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Applied Surface Science (v.248, #1-4)

Subject Index (pp. viii-xxxii).

Author Index (pp. i-vii).

Preface by A. Luches; Aaron Peled (Guest Editors) (pp. 1-2).

Spectroscopic assessment of rare-earth activated planar waveguides and microcavities by Luca Zampedri; Cristiana Tosello; Herv� Portales; Maurizio Montagna; Maurizio Mattarelli; Andrea Chiappini; Giancarlo C. Righini; Stefano Pelli; Gualtiero Nunzi Conti; Maurizio Martino; Sabine Portal; Ana C. Marques; Rui M. Almeida; Yoann Jestin; Maurizio Ferrari; Alessandro Chiasera (pp. 3-7).

This paper deals with glass-based photonic structures, used to control and modify the optical and spectroscopic properties of rare earth ions. The spectroscopic assessment of sol–gel-derived planar waveguides and 1D photonic band gap structures is reported. The spectroscopic, optical, and structural properties of planar waveguides with (100− x)SiO₂– xHfO₂– yErO_1.5 with y=0.3, 0.01; and x=10, 20, 30, 40 have been investigated by photoluminescence and Raman spectroscopy. The radiative quantum efficiency of the⁴I_13/2 metastable state of Er³⁺ ions is between 84 and 88% depending on the Si/Hf molar ratio. The sol–gel-derived one-dimensional cavity was realized by a Eu³⁺-activated dielectric layer placed between distributed Bragg reflectors (DBRs).

Keywords: Sol–gel method; Planar waveguides; Microcavities; Bragg reflectors; Luminescence

The electronic properties of carbon nanotubes studied by high resolution photoemission spectroscopy by R. Larciprete; A. Goldoni; S. Lizzit; L. Petaccia (pp. 8-13).

High resolution photoemission spectroscopy was used to follow the modification of the electronic properties of single wall carbon nanotubes determined by the interaction with adsorbed electron donor and acceptor species. Valence band, C1s and adsorbate core level spectra were monitored to reveal the adsorption and to follow the Fermi level shift induced by the charge exchange between C lattice and dopants. In the presence of nitrogen dioxide, a considerable charge withdrawal from C atoms takes place, which is revealed by the binding energy shift of the C1s peak. On the contrary, adsorbed H₂O does not appear to interact with nanotubes. For Li doping, the occurrence of an efficient electron injection into the tube structure is demonstrated by the evidence of Li ionisation, by the enhancement of the density of states near the Fermi level and by the partial conduction band filling, which originates a rigid shift of all C spectral structures.

Keywords: PACS; 73.22.-f; 73.63.Fg; 79.60.JvCarbon nanotubes; Electron doping; Photoemission spectroscopy

Time transient investigation of photo-induced electron localization at atomic step edges of Si (111) by Masashi Ishii; Bruce Hamilton (pp. 14-18).

To analyze a photo-induced electron localization process at atomic step edges of the Si-native oxide interface, the time transient signal of Kelvin force microscopy with a UV laser light source was investigated. The time constant of the photo-induced process for a laser wavelength λ=325nm had a linear dependence with respect to the laser power P_w. An electron transition model that takes into account photo- and thermal-effects revealed that the photo-induced localization is dominant for P_w>0.54mW. The small photo irradiation effect occurring at λ=441.6nm is explained by the low photo absorption efficiency for visible light.

Keywords: PACS; 78.47.+p; 73.50.Gr; 73.20.-rPhoto-induced electron localization; Si/SiO; _x; interface; UV laser; KFM; Time transient

Space and time resolved emission spectroscopy of Sr₂FeMoO₆ laser induced plasma by A. Santagata; A. Di Trolio; G.P. Parisi; R. Larciprete (pp. 19-23).

In this work the plasma dynamics induced during pulsed Nd:YAG ( λ=532nm) laser ablation of Sr₂FeMoO₆ targets has been studied by time- and space-resolved optical emission spectroscopy measurements in the range 250–650nm. The integral intensities of spectral lines were measured as a function of distance from the target surface and laser fluence in the presence of 5×10⁻⁵mbar of O₂ partial pressure. The plasma properties as well as ionic and atomic Strontium time-of-flights were measured as a function of laser fluence in the range 0.90–2.40Jcm⁻². The results show how the different plasma features can influence the film deposition process and the magnetic saturation properties.

Keywords: Pulsed laser ablation; Laser induced plasma diagnostics

Nonlinear-optical diagnostics for laser ablation and photo-heating of biotissue by A.A. Lalayan (pp. 24-27).

Tissue nonlinear spectroscopy has been investigated as a potential method for monitoring the laser photo-heating and laser ablation of biological tissues samples. The nonlinear optical phenomenon of the second harmonic generation (SHG) for femtosecond–picosecond duration laser beam pulses passing through collagen containing a layer of biotissue was used to monitor the photothermal processes induced by laser irradiation. The samples of biotissues were photo-heated by CW Nd:YAG laser. A picosecond Nd:YAG beam with 1064nm and pulse duration τ_imp=33ps was used for probing. After the laser heating of fasciae and tendon samples, the SHG radiation decreased six times in the area of irradiation. The laser ablation of skin samples was performed with a CW Nd:YAG laser at the power of 2W. As a result of laser ablation the SHG nonlinear signal increased by a factor of 2. The results demonstrate, that the SHG nonlinear phenomenon enables real-time monitoring of photo-heating and ablation processes of biological tissue in novel laser surgical procedures.

Keywords: PACS; 42.62.√b; 42.62.ky; 42.65.√k; 42.62.FiTissue heating; Laser ablation; Skin tissue; Second harmonic generation

UV–vis spectroscopy for on-line monitoring of Au nanoparticles size during growth by R. Salvati; A. Longo; G. Carotenuto; S. De Nicola; G.P. Pepe; L. Nicolais; A. Barone (pp. 28-31).

Gold nanoparticles have been prepared by alcoholic reduction of Au(III) ions in presence of a polymeric stabilizer (poly( N-vinyl pyrrolidone), PVP). On-line UV–vis spectroscopic characterization and transmission electron microscopy (TEM) analysis are presented. Optical spectroscopy data show that the temporal evolution of absorption spectra and the absorbance peak properties are correlated to the off-line size measurements obtained at chemical reaction end by TEM micrographs. The Au cluster size behaves linearly with time above a threshold temperature (70°C), according to a deposition-controlled growth mechanism.

Keywords: PACS; 73.20.Mf+; 78.67.BfOptical spectroscopy; Au clusters; Alcoholic reduction; Surface plasmon; Formation–growth mechanism

Measurement of the electrical size of a laser-induced plasma in a uniform field by A. Robledo-Martinez; H. Sobral; M. Villagr�n-Muniz (pp. 32-35).

Measurements of the electric field produced by laser-induced plasma in ambient air under an external (bias) are presented. The transient field induced by the plasma was monitored using a D-dot type probe. The plasma field was found to have a dipolar structure with its moment aligned with the bias field. The measurement of the induced dipolar moment gives the electric size of the plasma. These results were compared with fast photography and shadowgraphy which gave sizes of about 2–3mm in the time interval from 50 to 100ns. The electric size in the same interval was approximately three times larger than that obtained by the optical techniques. The difference is attributed to an ionized layer 2.6mm thick which reflects the spatial extent of the air ionized by UV radiation around the plasma.

Keywords: PACS; 52.50.Jm; 52.80.Mg; 52.70.DsLaser-induced plasmas; Plasma diagnostic techniques

Characterisation of thin films of organic phosphorescent materials using synchrotron radiation by J. Thompson; V. Arima; F. Matino; R. Cingolani; R.I.R. Blyth (pp. 36-39).

Synchrotron radiation photoemission and X-ray absorption spectroscopy (NEXAFS) have been used to investigate the electronic structure of evaporated films of the phosphorescent organic iridium complexes iridium tris-(2-(4-totyl)pyridinato-N,C²), iridium bis(2-(4,6-difluorophenyl)pyridinato-N,C²)picolinate, and iridium bis(2-(2′-benzothienyl)pyridinato-N,C³)-(acetylacetonate) and spin coated films of these materials in a polymer host. Resonant photoemission at the Ir N_6,7 edge indicates that the Ir 5d states are hybridised with the π orbitals of the organic ligands, in agreement with recent calculations. The nitrogen K-edge NEXAFS shows the difference in the unoccupied orbitals induced by the acetylacetonate group compared to those of the pyridinate ligands. Although the valence bands of the ex situ prepared films are not accessible to photoemission, the Ir 4f core levels remain visible, and demonstrate that the polymer host serves to lower the electron injection barrier in the iridium complexes in comparison to the pure films.

Keywords: PACS; 79.60.Fr; 78.70.DmPhotoemission; X-ray absorption; Iridium complexes; Organic molecules

Characterization of functionalised porphyrin films using synchrotron radiation by V. Arima; F. Matino; J. Thompson; R. Del Sole; G. Mele; G. Vasapollo; R. Cingolani; R. Rinaldi; R.I.R. Blyth (pp. 40-44).

Porphyrins and C₆₀ are strategic materials for the fabrication of nanoscale molecular devices by virtue of their optical, photo–electro-chemical and chemical properties. We have developed procedures to immobilise cobalt tetra-butyl-phenyl porphyrins (CoTBPPs) on gold surfaces via ligation to self-assembled monolayers of aromatic aminothiophenols (4-ATP). We have used synchrotron radiation photoemission and near-edge X-ray absorption, NEXAFS, to characterise such films, both in their native state, and with ligated fulleropyrrolidines N-methyl-2-( p-pyridyl)-3,4-fulleropyrrolidine (Py-C₆₀), forming charge-separation complexes which may have applications in solar cells. While photoemission spectra appear dominated by the individual CoTBPP and Py-C₆₀ components, we observe an apparent signature of charge separation in fulleropyrrolidine NEXAFS spectra.

Keywords: Porphyrins; Synchrotron radiation; Fulleropyrrolidines; Photoemission; NEXAFS

Characterization of LaMnO₃ laser ablation in oxygen by ion probe and optical emission spectroscopy by S. Amoruso; R. Bruzzese; R. Velotta; N. Spinelli; M. Vitiello; X. Wang (pp. 45-49).

Combined measurements of ion probe and optical emission spectroscopy have been employed to investigate the propagation of LaMnO₃ ablation plasma in oxygen background gas. The expansion dynamics as a function of the background pressure shows a transition from a free-plume, at low pressures, to a shock-wave-like expansion, at larger pressures. Plume splitting is observed in a pressure range which depends on the distance from the target surface. The distance-related pressure dependencies for the different expansion regimes have been rationalized in the frame of a simple model of plume propagation into the background gas.

Keywords: Laser ablation; Spectroscopy; Ion probe; Manganites

Photoexcitation-induced processes in amorphous semiconductors by Jai Singh (pp. 50-55).

Theories for the mechanism of photo-induced processes of photodarkening (PD), volume expansion (VE) in amorphous chalcogenides are presented. Rates of spontaneous emission of photons by radiative recombination of excitons in amorphous semiconductors are also calculated and applied to study the excitonic photoluminescence in a-Si:H. Results are compared with previous theories.

Keywords: PACS; 78.55.Qr; 74.81.Bd; 78.66.JgPhoto-induced processes; Photodarkening; Volume expansion; Radiative recombination; Amorphous semiconductors

Photoswitches operating upon ns pulsed laser irradiation by A. Athanassiou; K. Lakiotaki; M. Kalyva; S. Georgiou; C. Fotakis (pp. 56-61).

We present a potential photoswitch, which undergoes reversible mechanical actuation induced exclusively by photons. The photoswitch is a polymer-based film doped with spiropyran photochromic molecules. It undergoes repeatable mechanical cycles controlled by ns laser pulses of specific wavelengths. The polymer matrix is mechanically activated due to particular photoisomerization processes of the incorporated photochromic molecules, resulting in its contraction and lengthening in a highly controllable manner. We present herein the way that the switching time of this novel photoswitch depends on different laser parameters such as the energy and the repetition rate.

Keywords: PACS; 82.50.Hp; 61.80.Ba; 82.30.Qt; 07.10.CmLaser; Photochromic polymers; Spiropyran; Optomechanical actuation; Photoswitches

Study of hot-carrier-induced photon emission from 90nm Si MOSFETs by M. Gurfinkel; M. Borenshtein; A. Margulis; S. Sade; Y. Fefer; Y. Weizman; Yoram Shapira (pp. 62-65).

Measurements of photon emission and substrate current in metal-oxide-semiconductor field effect transistors at various temperatures have been carried out using electrical and NIR microscopy. The results received at room temperature have extended the correlation between the substrate current and the photon emission, which was previously found in the visible, to the NIR range. On the basis of this correlation, an empirical model based on the substrate current was used to describe the static emission intensity dependence on the transistor bias. Temperature resolved measurements show that the correlation between emission intensity and the substrate current appears to be coincidental.

Keywords: PACS; 85.30.Tv; 85.40.Qx; 78.60.FiMOSFET; Hot carrier luminescence; Photon emission; Substrate current; Semiconductor device models

Electron excitation in glasses followed by time- and space-measuring tools by E.W. Kreutz; A. Horn; R. Poprawe (pp. 66-70).

Temporal and spatial changes in the matrix of glasses (BK7 glass, fused silica, quartz) are investigated during and after irradiation by pulsed laser radiation (100 f_s< t_p<3ps) at the wavelength λ=800nm using high-speed photography, transient absorption spectroscopy, and Nomarski-microscopy to visualize the changes of optical properties, plasma formation and expansion, stress formation, modification, and cracking. Depending on the excitation conditions the glasses exhibit different excitation and relaxation channels including various types of defect centers in the glass. Compared to laser irradiation with pulse durations t_p in the nanosecond regime, when the glasses are heated within the irradiation zone for many nanoseconds resulting in an increase of the refractive index without cracking enabling the generation of photonic structures within the bulk, irradiation with pulse durations in the picosecond regime leads to cracking, thus enabling marking in the bulk and at the surface.

Keywords: PACS; 42.65.R; 06.60.J; 42.65.R; 78.47; 39.90; 78.47; 78.66.J; 64.70.PGlasses; fs- and ps-laser radiation; Interaction phenomena

Studying atomic-resolution by X-ray fluorescence holography by Hongyi Gao; Jianwen Chen; Honglan Xie; Huafeng Zhu; Ruxin Li; Zhizhan Xu (pp. 71-74).

In this work, the results of numerical simulations of X-ray fluorescence holograms and the reconstructed atomic images for Fe single crystal are given. The influences of the recording angles ranges and the polarization effect on the reconstruction of the atomic images are discussed. The process for removing twin images by multiple energy fluorescence holography and expanding the energy range of the incident X-rays to improve the resolution of the reconstructed images is presented.

Keywords: X-ray fluorescence holography; Atomic resolution; Multiple energy X-ray fluorescence holography; Numerical simulation

Recent progress in femtosecond holography by Huafeng Zhu; Jianwen Chen; Hongyi Gao; Honglan Xie; Ruxin Li; Zhizhan Xu (pp. 75-78).

The recent advancements of femtosecond (fs) holography are introduced. The experimental requirements and the time resolution are presented. Applications of femtosecond holography to signal processing, and other femtosecond holographic techniques such as femtosecond holographic imaging and microprocessing are detailed. A potential alternative of femtosecond holography is proposed, based on the sectional interference of reference pulse with the time stretched signal pulse.

Keywords: PACS; 42.40.Ht; 42.40.MyFemtosecond holography; Femtosecond spectral holography; Spectra hole burning

Time of flight transients analysis in photo-excited molecular doped polymers by N. Mirchin; A. Peled (pp. 79-85).

Charge transport in molecular doped polymers (MDP) is analyzed by a new formalism taking into account spatial dispersion effects also. Charge packets are injected in thin films of photoreceptor materials by pulsed UV photo-excitation to perform time of flight (TOF) experiments. The transient currents are related in this work to thermal and electric field excitation mechanisms using new dispersion parameters. The parameters used for describing the charge spatial dispersion are the velocity distribution within the moving charge packet and the trapping time. The formalism uses the classical electrodynamic equations with proper limiting conditions. This work analyzes the experimental transients using the equation of current displacement, and a simple deep trapping model. The results are different from those obtained for semiconductors.

Keywords: Molecular doped polymer (MDP); Photo-excitation; Insulator electrical transport

Kinetics of UV-induced darkening of titanium-oxide gels by N. Bityurin; A.I. Kuznetsov; A. Kanaev (pp. 86-90).

Several models of UV laser-induced darkening of titanium-oxide wet gels are considered, which fit well to the recently obtained experimental data on the darkening kinetics. They reveal a high initial quantum yield of the light-induced charge separation and the existence of a 10% limitation in the number density of the trapped electrons, as compared to the number density of possible traps. This limitation is attributed to the internal photo-effect, the recombination of trapped electrons with the fast holes and the interaction of newly created free electrons with the already trapped electrons.

Keywords: UV laser; Titanium-oxide gel; Darkening; Modeling

Photo-bleaching response in chlorophyll solutions by N. Mirchin; A. Peled (pp. 91-96).

Photo-excitation processes were investigated in chlorophyll solutions by irradiation with UV light sources. Photo-excited bulk effects during the bleaching experiments were diagnosed. The optical diagnostic was expressed by a Beer–Lambert matrix formulation and applied to the experimental results. The chromophores evaluated optical cross-section was 10⁻¹⁵cm² and the optical absorption coefficient dynamic variation was fitted to a simple reaction rate model. The bleaching rates were expressed by this model and fitted to the experimental data.

Keywords: Photo-bleaching; Photo-excitation; Chlorophyll

Writing single-mode waveguides in lithium niobate by ultra-low intensity solitons by E. Fazio; W. Ramadan; A. Petris; M. Chauvet; A. Bosco; V.I. Vlad; M. Bertolotti (pp. 97-102).

Optical waveguides can be conveniently written in photorefractive materials by using spatial solitons. We have generated bright spatial solitons inside lithium niobate which allow single-mode light propagation. Efficient waveguides have been generated with CW light powers as high as few microwatts. According to the soliton formation, waveguides can be formed with different shapes. Due to the slow response time of the lithium niobate, both for soliton formation and relaxation, the soliton waveguide remains memorised for a long time, of the order of months.

Keywords: PACS; 42.65.T; 42.65.W; 42.65.HSolitons; Optical waveguides; Photorefractive crystals

Electron and phonon dynamics in laser short pulses-heated metals by L.D. Pietanza; G. Colonna; M. Capitelli (pp. 103-107).

The simultaneous electron and phonon relaxation dynamic in a metal film subjected to a laser pulse has been theoretically investigated. A system of two coupled time- and energy-dependent Boltzmann equations describing the electron and phonon dynamics has been numerically solved. The collision processes considered are electron–electron (e–e) and electron–phonon (e–p) collisions. Our results show the non-equilibrium electron distribution and the electron and phonon relaxation dynamics both after a femtosecond and a picosecond laser perturbations.

Keywords: Electron; Phonon; Energy-dependent

Influence of the substrate temperature on the structure of Ge containing thin films produced by ArF laser induced chemical vapour deposition by E. L�pez; S. Chiussi; P. Gonz�lez; J. Serra; B. Le�n (pp. 108-112).

Ge, SiGe and SiGeC films were grown on Si(100) and Corning glass (7059) substrates by ArF-excimer laser induced chemical vapour deposition in parallel configuration. Different substrates temperatures ranging from 180 to 400�C, for a fixed reactant gas composition, were used at constant total pressure and laser power. The analysis of the films showed the existence of a relationship between the substrate temperature and the deposition rate as well as to the film properties. A comparison among the pure, binary and ternary Ge containing system was performed to study the influence of the presence of different gases in the reactant mixture. Structural properties of the deposited films were investigated by Raman and Fourier transform infrared spectroscopy. Their surface morphology was evaluated by scanning electron microscopy and atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) revealed the composition of the alloys and X-ray diffraction experiments demonstrated the polycrystallinity of some pure Ge films.

Keywords: PACS; 42.70; 81.15; 61.43 D; 33.80.G; 61.16C; 61.10; 33.60LCVD; Ge containing films; Thin films; FTIR; XRD

Compositional, structural and optical properties of Si-rich a-SiC:H thin films deposited by ArF-LCVD by E. L�pez; S. Chiussi; U. Kosch; P. Gonz�lez; J. Serra; C. Serra; B. Le�n (pp. 113-117).

Silicon-rich amorphous hydrogenated silicon carbon (a-SiC:H) films with C content up to 23% have been grown on Si and Corning glass substrates using ArF laser induced chemical vapor deposition (ArF-LCVD). This technique allows tailoring film composition by controlling deposition parameters such as precursor gas mixture (disilane and ethylene diluted in helium) and substrate temperature (180–400°C). The influence of both parameters on composition and bonding were studied by Fourier transform infrarred (FTIR) and X-Ray photoelectron spectroscopy (XPS). The optical gap of these semiconductors deposited at 250°C varied from 1.6 to 2.4eV and was determined by UV–vis spectroscopy. An additional analysis by profilometry and atomic force microscopy (AFM) have been done for determining the deposition rate and the roughness (rms<6nm) of the films as well as their surface morphology.

Keywords: PACS; 42.70.H; 33.80.G; 81.15; 61.43 D; 78.30.E; 78.20; 61.16C; 33.60LCVD; a-SiC:H; Bandgap tailoring; Thin films; FTIR; XPS

Epitaxial growth of tin oxide films on (001) TiO₂ substrates by KrF and XeCl excimer laser annealing by T. Tsuchiya; A. Watanabe; T. Kumagai; S. Mizuta (pp. 118-122).

Epitaxial SnO₂ thin films were prepared by excimer laser annealing of amorphous SnO₂ films on a (001) TiO₂ substrate. The amorphous SnO₂ film was prepared by a metal organic deposition (MOD) using di- n-butylbis (2,4-pentanedionate) tin at 300°C. When using a KrF excimer laser with fluence of 50 to 150mJ/cm², polycrystalline SnO₂ films were formed on (001) TiO₂ substrate at 25°C. At fluences of 200 and 250mJ/cm², (002) oriented SnO₂ films were obtained. When using a XeCl laser with fluences of 150 and 200mJ/cm², the (002) oriented SnO₂ films were obtained. Using the XRD φ scanning measurement, it was found that oriented SnO₂ films were epitaxially grown on the (001) TiO₂ substrate. The formation of the epitaxial SnO₂ on the (001) TiO₂ substrate was found to depend on the pre-irradiated amorphous SnO₂ film thickness, laser fluence and laser wavelength.

Keywords: PACS; 81.15.Fg; 81.15.-z; 81.16.Mk; 82.50.Hp; 73.61.LeSnO; ₂; Excimer laser; KrF; XeCl; MOD; Epitaxial growth; (0; 0; 1) TiO; ₂

Nanotechnological applications of nonlinear surface acoustic waves: Mechanism of brittle fracture by P. Hess; A.M. Lomonosov (pp. 123-128).

Strongly nonlinear surface acoustic waves (SAWs) with shock fronts were used to study impulsive fracture in anisotropic silicon crystals and isotropic fused quartz. With this method, spatially localized dynamic fracture was studied without an artificial pre-cracking. SAWs allow the investigation of mode I tensile stress and mode II shear stress fracture. For silicon, the difference between the measured critical fracture stress of 1–2GPa and the theoretical tensile strength of 22GPa is discussed in terms of Griffith's approach. However, due to the biaxial stress field applied with SAWs and the low ideal shear stress of 6.8GPa, the nucleation process may not be uniaxial and purely tensile in silicon. In fused quartz, nucleation occurred via tensile crack opening at the surface and propagation into the bulk proceeded at an angle of 55°–60° to the surface normal in the direction of SAW propagation. This behavior could be described theoretically by calculating the energy release rate as a function of direction and assuming that stable tip propagation is obtained under pure mode I conditions.

Keywords: PACS; 62.20.Mk; 43.25.+y; 62.30.+d; 68.35.JaSurface acoustic waves; Impulsive fracture; Tensile stress; Shear stress

Point defect production by ultrafast laser irradiation of alkali-containing silica glasses and alkali halide single crystals by S.M. Avanesyan; S. Orlando; S.C. Langford; J.T. Dickinson (pp. 129-137).

The high instantaneous powers associated with femtosecond lasers can color many nominally transparent materials. Although the excitations responsible for this defect formation occur at subpicosecond time scales, subsequent interactions between the resulting electronic and lattice defects complicate the evolution of color center formation and decay. These interactions must be understood in order to account for the long-term behavior of coloration. In this work, we probe the evolution of color centers produced by femtosecond laser radiation in soda lime glass and single-crystal sodium chloride at time scales from microseconds to hundreds of seconds. By using an appropriately chosen probe laser focused through the femtosecond laser spot, we can follow the changes in coloration due to individual or multiple femtosecond pulses, and follow the evolution of that coloration for long times after the femtosecond laser radiation is terminated. For the soda lime glass, the decay of color centers is well described in terms of bimolecular annihilation reactions between electron and hole centers. Similar processes are also occurring in single-crystal sodium chloride. Finally, we report fabrication of permanent periodic patterns in soda lime glass by two time coincident femtosecond laser pulses.

Keywords: Femtosecond laser pulse; Soda lime glass; Sodium chloride

Combining resonant/non-resonant processes: Nanometer-scale iron-based material preparation via CO₂ laser pyrolysis by R. Alexandrescu; I. Morjan; I. Voicu; F. Dumitrache; L. Albu; I. Soare; G. Prodan (pp. 138-146).

The laser pyrolysis as a tool for the gas-phase synthesis of nanoparticles is illustrated with recent results obtained in the preparation of iron-based nanostructures, where sensitized iron pentacarbonyl-based mixtures and ethylene as energy transfer agent are employed. The relation between the principal process conditions and the product characteristics is stressed. Iron–carbon core-shell nanoparticles with low mean size (about 4–5nm) and modified morphologies are obtained by an increase of ethylene flow. In case of γ-iron oxide nanopowder synthesis, low carbon contamination by ethylene depletion at increased system pressure, is observed.

Keywords: Laser pyrolysis; Sensitizer; Ethylene; Iron pentacarbonyl; Nanoparticles; Core-shell iron–carbon nanostructures; γ-Iron oxide nanoparticles

Growth of Al doped ZnO thin films by a synchronized two laser system by E. Gy�rgy; J. Santiso; A. Giannoudakos; M. Kompitsas; I.N. Mihailescu; D. Pantelica (pp. 147-150).

We report the deposition of Al doped ZnO thin films with the aid of a synchronised two laser system. The laser system consists of an ArF* excimer laser ( λ=193nm, τ∼12ns) and a Nd:YAG laser ( λ=355nm, τ∼10ns), for the time-matched ablation of the host (Zn) and dopant (Al) targets in oxygen atmosphere. Our approach allows for the independent and accurate setting of the laser fluences of the two lasers, in accordance with the energy requirements of the host and dopant materials. The method proposed by us permits also an in situ change of the doping conditions throughout the thin film growth process. The controlled modification of the dopant profile inside the growing film can be obtained relatively easily by the appropriate variation of the Nd:YAG laser fluence and/or number of pulses applied to the Al dopant target during the deposition process.

Keywords: PACS; 81.15.Fg; 81.70.Jb; 68.55.JkAl doped ZnO thin films; Laser deposition; Synchronized two laser system

Phase transitions induced by femtosecond laser pulse irradiation of indium phosphide by J. Bonse; S.M. Wiggins; J. Solis (pp. 151-156).

The structural transformation dynamics upon irradiation of single-crystalline indium phosphide with 150fs laser pulses at a wavelength of 800nm and with various fluences exceeding the melting or the ablation threshold has been investigated. Optical time-resolved reflectivity measurements were employed using two experimental set-ups to cover timescales up to 400ns after the pulsed excitation. A fs-resolution pump probe set-up covered the early stages of thermal and non-thermal melting and ablation. A real-time-resolved reflectivity set-up employing a streak camera and a photodiode was used for the investigation of the later stages of the resolidification process. In the ablation regime, the resolidification mechanisms have been analysed.

Keywords: PACS; 79.20.Ds; 78.47.+p; 64.70.-pLaser-induced phase transitions; Indium phosphide; Femtosecond laser pulse irradiation; Time-resolved reflectivity measurements; Melting; Ablation

Femtosecond laser-induced decomposition in triazenepolymer thin films by J. Bonse; S.M. Wiggins; J. Solis; T. Lippert; H. Sturm (pp. 157-162).

The damage induced by ultrashort, 130fs, near-infrared, 800nm, Ti:sapphire laser pulses in 1μm thick triazenepolymer films on glass substrates has been investigated. Real-time reflectivity measurements with a ps-resolution streak camera and a ns-resolution photodiode set-up have been performed to study in situ the structural transformation dynamics upon single-pulse excitation with laser fluences above the threshold of permanent damage. Scanning force microscopy has been used to probe ex situ the corresponding surface topography of the ablated spots. Modulated lateral force microscopy (M-LFM) has been applied to observe alterations of the local friction properties within and around the irradiated areas.

Keywords: PACS; 52.38.Mf; 79.20.DsLaser-induced phase transitions; Triazenepolymer film; Femtosecond laser pulse irradiation; Time-resolved reflectivity measurements; Scanning force microscopy; Ablation; Damage

The emission of atoms and nanoparticles during femtosecond laser ablation of gold by M. Vitiello; S. Amoruso; C. Altucci; C. de Lisio; X. Wang (pp. 163-166).

The properties of laser ablated plumes produced in high vacuum by 100fs Ti:sapphire pulses from a gold solid target were studied. Optical emission spectroscopy showed that the plume was formed by both atomic and non-atomic species in the whole investigated laser intensity range (10¹²–10¹³W/cm²), while atomic force microscopy analysis of deposits carried out at room temperature revealed the nanometric size of the non-atomic component, with a mean particle radius of tens of nanometers.

Keywords: PACS; 52.38.Mf; 52.50.Jm; 79.20.DsLaser ablation; Nanoparticles; Spectroscopy

Laser controlled nanodeposition of neutral atoms by E. Arimondo (pp. 167-171).

Optical forces produced by laser beams can produce atomic deposition at nanometer scale. The growth of atomic structures at surfaces is produced through direct deposition or by the modification of the surface properties using neutral atom lithography. This work reports current results of neutral atom lithography with cesium, gallium and barium. We explore the potential applications of nanofabrication by neutral atoms.

Keywords: Atom nanofabrication; Laser manipulation; Resist; Self-assembling monolayers

Microfabrication of 3D hollow structures embedded in glass by femtosecond laser for Lab-on-a-chip applications by Ya Cheng; Koji Sugioka; Katsumi Midorikawa (pp. 172-176).

Three-dimensional hollow microstructures acting as microfluidic and microoptical components were directly formed inside a photoetchable glass, Foturan, using femtosecond (fs) laser direct writing followed by post-annealing and successive chemical etching. Benefiting from a multiphoton process and a focus-shaping technique, a resolution as high as 10μm was achieved in both the transverse and longitudinal directions. Microreactors containing microchannels, microcells, and microvalves were fabricated by this technique, and functions like sample mixing and fluid switching were demonstrated. Also, microoptics, such as micromirrors and microbeam splitters, were fabricated by this technique. The microfluidic and microoptical components were also integrated into the same chip for creating microfluidic dye lasers. A dual-color microfluidic laser array which can simultaneously emit light with wavelengths centered at 568 and 618nm was also fabricated and its lasing properties examined.

Keywords: PACS; 87.80.Mj; 42.62.Cf; 42.82.Fv; 42.55.Mv3D microfabrication; Femtosecond laser; Photoetchable glass; Lab-on-a-chip

Time-resolved photoresponse of nanometer-thick Nb/NiCu bilayers by L. Parlato; G.P. Pepe; R. Latempa; C. De Lisio; C. Altucci; P. D’Acunto; G. Peluso; A. Barone; T. Taneda; R. Sobolewski (pp. 177-180).

We present femtosecond optical time-resolved pump-probe investigations of superconducting hybrids structures consisting of Nb/NiCu bilayers with various thickness. Measurements performed on pure Nb and NiCu films are also given. The photoresponse experiments provide the quasiparticle relaxation times in bilayers of different thickness ratios. The study of the photoresponse as a function of the temperature reveals the spatial evolution of the superconductor order parameter across the bilayers.

Keywords: PACS; 74.25.Gz; 74.70.Ad; 78.47.+pProximized superconducting-ferromagnetic bilayer; Pump-probe measurements; Non-equilibrium process

UV-initiated growth of gold nanoparticles in PMMA matrix by A. Alexandrov; L. Smirnova; N. Yakimovich; N. Sapogova; L. Soustov; A. Kirsanov; N. Bityurin (pp. 181-184).

Polymethylmethacrylate (PMMA) films containing HAuCl₄ (number density of 6×10¹⁹cm⁻³) were irradiated by a UV lamp and then annealed at various temperatures. The modification of the samples was investigated by in situ optical absorption spectroscopy and atomic-force microscopy (AFM). The disappearance of HAuCl₄ followed by gold nanoparticles growth in the films was revealed. The evolution of the size distribution of the nanoparticles during annealing was investigated using the Mie theory. The growth kinetics model based on the non-stationary first-order phase transition theory estimates a critical radius of 2nm for the growing nanoparticles at 75°C.

Keywords: Gold nanoparticles; UV irradiation; PMMA; Mie theory; Growth kinetics

Kinetic control of periodic surface patterning by laser photochemical deposition by Emmanuel Hugonnot; Jean-Pierre Delville (pp. 185-189).

We explored the real-time formation of periodic surface patterning resulting from laser-driven photochemical deposition in liquid solutions. Using the photochemical deposition of chromium hydroxide layers driven by a continuous wave (cw) Ar⁺ laser in an acidic potassium chromate solution, we analyzed the kinetics of three different types of patterning: dot array, periodic line writing and holographic grating formed by interfering two beams. In each case, the measured growth laws of the deposited films show the emergence of scaling regimes. This kinetic control, the versatility in monitoring the geometry of laser/medium interaction, and the flexibility of this approach offer valuable developments for substrate patterning for lithographic and holographic applications.

Keywords: PACS; 81.15.Fg; 81.10.Dn; 42.40.Eq; 42.70.GiPhotochemical deposition; Surface patterning; Laser; Chromate

Laser patterning of SiO_x-layers for the fabrication of UV diffractive phase elements by Malte Schulz-Ruhtenberg; J�rgen Ihlemann; J�rg Heber (pp. 190-195).

Diffractive phase elements (DPE), consisting of a patterned UV-transparent layer on a UV-transparent substrate, were fabricated by three steps. A UV-absorbing SiO_x-coating ( x<2) with a thickness matching to the required phase delay was deposited on a fused silica substrate. The coating was removed on a pixel array corresponding to a calculated two-dimensional quantized phase function (DPE-design). By a thermal annealing process the SiO_x-coating was oxidised to UV-transparent SiO₂, resulting in a UV-grade surface relief element.

Keywords: PACS; 42.70.Ce; 81.40.Tv; 81.65.CfLaser ablation; Diffractive phase elements; SiO; _x; SiO; ₂; UV-laser

Atomic lithography with barium atoms by A. Fioretti; A. Camposeo; F. Tantussi; E. Arimondo; S. Gozzini; C. Gabbanini (pp. 196-199).

We present the formation of structures created by barium atoms using a lithographic technique. The interaction of barium atoms with the resist, followed by an etching process, creates well defined structures with features below 100nm. The interaction of the ground state of Ba atoms with the molecules forming the self-assembled monolayer (SAM) is compared with the metastable Ba atoms–SAM interaction. The results show that metastable atoms require a lower Ba dose per SAM molecule to damage the resist, therefore increasing the efficiency of the process.

Keywords: PACS; 07.77.Gx; 42.82.Cr; 81.16.TaLithography; Nanofabrication; Atom optics

Near-field optical lithography method for fabrication of the nanodimensional objects by V.F. Dryakhlushin; A.Yu. Klimov; V.V. Rogov; N.V. Vostokov (pp. 200-203).

A new method of contact scanning near-field optical lithography has been developed to enable fabrication of elements with characteristic dimensions of 30–50nm. The method involves the deposition of a thin-layer polymer-metal coating, the thermal destructive deformation of a top metal layer with a probe of scanning near-field optical microscope (SNOM), the transfer of the pattern through the polymer by using dry etching and the formation of various nanoelements through this prepared mask. The method is applicable to any material, e.g. metal, dielectric, light/heavy doped semiconductors for the formation of nanometre objects.

Keywords: PACS; 73.20.Mf; 71.35.CcScanning near-field optical microscopy; Nanolithography

Growth of patterned thin metal oxide films on glass substrates from metallic bulk sources using a Q-switched YAG laser by N. Mir-Hosseini; M.J.J. Schmidt; L. Li (pp. 204-208).

This paper reports a novel technique of thin film deposition by using a 75W Q-switched Nd:YAG laser from bulk metal powder under atmospheric conditions. The laser radiation is transmitted through the substrate, before irradiation of the metallic target. The substrate and the target are in proximity contact, resulting in fast and efficient deposition. This process is faster and cheaper compared to the traditional methods for generating patterned oxide films on substrates. An initial relationship between the laser processing parameters and deposition showed an optimal operating region. SEM, XPS and RBS were used to characterise the materials. A thin SnO₂ film of 100–200nm thickness was identified in the coatings. Tin, copper and stainless steel powders were also examined and the deposition process was found to be feasible for all three.

Keywords: PACS; 81.15.F; 79.20.DNd:YAG laser; Laser deposition; PLD; Deposition on glass; Thin film deposition; Tin oxide; Laser ablation; RBS; XPS

Formation of colloidal GaAs and CdS quantum dots by laser ablation in liquid media by A.A. Lalayan (pp. 209-212).

In this work colloidal quantum dots (QDs) of GaAs and CdS semiconductors have been formed by laser ablation in the liquid media. The pulsed passive mode-locked Nd:YAG laser at 1064nm wavelength with pulse duration τ_imp=33ps and energy 30mJ was used. The luminescence of the colloidal QDs was excited by irradiation at 355nm, the third harmonic of the Nd:YAG laser. The optical absorption and the photoluminescence spectra of the GaAs and CdS colloidal QDs have been investigated. The large blue shift of the photoluminescence, connected to size effects, was evaluated. The location of the maximum of luminescence spectra at the wavelengths 405nm (CdS) and 420nm (GaAs) give calculated sizes of QDs of 2–3nm.

Keywords: PACS; 73.21.La; 71.20.Nr; 42.62.FiLaser ablation; GaAs; CdS; Colloidal quantum dots; Luminescence

Femtosecond laser micro-structuring of alumina ceramic by W. Perrie; A. Rushton; M. Gill; P. Fox; W. O’Neill (pp. 213-217).

Al₂O₃ ceramic has been micro-structured in air using 180fs, λ=775nm optical pulses in a fluence range 1.4< F<21Jcm⁻² with observed ablation rates of 25< V<900μm³/pulse. The threshold fluence was F_th=1.1Jcm⁻² at this ultrashort pulse-length in the NIR. Melting could be minimised using ultrafast optical pulses, improving the edge quality. By optimising the processing parameters, the residual surface roughness could be reduced below the pristine surface R_a=0.8μm. The debris produced consists mainly of single crystal nanoparticles of alumina with diameters from 20nm to 1μm with an average diameter of 300nm.

Keywords: PACS; 79.20.D; 42.62.CFemtosecond laser ablation; Micro-machining; Alumina; Re-deposition

A support of restoration intervention of the bust of St. Gregory the Armenian: Compositional investigations by laser induced breakdown spectroscopy by S. Acquaviva; M.L. De Giorgi; C. Marini; R. Poso (pp. 218-223).

Laser induced breakdown spectroscopy was employed in the restoration process of the bust of St. Gregory the Armenian. It was applied to carry out elemental chemical analyses of different details of the bust. The analyses showed that all the investigated pieces are covered by polluted layers, rich mainly in calcium which can be removed by laser ablation. The investigations performed on the cleaned surfaces confirm that the hair is composed essentially of silver and the stole of copper and that no foils were added during the stages of artwork realization. The interesting finding is that the decorative coating of the stole was realized in gold, instead of the supposed brass.

Keywords: PACS; 79.20.Ds; 42.62.−b; 52.50.Jm; 81.65.CfLaser applications; Laser induced breakdown spectroscopy; Metal work conservation; Surface cleaning

Photo-excited desorption of multi-component systems: Application to chalcogenide glasses by C. Mihesan; S. Gurlui; M. Ziskind; B. Chazallon; G. Martinelli; H. Zeghlache; M. Guignard; V. Nazabal; F. Smektala; C. Focsa (pp. 224-230).

This work presents a laser desorption study of Ga₅Ge₂₀Sb₁₀S₆₅ chalcogenide glasses. The desorption products have been analyzed by UV multi-photon ionization and time-of-flight mass spectrometry. Desorption mechanisms and plume dynamics have been investigated by studying the desorption products velocity distribution profiles in the frame of a Knudsen layer model. A peculiar behavior (broadening of the mass spectral lines) of the Ga component was found at high desorption–ionization delays and a tentative explanation has been proposed, based on the very different thermal properties of the sample constituents.

Keywords: PACS; 77.84.Bw; 68.43.Tj; 82.80.RtChalcogenide; Laser desorption; Multi-component systems

Laser-induced modification of glass–ceramics microstructure and applications by V.P. Veiko; Q.K. Kieu; N.V. Nikonorov; V.Ya. Shur; A. Luches; S. Rho (pp. 231-237).

The laser-induced modifications in two kinds of glass–ceramics (GCs) with composition TiO₂–SiO₂ (Sitall ST-50) and Li₂O–SiO₂ (Fotoform) were investigated for fabricating optical elements. The laser-induced change of refractive index and surface relief constituted the first step of this task. The second stage was a chemical processing including ion exchange (Li↔Na, K, Rb, for “Fotoform�? GCs) and etching of irradiated and non-irradiated areas. As a result of the above-mentioned processes, mini- and micro-optical components based on two GCs have been fabricated: lenses and lens arrays, waveguides and other waveguiding components, diffractive gratings, etc.

Keywords: Laser amorphization; Glass ceramics; Crystallization; Local heating; Micro-optics

Formation of large water clusters by IR laser resonant desorption of ice by C. Mihesan; M. Ziskind; B. Chazallon; C. Focsa; J.L. Destombes (pp. 238-242).

Large H₃O⁺(H₂O)_n clusters, up to n≈100, were produced by IR laser resonant desorption of an ice matrix using an optical parametric oscillator (OPO) at 3.1μm. The velocity distribution has been analyzed to characterize the laser–sample interaction and the plume dynamics desorption. The velocity distribution curves of the clusters show two distinct components corresponding to a phase explosion regime followed by vaporization. We discuss the shift of these curves with mass and the formation mechanism. A distinction in the desorption process is made between small and large clusters.

Keywords: PACS; 36.40.Qv; 36.40.Mr; 68.43.TjWater; Clusters; Desorption induced by photon stimulation

Polymerization of C₆₀ fullerene thin films by UV pulsed laser irradiation by E. Alvarez-Zauco; H. Sobral; E.V. Basiuk; J.M. Saniger-Blesa; M. Villagr�n-Muniz (pp. 243-247).

Fullerene C₆₀ thin films were grown by physical vapor deposition (PVD) onto Si (100) substrates at room temperature in a vacuum chamber kept at 10⁻⁶Torr. Photopolymerization of C₆₀ was performed by irradiation with a pulsed Kr-F laser. The films obtained at a fluence of 25mJ/cm² were no longer soluble in toluene, indicating the conversion of C₆₀ into a different solid phase. IR spectra of the irradiated films exhibit several new intense modes indicating the lowering of fullerene molecule symmetry. At the same time, the characteristic modes of pristine C₆₀ had reduced intensities or disappeared, indicating the contribution of sp³-bonding. Raman spectra of the modified C₆₀ films showed the lowering of C₆₀ symmetry as well, along with the increasing disorder due to sp³ carbon atoms. The highest applied irradiation of above 30mJ/cm² resulted in the broadening of G and D-bands related to the amorphous carbon phase. The optimal experimental conditions for fullerene photopolymerization for areas larger than 1cm², reducing the undesirable formation of other carbon phases, were found.

Keywords: PACS; 82.35; 68.55Fullerene; Polymerization; Thin films; Laser

Self assembled structures on fluoro-polymers induced with laser light at 157nm by Z. Kollia; E. Sarantopoulou; A.C. Cefalas; S. Kobe; P. Argitis; K. Missiakos (pp. 248-253).

Surface morphology and self assembled nano-structures induced on fluoro-polymer poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) with laser light at 157nm were observed for the first time. At low laser fluence, the surface morphology of exposed/non-exposed areas seem to be similar under atomic force microscopy investigation suggesting limited heating, surface stressing and chemical change of the remaining substrate. In contrast, semi-regularly spaced self organized surface topology with cylindrical structures, were formed on PTFEMA at 157nm when the laser fluence exceeded 1mJ/cm². The experimental findings enable polymer surface preparation with 157nm lasers for new applications such as DNA array fabrication with improved detection efficiency.

Keywords: Self assembly; 157; nm laser; Polymer; Surface treatment; Vacuum ultraviolet

Influence of polymer molecular weight on the UV ablation of doped poly(methyl methacrylate) by E. Rebollar; G. Bounos; M. Oujja; C. Domingo; S. Georgiou; M. Castillejo (pp. 254-258).

The influence of molecular weight ( M_W) in the KrF excimer laser (248nm) ablation of doped poly(methyl methacrylate) (PMMA) is investigated by means of optical microscopy and micro-Raman spectroscopy. Upon laser irradiation of films of PMMA of three different average M_W, 2.5, 120 and 996kDa, doped with iodonaphthalene and iodophenanthrene, gas filled bubbles were created in the films at irradiation fluences above 0.1J/cm², well below the ablation threshold of the films. The size and density of bubbles depend on the fluence and on the polymer M_W, with larger bubbles being observed at higher fluences and lower M_W. The changes of intensity of the polymer Raman bands upon irradiation provide information on cleavage of the backbone and side chains of the polymer. The results provide direct support for the bulk photothermal model, according to which ejection requires that a critical number of bonds are broken.

Keywords: Poly(methyl methacrylate); Polymer molecular weight; Laser ablation; Optical microscopy; Raman spectroscopy

Pulsed laser-induced phase transformations in CdTe single crystals by E. Gatskevich; G. Ivlev; P. Přikryl; R. Černý; V. Cháb; O. Cibulka (pp. 259-263).

Kinetics of laser-induced phase transitions in CdTe has been studied by in situ (during laser processing) and ex situ (before and after laser irradiation) methods. The samples were irradiated in air by a ruby laser with pulse duration of 80ns and energy density range from 0.02 to 0.5J/cm². Time-resolved reflectivity measurements were carried out at the wavelengths of λ₁=1064nm and λ₂=532nm. The time evolution of reflectivity for probing beams with photon energies below ( λ₁) and above ( λ₂) than the semiconductor energy gap was analyzed. The reflectivity value of CdTe at λ=694nm was measured versus irradiation energy density. The reflectivity was 0.28 at room temperature and 0.36 in the liquid phase. The changes in the surface morphology were studied by optical and atomic force microscopy for different energy densities of the laser irradiation.

Keywords: PACS; 61.72.C; 61.80.B; 78.55.EtA; _II; B; _VI; semiconductors; CdTe; Laser irradiation; Phase transformations; Reflectivity

Nd:YAG laser double wavelength ablation of pollution encrustation on marble and bonding glues on duplicated painting canvas by Sergei Batishche; Apostolis Englezis; Tatiana Gorovets; Andrei Kouzmouk; Uladzimir Pilipenka; Paraskevi Pouli; Hennady Tatur; Garyfallia Totou; Viktar Ukhau (pp. 264-269).

In the present study, a newly developed one-beam IR–UV laser cleaning system is presented. This system may be used for different applications in diverse fields, such as outdoors stonework conservation and canvas paintings restoration. The simultaneous use of the fundamental radiation of a Q-switched Nd:YAG laser at 1064nm and its third harmonic at 355nm was found appropriate to clean pollution crusts, while ensuring that no discoloration (“yellowing�?) would occur. The optimum ratio of UV to IR wavelengths in the final cleaning beam was investigated. In parallel, the same system was tested in diverse applications, such as the removal of bonding glues from duplicated canvases. The optimum laser parameters were investigated both on technical samples as well as on original paintings.

Keywords: PACS; 79.20.D; 42.62.−b; 52.75.Rx; 81.65.CfLaser cleaning; IR–UV combination; Marble; Pollution crust; Canvas; Glue

Excimer pulsed laser deposition and annealing of YSZ nanometric films on Si substrates by A.P. Caricato; G. Barucca; A. Di Cristoforo; G. Leggieri; A. Luches; G. Majni; M. Martino; P. Mengucci (pp. 270-275).

We report experimental results obtained for electrical and structural characteristics of yttria-stabilised zirconia (YSZ) thin films deposited by pulsed laser deposition (PLD) on Si substrates at room temperature. Some samples were submitted to thermal treatments in different ambient atmospheres (vacuum, N₂ and O₂) at a moderate temperature. The effects of thermal treatments on the film electrical properties were studied by C– V and I– V measurements. Structural characteristics were obtained by X-ray diffraction (XRD), X-ray reflectivity (XRR) and transmission electron microscopy (TEM) analyses. The as-deposited film was amorphous with an in-depth non-uniform density. The annealed films became polycrystalline with a more uniform density. The sample annealed in O₂ was uniform over all the thickness. Electrical characterisation showed large hysteresis, high leakage current and positive charges trapped in the oxide in the as-deposited film. Post-deposition annealing, especially in O₂ atmosphere, improved considerably the electrical properties of the films.

Keywords: Yttria-stabilised zirconia; Annealing treatments; Pulsed laser deposition; Electron microscopy; Grazing incidence X-ray diffraction; X-ray reflectivity

Double-pulse irradiation by laser-induced plasma-assisted ablation (LIPAA) and mechanisms study by Y. Hanada; K. Sugioka; I. Miyamoto; K. Midorikawa (pp. 276-280).

Double-pulse irradiation using a near-IR femtosecond laser ( λ=775nm) was used to study the mechanism of the laser-induced plasma-assisted ablation (LIPAA) process. The dependence of the ablation depth on the delay time between the first and the second pulse for various target-to-substrate distances was investigated. The first pulse generates the laser-induced plasma from the metal target, but does not induce ablation of the glass substrate. The second pulse induces the high-efficiency ablation of the substrate, delayed by several nanoseconds (ns). A possible mechanism of the conventional LIPAA process using a ns pulsed laser is discussed based on the obtained results.

Keywords: PACS; 52.50.J; 79.20.D; 06.60.JLaser-induced plasma-assisted ablation (LIPAA); Femtosecond laser; Double-pulse irradiation

Shadowgraphy of pulsed CO₂ laser ablation of polymers by W.O. Siew; T.Y. Tou; K.H. Wong (pp. 281-285).

Heavy plume expansions in air, helium and argon produced by pulsed CO₂ laser ablations of poly(methyl methacrylate) (PMMA) and polyimide (PI) were imaged by shadowgraphy. The PMMA was melted at 1–2mm depth beneath the surface followed by an outward expulsion of heavy plumes. A shock front was formed which detached from the first plume after several microseconds. A second, mushroom-shaped plume and a narrow ejection were also observed. In contrast, the mushroom-shaped plume structure was absent in PI ablation, but it was in the form of a single blob, which collapsed back to the target.

Keywords: PACS; 42.30.Va; 47.40.Dc; 07.68+mPolymer ablation; Molten front; Shock front; Plume collapse

Transfer of stoichiometry during pulsed laser ablation of multicomponent magnetic targets by S. Acquaviva; E. D’Anna; M.L. De Giorgi; M. Fernandez; A. Luches; G. Majni; S. Luby; E. Majkova (pp. 286-290).

Multicomponent magnetic alloy targets were ablated in vacuum with a XeCl excimer laser at three different fluences. The ablated material was collected onto unheated silicon substrates placed at different angles with respect to the target normal at the incident laser spot. Film composition was inferred by Rutherford backscattering spectrometry analyses. Experimental results reveal that the lighter element concentration is larger in films deposited at higher collecting angle. The observed effect is more evident at lower laser fluences. The dependence of composition variations on the collecting angle in the studied multielemental films are attributed to scattering effects among the ablated species in the plume.

Keywords: PACS; 79.20.D; 61.50.N; 75.50.KPulsed laser ablation; Stoichiometry; Amorphous magnetic films

Microstructural modification of LiNbO₃ crystals induced by femtosecond laser irradiation by P. Galinetto; D. Ballarini; D. Grando; G. Samoggia (pp. 291-294).

Microstructural modifications were induced by femtosecond laser irradiation on lithium niobate (LN) crystals and investigated by means of optical microscopy and micro-Raman spectroscopy. Commercial z-cut congruent LN substrates were irradiated with focused ultra-short laser pulses at 810nm, generated by a Ti:Sapphire oscillator or an amplified Ti:Sapphire laser system.At the focus region, either refractive index changes or material removal were observed by varying the irradiation conditions. The Raman spectrum shows in the illuminated regions the insurgence of Raman modes, which are forbidden in the used-scattering geometry. This phenomenon increases gradually by approaching the ablation region, where niobium oxides and Li-deficient surfaces are formed for the low energy and high repetition rate pulses from the Ti:Sapphire oscillator. Amorphous surfaces are obtained for high energy and low repetition rate pulses from the amplified Ti:Sapphire laser system.

Keywords: PACS; 79.20.Ds; 78.30.−J; 78.47.+pFemtosecond laser; Ablation; Raman spectroscopy; Lithium niobate

Characterisation of ultrashort pulse laser ablation of SmBaCuO by L. D’Alessio; A. De Bonis; A. Galasso; A. Morone; A. Santagata; R. Teghil; P. Villani; M. Zaccagnino (pp. 295-298).

The gaseous phase obtained by ablating a superconducting SmBa₂Cu₃O7−_x target with a Nd:glass laser ( λ=529nm, τ=250fs) has been characterised by optical emission spectroscopy, quadrupole mass spectrometry and ICCD imaging, to analyse the plume composition, energy and morphology. The results obtained show that femtosecond ablation creates plumes with different shapes and velocities as compared to nanosecond ablation. The plume angular distribution has a high cosine exponent and the optical emission spectroscopy evidences a low ionisation degree, coupled with a high kinetic energy of the particles. Films have been deposited by the ablation process and analysed by the conventional techniques used for solid state characterisation.

Keywords: PACS; 79.20.D; 81.15.F; 52.70; 74.76Laser ablation; Plasma; Thin film deposition; Superconductors

Ultra-fast laser ablation applied to deep-drilling of metals by S. Bruneau; J. Hermann; G. Dumitru; M. Sentis; E. Axente (pp. 299-303).

Mechanisms of ultra-fast laser ablation during deep-drilling of metals was studied using plasma diagnostics and morphological analyses of the laser-induced craters. Fast imaging and time- and space-resolved optical emission spectroscopy were employed to characterize the ablation plume. After irradiation, the crater morphology was analyzed by scanning electron microscopy and optical microscopy. From the correlation between the ablation plume characteristics and the shape of the laser-produced craters, it is shown that the nanoparticles have an important influence on the accuracy of micromachining by ultra-short laser pulses.

Keywords: PACS; 52.38.Mf; 61.82.Bg; 42.65.ReFemtosecond laser ablation; Micromachining; Laser-induced plasma

Ultrashort pulsed laser vaporisation of icosahedral Al–Pd–Mn by R. Teghil; L. D’Alessio; A. De Bonis; A. Galasso; P. Villani; M. Zaccagnino; A. Santagata; D.J. Sordelet (pp. 304-308).

In this work, Al₇₀Pd₂₀Mn₁₀ quasicrystalline targets were evaporated by a doubled Nd:glass laser with a pulse duration of 250fs. The produced plasma has been analysed by time of flight mass spectrometry, optical emission spectroscopy and fast imaging. The results indicate that the plume is more complex as compared to other quasicrystalline systems with the presence of quite large clusters and with a higher ionisation degree. The analyses on the deposited films indicate that the vaporisation is not congruent.

Keywords: PACS; 79.20.DS; 81.15.FG; 61.44.BRLaser ablation; Laser deposition; Quasicrystals

Interaction of a femtosecond laser-produced plasma plume with a time delayed pulse by D. Scuderi; D. Moreau; O. Albert; P.P. Pronko; J. Etchepare (pp. 309-312).

The use of a sequence of two ultra short light pulses enabled us to produce ions, neutrals and nanoparticles from a Ti metallic target and successively irradiate them. Efficient formation of nanoparticles was observed as well as their subsequent fragmentation into neutral atoms. The size distribution of the nanoparticles obeys a log–normal law, characterized by a statistical median diameter size of 70nm. Measurements of their spectral emission provides information regarding their temperature.

Keywords: PACS; 52.40; 52.50Femtosecond laser ablation; Aggregates; Blackbody emission

Nonlinear absorption mechanism in ablation of transparent materials by high power and ultrashort laser pulses by Peter G. Eliseev; Oleg N. Krokhin; Irina N. Zavestovskaya (pp. 313-315).

The processes of nonlinear absorption are considered in transparent materials like nitride semiconductor, sapphire and other dielectrics under ultrashort (femtosecond (fs)-range) laser pulses irradiation. The ablation threshold is in the multi-TW/cm² range. The power consumption under the ablation process is described in terms of tunneling absorption. The ablation threshold increases as about the third power of the energy bandgap of the material, in close agreement with the experimental data.

Keywords: PACS; 42.65−k; 78.20Tunneling absorption; Laser ablation; Femtosecond laser pulses

Tailoring of multilayer interfaces by pulsed laser irradiation by S. Luby; E. Majkova (pp. 316-322).

Multilayers (MLs) consisting of a few nm thick alternating layers of two different materials are broadly used in soft X-ray optics and in giant magnetoresistance (GMR) sensors. The efficiency of ML-based devices depends on the quality and thermal stability of the interfaces, which must be sharp at the nm scale. It is shown that, using heating with excimer laser pulses of 30ns and fluence of approximately 0.1Jcm⁻², the diffusion length for one laser pulse in the above mentioned MLs is in the region of nanometers, i.e. it closely matches the thickness of the ML sublayers. Therefore, pulsed laser induced diffusion can be used for controlled manipulation and tailoring of ML interface properties. Depending on the miscibility or immiscibility of the ML material combinations, the interfaces could be intermixed or even sharpened, which is attributed to the backdiffusion process. These phenomena are demonstrated for various combinations of ML building layers, like W/Si, Co/Ag, Fe/W and Co/W. The experimental samples were analyzed by X-ray reflectivity and X-ray diffuse scattering, combined with TEM.

Keywords: PACS; 61.10.Kw ;78.70.−gMultilayers; Pulsed laser irradiation; Interfaces; Intermixing; Backdiffusion

Broadening and attenuation of UV laser ablation plumes in background gases by Salvatore Amoruso; Bo Toftmann; J�rgen Schou (pp. 323-328).

The expansion of a laser-induced silver plume in a background gas has been studied in a variety of gases ranging from helium, oxygen and argon to xenon. We have measured the angular distribution of the total deposit of silver on an array of quartz crystal microbalances as well as the time-of-flight distribution with a Langmuir probe. The angular distribution broadens for all gases except for a minor pressure range for the helium background gas, in which a distinct plume narrowing occurs. The behavior of the collected, ablated silver atoms integrated over the full hemisphere is similar for all gases. This integral decreases strongly above a characteristic pressure, which depends on the specific gas. The ion time-of-flight signal shows a clear plume splitting into a fast and a slow component except for the ablation plume in a helium gas.

Keywords: Laser ablation; Plume expansion; Background gases

Structural and electrical characterization of PLZT 22/20/80 relaxor films obtained by PLD and RF–PLD by F. Craciun; M. Dinescu; P. Verardi; N. Scarisoreanu; A. Moldovan; A. Purice; C. Galassi (pp. 329-333).

Thin films of Pb_0.67La_0.22(Zr_0.2Ti_0.8)O₃ (PLZT 22/20/80) have been grown by pulsed laser deposition (PLD) and by PLD assisted by radiofrequency (RF) discharge in oxygen. All obtained films were polycrystalline, with perovskite cubic structure, but significant differences have been found in their phase content and surface morphology, as evidenced by XRD and AFM investigations. Films grown by RF-assisted PLD are (100)-oriented and have less amorphous phase, about two times larger grains and a more compact structure. Other significant differences have been found in the measured dielectric nonlinearities from the capacitance, loss and quasi-static field methods. These nonlinearities were connected with the movements of domain walls and/or domain switching, depending on field amplitude. Films obtained by RF–PLD show lower variation of dielectric properties with ac signal amplitude. This variation is about 1.2 times lower for RF–PLD films compared to PLD films. A high value of capacitance tunability (about 10% at a bias field of 80kV/cm and ac signal frequency 20MHz) was obtained for both films type, though, RF–PLD-deposited films have much lower dielectric loss, 2.5% instead of 4% at 1kHz.

Keywords: PACS; 77.84.Dy; 77.84.−s; 81.15.FgRelaxor; PLZT; Films; PLD; Dielectric properties

Pulsed laser deposition of nano-glassy carbon films by P.M. Ossi; C.E. Bottani; A. Miotello (pp. 334-339).

Carbon films have been deposited at room temperature on (100) Si substrates by pulsed laser ablation (PLA) from a highly oriented pyrolitic graphite source. Changing the laser power density from 8.5 to 19MWmm⁻² and using various ambient atmospheres (helium, argon from 0.6Pa to 2kPa), nano-sized cluster-assembled films were obtained. Scanning electron microscopy shows that the film morphology, changes with increasing ambient gas pressure. We observed in the sequence: dense columns, node-like morphology, platelets (only in argon) and an open dendritic structure. By atomic force microscopy, on representative films, we evaluated the size distribution and relative abundancy of aggregates of carbon clusters, as well as film roughness. Raman spectroscopy shows that all the films are sp² coordinated, structurally disordered and belong to the family of carbon nano-glasses. The estimated film coherence length gives an average size of about 5nm for the agglomerated carbon clusters in the films. The average number of carbon atoms per cluster depends on ambient gas pressure, but is nearly independent of laser intensity.

Keywords: PACS; 68.55.−a; 61.46.+w; 63.50.+x; 81.05.Uw; 81.15 FgCarbon; Clusters; Raman scattering; Pulsed laser deposition

Diamond-like carbon formation for various positions by pulsed laser deposition by Seong-Shan Yap; Teck-Yong Tou (pp. 340-343).

Pulsed laser ablation of pyrolytic graphite target was carried out by an Nd-YAG laser with λ=1064nm and fluence in the range of 1–10J/cm². The plume was produced by focusing the laser beam and rastering over a 6.5mm×6.5mm area on the graphite target. The substrates were placed at two positions: on-axis position facing the target and off-axis position in the target plane with 2mm offset from the ablation site. Diamond-like carbon was formed on the substrates at both positions and on the ablated area as detected by Raman spectroscopy. Rough and granular surface was observed for the samples placed in the target plane and smooth diamond-like carbon films for the samples placed facing the target as observed by SEM and optical microscopy.

Keywords: PACS; 79.20.D; 81.15.F; 68.55.2a; 81.05.TpDiamond-like carbon; Pulsed laser deposition; Off-axis geometry; On-axis geometry

Calcium phosphate thin films synthesized by pulsed laser deposition: Physico-chemical characterization and in vitro cell response by I.N. Mihailescu; P. Torricelli; A. Bigi; I. Mayer; M. Iliescu; J. Werckmann; G. Socol; F. Miroiu; F. Cuisinier; R. Elkaim; G. Hildebrand (pp. 344-348).

We review the progress made by us using pulsed laser deposition (PLD) of two bioactive calcium phosphates: octacalcium phosphate (OCP) and Mn doped carbonated hydroxyapatite (Mn-CHA). Coatings of these materials well suited for biomimetic medical prostheses and pivots were synthesized on titanium substrates with a pulsed KrF* UV laser source.The best deposition conditions for Mn-CHA thin films were 13Pa O₂, 400�C with post heat treatment of 6h in air enriched with water vapours. The coatings are stoichiometric and crystalline. For OCP, deposition at 150�C in 50Pa water vapor atmosphere, post treated by 6h annealing in hot flux of water vapours, resulted in stoichiometric, but poorly-crystallized films.Degradation tests show different behavior for the OCP and Mn-CHA coatings. In vitro cell growth shows excellent adherence and biocompatibility of osteoblasts and fibroblasts in both OCP and Mn-CHA coatings. Human osteoblasts display normal proliferation and viability, and good differentiation behaviour.

Keywords: PACS; 81.15.Fg; 87.68.+z; 87.17.−dPulsed laser deposition; Biomimetic; Coatings; Calcium phosphate; Octacalcium phosphate; Carbonated manganese-doped hydroxyapatite

Nanocrystalline Sm–Fe composites fabricated by pulse laser deposition at 157nm by S. Kobe; K. Žužek; E. Sarantopoulou; Z. Samardžija; Z. Kollia; A.C. Cefalas (pp. 349-354).

Sm–Fe thin films were deposited on a Si wafer coated with a ∼100nm thick layer of Ta by ablating a solid Sm–Fe target. The Sm–Fe target was ablated using a molecular fluorine laser with λ=157nm at low laser energy of ∼25mJ/pulse. The thickness of the deposited amorphous film (in vacuum) was ∼20nm and the dimensions of the nanocrystals deposited on the Si–Ta substrate (in He atmosphere) varied between 20 and 500nm. Using the low energy laser for growing Sm–Fe nanocrystals by pulse laser deposition (PLD) results in a composition, which remains the same as the composition of the initial target. The morphology and the type of the films depended on the depositing experimental conditions.

Keywords: 157; nm; Rare-earth magnets; Thin films; Pulse laser deposition; Morphology; Nanocrystalline

Pulsed laser deposition of hydroxylapatite thin films on biomorphic silicon carbide ceramics by J.P. Borrajo; J. Serra; S. Liste; P. Gonz�lez; S. Chiussi; B. Le�n; M. P�rez-Amor (pp. 355-359).

Hydroxylapatite (HA) coatings were produced by pulsed laser deposition (PLD) on biomorphic silicon carbide ceramics (Bio-SiC) by ablation of non-sintered HA discs with an ArF excimer laser (193nm, 25ns, 4.2Jcm⁻²) at different conditions of water vapour pressure and substrate temperature. The characterization of the coatings performed by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) techniques showed changes of the crystallinity of the coatings and the substitution of phosphate by carbonate groups in the HA structure, induced by the variations of the pressure and the substrate temperature.

Keywords: PACS; 81.15.Fg; 78.30.HvHydroxylapatite; Pulsed laser deposition; Laser ablation; Biomorphic silicon carbide

Plasma assisted pulsed laser deposition of hydroxylapatite thin films by E.L. Solla; J.P. Borrajo; P. Gonz�lez; J. Serra; S. Liste; S. Chiussi; B. Le�n; M. P�rez-Amor (pp. 360-364).

Thin films of hydroxylapatite (HA) were deposited on Si substrates by pulsed laser deposition (PLD), combined with radio frequency (RF) plasma, in different gas atmospheres. Physicochemical properties of HA films were studied using Fourier transform infrared spectroscopy (FTIR) and energy dispersive spectroscopy (EDS). The structure of these coatings was determined by X-ray diffraction (XRD). It has been observed that the gas atmosphere has an important role on the material properties. The FTIR spectra analysis revealed that the incorporation of a water vapour atmosphere during the PLD process is necessary to obtain crystalline coatings. The incorporation of the RF plasma in the PLD process causes a significant increase of the film growth rate, and a slight improvement of the crystallinity of the films.

Keywords: PACS; 52.38.Mf; 33.20.Ea; 33.20.Rm; 52.80.Pi; 81.15.FgPulsed laser deposition; Radio frequency plasma; Hydroxylapatite; Biomaterials; Bioactive coatings

Poly-crystallized hydroxyapatite coating deposited by pulsed laser deposition method at room temperature by Masahito Katto; Kou Kurosawa; Atushi Yokotani; Shoichi Kubodera; Akihiro Kameyama; Takeshi Higashiguchi; Takeyoshi Nakayama; Masahiro Tsukamoto (pp. 365-368).

We have deposited hydroxyapatite (HAp) films on Ti substrate by pulsed laser deposition using KrF excimer laser. We used HAp targets sintered at temperatures of 500, 700, 900 and 1100°C with densities between 1.5 and 2.4mg/mm³. SEM images of the coating surface revealed that the deposited films had spherical structures with diameter of 5μm. X-ray diffractometry (XRD) analysis showed that the deposited films contained amorphous HAp. Films deposited with a target sintered at 900°C showed that poly-crystallized HAp coating was achieved at room temperature.

Keywords: PACS; 42.62.Be; 81.15.FgHydroxyapatite; Pulsed laser deposition; Poly-crystals

Pulsed laser deposition of bioactive glass films in ammonia and disilane atmospheres by J.P. Borrajo; P. Gonz�lez; S. Liste; J. Serra; S. Chiussi; B. Le�n; M. P�rez-Amor (pp. 369-375).

The effect of two reactive gases on the properties of bioactive glass thin films produced by pulsed laser deposition (PLD) was studied. The ablation of a bioactive silica-based glass was carried out by an ArF excimer laser ( λ=193nm, Φ=4.2Jcm⁻², τ=25ns, f=10Hz) at various pressures of Si₂H₆/Ar and NH₃/Ar reactive mixtures. The bonding configuration and chemical environment of the resulting coatings were followed by Fourier transform infrared spectroscopy (FT-IR). The composition and bond arrangement of bioactive glass films were tuned by varying the chamber atmosphere. The results show how to adjust film characteristics for osteointegration of implants.

Keywords: PACS; 81.15.Fg; 78.30HvBioactive glass; Pulsed laser deposition; FT-IR; Ammonia; Disilane

Rare-earth doped chalcogenide thin films fabricated by pulsed laser deposition by P.K. Dwivedi; Y.W. Sun; Y.Y. Tsui; D. Tonchev; M. Munzar; K. Koughia; C.J. Haugen; R.G. DeCorby; J.N. McMullin; S.O. Kasap (pp. 376-380).

Erbium doped Ge–Ga–Se thin films were fabricated by the pulsed laser deposition (PLD) technique in vacuum using a KrF pulse laser with λ=248nm, and a pulse duration of 15ns. The films were fabricated at room temperature onto glass substrates. The morphological, optical and thermal properties of the films showed good optical and thermal stability. The mechanical properties including film adhesion are relatively poor for thicker films and the microstructure reveals the presence of droplets. Annealing in vacuum improved the film adhesion and substantially enhanced the efficiency of photoluminescence.

Keywords: PACS; 52.70K; 78.20C; 78.66J; 81.15FAmorphous chalcogenide; Thin film; Laser ablation; Pulsed laser deposition; Photoluminescence

Glass and glass ceramic materials obtained by pulsed laser deposition in the BaO–TiO₂–B₂O₃ system by L. Boroica; R. Medianu; M. Dinescu; I. Boroica (pp. 381-387).

We obtained glasses by using the classical method of melting in an electric furnace at 1100–1450°C for 2h. The obtained samples were characterized by differential thermal analyses and X-ray diffraction. By controlled thermal treatments the samples were crystallized. BaTiO₃ and other barium polititanates were identified. The thin layers were obtained by pulsed laser deposition and magnetron sputtering deposition. By controlled thermal treatments the glasses were transformed to partial and full crystalline materials. Atomic Force Microscopy and Electron Microscopy were used to characterize the materials.

Keywords: Glass; Glass ceramics; Titanates; Pulsed laser deposition; Magnetron-sputtering deposition

Pulsed laser deposition of tin-doped indium oxide (ITO) on polycarbonate by T.K. Yong; T.Y. Tou; B.S. Teo (pp. 388-391).

Indium tin oxide (ITO) films were deposited on polycarbonate (PC) substrates in oxygen at room temperature by pulsed laser deposition (PLD) using a Nd:YAG laser with 355 and 532nm wavelengths. The ITO films were analyzed by the four-point probe technique, atomic force microscopy (AFM) and UV–visible–Near IR spectrophotometry for electrical conductivity, surface morphological and optical transmission properties, respectively. The main plume species were identified by using a fiber optic spectrometer, which showed that the emission intensity produced by the 355nm laser wavelength was considerably stronger than that produced by the 532nm laser wavelength. The ITO film resistivity was an order of magnitude higher than that achieved by a KrF excimer laser, but comparable to ITO-coated substrates prepared by the sputtering method.

Keywords: PACS; 52.75.Rx; 79.20.D; 81.15.Fg; 85.40.SzPulsed laser deposition; Indium tin oxide; Polycarbonate; Nd:YAG laser

Dense and porous ZnO thin films produced by pulsed laser deposition by Y.W. Sun; J. Gospodyn; P. Kursa; J. Sit; R.G. DeCorby; Y.Y. Tsui (pp. 392-396).

Dense and porous zinc oxide (ZnO) thin films were deposited onto silicon substrates in vacuum and in 100mTorr O₂ at room temperature by pulsed laser deposition using 15ns krypton fluoride (KrF), λ=248nm, laser pulses with laser fluence of 3Jcm⁻². The structural, morphological, optical and photoluminescence properties of the as-grown and annealed ZnO thin films were studied. O₂ background gas during deposition and post-annealing treatment were essential to obtain a crystalline structure and strong ultraviolet (UV) luminescence emissions.

Keywords: PACS; 81.15Fg; 81.05Dz; 61.10−I; 78.40Fy; 78.55Mb; 78.55−m; 78.20CiZnO; Pulsed laser deposition; Thin film; Porous film; Photoluminescence; Optical constant

Pulsed laser deposition of Mg thin films on Cu substrates for photocathode applications by L. Cultrera; A. Pereira; C. Ristoscu; A. Clozza; F. Tazzioli; C. Vicario (pp. 397-401).

In this study, pulsed laser ablation of pure Mg targets (99.99%) using an XeCl excimer laser ( λ=308nm, τ=30ns) was used to grow Mg coatings on Cu substrates. A thin layer of Mg (100–200nm) was deposited in UHV of 5×10⁻⁶Pa to ensure high purity. A second ultra-thin layer of MgO of 10–20nm was deposited in oxygen at 10⁻²Pa pressure to protect the previous layer from atmospheric contamination.Measurements for determining the electron yield of the deposited samples under UV irradiation were performed on a diode structure in another UHV apparatus evacuated to 10⁻⁶Pa.

Keywords: Laser deposition; Photocathode applications; Mg thin films

Absorption and photoconductivity properties of ZnTe thin films formed by pulsed-laser deposition on glass by A. Erlacher; M. Ambrico; G. Perna; L. Schiavulli; T. Ligonzo; H. Jaeger; B. Ullrich (pp. 402-405).

Pulsed-laser deposition (PLD) of ZnTe was performed at λ_pld=1064nm and λ_pld=532nm employing nanosecond pulses of a Nd:YAG laser. Thin ZnTe films (thickness ≈2μm) were deposited at room temperature on fused silica glass substrates. X-ray diffraction revealed the influence of the ablation wavelengths on the deposited film texture. The film formed at λ_pld=532nm is amorphous, whereas the one ablated at λ_pld=1064nm was amorphous but contained zincblende and wurtzite crystallites as well. The samples exhibited a broad photocurrent response extending into the visible and infrared part of the spectrum to almost 1eV. The absorption coefficients, which were measured with standard constant photocurrent method (s-CPM), showed that the bandgap of the films is considerably shifted to lower energies of 1.0eV as compared to the crystalline source material of 2.26eV.

Keywords: Pulsed-laser deposition; X-ray diffraction; ZnTe thin films; Amorphous semiconductors

Structural and compositional analysis of transition-metal-doped ZnO and GaN PLD thin films by L.S. Dorneles; D. O’Mahony; C.B. Fitzgerald; F. McGee; M. Venkatesan; I. Stanca; J.G. Lunney; J.M.D. Coey (pp. 406-410).

We have studied the structural and magnetic properties of thin films of ZnO and GaN semiconductors doped with magnetic and non-magnetic transition-metals. The films were prepared on sapphire substrates by pulsed laser deposition from doped ceramic targets. Room temperature ferromagnetism was observed in ZnO (doped with Sc, Ti, V, Fe, Co or Ni) and in Mn-doped GaN films. In both cases, single crystal epitaxial growth was observed. The higher dopant:Zn ratio observed in the films is attributed to the preferential sputtering of Zn by energetic ions in the laser ablation plasma plume.

Keywords: Pulsed laser deposition; Ferromagnetic semiconductor; Sputtering

Structural and optical characterization of AlN films grown by pulsed laser deposition by C. Ristoscu; C. Ducu; G. Socol; F. Craciunoiu; I.N. Mihailescu (pp. 411-415).

AlN thin films were prepared on p-type Si(100) substrates heated at 800°C by pulsed laser ablation of AlN targets using an UV KrF* ( λ=248nm, τ_FWHM≤10ns) excimer laser. We report herewith new results in depositing AlN films from AlN targets and their characterization by X-ray diffraction (XRD), along with Fourier transform infrared (FTIR) investigations in reflection and spectroscopic ellipsometry data. The X-ray investigations confirm the formation of polycrystalline AlN films. We observed the complete absence of the Al line in the XRD spectra. The gradual decomposition of the AlN target in the zones beneath and around the crater, induced by nanosecond multipulse laser irradiation, was compensated by a low-pressure N₂ flux (0.1–10Pa) during deposition. The reflection IR spectra display features characteristic to LO phonons in AlN. Ellipsometric measurements evidenced a refractive index of 2.00 and an extinction coefficient of 0.0001 for AlN films with a thickness of about 100nm.

Keywords: PACS; 81.05.Ea; 81.15.Fg; 61.10.NzAlN; PLD; FTIR in reflection; Ellipsometry

Processing of mussel-adhesive protein analog copolymer thin films by matrix-assisted pulsed laser evaporation by T. Patz; R. Cristescu; R. Narayan; N. Menegazzo; B. Mizaikoff; P.B. Messersmith; I. Stamatin; I.N. Mihailescu; D.B. Chrisey (pp. 416-421).

We have demonstrated the successful thin film growth of a mussel-adhesive protein analog, DOPA-modified PEO–PPO–PEO block copolymer PF127, using matrix-assisted pulsed laser evaporation (MAPLE). The MAPLE-deposited thin films were examined using Fourier transform infrared spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and contact-angle measurements. We have found that the main functional groups of the mussel-adhesive protein analog are present in the transferred film. These adhesive materials have several potential electronic, medical, and marine applications.

Keywords: PACS; 81.15.FgMussel-adhesive protein; Matrix-assisted pulsed laser evaporation

Laser deposition of fibrinogen blood proteins thin films by matrix assisted pulsed laser evaporation by L. Stamatin; R. Cristescu; G. Socol; A. Moldovan; D. Mihaiescu; I. Stamatin; I.N. Mihailescu; D.B. Chrisey (pp. 422-427).

We report the first successful deposition of fibrinogen blood protein thin films by matrix assisted pulsed laser evaporation using a KrF^* excimer laser. We have demonstrate by Fourier transform infrared spectroscopy (FTIR) that our thin films are composed of fibrinogen and fibrin maintaining their chemical structures. FTIR spectra, atomic force microscopy (AFM) micrographs and fibrinogen concentration depend on the laser fluence. The best results for fibrinogen deposition were obtained using lower fluences.

Keywords: PACS; 87.14.Ee; 81.15.Fg; 81.15.AaFibrinogen; Matrix assisted pulsed laser evaporation

Deposition of ITO films on SiO₂ substrates by Fernande Fotsa Ngaffo; Anna Paola Caricato; Andrea Fazzi; Manuel Fernandez; Sandro Lattante; Maurizio Martino; Francesco Romano (pp. 428-432).

Pulsed ablation deposition (PAD) has been used to deposit indium tin oxide (ITO) films on SiO₂ substrates at room temperature using an ArF excimer laser. High optical transmission above 88% occurred in the visible region, the refractive index (2.0 at 540nm) was observed to be very close to the one of the bulk target; the extinction coefficient was low and almost constant (6×10⁻³) through the visible range. An energy gap of about 3.6eV has been calculated for the deposited films. The film thickness profilometer (FTP) and simulations using a computer code (refractor) give approximately the same result for the film thickness (≈370nm). The electrical resistivity was as low as 4×10⁻⁶Ωm. From the atomic force microscopy (AFM) observations, the films had a rough surface with average roughness ≈20nm. Pores were observed with a density of ∼150pores/μm² and average size of 250nm. Therefore films exhibited large surface area, which suggest applications in dye solar cells (DSC).

Keywords: Laser ablation; Pulsed ablation deposition; Indium tin oxide; Refractive index; Atomic force microscopy

Channels of energy redistribution in short-pulse laser interactions with metal targets by Leonid V. Zhigilei; Dmitriy S. Ivanov (pp. 433-439).

The kinetics and channels of laser energy redistribution in a target irradiated by a short, 1ps, laser pulse is investigated in computer simulations performed with a model that combines molecular dynamics (MD) simulations with a continuum description of the laser excitation and relaxation of the conduction band electrons, based on the two-temperature model (TTM). The energy transferred from the excited electrons to the lattice splits into several parts, namely the energy of the thermal motion of the atoms, the energy of collective atomic motions associated with the relaxation of laser-induced stresses, the energy carried away from the surface region of the target by a stress wave, the energy of quasi-static anisotropic stresses, and, at laser fluences above the melting threshold, the energy transferred to the latent heat of melting and then released upon recrystallization. The presence of the non-thermal channels of energy redistribution (stress wave and quasi-static stresses), not accounted for in the conventional TTM model, can have important implications for interpretation of experimental results on the kinetics of thermal and mechanical relaxation of a target irradiated by a short laser pulse as well as on the characteristics of laser-induced phase transformations. The fraction of the non-thermal energy in the total laser energy partitioning increases with increasing laser fluence.

Keywords: PACS; 61.80.Az; 79.20.Ds; 02.70.Ns; 64.70.DvLaser interactions; Molecular dynamics; Laser energy redistribution; Laser melting; Heat transfer; Laser-induced stresses

A computer program for determination of thin films thickness and optical constants by A.P. Caricato; A. Fazzi; G. Leggieri (pp. 440-445).

A computer simulation program for processing transmission spectra of amorphous optical thin films deposited on weakly absorbing substrates and evaluation of the refractive index n, extinction coefficient k and thickness d was developed. The computer code is the implementation of an optical characterisation algorithm based on the determination of the upper and lower envelopes of the transmission spectrum interference fringes. Inhomogeneities in the thickness of the analysed films, which are responsible of a shrinking in the fringes amplitude, can be considered in the program. Relative errors in the calculated values of n, k and d have been determined using simulated transmission spectra in both cases of homogeneous and inhomogeneous films. The thickness and the refractive index of uniform films are calculated with an accuracy ≤0.5%, while the accuracy in the case including inhomogeneities is ≤2%. Simulation results for chalcogenide thin films deposited by pulsed laser deposition (PLD) on microscope slabs and glass slides are reported.

Keywords: PACS; 07.05.Tp; 78.66.Bz; 78.20.−cTransmittance; Refractive index; Extinction coefficient; Pulsed laser deposition

Modelling the influence of pore size on the response of materials to infrared lasers – An application to human enamel by A. Vila Verde; Marta M.D. Ramos (pp. 446-449).

We present an analytical model for a ceramic material (hydroxyapatite, HA) containing nanometre-scale water pores, and use it to estimate the pressure at the pore as a function of temperature at the end of a single 0.35μs laser pulse by Er:YAG (2.94μm) and CO₂ (10.6μm) lasers. Our results suggest that the pressure at the pore is directly related to pore temperature, and that very high pressures can be generated simply by the thermal expansion of liquid water. Since the temperature reached in the pores at the end of the laser pulse is a strong function of pore size for Er:YAG lasers, but is independent of pore size for CO₂ lasers, our present results provide a possible explanation for the fact that human dental enamel threshold ablation fluences vary more for Er:YAG lasers than for CO₂ lasers. This suggests that experimentalists should analyse their results accounting for factors, like age or type of tooth, that may change the pore size distribution in their samples.

Keywords: PACS; 87.50.Hj; 42.62.Be; 44.30.+v; 02.60.−xDental enamel; Laser ablation; Mesoscopic modelling of composites; Er:YAG laser; CO; ₂; laser

Quantum modelling of photo-excited processes by Marta M.D. Ramos; Helena M.G. Correia (pp. 450-454).

In the framework of quantum field theory and the dipole approximation, a self-consistent quantum molecular dynamics method is used to investigate the effect of chain length on the probability of formation or decay of both singlet and triplet excitons due to photon absorption or emission in isolated poly( p-phenylene vinylene) (PPV) chains. We found that the probability of the photo-induced intra-molecular singlet exciton formation and decay increases linearly with chain length and the probability for triplet exciton formation and decay does not depend on the chain length. Polymers with long chains have thus an advantage over small molecules in solar cell and light-emitting diode (LED) applications because their efficiency depends on the number of intra-molecular singlet excitons formed or emitted in the device, which is expected to increase with the conjugation length.

Keywords: PACS; 78.20.Bh; 78.66.QnQuantum modelling; Photo-excited processes; Solar cell; LED; Conducting polymer

Analytical and numerical calculations of the temperature distribution in Si and Ge targets irradiated by excimer lasers by J.C. Conde; P. Gonz�lez; F. Lusqui�os; S. Chiussi; J. Serra; B. Le�n (pp. 455-460).

The calculations of the temperature distribution induced by excimer lasers in silicon and germanium by using different mathematical approaches are presented. In this work, the heat conduction differential equation is solved by: (i) conventional analytical method, where the thermal parameters, i.e., thermal conductivity, specific heat and density are temperature independent; (ii) the Kirchhoff transformation method, that incorporates the dependence of the thermal conductivity with the temperature through a polynomial function; (iii) a numerical approach, by using the finite elements method (ANSYS program), which allows the incorporation of all temperature dependent parameters and the phase changes of the material using the enthalpy function.A comparison of the temperature profile versus depth obtained for semi-infinite amorphous germanium and crystalline silicon materials when irradiated with an ArF excimer laser (193nm, 20ns) is presented. The melting depth for a given energy density is also evaluated by the different mathematical methods. The validity of these results and the reliability and advantages of the numerical methods is discussed.

Keywords: PACS; 02.60.−Cb; 42.62.−b; 81.15.LmFinite elements method; Excimer lasers; Temperature distribution

Finite elements analysis of heteroepitaxial SiGe layers grown by excimer laser by J.C. Conde; P. Gonz�lez; F. Lusqui�os; S. Chiussi; J. Serra; B. Le�n (pp. 461-465).

In this work, the finite elements analysis using ANSYS^® (8.0) of the heteroepitaxial SiGe alloy formation induced by excimer lasers is presented. The numerical simulation of the temperature distribution induced by KrF excimer laser (energy densities 0.50< Φ<0.55J/cm²) on thin amorphous Ge films (10nm thick) deposited on Si〈100〉 substrates is obtained. An acceptable agreement between the numerical simulations and the experimental results is found. The melting depth is also evaluated and the laser energy density threshold for the partial melting of the Si substrate is estimated. It allows us to determine the optimum conditions to achieve high quality epitaxy. For both the cases, the temperature profile versus time on the top of the Ge film and at the Ge/Si interface are obtained.

Keywords: PACS; 02.70.–C; 42.62.–b; 68.55.–a; 81.15.LmEpitaxial growth; Finite elements method; Pulsed laser induced epitaxy (PLIE)

Particles interaction with obstacles in a pulsed laser deposition system by A. Marcu; C. Grigoriu; K. Yatsui (pp. 466-469).

A new and simplified three-dimensional laser ablation plume model is proposed for simulating particles-obstacles interaction for non-standard pulsed laser deposition (PLD) systems such as the “shadow mask�?, also known as the“eclipse method�?, and plasma reflection (PLD/PR). The model is based on the direct Monte-Carlo method and a 3D finite-elements mesh. During deposition, for a significant fraction of the ablated particles, we observed that trajectories are affected by the obstacle even if no direct interaction takes place between the particle and the obstacle. A comparison between experimental and simulation results for thin film deposition by PLD/PR technique is presented. The observed effects regarding ablation plume particles interaction with obstacle and macro-particles are described.

Keywords: PACS; 81.15; 52.65PLD/PR; Surface quality; Plume behavior; Droplets

Dissymmetrization of micro-particle surface by laser-induced photochemical deposition by Emmanuel Hugonnot; Marie-H�l�ne Delville; Jean-Pierre Delville (pp. 470-474).

We investigate the surface dissymmetrization of micro-sized particles by using the photochemical reduction of chromate ions induced by a strongly focused CW Ar⁺ laser to nucleate and grow deposits onto one hemisphere of silica beads dispersed in a chromate solution. Growth of dissymmetric coatings is performed at λ=514nm with laser fluences varying from 1.3 to 10.1kW/cm². Rescaling of the measured deposit growth laws reduces to a single master behavior predicting the desired dissymmetry. The technique can be used to tailor micro-scale dissymmetric patterns by scanning with the beam.

Keywords: PACS; 81.15.Fg; 81.10.Dn; 42.40.Eq; 42.70.GiPhotochemical deposition; Surface patterning; Nano/micro-sized particles; Laser; Chromate

Laser photodeposition of thin semiconductor films from iron carbonyl vapors by S.A. Mulenko; A.V. Izvekov; Y.N. Petrov; V.P. Mygashko; V.S. Ovechko (pp. 475-478).

Iron carbonyl vapors (Fe(CO)₅) were used for laser chemical vapor deposition (LCVD) of nanometric structures based on iron oxides, Fe₂O3−_x (0≤ x≤1). The deposition process was done by focused Ar⁺ laser radiation ( λ_L= 488nm) on Si substrate surface with a power density about 10²W/cm² at vapor pressure of 666Pa. Content analysis of deposited films made by auger electron spectroscopy (AES) revealed the presence of iron (Fe), carbon (C) and oxygen (O). Scanning electron microscopy (SEM) showed that the deposited films surface had nanometric cluster structure. The films exhibited semiconductor properties in the range 170–340K.

Keywords: PACS; 81.16.Mk; 73.22-fLaser deposition; Carbonyl vapor; Thin films

Influence of the substrate/photo-active solution interaction in patterning and adhesion of photo-deposited films by Emmanuel Hugonnot; Marie-H�l�ne Delville; Jean-Pierre Delville (pp. 479-483).

Using the photo-chemical deposition of chromium hydroxide layers driven by a continuous Ar⁺ laser wave in a potassium chromate solution, we explored the adhesion and patterning properties of the induced deposit on glass substrates versus the composition and the pH of the photo-active solution. The experiments were performed with two interfering beams imprinting an optical pattern on the substrate and analyzing the resulting morphology of the deposit. The solubility, patterning and adhesion are investigated using both organic (acetic acid) and inorganic (HCl) acids. The observed adhesion as a function of the pH in the photo-deposition process (surface versus bulk) was compared for several substrates.

Keywords: PACS; 81.15.Fg; 81.10.Dn; 42.40.Eq; 42.70.GiPhoto-chemical deposition; Surface patterning; Adhesion; Laser; Chromate

Laser generated soliton waveguides in photorefractive crystals by V.I. Vlad; E. Fazio; M. Bertolotti; A. Bosco; A. Petris (pp. 484-491).

Non-linear photo-excited processes using the photorefractive effect are revisited with emphasis on spatial soliton generation in special laser beam propagation conditions. The soliton beams can create reversible or irreversible single-mode waveguides in the propagating materials. The important features are the 3D orientation and graded index profile matched to the laser fundamental mode. Bright spatial solitons are theoretically demonstrated and experimentally observed for the propagation of c.w. and pulsed femtosecond laser beams in photorefractive materials such as Bi₁₂ SiO₂₀ (BSO) and lithium niobate crystals. Applications in high coupling efficiency, adaptive optical interconnections and photonic crystal production are possible.

Keywords: PACS; 42.65.T; 42.65.W; 42.65.HSolitons; Optical waveguides; Photorefractive crystals

Analyses of regenerative bone matrix of rat tibia after laser photo-excitation by SEM and AFM by Vitor Baranauskas; Iv�nia Garavello; Zhao Jingguo; Maria Alice da Cruz-H�fling (pp. 492-498).

Atomic force microscopy (AFM) and scanning electron microscopy (SEM) have been used to assess the 3D organization at molecular and structural resolution during the healing course of experimentally injured tibiae in unirradiated and irradiated rats. Rat tibiae were surgically injured and HeNe laser radiation was transcutaneously applied after surgery. Newly formed collagen fibrils at the injury site of the irradiated tibiae had acquired improved lamellar organization close to the spatial organization of mature intact bone. The HeNe laser doses accelerated bone neoformation.

Keywords: Atomic force microscopy; Bone; Laser-induced healing

Design of double-clad ytterbium-doped microstructured fibre laser by A. D’Orazio; M. De Sario; L. Mescia; V. Petruzzelli; F. Prudenzano (pp. 499-502).

A Fabry–Perot ytterbium-doped laser, made by a double-clad microstructured optical fibre was designed for high power applications. The air holes extending along the propagation direction were designed to obtain an average cladding refractive index lower than that of the core. The rectangular inner cladding was chosen to enhance the absorption of the pump power. A slope efficiency S=93.6% and a threshold pump power P_th=217mW were calculated for a fibre L=4.4m long, Ytterbium concentration of N_Yb=6×10²⁵ions/m³, input mirror reflectivity of R₁=0.99 and output reflectivity of R₂=0.05.

Keywords: PACS; 42.81.Q; 78.66.J; 42.81.B; 42.60.DaOptical fibre laser; Microstructured optical fibre; Ytterbium-doped laser; Modelling

Design, analysis and fabrication of a new MEMS scanning device actuator by S. Eliahou-Niv (pp. 503-508).

In this paper, an improved mechanical device for producing a large angular movement of an optical element is described. The device can be used either for angular positioning or as a dynamic angular deflecting driver for optical components or systems. The device was designed using graph-presentation methods and numerical finite element method (FEM). The device was fabricated and tested as an angular driver of thin-film tilt interference filter for dense-wavelength division demultiplexing systems (DWDM) applications. Scaling-down analysis was carried out to show micro-electro-mechanical-systems (MEMS) suitability.

Keywords: Tunable-filter; Thin-film tilt interference filter; Scanning device; MEMS actuator

Photodeposited diffractive optical elements of computer generated masks by N. Mirchin; A. Peled; I. Baal-Zedaka; R. Margolin; M. Zagon; I. Lapsker; A. Verdyan; J. Azoulay (pp. 509-513).

Diffractive optical elements (DOE) were synthesized on plastic substrates using the photodeposition (PD) technique by depositing amorphous selenium (a-Se) films with argon lasers and UV spectra light. The thin films were deposited typically onto polymethylmethacrylate (PMMA) substrates at room temperature. Scanned beam and contact mask modes were employed using computer-designed DOE lenses. Optical and electron micrographs characterize the surface details. The films were typically 200nm thick.

Keywords: Photodeposition; Optical gratings; Optical microelements; Diffractive optical elements; DOE

Thin films of silica–carbon nanocomposites for selective solar absorbers by Dahn Katzen; Esthy Levy; Yitzhak Mastai (pp. 514-517).

In this paper, we describe new film structures based on porous silica and nanosized carbon for selective solar absorbers application. The films show high absorbance in the solar-spectral region and low emittance in the IR region. The best results for 1000nm thick films of nanocomposite silica–carbon has excellent optical parameters, absorbance α_s=0.94 and IR emissivity of ɛ=0.15. The films show good stability under the influence of humidity and high temperatures (250–300°C). This new solar absorber structure offers low cost production and both the materials are easily available and non-toxic. The overall process of film preparation is simple and works under “green-chemistry�? conditions.

Keywords: Selective solar absorber; Porous silica; Nanocomposites

Effects of wire feeding direction and location in multiple layer diode laser direct metal deposition by Waheed Ul Haq Syed; Lin Li (pp. 518-524).

This study investigates the effect of wire feeding direction, angle and location in a high power diode laser (HPDL) direct metal deposition (DMD) process for single and multilayered clad/parts. A 1.5kW diode laser was used to deposit single layer clad/track and build multilayer parts with different wire feeding conditions. These clad/parts were analysed using scanning electron microscopy (SEM), X-ray diffraction and optical microscopy. The best performance in terms of surface finish, geometry control and quality of sample was obtained by front feeding and placing the wire at the leading edge of the melt pool. By rear feeding, the best results were obtained by placing the wire at the trailing edge. The surface roughness increased by increasing the feeding angle for front feeding and decreased for rear feeding. The energy distribution, melt flow and rapid solidification processes were investigated.

Keywords: Rapid prototyping; Metallic wire; High power diode laser; Delivery angles; Direction and placement; Direct metal deposition

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Applied Surface Science (v.248, #1-4)