The quantitative evaluation of the carbon hybridization state by X-ray photoelectron spectroscopy (XPS) has been a surface-analysis problem for the last three decades due to the challenges associated with the unambiguous identification of the characteristic binding energy values for sp2 and sp3-bonded carbon. While the sp2 binding energy is well established, there is disagreement for the sp3 value in the literature. Here, we compute the binding energy values for model structures of pure and doped-diamond using density functional theory. The simulation results indicate that the large band-gap of diamond allows defects to pin the Fermi level, which results in large variations of the C(1s) core electron energies for sp3-bonded carbon, in agreement with the broad range of experimental C(1s) binding energy values for sp3 carbon reported in the literature. Fermi level pinning by boron is demonstrated by experimental C(1s) binding energies of highly B-doped ultrananocrystalline diamond that are in good agreement to simulations.
@article{arxiv.1902.02958,
title = {Fermi level pinning by defects can explain the large reported carbon 1s binding energy variations in diamond},
author = {Michael Walter and Filippo Mangolini and J. Brandon McClimon and Robert W. Carpick and Michael Moseler},
journal= {arXiv preprint arXiv:1902.02958},
year = {2019}
}