Low-Energy Electron Microscopy contrast of stacking boundaries: comparing twisted few-layer graphene and strained epitaxial graphene on silicon carbide

• Main Authors: de Jong, Tobias A, Chen, Xingchen, Jobst, Johannes, Krasovskii, Eugene E, Tromp, Ruud M, van der Molen, Sense Jan
• Format: Journal Article
• Language: English
• Published: 29-07-2022
• Subjects: Physics - Mesoscale and Nanoscale Physics
• DOI: 10.48550/arxiv.2207.14616

Phys. Rev. B 107, 075431, 22 February 2023 Stacking domain boundaries occur in Van der Waals heterostacks whenever there
is a twist angle or lattice mismatch between subsequent layers. Not only can
these domain boundaries host topological edge states, imaging them has been
instrumental to determine local variations in twisted bilayer graphene. Here,
we analyse the mechanisms causing stacking domain boundary contrast in Bright
Field Low-Energy Electron Microscopy (BF-LEEM) for both graphene on SiC, where
domain boundaries are caused by strain and for twisted few layer graphene. We
show that when domain boundaries are between the top two graphene layers,
BF-LEEM contrast is observed due to amplitude contrast and corresponds well to
calculations of the contrast based purely on the local stacking in the domain
boundary. Conversely, for deeper-lying domain boundaries, amplitude contrast
only provides a weak distinction between the inequivalent stackings in the
domains themselves. However, for small domains phase contrast, where electrons
from different parts of the unit cell interfere causes a very strong contrast.
We derive a general rule-of-thumb of expected BF-LEEM contrast for domain
boundaries in Van der Waals materials.