The basal plane of highly oriented pyrolytic graphite (HOPG) has been studied by reflection electron microscopy (REM) before, during, and after tunnelling with a scanning tunnelling microscope (STM). The STM was designed to replace the standard specimen holder of a commercially available transmission electron microscope (TEM). Three types of contrast are found to be causally linked to tunnelling: (1) A dark feature which follows the tip during scanning; we attribute this to reversible elastic shear strain due to repulsion between the surface and tip. This extends over tens of nanometers. (2) A permanent bright region which forms under the tunnelling tip with repeated scanning; we attribute this to the increase in RHEED reflectivity which results from cleaning of the surface by abrasion and/or oxidation, possibly catalysed by the W tip. WO3 particles from the tip may play a role in the oxidation reaction at the surface, as observed in independent HREM studies. (3) A permanent bright band of contrast extending beyond the tunnelling tip; further study of this defect is required.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics