Effect of humidity on the properties of NO2 sensors based on thin WO3 and SnO2 films modified with gold

The effect of humidity on the electrical and gas-sensitivity properties of NO2 sensors based on thin (∼100 nm) nanocrystalline films of tungsten trioxide and tin dioxide with additions of gold in the bulk and on the surface (Au/WO3:Au, Au/SnO2:Sb,Au) is investigated. It is found that the conductivity of these films in pure air increases only slightly as absolute humidity A rises from 2 to 16 g/m3, the responses for nitrogen dioxide in the concentration range of 0.45–10 ppm do not depend on humidity, and the response time is shortened as A rises. Analysis of experimental data using a model based on the assumed microcrystal availability in WO3 and SnO2 thin films connected by conductivity bridges shows that the values of the heat of adsorption ΔEN and activation energies of adsorption EaN and desorption EdN of ions NO2− on the films surface modified gold, do not depend on the humidity.