ELECTRONIC STATES OF ASYMMETRIC DIMERS AT THE SI(100)-(2 X-1) SURFACE IN ELECTRIC-FIELDS

Electronic structures of Si(100)-(2 x 1) in electric fields are calculated by the self-consistent pseudopotential method. Assuming an asymmetric dimer model, we obtain a characteristic change in the charge distribution around the dimer due to applied fields of 0.6 V/angstrom-1.8 V/angstrom. It is found that the field of negative tip voltage repels the electron charge around an up atom of the dimer and pushes it to the inside of the bulk, reducing the charge imbalance of the asymmetric dimer. This result is consistent with the recent scanning tunneling microscope (STM) experiment, which analyzed the relation between the buckling of dimers and applied fields.