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GeTe and GaSb thin films obtained by pulsed laser deposition were investigated by spectroscopic ellipsometry at controlled temperatures. The GeTe films were fully amorphous, while the GaSb films were partially crystalized in the as-deposited state. The Tauc-Lorentz model was employed to fit the experimental data. From the temperature study of the optical constants, it was observed the crystallization in the 150–160 °C range of GeTe amorphous films and between 230 and 240 °C of GaSb amorphous phase. A second transition in the resonance energy and the broadening parameter of the Lorentz oscillator was observed due to the crystallization of Sb after 250 °C. The temperatures of 85 °C and 130 °C are noticed as the start of the relaxation of the amorphous GeTe phase and as-deposited GaSb. The peaks of the imaginary part of the dielectric function red shifted after the phase change, while the variation with temperature of the crystalline phase follows the Varshni law. The electron-phonon coupling constants are 2.88 and 1.64 for c-GeTe and c-GaSb, respectively. An optical contrast up to 60% was obtained for GeTe films and a maximum value of 7.5% is revealed in the case GaSb, which is altered by the partial crystallinity of the as-deposited films. [ABSTRACT FROM AUTHOR]

Single and double layer phase change memory structures based on GeTe and GaSb thin films were deposited by pulsed laser deposition (PLD). Their crystallization behavior was studied using in-situ synchrotron techniques. Electrical resistance vs. temperature investigations, using the four points probe method, showed transition temperatures of 138 °C and 198 °C for GeTe and GaSb single films, respectively. It was found that after GeTe crystallization in the stacked films, Ga atoms from the GaSb layer diffused in the vacancies of the GeTe crystalline structure. Therefore, the crystallization temperature of the Sb-rich GaSb layer is decreased by more than 30 °C. Furthermore, at 210 °C, the antimony excess from GaSb films crystallizes as a secondary phase. At higher annealing temperatures, the crystalline Sb phase increased on the expense of GaSb crystalline phase which was reduced. Extended X-ray absorption fine structure (EXAFS) measurements at the Ga and Ge K-edges revealed changes in their local atomic environments as a function of the annealing temperature. Simulations unveil a tetrahedral configuration in the amorphous state and octahedral configuration in the crystalline state for Ge atoms, while Ga is four-fold coordinated in both as-deposited and annealed samples. [ABSTRACT FROM AUTHOR]

We have performed spectroscopic analysis of the plasma generated by Nd:YAG (λ = 266 nm) laser irradiation of thin indium zinc oxide films with variable In content deposited by combinatorial pulsed laser deposition on glass substrates. The samples were irradiated in 5 × 104 Pa argon using laser pulses of 5 ns duration and 10 mJ energy. The plasma emission spectra were recorded with an Echelle spectrometer coupled to a gated detector with different delays with respect to the laser pulse. The relative concentrations of indium and zinc were evaluated by comparing the measured spectra to the spectral radiance computed for a plasma in local thermal equilibrium. Plasma temperature and electron density were deduced from the relative intensities and Stark broadening of spectral lines of atomic zinc. Analyses at different locations on the deposited thin films revealed that the In/(In + Zn) concentration ratio significantly varies over the sample surface, from 0.4 at the borders to about 0.5 in the center of the film. The results demonstrate that laser-induced breakdown spectroscopy allows for precise and fast characterization of thin films with variable composition. [ABSTRACT FROM AUTHOR]

During the last years, femtosecond time-resolved spectroscopy (fsTRS) has become an important new tool to investigate low energy excitations in strongly correlated systems. By studying energy relaxation pathways linking various degrees of freedom (e.g., electrons, spin, or lattice), the interaction strengths between different subsystems can be deduced. Here we report on yet another application of fsTRS, where the technique is used to unambiguously determine the nature of the ground state in granular thin films of a prototype charge density wave system blue bronze, K0.3MoO3. These, potassium blue bronze, films, obtained for the first time ever, have been prepared by pulsed laser deposition and investigated by various standard characterization methods. While the results of all used methods indicate that the thin films consist of nanometer grains of K0.3MoO3, it is only the non-destructive fsTRS that demonstrates the charge density wave nature of the ground state. Furthermore, the comparison of the fsTRS data obtained in thin films and in single crystals shows the reduction of the charge density wave transition temperature and of the photoinduced signal strength in granular thin films in respect to single crystals, which is attributed to the granularity and crystal growth morphology. [ABSTRACT FROM AUTHOR]

We demonstrated that doping or covering with Au nanoclusters boosts gas sensing effectiveness of optical metal oxide sensors. The sensing response of pulsed laser deposited ZnO films as sensing element was tested by m-line technique for low concentration (1000 ppm) of butane in environmental N2. The optical interrogation was performed for three types of coatings: undoped ZnO, undoped ZnO structures partially covered with Au nanoclusters, or obtained from Au (0.5 wt %) doped ZnO targets. Nanocluster coating tripled the sensitivity, while doping resulted in an increase of up to 45% as compared with simple structures. [ABSTRACT FROM AUTHOR]

We report the detection of 100 ppm of butane in superatmospheric N2 or air with an m-lines setup. The sensing elements are ZnO-nanostructured coatings prepared by pulsed laser deposition. The deposition technique was optimized to obtain highly transparent films of 1 cm2 in area and several hundreds nanometer thick. ZnO structures preserve gas sensitivity even when deposited at room temperature. Refractive index variations down to 0.005 were detected and typical variations of about 20% were induced during ZnO film-butane contact. [ABSTRACT FROM AUTHOR]

The structure, chemical composition, and optical properties of tungsten trioxide thin films grown by pulsed laser deposition were investigated. An ultraviolet KrF* excimer laser (λ=248 nm, τFWHM≅20 ns, ν=2 Hz) was used for irradiation of tungsten trioxide targets in oxygen atmosphere. Our research focused on the effect of the ambient gas pressure and substrate temperature on the chemical composition, crystalline status, and optical properties of the obtained thin films. To this end, the films were studied by x-ray diffractometry Raman spectroscopy, and energy dispersive x-ray spectroscopy. Optical transmittance measurements were performed with a double beam spectrometer within the 400–1200 nm range. The films deposited at oxygen pressure values higher than 10 Pa and substrate temperatures above 300 °C consist of crystalline tungsten trioxide. Their average transmittance in the visible-infrared spectral region reaches about 85% appropriate for the envisaged applications. [ABSTRACT FROM AUTHOR]

Two step laser processing has been used for the formation of nano-lenslets transmitting in red/infrared region of the optical spectrum on the surface of arsenic sulphide glass films. In the first step the films were obtained by pulsed laser deposition (248 nm), while in the second step the lenslets were created by low power femtosecond (800 nm) laser irradiation. Photoexpansion of the material along with simultaneous migration of chalcogen atoms in the irradiated area was the main phenomena involved in the generation of these structures. The maximum photoexpansion observed was 5.1%. At higher laser power, material ablation was evidenced. [ABSTRACT FROM AUTHOR]

The effect of a pair of picosecond pulses on the ionization and deformation of a liquid tin microdroplet is studied for a range of incident pulse parameters. Faraday cups are used to measure ion kinetic energy distributions, together with high-resolution shadowgraphy to monitor target deformation and expansion. It is found that the introduction of a relatively weak first pulse results in an order-of-magnitude reduction of the number of ions with kinetic energies above 1 keV, and a strong shift of the kinetic energy distribution towards lower energies, while the expansion dynamics of the droplet can be kept similar to the single-pulse case. By controlling the relative intensity and the time delay between pairs of pulses with 52 ps duration, regimes are identified in which spherical final target shapes are combined with a reduced high-energy ion yield. The high-energy part of the observed ion distributions has been fitted with a self-similar expansion model, showing a 30-fold decrease in characteristic ion energy for pulse pairs. This combination of results is of particular importance for plasma sources of EUV radiation for nanolithography applications, in which picosecond-laser-produced target shapes can lead to significant improvements in source conversion efficiency, while a low high-energy ion yield is desirable from a source lifetime perspective. [ABSTRACT FROM AUTHOR]

The effect of a pair of picosecond pulses on the ionization and deformation of a liquid tin microdroplet is studied for a range of incident pulse parameters. Faraday cups are used to measure ion kinetic energy distributions, together with high-resolution shadowgraphy to monitor target deformation and expansion. It is found that the introduction of a relatively weak first pulse results in an order-of-magnitude reduction of the number of ions with kinetic energies above 1 keV, and a strong shift of the kinetic energy distribution towards lower energies, while the expansion dynamics of the droplet can be kept similar to the single-pulse case. By controlling the relative intensity and the time delay between pairs of pulses with 52 ps duration, regimes are identified in which spherical final target shapes are combined with a reduced high-energy ion yield. The high-energy part of the observed ion distributions has been fitted with a self-similar expansion model, showing a 30-fold decrease in characteristic ion energy for pulse pairs. This combination of results is of particular importance for plasma sources of EUV radiation for nanolithography applications, in which picosecond-laser-produced target shapes can lead to significant improvements in source conversion efficiency, while a low high-energy ion yield is desirable from a source lifetime perspective. [ABSTRACT FROM AUTHOR]

The mid-infrared range is an important spectrum range where materials exhibit a characteristic response corresponding to their molecular structure. A free-electron laser (FEL) is a promising candidate for a high-power light source with wavelength tunability to investigate the nonlinear response of materials. Although the self-amplification spontaneous emission (SASE) scheme is not usually adopted in the mid-infrared wavelength range, it may have advantages such as layout simplicity, the possibility of producing a single pulse, and scalability to a short-wavelength facility. To demonstrate the operation of a mid-infrared SASE FEL system in an energy recovery linac (ERL) layout, we constructed an SASE FEL setup in cERL, a test facility of the superconducting linac with the ERL configuration. Despite the adverse circumstance of space charge effects due to the given boundary condition of the facility, we successfully established the beam condition at the undulators and observed FEL emission at a wavelength of 20 μm. The results show that the layout of cERL has the potential for serving as a mid-infrared light source. [ABSTRACT FROM AUTHOR]

We investigate a hybrid thin film deposition procedure that significantly enhances reflectivity of La/B based nanoscale multilayer structures to be used as Extreme UV mirrors at 6.7 nm wavelength and beyond. We have analyzed the La-nitridation process in detail, and proposed a growth mechanism and deposition procedure for full, stoichiometric passivation of La, avoiding the formation of optically unfavorable BN formation at the LaN-on-B interface. A partial nitridation was applied and studied as a function of the nitridation delay. [ABSTRACT FROM AUTHOR]

The deposition of various distinct organic dyes, including ruthenium complex N3, melanin nanoparticle (MNP), and porphyrin-based donor-π-acceptor dye YD2-o-C8, by using matrix-assisted pulsed laser evaporation (MAPLE) for application to dye-sensitized solar cell (DSSC) is investigated systematically. It is found that the two covalently-bonded organic molecules, i.e., MNP and YD2-o-C8, can be transferred from the frozen target to the substrate with maintained molecular integrity. In contrast, N3 disintegrates in the process, presumably due to the lower bonding strength of metal complex compared to covalent bond. With the method, DSSC using YD2-o-C8 is fabricated, and an energy conversion efficiency of 1.47% is attained. The issue of the low penetration depth of dyes deposited by MAPLE and the possible resolution to it are studied. This work demonstrates that MAPLE could be an alternative way for deposition of organic dyes for DSSC. [ABSTRACT FROM AUTHOR]

A poly-(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM) bilayer structure has been realized by single step matrix-assisted pulsed laser evaporation (ss-MAPLE) technique using the same solvent for both the polymers under vacuum conditions. Our ss-MAPLE procedure allows the fabrication of polymeric multilayer device stacks, which are very difficult to realize with the conventional solvent assisted deposition methods. A proof of concept bilayer P3HT/PCBM solar cell based on ss-MAPLE deposition has been realized and characterized. This demonstration qualifies ss-MAPLE as a general and alternative technique for the implementation of polymeric materials in hetero-structure device technology. [ABSTRACT FROM AUTHOR]