Structural and electronic evolution on the Ge(111)-Ag surface.

Abstract

High-resolution core-level photoelectron spectroscopy has been used to study three different silver-induced surface reconstructions on the Ge(111) surface. At the lowest coverage a (4\ifmmode\times\else\texttimes\fi{}4) structure is formed, which displays a similar Ge 3d core-level line shape as the clean c(2\ifmmode\times\else\texttimes\fi{}8) surface. Details in the spectra are discussed with respect to possible models. The Ge(111)-Ag (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} structure Ge 3d spectrum is dominated by a very strong contribution assigned to the two topmost Ge layers in a missing top layer structure, similar to the Si(111)-Ag (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} surface. A weak bulk peak is present on the high-binding-energy side of the spectrum, while a third contribution assigned to Ge in phase boundaries is included in the fit on the lower-binding-energy side. A comparison with results obtained from the Ge(111)-Au \ensuremath{\surd}3 structure points to substantial differences between the two noble-metal-induced \ensuremath{\surd}3 reconstructions on the Ge(111) surface. Finally, after further deposition of silver at room temperature, the \ensuremath{\surd}3 geometry is locally broken creating a (6\ifmmode\times\else\texttimes\fi{}6) structure and a new surface-related peak emerges on the low-binding-energy side of the Ge 3d spectrum, which was interpreted as being due to Ge atoms floating on top of the outermost surface layer. The valence band also revealed the existence of small metallic silver islands.