Comparative study of the air and oxygen plasma oxidation of highly oriented pyrolytic graphite:: a scanning tunneling and atomic force microscopy investigation

Pieces of highly oriented pyrolytic graphite were submitted to oxidation by air and oxygen plasma and the resulting surface topographies were compared using atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Noticeable differences were found between the modes of attack in both of these media. The atomic flatness of the typical terraces of the pristine material is maintained upon air oxidation, but disappears upon oxygen plasma exposure giving rise to a smoothly roughened topography with hillocks surrounded by lower areas. Etch pits were Formed following both treatments, these being much more abundant in the case of plasma. Atomic resolution was easily achieved for the air oxidized samples away from pit and step edges, and less easily in the case of plasma treatment, where a superstructure was observed around some defect areas. Increasing the exposure time to both air and oxygen plasma brought about quantitative rather than qualitative changes (increase in edge recession, growth of pits in diameter, depth and concentration). The origin of the differences between the results of exposure to both types of reagent are discussed and some mechanistic insights into their interaction with carbon are deduced. (C) 2000 Elsevier Science Ltd. All rights reserved.