Hyperthermal atomic oxygen beam-induced etching of HOPG (0001) studied by X-ray photoelectron spectroscopy and scanning tunneling microscopy

Abstract

The basal planes of highly oriented pyrolytic graphite (HOPG) surfaces were exposed to atomic oxygen (AO) beam with a translational energy of approximately 5eV at room temperature. The characterization of the surfaces was carried out using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). The XPS spectra of the hyperthermal AO-exposed surfaces indicated that the oxygen coverage reached the saturated value of 0.94 with the AO fluence of approximately 4×1017 atomscm−2. The initial reaction site of the AO on the defect-free HOPG (0001) surface was observed as a protrusion in the STM images. In contrast, a hillock-like structure was formed at the AO-exposed HOPG (0001) surfaces at high AO fluences. The density of protrusions, observed in the initial AO/HOPG reaction, increased in proportion to the AO fluence. The reaction yield of hyperthermal AO with the defect-free HOPG (0001) surface was estimated to be 1.0×10−3. This value is two orders lower than that determined in the flight experiment aboard the space shuttle where the same chemical reaction was expected. The discrepancy was explained by the high reaction yield of the oxygen-covered prism planes of HOPG presented at the hillock surfaces.