The surface and bulk core lines in crystalline and disordered polycrystalline graphite

Surface and bulk components in angle-resolved core-level photoemission spectroscopy of graphite

“…Figure 1͑a͒ shows the C 1s line of HOPG measured at normal emission and at 10°intervals for emission angles between 20°and 70°. A clear increase in linewidth to the high binding-energy side can be observed, consistent with previous ARXPS studies, 3,4 indicating the presence of a low kinetic-energy component on the line associated with the surface of the sample. No difference in line shape could be observed for spectra taken at the same emission angle for samples cleaved by the two techniques outlined above, providing evidence that surface defects 10 may not be the origin of the observed behavior.…”

“…Moreover, we find that the natural ͑Lorentz-ian͒ linewidth of the bulk component is very narrow, 95Ϯ 3 meV, compared with the surface, 231Ϯ 8 meV ͑the latter is again consistent with SXPS measurements͒. 1,2,8 The value for the Lorentzian linewidth of the bulk C 1s component is similar to that used by Speranza and Minati 4 and that observed in small gas-phase molecules 14 and in diamond; 15 therefore the difference in bulk and surface linewidths may explain the apparent discrepancy between the lifetime broadening measured in SXPS and that which might be expected from comparison with closely related systems. 8,9 The changes in linewidth and asymmetry parameter between bulk and surface are significant and point to notable differences between the response to the core hole at the surface and in the bulk of graphite.…”

“…Controversy exists over the presence [1][2][3][4][5][6] or otherwise 7-9 of a surface corelevel component to the C 1s line, the magnitude of the surface-bulk core-level splitting ͑when such surface and bulk components are observed͒, and the potential influence of defects on the C 1s line shape. 10 It is important to resolve these inconsistencies if core-level photoemission is to be applied successfully to the detailed characterization of novel graphitic materials, particularly graphene, carbon nanotubes, and related few-layer structures.…”

Understanding the intrinsic water wettability of graphite

“…8.7 nm in HOPG (at 90° takeoff angle). 335 The number of sampled graphene layers (N GL ) can be calculated using the interlayer spacing (d) of HOPG: where d=0.336 nm for ZYA as determined by x-ray diffraction (Table 22 on page 146). The relative intensity of photoelectrons detected from the surface (I S ) is equal to 1/N GL , thus the surface contribution to the overall XPS signal is 3.9% and the bulk contribution (I B ) is 96.1%.…”

“…The relative intensity of photoelectrons detected from the surface (I S ) is equal to 1/N GL , thus the surface contribution to the overall XPS signal is 3.9% and the bulk contribution (I B ) is 96.1%. 335 An alternative approach is to calculate I S using the exponential decay equation:…”