Local density of states of partially oxidized ag(110) surfaces observed using scanning tunneling microscope light-emission spectroscopy

We have observed the scanning tunneling microscope (STM) light-emission spectra of partially oxidized Ag(110) surfaces with atomic spatial resolution. The STM image visualized Ag-O chains along the [001] direction as light rows, separated by a distance n x a from adjacent light rows. Here, n is an integer between 2 and 7, and a is the surface lattice constant of Ag in the [1-110] direction. The STM light-emission spectra were measured for tip locations over the light rows and the midpoints of the darkly imaged areas sandwiched by two adjacent light rows. While the spectral shapes of the STM light-emissions were identical, their amplitudes showed atomic-site dependence, i.e., the STM light-emission intensities showed atomic-site dependence without any spectral differences. The STM light-emission intensities at the midpoints of the dark areas increased with n. The STM light-emission intensities of the light rows were independent of the widths of the adjacent dark areas. The experimental results were analyzed by the dielectric theory of STM light-emission, and it was found that the observed atomic-site dependence is caused by electronic states localized along the light rows. These states are identified as the py and pz surface bands induced by adsorbed oxygen.