New approaches to deposit thermochromic VO2 films for "smart windows"

Vanadium dioxide (VO2) is one of the most attractive thermochromic materials, which shows large changes in optical and electrical properties at around 68degreesC nearly room temperature. We already reported that rf magnetron sputtering using V2O3 or V2O5 targets enable us to deposit polycrystalline thermochromic VO2 films with high reproducibility. (1)) However, the thickness of the VO2 films should be larger than 400 nm because stoichiometry x of the VOx film deposited on glass substrate was higher than 2 (slightly over oxidation state) in the early stages of the film growth. In this study, ZnO polycrystalline films were deposited as a buffer layer between the VO2, film and glass substrate also by rf magnetron sputtering, which have been known to exhibit <001> preferred orientation in the wide range of the deposition conditions. Very thin thermochromic VO2, films with thickness of 50 urn were successfully deposited on the ZnO coated glass substrate because of the heteroepitaxial relationship of VO2(010)[100]//ZnO(001)[100][010][(1) over bar(1) over bar0]. Such thin VO2 films could be applied for the "smart low-E windows" with the high total energy efficiency in architecture and automobiles.