Applied Surface Science (v.302, #C)

Preface (v).

This experimental study supports computational evidence that the excitation of d-band electrons have a significant impact on the material response of gold to an ultrashort laser pulse. A voltage biased Langmuir probe was used to detect the electron and positive ion emission from a 20 nm thick Au film at 343 nm, 515 nm and 1030 nm laser wavelengths. The laser wavelengths used provided photon energies above and below the interband transition threshold (ITT) for d-band excitation in gold (1.9 eV). Variations in optical properties of the Au film at different laser wavelengths were accounted for to ensure that comparisons were made at equal values of absorbed fluences. Data showed a significantly higher number of electrons emitted over a longer period when the energy of the incident photons exceeded the ITT. The electronic current generated at the probe indicated that the first electrons detected were primarily emitted via multiphoton photoemission. Electrons were also detected at later times when the photon energy exceeded the ITT and this was attributed to thermionic emission. The current generated from the positive ion emission was significantly lower than for electron emission, but indicated the formation of a plasma at a threshold fluence that increases with decreasing photon energy.
Keywords: Gold; Au; D-band; Femtosecond; Laser; Electron; Emission; Wavelength; Plasma;

High-speed laser ablation of metal with pico- and subpicosecond pulses by V.I. Mazhukin; M.M. Demin; A.V. Shapranov (6-10).
The mechanism of the high-speed ablation of aluminum with pico- and subpicosecond (10−11–10−13  s) laser pulses is considered. Mathematical modeling based on the continuum non-equilibrium two-temperature (TTM) model revealed that in a relatively narrow range of fluence 0.25–0.7 J/cm2, the regime of mechanical fragmentation of the irradiated surface is realized. The maximum values of the lattice temperature for the specified range of fluence are 2100–3500 K. The removal of the material is mechanical due to the negative stresses in the rarefaction wave following the shock wave. Explicit tracking of temporal and spatial position of the melting front has allowed establishing its role in the generation of superheated metastable states in the solid phase and the propagation of the shock wave. The removed material with total thickness of 60–100 nm is a collection of separate plates with thickness from 1 nm to 55 nm.
Keywords: Laser ablation; Pico- and subpicosecond pulses; Homogeneous melting; Heterogeneous melting;

Enhancing the visible light absorption of titania nanoparticles by S and C doping in a single-step process by M. Scarisoreanu; I. Morjan; R. Alexandrescu; C.T. Fleaca; A. Badoi; E. Dutu; A.-M. Niculescu; C. Luculescu; E. Vasile; J. Wang; S. Bouhadoun; N. Herlin-Boime (11-18).
We report the synthesis of carbon coated and sulfur doped titania nanoparticles using a continuous, single-step laser pyrolysis technique. We employed air as oxidant and C2H4 as laser energy transfer agent (sensitizer)/carbon donor, both carrying the TiCl4 vapors as a titania precursor. The volatile (CH3)2S2 was used to introduce sulfur as dopant in the nanopowders. The incorporation of C and S atoms in nanopowders with anatase dominant phase and with average particle diameter between 18 and 25 nm was performed through the addition of S2(CH3)2 and C2H4 to the reactive precursor mixtures. The samples were characterized by: EDX, XRD, TEM, XPS and UV–Vis spectroscopy. By the introduction of the sulfur precursor, the anatase-to-rutile ratio within the resulted TiO2-based nanoparticles decreased, as well as their bandgap energy values which are also lower than those of commercial TiO2 Degussa P25.
Keywords: Laser pyrolysis; Nanoparticles; C; S-modified TiO2; Band gap energy; UV–Vis spectroscopy;

Palladium nanoparticles produced by CW and pulsed laser ablation in water by M. Boutinguiza; R. Comesaña; F. Lusquiños; A. Riveiro; J. del Val; J. Pou (19-23).
Palladium nanoparticles are receiving important interest due to its application as catalyst. In this work Pd nanoparticles have been obtained by ablating a Pd target submerged in de-ionized using both, pulsed as well as continuous wave (CW) laser. The influence of laser parameters involved in the formation in nanoparticles has been studied. Crystalline phases, morphology and optical properties of the obtained colloidal nanoparticles were characterized by means of transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and UV/vis absorption spectroscopy. The obtained colloidal suspensions consisted of pure Pd nanoparticles showing spherical shape with diameters ranging from few nanometers to 5–60 nm. The moderate irradiance delivered by the CW laser favours high production of uniform nanoparticles.
Keywords: Palladium nanoparticles; Laser ablation; CW laser; Pulsed laser;

Exciting a metal by an ultrashort laser pulse, the electrons are driven out of thermal equilibrium, while the phonon system remains almost unaffected. During and after the irradiation, the electrons thermalize and transfer energy to the phonons. In this work, we investigate the electron–phonon coupling in gold. The dependence of the coupling strength on the phonon properties as well as the nonequilibrium electrons has been taken into account. For the phonon system, we utilize several phonon temperatures. For the electrons we apply different excitation scenarios depending on the laser fluence and the photon energy. We observe that for gold at electron temperatures below 2000 K, the phonon distribution may affect the coupling slightly. However, the electron distribution, especially under nonequilibrium conditions, governs the electron–phonon coupling factor significantly.
Keywords: Nonequilibrium; Metal; Electron–phonon coupling;

An intense laser probe 10 μm in diameter was formed on a specimen under transmission electron microscopy (TEM). A metal tip covered with a silver layer, of which apex was 60 nm in diameter, was placed on an arbitrary position in the laser probe, and a near-field light was induced at the apex by a tip-enhanced effect. With these light probes, micro- and near-field photo-excitation was demonstrated under TEM.
Keywords: Near-field; Photo-excitation; Transmission electron microscopy; Laser;

Plasmonic response and transformation mechanism upon single laser exposure of metal discontinuous films by C.E. Rodríguez; R.J. Peláez; C.N. Afonso; S. Riedel; P. Leiderer; D. Jimenez-Rey; A. Climent- Font (32-36).
Ag and Au discontinuous films were exposed to single nanosecond pulses of a homogenized beam of an excimer laser operating at 193 nm. For low fluences, the films convert into big, almost spherical and isolated nanoparticles (NPs) due to laser-induced dewetting. Their optical response exhibits a sharp surface plasmon resonance (SPR) consistent with that of spherical and non-interacting NPs. For higher fluences, the formation of many small NPs and almost no big NPs is observed instead. The SPR features change and the plasmonic response becomes influenced by multipolar interactions among neighbouring NPs. Low and high fluence regimes are respectively related to melting and boiling threshold of the metal, and additionally, craters appear in the latter regime.
Keywords: Laser irradiation; Silver; Gold; Nanoparticles; Plasmons; Interactions;

Laser deposition of sulfonated phthalocyanines for gas sensors by Premysl Fitl; Martin Vrnata; Dusan Kopecky; Jan Vlcek; Jitka Skodova; Jiri Bulir; Michal Novotny; Petr Pokorny (37-41).
Thin layers of nickel and copper tetrasulfonated phthalocyanines (NiPcTS and CuPcTS) were prepared by Matrix Assisted Pulsed Laser Evaporation method. The depositions were carried out with KrF excimer laser (energy density of laser radiation E L  = 0.1–0.5 J cm−2) from dimethylsulfoxide matrix. For both materials the ablation threshold E L-th was determined. The following properties of deposited layers were characterized: (a) chemical composition (FTIR spectra); (b) morphology (SEM and AFM portraits); and (c) impedance of gas sensors based on NiPcTS and CuPcTS layers in the presence of two analytes – hydrogen and ozone. The prepared sensors exhibit response to 1000 ppm of hydrogen and 100 ppb of ozone even at laboratory temperature.
Keywords: Matrix Assisted Pulsed Laser Evaporation; Substituted phthalocyanines; Gas sensors; Impedance measurement;

Reducing the incubation effects for rear side laser etching of fused silica by Klaus Zimmer; Martin Ehrhardt; Pierre Lorenz; Xi Wang; Csaba Vass; Tamás Csizmadia; Béla Hopp (42-45).
Laser-induced back side wet and dry etching (LIBWE and LIBDE) were developed for precise etching of transparent materials. However, LIBWE and LIBDE feature characteristics such as incubation effects and etching depth saturation, respectively, that can be unfavourable for applications in ultra-precision machining. Therefore, the techniques of LIBDE and LIBWE were combined in such a manner that the dielectric material was supplied with a thin-film-modified surface before etching by LIBWE.With this goal fused silica samples were covered with a thin chromium film for surface modification before LIBWE etching in acetone with 25 ns KrF excimer laser pulses. Etching with the first pulse was observed. At laser fluences adequate for hydrocarbon LIBWE (1 J/cm2) the etching rate for LIBDE is much higher than for LIBWE. In consequence, the etching rate decreases with increasing pulse number up to ten. The surface morphology depends very strong on the laser fluence and the pulse number. Smooth etchings were achieved at high fluences and low pulse numbers. However, uneven, wavy etched surfaces and micron pattern formation were observed for moderate and low laser fluences.
Keywords: Laser etching; Incubation effect; LIBWE; LIBDE; Fused silica;

Pulsed laser deposition in a delayed-double beam configuration is used to incorporate in situ Al in ZnO thin films. In this configuration, two synchronized pulsed-laser beams are employed to ablate independently a ZnO and an Al target. We investigated the effects of relative time delay of plasma plumes on the composition of the films with the aim of evaluating the performance of this technique to produce doped materials. Relative delay between plumes was found to control the incorporation of Al in the film in the range from 14% to 30%. However, to produce low impurity concentration of Al-doped ZnO (with Al incorporation less than 2%) the fluence used to produce the plasmas has more influence over the film composition than the relative plume delay. The minimum incorporation of Al corresponded to a relative delay of 0 μs, due to the interaction between plumes during their expansion.
Keywords: Double-beam pulsed laser deposition; Aluminum doped zinc oxide; Thin films; Plasma plume delay;

Structuring of glass fibre surfaces by laser-induced front side etching by Pierre Lorenz; Martin Ehrhardt; Klaus Zimmer (52-57).
The fabrication of sub-μm structures on glass fibre surfaces poses a big challenge for the laser processing. However, the laser-induced front side etching (LIFE) method has a great potential for the fast, nm-precision, and cost-effective production of surface structures. LIFE is a method for laser etching of transparent materials using thin absorber layers with a high absorption coefficient like metal layers. The LIFE process of the front surface of a fused silica wafer as well as of a glass fibre is studied in dependence on the laser parameters. A KrF excimer laser with a wavelength of 248 nm and a pulse duration of 25 ns was used. The resultant structures were analysed with microscopic methods (white light interferometry, scanning electron microscopy (SEM)). The analysing of the surface structures presented that the LIFE methods allow the fabrication of well-defined periodic sub-μm structures. Furthermore, the structuring process was simulated by a thermodynamic equation including an approach of the laser–plasma interaction. The theoretically predicted results presented a good agreement with the experimental results.
Keywords: LIFE; Laser etching; Glass fibre; Excimer laser;

Cleavage along the weakest Si{1 1 1} cleavage plane is measured by impulsive fracture using surface acoustic waves (SAWs) with steep shock fronts, generated by pulsed laser irradiation and recorded with a laser probe–beam-deflection setup. The theoretical cleavage strength, obtained by ab initio calculations for perfect single-crystal silicon lattices is compared with the strength resulting from an improved Polanyi–Orowan cleavage model. The critical strength of a real silicon crystal, measured by using calibrated elastic surface pulses with shocks, was employed to extract the corresponding critical length scale characterizing the cleavage process on the basis of the modified cleavage model. The extracted length scale of 7 nm can be connected with the size of the microstructural defect initiating failure. Usually stress generating surface defects are responsible for the nucleation of brittle fracture, especially in nanoscale systems with large surface areas.
Keywords: Silicon cleavage; Tensile strength; Nanoscopic length scales; Griffith equation; Surface shock waves;

Luminescent silicon nanocrystals produced by near-infrared nanosecond pulsed laser ablation in water by L. Vaccaro; L. Sciortino; F. Messina; G. Buscarino; S. Agnello; M. Cannas (62-65).
We report the investigation of luminescent nanoparticles produced by ns pulsed Nd:YAG laser ablation of silicon in water. Combined characterization by AFM and IR techniques proves that these nanoparticles have a mean size of ∼3 nm and a core–shell structure consisting of a Si-nanocrystal surrounded by an oxide layer. Time resolved luminescence spectra evidence visible and UV emissions; a band around 1.9 eV originates from Si-nanocrystals, while two bands centered at 2.7 eV and 4.4 eV are associated with oxygen deficient centers in the SiO2 shell.
Keywords: Laser ablation; Si-nanocrystal; Silica; Core–shell; Time-resolved luminescence; Atomic force microscopy; Micro-Raman; IR absorption;

Optical recording in copper–silica nanocomposite by Igor Dmitruk; Ivan Blonskiy; Petro Korenyuk; Viktor Kadan; Mykola Zubrilin; Andriy Dmytruk; Oleg Yeshchenko; Alexandr Alexeenko; Andriy Kotko (66-68).
The application of field enhancement effect, which takes place when light, interacts with surface plasmon, for optical recording has been suggested. Copper–silica nanocomposite demonstrates possibility of optical writing and erasing under irradiation by second harmonic (400 nm) and fundamental wavelength (800 nm) of femtosecond titanium–sapphire laser, respectively.
Keywords: Optical recording; Plasmon; Field enhancement; Nanocomposite;

Azo-derivatives thin films grown by matrix-assisted pulsed laser evaporation for non-linear optical applications by C. Constantinescu; A. Matei; I. Ionita; V. Ion; V. Marascu; M. Dinescu; C. Vasiliu; A. Emandi (69-73).
Azo-dye compounds, in bulk or as thin films, are extensively studied due to their particular optical properties. These properties include non-linear interaction, e.g. two-photon absorption, optical limiting and all-optical poling, with potential applications in optoelectronics and sensors development. Herein, we report on the deposition of pyrazolone derivatives, namely 1-phenyl-3-methyl-4-(1′-azo-2′-sodium carboxylate)-pyrazole-5-one thin films, for applications in second harmonic generation. Matrix-assisted pulsed laser evaporation was employed for layers growth, using a Nd:YAG device operating at 266 nm (4ω). The structure and surface morphology of the deposited films were examined by Fourier transform infrared spectroscopy, atomic force microscopy, and scanning electron microscopy. Spectroscopic-ellipsometry was employed to investigate thin film optical properties. Significant second harmonic generation capabilities of the compound were pointed out by using a femtosecond Ti:sapphire laser.
Keywords: Azo-derivatives; Thin films; MAPLE; Pulsed laser; Second harmonic generation;

Complex patterned gold structures fabricated via laser annealing and dealloying by Dong Wang; Jürgen Ihlemann; Peter Schaaf (74-78).
Gold films with periodic stripes of nanoporous structure are realized by using pulsed laser annealing in a mask projection arrangement in combination with a dealloying process. An Ag–Au alloy is first formed in the exposed areas of Ag/Au bi-layers by annealing, and then the Ag is removed from Ag–Au alloy by submerging in HNO3 solution and nanoporous gold is formed. The Ag top-layer in the unexposed areas of the Ag/Au bi-layers is also removed and the Au under-layer remains. Laser annealing is performed with 2 pulses and 10 pulses at different energy densities. Optimized laser annealing parameters for the 140 nm Ag/80 nm Au bi-layers is found with 10 pulses at fluences of 132 and 143 mJ/cm2.
Keywords: Laser annealing; Periodic structure; Nanoporous gold; Dealloying;

Generation of nanoparticles of bronze and brass by laser ablation in liquid by I.A. Sukhov; G.A. Shafeev; V.V. Voronov; M. Sygletou; E. Stratakis; C. Fotakis (79-82).
Nanoparticles of brass and bronze are generated by ablation of corresponding bulk targets in liquid ethanol. The experiments were performed using three pulsed lasers with different pulse duration: ytterbium fiber laser (80 ns), a Neodymium:YAG laser (10 ps), and femtosecond Ti:sapphire laser (200 fs). The generated nanoparticles (NPs) are characterized by UV–vis absorption spectroscopy, X-ray diffractometry, Raman scattering, and Transmission Electron Microscopy. The size of generated NPs lies in the range 10–25 nm depending on the laser source. The X-ray diffractometry reveals the change of phase composition of brass NPs compared to the initial target in case of ablation with 80 ns laser source, while with 10 ps laser pulses this effect is less pronounced. Brass NPs generated with pico- and femtosecond laser radiation show the plasmon resonance in the vicinity of 560 nm and no plasmon peak for NPs generated with longer laser pulses. Raman analysis shows the presence of Cu2O in generated NPs. The stability of generated NPs of both brass and bronze to oxidation is compared to that of Cu NPs generated in similar experimental conditions.
Keywords: Nanoparticles; Laser; Ablation; Liquid; Brass; Bronze;

Ferrocene carboxaldehyde thin films grown by matrix-assisted pulsed laser evaporation for non linear optical applications by Catalin Constantinescu; Andreea Matei; Valentin Ion; Bogdana Mitu; Iulian Ionita; Maria Dinescu; Catalin. R. Luculescu; Cristina Vasiliu; Ana Emandi (83-86).
Thin films of ferrocene carboxaldehyde, also known as cyclopentadienyl(formylcyclopentadienyl)iron, were grown on silicon and glass substrates by matrix-assisted pulsed laser evaporation technique, using a Nd:YAG device operating at 266 nm (4ω). Spectroscopic-ellipsometry, Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy investigations revealed that the films are homogeneous in thickness, with dense morphology and without cracks, low surface roughness (∼11 nm), and no significant chemical damage. Second harmonic generation capabilities of the thin films were evidenced by using a femtosecond Ti:sapphire laser.
Keywords: Pulsed laser; MAPLE; Thin film; Ferrocene carboxaldehyde; Second harmonic generation;

Characterization of ethylcellulose and hydroxypropyl methylcellulose thin films deposited by matrix-assisted pulsed laser evaporation by A. Palla-Papavlu; L. Rusen; V. Dinca; M. Filipescu; T. Lippert; M. Dinescu (87-91).
In this study is reported the deposition of hydroxypropyl methylcellulose (HPMC) and ethylcellulose (EC) by matrix-assisted pulsed laser evaporation (MAPLE). Both HPMC and EC were deposited on silicon substrates using a Nd:YAG laser (266 nm, 5 ns laser pulse and 10 Hz repetition rate) and then characterized by atomic force microscopy and Fourier transform infrared spectroscopy.It was found that for laser fluences up to 450 mJ/cm2 the structure of the deposited HPMC and EC polymer in the thin film resembles to the bulk. Morphological investigations reveal island features on the surface of the EC thin films, and pores onto the HPMC polymer films.The obtained results indicate that MAPLE may be an alternative technique for the fabrication of new systems with desired drug release profile.
Keywords: MAPLE; Hydroxypropylmethylcellulose; Ethylcellulose; Thin films; Drug delivery;

MAPLE deposition of nanomaterials by A.P. Caricato; V. Arima; M. Catalano; M. Cesaria; P.D. Cozzoli; M. Martino; A. Taurino; R. Rella; R. Scarfiello; T. Tunno; A. Zacheo (92-98).
The matrix-assisted pulsed laser evaporation (MAPLE) has been recently exploited for depositing films of nanomaterials by combining the advantages of colloidal inorganic nanoparticles and laser-based techniques. MAPLE-deposition of nanomaterials meeting applicative purposes demands their peculiar properties to be taken into account while planning depositions to guarantee a congruent transfer (in terms of crystal structure and geometric features) and explain the deposition outcome. In particular, since nanofluids can enhance thermal conductivity with respect to conventional fluids, laser-induced heating can induce different ablation thermal regimes as compared to the MAPLE-treatment of soft materials. Moreover, nanoparticles exhibit lower melting temperatures and can experience pre-melting phenomena as compared to their bulk counterparts, which could easily induce shape and or crystal phase modification of the material to be deposited even at very low fluences. In this complex scenario, this review paper focuses on examples of MAPLE-depositions of size and shape controlled nanoparticles for different applications highlights advantages and challenges of the MAPLE-technique. The influence of the deposition parameters on the physical mechanisms which govern the deposition process is discussed.
Keywords: MAPLE; Nanoparticles; Nanorods; Thin films; Titania; Deposition;

Retention of heavy metals on layered double hydroxides thin films deposited by pulsed laser deposition by A. Vlad; R. Birjega; A. Matei; C. Luculescu; B. Mitu; M. Dinescu; R. Zavoianu; O.D. Pavel (99-104).
Heavy metals are toxic and hazardous pollutants in the environment due to their nonbiodegradability and persistence, which can pose serious threats to living organisms. The ability of Mg–Al based layered double hydroxides (LDHs) thin films to retain heavy metals from aqueous solutions at different concentrations is a novel topic with prospects of attractive applications, such as detection of heavy metals. We report on the ability of a series of Mg–Al based layered double hydroxides thin films to detect Ni and Co cations in aqueous solutions.Uptake of heavy metals ions such as Ni2+, Co2+ from aqueous solutions was studied as function of contact time at a standard metal ion concentration.The LDHs thin films were deposited using pulsed laser deposition (PLD). The different adsorption mechanisms were studied in connection with different heavy metals used as probe cations. X-ray diffraction, atomic force microscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, Fourier transform infra-red spectroscopy were the techniques used for the investigation of as deposited and after heavy metals retention thin films.
Keywords: Thin films; Pulsed laser; Heavy metals uptake;

Pulsed laser deposition of Co3O4 nanocatalysts for dye degradation and CO oxidation by R. Edla; N. Patel; Z. El Koura; R. Fernandes; N. Bazzanella; A. Miotello (105-108).
Co3O4 nanoparticles (NPs) assembled coatings were synthesized using pulsed laser deposition (PLD) by taking advantage of phase explosion process. The coatings were prepared at substrate temperature of 150 °C by using three different laser fluences (3, 5, and 7 J/cm2) in order to tune the size of NPs. Structural property and surface morphology of NPs were investigated by Raman spectroscopy and electron microscopy respectively. The catalytic activity of these Co3O4 NPs coatings was tested for dye degradation as well as for CO oxidation. Co3O4 coating (3 J/cm2) was able to completely degrade Methylene blue dye with significantly high rate, via photo Fenton reaction under visible light irradiation, as compared to Co3O4 powder catalyst mainly owing to the size and nanocrystalline nature of NPs on the catalyst surface. Coating synthesized at low laser fluence (3 J/cm2) showed best catalytic activity. This particular coating also showed above 90% conversion efficiency of CO to CO2 at 250 °C with very high specific rate. The special features of NPs, such as narrow size distribution, small average size (5–20 nm), perfect spherical shape, low degree of agglomeration, and nanocrystalline phase, are the main factors responsible for the enhanced catalytic activity of the PLD produced Co3O4 NPs assembled coating.
Keywords: Pulsed-laser deposition; Cobalt oxide nanoparticles; Nanoparticles-assembled coating; Photocatalytic dye degradation; CO oxidation;

Picosecond laser induced periodic surface structure on copper thin films by Thi Trang Dai Huynh; Agnès Petit; Nadjib Semmar (109-113).
LIPSS (Laser Induced Periodic Surface Structure) formation on copper thin films induced by a picosecond laser beam (Nd:YAG laser at 266 nm, 42 ps and 10 Hz) was studied experimentally. Copper thin films were deposited on glass and silicon substrates by magnetron sputtering. The surface modifications of irradiated zones were analyzed by scanning electron microscopy. Two distinct types of LIPSS were identified with respect to the laser fluence (F), number of laser shots (N) and substrate material. Namely, with a number of laser shots (1000 <  N  < 10,000) and a fluence of (200 mJ/cm2  <  F  < 500 mJ/cm2), Low Spatial Frequency LIPSS (LSFL with a spatial period of Λ  ∼ 260 nm and an orientation perpendicular to polarization) and High Spatial Frequency LIPSS (HSFL with a spatial period of Λ  ∼ 130 nm and an orientation parallel to the polarization) were observed. The regime of regular spikes formation was determined for N  ≥ 1000. Moreover, the 2D-map of the relationship among LIPSS formation, laser fluence and number of laser shots on copper thin film with two different substrates was established. A physics interpretation of regular spikes and LIPSS formation on copper thin film induced by ps laser with overlapping multi-shots is proposed based on experimental data and the theory of Plateau-Rayleigh instability.
Keywords: LIPSS; Spikes; Metallic thin films; Picosecond laser beam;

Electron backscatter diffraction characterization of laser-induced periodic surface structures on nickel surface by Xxx Sedao; Claire Maurice; Florence Garrelie; Jean-Philippe Colombier; Stéphanie Reynaud; Romain Quey; Gilles Blanc; Florent Pigeon (114-117).
We report on the structural investigation of laser-induced periodic surface structures (LIPSS) generated in polycrystalline nickel target after multi-shot irradiation by femtosecond laser pulses. Electron backscatter diffraction (EBSD) is used to reveal lattice rotation caused by dislocation storage during LIPSS formation. Localized crystallographic damages in the LIPSS are detected from both surface and cross-sectional EBSD studies. A surface region (up to 200 nm) with 1–3° grain disorientation is observed in localized areas from the cross-section of the LIPSS. The distribution of the local disorientation is inhomogeneous across the LIPSS and the subsurface region.
Keywords: LIPSS; Ripples; Ultrafast laser; Femtosecond pulse; EBSD;

Display OmittedIn this paper the formation mechanisms of the femtosecond laser-induced periodic surface structures (LIPSS) are discussed. One of the most frequently used theories explains the structures by interference between the incident laser beam and surface plasmon-polariton waves. The latter is most commonly attributed to the coupling of the incident laser light to the surface roughness. We demonstrate that this excitation of surface plasmons contradicts the results of laser-ablation experiments. As an alternative approach to the excitation of LIPSS we analyse development of hydrodynamic instabilities in the melt layer.
Keywords: LIPSS; Plasmon; Ripples; Self-organization;

The effect of deposition atmosphere on the chemical composition of TiN and ZrN thin films grown by pulsed laser deposition by D. Craciun; G. Socol; N. Stefan; G. Dorcioman; M. Hanna; C.R. Taylor; E. Lambers; V. Craciun (124-128).
Very thin TiN and ZrN films (<500 nm) were grown on (1 0 0) Si substrates at temperatures up to 500 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser under residual vacuum or various mixtures of CH4 or N2. Auger electron spectroscopy investigations found that films contained a relatively low oxygen concentration, usually below 3.0 at%. Films deposited under residual vacuum or very low N2 pressures (<3 × 10−3  Pa) contained 3–6 at% C atoms in the bulk. This fraction grew to 8–10 at% when the deposition was performed under an atmosphere of 2 × 10−3  Pa CH4. To avoid C atoms incorporation into the bulk a deposition pressure of 10 Pa N2 was required. X-ray photoelectron spectroscopy investigations found that oxygen was mostly bonded in an oxynitride type of compound, while carbon was bonded into a metallic carbide. The presence of C atoms in the chemical composition of the TiN or ZrN improved the measured hardness of the films.
Keywords: TiN, ZrN; Hard coating; Pulsed laser deposition; X-Ray diffraction;

Determination of grain shape of laser-irradiated FePdCu thin alloy films by Marcin Perzanowski; Michal Krupinski; Arkadiusz Zarzycki; Yevhen Zabila; Marta Marszalek (129-133).
The irradiation with the 10 ns pulsed infrared Nd:YAG laser was applied to transform FePdCu multilayers into chemically ordered L10 phase. The X-ray diffraction methods (θ/2θ scan, ψ-scan, ω-scan) were used to trace the presence of L10 phase after laser annealing with different number of pulses. The size and shape of crystallites was determined depending on their orientation with respect to film plane. The (1 1 1) oriented crystallites of constituent metals were built as coherent domains spreading through multilayers during deposition of films. Laser annealing induced the transformation of multilayers to alloy, and the ordering of (1 1 1) oriented crystallites. Simultaneously, the (0 0 2) oriented crystallites appeared confirming the transformation to L10 alloy.
Keywords: Laser annealing; FePdCu multilayers; L10 ordering; Grain size and shape; X-ray diffraction;

Multifunctional thin films used as thermoresponsive substrate for engineering cell sheets represent an important area in tissue engineering. As the morphology and the chemical characteristics of the thin films directly control their interaction with cells, it is important to correlate these characteristics with the biological answer. In this study, thermally sensitive poly(N-isopropylacrylamide), (pNIPAAm) thin films were prepared by matrix assisted pulsed laser evaporation and utilized in L929 cell adhesion and detachment studies. Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) were used to determine the pNIPAAm thin films chemical and morphological characteristics. The FTIR data demonstrated that the functional groups in the MAPLE-deposited films remained intact for fluences in the range of 200–600 mJ cm−2. Within this fluence range, the AFM topographical studies showed that the roughness of the coatings was dependent on laser fluence and the obtained surfaces were characterized by a granular aspect. L929 cell viability studies onto the pNIPAAm coatings showed little or no toxic effect for fluences below 600 mJ cm−2, while for higher fluences, viability was decreased with more than 50%. The adhesion and detachment of the cell was found to be mainly dependent on the film surface morphology.
Keywords: MAPLE; Smart coatings; pNIPAAm;

Liquid Phase – Pulsed Laser Ablation: A route to fabricate different carbon nanostructures by Ahmed Al-Hamaoy; Evans Chikarakara; Hussein Jawad; Kapil Gupta; Dinesh Kumar; M.S. Ramachandra Rao; Satheesh Krishnamurthy; Muhammad Morshed; Eoin Fox; Dermot Brougham; Xiaoyun He; Mercedes Vázquez; Dermot Brabazon (141-144).
Carbon nanostructures in various forms and sizes, and with different speciation properties have been prepared from graphite by Liquid Phase – Pulsed Laser Ablation (LP-PLA) using a high frequency Nd:YAG laser. High energy densities and pulse repetition frequencies of up to 10 kHz were used in this ablation process to produce carbon nanomaterials with unique chemical structures. Dynamic Light Scattering (DLS), micro-Raman and High-Resolution Transmission Electron Microscopy (HRTEM) were used to confirm the size distribution, morphology, chemical bonding, and crystallinity of these nanostructures. This article demonstrates how the fabrication process affects measured characteristics of the produced carbon nanomaterials. The obtained particle properties have potential use for various applications including biochemical speciation applications.
Keywords: Liquid Phase – Pulsed Laser Ablation; Carbon nanoparticles; Carbon nanotubes; Separation science;

Femtosecond laser ablation of CaF2: Plasma characterization and thin films deposition by A. De Bonis; A. Santagata; A. Galasso; M. Sansone; R. Teghil (145-148).
Nanostructured thin films of CaF2 have been deposited in vacuum by ultra-short pulse laser ablation. The laser-induced plasma, characterized by optical emission spectroscopy and ICCD fast imaging, shows the presence of Ca and F atomic species, neutral and ionized, together with the CaF molecular species. Although continuous blackbody-like emission has not been detected from the plasma, the deposited films, characterized by Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy, are apparently formed by the coalescence of a large number of nanoparticles composed by stoichiometric CaF2.
Keywords: Calcium fluoride; Ultra-short pulse laser; Pulsed laser deposition; Nanoparticles;

Matrix shaped pulsed laser deposition: New approach to large area and homogeneous deposition by C.K. Akkan; A. May; M. Hammadeh; H. Abdul-Khaliq; O.C. Aktas (149-152).
Pulsed laser deposition (PLD) is one of the well-established physical vapor deposition methods used for synthesis of ultra-thin layers. Especially PLD is suitable for the preparation of thin films of complex alloys and ceramics where the conservation of the stoichiometry is critical. Beside several advantages of PLD, inhomogeneity in thickness limits use of PLD in some applications. There are several approaches such as rotation of the substrate or scanning of the laser beam over the target to achieve homogenous layers. On the other hand movement and transition create further complexity in process parameters. Here we present a new approach which we call Matrix Shaped PLD to control the thickness and homogeneity of deposited layers precisely. This new approach is based on shaping of the incoming laser beam by a microlens array and a Fourier lens. The beam is split into much smaller multi-beam array over the target and this leads to a homogenous plasma formation. The uniform intensity distribution over the target yields a very uniform deposit on the substrate. This approach is used to deposit carbide and oxide thin films for biomedical applications. As a case study coating of a stent which has a complex geometry is presented briefly.
Keywords: Pulsed laser deposition; Laser beam shaping; Stent;

Multi-jets formation using laser forward transfer by Emeric Biver; Ludovic Rapp; Anne-Patricia Alloncle; Philippe Delaporte (153-158).
The dynamics of multi-jets formation in liquid films has been investigated using the laser-induced forward transfer (LIFT) technique. This technique allows the deposition of micrometer-sized droplets with a high spatial resolution from a donor substrate to a receiver substrate. The donor was a silver nanoparticles ink-coated substrate. The interaction of the laser pulse with the donor ink layer generates an expanding bubble in the liquid which propels a jet towards the receiver. Silver lines have already been printed by depositing overlapping droplets in a “low speed” process. In order to increase the throughput, it is necessary to decrease the time between the depositions of two droplets. By scanning the beam of a high repetition rate UV picosecond laser (343 nm; 30 ps; 500 kHz) with a galvanometric mirror, successive pulses are focused on the silver nanoparticles ink-coated donor substrate. The shape and dynamics of single jets and adjacent jets have been investigated by means of a time-resolved imaging technique. By varying the distance between the laser spots, different behaviours were observed and compared to the printed droplets. A spacing of 25 μm between laser spots was found to generate both stable jets and well-controlled, reproducible droplets at high speed.
Keywords: LIFT; Multi-jets; Jet dynamics; Laser printing; Conductive ink; Nanoparticles; Picosecond laser;

Investigation of selective realignment of the preferred magnetic direction in spin-valve layer stacks using laser radiation by Isabel Berthold; Mathias Müller; Sascha Klötzer; Robby Ebert; Senoy Thomas; Patrick Matthes; Manfred Albrecht; Horst Exner (159-162).
Selective realignment of the preferred magnetization direction in a laser micro structured GMR spin-valve layer system (Ni81Fe19/Co90Fe10/Cu/Co90Fe10/IrMn/Ni81Fe19) with a total film thickness of 23 nm was studied. For this, patterns of isolated microstructures (500 μm × 200 μm) were fabricated by laser ablation. These micropatterns were annealed using laser irradiation at a temperature above the IrMn Néel temperature. During laser annealing, the sample was subjected to an external magnetic field in order to selectively realign the magnetic direction of the reference layer. Two different laser assisted annealing techniques were investigated applying either continuous or pulsed laser systems. After laser annealing, the magnetic properties of the micropatterns were investigated using a magnetic microsensor and magneto optical Kerr effect set up.
Keywords: Exchange bias; Magnetization reversal; Laser annealing; Field cooling; Giant magneto resistance; Spin-valve;

A novel patterning effect during high frequency laser micro-cutting of hard ceramics for microelectronics applications by Guillaume Savriama; Vincent Jarry; Laurent Barreau; Chantal Boulmer-Leborgne; Nadjib Semmar (163-168).
This paper investigates the laser micro-cutting of wide band gap materials for microelectronics industry purposes. An ultraviolet (355 nm) diode-pumped solid-state (DPSS) nanosecond laser was used in this investigation. The laser energy varied from 7 to 140 μJ/pulse with typical frequencies from 40 to 200 kHz. The effect of pulse energy and scanning speed on the depth of the cutting street of α-Al2O3 and glass was studied. Typical depths of 200 μm were achieved on α-Al2O3 for 140 μJ/pulse, 40 kHz at 13 mm/s. SEM images showed periodic patterns produced by periodic explosive boiling that can influence the achieved depth. The shape, size and periodicity of the recast material depended on the feed rate and the laser beam frequency. This periodic removal mechanism seems to be specific to dielectrics since it was not observed for semiconductors such as silicon or silicon carbide.
Keywords: Laser micromachining; Sapphire; Glass; Phase explosion; Microelectronics industry;

Laser prepared organic heterostuctures on glass/AZO substrates by Anca Stanculescu; Marcela Socol; Oana Rasoga; Ion N. Mihailescu; Gabriel Socol; Nicoleta Preda; Carmen Breazu; Florin Stanculescu (169-176).
This paper presents some studies about the bi-layer organic heterostructures realized with zinc phthalocyanine (ZnPc) as donor layer and 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) as acceptor layer, on substrate of glass covered by Al doped ZnO (AZO) layer. These heterostructures have been prepared using laser techniques: pulsed laser deposition (PLD) in an atmosphere of oxygen for AZO films deposition and matrix assisted pulsed laser evaporation (MAPLE) for organic films deposition. The influence of the deposition conditions on the transmission of the organic films has been analysed.The effect of the oxygen plasma treatment, with duration of 5 min and 10 min, on the surface topography, structural and optical properties of AZO layers deposited by PLD and, as consequence, on the optical and electrical properties of the single layer (ZnPc) and bi-layer (ZnPc/NTCDA) organic heterostructure, deposited by MAPLE, was investigated.
Keywords: Organic semiconductor; AZO; PLD; MAPLE; ZnPc; NTCDA;

Improving solar radiation absorbance of high refractory sintered ceramics by fs Ti:sapphire laser surface treatment by E. Cappelli; S. Orlando; D. Sciti; A. Bellucci; A. Lettino; D.M. Trucchi (177-183).
Samples of high refractory pressure-less sintered carbide ceramics (HfC based), polished by mechanical grinding to a surface roughness R a  ∼ 40 nm, have been surface treated, in vacuum, by fs Ti:sapphire laser, operating at 800 nm wavelength, 1000 Hz repetition rate and 100 fs pulse duration, at fluence varying in the range (∼6–25 J/cm2), to optimize their solar radiation absorbance, in such a way that they could operate as absorber material in an innovative conversion module of solar radiation into electrical energy. To this aim, an area of approximately 9.6 cm2 was treated by the fs laser beam. The beam strikes perpendicular to the sample, placed on a stage set in motion in the x, y, z-directions, thus generating a scanning pattern of parallel lines. The experimental conditions of laser treatment (energy fluence, speed of transition, overlapping and lateral step distance) were varied in order to optimize the radiation absorption properties of the patterned surface. In laser treated samples the absorption value is increased by about 15%, compared to the original untreated surface, up to a value of final absorbance of about 95%, all over the range of solar radiation spectrum (from UV to IR). The morphological and chemical effects of the treatment have been evaluated by SEM–EDS analysis. At very high fluence, we obtained the characteristic ablation craters and local material decomposition, while at lower fluence (in any case above the threshold) typical periodic nano-structures have been obtained, exploitable for their modified optical properties.
Keywords: fs surface laser treatments; Surface periodic structure; Solar radiation absorbance; Sintered carbide ceramic; SEM–EDS characterization;

Laser-induced electrochemical de- and repassivation investigations on plasma-oxidized aluminium alloys by Tristan O. Nagy; Ulrich Pacher; Ariane Giesriegl; Lukas Soyka; Günter Trettenhahn; Wolfgang Kautek (184-188).
In situ laser depassivation of plasma electrolytically oxididized (PEO) coatings on aluminium was investigated with nanosecond pulses. Ultraviolet radiation of 266 nm was chosen in order to achieve a high absorption in the dielectric coating. The additive accumulation of laser-induced material defects (incubation) affected the depassivation processes. Incubation occurred only at the edges of the ablation craters irradiated by the outer region of the Gaussian beam profile, where the local fluence is below the ablation threshold. The ablation rate in the spot center did not exhibit an incubation effect. Repassivation was interpreted by a linear combination of a high-field and a point defect growth model. At low overpotentials, field gradients affect the process driving the oxide growth at the buried interface. At high fields, corrosion reactions dominate at the oxide/solution interface.
Keywords: PEO-aluminium; Current-transients; Coatings; Laser-depassivation; Repassivation;

Laser-induced plasma spectroscopy (LIPS) with a frequency-quadrupled Nd:YAG laser (266 nm, pulse duration: 4 ns) was applied to a metallic layer system consisting of an electrodeposited copper layer (30 μm) on an aluminium substrate. A stratigraphic model describing the emission signal in dependence of the pulse number was developed, which can explain several effects originating from laser ablation of various thin top layers by means of the Gaussian beam cross section character. This model was applied to trace elements through layers with thicknesses that are in the range of the resolvable depth, given by the single-pulse ablation rate, by means of empirical fitting functions. Additionally, the contribution of redeposited bulk material to the characteristic shape of emission-traces when averaging spot arrays with varying spacing could be quantified. This can be used to estimate cross-contamination in analytical applications where ablations need to be performed at close spacing.
Keywords: LIPS; Coatings; Laser-stratigraphy; Redeposition;

Laser scribing of thin film solar cells attracts increasing attention for performing integrated interconnection. For high efficiency solar modules, low damage laser scribing techniques are needed. The optimization of the laser scribing process concerns all functional properties of the device but in particular the efficiency. The recently demonstrated nested circular scribing technique allows the in-process measurement of the shunt formation due to laser scribing (P3) of the thin film solar cell. By using this technique, the influence of laser fluence and pulse overlap on the electrical shunt resistance formation at laser scribing of Cu(InGa)Se2 solar cell with ultrashort laser pulses (tp  = 10 ps, λ  = 1.06 μm, v  = 2000 mm/s) was investigated. The TCO layer is removed when the laser fluence is about 0.3 J/cm2. The Cu(InGa)Se2 is removed completely to expose molybdenum when the laser fluence is about 3.5 J/cm2. For low defect scribing, a clear tendency of using a low pulse overlap and low laser fluences were found.
Keywords: Shunt resistance; Laser scribing; Solar cell; Laser ablation; Low defect;

Recent progress in the synthesis of magnetic titania/iron-based, composite nanoparticles manufactured by laser pyrolysis by C.T. Fleaca; M. Scarisoreanu; I. Morjan; R. Alexandrescu; F. Dumitrache; C. Luculescu; I.P. Morjan; R. Birjega; A.-M. Niculescu; G. Filoti; V. Kuncser; E. Vasile; V. Danciu; M. Popa (198-204).
We report the continuous, single step synthesis of titania/iron-based magnetic nanocomposites in a single step using gas-phase laser pyrolysis technique by separately and simultaneously introducing the precursors (together with C2H4 sensitizer) in the reaction zone: Fe(CO)5 on the central flow and, using air as carrier, TiCl4 on the annular coflow. The laser power and, for the last experiment, the injection geometry were modified in order to change the Fe/Ti ratio in the resulted nanopowders. Due to the specific geometry, the reaction zone (visible as a flame) have a reductive inner central zone surrounded by and oxidative environment, allowing the formation of the metallic–carbidic iron and/or iron-doped titania and iron oxide nanophases. The raw Fe-containing nanopowders have a ferromagnetic behavior, those synthesized at higher laser power and gas velocities show significant saturation magnetization M s values (10–12 emu/g), whereas those obtained (with higher yield and carbon content) at lower laser power and gas velocities (using wider central nozzle cross-section) have a very weak magnetization (M s  ∼ 0.05 emu/g) in spite of the higher ethylene carried Fe(CO)5 flow. The powders were annealed in air at 400 °C show lower carbon content and, for those highly Fe-doped, the hematite phase formation. Preliminary tests using UV light confirm the photocatalytic action of the annealed nanopowders in salicylic acid degradation process in solution.
Keywords: Laser pyrolysis; Iron-based magnetic nanocomposites; Titania;

ZnMnO diluted magnetic semiconductor nanoparticles: Synthesis by laser ablation in liquids, optical and magneto-optical properties by A.I. Savchuk; A. Perrone; A. Lorusso; I.D. Stolyarchuk; O.A. Savchuk; O.A. Shporta (205-208).
Nanoparticles of ZnO and Zn1−x Mn x O were synthesized by pulsed laser ablation in liquid medium (PLAL). Metal zinc target was used for preparing of pure ZnO nanostructures and Zn1−x Mn x O ceramic plates served for preparing of ternary nanoparticles. As synthesized nanomaterials are characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy analysis (EDS), atomic force microscopy (AFM), UV-vis absorption, photoluminescence and Faraday rotation spectroscopy. SEM images showed a well-defined flower-like nanostructures. Absorption edge of Zn0.95Mn0.05O nanoparticles in colloid solution exhibits blue shift due to confinement effect. The observed photoluminescence peaks are attributed to the band-edge transitions and vacancies or defects. The Faraday rotation as a function of photon energy demonstrates behavior typical for diluted magnetic semiconductors (DMSs) in paramagnetic state.
Keywords: Zn1−x Mn x O nanoparticles; Pulsed laser ablation in liquid; SEM; AFM; Optical absorption; Photoluminescence; Faraday rotation;

Gas Immersion Laser Doping for superconducting nanodevices by F. Chiodi; A. Grockowiak; J.E. Duvauchelle; F. Fossard; F. Lefloch; T. Klein; C. Marcenat; D. Débarre (209-212).
We have conceived and fabricated Superconductor/Normal metal/Superconductor Josephson junctions made entirely of boron doped Silicon. We have used Gas Immersion Laser Doping to fabricate SN bilayers with good ohmic interfaces and well controlled concentration and doping depth. Standard fabrication processes, optimised for silicon, were employed to nanostructure the bilayers without affecting their transport properties. The junctions thus fabricated are proximity superconducting and show well understood IV characteristics. This research opens the road to all-silicon, non-dissipative, Josephson Field Effect Transistors.
Keywords: Laser doping; Silicon; Boron; Nanostructures; Superconductivity; Josephson junctions;

Study of thermophysical properties of crystalline silicon and silicon-rich silicon oxide layers by O.O. Gavrylyuk; O.Yu. Semchyk; O.L. Bratus; A.A. Evtukh; O.V. Steblova; L.L. Fedorenko (213-215).
The interaction of laser irradiation with SiO x films and process of decomposition SiO x on SiO2 and Si nanocrystals under the action of laser irradiation are investigated. Using the Comsol Multiphysics software package, the mathematical modeling of temperature distribution in a c-Si wafer and also on it's surface are carried out. It is shown that laser pulses can efficiently warm the samples of crystalline silicon. During the laser pulse of 10 ns with intensity of 52 MW/cm2 the temperature up to 2100 K can be reached on the sample surface. The experimental investigation of IR spectra of the initial and laser annealed silicon wafer coated with SiO x film confirmed the phase transformation of silicon oxide films. The changing electrical conductivity of films after laser irradiation points at changing of electron traps as a result of the film structure transformation.
Keywords: Silicon oxide; Nanocrystal; Laser annealing; Thermoconductivity equation; Electrical conductivity;

Organic heterostructures based on arylenevinylene oligomers deposited by MAPLE by M. Socol; N. Preda; L. Vacareanu; M. Grigoras; G. Socol; I.N. Mihailescu; F. Stanculescu; M. Jelinek; A. Stanculescu; M. Stoicanescu (216-222).
Organic heterostructures were fabricated by matrix assisted pulsed laser evaporation (MAPLE) method using arylenevinylene oligomers based on triphenylamine (P78)/carbazole (P13) group and tris(8-hydroxyquinolinato)aluminum salt (Alq3). Optical properties of the organic multilayer structures were characterized by spectroscopic techniques: FTIR, UV–vis and photoluminescence (PL). A good transparency (over 60%) was remarked for the structures with two organic layers in the 550–800 nm range. Photoluminescence (PL) spectra proved that the emission characteristics of the materials have been preserved. IV characteristics of (ITO/oligomer/Alq3/Al and ITO/Alq3/Al) heterostructures were symmetrically while rectifying properties of these heterostructures have not been observed. A comparison between the heterostructures made of layers with different thickness reveals that the higher current (8 × 10−6  A at 1 V) was obtained for the ITO/P78/Alq3/Al heterostructure, which is characterized by a larger thickness of the double organic layer. AFM measurements revealed a similar topography while RMS values of the reported structures depend on the organic material.
Keywords: Organic heterostructures; MAPLE; Oligomer; Optoelectronic;

Impact of the apex of an elongated dielectric tip upon its light absorption properties by J. Bogdanowicz; M. Gilbert; S. Koelling; W. Vandervorst (223-225).
This paper discusses the impact of the hemispherical ending of a conical dielectric tip on its optical absorption capabilities. We show that the bottleneck for light coupling via the apex is its ability to resonantly interact with the incident light, which is only possible for apex radii commensurate with the wavelength. Once light has been fed into the apex, however, the fundamental guided mode of the dielectric tip is excited independently from the apex size. The existence and propagation of the fundamental mode from the apex into the shank are supported experimentally by the observation of periodic ripples close to the apex of a silicon tip irradiated with high-fluence green laser pulses. The periodicity and attenuation of these ripples along the tip axis are in excellent agreement with the theoretical properties of the fundamental guided mode.
Keywords: Semiconductors; Mie theory; Optical fiber; Light absorption; Laser damage; Atom probe tomography;

Surface ablation of transparent polymers with femtosecond laser pulses by C. Florian; F. Caballero-Lucas; J.M. Fernández-Pradas; J.L. Morenza; P. Serra (226-230).
In this work, a study of the laser ablation on the surface of poly methyl-methacrylate (PMMA) is presented. Experiments were performed with a femtosecond laser delivering 450 fs pulses at a wavelength of 1027 nm. The laser beam energy was controlled through a polarizer based attenuator and measured by a calibrated photodiode energy meter. A focusing method called z-scan is used to place the sample on the beam waist. This method uses a second energy meter placed behind the sample, which was used to monitor the energy transmitted across the sample in situ. Thus, the absorption was evaluated by comparing the measurements of both energy meters. The z-scan method is evaluated by studying the laser ablation in three different positions between the sample and the laser beam waist. It is found that above a threshold energy that depends on the focusing conditions, the absorbance of the samples increases with the pulse energy. After irradiation, dimensional analysis of the craters produced at different pulse energies is performed in order to determine the best focusing conditions and the ablation threshold for ablation of PMMA samples.
Keywords: Femtosecond laser; z-scan; Poly methyl-methacrylate (PMMA);

Microstructuring of soft organic matter by temporally shaped femtosecond laser pulses by Esther Rebollar; Jutta Mildner; Nadine Götte; Dirk Otto; Cristian Sarpe; Jens Köhler; Matthias Wollenhaupt; Thomas Baumert; Marta Castillejo (231-235).
Thin films of the biopolymers gelatine and chitosan were treated using femtosecond pulse shaping techniques combined with a microscope-based setup for material processing. The polymer films were irradiated with laser pulses of 35 fs and a central wavelength of 790 nm provided by an amplified Ti:Sapphire system. The effect of temporal pulse shaping, with quadratic and cubic spectral phases, on the induced morphology was analyzed by characterization of the created surface structures via scanning electron microscopy. We observed different material modification thresholds and different structure sizes for temporally asymmetric pulse shapes. The results indicate the possibility of control of the generated microstructures and are discussed in relation to the formation of free electrons and the different contributions of multi-photon and avalanche ionization processes.
Keywords: Femtosecond laser processing; Polymer films; Temporally shaped femtosecond pulses;

Laser surface modification of ultra-high-molecular-weight polyethylene (UHMWPE) for biomedical applications by A. Riveiro; R. Soto; J. del Val; R. Comesaña; M. Boutinguiza; F. Quintero; F. Lusquiños; J. Pou (236-242).
Ultra-high-molecular-weight polyethylene (UHMWPE) is a synthetic polymer used for biomedical applications because of its high impact resistance, ductility and stability in contact with physiological fluids. Therefore, this material is being used in human orthopedic implants such as total hip or knee replacements. Surface modification of this material relates to changes on its chemistry, microstructure, roughness, and topography, all influencing its biological response. Surface treatment of UHMWPE is very difficult due to its high melt viscosity.This work presents a systematic approach to discern the role of different laser wavelengths (λ  = 1064, 532, and 355 nm) on the surface modification of carbon coated UHMWPE samples. Influence of laser processing conditions (irradiance, pulse frequency, scanning speed, and spot overlapping) on the surface properties of this material was determined using an advanced statistical planning of experiments. A full factorial design of experiments was used to find the main effects of the processing parameters. The obtained results indicate the way to maximize surface properties which largely influence cell–material interaction.
Keywords: Laser; Surface modification; UHMWPE; Transmittance;

Processing conditions in pulsed laser ablation of gold in liquid for fabrication of nanowire networks by A.S. Nikolov; N.N. Nedyalkov; R.G. Nikov; I.G. Dimitrov; P.A. Atanasov; K. Maximova; Ph. Delaporte; A. Kabashin; M.T. Alexandrov; D.B. Karashanova (243-249).
The experimental conditions were investigated enabling one to fabricate Au nanowire networks by pulsed laser ablation in water. The study revealed that it is possible to produce alternatively nanoparticles (or aggregates) or nanowire networks at certain wavelengths depending on the laser fluence. An Au disc immersed in double-distilled water was used as a target. The second (λ SHG  = 532 nm) and the third (λ THG  = 355 nm) harmonics of a Nd:YAG laser system were utilized to produce different Au colloids. The values of the laser fluence for both wavelengths under the experimental conditions chosen were varied from several J/cm2 to tens of J/cm2. The optical extinction spectra of the colloids in the UV/vis region were obtained to evaluate the structure of the dispersed Au phase. Transmission electron microscopy (TEM) was applied to visualize the size and morphology of the colloidal particles. Their structure and phase composition were studied by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) and used to make an assumption on how they had been formed.
Keywords: Au nanowire networks forming; Nanosecond laser ablation; Noble metal aqueous colloid; Optical extinction spectrum; High resolution TEM image; Chain crystal structure;

Tailoring odorant-binding protein coatings characteristics for surface acoustic wave biosensor development by F. Di Pietrantonio; M. Benetti; V. Dinca; D. Cannatà; E. Verona; S. D’Auria; M. Dinescu (250-255).
In this study, wild type bovine odorant-binding proteins (wtbOBPs) were deposited by matrix-assisted pulsed laser evaporation (MAPLE) and utilized as active material on surface acoustic wave (SAW) biosensors. Fourier transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM) were used to determine the chemical, morphological characteristics of the protein thin films. The FTIR data demonstrates that the functional groups of wtbOBPs do not suffer significant changes in the MAPLE-deposited films when compared to the reference one. The topographical studies show that the homogeneity, density and the roughness of the coatings are related mainly to the laser parameters (fluence and number of pulses). SAW biosensor responses to different concentrations of R-(–)-1-octen-3-ol (octenol) and R-(–)-carvone (carvone) were evaluated. The obtained sensitivities, achieved through the optimization of deposition parameters, demonstrated that MAPLE is a promising deposition technique for SAW biosensor implementation.
Keywords: Matrix-assisted pulsed laser evaporation, SAW biosensors; Odorant-binding protein;

Tailored topography control of biopolymer surfaces by ultrafast lasers for cell–substrate studies by L. Rusen; M. Cazan; C. Mustaciosu; M. Filipescu; S. Sandel; M. Zamfirescu; V. Dinca; M. Dinescu (256-261).
Nowadays, the culture surfaces used for in vitro testing must be capable of possessing an improved interface for cell interactions and adhesion. For this reason, the materials used need to have an appropriate chemistry and architecture of its surface, resembling to the extracellular matrix. Within this context, in this work we combined the advantages of natural biopolymer characteristics (chitosan) with the flexibility in surface texturing by ultrafast laser for creating functional microstructured surfaces for cell–substrate in vitro studies. A Ti:Sapphire femtosecond laser irradiation (λ  = 775 nm and 387 nm) was used for tailoring surface morphological characteristics of chitosan based films (i.e. polymer “bubbles”, “fingertips” and “sponge-like” structures). These structures were investigated by scanning electron microscopy and atomic force microscopy. The morphology of the structures obtained was correlated with the response of oligodendrocytes cells line. In vitro tests on the patterned surface showed that early cell growth was conditioned by the microtopography and indicate possible uses of the structures in biomedical applications.
Keywords: Chitosan; Fs laser texturing; Cell bio-substrate interaction;

Functionalized antibiofilm thin coatings based on PLA–PVA microspheres loaded with usnic acid natural compounds fabricated by MAPLE by Valentina Grumezescu; Gabriel Socol; Alexandru Mihai Grumezescu; Alina Maria Holban; Anton Ficai; Roxana Truşcǎ; Coralia Bleotu; Paul Cǎtǎlin Balaure; Rodica Cristescu; Mariana Carmen Chifiriuc (262-267).
We report the fabrication of thin coatings of PLA–PVA microspheres loaded with usnic acid by matrix assisted pulsed laser evaporation (MAPLE) onto Ti substrate. The obtained coatings have been physico-chemically characterized by scanning electron microscopy (SEM) and infrared microscopy (IRM). In vitro biological assays have been performed in order to evaluate the influence of fabricated microsphere thin coatings on the Staphylococcus aureus biofilm development as well as their biocompatibility. SEM micrographs have revealed a uniform morphology of thin coatings, while IRM investigations have proved both the homogeneity and functional groups integrity of prepared thin coatings. The obtained microsphere-based thin coatings have proved to be efficient vehicles for usnic acid natural compound with antibiofilm activity, as demonstrated by the inhibitory activity on S. aureus mature biofilm development, opening new perspectives for the prevention and therapy associated to biofilm related infections.
Keywords: MAPLE; Microspheres thin coatings; PLA–PVA; Usnic acid; Anti-biofilm; Staphylococcus aureus;

Analysis of laser doping of silicon using different boron dopant sources by P. Prathap; J. Bartringer; A. Slaoui (268-274).
Implementation of selective emitter that decouples the requirements for front doping and metallization leads to improve the efficiency of crystalline silicon solar cells. Formation of such an efficient selective emitter using a laser beam with a suitable wavelength is an attractive method.The present work focuses on the analysis of laser doping of boron using different finite sources such as borosilicate glass (BSG) deposited by PECVD, spin-on solution and BCl3 gas source. KrF excimer laser (248 nm) was used for the selective doping. The surface dopant concentration and depth, as measured using SIMS, were controlled by variation of the laser fluence, pulse number and dopant source thickness. Depending on the type of BSG source, sheet resistance close to 20 Ω/sq was achieved at the laser fluences in the range, 2.5–5 J/cm2. The PECVD-BSG layers with a relatively higher thickness resulted in a lower sheet resistance of 20 Ω/sq with a junction of depth of ∼1 μm at a moderate laser fluence of 2.5 J/cm2. In the case of BSG deposited by spin-on source, a deeper junction of depth of ∼2.7 μm with a plateau profile of 1 μm was formed at a laser fluence of 3.1 J/cm2 that resulted in a lower sheet resistance of ∼31 Ω/sq. Redistribution of the dopant with pulse repetition was observed for the BSG deposited by BCl3 gas source.Pulse repetition at relatively lower laser fluences (>threshold energy) resulted in the best electrical results in combination with a limited laser induced damage in the silicon crystal. Also, multiple laser annealing resulted in redistribution of the dopant profiles in terms of enhanced junction depth.
Keywords: Laser doping; Selective emitter; Silicon solar cells;

Single Pulse Laser Induced Breakdown Spectroscopy (SP-LIBS), performed by nanosecond and femtosecond laser sources has been applied to the study of the depth profiling of the artificially obtained patina of a bronze sample. The results show improved performances of femtosecond LIBS compared to nanosecond one. The differences found in the analyses are related to the different laser–matter interaction processes induced by the different time duration of the laser pulses.
Keywords: Single-pulse LIBS; ns laser; fs laser; Copper alloy; Depth profiling.;

In-line measurements of chlorine containing polymers in an industrial waste sorting plant by laser-induced breakdown spectroscopy by N. Huber; S. Eschlböck-Fuchs; H. Scherndl; A. Freimund; J. Heitz; J.D. Pedarnig (280-285).
We report on laser-induced breakdown spectroscopy (LIBS) of chlorine containing waste polymers in-line of an industrial materials sorting plant. Material from municipal waste plastic collection containing different types of plastic pieces and impurities is measured without pre-treatment directly on the conveyor belt (conveyor speed 2 m/s). The encapsulated LIBS system mounted to the conveyor comprises a fast Nd:YAG laser and spectrometer with charge-coupled device (CCD) detector, a distance sensor, and a software for quasi real-time evaluation of measured LIBS spectra. Approximately 800,000 spectra are collected during the in-line measurement series using one laser pulse per spectrum. The optical plasma emission of Cl I at 837.6 nm is detected to identify waste polymers with high Cl content such as polyvinylchloride (PVC). The LIBS spectra are evaluated employing a fast linear correlation algorithm. The correlation histogram for more than 20,000 spectra shows three distinct peaks that are associated to different materials containing high amount of Chlorine (>20 wt %), Titanium, and low amount of Cl (<20 wt%). Signals of the LIBS sensor and a commercial near-infrared (NIR) optical reflection sensor were found to deviate for some samples. Such deviations might be caused by dark PVC samples that are detected by LIBS but missed by NIR reflection. Our results show that fast in-line identification of Cl containing waste polymer by LIBS is feasible under industrial conditions.
Keywords: Laser induced breakdown spectroscopy (LIBS); In-line measurement; Polyvinylchloride; Waste polymers; Fast detection; Linear correlation;

The redeposited material (debris) resulting from ablation of a potassium–magnesium silicate glass upon scanning femtosecond laser pulse irradiation (130 fs, 800 nm) in air environment is investigated by means of three complementary surface analytical methods. Changes in the electronic band structure of the glass constituent Magnesium (Mg) were identified by X-ray Absorption Near Edge Structure spectroscopy (XANES) using synchrotron radiation. An up-shift of ≈0.8 eV of a specific Magnesium K-edge absorption peak in the spectrum of the redeposited material along with a significant change in its leading edge position was detected. In contrast, the surface left after laser ablation exhibits a downshift of the peak position by ≈0.9 eV. Both observations may be related to a change of the Mg coordinative state of the laser modified/redeposited glass material. The presence of carbon in the debris is revealed by micro Raman spectroscopy (μ-RS) and was confirmed by energy dispersive X-ray spectroscopy (EDX). These observations are attributed to structural changes and chemical reactions taking place during the ablation process.
Keywords: Femtosecond laser ablation; Potassium–magnesium silicate glass; Debris; XANES; EDX; Raman spectroscopy;

Femtosecond double pulses with an inter pulse delay ranging from 100 fs up to 2 ns are used to study the dynamics of laser ablation of metals under ambient conditions far above the ablation threshold. To that end femtosecond double pulses of 30 fs pulse duration at 785 nm having the same intensities are focused onto the sample with a NA 0.5 microscope objective. Signals from element specific spectral line transitions and from reflection of the plasma plume are recorded as function of delay between the two pulses. The corresponding ablation structures are analyzed via atomic force microscopy. Based on these different observables four different enhancement regimes of the element specific signals are identified and discussed with respect to different transient stages of the ablation process. Both metals (Al and Ti) show qualitatively the same transient behavior. A maximum signal enhancement of about five is achieved at an inter pulse delay around 800 ps. The ablation volume is approximately the same as compared to the corresponding single pulse ablation volume with doubled fluence. This result serves as a route to increase the spatial resolution of far-field spectrochemical imaging via laser-induced breakdown spectroscopy on the few μm scale and below.
Keywords: Ultrashort laser ablation; Laser-induced breakdown spectroscopy; Titanium; Aluminum; Spectrochemical imaging;

Characterization of laser-induced plasmas of nucleobases: Uracil and thymine by I. Lopez-Quintas; M. Oujja; M. Sanz; A. Benitez-Cañete; C. Hutchison; R. de Nalda; M. Martin; R.A. Ganeev; J.P. Marangos; M. Castillejo (299-302).
In this work, nanosecond laser ablation plasmas generated at 266 and 1064 nm of the two pyrimidine nucleobases uracil and thymine were characterized using time-of-flight mass spectrometry, optical emission spectroscopy and temporally resolved third harmonic generation of a probe laser. This multiple technique approach provides insight into the role played by the irradiation wavelength on the composition and dynamics of plasma species and on the differences between the laser plasmas of the two nucleobases.
Keywords: Laser ablation plasmas; Harmonic generation; Time-of-flight mass spectrometry; Optical emission spectroscopy; Uracil; Thymine;

Film-free laser printing: Jetting dynamics analyzed through time-resolved imaging by A. Patrascioiu; J.M. Fernández-Pradas; J.L. Morenza; P. Serra (303-308).
The film-free laser-based microprinting technique allows high-resolution printing of transparent liquids without the need for the preparation of the liquid in thin-film form. Its operating principle relies on the tight focusing of ultrashort laser pulses in the liquid free-surface proximity producing upon absorption a rapidly expanding cavitation bubble that generates the ejection of micrometric liquid jets.While the technique proves feasible for microprinting, a deeper understanding of the influence on the printing process of its most relevant technological parameters is required. Therefore, in this work we analyze through time-resolved imaging the laser pulse energy influence on the bubble–jet dynamics of a film-free liquid ejection event. We simultaneously image the evolution of both cavitation bubble and ejected liquid, showing that for all the analyzed energies the transfer mechanism is mediated by the formation of two liquid jets which originate during the successive expansion-collapse cycles that the cavitation bubble undertakes close to the liquid free-surface. We find that the evolution of both bubble and jets depends strongly on the energy. The different bubble geometries that appear are interpreted in terms of the counter-jet interaction with the bubble, which in its turn depends on the energy.
Keywords: Laser printing; Laser-induced forward transfer; Cavitation bubble; Liquid jet; Time-resolved imaging;

Sulphated black crust is a common form of deterioration affecting stone used in monuments, usually occurs in contaminated atmospheres or urban environments. Its origin and cleaning have been studied extensively, for decades, in the case of carbonate rocks. Recent studies show that this form of alteration also affects granites. Scientific research on laser removal effectiveness of gypsum-rich black crust on granites needs to be scientifically addressed considering the inexistent references.This paper assesses the removal by laser of sulphate-rich black crusts on granite using the different harmonics of a Nd:YAG nanosecond pulsed laser (266 nm, 355 nm, 532 nm and 1064 nm). Effectiveness was evaluated using Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry (SEM–EDS), X-Ray Diffraction (XRD) and Attenuated Total Reflection-Fourier Infrared Transform Spectroscopy (ATR-FTIR). We also evaluated the effect of the radiation on granite-forming minerals and on the colour of the stone using Scanning Electron Microscopy and spectrophotometry colour measurements respectively.SEM–EDS, XRD and ATR-FTIR analyses show that the higher the wavelength, the more efficient the cleaning, so samples cleaned using 1064 nm pulsed laser recovered its original colour. Nevertheless, the Nd:YAG laser did not completely eliminate the crust, and gypsum crystals remaining on the rock surface are observed, even at the most effective wavelength.
Keywords: Laser cleaning; Cultural heritage; Black crust; Granite;

Multilayer polychrome coatings on medieval and Renaissance stone artefacts represent substantial challenges in laser cleaning. Therefore, polychromic models with classical pigments, minium P b 2 2 + Pb 4 + O 4 , zinc white (ZnO), and lead white ((PbCO3)2·Pb(OH)2) in an acrylic binder, were irradiated with a Q-switched Nd:YAG laser emitting at 532 nm. The studied medieval pigments exhibit strongly varying incubation behaviours directly correlated to their band gap energies. Higher band gaps beyond the laser photon energy of 2.3 eV require more incubative generation of defects for resonant transitions. A matching of the modification thresholds after more than four laser pulses was observed. Laser cleaning with multiple pulsing should not exceed ca. 0.05 J/cm2 when these pigments coexist in close spatial proximity.
Keywords: Laser cleaning; Pigments; Laser ablation;

Spinodal decomposition in AISI 316L stainless steel via high-speed laser remelting by Evans Chikarakara; Sumsun Naher; Dermot Brabazon (318-321).
A 1.5 kW CO2 pulsed laser was used to melt the surface of AISI 316L stainless steel with a view to enhancing the surface properties for engineering applications. A 90 μm laser beam spot size focused onto the surface was used to provide high irradiances (up to 23.56 MW/cm2) with low residence times (as low as 50 μs) in order to induce rapid surface melting and solidification. Variations in microstructure at different points within the laser treated region were investigated. From this processing refined lamellar and nodular microstructures were produced. These sets of unique microstructures were produced within the remelted region when the highest energy densities were selected in conjunction with the lowest residence times. The transformation from the typical austenitic structure to much finer unique lamellar and nodular structures was attributed to the high thermal gradients achieved using these selected laser processing parameters. These structures resulted in unique characteristics including elimination of cracks and a reduction of inclusions within the treated region. Grain structure reorientation between the bulk alloy and laser-treated region occurred due to the induced thermal gradients. This present article reports on microstructure forms resulting from the high-speed laser surface remelting and corresponding underlying kinetics.
Keywords: Laser remelting; Spinodal decomposition; Lamellar and nodular structures; 316L stainless steel;