Energy shifts and broadening of atomic electron levels near impurity-covered metal surfaces

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Abstract
The energy shifts and broadening of atomic levels near chemisorbed impurities on a metal surface are calculated using the complex scaling technique. It is shown that the presence of impurities on metal surfaces can both shift the positions and change the widths of electronic levels in atoms near the impurity. Results are presented for K, S, and Cl impurities. For electropositive impurities, the tunneling rates between the atom and the surface are increased. Due to the long-range electrostatic fields induced by the impurity, the atomic levels shift downward with respect to the Fermi energy. For atoms near an electronegative impurity, the widths of the atomic levels narrow due to an increased surface potential barrier between the atom and the surface. This barrier also shifts the atomic levels upward with respect to the Fermi level. The results of the calculation clearly show that the assumption of imagelike shifts of atomic levels near impurity-covered metal surfaces is not valid in the region where charge transfer typically occurs.