Carbon K-edge XANES spectromicroscopy of natural graphite

摘要

Carbon K-edge soft X-ray spectromicroscopy was used to obtain information on the orientation, purity and chemical composition of graphite within natural samples. Highly crystalline natural graphite had spectra indistinguishable from highly ordered pyrolytic graphite, but contained a wide variety of internal structures in the 100-500 nm size range. These structures were both physical (domains with differing sheet orientations) and chemical in nature. Graphite sheet orientations could vary from normal to the X-ray beam to nearly perpendicular within a few hundred nanometers. Chemical compositions ranged from pure crystalline material to nearly amorphous carbon. Little evidence for significant addition of O- or N-bearing groups was observed in these samples, although this may have been a result of the extraction techniques used. The range of carbon types found in the environment may provide clues to the types of thermal alteration and source mechanisms behind graphitic kerogen fractions.