The morphology of tin cluster assembled films and the effect of nitrogen

Thin films produced by depositing tin clusters with sizes between 5 and 10 nm onto silicon nitride substrates were found to be highly coalesced resulting in grains with sizes similar to 30 nm. Exposing the clusters to nitrogen before they were deposited significantly reduced the coalescence between them and resulted in granular films where the clusters mostly retained their shape. This is due to a small amount of tin nitride forming in the clusters. The coalesced and granular films were used to fabricate tin oxide gas sensors. This was done by depositing the two types of films onto silicon nitride chips and then oxidising them by baking at 250 A degrees C for 24 h. It was found that the sensors composed of uncoalesced clusters were much more sensitive to hydrogen. This was attributed to the smaller grain size and the larger surface area of the granular films.