Electrostatic sample-tip interactions in the scanning tunneling microscope.

Local surface photovoltage (SPV) measurements were used to measure how the electric field of a scanning tunneling microscope tip perturbs the electronic band structure at Si(001), Si(111)-(7x7), and H-terminated Si(111) surfaces. The results demonstrate that tip-induced band bending is important under typical STM conditions even on surfaces whose surface Fermi levels are nominally «pinned.» Spatially resolved measurements of band bending as a function of sample bias show that atomic-scale contrast in SPV images can result from local variations in the ability of the surface states under the tip to screen external electric fields