Periodic variations in the local surface potential of Si(111)-(5×2)-Au

The image-state-derived field-emission resonances (FERs) on a Si(111)-($7\ifmmode\times\else\texttimes\fi{}7$) surface that is partially covered by the gold-induced Si(111)-($5\ifmmode\times\else\texttimes\fi{}2$)-Au reconstruction, were probed by scanning tunneling spectroscopy measurements. On Si(111)-($5\ifmmode\times\else\texttimes\fi{}2$)-Au, a shift of the FER peak positions is observed compared to the bare $7\ifmmode\times\else\texttimes\fi{}7$ surface. Spatially resolved $dI/dV$ maps reveal a periodic variation of the higher-order FERs in the direction perpendicular to the chains of the quasi-one-dimensional Si(111)-($5\ifmmode\times\else\texttimes\fi{}2$)-Au reconstruction. The effect appears on a length scale of less than one nanometer and can be attributed to the local surface potential. Simple one-dimensional models reproduce the first seven FERs perfectly and allow extraction of the potential landscape. This landscape is confirmed by density-functional theory calculations, revealing an attractive well above the graphitic Si honeycomb chains due to low electron density.