Structural and electronic properties of cleaved Si(111) upon room-temperature formation of an interface with Ag

Abstract

Photoemission yield spectroscopy, low-energy-electron-diffraction (LEED), and Auger measurements are performed on a set of UHV cleaved silicon (111) surfaces with different bulk dopings as a function of silver coverage $\ensuremath{\Theta}$. The Ag layers are obtained by evaporation on the substrate kept at room temperature and $\ensuremath{\Theta}$ varies from zero to a few monolayers (ML). It is demonstrated that the interface forms in two steps. First, an ordered layer of silver develops on top of the 2\ifmmode\times\else\texttimes\fi{}1 reconstructed silicon which remains unperturbed. The silver layer exhibits a $(\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7})R$ 19.1\ifmmode^\circ\else\textdegree\fi{} structure and is completed at about 0.7 ML of Ag. Both the work function and the ionization energy decrease by the same amount, the density of surface states being only slightly perturbed. Then upon further silver deposition, the 1\ifmmode\times\else\texttimes\fi{}1 LEED structure of Ag(111) develops on top of the preceding ones which remain observable while new electron states induced by silver metal are added without changing the electronic character of the interface.