Structure-property relationship of nanocrystalline tin dioxide thin films grown on ((1)over-bar012) sapphire

This work demonstrates the correlation between the microstructure of nanocr ystalline SnO2 thin films and their electrical transport properties and sen sitivities to reducing gases. SnO2 thin films were deposited on the ((1) ov er bar 012) surface of alpha -Al2O3 (sapphire) using electron beam evaporat ion of a pure SnO2 ceramic source, followed by postdeposition annealing in synthetic air. SnO2 thin films with randomly oriented nanosized grains were obtained by annealing an amorphous SnO film deposited at room temperature. Films with nanosized SnO2 laminates were obtained by annealing epitaxial a lpha -SnO films deposited at 600 degreesC. The laminates are oriented with their (101) planes parallel to the substrate surface and have a high densit y of coherent twin boundaries. Hall measurements indicate that the electron concentration of the film with laminate grains is much lower than for the film with random grains. It is proposed that the high density twin boundari es inside the laminates trap conducting electrons and significantly reduce the electron concentration. As a result, the sensitivity to reducing gases of the laminar film is higher than that of the corresponding film with rand omly oriented SnO2 grains. It was also found that the grain size has strong effects on the sensitivity of SnO2 films. (C) 2001 American Institute of P hysics.