SUPERPERIODIC FEATURES OBSERVED ON GRAPHITE UNDER SOLUTION WITH SCANNING TUNNELING MICROSCOPY

Graphite has become one of the most commonly used substrates in scanning tunneling microscopy (STM). It is easily cleaved to yield atomically flat areas (and atomic resolution of the basal plane). However, it suffers some disadvantages. Steps are much more reactive than the basal plane and are easily decorated with contamination. Even clean surfaces yield unusual images: one example is the well-known giant corrugations out of the plane on graphite surfaces [1-3]. This paper deals with yet another unusual effect, which is the observation of superperiodic (SP) features in the plane of the basal layer. Structures with periods of up to several hundred angstroms may be seen on "clean" surfaces. These features have been reported by Hashizume et al [4] and Kuwabara et al. [5] in air while Lyding et al. [6] have reported similar air observations of graphite surfaces treated with a phosphotungstic acid solution. In this communication, we report these features as observed on a freshly cleaved graphite surface maintained under solution along with some details of the boundary between the "normal" and superperiodic graphite. Our characterization of graphite surfaces under solution with STM has revealed that a small percentage of the surface (approximately 1% or less) shows superperiodic features with observed periodicities in the plane ranging from approximately 45 to 440 angstrom with peak-to-peak amplitudes out of the plane extending from 2 to 5 angstrom. We see abrupt boundaries between the superperiodic and "normal" graphite with these boundaries showing high amplitude features.