Electric-field-induced changes in scanning tunneling microscopy images of metal surfaces

Electric-field-dependent changes of scanning tunneling microscopy (STM) images of metal surfaces, metallic surface alloys, and ultra-thin magnetic films are predicted. We present a two-state model that demonstrates the general conditions leading to an inversion of the corrugation pattern as a function of field strength, and relate the effects to field-induced changes of the potential barrier. This image reversal for a pure metal surface corresponds to a change from a normal to an anticorrugated STM image. For ordered surface alloys, a switch of the imaged chemical species is possible and may even cause a change from a p(1 X 1) to a c(2 X 2) image at different fields. We explicitly demonstrate the effects by first-principles calculations of the Fe(001) surface. (C) 1999 Elsevier Science B.V. All rights reserved.