EVOLUTION OF THERMOCHROMISM DURING OXIDATION OF EVAPORATED VANADIUM FILMS

Thin vanadium oxide films were made by vacuum evaporation followed by the annealing posttreatment in the presence of air. The thickness increased by a factor as large as approximately 2.3 on oxidation. Electron diffractograms indicated a bcc --> monoclinic transformation during the annealing, and electron micrographs showed pronounced grain growth. Temperature-dependent electrical conductivity as well as spectral transmittance was measured vs annealing time. At an initial thickness of 0.12-mu-m, it took a few hours to establish VO2 films with a well defined semiconductor-metal transition and concomitant thermochromic switching at approximately 57-degrees-C.