STM Observations at the Atomic Scale of a Tilt Grain Sub-Boundary on Highly Oriented Pyrolytic Graphite

Abstract

We report here the first observations ai the atomic of a symmetrical tilt grain sub-boundary with a STM. Trie edge dislocations observed ai the atomic along trie boundary fine can be understood in the trame of geometrical models. These STM images also reveal a local modification of the charge density near the Fermi level in trie junction area. Grain boundaries and grain sub-boundaries are crystallographic defects charactenstic of zone transitions between two crystals with dilferent orientations. The manifestations of this kind of defects at the macroscopic scale were the object of numerous studies (using TEM essentially). Other techniques such as High-Resolution Electron Microscopy (HREM) Iii, Grazing-Incidence X-ray Scattering technique (GIXS) (2) or Fresnel contrast analysis in low-resolution images (3) provide, in some cases, information at a smaller scale. However, these techniques are heavy to use and Iimited in their spatial resolution (lateral as well as vertical). Owing to trie development of Scanning Tunneling Microscope (STM) defects such as grain boundaries can be studied at the atomic scale. The lateral resolution achieved with this type of microscope (< 1 A) allows one to study the very fine structure of these defects (atomic displacements in the junction area). This is also of particular interest when the interatomic distances of the studied crystal are less than the lateral resolution of a HREM for example (2 A), in the case of graphite for instance (in-plane C-C distance of1.42 A). Although graphite is one of the most STM studied compound, few observations of grain boundaries were reported on Higuly Oriented Pyrolytic Graphite (HOPG). These stems mainly