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
π
∗
and
σ
∗
components of the carbon K-edge of graphite. This
π
∗
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
π−
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.