Scanning tunneling microscopy and ultraviolet photoemission spectroscopy studies of oxygen adsorption on Ru(1 0 1̄ 0)

Scanning tunneling microscopy (STM) and ultraviolet photoemission spectroscopy (UPS) measurements for oxygen adsorption on Ru(1 0 1̄ 0) were performed. The STM images taken on the c(2 × 4)-2O phase showed a c(2 × 4) symmetry, in which four Ru atoms without any oxygen atoms in between were supposed to be imaged as a bright spot. In the c(2 × 4)-2O phase, a domain boundary was identified. In the (2 × 1)p2mg-2O phase, the STM images arrays showed zigzag structures in the [1 2̄ 1 0] direction which is in accordance with the oxygen zigzag chains derived in earlier work for this phase. The UPS spectra showed that the O 2p state is located at 5.9 eV in binding energy. Upon oxygen adsorption, ΔΦ, the change in work function, increases from 0.5 eV in the c(2 × 4)-2O phase to 0.7 eV in the (2 × 1)p2mg-2O phase with respect to the clean Ru(1 0 1̄ 0) surface.