Selective surface modifications with a scanning tunneling microscope

A combination scanning tunneling microscope (STM) and scanning electron microscope has been used to selectively pattern and image Si(111) and Si(001) surfaces in a SEM chamber. Both positive and negative STM tip polarities produce marks on the surface with linewidths as small as 20 nm. We have transferred these patterns to the silicon substrate via selective wet chemical etching. We demonstrate a well-defined voltage threshold for patterning at negative tip bias. The modifications are consistent with a model based on hydrogen depassivation and electric field mediated deposition. The physical mechanism for positive tip bias patterning is shown to be different than that for negative bias. At positive bias, the patterning is consistent with selective surface contamination. (C) 1997 American Institute of Physics.