Magic angle and STEM-EELS mapping of the sp2/sp3 hybridization in heterogeneous carbonaceous materials

Abstract

Extensive research has been conducted on carbonaceous materials due to their unique combination of physical, chemical, and mechanical properties, which significantly rely on the hybridization of carbon atoms. Scanning transmission electron microscopy-electron energy loss spectroscopy is a powerful technique that enables the identification of carbon allotropes with high spatial resolution, utilizing specific spectral features. However, anisotropic materials like graphite and carbon nanotubes can exhibit variations in these spectral features based on their orientation relative to the electron beam. Optimized experimental conditions, referred to as magic angle conditions, permits overcoming this challenge. By implementing such conditions, we have successfully mapped the hybridization in a heterogeneous system containing three carbon allotropes, i.e. nanodiamonds, multi-walled carbon nanotubes, and lacey carbon. Moreover, a convolutional neural network has been created and trained to accurately identify and map these carbonaceous phases. Thus, the reported innovative approach allows nanoscale mapping of both hybridization and phase distributions for complex heterogeneous carbon systems.