Structural and optical characterization of VOx films doped with W by ion implantation

Formation of tungsten doped VO₂ thermochromic films was achieved by high-energy ion implantation and thermal annealing. The implantation was done at 1.0 MeV with W doses from 0.8 to 6×10¹⁵ ions/cm² on a multi-phased VO_x film on Si. Ion implantation caused substantial amorphization of the film due to irradiation damage. However, crystalline films with a dominant W-doped VO₂ phase were obtained by thermal annealing at 400°C for 60 minutes in air. The implanted films after annealing exhibit good thermochromism characterized by a sharp change in optical transmittance upon the phase transition with significantly reduced critical temperature, e.g., being 35°C for a W dose of 6×10 ¹⁵ ions/cm² in comparison to 68°C of the bulk VO₂. It was suggested that W-doped VO₂ film can be obtained by ion implantation and thermal annealing from a multi-phased or even an amorphous VO_x film which is easier to form than a single-phased VO₂