Scanning Tunneling Microscope Light Emission Spectra ofAu(110)−(2×1)with Atomic Spatial Resolution

We have measured the STM (scanning tunneling microscope) light emission spectra of $\mathrm{Au}\left(110\right)-(2\times 1)$ at 80 K with atomic spatial resolution. The individual Au atoms along the $(2\times 1)$ rows could be resolved in the STM image. Distinctly different emission spectra are observed depending on whether the tip is located over the atomic row or over the valley between the rows. The spectrum obtained over the row atoms can be ascribed to the emission by localized surface plasmons. The spectrum found over the valley contains emission from excitations atomically localized in the valley.