Modifications in the phase transition properties of predeposited VO2 films

Abstract

Thin films of the phase transition material vanadium dioxide (VO2) were deposited by thermal oxidation of e-beam evaporated vanadium on a variety of bulk materials. Substrate effects on transition temperature are confirmed as being due to a mismatch between film and substrate thermal expansion coefficients. Decreasing tensile stress results in a lowering of VO2 transition temperature. Effects of low-energy Ar+ bombardment on the electrical and optical properties of these predeposited VO2 films were investigated. Bombardment energies in the range 138–500 eV at 1.0–1.3 mA/cm2 for 120–180 s were provided by a Commonwealth Millatron. The higher Ar+ energies resulted in collapse of the VO2 optical transmittance hysteresis loop, while low-energy Ar+ ions caused both a downward shift in the transition temperature and a decrease in hysteresis loop width, suggesting a dependence of these quantities on intrinsic stress. In addition, large decreases in cold-state resistivity are reported and attributed to a reduction of the surface oxide by the low energy argon beam.