Intrinsic Properties of Multi-Layer TiO(2)/V(2)O(5)/TiO(2) Coatings Prepared via E-Beam Evaporation

Nanocomposite multi-layer TiO(2)/V(2)O(5)/TiO(2) thin films were prepared via electron-beam evaporation using high-purity targets (TiO(2) and V(2)O(5) purity > 99.9%) at substrate temperatures of 270 °C (TiO(2)) and 25 °C (V(2)O(5)) under a partial pressure of oxygen of 2 × 10(−4) mbar to maintain the stoichiometry. Rutherford backscattering spectrometry was used to confirm the layer structure and the optimal stoichiometry of the thin films, with a particle size of 20 to 40 nm. The thin films showed an optical transmittance of ~78% in the visible region and a reflectance of ~90% in the infrared. A decrease in transmittance was observed due to the greater cumulative thickness of the three layers and multiple reflections at the interface of the layers. The optical bandgap of the TiO(2) mono-layer was ~3.49 eV, whereas that of the multi-layer TiO(2)/V(2)O(5)/TiO(2) reached ~3.51 eV. The increase in the optical bandgap was due to the inter-diffusion of the layers at an elevated substrate temperature during the deposition. The intrinsic, structural, and morphological features of the TiO(2)/V(2)O(5)/TiO(2) thin films suggest their efficient use as a solar water heater system.