Effect of annealing temperature on electronic band structural, optical constant, and band gap of uranium dioxide films

Abstract

The physical and chemical properties of uranium oxides attracted the interest of people due to their wide use in the nuclear industry. In this work, the temperature-dependent optical properties of UO2 films are determined by spectroscopic ellipsometry. The thickness-controllable uranium dioxide (UO2) thin films were prepared fastly by spin-coating nano-UO2 inks on substrates. Inks of monodisperse UO2 nanoparticles with an average size of 6 nm were successfully synthesized via the thermal decomposition of uranyl acetate in a mixture solution. Structural characterization of the UO2 films was reported by X-ray diffraction and X-ray photoelectron spectroscopy. It demonstrated that the films keep stable as UO2 below 200 ℃, and changed to U3O8 after being heat-treated at 500 ℃ for 30 min in the air. Furthermore, the optical properties of the films were investigated by spectroscopic ellipsometry (SE). The bandgap of the UO2 film was determined as nearly 2.70 eV which is consistent with theoretical expectations (2.69 eV). and the U3O8 film was 2.33 eV. This study is helpful for the fundamental understanding of the properties of the uranium oxide system and contributes to the database of optical properties of UO2.