Variation of the local work function at steps on metal surfaces studied with STM

With a scanning tunneling microscope we have measured the apparent barrier height (ABH) on large terraces of the clean Cu(111) surface and large Au(111) terraces of the Au/Cu(111) surface, and the results are in good agreement with the correspondent surface work function. From the ABH images of these surfaces low-value valleys along steps are clearly visible, as expected from ``Smoluchowki smoothing.'' A simple simulation of the valley makes us to be able to determine that the smoothing-induced dipole moment for Au and Cu steps is $0.16\ifmmode\pm\else\textpm\fi{}0.05$ and $0.5\ifmmode\pm\else\textpm\fi{}0.15\mathrm{D}/\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{p}\mathrm{ }\mathrm{atom},$ respectively.