Surface dynamics studied by time-dependent tunneling current

Scanning tunneling microscopy (STM) is not only an excellent tool for the study of static geometric structures and electronic structures of surfaces due to its high spatial and energy resolution, but also a powerful tool for the study of surface dynamic behaviors, including surface diffusion, molecular rotation, and surface chemical reactions. Because of the limitation of the scanning speed, the video-STM technique cannot study the fast dynamic processes. Alternatively, a time-dependent tunneling current, I-t curve, method is employed in the research of fast dynamic processes. Usually, this method can detect about 1000 times faster dynamic processes than the traditional video-STM method. When placing the STM tip over a certain interesting position on the sample surface, the changing of tunneling current induced by the surface dynamic phenomena can be recorded as a function of time. In this article, we review the applications of the time-dependent tunneling current method to the studies of surface dynamic phenomena in recent years, especially on surface diffusion, molecular rotation, molecular switching, and chemical reaction.