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Applied Surface Science (v.257, #12)

Editorial Board (pp. ii).

E-MRS Symposium R: “Laser processing and diagnostics for micro and nano applications” by Robert W. Eason Guest Editor; Magdalena Nistor Guest Editor; Jacques Perrière Guest Editor; Javier Solis Guest Editor; Ioanna Zergioti Guest Editor (pp. 5125-5126).

Modeling of CW laser diode irradiation of amorphous silicon films by Z. Said-Bacar; Y. Leroy; F. Antoni; A. Slaoui; E. Fogarassy (pp. 5127-5131).

▶ The CW laser irradiation of amorphous silicon thin films has been modeled. ▶ The optical properties of thin films are sensitive to film thickness due to the interference effects. ▶ Power densities to reach the melting, crystallization and ablation thresholds are determined. ▶ Heating the substrate during the laser process and low scan speeds allow to reduce significantly the threshold power densities.The purpose of this work is to determine the optimal parameters required to crystallize thin amorphous silicon films on glass substrate with a continuous wave (CW) laser diode ( λ=808nm), using a numerical model developed in COMSOL Multiphysics. The numerical simulation of the laser crystallization process takes into account the solid–liquid phase change and the difference between the melting temperature of amorphous (Tm_a-Si=1420K) and that of crystalline silicon (Tm_c-Si=1690K). We have varied the main parameters controlling the crystallization process, namely the power and the scan speed of the laser beam. Furthermore the initial temperature as well as the thickness of the a-Si:H layer were also taken as a parameter to optimize the process. We have determined the melting, crystallization and ablation energy threshold versus the different operational parameters.

Keywords: CW laser; Amorphous silicon; Annealing; Thin film; COMSOL Multiphysics

Microstructures and mechanical properties of metallic NiCrBSi and composite NiCrBSi–WC layers manufactured via hybrid plasma/laser process by Nicolas Serres; Françoise Hlawka; Sophie Costil; Cécile Langlade; Frédérique Machi (pp. 5132-5137).

▶ This paper describes a combined plasma/laser process for the deposition of materials. ▶ The method is unique and deserves attention. ▶ This work focuses on the use of laser treatment as the means for enhancing mechanical properties of samples. ▶ The influence of the coating structures on the wear behaviour of in situ remelted coatings was investigated. ▶ The research results demonstrate that the remelted coatings have better mechanical performances with a high WC wt.%.Thermal spraying is already used in industry to protect mechanical parts against wear and/or corrosion, but results are not always satisfactory due to porosity and microstructures. In this study, atmospheric plasma spraying (APS) and in situ laser irradiation by diode laser processes were combined to modify structural characteristics of metallic NiCrBSi and composite NiCrBSi–WC coatings. The microstructure evolution was studied with the chemical composition analysis by XRD and SEM coupled with EDS techniques. Instrumented nanoindentation tests were also conducted employing a Berkovich indenter. Moreover, the effect of the influence of the volume fraction of the reinforcing WC particles on the formation and mechanical performances of the layer was also investigated. Results show that in situ laser remelting induces the growth of a dendritic structure which strongly decreases the porosity of as-sprayed coatings, without solidification cracking (one of the major defects that can occur during the solidification of metallic or composite alloys) and improves the mechanical properties of the layer. Indeed, the layer properties such as hardness, elastic modulus, shear strength and wear rate are dependent on the percentage of WC particles in the mixture.

Keywords: Plasma/laser hybrid process; Composite coatings; Microstructures; Nanoindentation; Wear

Development of laser deposited multilayer zone plate structures for soft X-ray radiation by Tobias Liese; Volker Radisch; Inga Knorr; Michael Reese; Peter Großmann; Klaus Mann; Hans-Ulrich Krebs (pp. 5138-5141).

As a novel approach, the combination of pulsed laser deposition and focused ion beam was applied to fabricate different types of multilayer zone plate structures for soft X-ray applications. For this purpose, high quality non-periodic ZrO₂/Ti multilayers were deposited by pulsed laser deposition on planar Si substrates and on rotating steel wires with layer thicknesses according to the Fresnel zone plate law. Linear focusing optics were fabricated by cutting slices out of the multilayers by focused ion beam and placing them directly over pinholes within Si₃N₄ substrates. Additionally, it was shown that laser deposition of depth-graded multilayers on a wire is also a promising way for building up multilayer zone plates with point focus. First experiments using a table-top X-ray source based on a laser-induced plasma show that the determined focal length and spatial resolution of the fabricated multilayer Laue lens corresponds to the designed optic.

Keywords: Pulsed laser deposition; Multilayers; Zone plate; Structure

Effect of laser energy, substrate film thickness and bioink viscosity on viability of endothelial cells printed by Laser-Assisted Bioprinting by Sylvain Catros; Bertrand Guillotin; Markéta Bačáková; Jean-Christophe Fricain; Fabien Guillemot (pp. 5142-5147).

▶ Laser Assisted Bioprinting parameters have a significant influence on printed cell viability. ▶ Increasing the laser energy tends to augment the cell mortality. ▶ Increasing the thickness of the hydrogel film on receiving substrate support cell viability after printing. ▶ Increasing the viscosity of the cell bioink support cell viability after printing.Biofabrication of three dimensional tissues by Laser-Assisted Bioprinting (LAB) implies to develop specific strategies for assembling the extracellular matrix (ECM) and cells. Possible strategies consist in (i) printing cells onto or in the depth of ECM layer and/or (ii) printing bioinks containing both cells and ECM-like printable biomaterial. The aim of this article was to evaluate combinatorial effects of laser pulse energy, ECM thickness and viscosity of the bioink on cell viability. A LAB workstation was used to print Ea.hy926 endothelial cells onto a quartz substrate covered with a film of ECM mimicking Matrigel™. Hence, effect of laser energy, Matrigel™ film thickness and bioink viscosity was addressed for different experimental conditions (8–24μJ, 20–100μm and 40–110mPas, respectively). Cell viability was assessed by live/dead assay performed 24h post-printing. Results show that increasing the laser energy tends to augment the cell mortality while increasing the thickness of the Matrigel™ film and the viscosity of the bioink support cell viability. Hence, critical printing parameters influencing high cell viability have been related to the cell landing conditions and more specifically to the intensity of the cell impacts occurring at the air–ECM interface and at the ECM–glass interface.

Keywords: Laser Assisted Bioprinting; Cell viability; Hydrogels

Laser printing of polythiophene for organic electronics by I. Zergioti; M. Makrygianni; P. Dimitrakis; P. Normand; S. Chatzandroulis (pp. 5148-5151).

▶ This method resulted in laterally well-resolved square deposits, without any observed damage on their surface even in the absence of a dynamic release layer and therefore avoids the risk of contamination. ▶ The electrical characterization of Al/P3HT/Al devices indicated that a space-charge-limited-current mechanism dominates the conductivity of bulk P3HT. ▶ An analysis of bottom-contact P3HT TFTs behavior showed that functioning P3HT TFTs could be fabricated with LIFT technique.We report on the development of hybrid organic/inorganic thin-film transistors using regioregular poly-3-hexylthiophene (P3HT) semiconductor material deposited by means of the solid-phase Laser Induced Forward Transfer (LIFT) technique. P3HT pixels were LIFT-printed onto Au/Ti source and drain electrodes formed on silicon dioxide/p⁺-type Si substrate. Deposition of the P3HT pixels was investigated as a function of the laser fluence using donor substrates with and without a dynamic release layer. Device electrical characterization reveals efficient field-effect action of the bottom gate on the organic channel. The transfer I_DS– V_GS characteristics exhibit well-defined sub-threshold, linear and saturation regimes designating LIFT as a promising technique for hybrid organic/inorganic transistor technology.

Keywords: Laser-induced forward transfer; Organic semiconductor; Nanosecond; Devices

Multilayer laser printing for Organic Thin Film Transistors by Ludovic Rapp; Sébastien Nénon; Anne Patricia Alloncle; Christine Videlot-Ackermann; Frédéric Fages; Philippe Delaporte (pp. 5152-5155).

▶ Laser printing of organic CuPc semiconductor leads to operational OTFTs. ▶ LIFT can print multilayer systems with high spatial resolution and no damage in the layers. ▶ Improvement of OTFT performances in printing a multilayer system made of organic semiconductor and metallic electrodes. ▶ Best OTFT performances obtained with silver electrodes.Functional laser printed Organic Thin Film Transistors (OTFTs) have been achieved from multilayer substrates composed with semiconductor and electrodes. The p-type copper phthalocyanine (CuPc) was used to form the active layer. Different kinds of metallic materials were used for source and drain electrodes. Multilayer donor substrates were prepared by the successive depositions of materials by either thermal evaporation under vacuum or laser printing. The materials were transferred together in a single step onto a receiver substrate by laser pulses in the picosecond regime. The latter substrate formed the gate and the dielectric of the transistor. The results are compared with the step-by-step laser printing process, where electrodes and organic layer were successively printed from two different donor substrates. The multilayer laser printing reveals an improvement of the performances of the OTFT devices.

Keywords: Laser-Induced Forward Transfer; Organic semiconductor; OTFT; Multilayer

Preparation of polyynes by laser ablation of graphite in aqueous media by Seung Keun Shin; Jae Kyu Song; Seung Min Park (pp. 5156-5158).

▶ Polyynes were synthesized by laser ablation of graphite in aqueous solution at 1064 nm. ▶ The formation rate and the size distributions were affected by pH. ▶ The larger polyynes were less stable.Polyynes were prepared by liquid-phase laser ablation of a graphite target at 1064nm and identified by analyzing UV absorption spectra in deionized water and various aqueous solutions. We observed that major UV absorption peaks coincide with the electronic transitions corresponding to linear hydrogen-capped polyynes (C_nH₂: n=6, 8, 10). The peak intensities increased when polyynes were produced by irradiating the target immersed in acidic media, while those were relatively weak in basic media. This leads us to conclude that OH⁻ or H⁺ ions play a certain role in the formation of polyynes.

Keywords: Polyyne; Laser ablation; Graphite

Control of ZnO nanowire arrays by nanosphere lithography (NSL) on laser-produced ZnO substrates by S. Garry; E. McCarthy; J.P. Mosnier; E. McGlynn (pp. 5159-5162).

Nanosphere lithography (NSL) is a successful technique for fabricating highly ordered arrays of ZnO nanowires typically on sapphire and GaN substrates. In this work, we investigate the use of thin ZnO films deposited on Si by pulsed laser deposition (PLD) as the substrate. This has a number of advantages over the alternatives above, including cost and potential scalability of production and it removes any issue of inadvertent n-type doping of nanowires by diffusion from the substrate. We demonstrate ordered arrays of ZnO nanowires, on ZnO-coated substrates by PLD, using a conventional NSL technique with gold as the catalyst. The nanowires were produced by vapor phase transport (VPT) growth in a tube furnace system and grew only on the areas pre-patterned by Au. We have also investigated the growth of ZnO nanowires using ZnO catalyst points deposited by PLD through an NSL mask on a bare silicon substrate.

Keywords: ZnO; Nanostructure; Growth; Nanosphere lithography

Dynamics of ZnO laser produced plasma in high pressure argon by V.E. Kaydashev; J.G. Lunney (pp. 5163-5167).

▶ Laser plume dynamics of ZnO in the high pressure (5×10³–10⁴Pa) Ar was investigated. ▶ Emission spectroscopy and Langmuir probe measurements were used for diagnostics. ▶ We followed the propagation of the external and internal shock waves in gas and plume. ▶ The plume dynamics of ZnO targets doped with Mg, Ga and Er was also studied.Pulsed laser deposition of ZnO in high pressure gas offers a route for the catalyst-free preparation of ZnO nanorods less than 10nm in diameter. This paper describes the results of some experiments to investigate the laser plume dynamics in the high gas pressure (5×10³–10⁴Pa) regime used for PLD of ZnO nanorods. In this regime the ablation plume is strongly coupled to the gas and the plume expansion is brought to a halt within about 1cm from the target. A 248nm excimer laser was used to ablate a ceramic ZnO target in various pressures of argon. Time- and space-resolved UV/vis emission spectroscopy and Langmuir probe measurements were used to diagnose the plasma and follow the plume dynamics. By measuring the spatial profiles of Zn I and Zn II spectral lines it was possible to follow the propagation of the external and internal shock waves associated with the interaction of the ablation plume with the gas. The Langmuir probe measurements showed that the electron density was 10⁹–10¹⁰cm⁻³ and the electron temperature was several eV. At these conditions the ionization equilibrium is described by the collisional-radiative model. The plume dynamics was also studied for ZnO targets doped with elements which are lighter (Mg), comparable to (Ga), and heavier (Er) than Zn, to see if there is any elemental segregation in the plume.

Keywords: Laser; Deposition; Nanorods; Plume; Dynamics

Simulation of ultrashort double-pulse laser ablation by Mikhail E. Povarnitsyn; Tatiana E. Itina; Pavel R. Levashov; Konstatntin V. Khishchenko (pp. 5168-5171).

▶ Double-pulse crater depth depends on the delay between pulses. ▶ Two pulses can produce the crater less than a single one. ▶ Ablation process can be suppressed by the second pulse. ▶ The longer delay the higher atomization and smaller clusterization. ▶The deeper thermodynamic trajectory enters into metastable liquid region the shorter lifetime of this state.In this paper, we study the mechanisms of femtosecond double-pulse laser ablation of metals. It was previously shown experimentally that the crater depth monotonically drops when the delay between two successive pulses increases. For delays longer than the time of electron–ion relaxation the crater depth can be even smaller than that produced by a single pulse. The results of the performed hydrodynamic simulation show that the ablation can be suppressed due to the formation of the second shock wave. The modeling results of the double-pulse ablation obtained for different delays correlate with the experimental findings.

Keywords: Double-pulse ablation; Crater formation; Suppression of ablation

Thermo-optical response of layered Bi nanostructures produced by pulsed laser deposition by M. Jiménez de Castro; R. Serna; M.G. Marzoa; A. Castelo; C.N. Afonso; E. Haro-Poniatowski (pp. 5172-5174).

This work reports optical transmission changes in layered Bi nanostructures (NSs) upon heating–cooling cycles up to temperatures above the melting temperature. The nanostructured films prepared by pulsed laser deposition consist of Bi NSs with different characteristic sizes that are organised in layers and embedded in an amorphous Al₂O₃ host. The spectral dependence of the optical transmission as well as its changes upon heating are reported. The combination of Bi NSs layers with more than one characteristic size allows controlling the width of the melting–solidification transition. Eventually, it is shown how a multiple temperature thermo-optical film can be designed and prepared.

Keywords: Pulsed laser deposition; Bi nanostructures; Melting–solidification; Thermal-optical properties

Carbon nitride films by RF plasma assisted PLD: Spectroscopic and electronic analysis by E. Cappelli; S. Orlando; D.M. Trucchi; A. Bellucci; V. Valentini; A. Mezzi; S. Kaciulis (pp. 5175-5180).

▶ In this paper we studied the effect of RF plasma on a-CN x films deposition. ▶ Nitrogen plasma resulted in better thickness, quality and Nitrogen uptake of films. ▶ The OES evidenced a reactivity enhancement of Nitrogen molecules in the RF plasma. ▶ The electrical resistivity is higher, due to a greater number of C–N bond formation.Carbon nitride (CN x) thin films have been grown on Si 〈100〉 by 193nm ArF ns pulsed laser ablation of a pure graphite target in a low pressure atmosphere of a RF generated N₂ plasma and compared with samples grown by PLD in pure nitrogen atmosphere. Composition, structure and bonding of the deposited materials have been evaluated by X-ray photoelectron spectroscopy (XPS), and Raman scattering. Significant chemical and micro-structural changes have been registered, associated to different nitrogen incorporation in the two types of films analyzed. The intensity of the reactive activated species is, indeed, increased by the presence of the bias confined RF plasma, as compared to the bare nitrogen atmosphere, thus resulting in a different nitrogen uptake in the growing films. The process has been also investigated by some preliminary optical emission studies of the carbon plume expanding in the nitrogen atmosphere. Optical emission spectroscopy reveals the presence of many excited species like C⁺ ions, C atoms, C₂, N₂; and CN radicals, and N₂⁺ molecular ions, whose relative intensity appears to be increased in the presence of the RF plasma. The films were also characterised for electrical properties by the “four-probe-test method” determining sheet resistivity and correlating surface conductivity with chemical composition.

Keywords: Carbon nitride films; RF plasma PLD; XPS analysis; Raman spectroscopy; Surface conductivity; Optical emission spectroscopy

Room temperature transparent conducting oxides based on zinc oxide thin films by J. Clatot; G. Campet; A. Zeinert; C. Labrugère; A. Rougier (pp. 5181-5184).

▶ Promising transparent conducting oxide. ▶ Low temperature depositions. ▶ Zinc oxide. ▶ Optical simulations.Doped zinc oxide thin films are grown on glass substrate at room temperature under oxygen atmosphere, using pulsed laser deposition (PLD). O₂ pressure below 1Pa leads to conductive films. A careful characterization of the film stoichiometry and microstructure using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) concludes on a decrease in crystallinity with Al and Ga additions (≤3%). The progressive loss of the (002) orientation is associated with a variation of the c parameter value as a function of the film thickness and substrate nature. ZnO:Al and ZnO:Ga thin films show a high optical transmittance (>80%) with an increase in band gap from 3.27eV (pure ZnO) to 3.88eV and 3.61eV for Al and Ga doping, respectively. Optical carrier concentration, optical mobility and optical resistivity are deduced from simulation of the optical data.

Keywords: Pulsed laser deposition; Transparent conducting oxide; Zinc oxide; Optical properties; Simulation

Application of printed nanocrystalline diamond film for electron emission cathode by Xiuxia Zhang; Shuyi Wei; Chongmin Lei; Jie wei; Bingheng Lu; Yucheng Ding; Changchun Zhu (pp. 5185-5189).

▶ A kind of diamond paste was developed by mixing nanodiamond powder with nanocrystalline graphite. ▶ The best proportion of the mixture with nano-graphite and nano-diamond and ethylic cellulose was 2:5:6. ▶ The nanocrystalline diamond emitters were exposed from the NDF uniformly with best proportion and after three-steps sintering and hydrogen plasma treatment process. ▶ Treatment process would make nanodiamond emission tip sharper and distribution uniformly, and enable the electron to tunnel in the film, and make electron emit easier, and enhance electron emission uniformity and stability.The low-cost and large area screen-printed nano-diamond film (NDF) for electronic emission was fabricated. The edges and corners of nanocrystalline diamond are natural field-emitters. The nano-diamond paste for screen-printing was fabricated of mixing nano-graphite and other inorganic or organic vehicles. Through enough disperse in isopropyl alcohol by ultrasonic nano-diamond paste was screen-printed on the substrates to form NDF. SEM images showed that the surface morphology of NDF was improved, and the nano-diamond emitters were exposed from NDF through the special thermal-sintering technique and post-treatment process. The field emission characteristics of NDF were measured under all conditions with 10⁻⁶Pa pressure. The results indicated that the field emission stability and emission uniformity of NDF were improved through hydrogen plasma post-treatment process. The turn-on field decreased from 1.60V/μm to 1.25V/μm. The screen-printed NDF can be applied to the displays electronic emission cathode for low-cost outdoor in large area.

Keywords: Screen-printing; Nano-diamond film (NDF); Electronic emission cathode

Liquids microprinting through a novel film-free femtosecond laser based technique by A. Patrascioiu; M. Duocastella; J.M. Fernández-Pradas; J.L. Morenza; P. Serra (pp. 5190-5194).

▶ The new laser based technique allows microprinting liquids in a film-free way. ▶ Uniform microdroplets can be printed with high resolution and reproducibility. ▶ Droplet size can be linearly controlled through laser pulse energy. ▶ The technique is feasible for biomolecule printing.Laser-induced forward transfer (LIFT) is a high resolution microprinting technique in which small amounts of material are transferred from a previously prepared donor thin film to a receptor substrate. The application of LIFT to liquid donor films allows depositing complex and fragile materials in solution or suspension without compromising the integrity of the deposited material. However, the main drawback of LIFT is the preparation of the donor material in thin film form, being difficult to obtain reproducible thin films with thickness uniformity and good stability.In this work we present a laser microprinting technique that is able to overcome the drawbacks associated with the preparation of the liquid film, allowing the deposition of well-defined uniform microdroplets with high reproducibility and resolution. The droplet transfer mechanism relies on the highly localized absorption of strongly focused femtosecond laser pulses underneath the free surface of the liquid contained in a reservoir.An analysis of the influence of laser pulse energy on the morphology of the printed droplets is carried out, revealing a clear correlation between the printed droplet dimensions and the laser pulse energy. Such correlation is interpreted in terms of the dynamics of the liquid displaced by a laser-generated cavitation bubble close to the free surface of the liquid. Finally, the feasibility of the technique for the production of miniaturized biosensors is tested.

Keywords: Microprinting; Microdroplets; Laser printing; Microarray

Laser-assisted production of tricalcium phosphate nanoparticles from biological and synthetic hydroxyapatite in aqueous medium by M. Boutinguiza; J. Pou; F. Lusquiños; R. Comesaña; A. Riveiro (pp. 5195-5199).

▶ CaP nanoparticles were obtained from synthetic and biologic HA. ▶ The method used was CO₂ laser ablation de-ionized water. ▶ Obtained nanoparticles were amorphous and spherical with a mean diameter of 25nm. ▶ Nanoparticles obtained from synthetic HA transform to tricalcium phosphate. ▶ Nanoparticles obtained from the biological HA mostly preserve its composition.Pulsed laser ablation technique has attracted great attention as a method for preparing nanoparticles. In this work, calcined fish bones and synthetic hydroxyapatite, have been used as target to be ablated in de-ionized water with a pulsed CO₂ laser to produce calcium phosphate nanoparticles. The obtained nanoparticles were amorphous and spherical in shape with a mean diameter of about 25nm. The microanalyses revealed that nanoparticles obtained from the synthetic HA undergo transformation to tricalcium phosphate. While nanoparticles obtained from the biological hydroxyapatite mostly preserve the composition of precursor material.

Keywords: Nanoparticles; Calcium phosphate; Laser ablation

Pulsed laser deposition and thermal characterization of Ni-doped La5Ca9Cu24O41 thin films by G.I. Athanasopoulos; M. Pervolaraki; E. Svoukis; J. Androulakis; R. Saint-Martin; A. Revcolevschi; J. Giapintzakis (pp. 5200-5203).

▶ Highly b-axis oriented polycrystalline Ni-doped La₅Ca₉Cu₂₄O₄₁ thin films grown by PLD. ▶ EDX shows stoichiometric target-to-film transfer of Ni concentration up to 6.6at.%. ▶ Out-of-plane thermal conductivity ( κ_b) decreases with increasing Ni doping level. ▶ κ_b( T) in pristine and Ni-doped films is similar to polycrystalline pellets. ▶ PLD is a promising technique to introduce Ni ions with switchable spin states in the LCCO lattice.Highly b-axis oriented polycrystalline Ni-doped La₅Ca₉Cu₂₄O₄₁ thin films have been grown on (001) SrTiO₃ substrates using the pulsed laser deposition technique. EDX measurements have revealed nearly stoichiometric target-to-film transfer of Ni concentration up to 6.6at.%. The 3ω method has been employed to carry out thermal conductivity measurements in the range 90–300K. The results indicate that the out-of-plane thermal conductivity ( κ_b) decreases with increasing Ni doping level. The temperature dependence of κ_b observed in pristine and Ni-doped films is similar to that observed in polycrystalline pellets indicating that the grain boundaries play a significant role in the heat transport.

Keywords: La; ₅; Ca; ₉; Cu; ₂₄; O; ₄₁; Thin film; Thermal conductivity; 3 omega; Pulsed laser deposition

Enhanced photoluminescence of rare-earth doped films prepared by off-axis pulsed laser deposition by R. Serna; S. Nuñez-Sanchez; Fei Xu; C.N. Afonso (pp. 5204-5207).

▶ PLD off-axis configuration provides larger film uniformity and enhanced PL lifetime for Er-doped as-grown thin films. ▶ PLD off-axis enables to decrease the impact of high kinetic energy species at the substrate centre, and consequently there is a decrease of induced defects. ▶ PLD off-axis configuration opens a route to prepare rare-earth doped materials with low defect densities and reduced Er–Er interaction.Alternate pulsed laser deposition from the host (Al₂O₃) and dopant (Er, Yb) targets has been used to prepare artificially nanostructured films in which the rare earth ion–ion separation is controlled in the nanometer scale in order to control energy transfer between ions. One series of films was prepared in the standard on-axis configuration, i.e. a static substrate being centred with respect to the plasma expansion axis. A second series of films was prepared by rotating the substrate with respect to a shifted axis parallel to the plasma expansion one (off-axis configuration). The latter configuration leads to films with enhanced thickness and Er related photoluminescence intensity uniformity. More interestingly, the Er related photoluminescence lifetime in as-grown films increases up to 2.5ms, which is much higher than the maximum value of 1ms obtained for the on-axis configuration films. This enhancement is discussed in terms of a decrease of defect density when using the off-axis configuration.

Keywords: Pulsed laser deposition (PLD); Thin film; Photoluminescence; Rare-earth; Erbium (Er); Ytterbium (Yb); Amorphous aluminum oxide (Al; ₂; O; ₃; )

Fixation of bioactive calcium alkali phosphate on Ti6Al4V implant material with femtosecond laser pulses by Christian Symietz; Erhard Lehmann; Renate Gildenhaar; Robert Koter; Georg Berger; Jörg Krüger (pp. 5208-5212).

.Display Omitted▶ Femtosecond laser fixing of a thin ceramic layer on a titanium alloy is presented. ▶ The dip-coated ceramic is transilluminated by the laser. ▶ The fixation process can be understood as superficial melting of the metal, which binds the ceramic powder. ▶ This technique can be applied to process large areas.Bone implants made of metal, often titanium or the titanium alloy Ti6Al4V, need to be surface treated to become bioactive. This enables the formation of a firm and durable connection of the prosthesis with the living bone. We present a new method to uniformly cover Ti6Al4V with a thin layer of ceramics that imitates bone material. These calcium alkali phosphates, called GB14 and Ca10, are applied to the metal by dip coating of metal plates into an aqueous slurry containing the fine ceramic powder. The dried samples are illuminated with the 790nm radiation of a pulsed femtosecond laser. If the laser fluence is set to a value just below the ablation threshold of the ceramic (ca. 0.4J/cm²) the 30fs laser pulses penetrate the partly transparent ceramic layer of 20–40μm thickness. The remaining laser fluence at the ceramic–metal interface is still high enough to generate a thin metal melt layer leading to the ceramic fixation on the metal. The laser processing step is only possible because Ti6Al4V has a lower ablation threshold (between 0.1 and 0.15J/cm²) than the ceramic material. After laser treatment in a fluence range between 0.1 and 0.4J/cm², only the particles in contact with the metal withstand a post-laser treatment (ultrasonic cleaning). The non-irradiated rest of the layer is washed off. In this work, we present results of a successful ceramic fixation extending over larger areas. This is fundamental for future applications of arbitrarily shaped implants.

Keywords: Bone implant; Bioceramic coating; Titanium; Calcium phosphate; Femtosecond laser

Modifications of roughness and wettability properties of metals induced by femtosecond laser treatment by P. Bizi-Bandoki; S. Benayoun; S. Valette; B. Beaugiraud; E. Audouard (pp. 5213-5218).

▶ Surface properties of 316L stainless steel and TA6V alloys were modified using a femtosecond laser. ▶ Irradiation conditions enabled to create a 3-scale topography made of superimposed periodic patterns on the processed surfaces. ▶ Initially hydrophilic surfaces were made hydrophobic after treatment ▶ Increasing the laser pulse number enhanced the hydrophobic behaviorTopographic and wetting properties of AISI 316L stainless steel and Ti–6Al–V alloys were modified via linearly polarized femtosecond laser pulse irradiation. In order to induce a gradual evolution of the surface topography and wettability, four samples of each alloy were irradiated with different number of pulses. From the topographic point of view, a multi-scale morphology made of nano- and micro-periodic ripples was induced. The increase in the number of pulses led to the appearance of a third scale structure of waviness that is due to the laser scanning. The wettability of alloys was changed from a hydrophilic behavior to a hydrophobic one without lowering surface energies by chemical coatings. The apparent contact angle (CA) increased with increasing the number of pulses. A rise of about 50° of the apparent CA of the Ti–6Al–V was noticed.

Keywords: Femtosecond laser texturing; Multi-scale surface structuration; Surface topography; Ripples; Wettability; Cassie–Baxter's model

3D features of modified photostructurable glass–ceramic with infrared femtosecond laser pulses by J.M. Fernández-Pradas; D. Serrano; S. Bosch; J.L. Morenza; P. Serra (pp. 5219-5222).

▶ Microchannels buried at different depths in Foturan were fabricated with femtosecond laser pulses at 1027nm wavelength. ▶ The microchannel size along the laser beam direction can be controlled through adjustment of the pulse energy for the different depths. ▶ The voxel size in the laser beam direction follows a logarithmic relationship with pulse energy, and an exponential relationship with focusing depth. ▶ Spherical aberration and self-focusing phenomena account for the laser intensity distribution inside Foturan.The exclusive ability of laser radiation to be focused inside transparent materials makes lasers a unique tool to process inner parts of them unreachable with other techniques. Hence, laser direct-write can be used to create 3D structures inside bulk materials. Infrared femtosecond lasers are especially indicated for this purpose because a multiphoton process is usually required for absorption and high resolution can be attained. This work studies the modifications produced by 450fs laser pulses at 1027nm wavelength focused inside a photostructurable glass-ceramic (Foturan^®) at different depths. Irradiated samples were submitted to standard thermal treatment and subsequent soaking in HF solution to form the buried microchannels and thus unveil the modified material. The voxel dimensions of modified material depend on the laser pulse energy and the depth at which the laser is focused. Spherical aberration and self-focusing phenomena are required to explain the observed results.

Keywords: Microchannels; Photostructurable glass–ceramic; Femtosecond laser microfabrication

Nano-scale and surface precipitation of metallic particles in laser interference patterned noble metal-based thin films by R. Catrin; D. Horwat; J.-F. Pierson; S. Migot; Y. Hu; F. Mücklich (pp. 5223-5229).

▶ One step laser interference patterning of Cu₃N and Pd_0.25Pt_0.75O_x. ▶ Thermal decomposition of metal nitride and oxide thin films. ▶ Laser-induced precipitation of metallic nanoparticles. ▶ Significant lowering of electrical resistivity.Laser interference patterning (also known as “laser interference metallurgy”) is used to locally tailor the microstructure of oxide (Pd_0.25Pt_0.75O_x) and nitride (Cu₃N) thin films to induce a chemical decomposition, which is responsible for a decrease of electrical resistivity. This technique allows hereby a laser-induced chemical decomposition of as-deposited oxide and nitride films, resulting locally in a porous microstructure due to the simultaneous emission of gaseous nitrogen and oxygen. The process locally generates at the nanometer scale metal precipitatation of Pt or Cu in the oxide or nitride matrix. Thus, isolated metallic clusters with low resistivity coexist with a high resistivity phase, establishing a preferential electrical conduction path and giving the system a lower effective resistivity. The decomposition process is investigated by four-point probe method, X-ray diffraction, spectrophotometry, white light interference, scanning and transmission electron microscopies.

Keywords: Noble metal oxide thin films; Laser interference patterning; Nanoparticles precipitation; Chemical decomposition; Tailored electrical resistivity; Magnetron sputtering; Transmission electron microscopy

Selective ablation with UV lasers of a-Si:H thin film solar cells in direct scribing configuration by S. Lauzurica; J.J. García-Ballesteros; M. Colina; I. Sánchez-Aniorte; C. Molpeceres (pp. 5230-5236).

▶ Ablation thresholds and scribing process parameters calculated for the materials involved in the a-Si:H thin film technology. ▶ Morphology study of the laser patterning at 355nm of wavelength and two different pulsewidth (picosecond and nanosecond). ▶ Consecution of the selective ablation from the film side of the thin films which make up the device. ▶ The study of the Raman crystalline fraction of the silicon layer shows good results for direct scribing ablation in the last laser step, with low affectation of the silicon structure. ▶ Potential use of alternative materials in the substrate configuration with full laser interconnection.Monolithical series connection of silicon thin-film solar cells modules performed by laser scribing plays a very important role in the entire production of these devices. In the current laser process interconnection the two last steps are developed for a configuration of modules where the glass is essential as transparent substrate. In addition, the change of wavelength in the employed laser sources is sometimes enforced due to the nature of the different materials of the multilayer structure which make up the device. The aim of this work is to characterize the laser patterning involved in the monolithic interconnection process in a different configurations of processing than the usually performed with visible laser sources. To carry out this study, we use nanosecond and picosecond laser sources working at 355nm of wavelength in order to achieve the selective ablation of the material from the film side. To assess this selective removal of material has been used EDX (energy dispersive using X-ray) analysis, electrical measurements and confocal profiles. In order to evaluate the damage in the silicon layer, Raman spectroscopy has been used for the last laser process step. Raman spectra gives information about the heat affected zone in the amorphous silicon structure through the crystalline fraction calculation. The use of ultrafast sources, such as picoseconds lasers, coupled with UV wavelength gives the possibility to consider materials and substrates different than currently used, making the process more efficient and easy to implement in production lines. This approach with UV laser sources working from the film side offers no restriction in the choice of materials which make up the devices and the possibility to opt for opaque substrates.

Keywords: Laser scribing; Selective ablation; a-Si:H

Fabrication of an integrated optical Mach–Zehnder interferometer based on refractive index modification of polymethylmethacrylate by krypton fluoride excimer laser radiation by Michael Koerdt; Frank Vollertsen (pp. 5237-5240).

▶ An additional parameter for refractive index control is offered by sensitization. ▶ Surface sensitization improves fabrication of waveguides in polymethylmethacrylate. ▶ The integrated optical Mach–Zehnder interferometer shows a visibility of over 15dB.It is known that deep ultraviolet (UV) radiation induces a refractive index increase in the surface layer of polymethylmethacrylate (PMMA) samples. This effect can be used for the fabrication of integrated optical waveguides. PMMA is of considerable interest for bio and chemical sensing applications because it is biocompatible and can be micromachined by several methods, e.g. structuring by photolithography, ablation and hot embossing. In the presented work direct UV irradiation of a common PMMA substrate by a krypton fluoride excimer laser beam through a contact mask has been used to write integrated optical Mach–Zehnder interferometers (MZI). MZI are used as sensitive bio and chemical sensors. The aim was to determine contact mask design and laser irradiation parameters for fabricating single-mode MZI for the infrared region from 1.30μm to 1.62μm. Straight and curved waveguides have been generated and characterized to determine the optical losses. The generation of channel waveguide structures has been optimized by a two step irradiation process to minimize the lithographic writing time and optical loss. By flood exposure to UV laser radiation in the first step the optical absorption of PMMA can be increased in the irradiated region. The required refractive index profile is then achieved with a second lithographic irradiation. The spectral behaviour of an unbalanced, integrated optical MZI fabricated by this excimer laser based contact mask method is shown for the first time. Further the optical intensity at the output port of a MZI has been measured while the optical path length difference was tuned by creating a temperature difference between the two arms of the MZI.

Keywords: Refractive index modification; Polymethylmethacrylate; Waveguide; Mach–Zehnder interferometer; Excimer laser

Direct laser printing for high efficiency silicon solar cells fabrication by G. Poulain; C. Boulord; D. Blanc; A. Kaminski; M. Gauthier; C. Dubois; B. Semmache; M. Lemiti (pp. 5241-5244).

▶ Laser assisted diffusion could be used to engineer the dopant profile of solar cells. ▶ Laser assisted doping step could be performed through the silicon nitride coating. ▶ Dopant diffusion could be achieved with UV light in nanoseconds regime.Silicon solar cells still require cost reduction and improved efficiency to become more competitive. New architectures can provide a significant increase in efficiency, but today most of the approaches need additional fabrication steps. In this context, laser processing offers a unique way to replace technological steps like photolithography that is not compatible with the requirements of the photovoltaic industry. In particular laser induced thermal effects can be used to activate or re-organise dopants at the silicon surface to design new emitter geometries. In this paper dopant diffusion using a nanosecond UV laser on phosphorous-doped silicon emitters is studied. The presence of a phosphosilicate glass underneath a silicon nitride layer leads to a local decrease of the emitter sheet resistance from 100Ω/sq to 20Ω/sq. Laser induced damage, phosphorus diffusion profile and electrical shunt are assessed in the perspective of selective emitter silicon solar cells fabrication compatible with electrochemical metal contacts deposition.

Keywords: Laser; Doping; Ablation; Silicon solar cells

Improvement in semiconductor laser printing using a sacrificial protecting layer for organic thin-film transistors fabrication by Ludovic Rapp; Christophe Cibert; Sébastien Nénon; Anne Patricia Alloncle; Matthias Nagel; Thomas Lippert; Christine Videlot-Ackermann; Frédéric Fages; Philippe Delaporte (pp. 5245-5249).

▶ DS4T semiconductor cannot be laser printed without DRL. ▶ Gold DRL contaminate the semiconductor surface. ▶ Well-resolved pixels of DS4T have been transferred with triazene polymer DRL.Laser-induced forward transfer (LIFT) has been used to deposit pixels of an organic semiconductor, distyryl-quaterthiophenes (DS4T). The dynamics of the process have been investigated by shadowgraphic imaging for the nanosecond (ns) and picosecond (ps) regime on a time-scale from the laser iradiation to 1.5μs. The morphology of the deposit has been studied for different conditions. Intermediate sacrificial layer of gold or triazene polymer has been used to trap the incident radiation. Its role is to protect the layer to be transferred from direct irradiation and to provide a mechanical impulse strong enough to eject the material.

Keywords: Laser-induced forward transfer; Organic semiconductor; Shadowgraphic visualizations; Nanosecond; Picosecond

2D spatially controlled polymer micro patterning for cellular behavior studies by V. Dinca; A. Palla-Papavlu; I. Paraico; T. Lippert; A. Wokaun; M. Dinescu (pp. 5250-5254).

A simple and effective method to functionalize glass surfaces that enable polymer micropatterning and subsequent spatially controlled adhesion of cells is reported in this paper. The method involves the application of laser induced forward transfer (LIFT) to achieve polymer patterning in a single step onto cell repellent substrates (i.e. polyethyleneglycol (PEG)). This approach was used to produce micron-size polyethyleneimine (PEI)-patterns alternating with cell-repellent areas. The focus of this work is the ability of SH-SY5Y human neuroblastoma cells to orient, migrate, and produce organized cellular arrangements on laser generated PEI patterns.

Keywords: Polyethyleneimine; Polyethyleneglycol; Patterns; Neuronal cells

Study of liquid deposition during laser printing of liquids by M. Duocastella; A. Patrascioiu; V. Dinca; J.M. Fernández-Pradas; J.L. Morenza; P. Serra (pp. 5255-5258).

▶ The slope of droplet volume versus laser energy line increases linearly with liquid film thickness. ▶ The slope increase is attributed to the displacement of more liquid by the cavitation bubble. ▶ The cavitation bubble generation is activated by a threshold independent of liquid film thickness.Laser-induced forward transfer (LIFT) is a direct-writing technique which can be used to successfully print various complex and sensitive materials with a high degree of spatial resolution. However, the optimization of its performances requires a deep understanding of the LIFT dynamics. Such understanding should allow correlating the phenomena underlying the liquid transfer process with the morphology of the obtained deposits. To this end, in this work it is presented a study related to two aspects: first, the correlation of the morphological characteristics of the transferred droplets with the variation of the film thickness combined with laser fluence; and second, a correlation of the dependences observed with the dynamics of the transfer process. The work is focused on the understanding of the observed dependences for which the information provided by time–resolved analysis on liquid transfer dynamics has proved to be crucial.

Keywords: LIFT; Laser printing; Microdroplets; Microarray

Thin films of polymer blends deposited by matrix-assisted pulsed laser evaporation: Effects of blending ratios by Irina Alexandra Paun; Valentin Ion; Antoniu Moldovan; Maria Dinescu (pp. 5259-5264).

▶ We obtain thin films of PEG:PLGA blends with different blending ratios using MAPLE. ▶ We study the influence of the blending ratios on the characteristics of the films. ▶ The films are smoother for blends with higher content of PEG. ▶ The intensity ratios in the FTIR spectra are consistent with the blending ratios. ▶ The films have lower refractive indices for blends with higher content of PEG.In this work, we show successful use of matrix-assisted pulsed laser evaporation (MAPLE) for obtaining thin films of PEG:PLGA blends, in the view of their use for controlled drug delivery. In particular, we investigate the influence of the blending ratios on the characteristics of the films. We show that the roughness of the polymeric films is affected by the ratio of each polymer within the blend. In addition, we perform Fourier transformed infrared spectroscopy (FTIR) measurements and we find that the intensities ratios of the infrared absorption bands of the two polymers are consistent with the blending ratios. Finally, we assess the optical constants of the polymeric films by spectroscopic ellipsometry (SE). We point out that the blending ratios exert an influence on the optical characteristics of the films and we validate the SE results by atomic force microscopy and UV–vis spectrophotometry. In all, we stress that the ratios in which the two polymers are blended have significant impact on the morphology, chemical structure and optical characteristics of the polymeric films deposited by MAPLE.

Keywords: Deposition; Polymer; Drug delivery

Parametric studies on iron–carbon composite nanoparticles synthesized by laser pyrolysis for increased passivation and high iron content by F. Dumitrache; I. Morjan; C. Fleaca; R. Birjega; E. Vasile; V. Kuncser; R. Alexandrescu (pp. 5265-5269).

▶ Fe-based/C core–shell particles at high Fe content were prepared by laser pyrolysis. ▶ Improved magnetic properties by the increase of the core iron content were obtained. ▶ High Fe (in at.%) was obtained by the diminishing the acetylene precursor.Iron/iron carbide core and carbon shell nanoparticles with improved magnetic properties were successfully synthesized by laser pyrolysis. As iron and carbon precursors, iron pentacarbonyl and pure or argon-diluted acetylene/ethylene mixtures, respectively, were used. The aim of the present optimization is the improvement of the magnetic properties of the nanomaterials by the increase of the iron percent in powders simultaneously to the maintaining of the protective character of the carbon coverage of nanoparticles. The chemical content and the crystalline structure were monitored by EDX, XRD and TEM techniques. In the first study, the content of acetylene as carbon source was diminished from 75% to 0%. Consequently the percent iron increased from 10at.% to 28at.% while oxygen remained relatively constant (around 5at.%). In the second step, only diluted ethylene was used (maximum 87.5vol.% Ar). In this case, an increase of iron to 46at.% is observed. An optimum 50% carbon source dilution was found. Above this value, the carbon content increases and below it, superficial oxidation increases through the diminishing of the carbon shell. The magnetic properties and the Fe phase composition of the Fe–C samples were analyzed by temperature dependent Mössbauer spectroscopy.

Keywords: Iron–carbon composite; Nanoparticles; Laser pyrolysis; Iron pentacarbonyl; Mössbauer spectroscopy

About graphene ribbons development in laser synthesized nanocarbon by L. Gavrila Florescu; E. Vasile; I. Sandu; I. Soare; C. Fleaca; R. Ianchis; C. Luculescu; E. Dutu; R. Birjega; I. Morjan; I. Voicu (pp. 5270-5273).

▶ Laser-induced pyrolysis is capitalizing very particular characteristics of laser radiation, presents tempting technological features and proves its ability for producing carbon nanopowders with controlled size and morphology. ▶ Laser-induced pyrolysis of a C₂H₂/SF₆ gas mixture leads to structural changes of the synthesized carbon nanopowders, from an altered turbostratic structure, with puckered graphene layers, up to well developed graphene bands, when C/F atomic ratio ≥3. ▶ The work is proposing to investigate the possibilities of changing, through laser-induced pyrolysis, the morphology of this last type of nanocarbon in order to have an ultimate material with a higher content of graphene ribbons with foreseen structure. ▶ Preliminary experimental data obtained by X-ray diffraction, Raman spectroscopy, high-resolution electron microscopy and its associated techniques (e.g. electron energy loss spectroscopy) from C₂H₂/SF₆ samples with C/F atomic ratio ≥3, proved the possibility to achieve these goals in situ by changing both gas composition and experimental parameters.The work presents preliminary studies with the goal to extend the share of long graphene ribbons in laser-synthesized carbon black. Investigations revealed the existence, as a major constituent, of graphene ribbons composed of up to 10–15 graphene layers, spaced at ∼0.35–0.37nm and of tens of nanometres in length. The samples used to study the development of this specific structure were obtained from sensitized acetylene-based mixtures and the experiments were performed following the variation of both the experimental parameters and gas composition.

Keywords: Laser pyrolysis; Graphene; Carbon nanopowders

Excimer laser accelerated hydrothermal synthesis of ZnO nanocrystals & their electrical properties by K.D.G.I. Jayawardena; Charles Opoku; James Fryar; S. Ravi P. Silva; Simon J. Henley (pp. 5274-5277).

▶ An excimer laser has been used on the traditional hydrothermal growth of ZnO. ▶ The laser is used in order to accelerate the process as well as to control the morphology. ▶ The morphology is observed to be dependent upon the laser fluence. The fluence is also seen to control the size distribution ▶ Narrow size distributed ZnO nanocrystals have been achieved using a fluence of 330mJcm⁻².The synthesis of ZnO nanocrystals is reported using a hydrothermal chemical growth technique combined with 248nm nanosecond excimer laser heating at fluences in the range 0–390mJcm⁻². The effect of laser heating in controlling the morphology of the nanocrystals is investigated using optical spectroscopy and electron microscopy characterization. Laser heating is shown to allow control of the crystal morphology from nanoparticles to nanorods as well as to modify the size distributions. The results indicate that not only does the laser accelerate the growth of nanocrystals, but can also produce crystals with a narrow size distribution possibly via photothermal size selection. An initial study of electrical conduction properties of ZnO nanocrystal thin films is also discussed.

Keywords: Zinc oxide; Nanocrystals; Laser heating; Morphology control

Characterization of Ag and Au nanoparticles created by nanosecond pulsed laser ablation in double distilled water by A.S. Nikolov; N.N. Nedyalkov; R.G. Nikov; P.A. Atanasov; M.T. Alexandrov (pp. 5278-5282).

▶ Chemical-free Ag and Au nanoparticles were produced by nanosecond laser ablation. ▶ The ablation process has been performed by Nd:YAG laser in double distilled water. ▶ As-prepared samples have been investigated by TEM and UV–VIS transmission. ▶ The laser fluence at 1064nm does not influence the average particle size. ▶ The mean size increases with the increasing of the laser fluence at the SHG.Pulsed laser ablation of Ag and Au targets, immersed in double-distilled water is used to synthesize metallic nanoparticles (NPs). The targets are irradiated for 20min by laser pulses at different wavelengths—the fundamental and the second harmonic (SHG) ( λ=1064 and 532nm, respectively) of a Nd:YAG laser system. The ablation process is performed at a repetition rate of 10Hz and with pulse duration of 15ns. Two boundary values of the laser fluence for each wavelength under the experimental conditions chosen were used—it varied from several J/cm² to tens of J/cm². Only as-prepared samples were measured not later than two hours after fabrication. The NPs shape and size distribution were evaluated from transmission electron microscopy (TEM) images. The suspensions obtained were investigated by optical transmission spectroscopy in the near UV and in the visible region in order to get information about these parameters. Spherical shape of the NPs at the low laser fluence and appearance of aggregation and building of nanowires at the SHG and high laser fluence was seen. Dependence of the mean particle size at the SHG on the laser fluence was established. Comments on the results obtained have been also presented.

Keywords: Ag; Au; Nanoparticles; Nanosecond pulsed laser ablation; As-prepared samples; TEM; UV–VIS extinction

Electrical assisted laser floating zone (EALFZ) growth of 2212-BSCCO superconducting fibres by M.F. Carrasco; V.S. Amaral; R.F. Silva; F.M. Costa (pp. 5283-5286).

▶ Superconducting fibres of Bi2Sr2CaCu2O8 ( 2212-BSCCO) were grown by electrical assisted laser floating zone ( EALFZ) technique. ▶ The current application during the LFZ growth induces a selective and more intense ionic migration along the fibre axis leading to a higher crystal alignment. ▶ The application of an electrical current through the crystallization interface improved the superconducting properties of 2212 fibres.The new electrical assisted laser floating zone ( EALFZ) technique was used to grow superconducting fibres of Bi₂Sr₂CaCu₂O₈ ( 2212-BSCCO). The application of an electrical current through the crystallization interface proved to advantageously modify the phase nature and texture of 2212-BSCCO polycrystalline fibres compared to conventionally laser floating zone ( LFZ) grown ones. The current application during the growth induces a selective and more intense ionic migration along the fibre axis. As a result, an increase in superconducting phase fraction and a decrease of residual melt were observed together with grain alignment intensification. The main outcome in the superconducting properties is the improvement of the critical current density at 77K, from 1.2×10³A/cm², in the LFZ fibres, to 2.8×10³A/cm², in the EALFZ processed ones.

Keywords: Superconductors; Laser floating zone; BSCCO; Fibre

Deposition of antibacterial of poly(1,3-bis-(p-carboxyphenoxy propane)-co-(sebacic anhydride)) 20:80/gentamicin sulfate composite coatings by MAPLE by R. Cristescu; C. Popescu; G. Socol; A. Visan; I.N. Mihailescu; S.D. Gittard; P.R. Miller; T.N. Martin; R.J. Narayan; A. Andronie; I. Stamatin; D.B. Chrisey (pp. 5287-5292).

▶ We deposit CPP:SA 20:80/gentamicin sulfate composite thin films by MAPLE. ▶ Deposition process did not caused important changes of polymer chemical structure. ▶ Composite thin films inhibit both Gram-positive and Gram-negative bacteria growths. ▶ MAPLE can be used to produce antibacterial implantable medical devices.We report on thin film deposition of poly(1,3-bis-(p-carboxyphenoxy propane)-co-sebacic anhydride)) 20:80 thin films containing several gentamicin concentrations by matrix assisted pulsed laser evaporation (MAPLE). A pulsed KrF* excimer laser was used to deposit the polymer–drug composite thin films. Release of gentamicin from these MAPLE-deposited polymer conjugate structures was assessed. Fourier transform infrared spectroscopy was used to demonstrate that the functional groups of the MAPLE-transferred materials were not changed by the deposition process nor were new functional groups formed. Scanning electron microscopy confirmed that MAPLE may be used to fabricate thin films of good morphological quality. The activity of gentamicin-doped films against Escherichia coli and Staphylococcus aureus bacteria was demonstrated using disk diffusion and antibacterial drop test. Our studies indicate that deposition of polymer–drug composite thin films prepared by MAPLE is a suitable technique for performing controlled drug delivery. Antimicrobial thin film coatings have several medical applications, including use for indwelling catheters and implanted medical devices.

Keywords: Poly(1,3-bis-(p-carboxyphenoxy propane)-co-(sebacic anhydride)) 20:80; Gentamicin; Matrix assisted pulsed laser evaporation; Drug delivery

MAPLE deposition of Mn(III) metalloporphyrin thin films: Structural, topographical and electrochemical investigations by R. Cristescu; C. Popescu; A.C. Popescu; S. Grigorescu; I.N. Mihailescu; A.A. Ciucu; S. Iordache; A. Andronie; I. Stamatin; E. Fagadar-Cosma; D.B. Chrisey (pp. 5293-5297).

▶ We deposited (5,10,15,20-tetraphenyl)porphinato manganese(III) chloride ((MnTPP)Cl) thin films by MAPLE. ▶ Globular structures with average diameters decreasing with laser fluence. ▶ Surface enhanced Raman effect was noticed on MAPLE-deposited thin films at 300mJ/cm². ▶ (MnTPP)Cl-coated Au-SPE is appropriate as a single mediator for dopamine sensing in the specific case of gold screen-printed electrodes.We report the deposition by MAPLE of metallized nanostructured (5,10,15,20-tetraphenyl)porphinato manganese(III) chloride thin films onto gold screen-printed electrodes, or 〈111〉 Si substrates. The deposited nanostructures were characterized by atomic force microscopy and exhibited globular structures with average diameters decreasing with laser fluence. Raman spectroscopy showed that no major decomposition appeared. We have investigated the Mn(III)-metalloporphyrin thin films by cyclic voltammetry in order to evaluate the potential bio/chemosensing activity on dopamine neurotransmitter analyte. We have found that the manganese(III)-porphyrin is appropriate as a single mediator for dopamine sensing in the specific case of gold screen-printed electrodes.

Keywords: Metalloporphyrins; Dopamine; Thin films; Matrix assisted pulsed laser evaporation

Thin films of arylenevinylene oligomers prepared by MAPLE for applications in non-linear optics by A. Stanculescu; L. Vacareanu; M. Grigoras; M. Socol; G. Socol; F. Stanculescu; N. Preda; E. Matei; I. Ionita; M. Girtan; I.N. Mihailescu (pp. 5298-5302).

▶ Thin films of arylenevinylene oligomers can be deposited by MAPLE. ▶ Preservation of chemical structures of films was tested by UV–Vis and PL. ▶ Deposited oligomers show nearly equal second-order NLO coefficients (<100mW). ▶ SH and TPL intensities change with x- and z-position on the film.This paper discusses two arylenevinylene oligomers with optical nonlinear properties. Their trans molecular structure was confirmed by Fourier Transform Infrared Spectroscopy and Nuclear Magnetic Resonance. Second Harmonic Generation and two-photon fluorescence have been observed on Matrix Assisted Pulsed Laser Evaporation-deposited thin films. We have seen two local maxima in UV–Vis spectra and a red shift of the photoluminescence peak for carbazole-based oligomer, which can be correlated with a higher conformational flexibility and with strong polarization interactions in the solid state. Scanning Electron Microscopy and Atomic Force Microscopy images have revealed a grainy morphology of the film deposited on titanium and a higher roughness for carbazole-based oligomer. Second harmonic measurements have shown nearly equal values of the second-order nonlinear optical coefficient for the triphenylamine and carbazole-based oligomers for P_laser<100mW. z-Scan and x-scan representations of the carbazole-based oligomer film have shown strong two-photon fluorescence intensity inside the sample confirming a volume process, and a strong second harmonic at the surface of the sample determined by the surface morphology.

Keywords: MAPLE; Arylenevinylene oligomers; SHG; Optical properties

Characterization of polymer thin films obtained by pulsed laser deposition by A. Palla-Papavlu; V. Dinca; V. Ion; A. Moldovan; B. Mitu; C. Luculescu; M. Dinescu (pp. 5303-5307).

▶ pulsed laser deposition of polyepichlorhydine polymer ▶ the deposited PECH layers show a trend of increased roughness as a function of fluence ▶ chemical structure of the deposited PECH layers preserved for laser fluences up to 1J/cm².The development of laser techniques for the deposition of polymer and biomaterial thin films on solid surfaces in a controlled manner has attracted great attention during the last few years. Here we report the deposition of thin polymer films, namely Polyepichlorhydrin by pulsed laser deposition. Polyepichlorhydrin polymer was deposited on flat substrate (i.e. silicon) using an NdYAG laser (266nm, 5ns pulse duration and 10Hz repetition rate).The obtained thin films have been characterized by atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and spectroscopic ellipsometry.It was found that for laser fluences up to 1.5J/cm² the chemical structure of the deposited polyepichlorhydrin polymer thin layers resembles to the native polymer, whilst by increasing the laser fluence above 1.5J/cm² the polyepichlorohydrin films present deviations from the bulk polymer.Morphological investigations (atomic force microscopy and scanning electron microscopy) reveal continuous polyepichlorhydrin thin films for a relatively narrow range of fluences (1–1.5J/cm²).The wavelength dependence of the refractive index and extinction coefficient was determined by ellipsometry studies which lead to new insights about the material.The obtained results indicate that pulsed laser deposition method is potentially useful for the fabrication of polymer thin films to be used in applications including electronics, microsensor or bioengineering industries.

Keywords: Pulsed laser deposition; Polyepichlorhydrin polymer; Thin films

Mg–Al layered double hydroxides (LDHs) and their derived mixed oxides grown by laser techniques by A. Matei; R. Birjega; A. Nedelcea; A. Vlad; D. Colceag; M.D. Ionita; C. Luculescu; M. Dinescu; R. Zavoianu; O.D. Pavel (pp. 5308-5311).

▶ Deposition of highly adherent thin films of double layered hydroxides of Mg and Al and their derived mixed oxides. ▶ Oriented LDH films were obtained by MAPLE from targets with the atomic ratio Mg/Al=3. ▶ PLD and MAPLE can be used to produce thin films displaying highly dispersed nano-sized Ag particles.Layered double hydroxides (LDHs) have been widely studied due to their applications as multifunctional materials, catalysts, host materials, anionic exchangers, adsorbents for environmental contaminants and for the immobilization of biological materials. As thin films, LDHs are good candidates for novel applications as sensors, corrosion resistant coatings or components in electro optical devices. For these applications, lamellar orientation-controlled film has to be fabricated.In this work, the successful deposition of LDH and their derived mixed oxides thin films by laser techniques is reported. Pulsed laser deposition (PLD) and matrix assisted pulsed laser evaporation (MAPLE) were the methods used for thin films deposition. The ability of Mg–Al LDHs as a carrier for metallic particles (Ag) has been considered. Frozen targets containing 10% powder in water were used for MAPLE, while for PLD the targets consisted in dry-pressed pellets.The structure and the surface morphology of the deposited films were examined by X-ray Diffraction, Atomic Force Microscopy, Scanning Electron Microscopy and Secondary Ion Mass Spectrometry.

Keywords: Matrix assisted pulsed laser evaporation (MAPLE); Pulsed laser deposition (PLD); Layered double hydroxides (LDH); Hydrotalcite-like materials

High temperature growth of InN on various substrates by plasma-assisted pulsed laser deposition by F. Stokker-Cheregi; A. Nedelcea; M. Filipescu; A. Moldovan; D. Colceag; V. Ion; R. Bîrjega; M. Dinescu (pp. 5312-5314).

▶ We aim to elucidate conflicting reports of InN growth at temperatures above 500°C. ▶ InN films were grown by RF-PLD on Si (100), Si (111), and sapphire (001), at 550°C. ▶ XRD measurements reveal the presence of InN in all samples.InN has attracted much attention due to its optical and electrical properties that make it suitable for the fabrication of infrared optical devices and high-speed electronic devices. In this work we report on the structural properties and morphology of InN thin films grown on different substrates by radiofrequency plasma beam assisted pulsed laser deposition. Sapphire and silicon substrates were considered for the growth of these films. The influence of substrate type and growth parameters on the morphology and structural properties of the resulting InN thin films is discussed. The structural analysis of the samples was performed by means of X-ray diffraction. The morphology of the thin films was investigated through atomic force microscopy. Although growth of InN from a metallic In target using nitrogen radiofrequency plasma assisted pulsed laser deposition was achieved for all the samples, growth conditions were found to play an important role on the crystal quality of the resulting thin films.

Keywords: Pulsed laser deposition; III-nitrides; Thin films

Characterization of gaseous phase and nanoparticles produced in ultra-short pulsed laser ablation of transition metal borides by A. De Bonis; R. Teghil; J.V. Rau; A. Galasso; S. Orlando; A. Santagata (pp. 5315-5318).

▶ Ultrashort PLA of zirconium and rhenium diborides produces a large number of nanoparticles. ▶ The stoichiometry of the deposited films is related to the nanoparticles composition. ▶ The main mechanism of material loss for nanoparticles is vaporization during the flight to the substrate.The plasma produced by ultra-short laser ablation of ZrB₂ and ReB₂ has been studied by ICCD imaging and time and space resolved optical emission spectroscopy. The aim was to clarify the mechanism of deposition leading to the morphology and composition found in the deposited films. The results indicate that for all systems the film characteristics are compatible with a deposition mechanism involving a growth from nanoparticles, ejected directly from the target, whose composition can be interpreted in terms of equilibrium vaporization during the flight from the target to the substrate.

Keywords: PACS; 79.20.Eb; 52.70.Kz; 81.05.Jefs laser induced nanoparticles; Metal borides; Ultra-short PLD

Growth modes of pentacene films obtained by pulsed laser deposition by G. Wisz; M. Kuzma; I. Virt; P. Sagan; I. Rudyj (pp. 5319-5323).

▶ We grew pentacene films by pulsed laser deposition. ▶ Substrate orientation controlled growth mode. ▶ Elementary cell parameters were calculated from electron diffraction measurements.Thin pentacene films were deposited on KCl and ITO/glass substrates by the pulsed laser deposition method (PLD) using a YAG:Nd³⁺ laser with a second harmonic ( λ=532nm). We compared the structure of the layer on differently oriented substrates with respect to the pentacene plasma plume – vertical and parallel orientation. The structure of the layers formed was examined using SEM, RHEED and THEED methods. The lattice parameters of the layer deposited on KCl were determined from THEED pattern ( a=5.928Å, b=7.874Å, c=14,98Å, α=76.54°, β=75.17°, γ=89.20°). The preferred direction[11¯0] of the layer growth on KCl substrate was addressed. The effect of the substrate orientation results in a different growth mode of the layers.

Keywords: Pentacene; PLD; Growth modes; Thin films

Homogeneous films by inverse pulsed laser deposition by L. Égerházi; Zs. Geretovszky; T. Szörényi; F. Bari (pp. 5324-5327).

Recently, we proposed an alternative arrangement to traditional on- or off-axis PLD geometries, termed inverse PLD (IPLD) that is capable of producing films of improved surface morphology. Two configurations of this new target-substrate arrangement were developed, namely static and co-rotating IPLD. In the static IPLD configuration, the substrate is stationary with respect to the ablated spot; while in the co-rotating IPLD configuration the substrate is fixed to the target surface and rotates simultaneously with the target, hence offering an appealingly simple approach to homogenize film properties.Here we report the growth of CN_x and Ti films, simultaneously deposited in the co-rotating and static IPLD arrangements. The homogeneity of the co-rotating films is described by a thickness inhomogeneity index, which allows for the comparison of films of different lateral dimension. A semi-analytical, semi-numerical model is proposed to derive the radial variation of the growth rate of co-rotating IPLD films from the lateral growth rate distributions measured along the symmetry axes of static IPLD films. The laterally averaged growth rate, LAGR is used to describe how the ambient pressure affects growth in the 0.5–50Pa domain. As an example, the absolute error between the measured and calculated radial growth rate variation, obtained at 5Pa, was less than 3%, while the LAGR of CN_x layers grown by co-rotating IPLD was predicted with 20% accuracy.

Keywords: Pulsed laser deposition; Large area; Thickness homogenization; Thickness inhomogeneity index (TII)

Hydrogen doping of MgO thin films prepared by pulsed laser deposition by M. Kodu; M. Aints; T. Avarmaa; V. Denks; E. Feldbach; R. Jaaniso; M. Kirm; A. Maaroos; J. Raud (pp. 5328-5331).

▶ Hydrogen doped MgO films grown by pulsed laser deposition method. ▶ Doping was provided by H₂ gas stored in cavities of milky MgO single crystal targets. ▶ H doping lowered the firing voltage up to 55V. ▶ The N₂ in the gas mixture lowered the FVs up to 38V.Hydrogen doped MgO films were grown by pulsed laser deposition method. Gaseous hydrogen stored in cavities of milky MgO single crystal targets provided doping in film deposition process. Clear MgO targets without hydrogen were used in the preparation of reference films. The influence of hydrogen doping on firing voltage (FV) of gas discharge and its AC frequency dependence was investigated. According to thermoluminescence experiments, the films grown from milky targets contained two kinds of electron traps with the activation energies of 0.051 and 0.31eV, while latter traps were absent in reference samples. The 0.31eV trap was assigned to the hydride ion H⁻ occupying an oxygen vacancy site in MgO crystal structure. Using standard gas mixture (Ne–10% Xe), FVs of hydrogen doped sample showed considerable frequency dependence and were up to 55V lower in comparison to the reference sample. The FVs of reference sample were shifted 14–28V to higher values when N₂ gas was added to the mixture. The N₂ addition lowered the FVs of hydrogen doped sample up to 38V and almost eliminated the FV frequency dependence.

Keywords: MgO; Plasma display panel; Gas discharge; Hydrogen; Doping; Thermoluminescence; Thin films

Characteristics of ZrC/ZrN and ZrC/TiN multilayers grown by pulsed laser deposition by D. Craciun; G. Bourne; G. Socol; N. Stefan; G. Dorcioman; E. Lambers; V. Craciun (pp. 5332-5336).

▶ ZrC, TiN and ZrN thin films and ZrC/TiN and ZrC/ZrN multilayers were deposited by laser ablation. ▶ These thin films and multilayers exhibited hardness values above 30GPa. ▶ Nanoindentation depths exceeded 10% of the films thickness.ZrC/ZrN and ZrC/TiN multilayers were grown on (100) Si substrates at 300°C by the pulsed laser deposition (PLD) technique using a KrF excimer laser. X-ray diffraction investigations showed that films were crystalline, the strain and grain size depending on the nature and pressure of the gas used during deposition. The elemental composition, analyzed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), showed that films contained a low level of oxygen contamination. Simulations of the X-ray reflectivity (XRR) curves acquired from films indicated a smooth surface morphology, with roughness below 1nm (rms) and densities very close to bulk values.Nanoindentation results showed that the ZrC/ZrN and ZrC/TiN multilayer samples exhibited hardness values between 30 and 33GPa, slightly higher than the values of 28–30GPa measured for pure ZrC, TiN and ZrN films.

Keywords: ZrC; ZrN; TiN; Pulsed laser deposition; Thin films; Multilayers

Nanocomposite oxide thin films grown by pulsed energy beam deposition by M. Nistor; A. Petitmangin; C. Hebert; W. Seiler (pp. 5337-5340).

Display Omitted▶ Indium tin oxide (ITO) films with large oxygen deficiency grown by PLD and PED. ▶ Nanocomposite ITO thin films with metallic In–Sn clusters embedded in oxide matrix. ▶ Metallic conductivity via percolation with a superconducting transition at about 6K. ▶ Melting and freezing of In–Sn clusters through resistivity measurements.Highly non-stoichiometric indium tin oxide (ITO) thin films were grown by pulsed energy beam deposition (pulsed laser deposition-PLD and pulsed electron beam deposition-PED) under low oxygen pressure. The analysis of the structure and electrical transport properties showed that ITO films with a large oxygen deficiency (more than 20%) are nanocomposite films with metallic (In, Sn) clusters embedded in a stoichiometric and crystalline oxide matrix. The presence of the metallic clusters induces specific transport properties, i.e. a metallic conductivity via percolation with a superconducting transition at low temperature (about 6K) and the melting and freezing of the In–Sn clusters in the room temperature to 450K range evidenced by large changes in resistivity and a hysteresis cycle. By controlling the oxygen deficiency and temperature during the growth, the transport and optical properties of the nanocomposite oxide films could be tuned from metallic-like to insulating and from transparent to absorbing films.

Keywords: Pulsed laser deposition; Pulsed electron beam deposition; Nanocomposite thin films; Indium tin oxide; Superconducting transition; Metallic clusters

Nanostructured PLD-grown gadolinia doped ceria: Chemical and structural characterization by transmission electron microscopy techniques by K. Rodrigo; H.J. Wang; S. Heiroth; N. Pryds; L. Theil Kuhn; V. Esposito; S. Linderoth; J. Schou; T. Lippert (pp. 5341-5346).

The morphology as well as the spatially resolved elemental and chemical characterization of 10mol% gadolinia doped ceria (CGO10) structures prepared by pulsed laser deposition (PLD) technique are investigated by scanning transmission electron microscopy accompanied with electron energy loss spectroscopy and energy dispersive X-ray spectroscopy. A dense, columnar and structurally inhomogeneous CGO10 film, i.e. exhibiting grain size refinement across the film thickness, is obtained in the deposition process. The cerium M_4,5 edges, used to monitor the local electronic structure of the grains, indicate apparent variation of the ceria valence state across and along the film. No element segregation to the grain boundaries is detected. These results are discussed in the context of solid oxide fuel cell applications.

Keywords: Key words; Gadolinia doped ceria; Ceria valence state; Pulsed laser deposition; Transmission electron microscopy; Electron energy loss spectroscopy; Thin films

Glassy carbon – A promising substrate material for pulsed laser deposition of thin Li1+_xMn₂O4−_δ electrodes by F. Simmen; M. Horisberger; B. Seyfang; T. Lippert; P. Novák; M. Döbeli; M. Mallepell; C.W. Schneider; A. Wokaun (pp. 5347-5353).

▶ The spinel LiMn₂O₄ is a promising candidate for future battery applications. ▶ Spinel thin films are used as model system to study the solid electrolyte interphase formation. ▶ Good electrochemical properties of LiMn₂O₄ films grown on glassy carbon substrates. ▶ Poor adhesion of LiMn₂O₄ on glassy carbon can be considerably improved.The spinel LiMn₂O₄ is a promising candidate for future battery applications. If used as a positive electrode in a battery, the charging capacity of such a battery element is limited by the formation of a solid electrolyte interphase like layer between the electrolyte and the spinel. To study the electrolyte–electrode interaction during electrochemical cycling, spinel thin films are deposited as model electrodes on glassy carbon substrates by pulsed laser ablation. The obtained polycrystalline oxide thin films show a well defined surface morphology and are electrochemical active. Adhesion of these thin films on glassy carbon is in general poor, but can be improved considerably by a surface pretreatment or adding a thin metallic coating to the substrate prior deposition. The best adhesion is obtained for films deposited on argon plasma pretreated as well as Pt coated glassy carbon substrates. During the electrochemical characterization of Li_1.06Mn₂O_3.8 thin film electrodes, no additional reactions of the substrate are observed independent of the used electrolyte. The best cycle stability is achieved for films on Pt coated glassy carbon substrates.

Keywords: Pulsed laser ablation; Battery; Thin films

Oxygen deficiency in oxide films grown by PLD by Y. Davila; A. Petitmangin; C. Hebert; J. Perrière; W. Seiler (pp. 5354-5357).

▶ The incorporation of oxygen atoms in oxide films grown by pulsed laser deposition depends upon the oxygen pressure and laser power density.The incorporation of oxygen atoms in oxide films grown by pulsed laser deposition depends upon the oxygen pressure and laser power density. By carefully controlling these two parameters it is possible to control the oxygen deficiency in the samples, and thus to change their physical properties from insulating and transparent to absorbing and conducting. By using X-ray diffraction, Rutherford backscattering spectroscopy and resistivity measurements, we show that depending upon the oxide materials oxygen deficiency in the films can induce either the growth of stable sub-oxide phases or the formation of nanocomposite films by phase separation. The first case corresponds to oxides with a mixed valency cation like Ti, which leads to the formation of stable, crystalline and highly conductive TiO_x sub-oxide phases. The second case is well described by the indium tin oxides (ITO) in which a large oxygen deficiency leads to metallic clusters embedded into a stoichiometric matrix, i.e. nanocomposite films. This phenomenon is due to the fact that sub-oxides of these compounds are not stable and thus the oxygen deficiency induced a phase separation.

Keywords: Oxygen incorporation; Pulsed laser deposition; Nanocomposite films; Transport properties

Pulsed laser ablation of GaAs using nano pulse length by P. Dubček; B. Pivac; S. Milošević; N. Krstulović; Z. Kregar; S. Bernstorff (pp. 5358-5361).

▶ GISAXS and AFM are compared to study the morphology of GaAs nanostructures deposited by PLD. ▶ the results of two techniques are in good agreement, despite the different resolutions. ▶ nanoparticle size and size distribution is controlled by the number of pulses applied.Ablation using very short pulses has shown a great promise in facilitating the growth of complex multi-element films with stoichiometries matching those of their parent materials. GaAs is an important material in the electronic and opto-electronic industries and due to its compound structure it is an intriguing candidate for pulsed laser deposition. This work investigates the effect of nanosecond laser pulse lengths on the ablation of GaAs in an inert atmosphere. The number of pulses was varied in order to find the optimal condition for nano particles formation in our setup. The deposited structures were studied by grazing incidence small angle X-ray scattering and atomic force microscopy. It is shown that the GaAs nanoparticle sizes and size distributions can be controlled partly by the number of laser pulses applied in their production.

Keywords: Pulsed laser deposition; GaAs; Grazing angle small angle X-ray scattering; Atomic force microscopy

Pulsed laser deposition of polymer–metal nanocomposites by Felix Schlenkrich; Susanne Seyffarth; Britta Fuchs; Hans-Ulrich Krebs (pp. 5362-5365).

Different polymer–metal nanocomposites, metal clusters on a polymer surface and for the first time also polymer/metal multilayers, were pulsed laser deposited at a wavelength of 248nm. Poly(methyl methacrylate) (PMMA) and Bisphenol A dimeth-acrylate (BisDMA), which strongly differ in their hardness of 3 and 180N/mm², respectively, were taken as polymer components. Metals Ag and Cu were chosen because of their different reactivity to polymers. When depositing Ag on PMMA, spherical clusters are formed due to high diffusion and total coalescence. For Cu, much smaller grains with partially elongated shapes occur because of lower diffusivity and incomplete coalescence. Compared to the results on the soft PMMA, the clusters formed on the harder BisDMA are much larger due to higher diffusivity on this underlayer. In PMMA/Cu multilayers, wavy layered structures and buckling is observed due to relaxation of compressive stress in the Cu layers. Smooth Cu layers with higher thicknesses can only be obtained, when the hardness of the polymer is sufficiently high, as in the case of BisDMA/Cu multilayers.

Keywords: Pulsed laser deposition; Nanocomposites; Cluster; Multilayer; Polymer–metal

ZnO nanoparticles produced by novel reactive physical deposition process by P. Thangadurai; I. Zergioti; S. Saranu; C. Chandrinou; Z. Yang; D. Tsoukalas; A. Kean; N. Boukos (pp. 5366-5369).

▶ Deposition of ZnO nanoparticles using a novel physical deposition process. ▶ Control of particles density and size. ▶ Structure and chemistry studied by transmission electron microscopy. ▶ Optical properties studied by photoluminescence.This paper reports the deposition of ZnO nanoparticles with controlled sizes and different particle densities and their structural, composition and optical properties. They were deposited by means of a DC magnetron based vacuum nanoparticle source onto different substrates (GaAs, Si and Ti/SiO₂/Si). We believe that this is the first time that such nanoparticles have been produced using this unique technique. Zinc was used as sputtering target to produce zinc nanoparticles which were oxidized in-line using molecular oxygen. The structural properties and chemistry of the ZnO were studied by transmission electron microscopy. An average particle size of 6(±2)nm was produced with uniform size distribution. The particle density was controlled using a quartz crystal monitor. Surface densities of 2.3×10¹¹/cm², 1.1×10¹³/cm² and 3.9×10¹³/cm² were measured for three different deposition runs. The ZnO particles were found to be single crystalline having hexagonal structure. Photoluminescence measurements of all samples were performed at room temperature using a cw He–Cd laser at 325nm excitation. The UV emission around 375nm at room temperature is due to excitonic recombination and the broad emission centered at 520nm may be attributed to intrinsic point defects such as oxygen interstitials.

Keywords: ZnO particles; Photoluminescence

Structural characterization of AlN films synthesized by pulsed laser deposition by A. Szekeres; Zs. Fogarassy; P. Petrik; E. Vlaikova; A. Cziraki; G. Socol; C. Ristoscu; S. Grigorescu; I.N. Mihailescu (pp. 5370-5374).

▶ We obtained AlN thin films by PLD in low-pressure N₂ from an AlN target with a pulsed KrF* excimer laser. ▶ TEM and XRD studies showed a strong dependence of the film structure on the N₂ content. ▶ The films grown at low nitrogen pressure (0.1Pa) were prevalently amorphous. ▶ Increasing N₂ pressure to 10Pa promotes the growth of cubic (≤ 10nm) crystallites.We obtained AlN thin films by pulsed laser deposition (PLD) from a polycrystalline AlN target using a pulsed KrF* excimer laser source (248nm, 25ns, intensity of ∼4×10⁸W/cm², repetition rate 3Hz, 10J/cm² laser fluence). The target–Si substrate distance was 5cm. Films were grown either in vacuum (10⁻⁴Pa residual pressure) or in nitrogen at a dynamic pressure of 0.1 and 10Pa, using a total of 20,000 subsequent pulses. The films structure was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and spectral ellipsometry (SE). Our TEM and XRD studies showed a strong dependence of the film structure on the nitrogen content in the ambient gas. The films deposited in vacuum exhibited a high quality polycrystalline structure with a hexagonal phase. The crystallite growth proceeds along the c-axis, perpendicular to the substrate surface, resulting in a columnar and strongly textured structure. The films grown at low nitrogen pressure (0.1Pa) were amorphous as seen by TEM and XRD, but SE data analysis revealed ∼1.7vol.% crystallites embedded in the amorphous AlN matrix. Increasing the nitrogen pressure to 10Pa promotes the formation of cubic (≤10nm) crystallites as seen by TEM but their density was still low to be detected by XRD. SE data analysis confirmed the results obtained from the TEM and XRD observations.

Keywords: Polycrystalline Aln thin films; Structural investigations; Pulsed laser deposition

Synthesis of nanocrystalline magnesium nitride (Mg₃N₂) powder using thermal plasma by Dong-Wook Kim; Tae-Hee Kim; Hyun-Woo Park; Dong-Wha Park (pp. 5375-5379).

▶ Nitrogen addition in plasma promoted the vaporization of magnesium. ▶ Injection of NH₃ in low temperature region improves the crystallinity of Mg₃N₂. ▶ The reaction mechanism can be written as: 2NH₃→2N+6H (at interface of Mg gas and NH₃); (2) 3Mg(g)+2N(g)→Mg₃N₂; overall reaction: 3Mg(g)+2NH₃(g)→Mg₃N₂+3H₂.Nanocrystalline magnesium nitride (Mg₃N₂) powder was synthesized from bulk magnesium by thermal plasma at atmospheric pressure. Magnesium vapor was generated through heating the bulk magnesium by DC plasma jet and reacted with ammonia gas. Injecting position and flow rates of ammonia gas were controlled to investigate an ideal condition for Mg₃N₂ synthesis. The synthesized Mg₃N₂ was cooled and collected on the chamber wall. Characteristics of the synthesized powders for each experimental condition were analyzed by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and thermogravity analysis (TGA). In absence of NH₃, magnesium metal powder was formed. The synthesis with NH₃ injection in low temperature region resulted in a formation of crystalline magnesium nitride with trigonal morphology, whereas the mixture of magnesium metal and amorphous Mg₃N₂ was formed when NH₃ was injected in high temperature region. Also, vaporization process of magnesium was discussed.

Keywords: PACS; 52.77.−j; 81.07.WxMagnesium nitride; Plasma

Pure and Nb-doped TiO_1.5 films grown by pulsed-laser deposition for transparent p–n homojunctions by E. Le Boulbar; E. Millon; J. Mathias; C. Boulmer-Leborgne; M. Nistor; F. Gherendi; N. Sbaï; J.B. Quoirin (pp. 5380-5383).

▶ Novel p-n homojunctions based on TCO thin films. ▶ Junctions resulting from stacking of two Ti–O phases deposited on a transparent substrate. ▶ Pure TiO_1.5 film acts as p-type semiconductor. ▶ TiO_1.5 doped with Nb film is n-type semiconductor. ▶ Rectifying behaviour characterized with a turn-on voltage of 2.45V.Pure and Nb-doped titanium oxide thin films were grown on sapphire substrates by pulsed-laser deposition in vacuum (10⁻⁷mbar). The PLD growth leads to titanium oxide thin films displaying a high oxygen deficiency (TiO_1.5) compared with the stoichiometric TiO₂ compound. The structural and electrical properties (phase, crystalline orientation, nature and concentration of charge carriers, etc.) of these titanium oxide films were studied by XRD measurements and Hall effect experiments, respectively. The undoped TiO_1.5 phase displayed a p-type semiconductivity. Doping this titanium oxide phase with Nb⁵⁺ leads to an n-type behaviour as is generally observed for titanium oxide films with oxygen deficiency (TiO_x with 1.7< x<2). Multilayer homojunctions were obtained by the stacking of TiO_1.5 (p-type) and Nb-TiO_1.5 (n-type) thin films deposited onto sapphire substrates. Each layer is 75nm thick and the resulting heterostructure shows a good transparency in the visible range. Finally, the I– V curves obtained for such systems exhibit a rectifying response and demonstrate that it is possible to fabricate p–n homojunctions based only on transparent conductive oxide thin films and on a single chemical compound (TiO_x).

Keywords: Pulsed-laser deposition; Titanium oxide; Oxygen deficiency; p–n junction; Transparent conductive oxide

Studies of laser-induced removal mechanisms for tokamak-like particles by A. Vatry; A. Marchand; Ph. Delaporte; D. Grojo; C. Grisolia; M. Sentis (pp. 5384-5388).

The removal of metallic and carbon particles is a great issue in the framework of the ITER (International Thermonuclear Experimental Reactor) project. Indeed, the presence of these particles in the vessel of a tokamak leads to safety risks.The laser process seems to be a very promising solution for this cleaning. However, the process optimization requires a good knowledge of the removal mechanisms. For this purpose, we investigated the influence of beam parameters, such as laser pulse duration and wavelength, on the cleaning efficiency. In this paper, two kinds of particles are chosen to be studied, carbon aggregates and tungsten droplets, because they are typical of dust collected in tokamak.The results show an influence of beam parameters on the tungsten particles removal efficiency (PRE), whereas this influence is not significant for carbon particles.To help the understanding of the removal mechanisms, substrates and particles were inspected by scanning electron microscopy, before and after the irradiation.We will see on this paper that even if carbon and tungsten particles strongly absorb the different laser wavelength used, the removal mechanisms of these particles are very different.

Keywords: Laser; Removal; Fusion reactor; Absorbing particles; Tungsten; Carbon

Two-photon polymerization of an epoxy–acrylate resin material system by R.J. Winfield; S. O’Brien (pp. 5389-5392).

▶ New epoxy-acrylate resin material used in 2-photon polymerization. ▶ Epoxy-acrylate structures formed directly. ▶ Stable structures formed in novel material system.Improved material systems are of great interest in the development of two-photon polymerization techniques for the fabrication of three dimensional micro- and nano-structures. The properties of the photosensitive resin are important in the realisation of structures with submicron dimensions. In this study investigation of a custom organic resin, cross-linked by a two-photon induced process, using a femtosecond Ti:sapphire laser, is described. A structural, optical and mechanical analysis of the optimised material is presented. The influence of both material system and laser processing parameters on achievable micro-structure and size is presented as are representative structures. Parameters include: laser power, photo-initiator concentration and material composition.

Keywords: Two-photon polymerization (2PP); Material system; Epoxy; Acrylate

Effects of processing parameters on laser cutting of aluminium–copper alloys using off-axial supersonic nozzles by A. Riveiro; F. Quintero; F. Lusquiños; R. Comesaña; J. Pou (pp. 5393-5397).

▶ Laser processing in pulsed mode using a supersonic cutting head reduces the maximum cutting speed 2–3 times in comparison to CW-mode processing. ▶ Results indicate the existence of two processing regimes: the low ( f<100Hz) and high pulse frequency ( f>100Hz) regimes. ▶ Results reveal a better performance of the assist gas jet to remove molten material under the high pulse frequency regime. ▶ Maximum cutting speed achieved when processing under the high frequency regime. ▶ Superior cut quality obtained when processing under the high frequency regime.Conventional laser cutting involves the utilization of converging coaxial nozzles to inject the assist gas used to remove the molten material. This processing system prevents the utilization of this technique to cut aluminium alloys for aerospace applications. The inefficient removal of molten material by the assist gas produces cuts with poor quality; very rough cuts, with a large amount of dross, and a large heat affected zone (HAZ) are obtained. An alternative to increase the assist gas performance is the utilization of off-axial supersonic nozzles. Removal of molten material is substantially increased and cuts with high quality are obtained. On the other hand, pulsed laser cutting offers superior results during the processing of high reflectivity materials as aluminium alloys. However, there are no experimental studies which explore the pulsed laser cutting of aluminium alloys by means of a cutting head assisted by an off-axis supersonic nozzle.The present work constitutes a quantitative experimental study to determine the influence of processing parameters on the cutting speed and quality criteria during processing by means of off-axial supersonic nozzles. Cutting experiments were performed in pulsed mode and the results explained under the basis of the molten material removal mechanisms. Performed experiments indicate a reduction in cutting speed as compared to continuous wave (CW) mode processing and the existence of two processing regimes as a function of the pulse frequency. Best results are obtained under the high pulse frequency one ( f>100Hz) because the superior capabilities of molten material removal of the supersonic jets are completely exploited in this processing regime.

Keywords: Laser cutting; Supersonic nozzles; Pulsed mode; Al-2024T3

The effect of UV irradiation on nanocrysatlline zinc oxide thin films related to gas sensing characteristics by A.M. Soleimanpour; Yue Hou; Ahalapitiya H. Jayatissa (pp. 5398-5402).

▶ The effect of ultraviolet (UV) light irradiation on the nanocrystalline ZnO thin films was investigated. ▶ The degree of crystallinity, electrical conductivity, optical properties and surface properties of ZnO thin films were measured as a function of UV irradiation time. ▶ It was found that the degree of crystallinity and electrical properties of ZnO films were affected by UV irradiation. ▶ It was observed that the gas sensing properties were affected by the UV irradiation.The effect of ultraviolet (UV) light irradiation on the nanocrystalline ZnO thin films was investigated. The degree of crystallinity, electrical conductivity, optical properties and surface properties of ZnO thin films were measured as a function of UV irradiation time. It was found that the degree of crystallinity and electrical properties of ZnO films were affected by UV irradiation, however, no noticeable change in the surface morphology was observed. The gas sensing properties of as-deposited and UV irradiated films were also measured. It was observed that the gas sensing properties were affected by the UV irradiation. The irradiation time less than 5min has improved the sensor while the irradiation time more than 5min degraded the sensor characteristics for a UV power density of 2.45Wcm⁻².

Keywords: Zinc oxide; Thin film; Gas sensor; UV irradiation; Crystallinity; X-ray diffraction (XRD)

Cost-effective SU-8 micro-structures by DUV excimer laser lithography for label-free biosensing by F.J. Sanza; M.F. Laguna; R. Casquel; M. Holgado; C.A. Barrios; F.J. Ortega; D. López-Romero; J.J. García-Ballesteros; M.J. Bañuls; A. Maquieira; R. Puchades (pp. 5403-5407).

Cost-effective SU-8 micro-structures on a silicon substrate were developed using 248nm excimer laser KrF projection, studying the influence of the different variables on the final pattern geometry, finding out that the most critical are exposure dose and post-bake condition. Also a novel and cost effective type of photomask based on commercial polyimide Kapton produced by 355nm DPSS laser microprocessing was developed, studying the influence of the cutting conditions on the photomask. Finally, as a likely application the biosensing capability with a standard BSA/antiBSA immunoassay over a 10×10 micro-plates square lattice of around 10μm in diameter, 15μm of spacing and 400nm in height was demonstrated, finding a limit of detection (LOD) of 33.4ng/ml which is in the order of magnitude of bioapplications such as detection of cortisol hormone or insulin-like growth factor. Low cost fabrication and vertical interrogation characterization techniques lead to a promising future in the biosensing technology field.

Keywords: Microfabrication; SU-8; Photolithography; Excimer laser; Label-free biosensing

Effect of plasma confinement on laser shock microforming of thin metal sheets by M. Morales; J.A. Porro; J.J. García-Ballesteros; C. Molpeceres; J.L. Ocaña (pp. 5408-5412).

▶ Laser shocks can be applied to produce microforming. ▶ Plasma confination with just a drop of water increases dramatically the bending angle. ▶ Final bending can be controlled on a relative wide range by a stable quasi-proportional relation to the number of applied pulses. ▶ With every additional pulse the deformation is reduced showing saturation in the incremental deformation.Laser shock forming is conceived as a non-thermal laser forming method of thin metal sheets using the shock wave induced by laser irradiation to modify the target curvature. The plastic deformation induced by the shock wave and the direct plasma pressure applied on the material generate a residual stress distribution in the material finally leading to its bending. Using water as a confinement medium for the plasma the pressure can be increased around 10 times and the final deformation has a dramatic increase.The effect can be made clearly apparent in thin specimens (up to 1mm). In the present study thin (100μm) stainless steel (AISI 316) strips (1mm long and 300μm wide) in single and double pinned configurations have been investigated.A Nd:YAG Laser (1064nm) with 10ns of pulse length (FWHM) and an energy of 21mJ per pulse is focused in the strip (spot diameter of the spot=500μm).Experimental and numerical studies of the influence of plasma confinement in the process and number of applied pulses are presented.The study shows that the final bending of the specimens can be controlled on a relative wide range by a stable quasi-proportional relation to the number of applied pulses and, what is considered as of major importance, that plasma confinement increases the generated pressure and thus the bending in the target.Laser shock microforming in confined configuration is considered as a technique allowing the successful processing of components in a medium range of miniaturization.

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

Laser ablation of advanced ceramics and glass-ceramic materials: Reference position dependence by D. Sola; A. Escartín; R. Cases; J.I. Peña (pp. 5413-5419).

In this work, we present the effect produced by modifying the reference position as well as the method of machining on the results obtained when advanced ceramics and glass-ceramic materials are machined by laser ablation. A Q-switched Nd:YAG laser at its fundamental wavelength of 1064nm with pulsewidths in the nanosecond range has been used. Morphology, depth and volume obtained by means of pulse bursts and grooves have been studied. Working within the same laser conditions, it has been shown that these values depend on the thermal, optical and mechanical features of the material processed. We have also studied the variation in the ablation yield when the position of the surface to be machined is modified. Material properties and work conditions are related to the results obtained.We have described and discussed the morphology, composition, microstructure and hardness of the materials processed.

Keywords: Laser ablation; Glass-ceramic; Alumina; 8YSZ; Advanced ceramics; Reference position; Hardness

Implications of transient changes of optical and surface properties of solids during femtosecond laser pulse irradiation to the formation of laser-induced periodic surface structures by J. Bonse; A. Rosenfeld; J. Krüger (pp. 5420-5423).

Display Omitted▶ Fs laser pulses transiently turn the silicon into a metallic state. ▶ LIPSS formation is caused by the interference of the laser pulse with a surface plasmon. ▶ LIPSS affect the energy coupling for subsequent laser pulses during the feedback stage.The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of silicon wafer surfaces by linearly polarized Ti:sapphire femtosecond laser pulses (pulse duration 130fs, central wavelength 800nm) is studied experimentally and theoretically. In the experiments, so-called low-spatial frequency LIPSS (LSFL) were found with periods smaller than the laser wavelength and an orientation perpendicular to the polarization. The experimental results are analyzed by means of a new theoretical approach, which combines the widely accepted LIPSS theory of Sipe et al. with a Drude model, in order to account for transient (intra-pulse) changes of the optical properties of the irradiated materials. It is found that the LSFL formation is caused by the excitation of surface plasmon polaritons, SPPs, once the initially semiconducting material turns to a metallic state upon formation of a dense free-electron-plasma in the material and the subsequent interference between its electrical field with that of the incident laser beam resulting in a spatially modulated energy deposition at the surface. Moreover, the influence of the laser-excited carrier density and the role of the feedback upon the multi-pulse irradiation and its relation to the excitation of SPP in a grating-like surface structure is discussed.

Keywords: PACS; 79.20.Ds; 71.36.+c; 68.47.FgFemtosecond laser ablation; Laser-induced periodic surface structures (LIPSS); Optical properties; Surface plasmon polaritons; Semiconductors; Silicon

UV laser-induced high resolution cleaving of Si wafers for micro–nano devices and polymeric waveguide characterization by R. Casquel; M. Holgado; J.J. García-Ballesteros; K. Zinoviev; C. Férnandez-Sánchez; F.J. Sanza; C. Molpeceres; M.F. Laguna; A. Llobera; J.L. Ocaña; C. Domínguez (pp. 5424-5428).

▶ Laser cleaving with a high precision in position of the crack generated (in the order of microns). ▶ Highly smooth facets reached. For polymeric waveguides, this means three times more of amount of light coupled, and reducing the risk of damage of the chips. ▶ Technique of cleaving useful for a variety of chips of different materials, dimensions, thicknesses, orientation of silicon, among others.In this work we propose a method for cleaving silicon-based photonic chips by using a laser based micromachining system, consisting of a ND:YVO₄ laser emitting at 355nm in nanosecond pulse regime and a micropositioning system. The laser makes grooved marks placed at the desired locations and directions where cleaves have to be initiated, and after several processing steps, a crack appears and propagate along the crystallographic planes of the silicon wafer. This allows cleavage of the chips automatically and with high positioning accuracy, and provides polished vertical facets with better quality than the obtained with other cleaving process, which eases the optical characterization of photonic devices.This method has been found to be particularly useful when cleaving small-sized chips, where manual cleaving is hard to perform; and also for polymeric waveguides, whose facets get damaged or even destroyed with polishing or manual cleaving processing. Influence of length of the grooved line and speed of processing is studied for a variety of silicon chips. An application for cleaving and characterizing sol–gel waveguides is presented. The total amount of light coupled is higher than when using any other procedure.

Keywords: Laser cleaving; Micro–nano photonic chips; Polymeric waveguides; Silicon fracture

Large negative refractive index modification induced by irradiation of femtosecond laser inside optical glasses by Tomohiro Hashimoto; Shuhei Tanaka (pp. 5429-5433).

▶ The refractive index modification (Δ n) inside a several optical glasses were investigated. ▶ The Δ n was fabricated by the irradiation of femtosecond laser pulses. ▶ The glasses were silicate or borosilicate system containing BaO, TiO₂, or La₂O₃ as a metal oxide. ▶ The Δ n and the profiles were measured with the qualitative phase microscopy. ▶ A glass containing TiO₂ showed relatively large decrease of the Δ n, Δ n<−0.01.We report on the refractive index modification (Δ n) and its cross sectional profile of the created lines inside the different types of optical glasses, containing BaO, TiO₂, or La₂O₃ as a metal oxide. The lines were fabricated by scanning a stage and focusing the femtosecond laser pulses, 800nm wavelength, a 250kHz repetition rate and 200fs pulse duration, from the Ti:sapphire regenerative amplifier system. The Δ n measurements were performed with the qualitative phase microscopy technique. As a result, it was found that the Δ n and its sign are different depending on glass types. For example, in the glasses containing TiO₂, the Δ n became smaller in the modified region and some of them showed relatively large decrease of the Δ n, Δ n<−0.01, with about 10μm width. Such a glass material could be useful for the compact optics and optical devices.

Keywords: Femtosecond laser; Laser processing; Optical glass; Refractive index modification

Modifications in silver-doped silicate glasses induced by ns laser beams by E. Cattaruzza; M. Mardegan; E. Trave; G. Battaglin; P. Calvelli; F. Enrichi; F. Gonella (pp. 5434-5438).

▶ Ion exchange from molten salt bath can be used to dope silicate glasses (soda-lime and borosilicate) with Ag. ▶ With a suitable choice of the post-exchange treatments (thermal annealing and/or UV laser irradiation) it is possible to induce the silver aggregation, namely to obtain metal nanocluster composite glasses. ▶ The role of irradiation parameters and of the host matrix structure in the aggregation phenomena are investigated to better understand the formation and the dissolution of the nanoparticles. ▶ Thermal treatments are able to induce formation of aggregates of few silver ions (for low T annealing) and silver metal particles 2–3nm in size (for high T annealing). Laser irradiation was able to induce Ag nanoparticles formation in the as-exchanged soda-lime samples. ▶ In the previously annealed Ag-doped soda-lime samples, the laser irradiation with a very large number of consecutive pulses induces a fragmentation of the silver nanoparticles. ▶ No effects were observed by laser irradiation of the Ag-doped BK7 glass samples.Glass layers for planar light waveguides prepared by Ag–Na ion exchange of different silicate glasses in molten salt baths are annealed and/or irradiated with a laser beam in the UV region, with different energy density values and total pulse numbers. The samples are mainly characterized by optical absorption spectroscopy, luminescence spectroscopy, and Rutherford backscattering spectrometry, in order to determine the role of irradiation parameters and of the host matrix structure in the aggregation phenomena. Photoluminescence spectroscopy gave information regarding the presence of Ag multimeric aggregates, the primal seeds for the growing (nano)crystals. The appearance of the plasmon resonance band in the optical absorption spectra proved the formation of Ag clusters and allowed the evolution steps of the clusterization process to be followed as a function of the energy deposited during the laser irradiation.

Keywords: Ion exchange; Waveguides; Metal nanoparticles, Laser irradiation

Influence of ordering change on the optical and thermal properties of inflation polyethylene films by Junko Morikawa; Akihiro Orie; Yuta Hikima; Toshimasa Hashimoto; Saulius Juodkazis (pp. 5439-5442).

▶ Micro-scale fabrication inside HDPE inflation film was carried out with 0.5–2μm pitch. ▶ Thermal diffusivity was determined using a micro-scale sensor with the thermal wave method. ▶ Thermal diffusivity increases 20% by the femto-second laser structuring. ▶ Birefringence modulation as high as Δ n∼1×10⁻³ can be recorded with laser irradiating sites. ▶ The relaxing of main polymer orientation or local change ordering on a micro-scale is induced.Changes of thermal diffusivity inside femtosecond laser-structured volumes as small as few percent were reliably determined (with standard deviation less than 1%) with miniaturized sensors. An increase of thermal diffusivity of a crystalline high-density polyethylene (HDPE) inflation films by 10–20% from the measured (1.16±0.01)×10⁻⁷m²s⁻¹ value in regions not structured by femtosecond laser pulses is considerably larger than that of non-crystalline polymers, 0–3%. The origin of the change of thermal diffusivity are interplay between the laser induced disordering, voids’ formation, compaction, and changes in molecular orientation. It is shown that laser structuring can be used to modify thermal and optical properties. The birefringence and infrared spectroscopy with thermal imaging of CH₂ vibrations are confirming inter-relation between structural, optical, and thermal properties of the laser-structured crystalline HDPE inflation films. Birefringence modulation as high as Δ n∼±1×10⁻³ is achieved with grating structures.

Keywords: PACS; 81.07.−b; 91.60.Hg; 61.46.−wThermal diffusivity; Femto-second laser structuring; Polymers; High density polyethylene

Modeling of femtosecond ablation of aluminum film with single laser pulses by A.V. Mazhukin; V.I. Mazhukin; M.M. Demin (pp. 5443-5446).

▶ Laser ablation dynamics for Al with 100fs, 3.95×10¹²W/cm² pulses wavelength 0.8μm. ▶ Non-equilibrium two-temperature model with hydrodynamic Stephan problem was used. ▶ Explicit tracking of boundaries permits exact determination of their velocities. ▶ High front velocities are caused by strong overheating of solid and liquid phases.Detailed investigation of pulsed laser ablation dynamics is performed for aluminum target under action of 100fs pulses with peak intensity 3.95×10¹²W/cm² and wavelength 0.8μm.Non-equilibrium two-temperature model with hydrodynamic Stephan problem was used for modeling. Explicit tracking of moving interphase boundaries permits exact determination of their velocity and amount of removed and evaporated material. Detailed ablation process is analyzed using the study of temperature, pressure and density evolution in the target. High phase front velocities (melting up to 5km/s and evaporation up to 350m/s) are caused by strong overheating of solid and liquid phases.

Keywords: Modeling; Femtosecond; Ablation; Non-equilibrium; Phase transition

Application of LIBS and TMA for the determination of combustion predictive indices of coals and coal blends by T. Ctvrtnickova; M.P. Mateo; A. Yañez; G. Nicolas (pp. 5447-5451).

▶ Problem of slagging propensity of coals in the energetic industry. ▶ Combination of Laser-Induced Breakdown Spectroscopy and Thermo-Mechanical Analysis. ▶ Prediction of the slagging undesirable phenomenon in coal fired power plants.Presented work brings results of Laser-Induced Breakdown Spectroscopy (LIBS) and Thermo-Mechanical Analysis (TMA) of coals and coal blends used in coal fired power plants all over Spain. Several coal specimens, its blends and corresponding laboratory ash were analyzed by mentioned techniques and results were compared to standard laboratory methods. The indices of slagging, which predict the tendency of coal ash deposition on the boiler walls, were determined by means of standard chemical analysis, LIBS and TMA. The optimal coal suitable to be blended with the problematic national lignite coal was suggested in order to diminish the slagging problems.Used techniques were evaluated based on the precision, acquisition time, extension and quality of information they could provide. Finally, the applicability of LIBS and TMA to the successful calculation of slagging indices is discussed and their substitution of time-consuming and instrumentally difficult standard methods is considered.

Keywords: Laser-Induced Breakdown Spectroscopy (LIBS); Thermo-mechanical analysis (TMA); Coal blends; Predictive indices

Combination of RF-plasma jet and Laser-induced plasma for breakdown spectroscopy analysis of complex materials by J.D. Pedarnig; J. Heitz; E.R. Ionita; G. Dinescu; B. Praher; R. Viskup (pp. 5452-5455).

▶ Laser induced breakdown spectroscopy (LIBS) is combined with secondary excitation. ▶ An atmospheric pressure RF plasma jet is used for secondary excitation in air. ▶ LIBS intensity of minor and major element emission lines is significantly increased. ▶ Ionization degree and plasma temperature are increased depending on time.Laser-induced breakdown spectroscopy method is modified using an external radiofrequency (RF) plasma jet that overlaps spatially with the laser-induced plasma. Short UV laser pulses (wavelength 193nm) are employed to ablate iron oxide ceramics, zinc oxide ceramics and polyethylene pressed pellets in ambient air background. An RF generator (frequency 13.56MHz, power ≤1kW) and a gas nozzle system are employed to generate a continuous jet of argon and nitrogen plasma expanding into air. The optical emission of the overlapped plasma is analyzed using an Echelle spectrometer equipped with an intensified CCD camera. The time dependence of optical emission intensities and of plasma parameters is investigated by varying the spectrometer delay time with respect to the laser pulse. The emission intensities of major (Fe, Zn) and minor (Mn, Al) elements are moderately increased with the RF plasma jet (≤2×). The intensities of atomic lines and molecular bands from ablated polymer material are increased also.

Keywords: PACS; 32.30.−r; 33.20.−t; 52.38.Mf; 52.75.Hn; 82.80.−dLaser ablation; Laser-induced breakdown spectroscopy; Atmospheric pressure plasma torch; Radiofrequency plasma; Oxide materials; Polymers

Interaction of gold nanoparticles with nanosecond laser pulses: Nanoparticle heating by N.N. Nedyalkov; S.E. Imamova; P.A. Atanasov; R.A. Toshkova; E.G. Gardeva; L.S. Yossifova; M.T. Alexandrov; M. Obara (pp. 5456-5459).

▶ Nanosecond laser radiation at λ=532nm results in efficient heating of gold nanoparticles. ▶ The laser heating can be sufficient to modify material located in close vicinity of the particle, as the affected zone is comparable to the particle size. ▶ Gold nanoparticle-assisted photothermal therapy of cancer cells demonstrates the potential of this method in efficient treatment of cancer.Theoretical and experimental results on the heating process of gold nanoparticles irradiated by nanosecond laser pulses are presented. The efficiency of particle heating is demonstrated by in-vitro photothermal therapy of human tumor cells. Gold nanoparticles with diameters of 40 and 100nm are added as colloid in the cell culture and the samples are irradiated by nanosecond pulses at wavelength of 532nm delivered by Nd:YAG laser system. The results indicate clear cytotoxic effect of application of nanoparticle as more efficient is the case of using particles with diameter of 100nm. The theoretical analysis of the heating process of nanoparticle interacting with laser radiation is based on the Mie scattering theory, which is used for calculation of the particle absorption coefficient, and two-dimensional heat diffusion model, which describes the particle and the surrounding medium temperature evolution. Using this model the dependence of the achieved maximal temperature in the particles on the applied laser fluence and time evolution of the particle temperature is obtained.

Keywords: Gold nanoparticles; Plasmons; Photothermal therapy

Recent developments in the formation and structure of tin–iron oxides by laser pyrolysis by R. Alexandrescu; I. Morjan; F. Dumitrache; R. Birjega; C. Fleaca; I. Soare; L. Gavrila; C. Luculescu; G. Prodan; V. Kuncser; G. Filoti (pp. 5460-5464).

▶ Sn(1− x₎Fe_xO₂ nanoparticulate material at higher Fe doping levels was synthesized. ▶ Sn(1− x₎Fe_xO₂ samples exhibit rutile SnO₂ structure with increasing Fe doping. ▶⁵⁷Fe Mössbauer spectroscopy of tin–iron oxides reveals a magnetic ordered phase.Complex oxides demonstrate specific electric and magnetic properties which make them suitable for a wide variety of applications, including dilute magnetic semiconductors for spin electronics. A tin–iron oxide Sn1−_xFe_xO₂ nanoparticulate material has been successfully synthesized by using the laser pyrolysis of tetramethyl tin–iron pentacarbonyl–air mixtures. Fe doping of SnO₂ nanoparticles has been varied systematically in the 3–10at% range. As determined by EDAX, the Fe/Sn ratio (in at%) in powders varied between 0.14 and 0.64. XRD studies of Sn1−_xFe_xO₂ nanoscale powders, revealed only structurally modified SnO₂ due to the incorporation of Fe into the lattice mainly by substitutional changes. The substitution of Fe³⁺ in the Sn⁴⁺ positions (Fe³⁺ has smaller ionic radius as compared to the ionic radius of 0.69Å for Sn⁴⁺) with the formation of a mixed oxide Sn1−_xFe_xO₂ is suggested. A lattice contraction consistent with the determined Fe/Sn atomic ratios was observed. The nanoparticle size decreases with the Fe doping (about 7nm for the highest Fe content). Temperature dependent⁵⁷Fe Mössbauer spectroscopy data point to the additional presence of defected Fe³⁺-based oxide nanoclusters with blocking temperatures below 60K. A new Fe phase presenting magnetic order at substantially higher temperatures was evidenced and assigned to a new type of magnetism relating to the dispersed Fe ions into the SnO₂ matrix.

Keywords: Tin oxide; Nanoparticles; Laser pyrolysis; Fe doped SnO; ₂; Tin–iron oxides; Mössbauer spectroscopy

The laser polarization as control parameter in the formation of laser-induced periodic surface structures: Comparison of numerical and experimental results by Olga Varlamova; Jürgen Reif; Sergey Varlamov; Michael Bestehorn (pp. 5465-5469).

▶ Self-organized surface patterns. ▶ Femtosecond laser ablation. ▶ Effect of laser polarization. ▶ Nonlinear-dynamic surface erosion model for laser-induced surface patterning.Considering self-organized surface pattering upon multi-pulse femtosecond laser irradiation, in particularly the strong dependence of ripples orientation on the laser polarization, we present numerical simulations from an adopted surface erosion model and compare the result to our experimental data on laser-induced nanostructures formation. We present the surface morphologies obtained by this model for different polarizations of the incident laser electric field and show good agreement with ripple formation produced by laser ablation experiments. The correlation of ripples orientation with laser polarization can be described within a model where the polarization causes a breaking of symmetry at the surface. Further we discuss a time evolution of pattern formation. Our results support the non-linear self-organization mechanism of pattern formation on the surface of solids.

Keywords: Self-organized structure formation; Femtosecond laser ablation; Laser induced instability; Laser polarization as control parameter

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Applied Surface Science (v.257, #12)

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Applied Surface Science (v.257, #12)