Liao, X.; Jeong, A.R.; Wilks, R.G.; Wiesner, S.; Rusu, M.; Felix, R.; Xiao, T.; Hartmann, C.; Bär, M.: Tunability of MoO3 thin-film properties due to annealing – in-situ monitored by hard x-ray photoemission. ACS Omega 4 (2019), p. 10985-10990
Open Accesn Version

The chemical and electronic structure of MoO3 thin films is monitored by synchrotron-based hard X-ray photoelectron spectroscopy while annealing from room temperature to 310 °C. Color-coded 2D intensity maps of the Mo 3d and O 1s and valence band maximum (VBM) spectra show the evolution of the annealing-induced changes. Broadening of the Mo 3d and O 1s spectra indicate the reduction of MoO3. At moderate temperatures (120−200 °C), we find spectral evidence for the formation of Mo5+ and at higher temperatures (>165 °C) also of Mo4+ states. These states can be related to the spectral intensity above the VBM attributed to O vacancy induced gap states caused by partial filling of initially unoccupied Mo 4d-derived states. A clear relation between annealing temperature and the induced changes in the chemical and electronic structure suggests this approach as a route for deliberate tuning of MoO3 thin-film properties.