Comparative study of single Cu, Ag, Au, and K atoms adsorbed on Si(111)-(7×7)

Using first-principles calculations, we have studied the geometrical, electronic, and dynamic properties in detail for a single K, Cu, Ag, and Au atoms adsorbed on Si(111)-7×7 surface. We have found that single noble metal Cu, Ag, and Au atoms favor the multicoordinate adsorption sites to saturate the maximum number of dangling bonds on Si(111)-7×7 surface. For Cu, Ag, and Au atoms adsorbed on the stable or metastable adsorption sites, the bright spots in the simulated negative bias scanning tunnel microscopy (STM) images are found right on the nearby Si adatoms which are induced by a combination of the charge redistribution and the height increase in Si adatoms induced by the single metal-atom adsorption. The finite increase in charge density between Cu, Ag, and Au atoms and the nearby bonding Si atoms indicate the bond is covalent in nature. In comparison, an alkali metal K atom loses its s electron to the Si surface, and the charge transfer results in the bright spot at the Si adatom in simulated negative bias STM image.