Nanocrystalline WO, films were produced by advanced reactive gas deposition
onto alumina substrates. The as-deposited films had a tetragonal crystal s
tructure and a mean grain size of around 6 nm, as found by X-ray diffractio
n and electron microscopy, Sintering at a temperature tau (S) > 770 K yield
ed monoclinic films, We investigated the gas-sensing properties of films si
ntered up to 870 K, After an initial "activation" at tau (S) = 750 K, the n
anocrystalline WO3 films showed excellent gas-sensing properties, even at r
oom temperature, on exposure to law concentrations of H2S in air. As little
as 10 ppm of H2S made the conductance increase by a factor of about 10(3)
within 10 min. The initial properties could be restored by heating the film
s to 530 K for 1 min.