A new technique for the sp${}^2$/sp${}^3$ characterisation of carbon materials

Abstract

We present a technique to determine the sp${}^3$/sp${}^2$ ratio of carbon materials which is based on the electron energy-loss spectroscopy and which uses the theoretical spectrum of graphite obtained from ab initio electronic structure calculations. The method relies on the separation of the ${\pi }^{\ast }$ and ${\sigma }^{\ast }$ components of the carbon K-edge of graphite. This ${\pi }^{\ast }$ spectrum is adopted and assumed to be transferable to other carbon systems given an appropriate parametrisation of the broadening. The method is applied on a series of Monte-Carlo generated amorphous carbon structures and is shown to be stable over a wide range of the energy windows for which spectral integration is performed. The results are found to be in good agreement with the sp${}^3$ fraction obtained from a microscopic scheme which uses the $\pi -$orbital axis vector (POAV1) analysis. The technique was also applied on a series of experimental spectra of amorphous carbon and was found to be in good agreement with the results obtained from a functional fitting approach.

5 pages, 4 figures, two tables revtex4, Submitted for publication to Phys. Rev. Lett