Soft X-ray absorption and emission study on anisotropic electronic structure of MoO3

Oxygen 1s soft X-ray absorption and emission spectroscopy (XAS and SXES) experiments have been carried out for layered MoO3 single crystal with three crystallography nonequivalent oxygen atoms; O1, O2, and O3 bonding with the Mo atoms along the b, c, and a axes, respectively. The polarization-dependent XAS results show that the conduction-band minimum of MoO3 consists of the O2 2pb components. The valence-band minimum (VBM) of MoO3 is, on the other hand, formed by the O2 2pa orbitals from the angular-dependent SXES spectra measured at the pre-edge of the O 1s absorption peak. The other SXES spectra have revealed that the O3 2pc states also contribute to the VBM and O1 2pb states locate at the bottom of the valence bands.