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This research is focused on investigation of coupled plasmonic/metal-semiconductor nanomaterials. A two-step laser-assisted method is demonstrated for formation of plasmonic Ag nanoparticles (NPs) distributed into porous metal–oxide semiconductors. The mosaic Ag-ZnO target is used for laser ablation and, subsequently, laser annealing of the deposited layer is applied. The plasmon resonance properties of the nanostructures produced are confirmed by optical transmission spectroscopy. The wurtzite structure of ZnO is formed with tilted c-axis orientation and, respectively, a mixed Raman mode appears at 580 cm−1. The oxygen pressure applied during a deposition process has impact on the morphology and thickness of the porous nanostructures, but not on the size and size distribution of AgNPs. The porous nanocomposites exhibited potential for SERS applications, most pronounced for the oxygen deficient sample, grown at lower oxygen pressure. The observed considerable SERS enhancement of R6G molecules on AgNP/ZnO can be attributed to the ZnO-to-molecule charge transfer contribution, enhanced by the additional electrons from the local surface plasmon resonance (LSPR) of AgNPs to the ZnO through the conduction band.

We study semi-regular arrays of Au nanoparticles (NP) obtained via UV laser irradiation of thin Au films on glass substrate. The NP structures are prepared from films of a thickness up to 60 nm produced by discharge sputtering or pulsed laser deposition, and annealed by nanosecond laser pulses at 266 or 308 nm, respectively, at fluencies in the range of 60–410 mJ/cm2. For the rare- and close-packed NP structures, consistent description of optical properties is derived from microscopic observation, measurements of the absorption, and Raman spectra, and modeling of the near-field intensity distributions. The absorption bands centered at 540–570 nm are ascribed to resonant absorption of the surface plasmons. For the band positions, half widths, and intensities, the dependence on the NP shape (partial spheres), size, size distribution, and also excitation energy is observed. The structures are characterized by markedly reduced dephasing times of ∼3 fs. It is shown, that laser annealing of thin Au films provides reliable and cost effective method for controlled preparation of semi-regular NP arrays favorable for photonic applications.

We demonstrate the possibility to fabricate wire structures composed by arranged magnetic particles using pulsed laser deposition (PLD) in the presence of a magnetic field. Ablation of Ni and Co targets was performed in air by nanosecond laser pulses delivered by a Nd:YAG laser system oscillating at 355 nm. Due to the high density of the ambient, particles and clusters were formed by condensation in the plasma plume close to the target. The strong deceleration of the ablated material under these conditions further benefited the efficiency of applying a magnetic field to the plume. We also studied the effect of the target-to-substrate distance and the ambient pressure on the morphology of the deposited structures.

The medical-grade polydimethylsiloxane (PDMS) elastomer is a widely used biomaterial in medicine for preparation of high-tech devices because of its remarkable properties. In this paper, we present experimental results on surface modification of PDMS elastomer by using ultraviolet, visible, and near-infrared ns-laser system and investigation of the chemical composition and the morphological structure inside the treated area in dependence on the processing parameters – wavelength, laser fluence and number of pulses. Remarkable chemical transformations and changes of the morphological structure were observed, resulting in the formation of a highly catalytically active surface, which was successfully functionalized via electroless Ni and Pt deposition by a sensitizing-activation free process. The results obtained are very promising in view of applying the methods of laser-induced micro- and nano-structuring and activation of biopolymers' surface and further electroless metal plating to the preparation of, e.g., multielectrode arrays (MEAs) devices in neural and muscular surface interfacing implantable systems.

This study deals with the development of a novel technique for formation of advanced Ag nanostructures (NSs) to be applied to high-resolution analyses based on surface enhanced Raman scattering (SERS). It has direct bearing on human health and food quality, e.g., monitoring small amount or traces of pollutants or undesirable additives. Three types of nanostructured Ag samples were produced using ion-beam deposition at glancing angle (GLAD) on quartz. All fabricated structures were covered with BI-58 pesticide (dimethoate) or Rhodamine 6G (R6G) for testing their potential for use as substrates for (SERS).

The process of formation and the characteristics are studied of noble metal nanostructures created by pulsed laser ablation in vacuum. Femtosecond (fs) and nanosecond (ns) laser systems lasing at different wavelengths are used. Several different modifications of the pulsed lased deposition (PLD) technique, as off-axis deposition and glancing angle deposition configurations are used to create nanostructures. Laser annealing of single or bimetal thin films is used to fabricate alloyed nanostructures. The possibility is demonstrated of tuning the optical properties of gold nanostructures on flexible substrates. Different experimental techniques, as fast photography, optical emission spectroscopy, FE-SEM, AFM, TEM, and Raman spectroscopy are applied to characterize the noble metallic nanostructures produced. The optical spectra of the Au and Ag nanostructures are also studied experimentally and theoretically. The theoretical simulation methods used are: molecular dynamic (MD), finite difference time domain (FDTD) and a method based on the generalized multi-particle Mie (GMM) theory. Applications of noble metal nanostructures to surface enhanced Raman spectroscopy (SERS) and biophotonics are briefly considered.

Simultaneous laser action from HF and N/sub 2/ is obtained, from a plasma cathode TEA laser, for the first time. The sliding discharge along the surface of a dielectric is used as a plasma cathode, for the main volumetric discharge. The laser operates at atmospheric pressure, with a gas mixture of SF/sub 6/:C/sub 3/H/sub 8/:N/sub 2/:He. For a typical flow rate ratio of 0.27:0.024:0.2:19.8 1 min/sup -1/, it produces simultaneously 160 mJ HF and 0.6 mJ N/sub 2/ laser outputs at 0.43% and 1.4/spl times/10/sup -3/% efficiencies respectively, at the moderate charging voltage of 28.5 kV. These output characteristics are obtained from a small active discharge volume and length of 10/sup 6/ cm/sup 3/ and 38 cm respectively. These values extend the performance, recently reported in the literature, of a sliding discharge HF/N/sub 2/ laser with corresponding simultaneous energy outputs of 12 mJ HF and 1.1 mJ N/sub 2/, to a higher energy output level, thus making the device suitable for a broader range of applications. This novel dual wavelength HF/N/sub 2/ laser system presented, can be particularly convenient for medical experiments, where the IR beam can be used for tissue ablation, while the UV beam can be used as the excitation source for fluorescence spectroscopic measurements, for the evaluation of the ablation process. Details are presented on the dependence of the laser performance parameters, such as output energy, discharge voltage and current and structure of the laser output pulses on the mixture composition and the circuit parameters.

The medical-grade polydimethylsiloxane (PDMS) elastomer is a widely used biomaterial in medicine and for preparation of high-tech devices because of its remarkable properties. In this work, we present the experimental results on drilling holes on the PDMS surface by using ultraviolet, visible or near-infrared ns-laser pulses and on studying the changes of the chemical composition and structure inside the processed areas. The material in the zone of the holes is studied by XRD, ?-Raman analyses and 3D laser microscopy in order to obtain information on the influence of different processing laser parameters, as wavelength, fluence and number of consecutive pulses on the material transformation and its modification.

For the laser drilling of aluminum nitride ceramic the processing results and the effects related to pulsed irradiation were investigated. Images of the drilled surface revealed regular, cylindrically shaped holes of about 100 μm in diameter independently of the laser wavelength (1064/532/355 or 266 nm). The holes were surrounded by circular heat-affected zones of larger diameter. A comparison of the elemental compositions of the original material and the processed one indicated a decrease of the nitrogen concentration in the affected area. The spectral analysis of the ablated material composition revealed the presence of ions and neutrals in dependence on the laser intensity applied. It was found that at intensity values close to the ablation threshold the ejected material consisted mainly of neutrals, while doubling of the intensity resulted in appearance of single-ionized Al species, which were also observed together with Al clusters in the mass spectra of the UV-excited plasma. Their prevailing content was revealed for drilling at higher intensities around 15 GW/cm2 at 532 nm. Results of model calculations indicated, in agreement with the experiment, that at the threshold the ceramic decomposes into gaseous nitrogen and solid Al particulates, while at a higher fluence the material particles vaporize and influence the quality of drilling. © 2007 Elsevier B.V. All rights reserved.

Thin Er, Yb co-doped Y2O3 films were grown by pulsed laser deposition from ceramic target. Subsequent ion implantation with 1.1 MeV Er+ ions to a fluence of 6 × 1014 at/cm2 at room temperature was performed in order to modify the structure of the as-deposited films. The as-deposited films have a polycrystalline column-like structure. Ion implantation induces defects into the as-deposited films. After annealing at 900 °C for 1 h in oxygen atmosphere, the films recrystallize in roundly shaped grain-like structure with grain size of about 100 nm. The Er3+ photoluminescence response was obtained for all the films by excitation through cross-relaxation of Yb3+ ions. The IR emission spectrum, consisting of two narrow peaks at 1415 and 1514 nm, differs from the typical spectra of Er-doped materials. The VIS emission spectrum observed in as-deposited films does not appear after implantation and subsequent 900 °C annealing. © 2007 Elsevier B.V. All rights reserved., This work was supported in part by EU project NANOPHOS, Contract IST-2001-39112 and by the Bulgarian Ministry of Education and Science under Contract MUF-1511.

Optically active Er3+:Yb3+ codoped Y 2O3 films have been produced on c-cut sapphire substrates by pulsed laser deposition from ceramic Er:Yb:Y2O3 targets having different rare-earth concentrations. Stoichiometic films with very high rare-earth concentrations (up to 5.5 × 1021 at cm - 3) have been achieved by using a low oxygen pressure (1 Pa) during deposition whereas higher pressures lead to films having excess of oxygen. The crystalline structure of such stoichiometric films was found to worsen the thicker the films are. Their luminescence at 1.53 μm and up-conversion effects have been studied by pumping the Yb3+ at 0.974 μm. The highest lifetime value (up to 4.6 ms) is achieved in films having Er concentrations of ≈ 3.5 × 1020 at cm- 3 and total rare-earth concentration ≈ 1.8 × 1021 at cm- 3. All the stoichiometric films irrespective of their rare-earth concentration or crystalline quality have shown no significant up-conversion. © 2005 Elsevier B.V. All rights reserved., This work has been partially supported by the EU project NANOPHOS (Contract IST-2001-39112), by the Bulgarian National Science Foundation (Contract MUF-02/05), by the Spanish Ministry of Education and Science (Project MAT2000-1135-C02-02) and by the CSIC-Bulgarian Academy of Sciences bilateral cooperation program.

Optically active thin films on Si substrates have been produced by laser ablation of a Nd-doped potassium gadolinium tungstate (Nd:KGW) single crystal. Films grown at low oxygen pressures (< 0.6 mbar) are potassium-deficient and appear to be mainly disordered. They show a poor photoluminescence (PL) performance that improves upon annealing in air at temperatures in the range 700-1000 °C. Films grown at high oxygen pressure (1 mbar) show instead good stoichiometry and the presence of a dominant textured gadolinium-tungstate phase compared to KGW. These films have low absorption, a refractive index close to that of bulk KGW and good PL performance, the emission lifetimes being longer (τ > 150 μs) under certain conditions than those measured in the single-crystal material. © Springer-Verlag 2001., This research was partially supported by CYCIT (Spain) under Project No. TIC1999-0866.

The paper presents a study of a physical method for fabrication of two-dimensional (2D) arrays composed of multi-component nanoparticles on a dielectric substrate. The method consists of two steps. In the first one, thin films composed of different metals are deposited by a classical PLD technique by using targets consisting of sections of different materials. Thin films composed of mixtures of different metals, as gold, silver, nickel, cobalt, iron, platinum, are thus deposited on a quartz substrate. By changing the area of the different sections in the target, thin films with different concentration of the metals are produced. The films fabricated are then annealed by nanosecond laser pulses delivered by a Nd:YAG laser system operating at its third harmonic. The modification of the films is studied as a function of the parameters of the incident radiation, as number of pulses and laser pulse fluence. It is found that the laser annealing can lead to a decomposition of the film into a monolayer of nanoparticles with a narrow size distribution. The optical properties of the structures produced are analyzed on the basis of their transmission spectra. The structures can be used in surface enhanced Raman spectroscopy (SERS) and magneto-optics.

In this work, ZnO nanostructures were fabricated on metal (a metal alloy containing Fe, Cr, Mn and Ni) coated silicon substrates by applying pulsed laser deposition. The samples were prepared at substrate temperatures in the range of 550 – 650 °C, oxygen pressure of 5 Pa, and laser fluence ≤ 1 J cm−2 i.e., process parameters usually used for thin-film deposition. We found that the metal layer's role is substantial in the preparation of nanostructures, the morphology of the catalyst layer determines the growth of the ZnO nanowalls and the increase of the process temperature leads to nanorods formation on the nanowalls.

The study prsented is focused on the optical properties of ZnO/AgNPs/ZnO multilayer nanocomposites. The optical properties of the nanostructures depend on the silver layer thickness. The optical spectral characteristics of Ag nanoparticles (AgNPs) nanostructured by laser irradiation in a ZnO medium were investigated theoretically and experimentally. The extinction spectrum was determined as a function of the nanoparticles size distribution and of the surrounding medium. The extinction efficiency calculated is red-shifted and broadened when the AgNPs are introduced in a ZnO environment. This result is in agreement with the experimental measurements, where the plasmon resonance peak position of the ZnO/AgNPs/ZnO composite is red-shifted, compared to the AgNPs/ZnO sample. Raisng the thickness of the Ag layer increases the resonance extinction. We also propose a method for controlling and tuning the SPR-based sensing of Ag nanoparticles in a ZnO medium.

3 pages, 3 figures., Thin Nd-doped potassium gadolinium tungstate [KGW or KGd(WO4)2] films are grown by pulsed laser deposition by ablation of a stoichiometric monocrystal target. Rutherford backscattering, x-ray diffraction, atomic force microscopy, and waveguide propagation analyses are performed. The as-grown films are optically active, as evidenced by the photoluminescence spectra centered at 1.068 µm. In some of the films, fine photoluminescence spectra between Stark levels are observed., This research was partially supported by the European Union, Project Nos. IC15-CT98-0807 and F-719 with the Ministry of Education and Science, Bulgaria. P.A.A. wishes to acknowledge the Scientific Committee of NATO, Spain, for financial support.

The subject of the present work is different types of nanostructured ZnO films produced by pulsed laser deposition. The influence was investigated of the surface morphology on the physicochemical and optical properties of the nanostructured films. X-ray photoelectron spectroscopy was used to study the composition and chemical state of the nanostructured ZnO. The changes occurring on the surface of the films after prolonged exposure in air are considered in the light of practical applications of ZnO films. The change in the number of adsorbed species on the surface with the time affects the surface conductivity, the latter in turn modifying the optical properties of the samples.

We present results of our recent study on the heating process and near field localization arising when gold nanoparticles are irradiated by ultrashort laser pulses at wavelength of 800 nm. The system under consideration consists of Au nanoparticles with diameter of 40, 80, or 200 nm in vacuum or deposited on different substrates. Substrate materials with different dielectric properties are used in order to sense and visualize the nanoparticle heating and near field electromagnetic distribution. The theoretical analysis is based on the optical properties obtained by the Mie scattering theory. The absorption coefficients calculations are implemented in a two-temperature heat model for estimation of the nanoparticle temperature. The near field distribution in the vicinity of the particles is calculated by the finite difference time domain (FDTD) method. It is found that at even moderate laser fluences the temperature of the particle can reach a value sufficient for bubble formation in biological tissues. The analysis of the near field distribution shows that when the particle is deposited on a substrate surface, the dielectric properties of the substrate define the spatial distribution and the enhancement of the near field intensity. The observed localization and field enhancement may result in a precise modification of the substrate with a resolution defined only by the nanoparticle size. Such modifications are experimentally observed in different substrates.

Highly textured pure and Al doped ZnO thin films have been produced by pulsed laser deposition for optical gas sensor application. The influence of the processing parameters such as substrate temperature and oxygen pressure applied during depositions, and dopant concentration on the structural, morphological, and optical properties of the films were investigated. All deposited films are textured along the (002) direction. The substrate temperature and the oxygen pressure have stronger influence on the film crystallinity compared to the presence of the dopants. The grain size of the films prepared from 2 wt% Al2O3 doped ZnO target is approximately the same as the one produced from pure ZnO tagret. The increase in the dopant concentration into the ZnO target (to 5 wt% Al2O3) leads to an increase of the in-plane grain size of the as-deposited films which is well known to increase the gas sensitivity. At the same time, the use of doped targets increase the droplets on the film surface which deteriorates the optical detection of the gas sensing effect. The increase of the dopant concentration reduces the film transmission in the visible range and the transmission cut-off edge is shifted to the shorter wavelengths. The films deposited from 2 wt% Al2O3 doped ZnO target at oxygen pressure of 0.05 mbar and 300°C substrate temperature have good mode properties which makes them good candidates for optical sensors.