The sp(2) and sp(3) fractions of unknown carbon materials: electron energy-loss near-edge structure analysis of C-K spectra acquired under the magic-angle condition by the electron nanobeam technique

In the present study, the authors describe a method for the quantification of the sp(2), sp(3) and intermediate hybridisations in several carbon (C) material samples. Electron energy-loss near-edge spectra were acquired using fast electrons (120keV) in an electron microscope in nanobeam configuration under the so-called “magic-angle” condition, and were analysed to extract the sp(2) and sp(3) fractions, and identify the possible mixed sp(2+?) hybridisations. The method consists in projecting the unknown spectra on a basis made up of pure sp(2) and sp(3) spectra, obtained under the same experimental conditions from graphite and diamond crystals, respectively. The residual spectra contain information about the intermediate hybridisations sp(2+?) occurring in the samples. The method was successfully tested on “ab initio” numerically generated spectra relative to amorphous C materials. Finally, it was applied to actual C amorphous and pyrolytic samples, and results were compared to those obtained by the most commonly used, conventional “three-Gaussian” method. The combined application of electron diffraction and spectroscopy, in the nanobeam configuration, yielded useful information about the atomic and electronic structure from very small volumes of the unknown C material.

Authors: Diociaiuti M, Casciardi S, Sisto R. ;full Source: Micron 2016 Jul 28; 90:97-107. doi: 10.1016/j.micron.2016.07.005. [Epub ahead of print] ;