Effect of as-deposited residual stress on transition temperatures VO2 thin films

Abstract

Transmittance loops upon thermal cycling of VO2 thin films were found to change among films with different fabrication conditions that lead to different transition temperatures (Tts) from that of a strain-free VO2 single crystal, 68 degreesC. The residual stresses in the films quantitatively determined from x-ray diffractometry were used to explain this variation. Electron spectroscopy for chemical analysis spectra showed that the difference in the binding energy of core electrons 2p(1/2) and 2p(3/2) of the vanadium atom are affected by residual stress and proportional to Tts of the films. The bond length between vanadium and oxygen atoms at room temperature varies with different residual stresses and, furthermore, affects the movements of both atoms during phase change (and hence the Tt of VO2 thin films). Residual stresses also affect the hysteresis span of the transmittance loop. The relationship between the residual stress of as-deposited VO2 films and the relative positions between vanadium and oxygen atoms are also delineated in detail.