where α is the absorbance, unitless; hν is photon energy, eV; A is an independent parameter of the photon energy for the respective transitions, eV; Eg is the band gap, eV.
The surface properties of the thin films were examined by the Atomic Force Microscopy (AFM) technique (Asylum research MFP-3D-BIO™). The surface area of the thin films and the root mean square (RMS) average roughness were determined by the Gwyddion software program, version 2.22 (http://gwyddion.net). The grain size was measured directly from cross sectional AFM images at the base of each grain.
The changes of the water contact angles were monitored by the sessile drop method (Surface Energy Evaluation (SEE) System, Advex Instruments). Static contact angle measurements by the sessile drop method were measured using a set of standard testing liquids at ambient temperature, 22 °C and 60% relative humidity. The data analysis was performed via SEE System software. Each resulting contact angle was an average of 5 measured values that were recorded 30 s after reposing each drop of 5 μL volume on the sample surface.