Structure modification of highly ordered pyrolytic graphite by Ar plasma beam scanning at different incident angles

Abstract

The surface of highly ordered pyrolytic graphite (HOPG) was modified by Ar plasma beam scanning at a controllable angle of incidence. The characteristics of plasma modified HOPG were investigated by atomic force microscope (AFM), micro-Raman, X-ray photoemission spectroscopy (XPS), and grazing incident angle of X-ray diffraction (GIAXRD). A smooth surface of HOPG can be obtained by adjusting the incident angles of Ar plasma beam scanning. The surfaces of HOPG become smoother with increasing angle of incidence after Ar plasma beam scanning. Raman spectra indicate that the plasma beam scanning breaks the hexagonal structures of sp2 C=C bonds near the surface of HOPG. The broken hexagonal network structures can form C–O bonds that increase the amount of oxygen on the surface of HOPG, supported by C1s and O1s XPS spectra. GIAXRD data support that the co-existence of both crystalline structures of 2H and 3R in HOPG. The carbon bond breaking in 2H and 3R is different and depends on the angle of incidence. Most broken carbon bonds form damaged aromatic rings near the surface of HOPG.