In situ infrared emission spectroscopic study of the adsorption of H 2O and hydrogen-containing gases on Ga 2O 3 gas sensors (original) (raw)
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Sensors and Actuators B: Chemical, 1996
N-type semiconducting Ga20 3 thin-films which are stable at high temperatures are used as a new basic material for gas sensors. This study investigates the extent to which a gas-filtering layer of compact, amorphous SiO2 is capable of modifying gas sensitivity. Using a sputtering technique and a Si target, the SiO2 layer, which, typically, has thicknesses of 30 nm and 300 nm, is deposited onto the Ga203 gas sensor. It was found that sensors with this surface layer structure had an extremely high specificity for H 2 when they were operated at 700°C. Other gases that were tested included CO, CO2, CH4, isobutene, ethanol, acetone, NO, NH3; variations of humidity and oxygen content were also investigated. There was a marked increase in H2-sensitivity between the modified and unmodified sensors.
Sensors and Actuators B: Chemical, 2010
a b s t r a c t Ga 2 O 3 nanowires (NWs) incorporated into capacitance-based room temperature gas sensors were functionalized with acetic and pyruvic acid (AC and PA, respectively) with the goal of achieving higher selectivity toward different groups of hydrocarbons. Fourier transform infrared spectroscopy (FTIR) was used to determine the geometry of the resulting adsorbate complexes. A bridge-like geometry was observed for adsorbed AC and a mixture of different geometries for PA, some of which had hydrogenbonded OH groups. In addition, FTIR studies showed evidence of the enolic form of PA adsorbed on the surface. The AC-functionalized NWs showed a significant decrease in response to such common analytes as acetone and nitromethane as well as to triethylamine (TEA). In the case of PA-functionalized NWs, no response was observed to nitromethane, however, the response to TEA increased one order of magnitude compared to the bare NWs. FTIR spectroscopy was used to obtain more insight into the mechanism of interaction of AC-and PA-functionalized NWs with these analytes. This work demonstrates the use of a bifunctional molecule (PA) to modify the response of an oxide sensor in a way that a monofunctional molecule (AC) cannot. A significant result of this work is that the functionalization chemistry does not presume the existence of OH groups on the initial oxide surface.
Sensors and Actuators B: Chemical, 1995
The effect of humidity on tin-oxide thick-film gas sensors has been studied in the case of carbon monoxide, methan methanol, butane and propane. The results are qualitatively explained under the assumption that water molecules dissocia on the tin-oxide surface and produce hydroxyl species capable of acting as electron donors. Moreover, palladium and vanadiw when used as additives, affect the overall behaviour of sensors in the presence of water vapour. To reduce the effect humidity, thin organometallic films have been deposited on top of thick tin-oxide-based sensors in order to act as filters. T1 results show that both the sensitivitjr df these sensors and the effect of humidity are decreased.
Materials Chemistry and Physics, 2020
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Investigation of the oxygen gas sensing performance of Ga 2O 3 thin films with different dopants
Sensors and Actuators B-chemical, 2003
The oxygen gas sensing performance of Ga2O3 semiconducting thin films doped with Ce, Sb, W and Zn have been investigated. These thin films have been prepared by the sol–gel process and were deposited on sapphire transducers with inter-digital electrodes and a platinum heater integrated. The sensors were exposed to various concentrations of oxygen gas in an ambient of nitrogen and the gas sensing performance has been examined. The responses of sensors doped with Ce, Sb, W and Zn were stable and reproducible at their respective operating temperatures. It was observed that Ga2O3 films doped with Ce, Zn and W are promising for oxygen gas sensing applications.
Ga2O3(Sn) Oxides for High-Temperature Gas Sensors
Nanomaterials
Gallium(III) oxide is a promising functional wide-gap semiconductor for high temperature gas sensors of the resistive type. Doping of Ga2O3 with tin improves material conductivity and leads to the complicated influence on phase content, microstructure, adsorption sites, donor centers and, as a result, gas sensor properties. In this work, Ga2O3 and Ga2O3(Sn) samples with tin content of 0–13 at.% prepared by aqueous co-precipitation method were investigated by X-ray diffraction, nitrogen adsorption isotherms, X-ray photoelectron spectroscopy, infrared spectroscopy and probe molecule techniques. The introduction of tin leads to a decrease in the average crystallite size, increase in the temperature of β-Ga2O3 formation. The sensor responses of all Ga2O3(Sn) samples to CO and NH3 have non-monotonous character depending on Sn content due to the following factors: the formation of donor centers and the change of free electron concentration, increase in reactive chemisorbed oxygen ions con...
Properties of metal oxide gas sensors with electrodes placed below the sensing layer
2014
In this work, we investigate the influence of position of electrodes on the sensitivity of hydrogen gas sensors based on TiO 2 thin films. We have prepared two types of sensors with platinum comb-like electrodes deposited on top and under the TiO 2 layer. Response of these sensors to hydrogen gas in the concentration range of 0 -10 000 ppm at temperature of 350 °C has been studied. The sensors with electrodes placed under the TiO 2 layer showed two orders of magnitude lower sensitivity for 10 000 ppm compared to sensors with electrodes on top of the layer, but it was considerably increased when thickness of the TiO 2 layer was lowered. This gives a possibility to improve the sensitivity of gas sensors in which the electrodes must be placed below the sensing layer for their protection from harsh environment.
On the Low-Temperature Response of Semiconductor Gas Sensors
Journal of Sensors
The present paper compares three different kinds of semiconductor gas sensing materials: metal oxides (MOX), hydrogenterminated diamond (HD), and hydrogenated amorphous silicon (a-Si:H). Whereas in MOX materials oxygen is the chemically reactive surface species, HD and a-Si:H are covalently bonded semiconductors with hydrogenterminated surfaces. We demonstrate that these dissimilar semiconductor materials exhibit the same kind of low-temperature gas response. This low-temperature response-mechanism is mediated by a thin layer of adsorbed water with the semiconductor materials themselves acting as pH sensors. In this adsorbate-limited state the gas sensitivity is limited to molecular species that can easily dissolve in H 2 O and subsequently undergo electrolytic dissociation. At higher temperatures, where a closed layer of adsorbed water can no longer exist, the gas response is limited by direct molecule-semiconductor interactions. In this latter mode of operation, MOX gas sensors respond to adsorbed gases according to their different oxidising or reducing properties. Hydrogenated amorphous silicon (a-Si:H), on the other hand, exhibits a significantly different cross sensitivity profile, revealing that gas-surface interactions may largely be restricted to analyte molecules with lone-pair and electron-deficient three-centre orbitals.