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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.

Silver and gold nanoparticles were synthesized by the sol-gel process in SiO 2 , TiO 2 , and ZrO 2 thin films. A versatile method, based on the use of coordination chemistry, is presented for stabilizing Ag + and Au 3+ ions in sol-gel systems. Various ligands of the metal ions were tested, and for each system it was possible to find a suitable ligand capable of stabilizing the metal ions and preventing gold precipitation onto the film surface. Thin films were prepared by spin-coating onto glass or fused silica substrates and then heat-treated at various temperatures in air or H 2 . atmosphere for nucleating the metal nanoparticles. The Ag particle size was about 10 nm after heating the SiO 2 film at 600°C and the TiO 2 and ZrO 2 films at 500°C. After heat treatment at 500°C, the Au particle size was 13 and 17 nm in the TiO 2 and ZrO 2 films, respectively. The films were characterized by UV-vis optical absorption spectroscopy and X-ray diffraction, for studying the nucleation and the growth of the metal nanoparticles. The results are discussed with regard to the embedding matrix, the temperature, and the atmosphere of the heat treatment, and it is concluded that crystallization of TiO 2 and ZrO 2 films may hinder the growth of Ag and Au particles.

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.

Colloidal CdSe/ZnS core-shell nanocrystals, with a narrow size distribution, were dispersed in a hybrid sol resulting from the hydrolysis of tetraethylorthosilicate and 3-glycidoxypropyltrimethoxysilane (GLYMO). In order to reduce the gelation time and the exposure of the nanoparticles to air, several catalysts of the GLYMO epoxy ring opening were employed for the sol preparation, such as imidazole, methyl-imidazole, pyridine, benzylamine, propylamine. The role of the various catalysts was monitored by optical absorption measurements in the near infrared region, by observing the evolution of the epoxy bands. Imidazole was found to provide the fastest gelation and the best results in terms of bubble disappearance from the gel structure. The variation in the optical properties of the semiconductor nanoparticles embedded in the matrix was monitored as a function of the gelation time and was compared to the optical absorption and photoluminescence spectra of the nanoparticles dissolved in a chloroform solution. A decrease in the gelation-time results in a closer resemblance between the optical properties of the CdSe/ZnS doped monoliths and those of the particles dissolved in the solvent, before incorporation in the matrix. The photoluminescence of the CdSe/ZnS nanocrystals is not bleached after they are trapped in the glassy matrix.

A new approach is presented for preparing In 2 O 3 thin films starting from inorganic precursors, based on a very simple but effective modification of the usual precipitation-peptization process. Indium nitrate was dissolved in methanol and In 3+ ions were chelated with acetylacetone before adding concentrated base to the resulting solution. Such a route allowed obtaining long-term stable sols, from which films could be deposited on glass substrates by spin-coating. Furthermore, the films exhibited a very good adhesion and uniformity, without any need for adding additives to the solution. The modification of the In precursor was confirmed by thermal analysis, while XRD studies revealed that the films prepared with the modified route result in smaller In 2 O 3 grains compared to the traditional precipitation-peptization process. Optical reflectance measurements on the films further highlighted the difference between the two processes. Gas-sensing tests carried out on the films deposited onto alumina substrates in the temperature range between 100 and 400°C showed that faster responses are obtained at temperatures higher than 250°C. The response value (R/R 0 , where R is the electrical resistance of the sensor in the test gas and R 0 that in dry air) to 100 ppb ozone is remarkably high: it is equal to 1500 for In 2 O 3 with a response time of about 1 minute. The recovery time is about 10 minutes.

The objective of this paper is to study the morphology, structure, and composition, as well as the thermal-induced morphological, structural, and chemical changes of copper(Cu)/ titanium nitride(TiN) bilayers versus Cu single layers, deposited on silicon substrates for microelectronic applications. These characterizations aimed to assess the reliability of Cu metallization for local interconnect and to investigate the barrier capability of TiN against Cu diffusion into the silicon (Si) substrate. Moreover, this paper provides a fundamental study of the temperature-induced interactions between Cu and Si, intermediated by the presence of a thin TiN layer. Cu thin films were sputtered onto Si substrates, with and without the interposition of thin TiN layers, and were successively annealed at temperature as high as 600 °C. Different nitrogen flux percentages in the sputtering mixture (Ar + N 2 ) were used for the deposition of the barriers. X-ray diffraction (XRD) analyses were carried out in order to study the structural evolution of the layers, before and after the annealing. Scanning electron microscopy (SEM) observations gave information about the surface and cross section morphology, and spatially resolved energy dispersive X-ray Spectroscopy (EDS) profiles provided chemical information about the cross-sectional distribution of the atomic species and their possible interdiffusion. The barrier efficacy has been demonstrated by comparing the morphological and chemical modifications of the annealed Cu layers, with and without the presence of the TiN layer, and their effects on the electrical properties of the Cu films.

The synthetic mechanism of uniformly dispersed Cu-nanocluster doped (0.05–1.0 wt%) silica glasses (copper ruby glasses) was investigated by UV–VIS and FTIR spectroscopy, DSC, XRD, surface area and density measurements at different stages of drying/densification up to glass formation. The monolithic gels were prepared from Cu(NO3)2, H2N(CH2)2NH(CH2)3Si(OCH3)3 (DAMO) and acid hydrolysed Si(OC2H5)4 (TEOS). DAMO was used to immobilize the Cu2+ ions in the silica matrix. The formation and decomposition of Cu–DAMO complexes in the silica gel monoliths were studied. The doped gels were densified under H2 and He gas atmospheres. A maximum matrix (SiO2) density of 1.70–1.73 g cm−3 (77–79% of the theoretical density) could be achieved in an H2 atmosphere at 900 °C. However a density close to silica glass 2.17 g cm−3 (>98.5% of theoretical) was achieved when the gels were densified in H2 up to 800 °C followed by He gas at 980 °C. The surface area data also confirmed this densification behaviour. Uniformly dispersed Cu metal nanoclusters were formed during the heat-treatment of the gels and as a result a surface plasmon (SP) band of Cu-nanoclusters (563–580 nm) was observed. The increase of heat-treatment temperature caused the growth of nanoclusters and as a consequence the SP band was blue-shifted. XRD data also confirmed this.

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.

Bulk borosilicate glasses were prepared by the sol−gel process and doped with gold nanoparticles. First, a sol of the host glass (with nominal molar composition of 10% B2O3−90% SiO2) was prepared, and then gold was introduced into the sol by means of a solution of a Au3+ complex. The resulting gels were dried at 60 °C and then heated in air at various temperatures up to 600 °C to nucleate the gold particles and sinter the glass matrix. Various gold ligands were tested, and thiourea was found to be the most effective ligand in preventing fast gold reduction and precipitation to the gel surface during drying. A model based on the formation of insoluble gold species during drying of the gel is discussed to explain the phenomenon of gold precipitation to the sample surface. The heated gels were studied by measurements of the BET specific surface area and of the apparent density, showing the densification of the matrix during the heat treatments. UV−vis optical absorption spectroscopy was used to monitor the f...

A chloride-based inorganic sol-gel route was used for preparing pure and metal (osmium, nickel, palladium, platinum)-doped SnO 2 sol. SnCl 4 was first reacted with propanol, then the resulting compound was hydrolyzed and subsequently mixed with solutions of the metal dopants. The obtained sols were used for depositing thin films by spin coating or for preparing powders by solvent evaporation at 110°C. FTIR spectroscopy and thermal analysis of the powders revealed that chlorine still bound to tin stabilized the sol against gelation by hindering the condensation reactions. Film characterizations showed that platinum and palladium, unlike nickel and osmium, were likely to form nanoparticles in the SnO 2 lattice. This result was discussed with regard to the different ways that platinum and palladium, on one hand, and nickel and osmium, on the other, modified the growth of SnO 2 grains and the film roughness and morphology. Dopants that formed nanoparticles (platinum, palladium) resulted in the roughest film, while dopants that did not form particles (nickel, osmium) resulted in SnO 2 grain size very close to that of pure SnO 2 .

Pure, Pd and Os modified SnO2 films were prepared by the sol gel process and used as active materials in gas sensing devices. The films have been prepared starting from tin tetrachloride in alcoholic solution hydrolysed with water. The modifier was added to the sol as inorganic salt. Pd acetate and Os chloride were the Pd and Os precursors respectively. A structural and morphological study was carried out by means of Atomic Force Microscope (AFM), Secondary Ion Mass Spectrometer (SIMS) and x-ray Diffraction (XRD). The electrical resistance variations as a function of various gaseous atmospheres and temperature were measured to evaluate the sensing properties of the films. CO, CH4, CH3OH and C2H5OH gases were used for the tests. Following results were obtained: Pd is present in the form of PdO nanoclusters in the polycrystalline SnO2 matrix as evidenced by XRD spectra whereas Os is a cationic modifier uniformly dispersed as evidenced in SIMS studies. Optimum sensing temperature and the sensitivity variations, with respect to the undoped films, differ according to the gaseous species. It looks therefore promising to use inexpensive, sol-gel derived, array of films in smart gas sensing devices that are able to recognise gas species and concentration.

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.

SiO2 films have been deposited by ion-beam sputtering techniques either without assistance or with Ar-ion assistance and the role of the substrate temperature during the deposition process on the film damage threshold by laser light at the wavelength of 308 nm (XeCl) has been investigated. The photoacoustic probe beam deflection technique has been used to determine damage thresholds and it is shown that this technique provides valuable information on the mechanisms leading to laser damage. It has been found that the samples deposited by the Ar-ion beam sputtering technique are characterized by higher damage thresholds at lower temperatures of the substrate than the SiO2 films deposited without ion assistance.

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.

Disorder and spectral broadening of vertically stacked InGaAs/GaAs V-grooved quantum wires have been investigated by means of microprobe luminescence. We show that the main spectral broadening mechanism originates from monolayer fluctuations at the bottom of the wire. A direct evidence of monolayer height islands of area $40\ifmmode\times\else\texttimes\fi{}40\mathrm{nm}$ formed at the bottom of the grooves is provided by atomic force microscopy. Lateral and vertical wire-to-wire fluctuations are found to be negligible on the micron scale.

We present an extended drift-diffusion modelling to study electron transport in semi-insulating n-GaAs Schottky-barrier diodes. The model accounts for hot-carrier dynamics and associated kinetics of electrical active traps. A field-enhanced capture cross-section of the two deepest electron traps, attributed to EL2 and EL3 centres, is found to determine the main characteristics of this device. A detailed description of the profile of the electric field, free charge and other related quantities is provided. The modelling compares well with available experimental results and confirms the suitability of this device to be used as a detector for nuclear radiation.

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.

Surface acoustic wave (SAW) delay lines without gas-sensitive coatings are used as thermal sensors for the thermoconductometric detection of gases and gas flows. The forced convection of 13 gases is analyzed in the linear approximation without regard for their interaction with the environment. Quartz, LiNbO3, Bi12GeO20, and Bi12SiO20 delay lines are used to detect H2, He, Ar, CH4, NH3, N2, and O2 at frequencies f=21–263 MHz and temperatures T=25–165 °C. The SAW “response” is measured as a function of the gas concentration n, the flow rate U, the temperature coefficient of the SAW velocity (TCV), and the working temperature Tp. The feasibility of controlling the level of the gas “response” and imparting selectivity to the choice of TCV and Tp is demonstrated. The threshold gas concentrations are 0.35% for CH4 and 0.1% for H2 and NH3 in nitrogen. A linear response is obtained in the interval U=20–200 ml/min.

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 report a clear evidence of bistability in the current–voltage characteristics of p‐i‐n heterostructures containing InGaAs V‐shaped quantum wires. The observed phenomenon is explained in the framework of a single carrier transport model in which the quantum wires act like traps for the vertical current. The charge trapping phenomenon is indeed demonstrated by temperature‐dependent photocurrent experiments.

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 sensing performance comparisons presented in this work were carried out by exploiting a suitable magneto-plasmonic sensor in both the traditional surface plasmon resonance configuration and the innovative magneto-optic surface plasmon resonance one. The particular multilayer transducer was functionalized with TiO2 Brookite nanorods layers deposited by matrix assisted pulsed laser evaporation, and its sensing capabilities were monitored in a controlled atmosphere towards different concentrations of volatile organic compounds mixed in dry air.

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.

In this work, the effects of the focus ion beam (FIB) milling process on the optical properties of semiconductor nanostructures were investigated. With this aim, a sensitive materials system based on InGaAs/GaAs quantum dots with well known and excellent optical properties was selected for the FIB treatment. The FIB technique was used to locally remove a metallic mask deposited on top of the quantum dot sample. The photoluminescence (PL) signal, collected from the circular openings, was used to infer the possible damage effects of the ion beam on the properties of the dots.

A new method to analyze isothermal capacitance transients of Schottky barriers is proposed. Isothermal capacitance transients, recorded at different temperatures by an automatized measurement system, are analyzed by comparing the capacitance values at the same time but different temperatures. This method is similar to that used in the standard deep‐level transient spectroscopy (DLTS), by inverting the role of time and temperature. The main parameters of the deep levels can be obtained as in the DLTS analysis. The analysis method is applied to Mo/GaAs Schottky barriers. Results have been compared with those obtained by standard DLTS analysis.

The structural and optical gas sensing properties of thin nanostructured ZnO films are investigated by total attenuation surface plasmon resonance technique. Ten nanometers thick ZnO films have been prepared by sol–gel route and thermally treated at 150 °C and 400 °C. Grazing incidence X-ray diffraction studies showed that the thermal treatment promotes the increase of grain size as the annealing temperature increases. The optical properties of both films are similar being the energy gap of the films annealed at 150 °C and 400 °C equal to 3.33 ± 0.05 eV and 3.25 ± 0.05 eV, respectively, both smaller than the energy gap of the bulk ZnO (3.37 eV). The surface plasmon resonance investigations show remarkable and reversible responses to different concentrations of methanol, ethanol, isopropanol and hexane vapours in dry-air. In both films the responses to ethanol and isopropanol are similar and larger than the responses to hexane and methanol. The responses to all vapours are larger in the film annealed at 400 °C except for the methanol for which both films exhibit similar responses.

The optical gas sensing properties of virgin TiO2 thin films and with inclusion of dot- and rod-shaped gold nanoparticles (NPs) prepared by a sol–gel method and annealed at 200 ◦ C have been investigated. The obtained nanostructures have been analysed from both optical and morphological points of view. In particular, the prepared films show interesting dynamic optical absorption sensing responses towards different kinds of alcohol vapours in the spectral range corresponding to the surface plasmon resonance (SPR) peak of the gold nanoparticles. Total attenuation surface plasmon resonance measurements in controlled atmosphere demonstrate a sensing activity due to variation of the thickness and the real part of the active sensing layer refractive index. © 2008 Elsevier B.V. All rights reserved.

This work explores the potential of thin films composed of shape-controlled colloidal TiO2 nanocrystals in optical gas sensing applications. To this purpose, an optical characterization of nanocrystal thin films has been performed by means of UV–vis spectroscopy and surface plasmon resonance (SPR) technique. In particular, this technique has been used as optical transduction method to test the sensing properties of the oxide films towards alcohol vapours. Numerical fitting routines have been employed to evaluate quantitatively the changes in the characteristic optical parameters for the investigated films during the sensing process. It has been found that rod-shaped TiO2 nanocrystals provided with close-packed monolayers of long-chain surfactants on their surfaces, maximize the sensor response, as they may help to achieve a higher degree of alcohol accumulation on the active material.

We develop a Monte Carlo simulator of the charge signal induced by an external radiation on semi-insulating GaAs detectors. Trapping and detrapping processes and the dynamics of generated carriers are consistently accounted for. The relative contributions to the charge signal of fast- and slow-time components are found to depend significantly upon the applied voltage. Calculations provide a physical interpretation of experimental results.