Controllable synthesis of α and β-Bi2O3 through anodization of thermally evaporated bismuth and its characterization

Abstract

Novel bismuth trioxide (Bi2O3) nanostructured films were fabricated via anodization using thermally evaporated bismuth films. The thin films were characterized by X-ray diffraction, UV–vis diffuse reflectance spectroscopy, photoluminescence, high resolution scanning electron microscopy and Raman spectroscopy. Our results showed that 300°C annealed Bi2O3, possessed good thermal stability with alpha phase. On annealing above 400°C, nanoparticles jointed together with an average size of 32nm. On further increasing the annealing temperature to 600°C, the nanostructures were transformed into metastable β-Bi2O3 film. The obtained nanostructures in the thin film surface consist of faceted particles of size 75 to 200nm. The band gap value of bismuth trioxide thin films decreases with increase in annealing temperature. Interference fringes present in the optical reflectance spectra confirmed the formation of smooth and uniform films prepared by anodization. Photoluminescence peaks arised due to the inhibition of spontaneous emission originating through Bi2O3 lattice defects such as oxygen vacancies and Bi interstitials. The gas sensing performance of bismuth trioxide thin films were obtained for the oxidizing gases NO2 and CO2 at room temperature. Sample post annealed at 300°C shows the better sensitivity for NO2 among the other annealed samples. Additionally, the relationship of the crystalline nature with best phase of Bi2O3 for the electrochemical performance was investigated. Among the Bi2O3 samples, Bi-300 and Bi-400 samples with good crystallinity had the highest capacitance of 85 and 90F/g at the scan rate 3mV/s. It shows that the Bi2O3 nanostructures can serve as promising electrode materials for supercapacitors.