1,721,046 research outputs found
Electrical and spectroscopic analysis in nanostructured SnO2: "long-term" resistance drift is due to in-diffusion
Full text linkA model for conductance in n-type non-degenerate semiconductors is proposed and applied to polycrystalline SnO2 used as a gas sensor. Particular attention is devoted to the fundamental mechanism of Schottky barrier formation due to surface states in nanostructured grains. Electrical and absorption infra-red spectroscopic analysis constitutes strong evidence for oxygen diffusion into the tin oxide grains. The model is then extended to include oxygen in- and out-diffusion. Thus, it is possible to explain the “long-term” resistance drift in oxygen for fully depleted grained samples in terms of tunneling through the double barrier.Fil: Malagù, Cesare. Universita Di Ferrara; Italia. Istituto di Acustica e Sensoristica “O. M. Corbino”; ItaliaFil: Giberti, Alessio. Universita Di Ferrara; ItaliaFil: Morandi, Sara. Universita di Torino; ItaliaFil: Aldao, Celso Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentin
Current–voltage characteristics of nanostructured SnO2 films
No full textThe conduction process in nanostructured SnO2 gas sensors under an external voltage has been studied, in order to work out the main differences between fully depleted and not fully depleted grains. With a model based on the double Schottky barrier which occurs at the interface between two adjacent grains, it has been shown that the shape of the current–voltage curves is completely different in the two cases. The conduction carriers available in not fully depleted grains respond to the external electric field, contributing to the total electrostatic potential, this being a crucial difference from fully depleted grains. In this work, we determined the shape of the barrier in both cases and provided a calculation of the electrical current as a function of the external bias, including tunneling and thermionic contributions. Theoretical simulations of current–voltage characteristics have been compared with experimental data
Evidence of a surface effect of UV light on WO3 thick-film gas sensors
No full textThe electrical conductance of a tungsten trioxide (WO3) thick-film gas sensors under UV illumination has been investigated. Measurements have been performed in two different environments: in pure nitrogen and in dry synthetic air. The effect of light on the electrical behavior has then been evaluated and interpreted. In particular, the observed increase in conductance after illumination of the surface is expected to be due to interband electronic transitions, since the bandgap of the material is smaller than the energy of the incident photons. An evidence for strong contribution of surface chemical processes to this variation,through surface barrier modulation, is given in this work
Spectroscopic and electrical evidence of transition to nanostructured behaviour in SnO2
No full textSnO2 sensors with two different average grain size showed diverse behaviors through electrical and spectroscopic characterizations. In the case of direct current electrical responses, the increase in conductance for the same temperature rise was, on average, about three times larger for larger grained samples. Impedance spectroscopic plots were obtained in dry air and were fitted with the same equivalent circuit for the two granulometries, showing important differences in the fitting parameters. The two techniques present interesting analogies for the same temperature variations. We interpreted this behaviour in terms of barrier modulation through gas chemisorption and oxygen indiffusion, also taking into account of tunneling contribution to conductivity
WO3 sensing properties enhanced by UV illumination: An evidence of surface effect
No full textThe behaviour of the conductance of a nanostructured WO3-based chemioresistive gas sensor under UV
illumination was investigated in a synthetic air and in a pure nitrogen environment. The observed increase
in conductance under illumination is expected to depend on interband electronic transitions, being the
bandgap of the material smaller than the energy of the incident photons. In the present work we show
an evidence that an important contribution to this increase is given by surface barrier modulation rather
than interband transitions. Indeed, the conductance variation from the dark to the light was interpreted
in terms of a direct effect of the light on the adsorbed oxygen ions
Electrical, optical and sensing properties of photo-activated ZnO thin films
No full textZinc oxide is a wide gap semiconductor whose chemical activity at surface can be enhanced by proper electromagnetic radiation. This property opens the door to room temperature gas sensing with this material. In this work, nanosized ZnO powder was synthesized by sol-gel technique. Then, structural and morphological characterizations were carried out by means of X-Ray Diffraction and SEM techniques. Thin films were deposited by spin coating technique on both glass and alumina substrates, to perform optical absorption spectra and electrical conductance measurements, respectively. The electro-optical properties were studied on the photo-activated films, in air and in nitrogen conditions, to investigate first on the basic surface-oxygen interaction in photo-activated condition. Then, gas measurements were also performed in air and in nitrogen, to acquire information on the photo-enhanced surface chemistry, in order to be applied to gas sensing
Sensing of typical gaseous malodors in organic decomposition products
No full textWe approached the problem of sensing gaseous pollutants and malodors originated as a result of
decomposition of organic compounds via chemoresistive sensors. A set of four sensors based on
screen-printed films of mixed tin and titanium oxides, mixed tungsten and tin oxides, and zinc oxide
has been tested vs. the main gaseous components of these malodors. N-butanol was also considered
because of its importance as a reference gas in the odorimetric intensity scale. We found that, under
proper working conditions, the films can sensitively detect such gases either in dry or in wet
environments, within the range of concentrations of interest for monitoring
Intra-grain oxygen diffusion influence on conductivity of polycrystalline semiconducting compounds.
No full textThe distribution of oxygen vacancies in metal oxide nanograins was modeled, considering the possibility of oxygen in- and out-diffusion, in a field-assisted and thermionic emission conduction model. Implications in electrical responses of SnO2 to oxygen concentration and temperature variations will be discussed and compared to an oxygen-free tin semiconducting compound
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