Scanning tunneling microscopy and spectroscopy investigation of the atomic and electronic structure of CoO islands on Ag(0 0 1)

Ultrathin CoO-films were deposited on Ag(0 0 1) by evaporation of Co in O2-atmosphere. During subsequent heating (400–500 K) well-ordered island with (0 0 1) and (1 1 1) orientation are formed. Scanning tunneling microscopy (STM) images of CoO(0 0 1) islands show a corrugation with the atomic periodicity of the Ag(0 0 1) substrate for gap voltages in the range of −1.5 to +1.5 V. (1 1 1) oriented Co oxide islands reveal a moiré-like modulation with hexagonal structure. The heights of the different islands, as measured by STM, depend in a characteristic way on the bias voltage. Maps of the tunneling current as a function of bias voltage have been recorded using scanning tunneling spectroscopy (STS) at a temperature of 100 K. The evaluation of the multidimensional data set allows the characterization of the CoO(0 0 1) and (1 1 1) oriented Co oxide islands as well as the Ag(0 0 1) substrate, with respect to the electronic density of states and the influence on the imaging contrast in STM.