Poisoning semiconductor oxides

The lifetime of metal oxide gas sensors in general is several years. Nevertheless poisoning effects can occur when exposed to silicones. An example of commercial Ga203-semiconductor gas sensors is shown in Fig. 5.32. 

In the application to semiconductors, especially, chlorine trifluoride should be a high-purity product. Such a product is commercially available with a chlorine trifluoride content of 99.9%-99.99%. Chlorine trifluoride is shipped as a liquid under its own vapor pressure in stainless steel cylinders. It is classified as an oxidizer and poison by DOT [79],... 

It is worthwhile pointing out again that the photo-electrons produced in XPS are incapable of passing through more than perhaps 1 to 5 nm of a solid. 1 hus. the most important applications of electron spectroscopy. like X-ray microprobc spectroscopy, are for the accumulation of information about surfaces. Kxam-ples of some of its uses include ideniihcaiion of active sites and poisons on catalytic surfaces, determination of surface contaminants on semiconductors, analysis of the composition of human skin, and study of oxide surface layers on metals and alloys. 

Titanium dioxide is an n-type semiconductor that is used in thin-film oxygen and humidity sensors [155, 156]. Doping with other metal oxides (e.g., iron oxides) increases the sensitivity and selectivity of the titania oxygen sensors [157, 158]. In comparison to zirconia, titania sensors have a better resistance against lead poisoning. 

Thermodynamic factors are expected to be different for the various stepwise mono-oxidation processes showed in eqs. 8-11. Equation 12 is another poisoning reaction, which can involve any species (with n = 1—3) and could compete with eq. 4, but it can be minimized by keeping low the concentration of C. It is worth noting that in the above scheme, it is implicitly assumed that SA is a chemical species also a semiconductor electrode can take this role. In the latter case, the optimization of the reactions involved in eq. 4 vs. eq. 5 can be obtained by modifying the level of the semiconductor conduction band by an applied bias. The irreversibility of the overall process is given, rather than by eq. 7, by removal of the negative charge from SA via an external circuit. 

Arsenic is a metalloid on the borderline between metals and nonmetals. Certain arsenic compounds, such as gallium arsenide (GaAs), are used as semiconductors. The white oxide As O is the assassin s poison arsenic. Two- or three-tenths of a gram is a lethal dose. On the other hand, some persons have built up a tolerance for it, so that they can ingest each day an amount that would normally be fatal. 

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