Electron standing waves on the Si(111)- 3×3-Ag surface

Electron standing waves have been observed near step edges and out-of-phase domain boundaries on the Si(111)-3×3-Ag surface using scanning tunneling microscopy at 6 K. This means that this surface has a two-dimensional free-electron-like surface electronic state. Their wavelengths change with the bias voltages, so that the dispersion relations between energy and wave number have been obtained. We have found two types of out-of-phase domain boundaries of the 3×3-Ag structure, one of which acts as a potential barrier for the surface-state electrons to make the standing waves, while the other type does not.