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.