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

TL;DR

This paper introduces a spectroscopic technique combining ab initio calculations and electron energy-loss spectroscopy to accurately determine the sp$^2$/sp$^3$ ratio in carbon materials, validated on both simulated and experimental data.

Contribution

The paper presents a novel method for characterizing carbon hybridization states using transferable spectral features derived from ab initio calculations.

Findings

Method is stable across various spectral integration windows.

Results agree well with microscopic POAV1 analysis.

Consistent with functional fitting approaches on experimental spectra.

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 $\pi^*$ and $\sigma^*$ components of the carbon K-edge of graphite. This $\pi^*$ 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.