Fabrication of V2O5/NiO double-layer film with hydrophilic property and evaluation of the effects of V2O5 coating on electro-optical parameters of NiO film

A double-layer V2O5/NiO super-hydrophilic surface was produced by spin-coating sol-gel method. The structural measurements have shown that V2O5 coating reduces the crystallinity of NiO thin film. The electrical characterization shows V2O5/NiO double-layer undergoes a transition from a semiconductor state to a metal phase at 250 degrees C. The band gap of NiO thin film (3.1 eV), has considerably shortened in V2O5/NiO double-layer film (2.8 eV). The thickness obtained from the cross-sectional image of V2O5/NiO sample is about 584 nm and shows an apparent interface between V2O5 and NiO layers. Besides, coating of V2O5 on NiO increases its surface roughness, which leads to more light scattering and less light transmittance. The super-hydrophilic nature of double-layer films (contact angle, theta < 7 degrees) at room temperature and under UV radiation indicates that those are suitable for self-cleaning application. The photoluminescence spectrum shows the extra V2O5 layer remarkably enhances UV and visible emissions of NiO thin film.