STRUCTURE AND OPTICAL-PROPERTIES OF ELECTROCHROMIC COPPER-OXIDE FILMS PREPARED BY REACTIVE AND CONVENTIONAL EVAPORATION TECHNIQUES

Copper oxide films (Cu(x)O) are deposited by thermal evaporation techniques using copper oxide (CuO) or copper (Cu) as starting material. By varying the deposition parameters, two main types of Cu(x)O film exhibiting different optical properties form. These are reddish gray and colorless films. The samples are characterised optically and morphologically. X-ray diffraction spectra reveal that evaporated Cu(x)O films are amorphous. Fourier-transform infrared spectra of the samples were studied to evaluate chemical identification. The refractive index, the extinction coefficient and the thickness of the films are evaluated from transmittance characteristics in the ultraviolet, visible and near-infrared regions. The refractive indices of the samples are between 2.9 and 3.1. The values determined for the optical constants are in agreement with the results found in the literature. We report for the first time that Cu(x)O films show reversible optical switching from the colored to bleached state. Optical transmittance measurements of the copper oxide film relative to indium tin oxide coated glass varied during coloring from spectral transmittance T(s) = 85-40%.