Atomic and electronic contributions to Si(111)-(7×7) scanning-tunneling-microscopy images

Bias-dependent scanning tunneling microscopy (STM), used in conjunction with atomic-charge superposition calculations, is shown to provide information on both atomic and electronic surface structure. Si (111) - (77) STM images measured with different bias voltages are compared with a number of recent structural models. Striking agreement is found with the stacking-fault-adatom model of Takayanagi. The unit-cell asymmetry found at negative sample bias is attributed to a stacking fault in one half of the unit cell, locally modifying the surface electronic structure.