Motion of Atomic Steps of Au(lll) Films on Mica

Abstract

We present a tunneling microscope investigaton of step motion on Au(lll) surfaces grown epitaxially on green mica. At ambient temperature and pressure, step edges of different heights move at typical rates of 50 Å/min over the course of an hour. Not all such surfaces have moving steps; surfaces with very low step densities are stable over an hour. On surfaces with moving steps, different parts of the steps move at different rates, so the shape of individual steps changes dramatically. We argue that this effect is not merely a mechanical scratching of the surface by the tip. This motion is not spontaneous but seems to be induced by external forces such as the bias between tip and surface, because step motion stops if tip scanning is stopped. These observations also hold for gold in a variety of aqueous solutions. We believe that the unstable behavior of the Au surfaces is due to a contamination during the preparation process. Thus we also present a detailed film preparation procedure for the gold on mica system. © 1991, American Chemical Society. All rights reserved.