Abstract
By combining results of adsorption/desorption measurements on powders and electrical conductivity studies on thick and thin films, the interaction of indium tin oxide with various ambient gas species and carbon monoxide as potential target gas was studied between room temperature and 700 °C. The results show that the indium tin oxide surfaces exhibit a significant coverage of water-related and carbonaceous adsorbates even at temperatures as high as 600 °C. Specifically carbonaceous species, which are also produced under carbon monoxide exposure, show a detrimental effect on oxygen adsorption and may impair the film’s sensitivity to a variety of target gases if the material is used in gas sensing applications. Consequently, the operating temperature of an ITO based chemoresistive carbon monoxide sensor should be selected within a range where the decomposition and desorption of these species proceeds rapidly, while the surface oxygen coverage is still high enough to provide ample species for target gas interaction.
Highlights
Indium tin oxide (ITO) is a degenerate n-type semiconductor composed of indium(III)oxide (In2 O3 ) and tin(IV) oxide (SnO2 ) with a typical mass ratio of 90:10
The surface of ITO powders and thicks films is host to oxygen adsorbates, but exhibits a significant coverage of various species that adsorb during ambient air exposure or from contaminations of the measuring gas
Notable adsorbates besides water and hydroxyl groups are carbon dioxide and other carbonaceous species, some of which are stable at temperatures of up to 700 °C
Summary
Indium tin oxide (ITO) is a degenerate n-type semiconductor composed of indium(III)oxide (In2 O3 ) and tin(IV) oxide (SnO2 ) with a typical mass ratio of 90:10. Its high intrinsic electrical conductivity of up to 1 × 104 S/cm makes the material one of the most important transparent conducting oxides (TCO). As such, it has found extensive application in the fabrication of transparent electrodes for liquid crystal displays (LCD) and touch screens, in organic light emitting diodes (OLED) and as antistatic coating for polymer films. ITO has seen considerable research as electrode material in gas sensing applications. It has been investigated for the detection of a variety of gases like
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