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

We have studied various defects present on the Cc(lll)-c(2 x 8) surface usi ng scanning tunneling microscopy (STM). Images at different bias-voltages r eveal defects that appear as voltage-dependent variations in brightness. Em pty-state images, in particular, taken with low bias voltages show characte ristic delocalized brightness variation around some defects. These particul ar defects have a net charge relative to the clean, unperturbed Ge(lll)-c(2 x 8) surface. We identify various types of defects and describe their char ge states. This unique observation of a delocalized variation in the images of Ce(111)-c(2 x 8) is attributed to the various charged defects allied to poor surface screening of this semiconducting surface. (C) 2000 Elsevier S cience B.V. All rights reserved.