Multi-scale quantitative analysis of carbon texture, nanotexture and structure: I. Electron diffraction-based anisotropy measurements

Abstract

Transmission electron microscopy is a technique of choice in the study of carbon materials, especially graphene-based carbon films, as it provides textural and structural information at a wide range of scales.The Selected Area (SA) diffraction mode yields valuable data regarding the textural arrangement of the graphene stacks. Specifically, the 002 arcs Opening Angle (OA) quantifies the degree of twist disorientation of the layers, and thus the material anisotropy. Depending on the SA aperture size, regions of interest from typically 0.01 to 10μm2 can be probed.This work aims to improve on existing methodologies and develop image analysis software tools designed for digital imaging. For easier use, maintenance and portability, these tools are based on the Python programming language.Briefly, the azimuthal intensity profile of the 002 diffraction ring is extracted and fitted by a model based on Gaussian functions, while a fit of the average radial profile provides the offset constant. We show that this single algorithm works for values of OA ranging from less than 25° up to ∼180°. Our method was validated on various pyrolytic carbon samples, specifically the dense, spherulitic deposits in TRISO nuclear fuel particles for 4th generation high temperature reactors.