Stacking-faults consisting of rhombohedral stacking-order, hexagonal and one-dimensional moiré superlattices in exfoliated highly oriented pyrolytic graphite

Abstract

Understanding the stabilization of rhombohedral stacking-order and moiré superlattices in structural defects produced by exfoliation is of importance towards applications in nanoscale low-dimensional systems and superconductivity. Here we report a statistical investigation of the stabilization-dynamics of rhombohedral ABC stacking-faults within locally-lifted sublattices, fabricated by exfoliation of highly oriented pyrolytic graphite (HOPG). Raman point/mapping spectroscopy applied to several tens of locally-lifted lattice-regions reveal a weak enhancement of the ratio of the integral area of the 2D band-components, namely within the frequency range from ∼2550 to 2670 cm⁻¹ (left shoulder) to that from ∼2670 to 2760 cm⁻¹ (right shoulder). A structural transition is demonstrated with HRTEM revealing the coexistence of hexagonal and one-dimensional moiré superlattices with periods D-1–2.04 nm, D-2–2.35 nm (coexisting superlattice-periodicities) and D ∼ 13 nm in the stacking-fault regions. Interestingly, selective area electron diffraction (SAED) of the latter revealed unusual doubled electron diffraction patterns. Stabilization of micron-scale stacking-faults of crystalline rhombohedral graphite (ABC stacking) was found as an additional transition, when applying the lifting approach to staircase-defects. Comparative investigations performed on commercially available grafoil revealed a different trend, with the presence of a disorder-rich rhombohedral graphitic phase compatible with a defective A|ABAB|BCBC|CACA|A stacking-sequence, analogous to that reported previously in other grafoil samples and in nitrates intercalated graphite.