Anisotropy analysis of ultra-fine grain graphite and pyrolytic carbon

Abstract

This paper presents the development of an analysis technique and software program to quantify the anisotropy of pyrolytic carbon or ultra-fine grain graphite using selected area electron diffraction (SAED) patterns from a transmission electron microscope. Results serve as input to a computer program that calculates the Bacon anisotropy factor (BAF) and orientation parameter (R). This was achieved by analyzing the SAED patterns to determine the full width half maximum of the two peaks on the (0001) diffraction ring, converting the SAED data into the same format as the X-ray data and then calculating the BAF and R. The methodology of calculating the BAF and R values from the SAED patterns was confirmed by comparing the calculated values with the BAF values resulting from ellipsometry measurements on two identical isotropic pyrolytic carbon (PyC) samples and resulted in a difference of less than 0.26%, while measurements on an anisotropic turbostratic pyrolytic carbon showed almost a 40% difference which may be due to the larger planar spacing changing the extraordinary refractive index and extraordinary extinction coefficient.