Formation of hydrogen tungsten bronze by proton implantation

Abstract

Proton ions were implanted into polycrystalline (c-) and amorphous (a-)WO 3 thin films at an acceleration energy of 60 keV to fluences from 1 × 10 17 cm −2 to 1 × 10 18 cm −2. The dc electrical conductivity and optical transmission spectra were measured on the thin films before and after the implantations. Upon the implantation, conductivity in c-WO 3 thin films at 300 K was significantly increased from 10 −5 Scm −1 to 10 −1 (for 1 × 10 17 cm −2), 10 1 (3 × 10 17 cm −2) or 10 2 Scm −1 (1 × 10 18 cm −2). The temperature dependence of conductivity changed from thermal-activation type (activation energy ∼0.13 eV) for the 1 × 10 17 cm −2 sample to degenerate type beyond the fluence of 2 × 10 17 cm −2. A similar conductivity increase was observed in the implanted a-WO 3 thin films; however, this increase was two orders of magnitude smaller than that in the corresponding c-WO 3 thin films. A broad optical absorption band peaking at ∼1 eV was observed for all the implanted specimens. This induced band is similar to that arising from plasma oscillation due to conduction electrons in hydrogen tungsten bronze. Therefore, it is concluded that hydrogen tungsten bronze was formed by implanting protons into polycrystalline and amorphous WO 3 thin films.