Abstract
Reactive dual-target DC magnetron sputtering was used to prepare In–Sn oxide thin films with a wide range of compositions. The films were subjected to annealing post-treatment at 400 °C or 500 °C for different periods of time. Compositional and structural characterizations were performed by X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Rutherford backscattering and scanning electron microscopy. Films were investigated for gas sensing at 200 °C by measuring their resistance response upon exposure to acetaldehyde mixed with synthetic air. We found that the relative indium-to-tin content was very important and that measurable sensor responses could be recorded at acetaldehyde concentrations down to 200 ppb, with small resistance drift between repeated exposures, for both crystalline SnO2-like films and for amorphous films consisting of about equal amounts of In and Sn. We also demonstrated that it is not possible to prepare crystalline sensors with intermediate indium-to-tin compositions by sputter deposition and post-annealing up to 500 °C.
Highlights
Monitoring of indoor air quality is of great importance since people in industrialized countries spend as much as 80% to 90% of their time inside buildings or vehicles [1]
Poor indoor air quality has been associated with the so-called “sick building syndrome”, which refers to situations in which the users of the building develop diffuse disease symptoms and discomfort connected with the time spent in some buildings without acquiring any specific illness [2]
Due to inherent uncertainties in quantifying oxygen in the nanostructured In–Sn oxide films with X-ray photoelectron spectroscopy (XPS) or EDS, oxygen‐to‐metal ratios were measured with Rutherford backscattering spectroscopy (RBS)
Summary
Monitoring of indoor air quality is of great importance since people in industrialized countries spend as much as 80% to 90% of their time inside buildings or vehicles [1]. Among the VOCs, acetaldehyde is important since it is highly reactive and irritating to the skin, eyes and respiratory tract. It is highly odorous; the human perception limit in air is as low as 70 ppb [3]. Potential sources for acetaldehyde emissions include various combustion processes (wood, wastes, fossil fuels, tobacco, etc.) [4], and acetaldehyde can be emitted by, e.g., polymeric building materials and emulsion paints, and it can be an intermediate in the natural respiration of plants [5,6]
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