A. Tepore

Physical and structural characterization of tungsten oxide thin films for NO gas detection

Abstract Tungsten trioxide (WO3) thin films were rf sputtered from a WO3 target in various oxygen/argon (O2/Ar) atmospheres and at different total pressures. A detailed structural and morphological investigation has been carried out on all obtained films by high resolution electron microscopy and nanodiffraction methods. Optical and electrical properties have been studied as function of deposition parameters. In addition, all obtained films were tested in controlled atmosphere in order to investigate their response to NO in the interval 2–100 ppm in dry air. The sputtering parameters were optimized in order to obtain the maximum sensitivity to NO gas. Finally, a close dependence between sputtering conditions, morphological features and physical properties was observed.

Titanium oxide thin films for NH3 monitoring: Structural and physical characterizations

Titanium oxide thin films have been deposited by thermal evaporation in vacuum and then have been analyzed before and after a suitable thermal annealing in order to test their application in NH3 gas-sensing technology. In particular, spectrophotometric and conductivity measurements have been performed in order to determine the optical and electrical properties of titanium oxide thin films. The structure and the morphology of such material have been investigated by high resolution electron microscopy and small area electron diffraction.

Properties of vanadium oxide thin films for ethanol sensor

Thin films of vanadium oxides for ethanol sensor applications were been prepared by means of rf reactive sputtering from a vanadium pentoxide target in an Ar–O2 atmosphere. Films with the best sensitivity and selectivity were obtained with 15% oxygen at a working temperature between 280 and 300 °C. These films show a very low sensitivity to CO, CO2, and CH4 and total insensivity to NH3.

Optical absorption and photoconductovity in amorphous indium selenide thin films

Abstract Optical absorption coefficient and photoconductivity measurements were performed on amorphous indium selenide thin films produced by vacuum evaporation. The dependence of the absorption coefficient α on the photon energy ħω at the edge of the absorption band is well described by the relation α h ω = B( h ω - E opt ) 2 where B is a quality factor and Eopt is the optical band gap. The steady state photoconductivity as a function of the temperature and light intensity is tentatively interpreted in terms of a simple kinetic model proposed by Weiser et al.

A novel nonenzymatic amperometric hydrogen peroxide sensor based on CuO@Cu2O nanowires embedded into poly(vinyl alcohol).

A new, very simple, rapid and inexpensive nonenzymatic amperometric sensor for hydrogen peroxide (H2O2) detection is proposed. It is based on the immobilization of cupric/cuprous oxide core shell nanowires (CuO@Cu2O-NWs) in a poly(vinyl alcohol) (PVA) matrix directly drop casted on a glassy carbon electrode surface to make a CuO@Cu2O core shell like NWs PVA embedded (CuO@Cu2O-NWs/PVA) sensor. CuO nanowires with mean diameters of 120-170nm and length in the range 2-5μm were grown by a simple catalyst-free thermal oxidation process based on resistive heating of pure copper wires at ambient conditions. The oxidation process of the copper wire surface led to the formation of a three layered structure: a thick Cu2O bottom layer, a CuO thin intermediate layer and CuO nanowires. CuO nanowires were carefully scratched from Cu2O layer with a sharp knife, dispersed into ethanol and sonicated. Then, the NWs were embedded in PVA matrix. The morphological and spectroscopic characterization of synthesized CuO-NWs and CuO@Cu2O-NWs/PVA were performed by transmission electron microscopy (TEM), selected area diffraction pattern (SAD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. Moreover a complete electrochemical characterization of these new CuO@Cu2O-NWs/PVA modified glassy carbon electrodes was performed by Cyclic Voltammetry (CV) and Cronoamperometry (CA) in phosphate buffer (pH=7; I=0.2) to investigate the sensing properties of this material against H2O2. The electrochemical performances of proposed sensors as high sensitivity, fast response, reproducibility and selectivity make them suitable for the quantitative determination of hydrogen peroxide substrate in batch analysis.

Structural and electrical properties of sputtered vanadium oxide thin films for applications as gas sensing material

A detailed structural and morphological investigation has been carried out by conventional transmission electron microscopy, high resolution electron microscopy and nanodiffraction methods on vanadium oxide films obtained by reactive rf sputter at a high power discharge (1000 W) and different O2/Ar ratio. Electrical characterization has been also performed in controlled atmosphere in order to investigate the influence of NO2 oxidizing gas on the material conductance as a function of deposition parameters. A strict relation between structure, morphology and resistance variation in controlled atmosphere has been observed.

ELECTRICAL PROPERTIES OF N-GASE SINGLE CRYSTALS DOPED WITH CHLORINE

Hall-effect and space-charge-limited-current (SCLC) measurements were performed on Cl-doped GaSe single crystals grown by the Bridgmann–Stockbarger method. The temperature dependence of the free electron density shows the characteristics of a partially compensated n-type semiconductor. The electrical properties are dominated by a deep donor level at about 0.57 eV below the conduction band. An electron trapping level between 0.56 and 0.62 eV below the conduction band has been observed by SCLC measurements. The trapping level concentration depends on the amount of dopant. Finally, the conduction band density-of-states effective mass was estimated to be 1.1 m0.

Gas-sensing properties of porphyrin dimer Langmuir-Blodgett films

Abstract Langmuir–Blodgett films of a 1:4 mixture of meso,meso′-buta-1,3-diyne-bridged Ni(II) octaethylporphyrin dimer and arachidic acid have been deposited onto various substrates. The isotherm at the air/water interface and absorbance measurements using polarised light are consistent with a planar statistical orientation of the porphyrin dimers which are probably prone onto the arachidic acid tails. The presence in the dimer of the acetylenic linking group allows the formation of a large and highly conjugated molecular structure; this has suggested the use of the films in gas sensing apparatus. Electrical characterisation in controlled atmosphere and with the simultaneous presence of interfering gaseous species, such as C2H5OH, NH3, and CO, suggest that this porphyrin dimer is a promising selective NO gas sensing material.

Kinetic behavior analysis of porphyrin Langmuir–Blodgett films for conductive gas sensors

Meso, meso′-buta-1,3-diyne-bridged Ni (II) octaethylporphyrin dimer thin films have been deposited by the Langmuir–Blodgett method and, for the first time, have been considered as the active layer in resistive gas sensors. In particular, the electrical conductivities of these films undergo a remarkable variation due to exposure to small concentrations of NO in air at an operating temperature of 50 °C. To interpret the behavior of such organic films, a model has been built up and the conductivity variation as a function of test gas concentrations and time has been derived. The fitting of theoretical and experimental behavior allows us to determine the number of adsorbed gas molecules per porphyrin dimer, response and recovery times, adsorption and desorption coefficients. The reliability of the model is proved by obtained results. In particular, the determined adsorption and desorption coefficients depend only on test gas species but are unaffected by other experimental conditions such as gas concentration.

Gas-sensing properties of sputtered thin films of tungsten oxide

Electrical, structural and morphological properties of thin films of deposited by the reactive RF sputtering method have been analysed. The fundamental electrical features of have been determined by Hall-effect measurements. Information about the structure and morphology of these films was obtained by transmission electron microscopy techniques. The investigations of electrical properties in a controlled atmosphere at various operating temperatures revealed that is particularly suitable for NO gas detection. In particular, the relative variation of the resistance of was found to be reversible and to follow a power-law relationship. The dependence of the electrical properties on the structure and morphology has also been discussed.