OBSERVATION AND CHARACTERIZATION BY SCANNING TUNNELING MICROSCOPY OF STRUCTURES GENERATED BY CLEAVING HIGHLY ORIENTED PYROLYTIC-GRAPHITE

In addition to atomically smooth plateaus, many different structures can be observed on freshly cleaved highly oriented pyrolytic graphite (HOPG) by scanning tunneling microscopy (STM). These features vary greatly in morphology and structure. Images at cleavage steps, graphite strands, and ultrasmall particles were obtained with atomic resolution. Also seen on a larger scale were island-forming fiber clusters and folded-over and broken flakes. The cleavage of HOPG thus leaves broken graphite pieces and other features, which can cover as much as 1-10% of the surface. These structures are characterized by high conductivity, high stability, and a graphitic atomic structure, which help serve to distinguish these STM images from those produced by species placed on HOPG. These results were used to explain images of some features obtained on HOPG coated with the polymer Nafion. These are assigned to unusual graphitic structures formed during sample preparation rather than to Nafion itself.