Atomic force microscopy characterization of sputtered vanadium oxide thin films grown on Al2O3 substrate

Vanadium oxide (V2O5) thin films, which are good candidates for the realization of gas detectors, have been grown on rough alumina substrates and characterized by atomic force microscopy (AFM). The films were prepared by radiofrequency reactive sputtering, with different concentrations of oxygen in the growth atmosphere; after deposition the samples were thermally treated in order to get the best sensitivity to different gases. Because of the structures already present on the rough alumina substrate, AFM showed large topographical variations (several hundred nanometers) for V2O5 films grown on a rough alumina substrate. For both thermally treated and untreated samples, the roughness increases with increasing percentage of oxygen, but the sample with the best sensing properties (15% of oxygen) shows a characteristic minimum. Moreover, we observe that the thermal treatment also produces a general decrease in roughness, which is especially marked in samples with a low percentage of oxygen. The sensor has been tested with NO2, and the best sensitivity was obtained for an operating temperature around 300 degrees C.