Dependence of microstructure and thermochromism on substrate temperature for sputter-deposited VO2 epitaxial films

A systematic study on the epitaxial growth of VO2 films deposited on sapphire by sputtering at various substrate temperatures (T-s) was carried out. The deposited films were characterized by x-ray diffraction, high energy electron diffraction, Rutherford backscattering spectrometry, atomic force microscopy, and spectrophotometry. Epitaxial VO2 was obtained from a T-s of 300 degrees C which is the lowest reported yet. Two epitaxial relationships, i.e., a dominant VO2(010)//sapphire (110), (001)//(001) and a secondary VO2(100)//sapphire (110), (010)//(001), were confirmed. The epitaxial films show strong dependence of the morphology and thermochromism on T-s. Films deposited at above 400 degrees C exhibit changes in resistivity of Delta R>10(4) upon switching, while those deposited at T-s=300 degrees C have reduced Delta R of 10(2). The film obtained at T-s=300 degrees C exhibits novel transition properties, i.e., a largely reduced tau(c) (45 degrees C) even without any doping, and very little thermal hysteresis. (C) 1997 American Vacuum Society.