When applied to the study of semiconducting nanosized particles, Fourier
transform infrared spectroscopy allows the simultaneous analysis of the
chemical reactions occurring at the nanoparticle surface and the resultant
variations of the electrical conductivity. This technique has been used to
compare the sensing potentiality of three semiconductors (tin oxide, indium
oxide and tungsten oxide nanoparticles) before they are integrated in the
fabrication process of actual gas sensors.
It has been found that the sensitivity to CO of tin oxide and indium oxide
nanoparticles is fairly good whereas that of tungsten oxide is quasi nil.
However, tungsten oxide, like indium oxide, is very sensitive to oxygen and
reducing treatments. The presence of humidity irreversibly affects the response
of tin oxide to CO and oxygen, whereas that of indium and tungsten oxides to
both gases seems to be relatively independent from the moisture content. It is
generally observed that a higher operating temperature leads to a more stable
baseline and a faster response. Moreover, the formation of surface carbonate
groups observed in several cases under CO adsorption does not imply a larger
response, thus confirming that the carbonate formation is not a significant
factor in the CO detection mechanism.