Sensing mechanism of SnO2-based sensors for alcohols

doi:10.1016/0925-4005(93)85069-M

Sensors and Actuators B: Chemical

Volume 14, Issues 1–3, June 1993, Pages 511-512

https://doi.org/10.1016/0925-4005(93)85069-M Get rights and content

References (3)

M.J. Madou et al.

There are more references available in the full text version of this article.

Cited by (16)

Substrate effects on the oxygen gas sensing properties of SnO <inf>2</inf> /TiO <inf>2</inf> thin films
2006, Applied Surface Science
Citation Excerpt :
It is well known that the TiO2-based photocatalyst with an anatase phase exhibits superior photocatalytic effects to that with a rutile phase and that the anatase phase transforms into the rutile phase at temperatures exceeding 800 °C [3,8]. Over the past decades, SnO2-based sensors have emerged as the method of choice for solid-state gas detection alarms in domestic, commercial and industrial premises [9–11] on account of their sensitivity to reducing gases in low concentrations and their ability to operate at low temperatures [12–18]. In a previous study, the current authors enhanced the surface electron density of films via photocatalytic effects and demonstrated the corresponding improvement obtained in the oxygen sensitivity of the films [19].
In this study, SnO₂/TiO₂ thin films are fabricated on SiO₂/Si and Corning glass 1737 substrates using a R.F. magnetron sputtering process. The gas sensing properties of these films under an oxygen atmosphere with and without UV irradiation are carefully examined. The surface structure, morphology, optical transmission characteristics, and chemical compositions of the films are analyzed by atomic force microscopy, scanning electron microscopy and PL spectrometry. It is found that the oxygen sensitivity of the films deposited on Corning glass 1737 substrates is significantly lower than that of the films grown on SiO₂/Si substrates. Therefore, the results suggest that SiO₂/Si is an appropriate substrate material for oxygen gas sensors fabricated using thin SnO₂/TiO₂ films.
Sensitivity enhancement for H<inf>2</inf> gas detection using a SnO<inf>2</inf>-Ag<inf>2</inf>O-PdO<inf>x</inf> nanocrystalline system
2006, Materials Science and Engineering: B
Thick film H₂ sensors were fabricated using SnO₂ loaded with Ag₂O and PdO_x. The composition that gave highest sensitivity for H₂ was in the wt.% ratio of SnO₂:Ag₂O:PdO_x as 93:5:2. The nano-crystalline powders of SnO₂–Ag₂O–PdO_x composites synthesized by sol–gel method were screen printed on alumina substrates. Fabricated sensors were tested against gases like H₂, CH₄, C₃H₈, C₂H₅OH and SO₂. The composite material was found sensitive against H₂ at the working temperature 125 °C, with minor interference of other gases. H₂ gas as low as 100 ppm can be detected by the present fabricated sensors. It was found that the sensors based on SnO₂–Ag₂O–PdO_x nanocrystalline system exhibited high performance, high selectivity and very short response time to H₂ at ppm level. These characteristics make the sensor to be a promising candidate for detecting low concentrations of H₂.
Effects of O <inf>2</inf> /Ar flow ratio on the alcohol sensitivity of tin oxide film
2006, Applied Surface Science
The aim of this study is to find the effects of oxygen flow rate during manufacturing on the sensitivity of SnO₂ (tin oxide) thin films to ethanol (C₂H₅OH). In this study, an RF sputtering process was employed to fabricate the SnO₂ thin films. The SnO₂ was deposited on gold electrode silicon microchips. A target composed of SnO₂ doped with 1 at.% Li was used with a working pressure of 3 mTorr. The RF power was fixed at 150 W. The reaction gas was a mixture of argon and oxygen. The total flow rate was constant at 50 sccm with the O₂/Ar ratio varying from 0.2 to 0.8. An annealing heat treatment was employed at 400 °C for 1 h to stabilize the properties of the films. The sensitivity of the film to ethanol was tested by placing the micro-reactor device on a hot plate, heated to 300 °C, and measuring the variation of electrical resistivity of the film with and without the presence of ethanol. The results show that an O₂/Ar flow ratio of 0.2 produces films with the highest ethanol sensitivity. Before heat treating, the ethanol sensitivity was 126. After heat treating at 400 °C for 1 h, the sensitivity decreased to 104.
Ethanol vapor detection in aqueous environments using micro-capacitors and dielectric polymers
2005, Sensors and Actuators, B: Chemical
A technique for the measurement of ethanol concentrations in aqueous mixtures is reported, in which a permeable membrane is used to transport ethanol vapors to a microelectromechanical (MEMS) chemi-capacitor array. The fixed plate micro-capacitors were filled with a polymeric dielectric material, siloxanefluoro alcohol (SXFA), whose dielectric constant increased upon absorption of ethanol vapor. Measurements of the mixture's liquid-phase concentration were made in the vapor-phase by sampling the saturated vapors through a hydrophobic, vapor permeable nanopore filter. The performance of these sensors was characterized over a range of ethanol/water mixture concentrations and flow cell temperatures. The limit of detection (LOD) for ethanol in water using the capacitive micro-sensors in the present arrangement was found to be 40 ppm.
Influence of noble metals on the structural and catalytic properties of Ce-doped SnO<inf>2</inf> systems
2004, Sensors and Actuators, B: Chemical
This paper discusses the influence of the presence of a second dopant (Pt or Pd) on the SnO₂·Ce matrix. The characteristics of the material and the catalytic activity of oxidizing methanol were evaluated. Two routes were used to prepare the SnO₂·5 mol% Ce·1 mol% NM (NM=Pt or Pd). Transmission electronic microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and chromatographic assays were used to study the samples. Almost no changes in the morphology were detected when the samples were prepared by the impregnation route. In contrast, preparation by the chemical route (modified polymeric precursor (MPP) route) revealed crystallite growth and CeO₂ segregation. No sample showed any metallic cluster, but all the samples containing noble metal displayed a very marked catalytic property, suggesting significant activity even at room temperature. The products formed were CO₂ and water, representing a competitive advantage from the standpoint of environmental protection.
Effects of crystal structures on gas sensing properties of nanocrystalline ITO thick films
2003, Sensors and Actuators, B: Chemical
Two kinds of nanocrystalline indium tin oxide (ITO) powders with different crystal structures—rhombohedral and cubic—were prepared using a coprecipitation process through the control of pH of a mixing solution and aging time after coprecipitation. The two powders have the same particle size of 15 nm in diameter but different morphologies (spherical for rhombohedral and rectangular for cubic). The gaseous ethanol sensing characteristics of the sensors prepared by the two ITO powders were quite different. The sensitivity of rhombohedral ITO sensor was high compared to that of the cubic ITO sensor across all temperatures. The reason for this is explained through the viewpoint of the binding energy as shown in XPS measurement and the surface structure relating to the crystal structure.

View all citing articles on Scopus

View full text