ABSTRACT Zinc 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,...
moreABSTRACT Zinc 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.
We approached the problem of sensing gaseous pollutants and malodors originating as a result of decomposition of organic compounds via chemoresistive sensors. A set of four screen-printed films based on two types of mixed tin and titanium...
moreWe approached the problem of sensing gaseous pollutants and malodors originating as a result of decomposition of organic compounds via chemoresistive sensors. A set of four screen-printed films based on two types of mixed tin and titanium oxides, mixed tungsten and tin oxides, and zinc oxide has been tested vs. the main gaseous components of 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 their monitoring. We also demonstrated that the array is robust under solicitation by harmful interference gases such as CO, C6H6, NO2 and NO.
ABSTRACT The 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...
moreABSTRACT The 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.
ABSTRACT Nanophased cadmium sulfide powder was synthesized with a simple route and characterized with thermal, structural and morphological analysis. Conductometric gas sensors based on thick films of synthesized CdS were fabricated by...
moreABSTRACT Nanophased cadmium sulfide powder was synthesized with a simple route and characterized with thermal, structural and morphological analysis. Conductometric gas sensors based on thick films of synthesized CdS were fabricated by means of screen-printing technology and their sensing properties were tested on a selection of alcohols, aldehydes, ketones and other gaseous compounds. We found that, at working temperature of 300 °C, the CdS films show a strong selectivity vs alcohols, proving that they can efficiently detect alcohols in mixtures where aldehydes and other interferers are present. The response was found to be proportional to the length of the alcoholic chain, and a possible sensing mechanism that accounts for this property was proposed.
Numerous medical studies show that tumor growth is accompanied by protein changes that may lead to the peroxidation of the cell membrane with consequent emission of volatile organic compounds (VOCs) by breath or intestinal gases that...
moreNumerous medical studies show that tumor growth is accompanied by protein changes that may lead to the peroxidation of the cell membrane with consequent emission of volatile organic compounds (VOCs) by breath or intestinal gases that should be seen as biomarkers for colorectal cancer (CRC). The analysis of VOCs represents a non-invasive and potentially inexpensive preliminary screening technique. An array of chemoresistive gas sensors based on screen-printed metal oxide semiconducting films has been selected to discriminate gases of oncological interest, e.g., 1-iodononane and benzene, widely assumed to be biomarkers of colorectal cancer, from those of interference in the gut, such as methane and nitric oxide.
ABSTRACT An algorithm for compensating water vapor pressure in CO detection is proposed here and tested on SnO2 thick-film gas sensors. For each sensor working at a fixed temperature, the conductance, G, is fitted by an analytical...
moreABSTRACT An algorithm for compensating water vapor pressure in CO detection is proposed here and tested on SnO2 thick-film gas sensors. For each sensor working at a fixed temperature, the conductance, G, is fitted by an analytical surface, whose expression can be inverted to determine the CO concentration once the water partial pressure is measured. As soon as the rate of water-vapor pressure change is slower than about 300 Pa/min, G is a function of the temperature, water vapor and CO concentration. If quicker water vapor variations occur instead, the sensing film undergoes a non-negligible transitory phenomenon during which G assumes different values even at fixed water vapor pressure and temperature. This phenomenon prevents the compensation from working properly. An explanation of the behavior is offered by the interpretation of kinetics equations at surface.
ABSTRACT Resistance and capacitance measurements, as a function of frequency, were carried out to analyze and model the electrical behavior of undoped titanium dioxide (TiO2) films. The sensing measurements were carried out in a chamber...
moreABSTRACT Resistance and capacitance measurements, as a function of frequency, were carried out to analyze and model the electrical behavior of undoped titanium dioxide (TiO2) films. The sensing measurements were carried out in a chamber with independent temperature, pressure, gas composition, and flow rate control. With the aim of evaluating the electrical response of the sample as a function of the surrounding atmosphere, a frequency range of 100 Hz–4 MHz was used (vacuum or air at atmospheric pressure). The resistance and capacitance responses were obtained with the help of impedance spectroscopy technique. The impedance response versus frequency allows the discrimination between grain-boundary capacitance (Cgb) and resistance (Rgb) contributions. A model, taking into account the possible effects due to grain size is proposed in order to work out the permittivity of the material.
ABSTRACT The 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...
moreABSTRACT The 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.
Nanopowders of pure and of Mn-, Ta- and Zr-loaded (5wt.%) WO3 were prepared and printed as thick films. Investigation of the influence of the doping on morphology, structure and gas response versus NO2 has been performed. Pure nanometric...
moreNanopowders of pure and of Mn-, Ta- and Zr-loaded (5wt.%) WO3 were prepared and printed as thick films. Investigation of the influence of the doping on morphology, structure and gas response versus NO2 has been performed. Pure nanometric WO3 was prepared by a modified sol–gel synthesis while loading was carried out by impregnation with Mn(II), Ta(V) and Zr(IV) chlorides. Addition
ABSTRACT A set of sensors based on nanostructured single and mixed metal oxides has been prepared and employed in acetaldehyde detection within 0.1–10 ppm, this range being useful for many applications. Electrical characterization has...
moreABSTRACT A set of sensors based on nanostructured single and mixed metal oxides has been prepared and employed in acetaldehyde detection within 0.1–10 ppm, this range being useful for many applications. Electrical characterization has been performed in laboratory at several working temperatures, in order to obtain the optimal operating condition. ZnO working within 450–550 °C, was found to best respond to acetaldehyde. The response vs. concentration curves for all the sensors was a power law with an exponent of 0.5, compatible with the oxidation of acetaldehyde catalyzed by the surface. A decay in the sensor response to acetaldehyde due to humidity was observed and discussed.
ABSTRACT Sensing of typical gaseous pollutants and malodors as a result of decomposition of organic compounds via chemoresistive gas sensors has been addressed. Screen-printed films of a solid solution of mixed Sn and Ti oxides, of mixed...
moreABSTRACT Sensing of typical gaseous pollutants and malodors as a result of decomposition of organic compounds via chemoresistive gas sensors has been addressed. Screen-printed films of a solid solution of mixed Sn and Ti oxides, of mixed W and Sn oxides, and ZnO have been selected for the purpose. We demonstrated that the choice of these films for this specific use leads to an improvement in selective detection of such gases under either dry or wet condition. An array of such sensors is shown to be suitable for implementation of deconvolution algorithms because it makes it easier the concentration data processing.
... [41] Michele Sacerdoti, Maria Chiara Dalconi, Maria Cristina Carotta, Barbara Cavicchi, Matteo Ferroni, Stefano Colonna, Maria Luisa Di Vona, Journal of Solid State Chemistry, 177,6 (2004) 1781-1788 . 1826 11th International Ceramics...
more... [41] Michele Sacerdoti, Maria Chiara Dalconi, Maria Cristina Carotta, Barbara Cavicchi, Matteo Ferroni, Stefano Colonna, Maria Luisa Di Vona, Journal of Solid State Chemistry, 177,6 (2004) 1781-1788 . 1826 11th International Ceramics Congress Page 10. ...
ABSTRACT We operated WO3 gas sensor at room temperature under UV illumination. The observed increase in conductance is expected to depend on interband electronic transition, being the bandgap of the material smaller than the incident...
moreABSTRACT We operated WO3 gas sensor at room temperature under UV illumination. The observed increase in conductance is expected to depend on interband electronic transition, being the bandgap of the material smaller than the incident light. Strong evidence that the main phenomenon is instead surface barrier modulation is given in the present work.
ABSTRACT Zinc 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,...
moreABSTRACT Zinc 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.
We approached the problem of sensing gaseous pollutants and malodors originating as a result of decomposition of organic compounds via chemoresistive sensors. A set of four screen-printed films based on two types of mixed tin and titanium...
moreWe approached the problem of sensing gaseous pollutants and malodors originating as a result of decomposition of organic compounds via chemoresistive sensors. A set of four screen-printed films based on two types of mixed tin and titanium oxides, mixed tungsten and tin oxides, and zinc oxide has been tested vs. the main gaseous components of 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 their monitoring. We also demonstrated that the array is robust under solicitation by harmful interference gases such as CO, C6H6, NO2 and NO.
ABSTRACT Nanophased cadmium sulfide powder was synthesized with a simple route and characterized with thermal, structural and morphological analysis. Conductometric gas sensors based on thick films of synthesized CdS were fabricated by...
moreABSTRACT Nanophased cadmium sulfide powder was synthesized with a simple route and characterized with thermal, structural and morphological analysis. Conductometric gas sensors based on thick films of synthesized CdS were fabricated by means of screen-printing technology and their sensing properties were tested on a selection of alcohols, aldehydes, ketones and other gaseous compounds. We found that, at working temperature of 300 °C, the CdS films show a strong selectivity vs alcohols, proving that they can efficiently detect alcohols in mixtures where aldehydes and other interferers are present. The response was found to be proportional to the length of the alcoholic chain, and a possible sensing mechanism that accounts for this property was proposed.
ABSTRACT One of the main applications of metal oxide gas sensors is the environmental monitoring of urban and industrial areas, where the pollution level may become dangerously high. In this frame, environmental temperature plays a...
moreABSTRACT One of the main applications of metal oxide gas sensors is the environmental monitoring of urban and industrial areas, where the pollution level may become dangerously high. In this frame, environmental temperature plays a fundamental role, since it may influence the sensor signal. This work aims at measuring ambient temperature induced conductance variation, and to suggest a theoretical model to account for that.
ABSTRACT Sensing of light alkanes via chemoresistive gas sensors has been addressed. Screen-printed films of a solid solution of mixed Sn and Ti oxides have been selected for the purpose. We demonstrate that the films sensitively detect...
moreABSTRACT Sensing of light alkanes via chemoresistive gas sensors has been addressed. Screen-printed films of a solid solution of mixed Sn and Ti oxides have been selected for the purpose. We demonstrate that the films sensitively detect 100 ppm of such gases and 500 ppm of methane, the two levels being by far lower than the alarm limits for these gases. Information about the working mechanism of chemical reactions on the surface has been discussed under either dry or wet condition.
... Acknowledgments The authors wish to thank Silvia Cirillo for the thesis work, from which the present analysis started. References ... Cervi A, Carotta MC, Giberti A, Guidi V, Malagu` C, Martinelli G,Puzzovio D (2008) Metal-oxide solid...
more... Acknowledgments The authors wish to thank Silvia Cirillo for the thesis work, from which the present analysis started. References ... Cervi A, Carotta MC, Giberti A, Guidi V, Malagu` C, Martinelli G,Puzzovio D (2008) Metal-oxide solid solutions for light alkane sensing. ...
ABSTRACT Photo-enhanced surface chemical activity of cadmium sulfide gives rise to a wide class of surface-dependent phenomena, such as heterogeneous photocatalysis, chemoresistivity, and chemiluminescence, which have several...
moreABSTRACT Photo-enhanced surface chemical activity of cadmium sulfide gives rise to a wide class of surface-dependent phenomena, such as heterogeneous photocatalysis, chemoresistivity, and chemiluminescence, which have several technological and scientific applications. In this work, the photochemical properties of nanostructured cadmium sulfide films are investigated by means of electrical conductance measurements in controlled atmosphere, while irradiated by light of wavelengths ranging from 400 to 645 nm. Chemisorption of benzene, carbon monoxide, methane, ethanol, and hydrogen sulfide onto CdS surface has been analyzed as a function of the wavelength, in a gas concentration range of the order of parts per million. It resulted that the increase of photoconductance with gas adsorption is resonant with the bandgap energy. It turns out that this resonant enhancement of the surface chemical activity can be of advantage for all the optical and chemical mechanisms that depend upon it. An interpretation of these results, in terms of electronic optical transitions and Fermi level shift induced by light, is proposed.
ABSTRACT An algorithm for compensating water vapor pressure in CO detection is proposed here and tested on SnO2 thick-film gas sensors. For each sensor working at a fixed temperature, the conductance, G, is fitted by an analytical...
moreABSTRACT An algorithm for compensating water vapor pressure in CO detection is proposed here and tested on SnO2 thick-film gas sensors. For each sensor working at a fixed temperature, the conductance, G, is fitted by an analytical surface, whose expression can be inverted to determine the CO concentration once the water partial pressure is measured. As soon as the rate of water-vapor pressure change is slower than about 300 Pa/min, G is a function of the temperature, water vapor and CO concentration. If quicker water vapor variations occur instead, the sensing film undergoes a non-negligible transitory phenomenon during which G assumes different values even at fixed water vapor pressure and temperature. This phenomenon prevents the compensation from working properly. An explanation of the behavior is offered by the interpretation of kinetics equations at surface.
ABSTRACT Resistance and capacitance measurements, as a function of frequency, were carried out to analyze and model the electrical behavior of undoped titanium dioxide (TiO2) films. The sensing measurements were carried out in a chamber...
moreABSTRACT Resistance and capacitance measurements, as a function of frequency, were carried out to analyze and model the electrical behavior of undoped titanium dioxide (TiO2) films. The sensing measurements were carried out in a chamber with independent temperature, pressure, gas composition, and flow rate control. With the aim of evaluating the electrical response of the sample as a function of the surrounding atmosphere, a frequency range of 100 Hz–4 MHz was used (vacuum or air at atmospheric pressure). The resistance and capacitance responses were obtained with the help of impedance spectroscopy technique. The impedance response versus frequency allows the discrimination between grain-boundary capacitance (Cgb) and resistance (Rgb) contributions. A model, taking into account the possible effects due to grain size is proposed in order to work out the permittivity of the material.
... M. Cristina Carotta, Alessio Giberti, Vincenzo Guidi, Cesare Malagù, Beatrice Vendemiati, and Giuliano Martinelli INFM-Dipartimento di Fisica, Università di ... Further on, some of powders synthesized via sol-gel route at our...
more... M. Cristina Carotta, Alessio Giberti, Vincenzo Guidi, Cesare Malagù, Beatrice Vendemiati, and Giuliano Martinelli INFM-Dipartimento di Fisica, Università di ... Further on, some of powders synthesized via sol-gel route at our laboratory, are described: in particular, SnO2, TiO2 ...
Nanopowders of pure and of Mn-, Ta- and Zr-loaded (5wt.%) WO3 were prepared and printed as thick films. Investigation of the influence of the doping on morphology, structure and gas response versus NO2 has been performed. Pure nanometric...
moreNanopowders of pure and of Mn-, Ta- and Zr-loaded (5wt.%) WO3 were prepared and printed as thick films. Investigation of the influence of the doping on morphology, structure and gas response versus NO2 has been performed. Pure nanometric WO3 was prepared by a modified sol–gel synthesis while loading was carried out by impregnation with Mn(II), Ta(V) and Zr(IV) chlorides. Addition
