Tip-enhanced Raman scattering spectroscopy of nanometer-scale domains in Ni(110)-(2×1) O surface

We have succeeded in detecting Raman scattered light from a monolayer-oxygen-covered domain with a nanometer-scale lateral extent in the Ni(110)-(2×1) O surface by tip-enhanced Raman scattering (TERS) spectroscopy. A mosaic of light and dark nanometer-size domains is observed in the scanning tunneling microscope (STM) image of the surface. In the TERS spectra taken when the STM tip was fixed over the dark domain, a peak that exceeded the uncertainty of the background signal level was observed at 30meV. This peak disappeared when the tip was moved over the light domain adjacent to the dark domain. Since the Raman shift energy agrees well with one of the vibrational energies of oxygen reported for the Ni(110)-(2×1) O surface, we conclude that only the dark domain is covered with oxygen atoms.