sp3/sp2 characterization of carbon materials from first-principles calculations: X-ray photoelectron versus high energy electron energy-loss spectroscopy techniques

We have performed X-ray photoelectron spectroscopy (XPS) and high energy electron energy-loss spectroscopy (HEELS) calculations from first principles on a series of Monte Carlo generated amorphous carbon materials and have used a technique which separates the π* and σ* components of the energy-loss near-edge structure spectra of carbon materials on the basis of the ab initio electronic structure calculations of graphite to determine the sp3 fraction of the carbon systems. While the XPS technique is found to probe the local coordination geometry, the sp3 fractions resulting from the HEELS technique are found to be in very good agreement with those based on the π-orbital axis vector analysis which accounts for the effects of non-planarity in 3-coordinated systems.