Electronic structure changes of Si(001)-(2x1) from subsurface Mn observed by STM

The deposition of Mn atoms onto the Si(001)-(2x1) reconstructed surface has been studied using scanning tunneling microscopy (STM) and first-principles electronic structure calculations. Room-temperature deposition of 0.1 ML (monolayer) of Mn gives rise to a disordered surface structure. After in situ annealing between 300 and 700 degrees C, most of the Mn is incorporated into three-dimensional manganese silicide islands, and Si dimer rows reappear in the STM images on most of the substrate surface. At the same time, rowlike structures are visible in the atomic-scale STM images. A comparison with calculated STM images provides evidence that Mn atoms are incorporated into the row structures in subsurface interstitial sites, which are the lowest-energy position for Mn on Si(001). The subsurface Mn alters the height and local density of states of the Si dimer atoms, causing them to appear 0.6 A higher than a neighboring Si dimer with no Mn below. This height difference that allows the detection the subsurface Mn results from a subtle interplay of geometrical and electronic effects.