Electric field effects in STM imaging

We present a high voltage extension of the Tersoff-Hamann theory of STM images, which includes the effect of the electric field between the tip and the sample. The theoretical model is based on first principles electronic structure calculations and has no adjustable parameters. We use the method to calculate theoretical STM images of the monohydrate Si(100)-H(2$\times$1) surface with missing hydrogen defects at $- 2$~V and find an enhanced corrugation due to the electric field, in good agreement with experimental images.