Quasi-1D, rectangular-like and hexagonal moiré superlattices in exfoliated highly oriented pyrolytic graphite

Understanding the dynamics of structural collapse in hexagonal moiré superlattices is of importance towards the stabilization of exotic superconductive phenomena in quasi-1D superlattices. Here we investigate unusual exfoliation-induced structural transformations of hexagonal moiré superlattices, in a μm-thin lamella of highly oriented pyrolytic graphite (HOPG). By employing a combination of experimental techniques, namely transmission electron microscopy (TEM), high resolution TEM (HRTEM) and selective area electron diffraction (SAED) we systematically investigate the collapse of hexagonal moiré superlattices into rectangular-like and quasi-1D superlattices in an exfoliated lamella. Interestingly, the rectangular-like lattice reveals perpendicular super-periodicities D₁ ~ 17 nm and D₂ ~ 9 nm. The width of the quasi-1D channels was found to vary from ~5 nm to ~13 nm, with a super-periodicity D ~ 3 nm. Most importantly, systematic SAED acquisitions reveal a splitting of the electron diffraction signals into multiple components, consisting of doubled and tripled diffraction rings. We interpret these as a clear indicator of structural disorder which results from an interplay of exfoliation-induced structural transitions, namely interlayer-sliding, local layer-rotation (twisting) and significant wrinkling (strain) effects.