Bi to β-Bi2O3 thin films transformation by thermal oxidation in air at low temperature

Bismuth oxidation by thermal treatment has been studied by several groups, however, low temperature (well below melting) oxidation is rarely reported in the literature. In this work, we focused on the straightforward phase transition from bismuth to the β-Bi2O3 phase, by gradually heating the bismuth film. This is proved that by carrying out the oxidation process at the low temperature 175 °C (as compared to the melting temperature 271 °C) it is possible to turn pristine bismuth into β-Bi2O3. In order to achieve this transformation, the thermal treatment was span for up to 10 h, finding that at 6 h the initially opaque bismuth film becomes optically translucid, meaning that the bismuth oxide beta phase is reaching downwards to the substrate. For 8 and 10 h of thermal treatment the bismuth film is clearly fully oxidized. The bismuth to β-Bi2O3 transformation was characterized by using Raman micro-spectroscopy, UV–Vis Spectroscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Our results demonstrated a feasible, simple and reliable method for the synthesis of β-Bi2O3, at well below melting temperature. [Display omitted] •Metallic bismuth thin films were the precursors to obtain the beta phase of bismuth oxide by thermal oxidation.•Bismuth thin films were slowly oxidized at low temperature.•Bi oxidizes gradually towards β-Bi2O3.•Optical, structural, and morphological features of the Bi/β-Bi2O3 thin films are reported.