Charged defects on Ge(111)-c(2×8): characterization using STM

We have studied various defects present on the Ge(111)-c(2×8) surface using scanning tunneling microscopy (STM). Images at different bias-voltages reveal defects that appear as voltage-dependent variations in brightness. Empty-state images, in particular, taken with low bias voltages show characteristic delocalized brightness variation around some defects. These particular defects have a net charge relative to the clean, unperturbed Ge(111)-c(2×8) surface. We identify various types of defects and describe their charge states. This unique observation of a delocalized variation in the images of Ge(111)-c(2×8) is attributed to the various charged defects allied to poor surface screening of this semiconducting surface.