Vanadium dioxide (VO2) is a promising candidate for various thermochromic devices. Layering M film with amorphous silicon suboxide (a-SiOx) is an effective approach for controlling the thermochromic spectrum efficiently, since a-SiOx possesses an easily adjustable refractive index over a wide range. However, the crystalline quality of VO2 is so sensitive to under- and/or over-coated materials that the a-SiOx coatings may be disadvantageous with respect to material suitability. In this study, the controllability of the thermochromic spectrum of VO2 by employing a-SiOx layer was evaluated under several fabrication conditions and, as a result, it was found that an a-SiOx layer can control thermochromism well without any decline in the stability of VO2 crystalline growth, which strongly suggests the possibility of expansion in the optical design for efficient thermochromic control. (C) 2008 Elsevier B.V. All rights reserved.