Top-down fabrication of atomic patterns in twisted bilayer graphene

TL;DR

This paper demonstrates a top-down method using STEM to precisely pattern atoms in twisted bilayer graphene, combining global and local parameters for atomic-scale engineering with feedback control.

Contribution

It introduces a novel approach integrating top-down electron beam patterning with bottom-up atom migration control in graphene.

Findings

Atomic patterns can be precisely defined using STEM and feedback control.

Substrate temperature influences adatom and vacancy diffusion.

The method enables arbitrary atomic patterning with limited human intervention.

Abstract

Atomic-scale engineering typically involves bottom-up approaches, leveraging parameters such as temperature, partial pressures, and chemical affinity to promote spontaneous arrangement of atoms. These parameters are applied globally, resulting in atomic scale features scattered probabilistically throughout the material. In a top-down approach, different regions of the material are exposed to different parameters resulting in structural changes varying on the scale of the resolution. In this work, we combine the application of global and local parameters in an aberration corrected scanning transmission electron microscope (STEM) to demonstrate atomic scale precision patterning of atoms in twisted bilayer graphene. The focused electron beam is used to define attachment points for foreign atoms through the controlled ejection of carbon atoms from the graphene lattice. The sample environment is staged with nearby source materials, such that the sample temperature can induce migration of the source atoms across the sample surface. Under these conditions, the electron-beam (top-down) enables carbon atoms in the graphene to be replaced spontaneously by diffusing adatoms (bottom-up). Using image-based feedback-control, arbitrary patterns of atoms and atom clusters are attached to the twisted bilayer graphene with limited human interaction. The role of substrate temperature on adatom and vacancy diffusion is explored by first-principles simulations.