Highly Oriented Pyrolytic Graphite by Core Level and Valence Band XPS

Abstract

Both core level and valence band XPS spectra were obtained from a Union Carbide highly oriented pyrolytic graphite (HOPG) monochromator sample. Compared to Du Pont and Amoco pitch-based carbon fibers with different modulus and some PAN-based carbon fibers, the HOPG had much less oxygen components on the surface than the carbon fibers, except Du Pont E-120 high modulus pitch-based carbon fiber. [See Y. Xie and P. M. A. Sherwood, Appl. Spectrosc. 43, 1153 (1989); Chem. Mater. 1, 427 (1989); 2, 293 (1990); Appl. Spectrosc. 44, 797 (1990); Chem. Mater. 3, 164 (1991); Appl. Spectrosc. 44, 1621 (1990); 45, 1158 (1991); Y. Xie, T. Wang, O. Franklin, and P. M. A. Sherwood, ibid. 46, 645 (1992).] No nitrogen was found on the HOPG surface, nor on any of the pitch-based carbon fibers measured in our laboratory, but nitrogen was shown in all the PAN-based carbon fibers. Our previously reported work [Y. Xie and P. M. A. Sherwood, Chem. Mater. 1, 427 (1989); 2, 293 (1990); Appl. Spectrosc. 44, 797 (1990); Chem. Mater. 3, 164 (1991); Appl. Spectrosc. 44, 1621 (1990); 45, 1158 (1991); Y. Xie, T. Wang, O. Franklin, and P. M. A. Sherwood, ibid. 46, 645 (1992)] showed that XPS valence band spectra were more sensitive to chemical environment on the carbon fiber surface than core level spectra and could be well interpreted by X–α calculations with model compounds. Although both HOPG and E-120 samples had little oxygen on their surfaces (with E-120 even less), the valence band spectra of these two samples showed that the oxygen species in the HOPG surface and E-120 fiber surface were different because the separations between the O 2s peak and the C 2s peak in the two spectra are different.