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Applied Surface Science (v.258, #23)

Editorial Board (pp. ii).

E-MRS symposium R: “Laser materials processing for micro and nano applications” by Nini Pryds Guest Editor; Craig B. Arnold Guest Editor (pp. 9105-9106).

Micro-scale patterning of indium tin oxide film by spatially modulated pulsed Nd:YAG laser beam by Jinsoo Lee; Seongsu Kim; Myeongkyu Lee (pp. 9107-9111).

► Indium tin oxide thin film is directly patterned by a spatially modified Nd:YAG laser beam. ► Sharp-edged clean patterns with feature size as small as 4μm are obtained. ► This parallel process provides much higher throughput than the tradition photoablation method.Here we demonstrate that indium tin oxide (ITO) films deposited on glass can be directly patterned by a spatially -modulated pulsed Nd-YAG laser beam (wavelength=1064nm, pulse width=6ns) incident onto the film. This method utilizes a pulsed laser-induced thermo-elastic force exerting on the film which plays a role to detach it from the substrate. Sharp-edged clean patterns with feature size as small as 4μm could be obtained. The threshold pulse energy density for patterning was estimated to be ∼0.8J/cm² for 150nm-thick ITO film, making it possible to pattern over one square centimeter by a single pulse with energy of 850mJ. Not only being free from photoresist and chemical etching steps, the presented method can also provide much higher throughput than the tradition photoablation process utilizing a tightly focused beam.

Keywords: Indium tin oxide (ITO) film; Patterning; Laser

Structural properties of ZnO films grown by picosecond pulsed-laser deposition by L. Lansiart; E. Millon; J. Perrière; J. Mathias; A. Petit; W. Seiler; C. Boulmer-Leborgne (pp. 9112-9115).

► Textured and epitaxial ZnO films grown by picosecond pulsed-laser deposition. ► Epitaxial relationships evidenced on c-cut and r-cut sapphire substrates. ► Nanocrystallised ZnO films obtained with a growth rate 10 times greater than in nanosecond PLD.Zinc oxide thin films have been grown on c-cut (0001) and r-cut (11¯02) sapphire substrates by pulsed-laser deposition using a Nd:YAG laser operating at 355nm in picosecond regime (pulse duration: 42ps). The composition and the structural properties of the films have been investigated by scanning electron microscopy, Rutherford backscattering spectroscopy and X-ray diffraction according to different substrate temperatures. The RBS spectra show a Zn/O ratio close to 1.1 with a constant in-depth oxygen concentration. The XRD diagrams in Bragg–Brentano geometry display a preferred orientation depending on the used substrate. The large width of XRD peaks is indicative of a small coherence length. In addition, according to the pole figures recorded in asymmetric configuration, epitaxial relationships between substrate and film are evidenced. An increase in the substrate temperature leads to a film crystalline quality improvement. The results are discussed regarding the well-known properties of ZnO films obtained by nanosecond and femtosecond PLD.

Keywords: Pulsed-laser deposition; Zinc oxide; Picosecond; Epitaxy

Oxygen background gas influence on pulsed laser deposition process of LaAlO₃ and LaGaO₃ by S. Amoruso; C. Aruta; P. Aurino; R. Bruzzese; X. Wang; F. Miletto Granozio; U. Scotti di Uccio (pp. 9116-9122).

► Effects of background gas pressure on oxides deposition in oxygen by PLD. ► Effects of substrate temperature on oxides growth rate in oxygen by PLD. ► Role of the energetic plume on the growth of oxides interfaces. ► Influence of plume features on conducting properties of polar/nonpolar interfaces.We investigate pulsed laser ablation of LaAlO₃ and LaGaO₃ with a focus on the influence of oxygen background gas pressure on the plume expansion dynamics and deposition rate. The ablation plume is characterized by exploiting fast photography and time- and space-resolved optical emission spectroscopy. The variation of the deposition rate with the oxygen background pressure was obtained at 800°C by reflection high-energy electron diffraction, and compared to that measured at room temperature by means of a quartz crystal microbalance. The experimental findings allow one to address the various stages of plume expansion as a function of the background oxygen pressure as well as the changes induced on the plume species kinetic energy and composition. On the base of our experimental results, the possible influence of various mechanisms, such as subplantation and oxygen vacancy formation, on the growth of oxides interfaces is addressed.

Keywords: PACS; 52.38.Mf; 52.50.−b; 79.20.DsPulsed laser deposition; Oxides; Plasma plume spectroscopy

Excimer lasers drive large-area microprocessing by Ralph Delmdahl; Jean-Luc Tapié (pp. 9123-9127).

► Multi-hundred watt UV excimer lasers are used in industrial high-volume microprocessing. ► Excimer laser operational lifetime of two years under typical production conditions yields affordable high power UV laser processing. ► Laser lift-off processing of LEDs is facilitated by the large per-shot-area of excimer lasers.Excimer lasers emitting in the UV to far UV region are by nature the laser sources enabling the highest optical resolution and strongest material–photon interaction. At the same time, excimer lasers deliver unmatched UV pulse energies and output powers up to the kilowatt range. Thus, they are the key to fast and effective large area processing of smallest structures with micron precision. As a consequence, excimer lasers are the UV technology of choice when it comes to high-performance microstructuring with unsurpassed quality and process repeatability in applications such as drilling advanced ink jet nozzles or patterning biomedical sensor structures.

Keywords: Excimer laser; Microprocessing; Large-area ablation; Ink-jet nozzle drilling; Marking; Laser lift-off

Towards a laser fluence dependent nanostructuring of thin Au films on Si by nanosecond laser irradiation by F. Ruffino; A. Pugliara; E. Carria; L. Romano; C. Bongiorno; G. Fisicaro; A. La Magna; C. Spinella; M.G. Grimaldi (pp. 9128-9137).

Display Omitted► Au nanoclusters are produced by nanosecond laser irradiations of thin Au film on Si. ► The shape, size, and surface density of the Au nanoclusters are tunable by laser fluence. ► The formation dynamic of the Au nanoclusters under nanosecond laser irradiation is analyzed.In this work, we study the nanostructuring effects of nanosecond laser irradiations on 5nm thick Au film sputter-deposited on Si. After deposition of Au on Si substrate, nanosecond laser irradiations were performed increasing the laser fluence from 750 to 1500mJ/cm². Several analyses techniques, such as Rutherford backscattering spectrometry, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy were crossed to study the morphological evolution of the Au film as a function of laser fluence. In particular, the formation of Au nanoparticles was observed. The analyses allowed a quantitative evaluation of the evolution of the nanoparticles size, surface density, and shape as a function of the laser fluence. Therefore, a control the structural properties of the Au nanoparticles is reached, for example, for applications in Si nanowires growth or plasmonics.

Keywords: Nanosecond laser irradiation; Gold; Silicon; Nanostructuring; Atomic force microscopy; Scanning electron microscopy; Transmission electron microscopy

Laser-induced front side etching of fused silica with XeF excimer laser using thin metal layers by Pierre Lorenz; Martin Ehrhardt; Anja Wehrmann; Klaus Zimmer (pp. 9138-9142).

► We study laser-induced front side etching of fused silica with a XeF excimer laser. ► Different metal layers as absorber are used. ► The LIFE method allows nm-precision etching with etching depths up to 150nm. ► The measurement results are compared to the results calculated by a thermal model.Laser-induced front side etching (LIFE) is a method for laser etching of transparent materials using thin absorber layers, e.g., for precision engineering or even optical applications.Aluminium, chromium, molybdenum, silver as well as titanium with various layer thicknesses (5–100nm) were applied as absorber for etching trenches in fused silica with nanosecond XeF excimer laser radiation. The sample surfaces were processed at laser fluences up to 10J/cm² and laser pulse numbers from 1 to 10 pulses.A linear growth of the etching depth at rising laser fluence was found. The film thickness dependency is more complex and mostly influenced by the optical properties of the thin metal films.The influence of the laser fluence, the number of pulses, the absorber material as well as the absorber layer thickness on the etching process, the etching depth, and the surface modification were presented and discussed.A simple model is given that allows the discussion of the etching depth in dependency on the laser fluence and the metal film thickness.The measurements represented a good agreement with the calculated results by a thermal model.The LIFE method allows nm-precision etching of fused silica with etching depths up to 150nm.

Keywords: Laser-induced front side etching; LIFE; Metallic absorber; Fused silica; Laser

Structural, optical and magnetic resonance properties of TiO₂ fibres grown by laser floating zone technique by J. Rodrigues; M. Peres; A.J.S. Fernandes; M.P.F. Graça; N.A. Sobolev; F.M. Costa; T. Monteiro (pp. 9143-9147).

► TiO₂ fibres grown by the laser floating zone technique for the first time. ► Magnetic, optical and structural characterization was performed. ► Structured luminescence with two zero-phonon lines followed by a phonon sideband. ► Fe³⁺ and Cr³⁺ present as substitutional impurities alongside with Ti³⁺ interstitials. ► A discussion of the chemical nature of the defect responsible for the luminescence is performed.TiO₂ fibres grown by the laser floating zone technique show the rutile crystalline phase as identified by X-ray diffraction and Raman spectroscopy. Scanning electron microscopy evidences a uniform surface, free of inclusions and without low-angle grain boundaries and bubbles. At low temperatures, the fibres luminescence is dominated by a richly structured optical centre with two well-defined zero-phonon lines at 1.579eV and 1.574eV followed by an intense vibronic sideband with a maximum close to 1.47eV. Electron paramagnetic resonance revealed that substitutional chromium and iron ions are present as contaminants in the grown fibres, alongside with Ti³⁺ interstitials and other structural defects. The chemical nature of the defect responsible for the structured near-infrared luminescence is discussed.

Keywords: TiO; ₂; LFZ; PL; EPR

Au nanoparticle arrays produced by Pulsed Laser Deposition for Surface Enhanced Raman Spectroscopy by N.R. Agarwal; F. Neri; S. Trusso; A. Lucotti; P.M. Ossi (pp. 9148-9152).

► We produced gold nanoparticles using Pulsed Laser Deposition at different pressures. ► We have made the analysis of the light emission intensity profiles of the plume. ► Good performance of the substrates for SERS applications is reported.Using UV pulses from KrF excimer laser, Au targets were ablated in varying pressures of argon to deposit Au nanoparticle (NP) arrays. The morphology of these films from island structures to isolated NPs, observed by SEM and TEM, depends on the gas pressure (10–100Pa) and pulse number keeping other deposition parameters constant. By fast imaging of the plasma with an iCCD camera at different time delays with respect to the arrival of the laser pulse, we study the plasma propagation regime and we measured its initial velocity. These data and the measured average ablated mass per pulse were introduced to the mixed propagation model to calculate the average asymptotic size of clusters grown in the plume which were compared with NP sizes from TEM measurements. UV–visible Spectroscopy revealed changes of surface plasmon resonance with respect to NP size and spatial density and distribution on the surface. Suitable wavelength to excite the localized surface plasmon was chosen to detect ultra-low concentrations of Rhodamine and Apomorphine as an application to biomedical sensors, using Surface Enhanced Raman Spectroscopy (SERS). A comparison of SERS spectra taken under identical conditions from commercial substrates and from PLD substrates show that the latter have superior performances.

Keywords: Laser ablation; Nanoparticles; Surface Enhanced Raman Spectroscopy

Influence of mechanical stress on nanosecond laser-induced damage threshold of fused silica by Guido Mann; Mathias Jurke; Mohammadali Zoheidi; Jörg Krüger (pp. 9153-9156).

► Laser-induced damage thresholds of fused silica vs. mechanical stress were determined. ► A laser wavelength of 1064nm and a pulse width of 12ns were used. ► A bulk LIDT value of about 700J/cm² was found. ► The damage threshold was independent on mechanical stress up to 220N/mm² ► No influence of the polarization state on the LIDT was observed.Optical multimode fibers made of fused silica are widely used for transmission of high power laser pulses. Bending of fibers creates mechanical stress inside the material. The bend stress of a fiber can be calculated from bend radius, geometrical fiber parameters and Young's Modulus of the fiber core material and reaches typically values of 220MPa. A thermo-elastic model of Kusov et al. predicts a quadratic dependence of laser-induced damage threshold fluence with applied stress.In the present study, fiber preform material F300 (Heraeus) was loaded mechanically with pressures up to 220MPa representing 20% of the pressure resistance of fused silica. Bulk laser-induced damage thresholds (LIDT) were evaluated using a longitudinal multimode Q-switched Nd:YAG laser (1064nm) at a pulse duration of 12ns with polarization states parallel and perpendicular to the stress direction. LIDT of fused silica samples of about 700J/cm² were found. LIDT did not show a dependence on mechanical pressure and polarization state which is a consequence of the small ratio of maximum applied stress (220MPa) to Young's Modulus of fused silica (72.5GPa).

Keywords: Laser-induced damage threshold; LIDT; Nanosecond Laser; Fused silica; Mechanical stress; Optical fiber

Optical properties of LFZ grown β-Ga₂O₃:Eu³⁺ fibres by N.F. Santos; J. Rodrigues; A.J.S. Fernandes; L.C. Alves; E. Alves; F.M. Costa; T. Monteiro (pp. 9157-9161).

► Undoped and Eu-doped β-Ga₂O₃ fibres were grown by laser floating zone. ► Morphological, structural and optical characterization was performed. ► For heavily doped samples, an additional Eu₃Ga₅O₁₂ crystalline phase was identified. ► Optical centres are discussed with respect to their possible phase origin and site symmetry.Due to their relevance for electronic and optoelectronic applications, transparent conductive oxides (TCO) have been extensively studied in the last decades. Among them, monoclinic β-Ga₂O₃ is well known by its large direct bandgap of ∼4.9eV being considered a deep UV TCO suitable for operation in short wavelength optoelectronic devices. The wide bandgap of β-Ga₂O₃ is also appropriate for the incorporation of several electronic energy levels such as those associated with the intra-4 fⁿ configuration of rare earth ions. Among these, Eu³⁺ ions (4 f⁶) are widely used as a red emitting probes both in organic and inorganic compounds. In this work, undoped and Eu₂O₃ doped (0.1 and 3.0mol%) Ga₂O₃ crystalline fibres were grown by the laser floating zone approach. All fibres were found to stabilize in the monoclinic β-Ga₂O₃ structure while for the heavily doped fibres the X-ray diffraction patterns show, in addition a cubic europium gallium garnet phase, Eu₃Ga₅O₁₂. The spectroscopic properties of the undoped and Eu doped fibres were analysed by Raman spectroscopy, low temperature photoluminescence (PL) and photoluminescence excitation (PLE). The Eu³⁺ luminescence is mainly originated in the garnet, from where different europium site locations can be inferred. The spectral analysis indicates that at least one of the centres corresponds to Eu³⁺ ions in dodecahedral site symmetry. For the lightly doped samples, the spectral shape and intensity ratio of the⁵D₀→⁷F_J transitions is totally different from those on Eu₃Ga₅O₁₂, suggesting that the emitting ions are placed in low symmetry sites in the β-Ga₂O₃ host.

Keywords: LFZ; Ga; ₂; O; ₃; Eu; PL; PLE

Laser annealing of bimetal thin films: A route of fabrication of composite nanostructures by N.N. Nedyalkov; Ru. Nikov; A.Og. Dikovska; P.A. Atanasov; G. Obara; M. Obara (pp. 9162-9166).

The paper presents results on laser nanostructuring of bimetallic thin films. The thin films are deposited by classical on-axis pulsed laser deposition technology by using targets consisted of two sections composed of different metals. Using this technique gold/nickel or gold/silver thin films are deposited on quartz substrate. By changing the area of the different sections of the target, thin films with different concentrations of the two metals are obtained. The as fabricated films are then annealed by nanosecond laser pulses delivered by Nd:YAG laser system operated at λ=355nm. The modification of the produced films is studied as a function of the parameters of the incident irradiation as pulse number and laser fluence, the composition of the thin films, and characteristics of the environment. It is found that the laser annealing may lead to nanostructuring of the films as at certain conditions the thin films are decomposed into a monolayer of nanoparticles with narrow size distribution. The performed EDX analyses indicated that the fabricated particles are composed by a bimetallic system of the basic metals used. The extinction spectra of the obtained structures show plasmon excitations as the resonance wavelength can be efficiently tuned in a wide range by changing the ratio of the basic metals in the films. The obtained structures can be used in SERS and magneto-optics.

Keywords: Laser nanostructuring; Nanoparticle fabrication; Bimetallic nanostructures

Laser induced simultaneous etching of silicon and deposition of carbon materials by A. Rashid; K. Piglmayer (pp. 9167-9170).

► Single step laser assisted processing of Si-surfaces. ► Simultaneous etching of Si and deposition of carbon material. ► Carbon coated etch pits can be created. ► High processing rates and big aspect ratios of etch pits achievable.Silicon (100) substrates have been irradiated in a gaseous atmosphere of diiodo-methane (CH₂I₂) by employing two different types of laser sources. Either focused 248nm excimer laser pulses or 532nm cw laser radiation have been used. Below the melting temperature of Si, complex etching of Si and deposition of carbon appear simultaneously only for irradiation with 248nm. Above the Si-melting point, the precursor allows efficient etching of Si with a simultaneous deposition of carbon materials for both wavelengths. In particular with focused 532nm radiation high processing rates and aspect ratios of the structures can be achieved.

Keywords: Laser; Etching; Deposition; Photolysis; Carbon

Laser assisted fabrication of random rough surfaces for optoelectronics by V. Brissonneau; L. Escoubas; F. Flory; G. Berginc; G. Maire; H. Giovannini (pp. 9171-9174).

► Random rough surfaces are photofabricated using an argon ion laser. ► Speckle and surface correlation function are linked. ► Exposure beam is modified allowing tuning the correlation. ► Theoretical examples are presented. ► Experimental results are compared with theoretical expectation.Optical surface structuring shows great interest for antireflective or scattering properties. Generally, fabricated surface structures are periodical but random surfaces that offer new degrees of freedom and possibilities by the control of their statistical properties. We propose an experimental method to create random rough surfaces on silicon by laser processing followed by etching. A photoresist is spin coated onto a silicon substrate and then exposed to the scattering of a modified laser beam. The beam modification is performed by using a micromirror matrix allowing laser beam shaping. An example of tuning is presented. An image composed of two white circles with a black background is displayed and the theoretical shape of the correlation is calculated. Experimental surfaces are elaborated and the correlation function calculated from height mapping. We finally compared the experimental and theoretical correlation functions.

Keywords: Laser; Rough; Random; Structuration; Scattering

Enhancement of superconductivity in LFZ-grown BSCCO fibres by steeper axial temperature gradients by J.M. Vieira; R.A. Silva; R.F. Silva; F.M. Costa (pp. 9175-9180).

► Axial temperature gradients in the laser floating zone technique were calculated. ► Thinner fibres exhibit steeper temperature gradient. ► Increasing the temperature gradient a better grain alignment is obtained. ► An improvement on the superconducting properties is obtained in the thinner fibres.Laser floating zone (LFZ) method was employed to grow superconducting polycrystalline Bi–Sr–Ca–Cu–O fibres of 2:2:1:2 nominal composition with two different diameters (1.75 and 2.50mm). The temperature profile at the solid/liquid interface was calculated along the fibre radii from estimations of the heat transfer coefficient and thermal conductivity of the fibres. Values of temperature gradient G=3.17×10⁵Km⁻¹ and G=2.65×10⁵Km⁻¹ at the fibre centre were obtained for the thinner and the thicker fibres, respectively. Growth under a steep temperature gradient has significant consequences on the microstructure of the thinner fibres: an improved texture and the absence of the copper-free Bi_x(Sr,Ca)_yO_z secondary phase. These features lead to the superior transport properties of the thinner fibres that present a higher value of critical current density ( J_C=2200Acm⁻²) than the wider ones ( J_C=1400Acm⁻²).

Keywords: Superconducting fibres; BSCCO; Laser floating zone technique; Thermal gradient

Enhancement of ZnO photoluminescence by laser nanostructuring of Ag underlayer by M.E. Koleva; A.Og. Dikovska; N.N. Nedyalkov; P.A. Atanasov; I.A. Bliznakova (pp. 9181-9185).

► The results of synthesis and characterization of Ag/ZnO nanocomposite heterostructures are presented. ► The size distribution of the Ag nanoparticles depends on the laser deposition and laser annealing procedures. ► The photoluminescent intensity of ZnO layers is strongly enhanced by plasmon absorption in Ag nanoparticles.Results are presented on the synthesis and characterization of nanocomposite Ag/ZnO heterostructures on fused quartz substrates. The experiments were performed by pulsed laser deposition (PLD) using a third harmonic Nd:YAG laser in a vacuum chamber. The ablation of a rotated Ag target was followed by laser modification of the deposited layer and subsequent deposition of ZnO. The process factors, such as the silver film thickness and the post-deposition annealing procedures, were varied in view of controlling the diameter and size distribution of the Ag nanoparticles. The annealing regimes were modified by varying the laser irradiation energy on the Ag layers. The effect on the Ag/ZnO properties is discussed. It is demonstrated that the photoluminescence intensity of ZnO nanolayers is significantly enhanced by plasmon absorption in the Ag nanoparticles and a shift to the lower wavelengths.

Keywords: PLD; Laser nanostructuring; Ag nanoparticles; nanocomposites; ZnO photoluminescence; Surface plasmon resonance

Photon synthesis of iron oxide thin films for thermo-photo-chemical sensors by S.A. Mulenko; Yu.N. Petrov; N.T. Gorbachuk (pp. 9186-9191).

► We report of UV photon synthesis of iron oxide thin films for multi-parameter sensors. ► Semiconductor properties of thin films are stipulated by iron oxides content. ► We obtained renewable thermo-photo-chemical sensors based on iron oxide thin films.Ultraviolet photons of KrF-laser (248nm) and of photodiode (360nm) were used for the synthesis of iron oxide thin films with variable thickness, stoichiometry and electrical properties. The reactive pulsed laser deposition (RPLD) method was based on KrF-laser and photon-induced chemical vapor deposition (PCVD) was based on a photodiode. Deposited films demonstrated semiconductor properties with variable band gap ( E_g). The film thickness (50–140nm) and E_g depended on the laser pulse number, oxygen and iron carbonyl vapor pressure in the deposition chamber, and exposure time to the substrate surface with ultraviolet (UV) radiation. Sensing characteristics strongly depended on electrical and structural properties of such thin films. Iron oxide films were deposited on 〈100〉 Si substrate and had large thermo electromotive force (e.m.f.) coefficient ( S) and high photosensitivity ( F). The largest value of the S coefficient obtained by RPLD was about 1.65mV/K in the range 270–290K and by PCVD was about 1.5mV/K in the range 280–322K. The largest value F obtained by RPLD and PCVD was about 44 V_c/W and 40 V_c/W, accordingly, for white light at power density ( I≅0.006W/cm²). It was shown that the S coefficient and F strongly depended on E_g. Moreover, these films were tested as chemical sensors: the largest sensitivity of NO molecules was at the level of 3×10¹²cm⁻³. Our results showed that RPLD and PCVD were used to synthesize semiconductor iron oxide thin films with different sensing properties. So iron oxide thin films synthesized by UV photons are up-to-date materials for multi-parameter sensors: thermo-photo-chemical sensors operating at moderate temperature.

Keywords: Photon; Synthesis; Oxide; Film; Sensor

Pulsed laser deposition of strontium-substituted hydroxyapatite coatings by I. Pereiro; C. Rodríguez-Valencia; C. Serra; E.L. Solla; J. Serra; P. González (pp. 9192-9197).

► Strontium-substituted hydroxyapatite coatings by pulsed laser deposition. ► Strontium carbonate powders as an adequate source of strontium for PLD. ► Efficient incorporation of Sr and carbonate groups in the hydroxyapatite structure. ► Linear incorporation of Sr accompanied by a similarly linear withdrawal of Ca. ► Fine control of the Sr content in the obtained coatings.The growing evidence of the beneficial role of strontium in bone has increased the interest of developing strontium-containing biomaterials for medical applications, and specifically biocompatible coatings that can be deposited on metallic implants to benefit from their load-bearing capabilities. In this work, strontium-substituted hydroxyapatite (Sr-HA) coatings have been fabricated by pulsed laser deposition (PLD) from initial targets obtained after mixing and compacting commercial HA and SrCO₃ powders in different proportions. The films thus fabricated were then structurally, morphologically and chemically characterized using scanning electron microscopy, optical profilometry, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The macroscopic morphology of the films presented in all cases equivalent spherical shaped aggregates of typical calcium phosphate coatings. The results reveal, however, the incorporation of Sr²⁺ and carbonate groups in the coatings as a function of the SrCO₃ content in the ablation target, being the incorporation of Sr²⁺ a linear phenomenon that is accompanied by a similarly linear withdrawal of Ca²⁺. The role of Sr²⁺ in the modification of the HA structure and a possible mechanism of substitution of Sr²⁺ atoms in place of Ca²⁺ atoms are discussed.

Keywords: Hydroxyapatite coating; Strontium; Laser ablation

Thin films deposited by femtosecond pulsed laser ablation of tungsten carbide by A. De Bonis; R. Teghil; A. Santagata; A. Galasso; J.V. Rau (pp. 9198-9201).

► We have deposited amorphous tungsten carbide films by ultra-short PLD. ► In the films different W–C phases are present. ► The films are formed mainly by particles with nanometric size. ► We propose that the particles are directly ejected from the target.Ultra-short Pulsed Laser Deposition has been applied to the production of thin films from a tungsten carbide target. The gaseous phase obtained by the laser ablation shows a very weak primary plume, in contrast with a very strong secondary one. The deposited films, investigated by Scanning Electron Microscopy, Atomic Force Microscopy, X-Ray Photoelectron Spectroscopy and X-Ray Diffraction, present a mixture of WC and other phases with lower carbon content. All films are amorphous, independently from the substrate temperature. The characteristics of the deposits have been explained in terms of thermal evaporation and cooling rate of molten particles ejected from the target.

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

Polarization dependence of the optical absorption of a subwavelength tip by A. Vella; N. Sevelin-Radiguet; J. Houard; B. Deconihout (pp. 9202-9207).

► We investigate the polarization dependence of the absorption of a subwavelength tip illuminated by an ultra short laser pulse. ► Different behaviors are reported on metallic (Al) and semi conducting (Si) tips. ► The experimental results are discussed and explained using electromagnetic theory in the simplified cylindrical geometry. ► Numerical simulations in a more real geometry are also presented. ► The limits of the cylindrical model are shown.Laser assisted atom probe tomography is used to investigate the polarization dependence of the absorption of a subwavelength tip illuminated by an ultra short laser pulse. Al and Si tips are investigated and experimental results are discussed and explained using electromagnetic theory in the simplified cylindrical geometry. Numerical simulations in a more real geometry are also presented and used to show limits of the cylindrical model and to show the role of the very end tip apex in the absorption process.

Keywords: JEL classification; 68.43.Tj; 79.70.+9; 42.65.−k; 42.65.kyOptical nanoobject; Field emission; Atom probe

Nanoscale concentration and strain distribution in pseudomorphic films Si1−_xGe_x/Si processed by pulsed laser induced epitaxy by L. Vincent; F. Fossard; T. Kociniewski; L. Largeau; N. Cherkashin; M.J. Hÿtch; D. Debarre; T. Sauvage; A. Claverie; J. Boulmer; D. Bouchier (pp. 9208-9212).

► Si1−_xGe_x/S_i pseudomorphic layers were synthesized by pulsed laser induced epitaxy. ► We performed strain and concentration measurements at the nanometer scale. ► Ge profiles are graded from the interface to the surface due segregation effects. ► The Ge profile is largely influenced by the temporal characteristics of the laser. ► A double peak laser pulse induces a two-stage solidification process.We report on the structural analysis of Si1−_xGe_x pseudomorphic layers synthesized by pulsed laser induced epitaxy (PLIE) using a nanosecond excimer laser. We focus here on the local determination of strain and related Ge concentration. First, a Ge amorphous layer is predeposited on a Si substrate. Successive laser pulses induce the incorporation of Ge atoms in the molten substrate layer and lead to the synthesis of a graded Si1−_xGe_x alloy over a depth which depends on the laser fluence. The Si1−_xGe_x layers are coherently strained and free of defects. The in-depth Ge concentration distribution is investigated by RBS and HAADF STEM. The strain fields are specifically explored using the new dark-field electron holography (Holodark) technique, offering mapping of the full strain tensor in two dimensions with a high precision. Independently determined strain and Ge concentration distributions over a distance of 150nm from the surface are found to be well consistent. An unexpected but reproducible depletion of Ge is evidenced inside the SiGe layer. This feature is shown to be related to the shape of the temporal characteristics of laser pulses. In particular, the second contribution, which occurs 32ns later, is involved in a two-stage solidification process.

Keywords: Melting; Segregation; Solidification

Femtosecond laser processing as a versatile tool for advanced solid state lighting sources: From efficacy enhancement to colour temperature control by Ladislav Kuna; Christian Sommer; Frank Reil; Joachim R. Krenn; Paul Hartmann; Peter Pachler; Hans Hoschopf; Franz P. Wenzl (pp. 9213-9217).

► Selective ablation of the sapphire flipside surface of flip-chip LEDs. ► Fabrication of arbitrarily shaped structures in the volume of silicone layers. ► Two-photon-polymerization of microlenses on the sapphire flipside surface of flip-chip LEDs.We report on a wealth of possibilities femtosecond (fs-) laser processing provides for future advancements of device efficacy and white light quality of light-emitting diodes (LEDs) for solid state lighting applications. We discuss three different processing approaches, subtractive, volume and additive structuring, as well as their individual applicabilities and advantages with respect to locally controlled enhancement of light-extraction, modification of the light distribution and adjustment of a desired colour temperature in phosphor conversion based white LEDs.

Keywords: Solid state lighting; Light-emitting diodes; Two-photon-polymerization

Antibacterial and surface-enhanced Raman scattering (SERS) activities of AgCl cubes synthesized by pulsed laser ablation in liquid by Chenbo Dong; Zijie Yan; Jacklyn Kokx; Douglas B. Chrisey; Cerasela Zoica Dinu (pp. 9218-9222).

► We synthesized AgCl nanocubes using pulsed laser ablation in liquid. ► We examined the antibacterial capabilities of AgCl nanocubes. ► We demonstrate that AgCl nanocubes have SERS properties. ► We envision AgCl nanocubes being serving as analytical tools for detection and decontamination.We used pulsed laser ablation in liquid to fabricate silver chloride (AgCl) nanocubes directly from a bulk Ag target in sodium chloride (NaCl) solution. We optimized particle size and investigated the surface properties of the cubes for their Surface Enhanced Raman Scattering (SERS) behavior relative to Rhodamine 6G (R6G). The SERS behavior was related to the surface properties, clearness, and morphology, i.e., varied atomic arrangements and surface energies of different facets of the cubes. In addition, we have demonstrated that our easily synthesized AgCl cubes were antibacterial with a high efficiency to decontaminate Escherichia coli upon contact. Our results can be extended to generate particle-based coatings with antibacterial properties.

Keywords: AgCl cubes; E. coli; Antibacterial; Killing capabilities

Selective gold nanoparticles formation by pulsed laser interference by R.J. Peláez; G. Baraldi; C.N. Afonso; S. Riedel; J. Boneberg; P. Leiderer (pp. 9223-9227).

► Exposure of discontinuous gold films to laser interference produces 2D and 1D patterns of round nanoparticles surrounded by non-transformed areas. ► The optical response of the patterns is dominated by the surface plasmon resonance of the gold nanoparticles. ► The accumulation of metal at some areas of the pattern is consistent with mass transport towards the lower temperature regions. ► The size of the nanoparticles depends on the initial effective thickness; the thicker the films the bigger the nanoparticles. ► Multiple laser exposures produce in alternating areas with different nanoparticle dimensions.Discontinuous Au films are prepared on glass substrates by pulsed laser deposition with two different metal coverages that lead to a film being formed by irregular coalesced nanoparticles (NPs) and to another film close to the percolation limit. The films are exposed to three interfering beams at different intensities produced by the fourth harmonic of a Nd:YAG laser (266nm, 10ns). Scanning electron microscopy and extinction spectra are used respectively to study the structural and optical properties before and after the laser structuring. Round metal NPs appear in the laser transformed areas due to melting followed by rapid solidification that is reflected in the extinction spectra by the appearance of a surface plasmon resonance around 530–540nm. The areas with NPs are surrounded by non-transformed areas forming a periodic pattern that evolves from a 2D array to parallel lines when local laser intensity increases to cover the whole sample at high intensity. The accumulation of several pulses at low fluence can also transform the metal film almost completely by creating alternating areas having different NP dimensions. The accumulation of metal in some areas of the pattern is consistent with mass transport towards the lower temperature regions.

Keywords: Laser; Patterning; Interference; Metal; Films; Nanoparticles; Melting

Optical and electrical properties of laser doped Si:B in the alloy range by A. Bhaduri; T. Kociniewski; F. Fossard; J. Boulmer; D. Débarre (pp. 9228-9232).

► Optically controlled GILD laser doping process reaches 3% B in Si by 0.03% steps. ► GILD made B-doped Si pseudomorphic layers at up to 3% B/Si by controlled 0.03% steps. ► 4-Point probe, XRD and FTIR reflectance show coherent results on GILD-doped Si. ► Drude model and FTIR reflectance give B density in Si:B layers up to 6×10²⁰cm⁻³.We have probed the dopant activity of silicon B-doped by Gas Immersion Laser Doping (GILD). Here, we report on the comparison of optical, electrical and structural properties of Si:B, over a wide concentration range, up to 1.5×10²¹cm⁻³ by steps of 1.5×10¹⁹cm⁻³. Data obtained by reflectance FTIR spectroscopy are used within a Drude model to extract concentration, thickness and mobility. Resulting carrier concentration and conductivity are checked with 4-point probe electrical and X-ray diffraction measurements. FTIR proved to be very sensitive to the dopant distribution inside the layer, despite its thinness. It clearly reveals a moderate dopant accumulation at the interfaces.

Keywords: Laser doping; GILD; Silicon; Boron; Drude model; FTIR spectroscopy

Formation of laser-induced periodic surface structures on fused silica upon multiple parallel polarized double-femtosecond-laser-pulse irradiation sequences by Arkadi Rosenfeld; Marcus Rohloff; Sandra Höhm; Jörg Krüger; Jörn Bonse (pp. 9233-9236).

Display Omitted► LIPSS formation studied for double-fs-pulses (160fs, 800nm) of different fluences. ► Close to the damage threshold predominantly HSFL are observed. ► The HSFL period remains almost constant ∼375nm (delay independent). ► At high fluences and for short delays a transient metallic state is created (LSFL regime). ► A transition of the LSFL period from 750 to 530nm is observed in the sub-ps delay range.The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica with multiple irradiation sequences of parallel polarized Ti:sapphire femtosecond laser pulse pairs (160fs pulse duration, 800nm central wavelength) was studied experimentally. For that purpose, a Michelson interferometer was used to generate near-equal-energy double-pulse sequences allowing the temporal pulse delay between the parallel-polarized individual fs-laser pulses to be varied between 0 and 40ps with ∼0.2ps temporal resolution. The surface morphologies of the irradiated surface areas were characterized by means of scanning electron and scanning force microscopy. In the sub-ps delay range a strong decrease of the LIPSS periods and the ablation crater depths with the double-pulse delay was observed indicating the importance of the laser-induced free-electron plasma in the conduction band of the solids for the formation of LIPSS.

Keywords: Laser-induced periodic surface structures (LIPSS); Femtosecond laser ablation; Double-pulse experiments; Fused silica; Michelson interferometer

Carbon nanotube growth from metallic nanoparticles deposited by pulsed-laser deposition on different substrates by Mireille Gaillard; Chantal Boulmer-Leborgne; Nadjib Semmar; Éric Millon; Agnès Petit (pp. 9237-9241).

► The size of Fe or Ni nanoparticles depends on the combined effect between catalyst/substrate natures. ► A higher surface tension as for metal substrate, leads to nanoparticle formation with sizes larger than those obtained on insulating substrates. This is linked to the adhesion strength of catalyst particle on substrate. ► Tip growth (typically multi-walled nanotubes) is observed from catalyst nanoparticles on insulating substrates and base growth (bamboo-like nanotube) for conductor substrate.Carbon nanotubes carpets were grown by RF plasma enhanced chemical vapor deposition on various substrates coated by Fe and Ni transition metals that act as catalyst. C₂H₂ gas was used for the carbon source. The results show that carbon nanotubes CNT can be grown on Si₃N₄/Si and SiO₂/Si substrates only with an Fe catalyst. They are typically formed by multi-walled graphene layers, and can be obtained for a temperature as low as 550°C. Nanotubes grown on TiN/SiO₂/Si substrate from Fe or Ni catalysts present bamboo-like nanostructures and are obtained for particular experimental conditions. This study demonstrates substrate-to-catalyst effect on the CNT growth and their microstructures indicating that the adhesion force of nanoparticles on substrates is a main parameter. Catalyst particles are spherical and several tens of nm in diameter (weak adhesion strength) when deposited onto SiO₂/Si or Si₃N₄/Si, the tip growth mode of nanotube is favored. On TiN/SiO₂/Si substrate, particles are larger (large adhesion strength) and CNT growth is no more in tip mode, bamboo-like structures are obtained. When an Fe-Ni catalyst multilayer has been deposited onto the different substrates, carbon nanotube microstructures show multi-walled graphene parallel layers on Si₃N₄/Si and SiO₂/Si insulating substrates, and bamboo-like microstructures on TiN/SiO₂/Si conductor substrate.

Keywords: Nanoparticles; Carbon nanotube growth; PECVD; PLD

On the origin of metallic conductivity at the interface of LaAlO₃/SrTiO₃ by Y.Z. Chen; D.V. Christensen; F. Trier; N. Pryds; A. Smith; S. Linderoth (pp. 9242-9245).

► Metallic interfaces are observed when insulating amorphous films of LaAlO₃, La₂O₃, or Al₂O₃ are deposited on crystalline SrTiO₃ substrates by pulsed laser deposition, whereas the deposition of amorphous LSMO films results in an insulating interface. ► The interfacial conductivity of the SrTiO₃-based hetero-structures with amorphous over-layers shows strong dependences on both film thickness and oxygen pressure during film growth. ► The occurrence of metallic interfaces in these complex oxide hetero-structures is probably due to redox reactions at the STO substrate surface.To determine the origin of the quasi-two-dimensional electron gas formed at the interface between the two complex oxides of LaAlO₃ (LAO) and SrTiO₃ (STO), various amorphous films of LAO, La₂O₃, Al₂O₃, and La_7/8Sr_1/8MnO₃ (LSMO), were deposited on TiO₂-terminated (001) STO substrates by pulsed laser deposition at room temperature. Metallic interfaces are observed when the over-layers are amorphous LAO, La₂O₃, or Al₂O₃, while insulating interfaces are observed when the over-layer is LSMO. The interfacial conductivity of these SrTiO₃-based hetero-structures shows strong dependence on both film thickness and oxygen pressure during film growth. The possible origin for the occurrence of metallic interfaces in these complex oxide hetero-structures due to redox reactions at the STO substrate surface is discussed. A thermodynamic criterion for designing either metallic or insulating interfaces between complex oxides is proposed.

Keywords: Complex oxides; Interface; Metal–insulator transition; SrTiO; ₃; surface

Dynamic light scattering in gold colloids prepared by laser ablation in water by M. Zimbone; L. Calcagno; P. Baeri; G.C. Messina; G. Compagnini (pp. 9246-9249).

► We present a dynamic light scattering analysis on gold colloids prepared by laser ablation in water. ► Diffusivities have been determined either on as-prepared particles and aggregates. ► The properties of the aggregates are obtained in the liquid state, avoiding deposition.A polarized and depolarized dynamic light scattering analysis on gold nano-colloids prepared by laser ablation in water has been conducted. This technique allows a simultaneous measurement of the translational and rotational diffusivities and has been applied to characterize ‘as-prepared’ and aggregated colloids obtained either by “spontaneous” or with “controlled” procedure. A simple model was applied to obtain information on the size, shape and anisotropy properties of the nanoparticles directly in the liquid state. The ‘as-prepared’ Au nanoparticles (AuNPs) are spherical, while a prolate ellipsoidal shape can be attributed to the aggregated nanoparticles. Depolarized dynamic light scattering results a powerful technique to determine the size and shape of AuNPs directly in solution.

Keywords: Gold nanoparticles; Light scattering; Plasmon resonance; Laser ablation

Magnetic core/shell nanoparticle thin films deposited by MAPLE: Investigation by chemical, morphological and in vitro biological assays by R. Cristescu; C. Popescu; G. Socol; I. Iordache; I.N. Mihailescu; D.E. Mihaiescu; A.M. Grumezescu; A. Balan; I. Stamatin; C. Chifiriuc; C. Bleotu; C. Saviuc; M. Popa; D.B. Chrisey (pp. 9250-9255).

► We deposit magnetic Fe₃O₄/oleic acid/cephalosporin nanoparticle thin films by MAPLE. ► Thin films have a chemical structure similar to the starting material. ► Cephalosporins have an additive effect on the grain size and induce changes in grain shape. ► MAPLE can be used to develop novel strategies for fighting medical biofilms associated with chronic infections.We report on thin film deposition of nanostructured Fe₃O₄/oleic acid/ceftriaxone and Fe₃O₄/oleic acid/cefepime nanoparticles (core/shell/adsorption-shell) were fabricated by matrix assisted pulsed laser evaporation (MAPLE) onto inert substrates. The thin films were characterized by profilometry, Fourier transform infrared spectroscopy, atomic force microscopy, and investigated by in vitro biological assays. The biological properties tested included the investigation of the microbial viability and the microbial adherence to the glass coverslip nanoparticle film, using Gram-negative and Gram-positive bacterial strains with known antibiotic susceptibility behavior, the microbial adherence to the HeLa cells monolayer grown on the nanoparticle pellicle, and the cytotoxicity on eukaryotic cells. The proposed system, based on MAPLE, could be used for the development of novel anti-microbial materials or strategies for fighting pathogenic biofilms frequently implicated in the etiology of biofilm associated chronic infections.

Keywords: Fe; ₃; O; ₄; /oleic acid/cephalosporin nanoparticles; Core/shell; Magnetic nanoparticle; Matrix assisted pulsed laser evaporation; Antimicrobial activity

Surface modification of UHMWPE with infrared femtosecond laser by J.M. Fernández-Pradas; S. Naranjo-León; J.L. Morenza; P. Serra (pp. 9256-9259).

.Display Omitted► Ultra High Molecular Weight Polyethylene surface was modified with femtosecond laser pulses at 1027nm wavelength. ► Surface roughness is increased. ► Ablation efficiency is maximum for 6μJ pulses. ► Irradiated surfaces remain almost chemically unaltered.Ultra-high-molecular-weight polyethylene (UHMWPE) is a polymer with mechanical and corrosion properties, which make it appropriate for using in biomedical devices such as hip and knee prostheses. The surface morphology and chemistry of UHMWPE influence its biocompatibility. A laser with wavelength at 1027nm delivering 450fs pulses at a repetition rate of 1kHz is used to modify the surface of UHMWPE samples with 0.45μm root mean square surface roughness. Micrometric resolution is achieved with the use of a focusing lens of 0.25NA and pulse energies of few microjoules.The study focuses in the influence of different pulse energies and pulse overlaps on the laser-induced surface roughness and ablation yield. Confocal microscopy is used to characterize changes in the morphology of the irradiated surfaces, and their chemical structure is analyzed by attenuated total reflectance infrared and Raman spectroscopies.The roughness increases as the pulse energy increases until it reaches a maximum. The ablation yield increases with the pulse energy and pulse overlap. However, the ablation yield per pulse is lower for higher pulse overlap. Pulses of 6μJ have the highest ablation efficiency. Infrared and Raman spectra of samples irradiated with low energy pulses are similar to those of the pristine sample. However, some CC and CO bonds can be detected after irradiation with the highest pulse energies.

Keywords: Femtosecond laser processing; UHMWPE; Polymer

Laser synthesized nanopowders for polymer-based composites by Lavinia Gavrila-Florescu; Ion Sandu; Ana Stan; Elena Dutu; Ion Voicu (pp. 9260-9262).

► Laser induced synthesis is a versatile method to produce nanopowders. ► Synthesized carbon and silicon carbide were used to elaborate polymer-based composites. ► Epoxy /phenol resin based composites with improved properties were obtained.The paper presents the different laser-synthesized carbon and silicon carbide nanostructures used as fillers for composites with epoxy or phenol resin matrix reinforced with glass or carbon fiber. The effect of nanoadditives on the composites’ mechanic and tribologic characteristics is presented. The addition of 2% nanocarbon or 5% SiC has led to the improvement of tensile strength and tensile modulus with 10–15% and 15–20%, respectively. The dry friction coefficient for nanocarbon-containing composites was decreased up to 25% for composites containing nanocarbon, whereas for carbon–carbon composites filled with silicon carbide, this parameter has increased with more than 50%.

Keywords: Carbon nanopowders; Laser; Composites; Silicon carbide

Laser-matter structuration of optical and biological materials by L. Hallo; C. Mézel; F. Guillemot; B. Chimier; A. Bourgeade; C. Regan; G. Duchateau; A. Souquet; D. Hebert (pp. 9263-9269).

► In this study we model nanomaterial structuring. ► The laser energy deposition is discussed first. ► Full and approximate models are discussed. ► Dynamic material response is addressed via hydrodynamics. ► Sild effects are accounted forInteraction of ultrafast laser, i.e. from the femtosecond (fs) to the nanosecond (ns) regime, with initially transparent matter may produce very high energy density hot spots in the bulk as well as at the material surface, depending on focusing conditions. In the fs regime, absorption is due to ionisation of the dielectric, which enables absorption process to begin, and then hydrodynamic to take place. In the ns regime both absorption and hydrodynamic are coupled to each other, which complexifies considerably the comprehension but matter structuration looks similar. A numerical tool including solution of 3D Maxwell equations and a rate equation for free electrons is first compared to some available simple models of laser energy absorption. Then, subsequent material deformation, i.e. structuration, is determined by solving hydrodynamic equations, including or not solid behaviour. We show that nature of the final structures strongly depends on the amount of deposited energy and on the shape of the absorption zone. Then we address some problems related to laser-matter structuration of optical and biological materials in the fs, ps and ns regimes.

Keywords: Laser processing; In-bulk and surface interactions; Matter structuration

Development of an industrial tool to make passivation layers for UV sensors improvement by Yannick Larmande; Vanessa Vervisch; Philippe Delaporte; Thierry Sarnet; Marc Sentis; Hasnaa Etienne; Frank Torregrosa (pp. 9270-9273).

► We have reached a sheet resistance lower than 500Ω/sq for a junction depth of 29nm and an abruptness of 3nm/dec. ► Electrical measurements on diodes have revealed a significant leakage current of around 10⁻⁵A/cm², revealing the presence of defects inside the junction. ► Light Beam Induced Current (LBIC) characterization has shown that the defects are localized at the edge of the laser beam.Today, the collection of generated charges is a limiting problem for the realization of UV sensors. Indeed, the native silicon oxide of the surface acts as a region of recombination centers . Then, the sensors exhibit a low sensitivity in the UV wavelengths. An approach to overcome this drawback is the realization of a few nanometers thick passivation layer at the surface by creating an ultra-shallow junction (USJ) with a high activation level.The realization of such junctions requires two steps: first, the implantation of dopants which consists in introducing impurities at the surface of the substrate, then the thermal activation of these dopants to obtain the electrical characteristics of the junction. The Plasma Immersion Ion Implantation (PIII) process allows us to implant dopants in a very thin layer (10–20nm) into the silicon substrate . These impurities are located in interstitial sites in the silicon, and need an activation process to modify the electrical properties of the layer. The step is performed by means of an excimer laser annealing process (ELA) to melt a very thin layer of the silicon substrate and then activate the dopants without diffusion. In the framework of the ALDIP project (Laser Activation of Dopants implanted by Plasma Immersion), IBS Company has developed with its partners a cluster to realize these two steps with industrial production rates and cleanliness.Four-point probe measurements and SIMS analyzes have been used to characterize the junctions realized with this process. We have reached a sheet resistance lower than 500Ω/sq for a junction depth of 29nm and an abruptness of 3nm/dec. Nevertheless, electrical measurements on diodes have revealed a significant leakage current of around 10⁻⁵A/cm², revealing the presence of defects inside the junction. Light Beam Induced Current (LBIC) characterization has shown that these defects are localized at the edge of the laser beam.

Keywords: Excimer laser annealing; Plasma Immersion Ion Implantation; Ultra shallow junctions; Passivation layer; UV sensors

Angular distribution of species in pulsed energy beam deposition of oxide films by M. Nistor; F. Gherendi; N.B. Mandache (pp. 9274-9277).

► Thickness profiles of Ba_xSr1−_xTiO₃ thin films were measured. ► Comparison between pulsed laser (PLD) and pulsed electron beam deposition (PED). ► The film thicknesses profile of PED has a slightly broader shape than that of PLD. ► The film stoichiometry is preserved at all angles.Pulsed energy beam deposition methods like pulsed-laser deposition (PLD) or pulsed-electron beam deposition (PED) allow the formation of smooth, dense and crystalline oxide thin films. The angular distribution of the ablated flux from the target and the thin film thickness profile were extensively studied for PLD for a wide range of materials and growth conditions. In the case of complex oxide compounds, the angular distribution of the various species emitted by the target will determine the precise composition of the films. In this work we report on the determination of the angular distributions of the species emitted from a Ba_xSr1−_xTiO₃ (BST) target. A comparison between these results obtained by PED and PLD methods is presented and discussed in the frame of Anisimov's model. A slightly broader shape of the angular distribution for PED than that for PLD is explained taking into account the differences in the spot size and fluence between the pulsed electron beam and laser beam and a small collisional broadening of the angular distribution in the case of PED. The stoichiometry is preserved at all angles.

Keywords: Pulsed laser deposition; Pulsed electron beam deposition; BST thin films; Angular distribution of the species

Aligned metallic nanoparticles on rippled surfaces: Optical characterization using generalized ellipsometry by T.W.H. Oates (pp. 9278-9282).

► Optical properties of aligned silver nanospheres and nanorods are investigated. ► Effective dielectric functions are determined using generalized ellipsometry. ► The DFs are highly anisotropic due to the plasmon resonances in the silver particles. ► A 2-fold symmetric anisotropy in the LO mode is caused by tilting of the particles.Oblique-angle deposition of metallic island films onto self-organized rippled surfaces results in arrays of particles and wires with characteristic dimensions below 50nm. Films of the noble metals exhibit distinct optical properties due to localized plasmon resonances. Here the films are characterized using generalized spectroscopic ellipsometry. Due to the small characteristic dimensions we can describe the optical properties using an effective medium approach. The dielectric properties are highly anisotropic and a biaxial dielectric tensor description is required. The plasmonic resonances provide a means to tune the form birefringence by adjusting the metal fraction, from aligned nanoparticles with anisotropic localized plasmon resonances, to arrays of nanowires with orthogonal metallic and dielectric properties. The deposition of the particles on one side of the ripple ridges causes additional anisotropy that shows a 2-fold symmetry upon rotation in the substrate plane. This is associated with a longitudinal plasmon resonance in the out-of-plane direction.

Keywords: Plasmon; Metamaterials; Dielectric function; Ellipsometry

Porous nanoparticles of Al and Ti generated by laser ablation in liquids by P.G. Kuzmin; G.A. Shafeev; G. Viau; B. Warot-Fonrose; M. Barberoglou; E. Stratakis; C. Fotakis (pp. 9283-9287).

► Nanoparticles of either Al or Ti are generated by laser ablation in hydrogen-saturated liquids. ► Nanoparticles contain cavities. ► The morphology of generated particles depends on the laser pulse duration.Experimental results are presented on the generation of porous nanoparticles of either Al or Ti by laser ablation of solid targets in ethanol, water, and n-propanol saturated with hydrogen. The nanoparticles are characterized by high resolution transmission electron microscopy (HR TEM) and optical absorption spectroscopy. Saturation of the liquid with gaseous hydrogen leads to the formation of internal cavities in nanoparticles. In the case of short laser pulses (180fs, Ti:sapphire laser at 800nm wavelength), the nanoparticles are mostly spherical with the size of 30–50nm at concentration about 10¹⁵cm⁻³. The cavity occupies from 20 to 50% of the particle volume. Longer laser pulses (70ns, Nd:YAG laser at 1064nm wavelength) generate facetted nanoparticles with facetted cavities inside. The mechanism of formation of cavities is discussed on the basis of temperature-dependent solubility of hydrogen in metals.

Keywords: Laser; Ablation; Liquid; Nanoparticles; Aluminum; Titanium; Hydrogen

Numerical simulation of laser ablation for photovoltaic materials by P. Stein; O. García; M. Morales; H.P. Huber; C. Molpeceres (pp. 9288-9291).

► Implementation of the two-temperature model into Abaqus. ► Reproduction of the behavior of ultra-short laser pulse interaction with metals. ► Numerical predicition of ablation thresholds.The objective of this work is to help understanding the impacts of short laser pulses on materials of interest for photovoltaic applications, namely aluminum and silver. One of the traditional advantages of using shorter laser pulses has been the attempt to reduce the characteristic heat affected zone generated in the interaction process, however the complex physical problem involved limitates the integration of simplified physical models in standard tools for numerical simulation. Here the interaction between short laser pulses and matter is modeled in the commercial finite-element software Abaqus. To describe ps and fs laser pulses properly, the two-temperature model (TTM) is applied considering electrons and lattice as different thermal transport subsystems. The Material has been modeled as two equally sized and meshed but geometrically independent parts, representing each the electron and the lattice domain. That means, both domains match in number and position of the respective elements as well as in their shape and their size. The laser pulse only affects the electron domain so that the lattice domain remains at ambient temperature. The thermal connection is only given by the electron-phonon coupling, depending on the temperature difference between both domains. It will be shown, that melting and heat affected zones getting smaller with decreasing pulse durations.

Keywords: Ultra-short laser pulses; Two-temperature model; Numerical simulation; Abaqus

Application of holographic sub-wavelength diffraction gratings for monitoring of kinetics of bioprocesses by Tomas Tamulevičius; Rimas Šeperys; Mindaugas Andrulevičius; Vitoldas Kopustinskas; Šarūnas Meškinis; Sigitas Tamulevičius; Valeryia Mikalayeva; Rimantas Daugelavičius (pp. 9292-9296).

► Refractive index sensor based on DLC holographic sub-wavelength period grating. ► Spectroscopic analysis of polarized white light reflected from the grating. ► Control of critical wavelength shift and reflectivity changes. ► Testing of model liquid analyte materials. ► Evaluation of interaction between B. subtilis cells and lysozyme.In this work we present a refractive index (RI) sensor based on a sub-wavelength holographic diffraction grating. The sensor chip was fabricated by dry etching of the finely spaced ( d=428nm) diffraction grating in SiO_x doped diamond like carbon (DLC) film. It is shown that employing a fabricated sensor chip, and using the proposed method of analysis of data, one can inspect kinetics of processes in liquids occurring in the vicinity of the grating surface. The method is based on the spectral composition analysis of polarized polychromatic light reflected from the sub-wavelength diffraction grating. The RI measurement system was tested with different model liquid analytes including 25wt.%, 50wt.% sugar water solutions, 10°C, 50°C distilled water, also Gram-positive bacteria Bacillus subtilis interaction with ion-permeable channels forming antibiotic gramicidin D and a murolytic enzyme lysozyme. Analysis of the data set of specular reflection spectra enabled us to follow the kinetics of the RI changes in the analyte with millisecond resolution. Detectable changes in the effective RI were not worse than Δ n=10⁻⁴.

Keywords: Refractive index sensor; Laser interference lithography; Sub-wavelength diffraction grating; SiO; _x; doped DLC; Lysozyme; B. subtilis

KTa_0.65Nb_0.35O₃ thin films epitaxially grown by pulsed laser deposition on metallic and oxide epitaxial electrodes by A. Bouyasfi; M. Mouttalie; V. Demange; B. Gautier; A. Grandfond; S. Députier; S. Ollivier; L’ H. Hamedi; M. Guilloux-Viry (pp. 9297-9301).

► Ferroelectric KTa_0.65Nb_0.35O₃ thin films grown by pulsed laser deposition. ► KTa_0.65Nb_0.35O₃ epitaxially grown on Pt and LaNiO₃ epitaxial electrodes. ► Influence of oxide vs. metal electrode on ferroelectric's structural properties. ► AFM/TUNA mode investigation of KTa_0.65Nb_0.35O₃/Pt heterostructure. ► Asymmetry of the conduction mechanisms (positive vs. negative applied voltage).Ferroelectric KTa_0.65Nb_0.35O₃ (KTN) thin films were grown by pulsed laser deposition on Pt and LaNiO₃ epitaxial electrodes, on (100) and (110) SrTiO₃ substrates. The effect of the nature of the electrode on structural and microstructural quality of KTN films was investigated. While epitaxial KTN thin films were successfully obtained on both electrodes, two orientations compete on Pt, whatever the main orientation of Pt is (100) or (110). On LaNiO₃ in contrast, pure (100) and (110) oriented KTN films were achieved with a high crystalline quality illustrated by narrow ω-scans (Δ ω=0.56° and Δ ω=0.80° for (100) and (110) KTN, to be compared to 0.048° and 0.22° for (100) and (110) LaNiO₃, respectively). Electrical measurements performed in tunneling atomic force microscopy (TUNA mode) on a KTN/Pt heterostructure showed a high asymmetry of the conduction mechanisms when a positive or a negative bias is applied on the sample. In particular leakage currents appear even at very low positive applied voltage. TUNA imaging operated at a moderate negative applied voltage of −3V shows that some areas corresponding to grain boundaries seem to be more leaky than others.

Keywords: Ferroelectrics; Thin films; KTN; Electrodes; AFM; TUNA

MAPLE deposition of PLGA:PEG films for controlled drug delivery: Influence of PEG molecular weight by Irina Alexandra Paun; Antoniu Moldovan; Catalin Romeo Luculescu; Angela Staicu; Maria Dinescu (pp. 9302-9308).

► We obtained implants from indomethacin cores coated with PLGA:PEG films grown by MAPLE. ► The implants were studied in vitro, in media close to those encountered inside the body. ► The influence of the molecular weight of PEG (1450Da versus 10kDa) was investigated. ► PEG of high molecular weight enhanced the blood compatibility of the implants. ► PEG of high molecular weight increased the drug release rates from the implants.Implantable devices consisting of indomethacin (INC) cores coated with poly(lactide-co-glycolide):polyethylene glycol films (i.e. PLGA:PEG films) deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) were produced. To predict their behavior after implantation inside the body, the implants were studied in vitro, in media similar with those encountered inside the body (phosphate buffered saline (PBS) pH 7.4 and blood). The influence of the molecular weight of PEG (i.e. low (1450Da) versus high (10kDa) molecular weights) on the characteristics of the implants was investigated, in terms of morphology, blood compatibility and kinetics of the drug release. The use of PEG of high molecular weight resulted in larger pores on the implants surfaces, enhanced blood compatibility of the implants and higher drug delivery rates. For both molecular weights PEGs, sustained release of INC was maintained over a three weeks interval. Theoretical fitting of the drug release data with Higuchi's model indicated that the INC was released mainly by diffusion, most probably through the pores formed in PLGA:PEG films during PBS immersion.

Keywords: MAPLE; Polymers; Drug delivery

A simple model for flyer velocity from laser-induced forward transfer with a dynamic release layer by James Shaw-Stewart; Thomas Lippert; Matthias Nagel; Frank Nüesch; Alexander Wokaun (pp. 9309-9313).

► First model for LIFT flyer velocity, based on explosive Gurney energy model. ► Model takes into account laser beam and decomposition energies as inputs and assumes all deposited laser energy above a threshold is used as kinetic energy of decomposition products and the flyer. ► Experimental flyer velocities obtained by shadowgraphy of aluminium flyers in vacuum. ► Model velocities fit experimental velocities well just by adjusting reflective losses of laser beam energy.A simple 1-D model has been developed for the velocity of flyers in vacuum generated by laser-induced forward transfer (LIFT) with a dynamic release layer (DRL). It is an extension of a laser ablation model for metal flyer plates based on the Gurney model of explosive output for driving metal fragments. The model has been extended to the bilayer system of a DRL overlain with a transfer layer. The suitability of the model has been checked with experimental velocity data obtained from shadowgraphy. The experiments used bilayer samples of triazene polymer/aluminium, ablated from the backside through the substrate at reduced pressure (5×10⁻²mbar). The results suggest that the Gurney energy approach provides the basis of a viable, physically relevant, algebraic model for LIFT, but other loss mechanisms still need be incorporated, particularly thermal loss into the fused silica substrate.

Keywords: Gurney energy; Flyer velocity; model; LIFT; laser ablation; DRL

Large scale microstructuring on silicon surface in air and liquid by femtosecond laser pulses by M. Ulmeanu; F. Jipa; C. Radu; M. Enculescu; M. Zamfirescu (pp. 9314-9317).

► Large-scale microstructures were formed on the surface of silicon with dimensions of 1mm×1mm by femtosecond laser line-by-line scanning irradiation, in air and liquid assisted. ► Scanning electron microscopy investigations exhibited homogeneous surface microstructures, such as, ripples with sub-wavelengths dimensions, Si pillars and directional arranged bacilliform structures. ► The dependence of the surface morphology on laser energy and scanning speed was analyzed.Large-scale microstructures were imprinted on the surface of silicon with dimensions of 1mm×1mm by femtosecond laser line-by-line scanning irradiation. The scanning was made under air and under chlor/hydrogen based liquid layers. Scanning electron microscope investigations evidenced homogeneous surface microstructures, such as: ripples with sub-wavelengths dimensions, Si pillars and directional oriented bacilliform structures. The dependence of the surface morphology on laser energy, scanning speed and irradiation media was analyzed. In air, the microstructure changes from directional-arranged bacilliform structures to well-known ripple structures with a width of about 525nm. When using the liquid media, we observe ripple structures with a width of about 370nm and an overlapping of those that evolve in certain regions into Si pillars. The surfaces show interesting gradient topography behaviour which could be used as model scaffolds for the systematic exploration of the role of 3D micro/nano morphology on cell adhesion and growth. By using chlor and hydrogen based liquids we were able to explore the microstructuring of the silicon by line-by-line irradiation process using the femtosecond laser.

Keywords: Femtosecond laser; Si structuring; Chlor based liquids; H based liquids

Stability of contamination-free gold and silver nanoparticles produced by nanosecond laser ablation of solid targets in water by R.G. Nikov; A.S. Nikolov; N.N. Nedyalkov; I.G. Dimitrov; P.A. Atanasov; M.T. Alexandrov (pp. 9318-9322).

► Au and Ag colloids were prepared by nanosecond laser ablation of solids in water. ► The alteration of the produced colloids during one month was investigated. ► Optical transmission spectra of the samples were measured from 350 to 800nm. ► TEM measurements were made of as-prepared colloids and on the 30-th day. ► Zeta potential measurements were performed of as-prepared samples.Preparation of noble metal nanoparticle (NPs) colloids using pulsed laser ablation in water has an inherent advantage compared to the different chemical methods used, especially when biological applications of the colloids are considered. The fabrication method is simple and the NPs prepared in this way are contamination free.The method of laser ablation of a solid target in water is applied in the present work in order to obtain gold and silver NP colloids. The experiment was preformed by using the fundamental wavelength (1064nm) of a Nd:YAG laser system. The target immersed in double distilled water was irradiated for 20min by laser pulses with duration of 15ns and repetition rate of 10Hz. The sedimentation and aggregation of NPs in the colloids, stored at constant temperature, as a function of the time after preparation were investigated. The analyses are based on optical transmission spectroscopy in UV and vis regions. The change of the plasmon resonance wavelength as a function of time was studied. Zeta potential measurement was also utilized to measure the charge of the NPs in the colloids. The size distribution of the NPs and its change in time was determined by transmission electron microscopy (TEM). On the basis of the results obtained, the optimal conditions of post fabrication manipulation with gold and silver colloids are defined in view of producing stable NPs with a narrow size distribution.

Keywords: Ag; Au nanoparticles; Nanosecond laser ablation; Aqueous colloids; Aggregation; Sedimentation

Strain and lattice distortion in (110)-epitaxial orthorhombic TbMnO₃ multiferroic thin films grown by pulsed laser deposition by Y. Hu; M. Bator; M. Kenzelmann; T. Lippert; C. Niedermayer; C.W. Schneider; A. Wokaun (pp. 9323-9325).

► Orthorhombic TbMnO₃ thin films were deposited by pulsed laser deposition. ► The films grow with (110)-epitaxy on the (110) NdGaO₃ and YAlO₃ substrates. ► The o-TbMnO₃ thin films are single phase and untwinned. ► The film (110)-planes are made more square-like by epitaxial growth. ► With increasing thickness the film structure relaxes and mosaicity increases.Untwinned single phase thin films of multiferroic orthorhombic TbMnO₃ are deposited by pulsed laser deposition on (110)-oriented NdGaO₃ and YAlO₃ substrates. X-ray diffraction measurements show that these films grow with a (110)-expitaxy on both substrates and the (110)-plane of a film shows a more square-like distortion imposed by the underlying substrate. Therefore, these films are under tensile strain along the [001] direction on NdGaO₃. In the case of TbMnO₃ on YAlO₃, the film shows an unexpected tensile strain also along [001] contrary to expectations. X-ray reciprocal mapping confirms that with increasing thickness the film lattice parameters relax towards bulk values. In addition, an increase in mosaicity is also observed.

Keywords: Multiferroic; Thin film growth; PLD; Strain

Development of systems for the laser synthesis of nanoparticles starting from liquid precursors by E. Popovici; C. Luculescu; R. Alexandrescu; C. Fleaca; F. Dumitrache; R. Barjega; M. Scarisoreanu; E. Dutu; A. Barbut; I. Morjan; E. Vasile (pp. 9326-9332).

► An original evaporator system was designed and instrumentation was developed. ► The process occurs in the gas phase, over the boiling temperature of the substances. ► The control system allows the maintaining of the overall system temperature.The laser synthesis of nanoparticles starting from liquid precursors is particularly suitable as synthesis technique for obtaining nanoparticles. In the present work the laser pyrolysis is performed in a novel setup where the liquid precursor is brought with the aid of an original evaporator system to temperatures in excess of the boiling point and is finally fed into the reactor under the form of heated vapors.The process occurs in the gas phase and ensures the avoidance of the condensation. The temperature control system allows for the maintaining of the overall system temperature below the decomposition temperature and above the boiling. Temperatures up to 500°C are assured for the mixed precursors. The control of the amount of the active substances is performed upstream, in the liquid phase. The set-up is able to offer safety conditions at the synthesis of substances with high toxicity. This experimental set-up was proposed in order to synthesize TiO₂ nanoparticles from TTIP because its boiling temperature is relatively high (239°C grades). Different analytical techniques such as EDX, TEM, XRD and HRTEM were used in order to evaluate the structural characteristics of the produced nanopowders.

Keywords: Laser pyrolysis; Sensitizer; Nanoparticles; Titania; Anatase; Liquid precursors

PLD and RF discharge combination used for preparation of photocatalytic TiO₂ layers by Jan Remsa; Jan Mikšovský; Miroslav Jelínek (pp. 9333-9336).

► Pulsed laser deposition technique combined with the radio-frequency discharge. ► Polycrystalline titanium dioxide layers at substrate temperatures 85°C and 150°C. ► TiO₂exhibited photocatalytic characteristics tested by two methods.Utilizing pulsed laser deposition technique combined with the radio-frequency discharge (between the target and the substrate), we were able to grow polycrystalline titanium dioxide layers (anatase, rutile) at substrate temperatures 85°C and 150°C. Besides the discharge no additional substrate heating was applied. The layers were prepared from pure titanium and titanium dioxide targets. To optimize deposition conditions, the oxygen background pressure, fluence (from 2Jcm⁻² to 9Jcm⁻²), and discharge power were varied. Silicon wafers (111), fused silica, and polyethylene tubes were used as substrates. The layers’ crystalline structure was determined by X-ray diffraction. Atomic force microscopy was used to characterize the surface properties. Two methods were implemented to determine TiO₂ photocatalytic characteristics: 4-chlorphenol solution degradation evaluated by pH measurement and the decomposition of Oleic acid evaluated by the change of the water contact angle on the surface layer. Both methods indicated similar results: the highest photoactivity was observed on the layers consisting from anatase phase and mixture of anatase and rutile.

Keywords: Pulsed laser deposition; Titanium dioxide; Photocatalysis; RF discharge; Thin films

Effects of substrate temperature on nanoparticle-assembled Fe films produced by ultrafast pulsed laser deposition by G. Ausanio; V. Iannotti; S. Amoruso; X. Wang; C. Aruta; M. Arzeo; R. Fittipaldi; A. Vecchione; R. Bruzzese; L. Lanotte (pp. 9337-9341).

► Effects of substrate temperature on nanoparticle-assembled Fe films produced by fs-PLD. ► Low temperature magnetic behavior of nanoparticle-assembled Fe films produced by fs-PLD. ► Role played by the Fe oxide shell in stabilizing the core magnetic moments. ► Influence of the spin disorder in surface oxidized Fe nanoparticles on low temperature coercivity.Ultrafast pulsed laser deposition is an interesting technique for the synthesis of nanoparticles (NP) and NP-assembled films (NPA). The NPA films show a structure with agglomerates of NPs sticking to one another, with a significant shape and orientation anisotropy and negligible coalescence. In this communication, we report preliminary results concerning the effect of the substrate temperature on the magnetic response of the NPA films in the case of Fe NPs deposited on Si (100). The experimental data evidence a clear role of the substrate temperature on the hysteresis loop of the deposited NPA films due to the aggregation and oxidation degree of the NPs.

Keywords: Ultrashort pulsed laser deposition; Nanoparticle-assembled magnetic films; Oxidation; Coercivity

FEM numerical analysis of excimer laser induced modification in alternating multi-layers of amorphous and nano-crystalline silicon films by J.C. Conde; E. Martín; S. Stefanov; P. Alpuim; S. Chiussi (pp. 9342-9346).

► nc-Si:H is a material with growing importance for a large-area of nano-electronic, photovoltaic or biomedical devices. ► UV-ELA technique causes a rapid heating that provokes the H₂ desorption from the Si surface and bulk material. ► Next, diffusion of P doped nc-Si films and eventually, for high energy densities would be possible to reach the melting point. ► These multilayer structures consisting of thin alternating a-Si:H(10nm) and n-doped nc-Si:H(60nm) films deposited on SiO₂. ► To optimize parameters involved in this processing, FEM numerical analysis of multilayer structures have been performed. ► The numerical results are compared with exhaustive characterization of the experimental results.UV excimer laser annealing (UV-ELA) is an alternative annealing process that, during the last few years, has gained enormous importance for the CMOS nano-electronic technologies, with the ability to provide films and alloys with electrical and optical properties to fit the desired device performance. The UV-ELA of amorphous (a-) and/or doped nano-crystalline (nc-) silicon films is based on the rapid (nanoseconds) formation of temperature profiles caused by laser radiation that is absorbed in the material and lead to crystallisation, diffusion in solid or even in liquid phase.To achieve the desired temperature profiles and to optimize the parameters involved in the processing of hydrogenated nanocrystalline silicon (nc-Si:H) films with the UV-ELA, a numerical analysis by finite element method (FEM) of a multilayer structure has been performed. The multilayer structures, consisting of thin alternating a-Si:H(10nm) and n-doped nc-Si:H(60nm) layers, deposited on a glass substrate, has also been experimentally analyzed.Temperature profiles caused by 193nm radiation with 25ns pulse length and energy densities ranging from 50mJ/cm² to 400mJ/cm² have been calculated. Numerical results allowed us to estimate the dehydrogenation process of the different layers and the diffusion of phosphorous (P) in Si layers as well as their structural modifications as a function of the applied laser energy density. Numerical results are compared with exhaustive characterization of the experimental results.

Keywords: Excimer laser annealing; a-Si; nc-Si; Dehydrogenation; Numerical modelling

Enthalpy based modeling of pulsed excimer laser annealing for process simulation by M. Hackenberg; P. Pichler; K. Huet; R. Negru; J. Venturini; A. Pakfar; C. Tavernier; A. La Magna (pp. 9347-9351).

► A enthalpy-based model for pulsed excimer laser annealing was developed. ► The model predicts similar temperature and phase evolution than the phase-field model. ► Undercooling is found to be negligible in a TCAD model. ► The melt depth found in experiment is reproduced by simulation.We present an enthalpy-based model for pulsed excimer laser annealing of crystalline silicon in the melting regime that integrates into the technology computer-aided design (TCAD) suite Sentaurus Process of Synopsys. The currently one-dimensional model includes laser absorption, a transient simulation of the heat flux, melting of the surface layer, and undercooling during recrystallization. To verify the model, its predictions for a laser pulse with a duration of ∼150ns and a wavelength of 308nm were compared to those of a phase-field implementation of melting laser annealing by La Magna et al. The two models show a good agreement for the melt depth, melt duration, and melt front dynamics. In a second step, model predictions were compared to melt depths extracted from SIMS measurements of ion implanted and excimer-laser-annealed silicon samples. They were found to agree within the experimental error. Variation of the beam parameters indicated a strong influence of laser energy density fluctuations on the melt depth.

Keywords: Excimer laser annealing; Silicon; Simulation; TCAD

Laser induced forward transfer aluminum layers: Process investigation by time resolved imaging by Thomas Mattle; James Shaw-Stewart; Christof W. Schneider; Thomas Lippert; Alexander Wokaun (pp. 9352-9354).

► Side- and front-on shadowgraphy. ► Aluminum flyer is ejected intact for all tested energies. ► Indications of bending of the aluminum flyer are shown.Laser induced forward transfer of an aluminum thin film on a triazene polymer as a sacrificial layer has been studied with time resolved imaging. Both side- and front-on imaging of the process give a more detailed understanding of the stability of the ejected material during flight. For high fluence ablation (800mJ/cm²) the flyer is stable for 400ns and gets decomposed completely when interacting with the shockwave after 1μs. Material detachments on the edges of the flyer are observed at an early stage of the ablation process (<200ns) which leads to a pixel smaller than its ablation cross section.For low laser fluence (200mJ/cm²) the flyer has the size of the ablation spot and keeps its shape for nearly 1μs. The back pressure of the decomposed triazene polymer bends the flyer towards the direction of flight and indications for folding are observed.

Keywords: Laser transfer; LIFT; Shadowgraphy

Composition and species evolution in a laser-induced LuMnO₃ plasma by Matthias Bator; Yi Hu; Martin Esposito; Christof W. Schneider; Thomas Lippert; Alexander Wokaun (pp. 9355-9358).

► Plasma mass spectrometry and spectroscopy of LuMnO₃. ► Comparison of the plasma composition and evolution under different conditions. ► Different plasma composition and evolution for vacuum and O₂/N₂O background. ► Relation of mass spectrometry results with observations in emission spectroscopy. ► Most advantageous growth conditions for LuMnO₃ in N₂O background.Pulsed laser deposition is often used to grow multi-elemental thin films from stoichiometric targets. The growth process is influenced by a wide variety of parameters like the target composition, background gases, laser wavelength, laser fluence, or spot size. The changes these parameters induce in the film growth also affect the plasma plume and species formed during laser ablation. For oxide growth O₂, and sometimes N₂O, is utilized as background gas to achieve the required oxygen composition for the as-grown film. Mass spectrometry combined with time- and space resolved emission spectroscopy is used to investigate the behavior and evolution of plasma species in the plasma plume during the ablation process of LuMnO₃ dependent on the background gas.

Keywords: Pulsed laser deposition; Rare-earth manganates; Emission spectroscopy; Plasma characterization; Plasma mass spectrometry

CW laser induced crystallization of thin amorphous silicon films deposited by EBE and PECVD by Z. Said-Bacar; P. Prathap; C. Cayron; F. Mermet; Y. Leroy; F. Antoni; A. Slaoui; E. Fogarassy (pp. 9359-9365).

► The effect of hydrogen in CW laser crystallization of hydrogenated amorphous silicon thin films has been investigated. ► Large hydrogen content results in decohesion of the films due to hydrogen effusion. ► Very low hydrogen content or hydrogen free amorphous silicon film are suitable for crystallization induced by CW laser. ► Grains of size between 20 and 100μm in width and about 200μm in long in scanning direction are obtained with these latter films.This work presents the Continuous Wave (CW) laser crystallization of thin amorphous silicon (a-Si) films deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) and by Electron Beam Evaporation (EBE) on low cost glass substrate. The films are characterized by Elastic Recoil Detection Analysis (ERDA) and by Fourier-Transform Infrared (FTIR) spectroscopy to evaluate the hydrogen content. Analysis shows that the PECVD films contain a high hydrogen concentration (∼10at.%) while the EBE films are almost hydrogen-free. It is found that the hydrogen is in a bonding configuration with the a-Si network and in a free form, requiring a long thermal annealing for exodiffusion before the laser treatment to avoid explosive effusion. The CW laser crystallization process of the amorphous silicon films was operated in liquid phase regime. We show by Electron Backscatter Diffraction (EBSD) that polysilicon films with large grains can be obtained with EBE as well as for the PECVD amorphous silicon provided that for the latest the hydrogen content is lower than 2at.%.

Keywords: Hydrogenated amorphous silicon; Polycrystalline silicon; CW laser; Crystallization; Thin film

Growth and transport properties of HT–Li_xCoO₂ thin films deposited by pulsed laser deposition by E. Svoukis; G.I. Athanasopoulos; A. Moradpour; O. Schneegans; A. Revcolevschi; J. Giapintzakis (pp. 9366-9369).

► Highly c-axis oriented HT–Li_xCoO₂ thin films are grown on (0001) Al₂O₃ substrates by PLD. ► Deposition conditions change both surface roughness and resistivity of the thin films. ► The CP–AFM revealed very good surface roughness is an important issue in exploiting this material in novel devices. ► PLD is a promising technique for the growth of thin films of materials that contain volatile components.The successful in situ growth of single phase, c-axis oriented, layered structured Li_xCoO₂ thin films on (0001) Al₂O₃ substrates by pulsed laser deposition is reported. Thin films were grown in an oxygen pressure of 1mbar and substrate temperatures varying from 300 up to 600°C. It is found that the surface roughness and electrical resistance of the films depends strongly on the deposition temperatures.

Keywords: LiCoO; ₂; Pulsed laser deposition; Thin films; CP–AFM

Fabrication of sub-micrometric metallic hollow-core structures by laser interference lithography by Noemí Pérez; Txaber Tavera; Ainara Rodríguez; Miguel Ellman; Isabel Ayerdi; Santiago M. Olaizola (pp. 9370-9373).

► Arrays of hollow-core sub-micrometric structures are fabricated. ► Laser interference lithography is used for the pattering of the resist sacrificial layer. ► The removal of the sacrificial layer gives rise to metallic channels with a maximum crosssectional area of 0.1μm². ► These structures can be used in nanofluidics.This work presents the fabrication of hollow-core metallic structures with a complete laser interference lithography (LIL) process. A negative photoresist is used as sacrificial layer. It is exposed to the pattern resulting from the interference of two laser beams, which produces a structure of photoresist lines with a period of 600nm. After development of the resist, platinum is deposited on the samples by DC sputtering and the resist is removed with acetone. The resulting metallic structures consist in a continuous platinum film that replicates the photoresist relief with a hollow core. The cross section of the channels is up to 0.1μm². The fabricated samples are characterized by FESEM and FIB. This last tool helps to provide a clear picture of the shape and size of the channels. Conveniently dimensioned, this array of metallic submicrometric channels can be used in microfluidic or IC cooling applications.

Keywords: Laser interference lithography; Microchannels; Micro/nanofabrication

Temporal pulse shaping effects on aluminium and boron ablation plumes generated by ultrashort pulsed laser ablation and analyzed by time- and space-resolved optical spectroscopy by F. Bourquard; J.-P. Colombier; M. Guillermin; A.-S. Loir; C. Donnet; R. Stoian; F. Garrelie (pp. 9374-9378).

► Time- and space-resolved emission spectroscopy of femtosecond laser ablation plume of aluminium and boron. ► Temporal shaping of femtosecond laser pulses influence on plasma plume. ► Increasing pulse duration or double pulses delay rises ionization rate of aluminium plasma particularly with long pulses. ► Double pulses enhance ionization of aluminium plasma by shielding of the second pulse. ► Increasing pulse duration or double pulses delay decreases boron nanoparticle amount especially with double pulses.This paper focuses on the effect of temporal shaping of femtosecond laser pulses on laser ablation of aluminium and boron. The influence on plasma composition is deduced from optical emission investigations. Irradiation generated by the temporal tailoring of an incident laser pulse into double pulses or longer pulses is examined and compared to results deduced from hydrodynamic simulations of plasma temperature profiles. Above the ion formation threshold, increasing the delay in the double pulses sequence or increasing the pulse duration leads to an increase of the ion emission of the plasma plume of aluminium or boron. The observed increase with a saturation of ion emission at long delays or long pulse durations result from an interaction between the shaped laser pulse and the expanding matter after the onset of the plasma. Irradiation of boron with long pulses or double pulses reduces the production of nanoparticles, compared to the case of short pulses. Temporal shaping does not significantly affect the nanoparticle temperature, in spite of significant variations in the quantity of the ejected nanoparticles.

Keywords: Femtosecond ablation; Plasma; Nanoparticles; Temporal shaping

Influence of solution properties in the laser forward transfer of liquids by V. Dinca; A. Patrascioiu; J.M. Fernández-Pradas; J.L. Morenza; P. Serra (pp. 9379-9384).

► Influence of viscosity on the LIFT dynamics in the case of a Newtonian liquid. ► A very broad range of viscosities (1.9–850mPas) can be LIFT printed. ► Printing uniformity correlates well with the stability of the ejection process.The influence of the viscosity of the printed solution on the laser-induced forward transfer (LIFT) of liquids is investigated. A set of water and glycerol mixtures with different glycerol content are prepared with the aim of having a collection of solutions covering a wide range of viscosities, from 1.9 to 850mPas. Arrays of micrometric droplets of those solutions are spotted through LIFT and characterized by means of optical microscopy, revealing that for all the analyzed solutions there always exists a range of laser fluences leading to the formation of regular circular droplets, with that range increasing and widening with viscosity.The dynamics of liquid ejection is investigated through time-resolved imaging with the aim of understanding the role of viscosity in the process, and its influence on the morphology of the deposited droplets. The acquired stop-action movies reveal that liquid transfer proceeds mainly through jetting, with the exception of LIFT at low viscosities and high laser fluences, in which bursting develops. From this study it is concluded that viscosity plays an important role in the stabilization of liquid ejection and transport, which contributes to the uniformity of the deposited droplets.

Keywords: Laser forward transfer; Biomolecule printing; Time-resolved imaging

The role of the substrate material type in formation of laser induced periodical surface structures on ZnO thin films by Marian Zamfirescu; Adrian Dinescu; Mihai Danila; Gabriel Socol; Catalina Radu (pp. 9385-9388).

► LIPSS were produced by femtoseconds laser beam on ZnO films deposited by PLD. ► The nanostructures morphology depends on substrate material. ► The XRD measurements demonstrate the polycrystalline structure of the ZnO LIPSS. ► Fused silica and c-Al₂O₃ substrates are the most suitable for producing ZnO ripples.Laser induced periodical surface structures (LIPSS) are obtained on extended area of zinc oxide thin films by femtosecond laser pulses. The ZnO films deposited by pulsed laser deposition (PLD) technique were irradiated by femtosecond laser beam with 200fs pulse duration, at 775nm central wavelength and 2kHz repetition rate. The irradiation conditions such as laser fluence and scanning speed were varied for each sample. The morphology and the crystalline structure of the LIPSS on ZnO films were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) for different substrates such as fused silica, crystalline SiO₂, MgO, Al₂O₃, or Si wafers with different crystal orientation. The LIPSS appear on all ZnO films, deposited on crystalline substrates, as well as on amorphous substrates. However, more irregular nanostructures, such as bifurcations or nanodroplets were observed on ZnO with MgO, and r-Al₂O₃ substrates. The ZnO LIPSS are polycrystalline when fused silica, and SiO₂ (0001) substrates are used.

Keywords: Femtosecond laser; Nanostructure; Ripples; Zinc oxide; Crystalline structure

Plasma dynamics and structural modifications induced by femtosecond laser pulses in quartz by J. Hernandez-Rueda; D. Puerto; J. Siegel; M. Galvan-Sosa; J. Solis (pp. 9389-9393).

► Irradiation of quartz with single fs laser pulses at increasing pulse energies. ► Ablation at high local fluences and surface depression at low fluences. ► Fs-microscopy shows that free electron plasma causes surface depression. ► Surface depression is consistent with an increased material density. ► Low steady-sate reflectivity indicates creation of defects.We have investigated plasma formation and relaxation dynamics induced by single femtosecond laser pulses at the surface of crystalline SiO₂ (quartz) along with the corresponding topography modifications. The use of fs-resolved pump-probe microscopy allows combining spatial and temporal resolution and simultaneous access to phenomena occurring in adjacent regions excited with different local fluences. The results show the formation of a transient free-electron plasma ring surrounding the location of the inner ablation crater. Optical microscopy measurements reveal a 30% reflectivity decrease in this region, consistent with local amorphization. The accompanying weak depression of ≈15nm in this region is explained by gentle material removal via Coulomb explosion. Finally, we discuss the timescales of the plasma dynamics and its role in the modifications produced, by comparing the results with previous studies obtained in amorphous SiO₂ (fused silica). For this purpose, we have conceived a new representation concept of time-resolved microscopy image stacks in a single graph, which allows visualizing quickly suble differences of the overall similar dynamic response of both materials.

Keywords: Pump-probe; Quartz; Femtosecond laser; Plasma; Dynamics; Microscopy; Fused silica

Fe-inserted and shell-shaped carbon nanoparticles by cluster-mediated laser pyrolysis by C.T. Fleaca; F. Dumitrache; I. Morjan; R. Alexandrescu; I. Sandu; C. Luculescu; S. Birjega; G. Prodan; I. Stamatin (pp. 9394-9398).

Display Omitted► Iron-inserted carbon nanoparticles were obtained by laser pyrolysis technique. ► Two different structures (shell-shape and turbostratic) were found in the same experiment. ► Increasing the pressure causes the increasing in carbon crystallinity/decreasing the Fe content. ► Iron nanoinclusions are protected from oxidation by the carbon matrix. ► Magnetism-related applications of these nanoparticles in life sciences are proposed.We report here the high-yield continuous synthesis of carbon nanoparticles with and without Fe content by laser pyrolysis technique. The laser beam decomposes (via C₂H₄ sensitizer) the Fe(CO)₅ as Fe clusters which absorb themselves the laser radiation. They trigger the fast carbon particles formation by exothermic dehydrogenation/polymerization of the surrounded C₂H₂ molecules. This combination between Fe clusters and C₂H₂ generates nanoparticles with unusual structure. Depending on the gas pressure in the reaction chamber, two kinds of nanoparticles were obtained: at lower pressure, 30–40nm diameter particles with a defective structure, part of them crowded with Fe clusters (3–6nm) and two types of nanoparticles (around 50–60nm) at the highest pressure. Some of them have a shell-shape structure, presenting a distinct envelope, other with a turbostratic arrangement, and few containing one or several smaller (3–20nm) Fe nanoparticles trapped inside. We consider that these particular structures of our nanoparticles may be useful in applications such as MRI applications, drug delivery or catalysts.

Keywords: PACS; 82.30.Lp; 81.16.−c; 81.07.−b; 62.23.PqLaser pyrolysis; Iron–carbon nanoparticles; Shell-shape nanoparticles

Ag clustering investigation in laser irradiated ion-exchanged glasses by optical and vibrational spectroscopy by E. Trave; E. Cattaruzza; F. Gonella; P. Calvelli; A. Quaranta; A. Rahman; G. Mariotto (pp. 9399-9403).

► We modify the properties of Ag⁺ exchanged glasses by thermal and laser treatment. ► The induced microstructural changes are analyzed by optical and Raman spectroscopy. ► Ag-based species in the glass show a peculiar PL activity in the UV–Vis range. ► Raman and OA analysis allow for determining the Ag cluster size evolution. ► Laser processing leads to different cluster formation and fragmentation mechanisms.Ion exchange process is widely used to dope silicate glass layers with silver for several applications, ranging from light waveguide to nanostructured composite glass fabrication. The silver-doped structure and its physical properties depend on the preparation parameters as well as on subsequent treatments. In particular, laser irradiation of the ion exchanged glasses has been demonstrated to be an effective tool to control cluster size and size distribution. Nevertheless, a complete comprehension of the basic phenomena and a systematic characterization of these systems are still lacking. In this paper, an extended optical characterization is presented for soda-lime glass slides, doped with silver by Ag⁺–Na⁺ ion exchange, thermally treated and irradiated with a Nd:YAG laser beam at different wavelengths, and for different energy density. The samples were characterized by various spectroscopic techniques, namely, optical absorption, photoluminescence and micro-Raman analysis. The availability of all these characterization techniques allowed pointing out a suitable scenario for the Ag clustering evolution as a function of the ion exchange, annealing and laser irradiation parameters.

Keywords: Laser irradiation; Ion exchange; Optical spectroscopy; Raman spectroscopy; Cluster nucleation; Glass nanocomposite

Laser-induced Coulomb explosion in C and Si nanoclusters: The determining role of pulse duration by C. Chenard-Lemire; L.J. Lewis; M. Meunier (pp. 9404-9407).

► We investigate the interaction of ultrashort laser pulses with small (less than ∼4nm) carbon and silicon nanoclusters. ► We find that the outer-ionization mechanism goes through a peak for very short (fs) pulses. ► The peak position depends exclusively on pulse duration. ► Other parameters only affect the peak intensity. ► Our results show that Coulomb explosion is almost entirely determined by the pulse duration.We investigate, at the quantum-mechanical level, the interaction of ultrashort laser pulses with small (less than ∼4nm) carbon and silicon nanoclusters. We find that the outer-ionization mechanism—by virtue of which electrons are ejected from the outer shells of the clusters—goes through a peak for very short (fs) pulses, whose position depends exclusively on the duration of the pulse while other parameters, such as laser fluence and cluster size, only affect its intensity. Our results thus establish that Coulomb explosion, an important process for the disintegration of materials under intense laser pulses, is almost entirely determined by the duration of the pulse while other “experimental” parameters have relatively modest effects.

Keywords: Coulomb explosion; Laser ablation; Nanoclusters

Band gap tuning of ZnO nanoparticles via Mg doping by femtosecond laser ablation in liquid environment by E. Chelnokov; M. Rivoal; Y. Colignon; D. Gachet; L. Bekere; F. Thibaudau; S. Giorgio; V. Khodorkovsky; W. Marine (pp. 9408-9411).

► Femtosecond laser ablation synthesis of Mg doped ZnO nanoparticles. ► Electronic properties of ZnO are modified by Mg. ► Band gap and exciton energy shifts to the blue. ► The exciton energy shift is saturated at Mg content of about 20%. ► Phase separation at Mg content is at more than 25%. ► Mechanism of exciton pinning – recombination via new surface states.We use multiphoton IR femtosecond laser ablation to induce non-thermal non-equilibrium conditions of the nanoparticle growth in liquids. Modifications of the electronic properties of ZnO NP were achieved by Mg ion doping of targets prepared from mixtures of Zn and Mg acetylacetonates. The nanoparticle sizes were 3–20nm depending on the ablation conditions. X-ray fluorescence indicates that stoichiometric ablation and incorporation of Mg in nanocrystalline ZnO occurs. HRTEM observations show that nanoparticles retain their wurtzite structure, while at high Mg concentrations we detect the MgO rich domains. Exciton emissions exhibit relatively narrow bands with progressive and controlled blue shifts up to 184meV. The exciton energy correlates to band edge absorption indicating strong modification of the NP band gaps. Stabilisation of the exciton blue shift is observed at high Mg concentration. It is accompanied by the formation of structure defects and ZnO/MgO phase separation within the nanoparticles.

Keywords: Laser ablation; Zinc oxide; ZnO/MgO; Exciton emission; HRTEM

Microdroplet deposition through a film-free laser forward printing technique by A. Patrascioiu; J.M. Fernández-Pradas; J.L. Morenza; P. Serra (pp. 9412-9416).

► Circular droplets are obtained for a wide range of focusing depths at fixed energy. ► Focusing depth variation study reveals two abrupt transitions in droplet diameter. ► Liquid ejection mechanism is mediated by two types of jets of different origin. ► Evolution of jets depends on the focusing depth accounting for the seen transitions.A recently developed film-free laser forward microprinting technique allows printing transparent and weakly absorbing liquids with high resolution and reproducibility. Its operating principle consists in the tight focusing of ultrashort laser pulses inside the liquid, and near its free surface, such that all the laser energy is absorbed in a small region around the beam waist. A cavitation bubble is then created inside the liquid, whose subsequent expansion results into the ejection of liquid. The collection of the ejected liquid on a substrate leads to the deposition of micron-sized droplets.In this work, we investigate a relevant process parameter of the technique, namely the laser focusing depth, and its influence on the morphology of the deposited droplets. The study reveals that for a fixed laser pulse energy there exists a relatively wide range of focusing depths at which circular and uniform droplets can be printed. The process of liquid ejection is also investigated. Time-resolved images reveal that liquid ejection proceeds through the formation of two kinds of jets which display clearly differentiated dynamics, and which could provide an interpretation for the dependence observed between the morphology of the deposited droplets and the laser focusing depth.

Keywords: Laser direct-writing; Laser printing; Micropatterning; Time-resolved imaging

Electronic excitation and relaxation processes in wide band gap dielectric materials in the transition region of the Keldysh parameter by Nikita S. Shcheblanov; Elena P. Silaeva; Tatiana E. Itina (pp. 9417-9420).

Numerical modeling of electronic excitation processes induced by ultra-short laser pulses in dielectric materials is performed. The developed model is based on a detailed kinetic description and accounts for the absence of equilibrium in the electronic subsystem. The photoionization process is first analyzed for different laser intensities. It is shown that the probability of this process depends strongly on the Keldysh parameter and effective ionization potential, which are calculated as a function of the laser field. Electron energy distributions are calculated and the average energy is analyzed as a function of laser parameters. For laser intensities corresponding to the maximum of this dependency, only around 1% of electrons are shown to achieve the energy required for the impact ionization.

Keywords: PACS; 78.20.Bh; 72.20.Jv; 52.50.Jm; 42.65.Re; 72.80.SkUltra-short laser pulse; Dielectrics; Photoionization; Numerical modeling; Electronic excitation; Femtosecond

Laser processing issues of nanosized intermetallic Fe–Sn and metallic Sn particles by R. Alexandrescu; I. Morjan; F. Dumitrache; R. Birjega; C. Fleaca; Iuliana Morjan; M. Scarisoreanu; C.R. Luculescu; E. Dutu; V. Kuncser; G. Filoti; E. Vasile; V. Ciupina (pp. 9421-9426).

► Intermetallic Fe–Sn and metallic Sn nanoparticles synthesized by laser pyrolysis. ► Fe(CO)₅ and Sn(CH₃)₄ were used as precursors. ► FeSn₂, Sn and Fe₃SnC phases were identified by XRD. ► Complex core–shell structural characteristics were found by HRTEM analysis. ► Higher magnetization was found in samples with increased Fe/Sn atomic ratio.Intermetallic Fe–Sn and nanocrystalline metallic Sn nanoparticles have been successfully synthesized from organic precursors using the laser pyrolysis technique with ethylene as sensitizer. Nano-structured Sn (single phase) was prepared by the pyrolysis of Sn(CH₃)₄ (TMT) vapors. Controlled Fe/Sn atomic ratios, ranging from 0.69 to 1.64 were obtained for the prepared Fe–Sn nanopowders by the control of Fe(CO)₅ and TMT flows, respectively. XRD studies evidence three main phases: the tetragonal metallic Sn phase and the intermetallic FeSn₂ phase and, to a much lesser extent, the cubic ternary carbide Fe₃SnC. Complex core–shell structural characteristics were found by HRTEM analysis. More complete information about the Fe phase distributions in the new intermetallic Fe–Sn nanomaterial is provided by temperature dependent⁵⁷Fe Mössbauer spectroscopy.

Keywords: Intermetallics; Nanostructured; FeSn; ₂; Sn; Nanoparticles; Laser pyrolysis

Surface energy tailoring of glass by contact printed PDMS by A. Lamberti; M. Quaglio; A. Sacco; M. Cocuzza; C.F. Pirri (pp. 9427-9431).

Display Omitted► Tuning PDMS surface energy (SE) changing its composition. ► Permanent SE modification and transferable to other surfaces by contact printing. ► PDMS mold by lift-off technique using Laser Direct Writing lithography. ► General equation of Cassie model applied to describe this composite surface. ► Predicted contact angle values in good agreement with experimental results.A simple contact printing method to modulate the surface wettability of glass employing poly(dimethyl)siloxane (PDMS) mold was investigated. PDMS is a well known material in microfluidics and soft lithography for biomedical applications, being easy to process, low cost, biocompatible and transparent. Moreover its wettability can be tuned, by the exposure to oxygen plasma, UV-ozone or chemical oxidant solutions, or by surface functionalization. Unfortunately the effects of these treatments are not so stable in time. In this work a method to modify the surface energy (SE) of PDMS by changing its composition is proposed. Different mixing ratios (polymer base/curing agent) are analyzed evidencing that SE decreases while increasing the content of the polymer base, permanently modifying the surface behavior. As a thin layer of PDMS can be transferred to glass surfaces by contact printing, it is possible to locally change the wettability of glass simply patterning PDMS. In this work a SE patterning technique for glass surfaces by PDMS transfer is proposed. The technological process is based on the fabrication of PDMS molds by lift-off technique using Laser Direct Writing (LDW) lithography to process commercial photoresist. The transferring process for structures having a width of 10μm was studied for a chosen PDMS composition, analyzing the surface energy of the patterned thin film by contact angle (CA) measurements.

Keywords: PDMS; Surface energy; Contact printing; Laser Direct Writing

Effect of surface topography in the generation of chemical maps by laser-induced plasma spectroscopy by I. Lopez-Quintas; V. Piñon; M.P. Mateo; G. Nicolas (pp. 9432-9436).

► Analysis and chemical mapping by laser-induced breakdown spectroscopy (LIBS). ► Influence of surface roughness in the LIBS signals. ► Confocal measurements for the surface roughness data.The development of technologically advanced materials is propelling the improvement of surface analytical techniques. In particular, the composition and hence the properties of most of these new materials are spatial dependent. Between the techniques able to provide chemical spatial information, laser-induced plasma spectroscopy known also as laser-induced breakdown spectroscopy (LIBS) is a very promising analytical technique. During the last decade, LIBS was successfully applied to the analysis of surfaces and the generation of chemical maps of heterogeneous materials. In the LIBS analysis, several experimental factors including surface topography must be taken into account. In this work, the influence of surface roughness in LIBS signal during the point analysis and acquisition of chemical maps was studied. For this purpose, samples of stainless steel with different surface finishes were prepared and analyzed by LIBS. In order to characterize the different surfaces, confocal microscopy images were obtained. Afterwards, both topographic and spectroscopic information were combined to show the relationship between them. Additionally, in order to reveal the effect of surface topography in the acquisition of chemical maps, a three dimensional analysis of a sample exhibiting two different finishes was carried out.

Keywords: Laser-induced plasma spectroscopy; Laser-induced breakdown spectroscopy; Chemical mapping; Surface texture; Roughness

Laser surface modification of PEEK by A. Riveiro; R. Soto; R. Comesaña; M. Boutinguiza; J. del Val; F. Quintero; F. Lusquiños; J. Pou (pp. 9437-9442).

► Role of laser irradiation wavelength on the surface modification of PEEK (polyether-ether-ketone) was investigated. ► Adequate processing conditions to improve wettability, roughness, and cell adhesion characteristics are determined. ► A design of experiments (DOE) methodology was performed. ► UV (355nm) radiation is the most promising laser radiation for improving the adhesive surface properties of PEEK.Polyether-ether-ketone (PEEK) is a synthetic thermoplastic polymer with excellent mechanical and chemical properties, which make it attractive for the field of reconstructive surgery. Nevertheless, this material has a poor interfacial biocompatibility due to its large chemical stability which induces poor adhesive bonding properties. The possibilities of enhancing the PEEK adhesive properties by laser treatments have been explored in the past. This paper presents a systematic approach to discern the role of laser irradiation wavelength on the surface modification of PEEK under three laser wavelengths ( λ=1064, 532, and 355nm) with the aim to determine the most adequate processing conditions to increase the roughness and wettability, the main parameters affecting cell adhesion characteristics of implants. Overall results show that the ultraviolet ( λ=355nm) laser radiation is the most suitable one to enhance surface wettability of PEEK.

Keywords: Laser; Surface modification; PEEK; Design of experiments (DOE)

Optimization of laser-firing processes for silicon-heterojunction solar-cell back contacts by I. Sánchez-Aniorte; R. Barrio; A. Casado; M. Morales; J. Cárabe; J.J. Gandía; C. Molpeceres (pp. 9443-9446).

One of the key steps to achieve high efficiencies in amorphous/crystalline silicon photovoltaic structures is to design low-ohmic-resistance back contacts with good passivation in the rear part of the cell. A well known approach to achieve this goal is to use laser-fired contact (LFC) processes in which a metal layer is fired through the dielectric to define good contacts with the semiconductor. However, and despite the fact that this approach has demonstrated to be extremely successful, there is still enough room for process improvement with an appropriate optimization. In this paper, a study focused on the optimal adjustment of the irradiation parameters to produce laser-fired contacts in a-Si:H/c-Si heterojunction solar cells is presented. We used samples consisting of crystalline-silicon (c-Si) wafers together with a passivation layer of intrinsic hydrogenated amorphous silicon (a-Si:H(i)) deposited by plasma-enhanced chemical deposition (PECVD). Then, an aluminum layer was evaporated on both sides, the thickness of this layer varied from 0.2 to 1μm in order to identify the optimal amount of Al required to create an appropriate contact. A q-switched Nd:YVO₄ laser source, λ=532nm, was used to locally fire the aluminum through the thin a-Si:H(i)-layers to form the LFC. The effects of laser fluences were analyzed using a comprehensive morphological and electrical characterization.

Keywords: Laser firing; Laser processing; Heterojunction; Solar cell; Surface treatment

Nanosecond laser ablation processes in aluminum-doped zinc-oxide for photovoltaic devices by D. Canteli; S. Fernandez; C. Molpeceres; I. Torres; J.J. Gandía (pp. 9447-9451).

► A study of the ablation of AZO thin films deposited at different temperature conditions with nanosecond UV laser light for photovoltaic devices has been performed. ► The ablation threshold of AZO thin films was measured and related with the absorption coefficient of the films at the laser wavelength, showing a direct correspondence. ► A change in the material structure in the areas closest to the edges of laser grooves made in samples deposited at temperatures below 100°C was observed and studied.Aiming to a future use in thin film solar modules, the processing of aluminum doped zinc oxide thin films with good optoelectronic properties with a nanosecond-pulsed ultraviolet laser has been studied. The ablation threshold fluence of the films has been determined and associated with the material properties. The ablation process has been optimized and grooves with good properties for photovoltaic devices have been obtained. The morphology of the ablated surfaces has been observed by confocal microscopy and its structure has been characterized by Raman spectroscopy. The influence of ablation parameters like focus distance, pulse energy and repetition frequency in the groove morphology has been studied with special attention to the thermal effects on the material structure.

Keywords: Laser processing; Aluminum zinc oxide

Picosecond laser-induced formation of spikes in a single crystal superalloy by Wei Zhang; Guanghua Cheng; Qiang Feng; Lamei Cao (pp. 9452-9456).

► Transition from ripples to spikes with pulse number. ► Laser fluence has a significant effect on the spike separation. ► Relationship between structures and their parametric dependence is established. ► Capillary waves are responsible for the formation of spikes.The characteristics of laser-induced periodic surface structures (LIPSS) were investigated after laser irradiation with different pulse duration under a certain range of laser fluence (0.25≤ Φ≤1.91J/cm²) and pulse number (11≤ N≤560). Spikes were generated by picosecond laser irradiation in ambient air, in comparison with only periodic ripple structures introduced by nanosecond and femtosecond laser irradiation. Microstructural investigations indicate that these spikes were initiated by the fragment of periodic ripple ridges or corrugation on the smooth surface with subsequent pulses, and their separation increased with increasing the laser fluence. Surface capillary waves associated with the resolidification process can be employed to explain the formation of spikes by picosecond laser irradiation.

Keywords: Picosecond laser; Ripples; Spikes; Capillary waves

Lithium niobate bulk crystallization promoted by CO₂ laser radiation by N.M. Ferreira; F.M. Costa; R.N. Nogueira; M.P.F. Graça (pp. 9457-9460).

► Crystallization of LiNbO₃ nanocrystals in a SiO₂ matrix by CO₂ laser irradiation process. ► Samples heat-treated at 650°C (4h) and laser treated (4W/500s) show similar morphology. ► Glass–ceramics produced by laser process requires a very low processing time.The crystallization induced by laser radiation is a very promising technique to promote glass/ceramic transformation, being already used to produce crystalline patterns on glass surfaces. In this work, a SiO₂–Li₂O–Nb₂O₅ glass, prepared by the sol–gel route, was submitted to CO₂ laser radiation and conventional heat-treatments in order to induce the LiNbO₃ crystallization. The structure and morphology of the samples prepared by both routes was analyzed as a function of exposure time, radiation power and heat-treatment temperatures by XRD, Raman spectroscopy and SEM. The results reveal a correlation between the crystallization degree of LiNbO₃ particles and glass matrix with the heat treatment type and experimental parameters. An heat-treatment at 650°C/4h was necessary to induce crystallization in heat treatments samples while 4W/500s was enough for laser radiation ones, corresponding a reduction time processing of ∼14000s.

Keywords: Glass–ceramics; Sol–gel; Lithium niobate; Laser treatment; Structural properties

Modelling nanoparticles formation in the plasma plume induced by nanosecond pulsed lasers by M. Girault; L. Hallo; L. Lavisse; M.C. Marco de Lucas; D. Hébert; V. Potin; J.-M. Jouvard (pp. 9461-9465).

► Nanoparticles spatial localization in the plume induced by a pulsed laser. ► Plasma plume obtained by laser irradiation. ► Particles and debris formation. ► Powder generation. ► Conditions of formation.Nanoparticles formation in a laser-induced plasma plume in the ambient air has been investigated by using numerical simulations and physical models. For high irradiances, or for ultrashort laser pulses, nanoparticles are formed by condensation, as fine powders, in the expanding plasma for very high pairs of temperature and pressure. At lower irradiances, or nanosecond laser pulses, another thermodynamic paths are possible, which cross the liquid–gas transition curve while laser is still heating the target and the induced plasma. In this work, we explore the growth of nanoparticles in the plasma plume induced by nanosecond pulsed lasers as a function of the laser irradiance. Moreover, the influence of the ambient gas has also been investigated.

Keywords: Laser processing; Nanopowders; Modeling

Adsorption properties of Mg–Al layered double hydroxides thin films grown by laser based techniques by A. Matei; R. Birjega; A. Vlad; M. Filipescu; A. Nedelcea; C. Luculescu; R. Zavoianu; O.D. Pavel; M. Dinescu (pp. 9466-9470).

► Laser techniques MAPLE and PLD can successfully be used to produce LDHs thin films. ► Hydration treatments of the PLD and MAPLE deposited films lead to the LDH reconstruction effect. ► The Ni retention from aqueous solution occurs in the films via a dissolution–reconstruction mechanism. ► The films are suitable for applications in remediation of contaminated drinking water or waste waters.Powdered layered double hydroxides (LDHs) have been widely studied due to their applications as catalysts, anionic exchangers or host materials for inorganic and/or organic molecules. Assembling nano-sized LDHs onto flat solid substrates forming thin films is an expanding area of research due to the prospects of novel applications as sensors, corrosion-resistant coatings, components in optical and magnetic devices.Continuous and adherent thin films were grown by laser techniques (pulsed laser deposition – PLD and matrix assisted pulsed laser evaporation – MAPLE) starting from targets of Mg–Al LDHs. The capacity of the grown thin films to retain a metal (Ni) from contaminated water has been also explored. The thin films were immersed in an Ni(NO₃)₂ aqueous solutions with Ni concentrations of 10⁻³% (w/w) (1g/L) and 10⁻⁴% (w/w) (0.1g/L), respectively. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX) were the techniques used to characterize the prepared materials.

Keywords: Layered double hydroxides; Thin films; PLD; MAPLE

Matrix assisted pulsed laser evaporation of Mn₁₂(Propionate) thin films by M. Pervolaraki; F. Sima; G. Socol; C.M. Teodorescu; N.G. Gheorghe; M. Socol; I.N. Mihailescu; E.E. Moushi; A.J. Tasiopoulos; G.I. Athanasopoulos; Z. Viskadourakis; J. Giapintzakis (pp. 9471-9474).

► Deposition of Mn₁₂(Propionate) films using MAPLE. ► Identification of growth conditions for continuous and smooth films. ► Unusual steps in magnetic hysteresis loop of deposited films.Single molecule magnets are of great interest due to a multitude of potential applications for some of which thin films are required. Traditional physical vapor deposition techniques are not suitable for the deposition of these fragile materials with low decomposition temperatures. Matrix Assisted Pulsed Laser Evaporation technique has been employed for the growth of thin films of the single molecule magnet Mn₁₂(Propionate) on Si and glass substrates. In this paper we report on the appropriate growth conditions and also the morphology, chemical composition and magnetic behavior of the films. Continuous Mn₁₂(Propionate) films with properties similar to bulk materials have been obtained.

Keywords: Single molecule magnets; Mn; ₁₂; (Propionate); MAPLE; Thin films

Pulsed laser deposition of highly textured La₅Ca₉Cu₂₄O₄₁ films on SrLaAlO₄ (100) and Gd₃Ga₅O₁₂ (100) substrates by M. Pervolaraki; I. Pasuk; G.E. Stan; J. Giapintzakis (pp. 9475-9479).

► Growth of highly b-axis oriented LCCO films on SrLaAlO₄ (100) and Gd₃Ga₅O₁₂ (100) substrates. ► The grain size depends strongly on the substrate temperature and the oxygen pressure. ► Purely b-axis oriented LCCO films were deposited on Gd₃Ga₅O₁₂ single crystals usingPO2=20Pa and T_sub=850°C.The growth of La₅Ca₉Cu₂₄O₄₁ thin films on SrLaAlO₄ (100) and Gd₃Ga₅O₁₂ (100) substrates by pulsed laser deposition is reported in this paper. The influence of deposition process parameters, such as oxygen pressure, substrate temperature, and laser repetition rate, on the crystallinity, orientation and microstructure of the films has been investigated. X-ray diffraction and atomic force microscopy studies showed a clear dependence of the film crystallographic orientation and morphology (grain size) on the substrate temperature and the oxygen pressure used in the deposition process.

Keywords: La; ₅; Ca; ₉; Cu; ₂₄; O; ₄₁; thin films; PLD; SrLaAlO; ₄; (1; 0; 0) substrate; Gd; ₃; Ga; ₅; O; ₁₂; (1; 0; 0) substrate

A wide-range model for simulation of pump-probe experiments with metals by Mikhail E. Povarnitsyn; Nikolay E. Andreev; Eugeny M. Apfelbaum; Tatiana E. Itina; Konstatntin V. Khishchenko; Oleg F. Kostenko; Pavel R. Levashov; Mikhail E. Veysman (pp. 9480-9483).

► Pump-probe experiments provide an integral test of the models in the theoretically difficult regime of warm dense matter. ► The target material motion is evident for heating by femtosecond pulses of intensity more than 10¹⁴W/cm². ► Phase shift of S and P-polarized pulses is different because of separated zones of absorption. ► Uncertainty in the pulse energy determination of ∼10% gives substantial deflection of the theoretical curves. ► The surface target oxide films may result in bigger phase shift in experiment.High precision pump-probe experiments can provide a valuable information about material states out of equilibrium. A wide-range numerical model is used for the description of material response on ultrashort laser action. The model is developed on the basis of two-temperature hydrodynamics with heat transport, ionization, plasma expansion, electron-ion collisions and two-temperature equation of state for an irradiated substance. Comparison of experimental findings with the results of simulation is used both for the numerical model verification and for calculation of plasma thermodynamic parameters that cannot be measured directly in experiment. An aluminum target is heated by an intense 400nm (2 ω) pump laser pulse that is incident normal to the planar target. Weak S- and P-polarized probe pulses with wavelength 800nm (1 ω) are used for diagnostics of the plasma. Both probe pulses illuminate the target at a 45° angle. Calculation of the reflectivity and phase shift of probe pulses with both polarizations are in good agreement with experiment.

Keywords: Laser-metal interaction; Pump-probe experiment; Phase shift; Transport properties

Production of TiO₂ crystalline nanoparticles by laser ablation in ethanol by M. Boutinguiza; B. Rodriguez-Gonzalez; J. del Val; R. Comesaña; F. Lusquiños; J. Pou (pp. 9484-9486).

► Nanoparticles of TiO₂ have been obtained by laser ablation of Ti submerged in ethanol using CW laser. ► The use of CW laser contributes to control the size distribution and to complete oxidation. ► The particles formation mechanism is the melting and rapid solidification.TiO₂ nanoparticles have received a special attention due to their applications in many different fields, such as catalysis, biomedical engineering, and energy conversion in solar cells. In this paper we report on the production of TiO₂ nanoparticles by means of a pulsed laser to ablate titanium metallic target submerged in ethanol. The results show that titanium crystalline dioxide nanoparticles can be obtained in a narrow size distribution. Crystalline phases, morphology and optical properties of the obtained colloidal nanoparticles were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and UV/vis absorption spectroscopy. The produced particles consisted mainly of titanium oxide crystalline nanoparticles showing spherical shape with most diameters ranging from 5 to 50nm. Nanoparticles are polycrystalline exhibiting the coexistence of the three main phases with the predominance of brookite.

Keywords: Nanoparticles; Laser ablation; Titanium oxide

Formation of femtosecond laser induced surface structures on silicon: Insights from numerical modeling and single pulse experiments by T.J.-Y. Derrien; R. Torres; T. Sarnet; M. Sentis; T.E. Itina (pp. 9487-9490).

► Theoretical conditions for exciting SPP in Si are verified. ► SPP model explains why a seed is needed to produce single shot ripples. ► Two regimes of ripples are identified and explained by numerical simulations. ► The presented results have a strong correlation with experiments.Laser induced periodic surface structures (LIPSS) are formed by multiple irradiation of femtosecond laser on a silicon target. In this paper, we focus and discuss the surface plasmon polariton mechanism by an analysis of transient phase-matching conditions in Si on the basis of a single pulse experiment and numerical simulations. Two regimes of ripple formation mechanisms at low number of shots are identified and detailed. Correlation of numerical and experimental results is good.

Keywords: LIPSS; Black Silicon; Ripples; Femtosecond laser; Surface plasmon polariton

Nanostructure formation upon femtosecond ablation from silicon: Effect of double pulses by Juergen Reif; Olga Varlamova; Mourad Bounhalli; Marco Muth; Tzanimir Arguirov (pp. 9491-9495).

► Regular surface modulation (ripples) extending above and below pristine surface. ► Strongly modulated ring around flat shallow center. ► Formation of monodispersed crystalline nanoparticles all over modified area.To study the dynamics of laser-ablation induced structure formation (LIPPS), silicon was irradiated by (above-threshold) pulse pairs with a variable time-lag between 100fs and a few picoseconds. With increasing pulse-to-pulse delay we find a significant change in ablated-area morphology: the central range of the irradiated spot becomes less and less depressed whereas a surrounding ring structure exhibits increasingly coarser modulation, typical for strong irradiation, where the ripples are characterized by an alternation between elevation above and depression below the unaffected surface level. At the spot center the ablation depth decreases with increasing pulse separation, showing only structures usually observed for weak irradiation. Micro-Raman spectroscopy of the modified areas indicates an unexpectedly high, almost mono-dispersed, abundance of confined nanostructures. The results clearly seem to rule out structure formation by any interference-induced modulated ablation. Instead, they support the model of self-organized structure formation upon the creation of a thermally unstable, “soft” state of the target after laser impact.

Keywords: Laser induced periodic structures (ripples); Self-organized structure formation; Silicon; Femtosecond ablation

Epitaxial growth of Nb-doped SrTiO₃ films by pulsed laser deposition by M. Markovich; J. Roqueta; J. Santiso; E. Lakin; E. Zolotoyabko; A. Rothschild (pp. 9496-9500).

► Epitaxial films of Nb-doped SrTiO₃ were grown on (001)-oriented SrTiO₃ single crystal substrates. ► Films were deposited in vacuum (5×10⁻³mTorr) or under oxygen flow (60mTorr). ► Highly strained coherent films were obtained up to a film thickness of 200nm. ► Films deposited in oxygen had higher concentration of point defects than films grown in vacuum. ► Strain relaxation in thick films (>200nm) occurred by redistribution of point defects and 3D growth.Nb-doped SrTiO₃ thin films are potential candidates for transparent conducting oxide electrodes and other applications in oxide electronics and optoelectronics. In this work we grew epitaxial films of Nb-doped SrTiO₃ on (001)-oriented SrTiO₃ single crystal substrates and examined their crystal structure, defects and strain state by means of high-resolution X-ray diffraction (mapping in reciprocal space) and complementary methods. The films were deposited by pulsed laser deposition (PLD) under oxygen flow (60mTorr) or in vacuum (5×10⁻³mTorr). The substrate temperature was 700°C and the substrate-to-target distance was 55 or 70mm, respectively. Strained epitaxial films with homogeneous concentration of point defects and dopants were obtained in both cases as long as the film thickness did not exceed 200nm. Films deposited in oxygen displayed considerably higher concentration of point defects (presumably cation vacancies) than their vacuum-deposited counterparts. Films of intermediate thickness (between 200 and 1000nm) exhibited significant structural inhomogeneity accompanied by strain relaxation via redistribution of point defects across the film. Thicker films (>1000nm) grown in oxygen exhibited changes in the film growth mode and the resultant microstructure, providing a complementary mechanism for strain relaxation.

Keywords: SrTiO; ₃; Pulsed laser deposition (PLD); Strain; Reciprocal space map (RSM); Defects

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Applied Surface Science (v.258, #23)

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Applied Surface Science (v.258, #23)