Scanning tunneling microscopy and spectroscopy of the thermally oxidized (0001) basal plane of highly oriented pyrolitic graphite

Scanning tunneling microscopy and spectroscopy (STM/STS) are used to study thermal oxidation effects on an HOPG surface. The STM images reveal circular pits randomly distributed over atomically flat terraces. The detailed studies near the pit edges show (root 3 x root 3)R30 degrees superstructure, electron density of state oscillations or extra contrast regions. The precise STS measurements on the bottom of the pits and on the top plane away from the pits on the thermally oxidized graphite do not show substantial differences in comparison to pure unoxidized graphite. The STS I/V measurements recorded near the pit edges, where extra contrast appeared show distinct asymmetric form. In our interpretation the specific tunneling current shape is due to created oxygen functionalities (C-OH, C-OOH)on the graphite surface and is not related to perturbation caused by step. The influence of oxygen functionalities on the tunneling current is discussed. (C) 1998 Elsevier Science B.V.