Enrichment of rhombohedral stacking by mechanical exfoliation of graphite

TL;DR

Mechanical exfoliation, especially blade-assisted, significantly enriches rhombohedral (ABC) stacking in graphite flakes, facilitating studies of its unique electronic phases.

Contribution

This work demonstrates that routine and blade-assisted mechanical exfoliation methods increase ABC stacking content in graphite, improving sample quality for topological phase research.

Findings

ABC content increases from 3% to 26% after exfoliation.

Blade-assisted exfoliation boosts ABC content to 75% in thin flakes.

Wrinkles influence domain wall movement and stacking order.

Abstract

Rhombohedral (ABC) graphite hosts a surface-localized flat band that supports correlated and topological electronic phases, but its experimental study is limited by the scarcity of ABC stacking in natural graphite, which is dominated by Bernal (AB) stacking. Here we show that the routine mechanical exfoliation step itself enriches the rhombohedral content of graphite flakes, and that a simple blade-assisted exfoliation step, which introduces additional shear, amplifies the effect further. Using large-area Raman 2D-band skewness mapping we measure ABC content at area fractions of 3\% in the pristine source crystal, 16\% after conventional exfoliation, and 26\% after blade-assisted exfoliation for thick flakes. In thin flakes ($<20$ layers) the per-flake area fraction reaches 75\% in the upper tail of the distribution. Tracking individual flakes before and after blade-assisted exfoliation shows that wrinkles seed AB-ABC domain walls, and uniaxial strain can move these walls. Blade-assisted mechanical exfoliation therefore removes one of the bottlenecks to the preparation of ABC-rich graphite samples for studies of correlated and topological phases in rhombohedral graphite.