ORIGIN OF DARK REGIONS IN SCANNING-TUNNELING-MICROSCOPY IMAGES FORMED BY THERMAL-OXIDATION OF SI(111) SURFACE

We report on the theoretical analysis of dark regions in scanning tunneling microscopy (STM) images formed on a Si(111) surface oxidized at room- and high-temperatures. We have found that the darkness of surface Si atoms in STM images depends on whether or not the dangling bond of the outermost Si atom is terminated by an O atom. The reason for this is that STM current flows through dangling bond states, which are eliminated by termination with O atoms. Based on calculations, we have found the dark regions to be oxidized regions and the darker regions to be more deeply oxidized regions. This is consistent with experimental results previously reported.