View of the empty states of the Si(100)-(2×1) surface via scanning tunneling microscopy imaging at very low biases

It is shown that the use of very-low-bias voltages in scanning tunneling microscopy of the Si(100)-2×1 surface achieves significantly greater sensitivity to the electronic states of the top atomic layer than does the use of typical larger bias voltages. Measurements with the increased sensitivity demonstrate that the conventional interpretation of empty-state images of Si(100) is inadequate. New spectroscopic assignments for observed features are proposed.