STM STUDY OF SINGLE-CRYSTAL GRAPHITE

Freshly cleaved surfaces of single-crystal graphite (SCG) are shown to have very large expanses of step-free surface; however, the tunnelling signal is found to be considerably noisier than with HOPG. We speculate that the noise is due to carbon adatoms hopping onto the STM tip. Carbon adatoms are normally immobilized at steps. The lower step density on SCG results in an increased average surface concentration of carbon adatoms as compared with HOPG. Atomically resolved topographic images of the (0001) surface of SCG were also obtained. They show the same trigonal symmetry that characterizes the analogous images of HOPG, but with a two- to three-fold increase in corrugation depth. In addition to the low density of steps, SCG is relatively devoid of graphitic artifacts and pseudo-periodic features that have been mistaken for DNA and other genuine molecular structures, implying that SCG may be a useful substrate for STM studies of biological samples.