped GdVO₄ films was increased by a factor of 1.7 in comparison with that of GdVO₄:Eu³⁺ films. The enhanced luminescence results not only from the improved crystallinity but also from the reduced internal reflections caused by rougher surfaces. The luminescent intensity and surface roughness exhibited similar behavior as a function of oxygen pressure.

Keywords: PACS; 78.20−e; 78.55−m; 78.66−wGdVO; ₄; :Eu; ³⁺; Li-doping; Thin film phosphors; Surface morphology; Photoluminescence

Pulsed laser deposition of aluminum nitride thin films for FBAR applications by C. Cibert; M. Chatras; C. Champeaux; D. Cros; A. Catherinot (pp. 8151-8154).

Aluminum nitride thin films have been deposited by pulsed laser deposition on fused silica, Si (100) and Mo(110)-coated Si substrates. FTIR measurements show that only pure AlN phase is present in films, confirmed by UV-V spectroscopy where a strong absorption peak occurs at 206nm, characteristic of AlN. C-axis oriented films have been obtained at a temperature of 800°C on Si (100) substrate, and at a temperature of 200°C on Mo(110)-coated Si substrates. AFM experiments show that AlN film surface is very smooth (3.0nm rms) without any particulate and droplet.

Keywords: Aluminum nitride; Pulsed laser deposition; Film Bulk Acoustic wave Resonator

Pulsed laser deposition of amorphous carbon/silver nanocomposites by G. Matenoglou; G.A. Evangelakis; C. Kosmidis; S. Foulias; D. Papadimitriou; P. Patsalas (pp. 8155-8159).

Metal/amorphous carbon (a-C:M) composite films are emerging as a category of very important engineering materials for surface protection. We implement pulsed laser deposition (PLD) to grow pure a-C and a-C:Ag nanocomposites. Our PLD process is assisted by a static electric field. We investigate the structural features of the a-C:Ag nanocomposites and the bonding configuration of the a-C matrix with respect to the electric field and the composition of the PLD target. For this study we use Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS) and X-ray diffraction (XRD). We show that the Ag mean grain size and the sp² content of the a-C matrix are increasing with increasing Ag content in the films.

Keywords: Pulsed laser deposition; Carbon; Composite

The dependence of the size distribution of the pulsed laser deposited micron sized particles from the laser fluence and its influence to the thickness of the deposited layer by N. Kresz; T. Smausz; B. Hopp (pp. 8160-8164).

During the pulsed laser deposition of Teflon the thin layer is built up by particles with dimensions from molecular to micrometer range deposited onto the substrate surface. With the knowledge of the size distribution of the deposited particles we used a model for simulating and predicting the growth of the thin film. An ArF excimer laser was used to deposit Teflon particles on the surface of a Silicon wafer under real PLD conditions. The target was pre-ablated by 1000 pulses, the pressure in the PLD chamber was 2×10⁻⁵Torr and the substrate temperature was 250°C. The number of the particulates deposited by 10 laser pulses and their size distribution were determined by atomic force (AFM) and optical microscopes. Based on the AFM images the relation between the dimensions and volume of the investigated grains was also determined. At 3.2J/cm² laser fluence the size distribution of the particulates with dimensions above 500nm could be well described with a first order exponential decay function having 2.38μm decay constant. Below 100nm the number of deposited Teflon grains increased by several orders of magnitude, however, their contribution to the total volume of the transferred material was found to be only about 2%. The results of the numerical simulations of the thin film growth were in good agreement with our previous PLD experiments. The minimum number of the pulses required to obtain a contiguous layer and its thickness could also be estimated.

Keywords: PACS; 52.38.Mf; 81.15.Fg; 81.15.Aa; 68.55.Jk; 07.79.Lh; 81.05.LgPulsed laser deposition; Ablation; Thin film growth; Polytetrafluoroethylene; Atomic force microscope

Rare-earth implanted Y₂O₃ thin films by A. Peeva; A.Og. Dikovska; P.A. Atanasov; M. Jiménez de Castro; W. Skorupa (pp. 8165-8168).

Thin Er, Yb co–doped Y₂O₃ films were grown by pulsed laser deposition from ceramic target. Subsequent ion implantation with 1.1MeV Er⁺ ions to a fluence of 6×10¹⁴at/cm² at room temperature was performed in order to modify the structure of the as-deposited films. The as-deposited films have a polycrystalline column-like structure. Ion implantation induces defects into the as-deposited films. After annealing at 900°C for 1h in oxygen atmosphere, the films recrystallize in roundly shaped grain-like structure with grain size of about 100nm. The Er³⁺ photoluminescence response was obtained for all the films by excitation through cross-relaxation of Yb³⁺ ions. The IR emission spectrum, consisting of two narrow peaks at 1415 and 1514nm, differs from the typical spectra of Er-doped materials. The VIS emission spectrum observed in as-deposited films does not appear after implantation and subsequent 900°C annealing.

Keywords: Rare-earth implanted thin films; Y; ₂; O; ₃; PLD

Europium and samarium doped calcium sulfide thin films grown by PLD by S. Christoulakis; M Suchea; N. Katsarakis; E Koudoumas (pp. 8169-8173).

Europium and samarium doped calcium sulfide thin films (CaS:Eu,Sm) with different thickness were prepared by the pulsed laser deposition technique using sintered targets. A typical homemade deposition chamber and XeCl excimer laser (308nm) were employed and the films were deposited in helium atmosphere onto silicon and corning glass substrates. Structural investigations carried out by X-ray diffraction and atomic force microscopy showed a strong influence of the deposition parameters on the film properties. The films grown had an amorphous or polycrystalline structure depending on growth temperature and the number of pulses used, the same parameters affecting the film roughness, the grain shape and dimensions, the film thickness and the optical transmittance. This work indicates that pulsed laser deposition can be a suitable technique for the preparation of CaS:Eu,Sm thin films, the film characteristics being controlled by the growth conditions.

Keywords: PACS; 81.15.Fg; 68.55.−a; 68.55.Ac; 68.60.−p; 68.37.Ps; 61.10.Nz; 78.20.−e; 81.05.−tPulsed laser deposition; Thin films; Phosphor materials; Surface properties

The effect of the fluence on the properties of La–Ca–Mn–O thin films prepared by pulsed laser deposition by S. Canulescu; Th. Lippert; A. Wokaun; M. Döbeli; A. Weidenkaff; R. Robert; D. Logvinovich (pp. 8174-8178).

Thin films of La_0.6Ca_0.4MnO_3−δ were deposited on SrTiO₃(100) by PRCLA (Pulsed Reactive Crossed-Beam Laser Ablation). The dependence of the structural and transport properties of the films on the laser fluence and different target to substrate distances during the growth are studied. Both parameters have a direct influence on the films thickness and velocity of the ions arriving at the substrate, which influence the film properties directly.The surface roughness of the La_0.6Ca_0.4MnO_3−δ thin films is depending mainly on the laser fluence and less on the target-substrate distance. Lower laser fluences and therefore lower growth rates yield film with lower roughness, i.e. in the range of 0.2nm. The electronic transport measurements show a decrease of the transition temperature from metal to semiconductor with an increase of the target to substrate distance. This is related to an increase of the films thickness and therefore decrease of the strain in the films due to the lattice mismatch with the substrate. The magnetoresistance values are also strongly affected by the tensile strain, i.e. they increase for higher strained films.

Keywords: PRCLA; PLD; Magnetoresistance; Manganite

AFM and complementary XRD measurements of in situ grown YBCO films obtained by pulsed laser deposition by M. Brănescu; A. Vailionis; J. Huh; A. Moldovan; G. Socol (pp. 8179-8183).

We report an optimized kinetic regime to grow in situ YBa₂Cu₃O7−_δ (YBCO) films on LaAlO₃ substrates, by pulsed laser deposition (PLD), which is technically more advantageous than the usual one. Atomic force microscope (AFM) pictures show that the in situ grown YBCO films have much smoother surfaces than the post-deposition annealed YBCO films. The influence of the substrate's surface quality and that of the pulsed laser fluence used in the deposition process on the surface quality and on the critical temperature ( T_C) of the in situ YBCO films are described. For measurements we utilized the atomic force microscopy and X-ray diffraction (XRD) techniques.

Keywords: In situ; PLD growth; YBCO films; LaAlO; ₃; substrate; AFM; XRD

High-k dielectric oxides obtained by PLD as solution for gates dielectric in MOS devices by M. Filipescu; N. Scarisoreanu; V. Craciun; B. Mitu; A. Purice; A. Moldovan; V. Ion; O. Toma; M. Dinescu (pp. 8184-8191).

The aim of this work was to find the suitable high-k dielectric compound to be used as gate dielectric in MOS devices. Thin films of zirconia (ZrO₂), zirconium silicate (ZrSi_xO_y), hafnia (HfO₂) and hafnium silicate (HfSi_xO_y) with thickness in the nanometer range have been obtained by pulsed laser deposition (PLD), assisted or not by radio-frequency discharge.For thin films of ZrO₂ and HfO₂, high purity targets of metallic Zr and Hf, respectively, have been ablated in oxygen reactive atmosphere. Alternative ablation of Zr and Si, respectively, Hf and Si targets in oxygen reactive atmosphere was used to obtain thin films of ZrSi_xO_y and HfSi_xO_y. Laser fluence (3–6J/cm²), oxygen pressure (10⁻³ to 10⁻¹mbar) and laser wavelength (355 and 532nm) were varied during deposition.The thin films were investigated using X-ray diffraction, atomic force microscopy (AFM) and secondary ion mass spectroscopy, electrical characterization. Low leakage current values (in the range of 10⁻³ to 10⁻⁷A/cm²) were measured for all thin films deposited by radio-frequency beam assisted pulsed laser deposition (RF-PLD). Scanning electron microscopy (SEM) and atomic force microscopy investigations showed surface roughness of the order of a few angstroms, for films deposited by RF-PLD.

Keywords: ZrO; ₂; ZrSi; _x; O; _y; HfO; ₂; HfSi; _x; O; _y; Pulsed laser deposition; Leakage current; Atomic force microscopy

Thin films of NdFeB deposited by PLD technique by C. Constantinescu; N. Scarisoreanu; A. Moldovan; M. Dinescu; L. Petrescu; G. Epureanu (pp. 8192-8196).

Neodymium–iron–boron (NdFeB) is a material with important magnetic properties, mostly used in permanent magnet fabrication. Thin layers of NdFeB are needed for miniaturization in electrical engineering, electronics and for high-tech devices.In this paper we applied pulsed lased deposition (PLD) in vacuum for obtaining thin films of NdFeB from stoichiometric targets. The influence of different buffer layers and of the laser parameters (wavelength and fluence) on the NdFeB structures, composition and magnetic properties have been investigated.The obtained structures were characterized by atomic force microscopy (AFM) and optical microscopy. Vibrating sample magnetometry (VSM) has been performed for specific magnetic characterization.

Keywords: NdFeB; PLD technique; Wavelength

Carbon nitride films of uniform thickness by inverse PLD by L. Egerhazi; Zs. Geretovszky; T. Szörényi (pp. 8197-8200).

In the present contribution we report on a target–substrate arrangement to considerably improve the homogeneity of films produced in the static-substrate inverse pulsed laser deposition (IPLD) configuration.Carbon nitride films were grown in a modified IPLD geometry, by holding a silicon substrate in the target plane and jointly rotating it with the target at 5.5rpm. The graphite target was ablated by KrF excimer laser pulses in nitrogen atmosphere of 5Pa pressure. The laser fluence was kept at a constant value (∼7J/cm²) in each experiment. Typically a 1cm×1cm large silicon substrate was fixed to the target within the ablated track of approx. 10mm radius. The thickness distribution of the films was measured by profilometry on masked steps. The maximum relative deviation of the film thickness was ±6% and typically around ±2.5%. The homogeneity of the refractive index and the extinction coefficient was found to be ±0.55% and ±3.58%, respectively. An additional benefit of this co-rotating IPLD geometry is its appealing simplicity, i.e. that the target and substrate are rotated by the same motor.

Keywords: Homogenization; Rotation; Ellipsometry

Magnetic properties of Fe₃O₄ thin films grown on different substrates by laser ablation by M.L. Paramês; Z. Viskadourakis; M.S. Rogalski; J. Mariano; N. Popovici; J. Giapintzakis; O. Conde (pp. 8201-8205).

Magnetite thin films have been grown onto (100)Si, (100)GaAs and (0001)Al₂O₃, at substrate temperatures varying from 473 to 673K, by UV pulsed laser ablation of Fe₃O₄ targets in reactive atmospheres of O₂ and Ar, at working pressure of 8×10⁻²Pa. The influence of the substrate on stoichiometry, microstructure and the magnetic properties has been studied by X-ray diffraction (XRD), conversion electron Mössbauer spectroscopy (CEMS) and magnetic measurements. Magnetite crystallites, with stoichiometry varying from Fe_2.95O₄ to Fe_2.99O₄, are randomly oriented for (100)GaAs and (100)Si substrates and exhibit (111) texture if grown onto (0001)Al₂O₃. Interfacial Fe³⁺ diffusion, which is virtually absent for (100)Si substrates, was found for both (0001)Al₂O₃ and (100)GaAs, with some deleterious effect on the subsequent microstructure and magnetic behaviour.

Keywords: PACS; 81.15.Fg; 76.80.+y; 75.50.Gg; 75.70.AkFe; ₃; O; ₄; thin films; Gallium arsenide; Sapphire and silicon substrates; PLD; CEMS; Magnetic characterisation

Optical and structural properties of undoped and palladium doped indium tin oxide films grown by pulsed laser deposition by T.J. Stanimirova; P.A. Atanasov; M. Stankova; I.G. Dimitrov; T.R. Stoyanchov (pp. 8206-8209).

The purpose of the present investigation is the fabrication of undoped and palladium doped indium tin oxide films by pulsed laser deposition and the analyses of their optical, waveguide and structural properties in view of optical sensor applications. The films are deposited at oxygen pressure from 5 to 20Pa and substrate temperature between 200 and 450°C. Palladium is used as a dopant since it is critical in improving the sensor's properties. The X-ray diffraction spectra show that all films are polycrystalline with preferential [111] orientation. The optical transmittance measured in the visible region has maximum values of 85–90% for films grown at oxygen pressure 15Pa independently of the substrate temperature used. SEM, AFM and optical and investigations revealed that indium tin oxide films with 1wt.% Pd have higher transmittance and better surface morphology than those with 3wt.% Pd concentration. ITO films with minimum propagation losses of 2dBcm⁻¹ were deposited at substrate temperature 200°C and oxygen pressure 5Pa, but doped ITO films with minimum propagation losses were obtained at 400°C and 15Pa.

Keywords: Indium tin oxide (ITO); Pd dopant; Laser ablation; Optical properties

Preparation and characterization of titanium oxy-nitride thin films by M. Braic; M. Balaceanu; A. Vladescu; A. Kiss; V. Braic; G. Epurescu; G. Dinescu; A. Moldovan; R. Birjega; M. Dinescu (pp. 8210-8214).

The interest in TiN_xO_y films has increased recently due to their properties dependence on the N/O ratio.In this work, we studied comparatively the influence of different flow rate ratios of the reactive gases (O₂ and N₂) on the properties of the TiN_xO_y films deposited by two different methods: rf pulsed laser deposition (rf PLD) and reactive pulsed magnetron sputtering (RPM).Film structure and composition were studied by XRD and XPS methods, while film surface morphology was analyzed with AFM. Mechanical characteristics as Vickers microhardness and adhesion (scratch tests) were also determined.

Keywords: Ti oxy-nitride; Physical; Microchemical and mechanical properties

Influence of in situ nitrogen pressure on crystallization of pulsed laser deposited AlN films by S. Bakalova; A. Szekeres; A. Cziraki; C.P. Lungu; S. Grigorescu; G. Socol; E. Axente; I.N. Mihailescu (pp. 8215-8219).

Aluminum nitride (AlN) thin films obtained by pulsed laser deposition (PLD) with a KrF^* laser source ( λ=248nm, τ≥7ns) at a substrate temperature of 800°C and different values of ambient nitrogen pressure up to 10Pa have been studied. Precursors in the plasma plume were studied by optical multichannel emission spectroscopy. Emission spectra taken close to the target revealed the presence of atomic, single and multiple ionized Al and N species, as well as AlN molecular species. The analysis of the XRD patterns revealed that all films had a polycrystalline structure with mixed cubic and hexagonal phases. For AlN films deposited in vacuum, the structure is predominantly cubic with a small fraction of hexagonal phase. The cubic phase had a lattice parameter of 0.4045nm. The films deposited in nitrogen ambient have a cubic crystalline structure. At maximum nitrogen pressure of 10Pa the lattice parameter decreases to a=0.3949nm.

Keywords: Pulsed laser deposition; Aluminium nitride; Plasma diagnostics; X-ray Diffractometry

Diamond-like carbon films prepared by reactive pulsed laser deposition in hydrogen and methane ambient by Judit Budai; Sára Tóth; Zsolt Tóth; Margit Koós (pp. 8220-8225).

The properties of amorphous hydrogenated carbon (a-C:H) films, like their hardness and optical band gap drastically depends on their hydrogen content. By reactive pulsed laser deposition in hydrogen containing gas, the hydrogenation of the films can be achieved. The application of reactive gases of different chemical composition can influence the film properties in a different manner. Therefore, we investigated deposition of a-C:H films in H₂ and CH₄ atmosphere (0.001–50Pa). The deposited films were characterized by Raman spectroscopy, spectroscopic ellipsometry and infrared spectroscopy. The optical and structural properties of the films prepared in the two different ambient gas show similarities: at low pressure below 1Pa, the films are diamond-like, at ∼1–10Pa, the films become graphite-like and at higher pressures, the films show polymer-like properties. Differences in the films prepared in H₂ and CH₄ are found in their thickness and infrared absorption. When increasing the pressure up to medium pressures the thicknesses of both series of films increase, and the films become thinner in the highest pressure domain. However, the films prepared in CH₄ are ∼1.5 times thicker than the films prepared in H₂. Since the mass differences of C atoms and CH₄ is small, the CH_x radicals are efficiently accelerated by the carbon plasma and are incorporated into the films, too.

Keywords: PLD; Carbon film; Plasma-gas interaction

Pulsed laser growth and characterization of thin films on titanium substrates by L. Lavisse; J.M. Jouvard; L. Imhoff; O. Heintz; J. Korntheuer; C. Langlade; S. Bourgeois; M.C. Marco de Lucas (pp. 8226-8230).

Colored layers were obtained by laser surface treatment of Ti substrates with a pulsed Nd:YAG Q-switched laser. The changes in the morphology, structure and chemical composition of the layers were studied by SEM, EDS, XPS, SIMS and Raman spectroscopy as a function of the laser fluence in the 4–60Jcm⁻². For laser fluences lower than 25Jcm⁻², the layers are colorless or yellow. Their surface is smooth, but they display cracks which increase when the fluence increases. The O/Ti ratio, determined by XPS analysis, varies from 0.7 (colorless layers) to 1.3 (yellow layer). Moreover, XPS spectra evidence non-negligible amounts of nitrogen and carbon in these layers. Raman spectra show large bands which support the formation of titanium oxy-carbo-nitride.For laser fluences higher than 25Jcm⁻², the layers are purple and blue and very rough sample surfaces were obtained. As a consequence of this, XPS analysis could not be used to obtain quantitative information on the layer composition. Finally, Raman spectra clearly showed the increasing formation of anatase and rutile phases of TiO₂ in these layers when the laser fluence increases.

Keywords: Laser surface treatments; Titanium oxides; Titanium nitrides; Thin films

The spatial thickness distribution of metal films produced by large area pulsed laser deposition by Nini Pryds; Jørgen Schou; Søren Linderoth (pp. 8231-8234).

Thin films of metals have been deposited in the large-area Pulsed Laser Deposition (PLD) Facility at Risø National Laboratory. Thin films of Ag and Ni were deposited with laser pulses from an excimer laser at 248nm with a rectangular beam spot at a fluence of 10J/cm² on glass substrates of 127mm diameter positioned 80mm from the target in vacuum. We have explored the distribution of deposited material on a stationary substrate from a fixed point of impact on the target relative to the substrate. In all cases the angular distribution of the deposited metal layers shows a distinct “flip-over” of the plume. The thickness of the deposited films over the full area has been determined by energy-dispersive X-ray spectrometry in a scanning electron microscope (SEM). The measured distributions were then compared with analytical expressions. Finally, the angular distribution of the film thickness has been utilized in an algorithm for production of films over large areas.

Keywords: Plused laser deposition; Pressure; Plume

Preparation of hydrogenated amorphous carbon films from polymers by nano- and femtosecond pulsed laser deposition by Judit Budai; Miklós Bereznai; Gábor Szakács; Edit Szilágyi; Zsolt Tóth (pp. 8235-8241).

Hydrogenated amorphous carbon (a-C:H) films can be simply produced by pulsed laser deposition (PLD) from targets containing hydrogen and carbon, e.g. polymers. Films deposited from polyethyleneterephtalate (PET) and polycarbonate (PC) were compared to samples prepared from glassy carbon. Several lasers were used to explore the influence of pulse duration (∼30ns and ∼500fs) and wavelength (248 and 193nm) on the properties of laser deposited films. The film composition was characterized by Rutherford backscattering spectrometry and elastic recoil detection analysis. Variable angle spectroscopic ellipsometry gave information about the thickness and optical properties of the films. It was demonstrated that a consistent interpretation of the laser ablation, caused by rather different laser sources on various targets, is possible using the parameter of volumetric power density (intensity divided by light or heat penetration depth). PLD from polymer targets resulted in amorphous hydrogenated films, where hydrogen and oxygen content was decreased compared to the composition of the original target. PLD from glassy carbon target resulted in graphitic, diamond like and porous carbon films with increasing volumetric power density.

Keywords: Pulsed laser deposition; Carbon and polymer target; Laser ablation

Pulsed laser deposition of the NiTiCu thin film alloy by A. Morone (pp. 8242-8244).

Ni–Ti–Cu alloy present different properties: shape memory effect, super-elasticity and biocompatibility which allow it to be used in different fields: from biomedical to micro electro mechanical systems. It is complex to obtain these properties in thin films of Ni–Ti–Cu alloy deposited on Si substrates. In this work preliminary results, in situ X-ray fluorescence data, ex situ X-ray diffraction data of Ni–Ti–Cu thin film will be reported. These measurements will allow to control the correct growth of the thin film alloy produced by laser deposition.

Keywords: Ni–Ti–Cu alloy; Laser deposition; X-ray

Diamond-like carbon coated ultracold neutron guides by S. Heule; F. Atchison; M. Daum; A. Foelske; R. Henneck; M. Kasprzak; K. Kirch; A. Knecht; M. Kuźniak; T. Lippert; M. Meier; A. Pichlmaier; U. Straumann (pp. 8245-8249).

It has been shown recently that diamond-like carbon (DLC) with a sp³ fraction above 60% is a better wall coating material for ultracold neutron applications than beryllium. We report on results of Raman spectroscopic and XPS measurements obtained for diamond-like carbon coated neutron guides produced in a new facility, which is based on pulsed laser deposition at 193nm. For diamond-like carbon coatings on small stainless steel substrates we find sp³ fractions in the range from 60 to 70% and showing slightly increasing values with laser pulse energy and pulse repetition rate.

Keywords: PACS; 79.20.Ds; 14.20.Dh; 78.30.Jw; 33.60.FyDiamond-like carbon; Characterization methods; sp; ³; bonding; Pulsed laser deposition; Ultracold neutrons

Structural and optical properties of YVO₄ thin films by D.R. Milev; P.A. Atanasov; A.Og. Dikovska; I.G. Dimitrov; K.P. Petrov; G.V. Avdeev (pp. 8250-8253).

In this work, thin YVO₄ films were deposited on amorphous SiO₂ substrates by pulsed laser deposition (PLD). Ceramic targets of pure and doped (Er and Er, Yb) YVO₄ were prepared and used for ablation. The influence of the substrate temperature and oxygen pressure applied during the depositions was investigated. Crystalline films were obtained at temperatures higher than 500°C. The films with the best crystallinity were obtained at 5Pa oxygen pressure and 700°C substrate temperature. All the films are transparent in the visible and near infrared region of spectra. The crystalline samples show difference in the refractive indexes Δ n (Δ n= n_TE− n_TM) for the TE and TM polarizations. It was evaluated to be about 0.08.

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

BST thin films obtained by PLD for applications in electronics by N. Scarisoreanu; M. Filipescu; A. Ioachim; M.I. Toacsan; M.G. Banciu; L. Nedelcu; A. Dutu; M. Buda; H.V. Alexandru; M. Dinescu (pp. 8254-8257).

Barium strontium titanate (BST) bulk ceramic with composition Ba_0.5Sr_0.5TiO₃ was produced by solid-state reaction and was used as target for PLD thin film deposition. A Nd-YAG laser, working at 5–10Hz and different wavelengths has been used. Thin films of stoichiometric BST were deposited on alumina substrate with the thickness between 400 and 500nm. An aditional annealing was carried out at 800°C for 6h. XRD and SEM were used for sample characterization. Capacity measurements were performed versus temperature at 100kHz in a large temperature range. A diffuse ferroelectric–paraelectric phase transition with T_C=−72°C for the BST thin film was determined. A 5% tunability was measured in the transition region.

Keywords: Barium strontium titanate; Film; PLD; Tunability

Morphological and structural studies of WO_x thin films deposited by laser ablation by M. Filipescu; S. Orlando; V. Russo; A. Lamperti; A. Purice; A. Moldovan; M. Dinescu (pp. 8258-8262).

Tungsten oxide is an interesting compound with many applications in gas sensors, electrochromic and photochromic devices. Thin films of tungsten oxide were obtained by pulsed laser deposition (PLD) and radio frequency assisted PLD (RF-PLD). A tungsten target was ablated in reactive oxygen atmosphere (0.01–0.05mbar). The deposition parameters such as laser fluence, substrate temperature, radiofrequency power were varied, while different materials (Corning glass and silicon) have been used as substrates. The obtained films showed good adhesion to the substrate and uniform surface aspect, which are important properties for applications. X-ray diffraction, Auger electron, Raman spectroscopies and atomic force microscopy were used for characterization.

Keywords: PLD; RF-PLD; Tungsten oxide; X-ray diffraction; Auger electron; Raman spectroscopies

Growth of LiNbO₃ thin films on sapphire by pulsed-laser deposition for electro-optic modulators by S. Kilburger; R. Chety; E. Millon; Ph. Di Bin; C. Di Bin; A. Boulle; R. Guinebretière (pp. 8263-8267).

Thin films of lithium niobate (LiNbO₃: LN) have been successfully deposited onto c-axis sapphire substrates using the pulsed-laser deposition technique in order to grow epitaxially the expected phase. Films have been characterized by different techniques. X-ray diffraction measurements of these films deposited at temperature ranging from 600 to 750°C and at oxygen pressures ranging from 10 to 30Pa show the intense (0006) peak of LN. In addition, epitaxial relationships between the LN thin films and the sapphire substrate are evidenced. The Rutherford backscattering spectroscopy measurements indicate that the films are nearly stoichiometric. The LN films are very smooth and practically free of droplets as highlighted by AFM experiments. The optical properties evaluated by m-line spectroscopy show a rather good light confinement but the grain size of crystallites in the films has to be improved to limit the optical losses.

Keywords: LiNbO; ₃; Thin films; Epitaxy; Pulsed-laser deposition; Optical waveguides; Modulator

Nanocrystalline Er:YAG thin films prepared by pulsed laser deposition: An electron microscopy study by Daniela Stanoi; Andrei Popescu; Corneliu Ghica; Gabriel Socol; Emanuel Axente; Carmen Ristoscu; Ion N. Mihailescu; Andrea Stefan; Serban Georgescu (pp. 8268-8272).

We report the synthesis of well crystallized stoichiometric Er:YAG thin films by pulsed laser deposition from Er:YAG targets in low pressure oxygen, followed by a post-deposition treatment at 1400°C in environmental air for 19h. The structure and morphology of the films were examined by transmission electron microscopy and selected area electron diffraction. We demonstrated that the subsequent application of pulsed laser deposition and heat treatment resulted in the formation of well crystallized single phase cubic Er:YAG nanostructured coatings.

Keywords: Wave guides amplifiers; Er:YAG thin films; PLD; Heat treatments

Li doping effect on the luminescent characteristics of YVO₄:Eu³⁺ thin films grown by pulsed laser deposition by Jung Hyun Jeong; Hyun Kyoung Yang; Kyoo Sung Shim; Ye Ran Jeong; Byung Kee Moon; Byung Chun Choi; Jong Seong Bae; Soung Soo Yi; Jung Hwan Kim (pp. 8273-8277).

Influence of Li doping on the crystallization, surface morphology and luminescent properties of YVO₄:Eu³⁺ films has been investigated. The films have been grown using pulsed laser deposition method on Al₂O₃ (0001) substrates under different oxygen pressures. The substrate temperature was fixed at 600°C and the range of oxygen pressure was 20.00–46.66Pa. The crystallinity and surface morphology of the films were investigated using X-ray diffraction (XRD) and atomic force microscope (AFM), respectively. The emitted radiation at 312nm excitation was dominated by a red emission peak at 620nm radiated from the transition of⁵D₀–⁷F₂ of Eu³⁺ ions. In particular, the incorporation of Li⁺ ions into YVO₄ lattice could induce the increase of the intensity of the photoluminescence. The enhanced luminescence may be resulted not only from the improved crystallinity, but also from the reduced internal reflections caused by rougher surfaces. The luminescent intensity and surface roughness exhibited similar behavior as a function of oxygen pressure.

Keywords: PACS; 78.20.−e; 78.55.−m; 78.66.−wYVO; ₄; :Eu; ³⁺; Li-doping; Thin film phosphors; Surface morphology; Photoluminescence

Thin films of advanced oxidic materials obtained by pulsed laser deposition by C. Vasiliu; G. Epurescu; C. Grigorescu; M. Elisa; G. Pavelescu; A. Purice; A. Moldovan; M. Dinescu (pp. 8278-8281).

Thin films of complex oxides have been deposited by pulsed laser ablation, starting from glass targets. Glass oxide targets were prepared by a non-conventional wet method and consisted of a matrix having the composition: Li₂O, BaO, Al₂O₃, La₂O₃ and P₂O₅, respectively, non-doped and doped with Nd₂O₃.The films were deposited on silicon substrates using the fourth harmonic of a Nd:YAG laser (266nm), in an oxygen background atmosphere. The influence of the deposition parameters on the morphological and optical properties of the oxide films was particularly investigated. IR absorption spectroscopy, optical microscopy, X-ray diffraction and atomic force microscopy were used to characterize the targets and the deposited thin films.

Keywords: PLD; Doped glasses; Atomic force microscopy

Study of the composition transfer in the pulsed laser deposition of silicon substituted hydroxyapatite thin films by E.L. Solla; J.P. Borrajo; P. González; J. Serra; S. Chiussi; B. León; J. García López (pp. 8282-8286).

The field of biomaterials has lately been showing an important interest in the production of bioactive ceramic coatings capable of improving the adhesion of metal prostheses to the living tissue. Among these ceramics, the most notable is hydroxyapatite (HA) due to its similarities with the mineral part of the bone. The need to emphasize these resemblances led to the production of silicon substituted HA (Si-HA), a material which has shown better biological performance compared to the traditional HA.Coatings were prepared by pulsed laser deposition (PLD) technique, starting from mixtures of pure HA with Si powders. The laser–matter interaction successfully transferred the Si-HA to the substrate incorporating the Si atoms within its structure. The Si-HA thin films were characterized in terms of structure and chemical composition by many different techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XPS), energy dispersive spectroscopy (EDS) and ion beam spectroscopy techniques such as Rutherford back scattering (RBS), particle induced X-ray emission (PIXE), elastic recoil detection (ERD) and nuclear reaction analysis (NRA). The analysis demonstrated that Si is efficiently transferred to the HA structure in the form of SiO₄⁴⁻ groups. The dependence of the target composition on the film growth and on the Si content of the coatings is also presented.

Keywords: Silicon substituted hydroxyapatite; FTIR; Pulsed laser deposition; Bioactive coatings; Biomaterials

Surface microstructuring of silica glass by laser-induced backside wet etching with a DPSS UV laser by Hiroyuki Niino; Yoshizo Kawaguchi; Tadatake Sato; Aiko Narazaki; Ryozo Kurosaki (pp. 8287-8291).

Deep microtrenches having a high aspect ratio on the surfaces of silica glass were fabricated by laser-induced backside wet etching (LIBWE). The focused laser beam of a diode-pumped solid state (DPSS) UV laser at λ=266nm on the repetition rate of 30–40kHz was directed to the sample cell of the glass by a galvanometer-based point scanning system. Vertical and inclined trench structures were successfully fabricated on the glass by changing the incident angle of the laser beam. The depth of filed (DOF) in LIBWE was analyzed by inclined laser irradiation. Flexible rapid prototyping by the mask-less exposure system was demonstrated.

Keywords: Silica glass; Depth of filed; DPSS UV laser; Oblique incidence; Galvanometer-based point scanning

Laser-induced synthesis of nanostructured thin films by P. Heszler; L. Landström; C.G. Granqvist (pp. 8292-8299).

We present a number of important characteristics of laser techniques for preparation of nanostructured thin films with foci on laser ablation (LA) and laser-assisted chemical vapor decomposition (LCVD). Size-related features and structures of the deposited layers are associated with process parameters. Whenever possible, the performance of the deposits is compared to that of films prepared by other methods ( e.g., physical vapor synthesis such as gas deposition, sputtering, etc.). The LA and LCVD methods allow a wide variety of materials to be prepared. A number of promising applications emerge when one combines this versatility with the potential for making certain types of nanostructured layers. These possibilities are also discussed.

Keywords: Laser-assisted CVD; Laser ablation; Nanoparticles; Nanostructured thin films

Buried channel waveguides in Yb-doped KY(WO₄)₂ crystals fabricated by femtosecond laser irradiation by C.N. Borca; V. Apostolopoulos; F. Gardillou; H.G. Limberger; M. Pollnau; R.-P. Salathé (pp. 8300-8303).

We report on the fabrication of optical channel waveguides inside KY(WO₄)₂ crystals, both undoped and Yb-doped, for applications in compact solid-state lasers and three-dimensional photonic devices. Nonlinear absorption of femtosecond laser pulses has been employed in order to induce refractive-index changes in these crystals. The irradiation damage results in a decrease of the material density compared to the surrounding bulk. In this work, two types of buried channel waveguides have been fabricated in the KY(WO₄)₂ crystals. First ones (type I) were formed in the vicinity of the irradiated regions due to the presence of an induced compressive lattice strain, which causes an increase of the local refractive index. Light can be better confined in the second (type II) of channel waveguides that are created between pairs of damaged regions. For the best confined channels (type II), the propagation loss value measured at 1μm amounted to 2–2.5dB/cm.

Keywords: Femtosecond-laser writing; Burried channel waveguides; KY(WO; ₄; ); ₂; crystals

Nanohole processing on silicon substrate by femtosecond laser pulse with localized surface plasmon polariton by Petar A. Atanasov; Hiroto Takada; Nikolay N. Nedyalkov; Minoru Obara (pp. 8304-8308).

We demonstrate nanohole fabrication on silicon surface by femtosecond laser pulse irradiation mediated by gold nanoparticles. Gold spheres with diameters of 40, 80 or 200nm are placed on the silicon substrate surface by a spin-coating method. The laser pulse with duration of 150fs and wavelength of 820nm is used to irradiate the Si substrate. Laser fluences applied are in the range of 140–300mJ/cm², i.e. below or near the ablation threshold fluence of the bulk silicon substrate without gold particles. The morphological changes of the laser-irradiated areas are investigated by scanning electron microscope (SEM) and atomic force microscope (AFM). Their dependence on the particle diameter, shape and laser fluence is investigated. The ablated surface morphologies are found to strongly depend on the polarization and the energy of the laser pulse. Nanoholes with diameters of about 150nm and depths in the range of 30nm are produced in the case of 200nm diameter particles at fluences below the threshold for Si without Au particles. At fixed laser fluence the diameter and depth of the holes increase with the particle sizes. The optical field enhancement factor on the Si surface is calculated using an FDTD simulation code. A maximal value of about 26 is obtained for 200nm Au particles. The comparison between the theoretical results for the electromagnetic field enhancement factor achieved and the experimental results is made in order to explain the physics of the nanomachining process.

Keywords: Nanohole; Femtosecond pulse; Au nanoparticles; Surface plasmon polariton

Experimental investigation of ablation mechanisms involved in dry laser cleaning by D. Grojo; A. Cros; Ph. Delaporte; M. Sentis (pp. 8309-8315).

The various ablation mechanisms possibly involved in ‘laser-particle-surface’ interaction were investigated by means of in situ diagnostics. Different kind of transparent and absorbing particles were irradiated by UV nanosecond laser pulses. Optical microscopy was employed to measure particle removal efficiencies and fluence thresholds. Fast imaging with the aid of an intensified charged coupled device (ICCD) camera was used to characterize the ejection of species on a microsecond time scale. The present study shows that laser irradiation of particles can induce the damage of surfaces as a result of near-field enhancement underneath particles and/or thermal contact with hot particles. During the experiments of laser ablation of contaminants made of carbon-based materials, the contribution of the photochemical degradation was evaluated. The photochemical ablation mechanism is of great interest for the removal of contaminates at low laser fluence. The results of this study are discussed in terms of admissible mechanisms which lead to particle removal in dry laser cleaning experiments with nanosecond laser pulses.

Keywords: Laser-particle-surface; Dry laser cleaning; Photochemical ablation

Direct laser manufacturing with coaxial powder injection: Modelling of structure of deposited layers by A.V. Gusarov; I. Smurov (pp. 8316-8321).

Direct Laser Manufacturing (DLM) with coaxial powder injection is applied for fabrication of near net shape objects from metallic powder. The proposed model includes analysis of the two-phase flow formed by the coaxial nozzle, particles heating by the laser beam, and deposit formation. The experimentally observed deposit looks like a porous array of separate intersecting particles. The density of the deposit is determined by competition between kinetic energy of the liquid droplets at impact and surface tension forces preserving their spherical shape. It is shown that the density, the mean coordination number and the maximum radius of the necks formed between particles increase with the impact velocity. The particles are bound preferentially in the vertical direction. The bounding anisotropy decreases with the impact velocity. The neck size distribution changes from a very narrow one at low velocities to a wide distribution at high velocities. The radial distribution function indicates that short linear chains of particles are formed at low impact velocities, these chains disappearing at higher velocities.

Keywords: Direct manufacturing; Coaxial nozzle; Deposit structure

Experimental and theoretical analysis of the laser shock cleaning process for nanoscale particle removal by Dongsik Kim; Bukuk Oh; Deoksuk Jang; Jeong-Wook Lee; Jong-Myoung Lee (pp. 8322-8327).

The laser shock cleaning (LSC) process has been shown to be effective for removing submicron-sized contaminant particles from solid surfaces and thus bears strong potential in various applications. In this work, experimental and theoretical analysis are conducted to reveal the underlying physical mechanisms of the LSC process, with emphasis on the laser-induced hydrodynamics and the effect of external gas-jet injection through a nozzle. A two-dimensional theoretical model is proposed for rigorous simulation of the hydrodynamic phenomena occurring in the LSC process. The hydrodynamics computed by the model is in qualitative agreement with experimental observations and reveal the details of the physics involved in the cleaning process. The effect of gas blowing on the cleaning performance is analyzed both experimentally and theoretically. The results indicate that the gas flow can significantly change the hydrodynamics and increase the cleaning efficiency by reducing the chance of particle redeposition.

Keywords: Laser cleaning; Laser-induced breakdown; Particle removal; Shock wave

Electrodes for microfluidic devices produced by laser induced forward transfer by Chris Germain; Luc Charron; Lothar Lilge; Ying Y. Tsui (pp. 8328-8333).

The laser induced forward transfer (LIFT) process was used to create conductive lines and pads for rapid prototyping and repairing microdevices. Single 0.1–10μJ pulses from a 120fs 800nm titanium:sapphire laser were used to transfer films consisting of 40–80nm thick gold to create the lines. Experiments were conducted in air ambient. The laser was focused using 4× and 10× microscope objectives and produced 5–20μm diameter metal spots which were overlapped to produce conductive lines. Electrodes with widths between 10 and 50μm have been produced and their resistances have been measured. The resistivities of these LIFT produced Au electrodes were found to be approximately (1–4)×10⁻⁶Ωm. It has also been shown that the conductivity of the lines can be further improved by electrical curing. The LIFT process was used to repair heaters for microfluidic applications and preliminarily create electrodes for control of electro-osmotic flow in microfluidic devices.

Keywords: Laser; Laser induced forward transfer (LIFT); Micropatterning; Microfluidic devices

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Applied Surface Science (v.253, #19)

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Applied Surface Science (v.253, #19)