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Deposition and structural characterization of SmxSyOz-based thin films are reported. The chemical synthesis of the SmxSyOz compounds is performed by thermolysis of dithiocarbamate precursors, followed by the drop casting deposition of the synthesized material, and by the thermal treatment at different temperatures (250 °C, 500 °C and 900 °C) and atmospheric conditions (nitrogen and air). Structural and morphological properties have been investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction, and were found to depend closely on the treatment conditions. In particular, the treatment at temperatures as high as 900 °C and in a nitrogen atmosphere enhances the crystalline nature of the films and increases the samarium content in comparison to the oxygen content. Therefore, the temperature of 900 °C and the nitrogen atmosphere represent the optimal treatment conditions, among the process parameters, to obtain a single phase of Sm2SO2.

Aluminum nitride (AlN) thin films were deposited on SiO 2 /Si substrates by radiofrequency (RF) magnetron sputtering using an aluminum target. The influence of the deposition parameters – such as nitrogen concentration in the sputtering atmosphere, RF power, total working pressure and substrate bias voltage – on the structure, morphology and composition of the thin films was discussed. The structure was studied using X-ray diffraction (XRD), the morphology was studied using scanning electron microscopy (SEM) and the composition was studied using energy dispersive spectroscopy (EDS). These investigations showed that all of the films grew preferentially along the c-axis regardless of the deposition conditions, without the application of external heating, whereas the grain size and morphology strongly depended on the process parameters. Additional energy, which was supplied to the growing films by increasing the power or decreasing the working pressure, improved the crystallinity, but compressive stress was induced in the samples, thus resulting in a surface morphology evolution.

The optical sensing properties of nanometric polyimide films towards ethanol and methanol vapours have been investigated by surface plasmon resonance technique. To this purpose polyimide sensing layers have been deposited onto gold/glass substrates by glow-discharge-induced vapour deposition polymerization technique. The sensible layer shows reversible and stable responses to different concentrations of methanol and ethanol vapours. A linear dependence between the change in reflectivity and the vapours concentration is observed being the sensitivity to both vapours similar, however, the response is larger in presence of ethanol vapours. Numerical fitting routines on surface plasmon resonance curves indicate that optical changes are motivated by an absorption process of the analyte. This produces a detectable increase of the real refractive index and a swelling process in the polyimide layer.

The desiccation process of lasagna pasta is usually accompanied by bending and breaking of the dry pasta slices, due to self generated internal stress. The diffusive transfer of water through the slice bulk is responsible of these phenomena, leading to excessive product reject. The water sorption equilibrium and kinetics of drying were measured for different pasta mixtures. Measurements have been performed by means of a novel equipment based on a raw alumina substrate (3 x 3mm sized) equipped with gold interdigitated electrodes, and a strict analogy exists between current and water diffusion data. Moreover, in situ measurements have been performed in an Italian pasta factory with an on line system assembled on the desiccation apparatus. Results of the sorption studies show a Case II diffusion mechanism, with the formation of a glassy shell around the pasta sample during desiccation at low water vapour activities, which prevents the further desiccation of the internal humid core. Thus, an accurate control of the humidity both in the sample and the external environment was performed to avoid stress generation in the material and cracks formation. The measuring device provided an accurate control of the sample humidity and a fast response to external environment modifications during desiccation. (c) 2004 Elsevier Ltd. All rights reserved.

In this work we show the capability of a sol–gel based electronic nose to be used in qualitative and quantitative analysis with the aim to recognize common volatile compounds usually present in the headspace of foods. Acetone, hexanal and 2-pentanone were chosen for this kind of measurements, performed both in dry air and in mixture of 50% humidity, just to simulate the experimental set-up in real applications. Moreover, different mixtures of 2-pentanone and hexanal at low concentration were investigated. We show how linear technique, such as principal component analysis (PCA) algorithm can be used for inspecting data distribution in simple cases like cluster discrimination. Moreover, non-linear techniques for difficult regression problems, such as artificial neural networks (multi-layer perceptron (MLP) and radial basis function (RBF)) are needed in particular for the prediction of different concentrations.

Pure and Pd, Pt and Os activated tin oxide thin films have been prepared by the sol–gel process. The physical properties have been investigated by various techniques such as Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) to obtain information on chemical, structural and morphological composition of the layers. In particular microstructure and morphology has been shown to be dependent on the presence of the doping element. Integrated gas micro-sensors were obtained that showed the different sensing characteristics depending also on doping elements. PCA analysis was performed on an array consisting of the prepared sensors and the results have shown the capability to discriminate different air pollutants.

In this paper, a novel electronic nose based on a metal oxide gas sensors array, prepared by means of the sol–gel method in the form of thin films, is described, including the fabrication process. Two different configurations of the array were developed: one consisting of sensors with the same sensing layer (SnO2) but different geometry and material for the electrical electrodes, and another consisting of chemically modified SnO2 thin films. Examples of application to the analysis of air pollutants (CO, NO2, CH4, C2H5OH and CH3OH) and different foods (oil, milk, tomato, wine, ground coffee). Recognition of different air contaminants and of the aroma of foods is achieved by using the principal component analysis (PCA). Good discrimination among the clusters has been obtained indicating promising results for the application of our sensor array as electronic nose, in particular in the food industry for the classification of different olive oils.

The paper presents two neural networks based on the adaptive resonance theory (ART) for the recognition of several odors subjected to drift. The neural networks developed by Grossberg (supervised and unsupervised) have been used for two different drift behaviors. One in which the clusters end up to overlap each other and the other when they do not. The latter case is solved by unsupervision, which is useful to track the moving clusters and possibly discover new odors autonomously. (C) 2000 Elsevier Science S.A.

The investigation of the surface and interface of a multilayer coating is a key factor for producing high quality optical device. In this work, we present a non-destructive technique as X-ray reflectivity to study deeply the chemical and structural quality of the multilayer. XPS depth profile analysis and AFM images have been used to evaluate the chemical intermixing and the surface roughness in order to verify the X-ray results.

Structural characterization of InGaAs/GaAs quantum wires grown by MOVPE on V-grooved substrates was performed by means of transmission electron microscopy (TEM). Both ‘bent-shaped’ and ‘V-shaped’ quantum wires were studied. For both types of nanostructure, single and multiple structures were considered, together with single V-shaped wires, with different In mole fractions, ranging between 10 and 20%. Direct visualization of the structure of these materials allowed correlation of the growth conditions with the resulting microstructure. A deeper understanding of optical properties of the materials was obtained also, by direct visualization of the confinement region and by analysis of the evolution of the planes of growth.

Hafnium oxide (HfO2) films were deposited on silica and glass substrates by ion (Xe+) assisted deposition with increasing ion momentum transfer to the growing film. The relationship among the ion momentum values, the crystalline phase and the refractive index (packing density) has been worked out by means of X-ray diffraction and spectrophotometric analysis. Compaction of the films by ion beam assistance is clearly evidenced by the changes in their microstructure. A three steps transition from a random monoclinic phase, via amorphous phase, up to an highly phase oriented (fiber texture), as a function of ion momentum, has been found.

Gas sensors based on SnO 2 films deposited by sol-gel on a Si substrate have been fabricated, characterised and tested. The results of structural characterisation and the sensing tests have shown the validity of this technological approach, which is a very promising step towards the full integration of the gas sensors in VLSI Si technology.

Vanadium oxide (V2O5) and tungsten oxide (WO3) thin films were investigated with the aim to obtain information about their physical and gas sensing properties. The analysis in the presence of different NO concentrations have shown that both materials are able to detect nitrogen oxide, but their responses exhibit different characteristics. In particular, tungsten oxide was found to be more suitable to be used in the field of application for detecting low concentrations. In addition, a mechanism of detection has been considered.

The main limitation in using plastics for optical components is the softness of their surface, which is responsible for low impact and abrasion resistance and for weak adhesion between the film and the substrate. Protecting the substrate with a hard film can increase the impact resistance of polymeric lenses. However, deposition of thin films on chemically cleaned plastic substrates has resulted in fast delamination of the coating. This paper discusses the problems associated with coated plastics, it presents the ion assistance as one of the solutions and it finally identifies the relevant parameters. A hard oxide layer with additional ion pre-treatment is proposed as protection for plastic optics. The adhesion between the film and the substrate has been evaluated by a scratch-test and the hardness has been calculated by measuring the radius of the stylus track.

Silica thin films have been deposited by a dual-ion-beam sputtering technique using argon or xenon ions mixed with oxygen ions in the assisting beam and the role of the assisting-ion-beam parameters on the laser-damage-threshold at 308 nm (XeCl laser) has been investigated. It is shown that a proper choice of these parameters allows a considerable increase of the laser-induced damage threshold. Lower damage thresholds (1 J/cm 2 ) were found for the xenon/oxygen assisted samples. Whereas, the highest damage threshold (8 J/cm 2 ) was found for the argon-ion assisted sample and its value was also much higher than that (2.9 J/cm 2 ) of the non-assisted films. Damage thresholds have been determined by the photoacoustic mirage technique and it is demonstrated that this technique can provide useful information on the mechanisms responsible for laser damage.

Gas detection by means of metal oxide semiconductor sensors is ascribed to the change of resistance due to the modulation of the intergrain potential barrier (grain contribution) and of the metal semiconductor barrier at the contacts (contact contribution). We present a method for measuring the contribution of the contact and the grain resistance separately during exposure to CO and CH4 by employing the square and collinear four probe array (David S. Perloff, Four-point sheet resistance correction factors fot thin rectangular samples, Solid State Electron. 20 (1977) 681–687). The electronic properties are investigated by means of Hall effect measurements according to grain boundary scattering mechanism.

Dual ion-beam sputtering deposition is a very promising technique for fabricating optical coatings thanks to its very good control of the deposition parameters. Unfortunately, the different sputtering yields of the elements composing the films modify the stoichiometry and, consequently, may cause an increase of the absorption in the UV range and an undesirable variation of the refractive index. In this work we investigate the influence of ion-beam assistance on some oxide materials: SiO 2 , ZrO 2 , and HfO 2 . The sputtering yield has been measured by varying the mass (Ar, Xe) and energy (100–1000 eV) of the bombarding ions. The yield measurements were compared with the calculated yields using Sigmund's model. Different screening functions for different characteristic energy ranges were necessary to fit the experimental results.

Two approaches for gas recognition in binary mixtures have been developed for imcoated surface acoustic wave (SAW) sensors based on gas thermal conductivity principle. The first approach utilizes the difference thermal conductivity of the ambient atmosphere with respect to a reference gas as general property to test the responses of the sensing elements. Selecting the operating temperature and the reference gas, a single gas is distinctly detected. The second approach is based on the inherent property of the SAW devices, whose response is monitored by the temperature coefficient of delay (TCD). Choosing the operating temperature and the substrate material, the SAW response for a test gas is rejected. Experimental measurements are shown and discussed.

Polypyrrole thin films have been deposited onto a glass substrate by the Langmuir-Blodgett technique to fabricate a selective ammonia (NH 3 ) gas sensor. The d.c. electrical resistance of the sensing elements is found to exhibit a specific increase upon exposure to different gases such as NH 3 , CO, CH 4 , H 2 in N 2 and pure O 2 . The polypyrrole thin-film detector shows a considerable increase of resistance when exposed to NH 3 in N 2 , and negligible response when exposed to comparable concentrations of interfering gases such as CO, CH 4 , H 2 in N 2 and pure O 2 . The calibration curve for NH 3 in N 2 at room temperature is measured in the concentration range from 0.01 to 1%. The relative change of the electrical resistance is about 10% for the lower detectable limit of 100 ppm of NH 3 in N 2 . The sensitivity of the Langmuir-Blodgett polypyrrole towards ammonia is considerably higher than that of the electrochemical polypyrrole. The fast rise time and the high sensitivity of the detector are reported as a function of number of the polypyrrole layers. Long-term aging tests of the selective NH 3 gas sensor are performed.

We present an X-ray reflectivity study of thin TiN and TiOxNy films grown on Si(100) substrate by the dual-ion-beam-sputtering technique. The thickness range of the deposited films varies between 25 and 35 nm. We demonstrate that low-angle X-ray reflectivity is a powerful tool for studying the early stages of growth and the surface and interface properties of these films. We found that an oxidation of the TiN film surface occurs, yielding a 2 nm thick TiO2 film, if the films are exposed to air after the growth. Furthermore, an interface layer 1.5 nm thick with electron density near that of SiO2 is present at the substrate–film interface. The thickness of the interface layer increases by more than three times after 7–8 months (aging). The formation of the oxide layers is independent of the growth mode, i.e. growth with and without ion assistance. In addition, the formation of a TiO2 surface layer is also observed for TiOxNy films. The samples synthesized by employing ion-beam assistance show a much lower surface roughness (∼0.8 nm) compared to the samples deposited without ion-beam assistance (∼1.5 nm). This finding demonstrates that films with improved structural and surface properties can be obtained by using dual-ion-beam-sputtering. © 1997 Elsevier Science S.A. All rights reserved.

In previous studies, various semi-insulating LEC GaAs crystals were irradiated with photons in the diagnostic energy range (20–100 keV), in view of a possible application in digital radiography. Solid-state and irradiation measurements, together with Monte Carlo simulations, have indicated good candidates for this application among the crystals we have investigated. In this paper we present results concerning the detection characteristics (detection efficiency, charge-collection efficiency and energy resolution as functions of the bias voltage) of one of these materials and the images obtained by a pixel detector made on the same material and a bump-bonded electronic system.

We present a preliminary study of the performance of semi-insulating indium phosphide (InP) crystals and its possible use in nuclear radiation detection at room temperature. Devices having an active area of 12 mm 2 showed a 5% resolution (FWHM) for 5.48 MeV alpha particles. Analyses of photo spectra indicated that the trapping of holes was primarily responsible for degrading the alpha response.

Forward and reverse current-voltage ( I - V ) characteristics of Ti GaAs diodes prepared by ion beam sputtering (IBS) have been measured in the temperature range from 100 to 360 K. The correlation between the different sputtering preparation conditions and current transport mechanism is discussed. The analysis indicates that the thermionic emission is the main transport mechanism for all the samples. However at low temperature the diodes show a deviation from this behaviour. The departure from ideal conditions is interpreted as a direct effect of barrier height inhomogeneities at the metal-semiconductor interface.

ZnO-on-Si surface acoustic wave (SAW) delay lines have been examined as detectors of some combustible gases (CO, NO, H2), reactive gas such as O2 and other gases (CH4, N2, Ar). Measurements have been performed at temperatures of 20–160 °C, operation frequencies of 100–200 MHz and atmospheric pressure. The ZnO thin films have been prepared by reactive r.f. diode sputtering in an O2/Ar atmosphere. The piezoelectric ZnO films deposited on the acoustic propagation path ensure both electromechanical transduction and gas detection. The relative changes of SAW phase velocity (acoustic response) upon absorption and desorption of a gas have been measured and compared with the change of electrical resistivity (electrical response) measured on the sensor in the same conditions. The effect of preliminary NO exposure on the acoustic responses for other gases is demonstrated. The time dependence of the acoustic response to NO is shown to be remarkably different from both its electrical response and from the acoustic responses to all other test gases. Therefore the shape of the time dependence can be used as a qualitative parameter for selective identification of NO. The relatively small interaction of Ar and N2 with ZnO film makes them good carriers for other gases. Concerning the acoustic response, two possible processes of gas-molecule sorption by the ZnO film are briefly discussed.

The Gaussian dielectric function and its derivatives with respect to the main physical parameters have been studied to obtain a simplified line-shape formula for the high temperature photoreflectance spectra. The model has been used to fit the experimental data obtained from InAs/GaAs and GaAs/AlGaAs Multiple Quantum Wells.

The electrical properties of a Ti/GaAs Schottky diode were investigated using electrical measurements under forward bias. The current, the low and high frequency capacitance and DLTS measurements evidence and describe in a consistent way the existence of a thin layer of defects induced by the metal deposition process near the interface. The quasi-saturation of the current and the excess low frequency capacitance are analysed by means of a generalization of a dipole layer model. The high density of states extending for several hundreds of Angstrom in the semiconductor is also evidenced by high frequency capacitance measurements. DLTS measurements using positive pulses confirm the presence of the traps and, together with the temperature analysis of the cut-off frequency, allow to study the trap emission process over a wide range of temperatures.

The oxygen gas-sensing characteristics of ZnO sputtered thin films, undoped or Li doped, versus their working temperatures are reported in this paper. The Li content and the O/Zn ratio are obtained by measurements of nuclear reaction analysis (NRA) and Rutherford back-scattering (RBS), respectively. The structural properties of ZnO and ZnO(Li) films are studied by means of X-ray diffraction (XRD); the preferential orientation of the thin films is found to be (002). We have measured the variation of the electrical conductance for O2 concentrations between 100 and 2 × 105 ppm by means of absorption isotherms at temperatures varying from 400 to 550 °C. The oxygen sensitivity and the response times for these ZnO thin films are reported here; the possible interaction mechanisms of gaseous O2 with the bulk of pure or Li-doped films will also be given.

The deposition of cadmium telluride films on cadmium telluride substrates by closed-tube chemical vapour deposition was investigated. Gaseous hydrochloric acid, obtained by thermal dissociation of ammonium chloride, was used as transporting agent. Several film deposition runs were performed by varying the experimental growth conditions, in order to determine the best growth conditions for obtaining good quality CdTe films. The physical properties of the films were investigated by means of optical and scanning electron microscopy, X-ray diffraction and Auger electron spectroscopy. The influence of the main deposition parameters on the growth rate and the film morphology was studied.

The epitaxial growth of CdTe films on CdTe crystals has been investigated. The film growth has been performed by the closed-tube chemical vapour deposition method with hydrochloric acid as transporting agent. The morphology and the structure of films grown under different experimental conditions have been studied. The best growth conditions are the following: source temperature of 700°C, deposition temperature of 600°C, HC1 concentration of 0.86 mg/cc and growth time of 60 h. Best films show a regular distribution of crystalline grains with typical dimensions of about 30–50 μm. Small amounts of chlorine in the film have been detected by Auger electron spectroscopy. Finally, the electrical properties of CdTe films deposited on n-type crystals have been studied and discussed.

The deposition of ZnO films by reactive sputtering has been investigated in order to study the dependence of the film properties on the main deposition parameters (RF power, substrate temperature, 8 2 content in discharge gas). The orientation and morphology of the crystalline grains have been studied by means of X-ray diffraction measurements. Films deposited on microscope slides generally present crystalline grains well oriented with the c-axis perpendicular to the substrate surface. Measurements of electrical resistivity show that the presence of oxygen in the discharge gas gives rise to films with resistivity ranging from 10 3 to 10 8 ohm cm. The correlation between structural and electrical properties of the ZnO films and the deposition parameters is discussed.