Stabilization of μm-scale rhombohedral ABC stacking-faults and absence of structural relaxation within disclination-rich structures in commercially available natural graphite and grafoil

Abstract

The recent observation of superconductive effects in rhombohedral graphene and in pyrolytic graphite systems exhibiting stacking faults have attracted a significant attention. Here we report an advanced investigation of stacking faults in multilayered lamellae of natural graphite and grafoil, by employing a combination of Raman point/mapping spectroscopy, scanning and transmission electron microscopy (SEM, TEM/HRTEM). The presented work identifies significant local structural transitions and an anomalous stabilization of rhombohedral stacking order occurring within μm-scale ripplocation-like defect-structures (first-category of stacking fault). Interestingly, we demonstrate an abrupt enhancement in the intensity of the left shoulder of the 2D band (of the Raman spectra) in sample's regions exhibiting an intersection between these defect structures. Extensive Raman mapping analyses demonstrate coexistence of rhombohedral ABC and Bernal ABA phases also within other sample's regions (second category of stacking-fault). This interpretation is further supported by comparative analyses performed in as-purchased strain-rich grafoil films. Interestingly, no structural relaxation of rhombohedral ABC stacking into ABA Bernal ordering was found in the analysed defect-regions.