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Exploiting Lattice Strain and Moiré Effects to Control Plasma-Patterning of Twisted 2D Atomic Sheets

Huck Beng Chew, University of Illinois at Urbana-Champaign

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Huck Beng Chew, Soumendu Bagchi, Yue Cui

Plasma-etching is a promising approach to pattern holes in graphene nanostructures, but the patterned hole sizes and distributions are often random in nature which hinders practical application of the plasma-etched graphene nanostructure. Meanwhile, recent studies have uncovered highly periodic moiré patterns present in twisted bilayer graphene sheets, caused by periodic commensurability between the honeycomb lattices of the individual layers. Potentially, the resulting periodic, localized strain distributions in twisted bilayer graphene sheets can be harnessed to bias the plasma-etching rates, thereby enabling unprecedented control over the plasma-patterned graphene nanostructures. This research proposes to use Blue Waters Peta-Scale Supercomputing Facilities to test this hypothesis, combining two distinct research areas, by computationally modeling the detailed plasma-etching processes of twisted bilayer graphene sheets.

This is the second year request for Blue Waters resources on this topic.  In our second year request, large-scale, massively-parallel molecular dynamics (MD) simulations will be used to quantify the plasma-etching mechanisms as a function of twist angle and in-plane lattice strains to simulate the presence of twist and edge dislocations. These MD simulation results will be coupled to time-accelerated Monte Carlo algorithms to establish a manifold of possible plasma-etched patterns as a function of twist angle of the bilayer graphene. In turn, electronic structure calculations will be performed to elucidate the effects of the plasma-etched patterns on changes to the electronic properties of twisted bilayer graphene sheets, and to understand the mechanisms by which the periodic commensurability and lattice strains modulates the etch rates.

In our first year request, Blue Waters resources was used to elucidate the (thermal) stability of twisted graphene sheets subjected to temperatures relevant to the plasma-etching conditions. We uncovered distinct local potential minima for distinct twist angles where the finite sheets remain thermally stable.