Crystallographic orientation errors in mechanical exfoliation

TL;DR

This study quantifies the crystallographic orientation errors introduced during mechanical exfoliation of graphite, revealing that while facets show wide angular variation, true orientations are more precise, informing better control in 2D material preparation.

Contribution

The paper provides quantitative analysis of orientation errors in exfoliated flakes, linking facet angles to true crystallographic orientations and identifying fracture patterns along armchair lines.

Findings

Facet angles show ~5° variation after exfoliation.

True orientations are within ~1.5° accuracy.

Fractures predominantly occur along armchair lines.

Abstract

We evaluate the effect of mechanical exfoliation of van der Waals materials on crystallographic orientations of the resulting flakes. Flakes originating from a single crystal of graphite, whose orientation is confirmed using STM, are studied using facet orientations and electron back-scatter diffraction (EBSD). While facets exhibit a wide distribution of angles after a single round of exfoliation ($ \sigma \approx 5^o $), EBSD shows that the true crystallographic orientations are more narrowly distributed ($ \sigma \approx 1.5^o $), and facets have an approximately error from the true orientation. Furthermore, we find that the majority of graphite fractures are along armchair lines, and that the cleavage process results in an increase of the zigzag lines portion. Our results place values on the rotation caused by a single round of the exfoliation process, and suggest that when a 1-2 degree precision is necessary, the orientation of a flake can be gauged by the orientation of the macroscopic single crystal from which it was exfoliated.