Susbtrate-Induced Stabilization and Reconstruction of Zigzag Edges in Graphene Nanoislands on Ni(111)

TL;DR

This study combines STM and DFT to identify the most stable zigzag edge structures of graphene on Ni(111), revealing how stacking influences edge stability and reconstruction, with implications for nanoisland shape and stability.

Contribution

It demonstrates the role of stacking and substrate interactions in stabilizing specific graphene edge structures and their reconstruction behavior on Ni(111).

Findings

Triangular nanoislands have stable zigzag hollow edges.

Hexagonal islands' top edges reconstruct into (57) defects.

DFT favors top-fcc stacking over top-hcp stacking.

Abstract

We combine experimental observations by scanning tunneling microscopy (STM) and density functional theory (DFT) to reveal the most stable edge structures of graphene on Ni(111) as well as the role of stacking-driven activation and suppression of edge reconstruction. Depending on the position of the outermost carbon atoms relative to hollow and on-top Ni sites, zigzag edges have very different energies. Triangular graphene nanoislands are exclusively bound by the more stable zigzag hollow edges. In hexagonal nanoislands, which are constrained by geometry to alternate zigzag hollow and zigzag top edges along their perimeter, only the hollow edge is stable whereas the top edges spontaneously reconstruct into the (57) pentagon-heptagon structure. Atomically-resolved STM images are consistent with either top-fcc or top-hcp epitaxial stacking of graphene and Ni sites, with the former being favored by DFT. Finally, we find that there is a one-to-one relationship between the edge type, graphene stacking, and orientation of the graphene islands.