A. Giannoudakos

Effects of experimental parameters in quantitative analysis of steel alloy by laser-induced breakdown spectroscopy

Abstract Calibration curves for the elements Cr, Ni and Mn in commercial steel alloy samples were obtained employing the Internal Standardization method in atmospheric air pressure. A number of experimental parameters have been optimized in order that the produced calibration curves showed good linearity over a broad range of concentrations covered by the alloy elements. Emphasis was given to the development of the method for field analysis and for the on-line control of production processes.

Growth of Au–TiO2 nanocomposite thin films by a dual-laser, dual-target system

Nanocomposite thin films formed by gold nanoparticles embedded in a titanium dioxide matrix have been synthesized by pulsed laser deposition. Two synchronized laser sources, an ArF* excimer (λ=193nm, τFWHM∼12ns) laser and a frequency tripled Nd:yttrium aluminium garnet (λ=355nm, τFWHM∼10ns) laser, were used for the simultaneous ablation of the titanium dioxide and gold targets. The optical absorption characteristics of the obtained nanocomposites were investigated as a function of laser parameters used for the ablation of the gold target. The obtained results proved the possibility of tuning the optical properties of gold–titanium dioxide nanocomposites with the proper choice of laser irradiation parameters. Band gap narrowing and absorption in the visible spectral region induced by the incorporation of gold enable the design of nanostructured thin films to be achieved for photocatalysts and solar energy converters.

Structure and optical properties of amorphous lead-germanate films developed by pulsed-laser deposition

Lead-germanate materials are attractive systems for photonics applications. In this context, amorphous lead-germanate films were grown by pulsed-laser deposition at different substrate temperatures and oxygen pressures using a glassy target of composition 0.4PbO-0.6GeO(2). Optical and infrared measurements showed that the substrate temperature has a strong influence on the optical quality and stability of the deposited films. An accurate characterization of films was achieved by comparing experimental and simulated transmittance spectra in the infrared, and allowed to probe the structural evolution and variations in composition as a function of oxygen pressure. The results showed that the difference in reactivity of lead and germanium toward oxygen in the laser-produced plasma allows for composition adjustments in the lead-germanate films by varying the oxygen pressure in the deposition chamber.

Development and characterization of ZnO, Au/ZnO and Pd/ZnO thin films through their adsorptive and catalytic properties.

In this paper, we report (a) the development of ZnO thin films prepared by pulsed laser deposition and partially covered with nano-particles Pd or Au and (b) their physicochemical study, in order to investigate their catalytic and/or adsorptive properties. It is the first time where two different and popular methods, namely pulsed laser deposition and reversed flow-inverse gas chromatography, are combined. The inverse gas chromatographic technique with the corresponding time-resolved analysis is used for the first time in order to characterise compounds in the nano-scale domain. We focus on the determination of physicochemical quantities mainly concerning the adsorption in thin films, with (Pd/ZnO) or without (Au/ZnO) catalytic behaviour. Thus, entropy and other important physicochemical quantities are calculated which reveal the mechanism of adsorption as well as of isomerization-hydrogenation of 1-butene and contribute to the study of heterogeneity of thin film surfaces. The programs used have been written in Fortran. An important achievement is also the determination of the standard deviations of the kinetic constants.

Accurate wavelength calibration in the near-infrared for multielement analysis without the need for reference spectra

A new technique has been developed for an instant, precise, and accurate wavelength calibration over a wide pixel array for simultaneous, multielement spectral analysis based on an inverse numerical solution to the grating dispersion function. This technique is applicable to multielement analytical applications such as laser-induced breakdown spectroscopy (LIBS), particularly when using high-density gratings in the upper visible and in the near-infrared, where nonmetallic elements are detected. This application overcomes the need to use reference spectra for each window of observation and is tested on a commercially available LIBS instrument.

Rapid, automated measurement of layer thicknesses on steel coin blanks using laser-induced-breakdown spectroscopy depth profiling

We report application of a near-real-time method to determine layer thickness on electroplated coin blanks. The method was developed on a simple laser-induced-breakdown spectroscopy (LIBS) arrangement by monitoring relative emission-line intensities from key probe elements via successive laser ablation shots. This is a unique LIBS application where no other current spectroscopic method (inductively coupled plasma or x-ray fluorescence) can be applied effectively. Method development is discussed, and results with precalibrated coins are presented.

Hydrogen Microsensor Based on NiO Thin Films

A multitude of industries use H2 either as part of their process or as a fuel. All these applications motivate nowadays the development of hydrogen sensor devices which enable its safe and controlled use. Since H2 is explosive above the lower explosion limit at 40,000 ppm, devices which permit the detection of its presence and measure its concentration become indispensable. In this work, we present a microsensor based on NiO thin films produced with dc reactive magnetron sputtering on GaAs, with an incorporated Pt heater, all on a DO-8 package ready for use. The microsensor was tested to H2 concentrations 5,000 and 10,000 ppm at different working temperatures. The change of the electrical resistance of NiO thin films was the signal for hydrogen sensing. The response of the sensor was not proportional to concentration of the gas neither to the working temperature.

Pulsed laser deposition of thin films: elimination of particulates by second laser irradiation

Pulsed laser deposition of thin films has besides numerous advantages a major shortcoming which is the presence of particulates of various shapes and dimensions both on surface and inside obtained structures. Indeed, in many key technological applications the use of completely particulates free films is mandatory. We demonstrated that the origin of size and density of particulates depend on specific experimental conditions. Nevertheless, the proper choice of deposition conditions (i.e. ablating laser wavelength and fluence, target-collector separation distance, growing temperature, ambient gas nature and pressure) allows for the decrease under a certain extent of pollution with particulates, but not for their complete elimination. This lecture reports our successful attempts to obtain completely particulates free deposited structures using two synchronized pulsed laser sources. The first, UV laser source was used to ablate the target material. The second, IR laser system was directed parallel to the target surface. The role of the second laser was to heat and vaporize the particulates present in the tail of the plasma ablated by the pulsed UV laser source.