Optical investigation of redox properties of amorphous V$_{2}$O$_{5}$ thin films

We report a high sensitivity of the optical properties of amorphous V$_{2}$O$_{5}$ thin films to redox reaction. Temperature dependence of spectroscopic ellipsometry data showed that the amorphous V$_{2}$O$_{5}$ films were optically anisotropic and the optical constants of the films changed irreversibly in high vacuum at around 420-480 K. Formation of oxygen vacancies in V$_{2}$O$_{5}$ film by the reduction process may result in the anisotropic changes in the optical constants and optical band gaps. Layered structure of V$_{2}$O$_{5}$ and structural relaxation by the formation of vanadyl oxygen vacancies were attributed to the optical anisotropy and the changes in the optical properties, respectively.