A total current spectroscopy study of metal oxide surfaces: I. Unoccupied electronic states of ZnO and MgO

Unoccupied density of states (DOS) for the polar (0001) Zn, (000 (1) over b ar) O and non-polar (10 (1) over bar 0) ZnO surfaces and for a MgO(001)-c(2 x 2) thin film were studied using total current spectroscopy (TCS). TC spe ctra of the ZnO surfaces reveal the Zn 4s-O 2p band (6.2 eV) and two DOS ma xima in the Zn 4p-O 2p band which exhibited different energy positions on t he Zn-terminated (8.1 eV) and O-terminated (11.0 eV) surfaces. In the TC sp ectra of the MgO thin film, the energy location of Mg-derived (8.0, 14.8 an d 21.0 eV) and O-derived (11.6, 14.2 and 18.5 eV) maxima of DOS were determ ined. Previously reported data on DOS of these materials is discussed, and it is shown that additional detailed information on the energy structure of unoccupied DOS in ZnO and MgO in the 5-25 eV range above EF has been found .