  Graphene is of great scientific interest due to a variety of unique
properties such as ballistic transport, spin selectivity, the quantum hall
effect, and other quantum properties. Nanopatterning and atomic scale
modifications of graphene are expected to enable further control over its
intrinsic properties, providing ways to tune the electronic properties through
geometric and strain effects, introduce edge states and other local or extended
topological defects, and sculpt circuit paths. The focused beam of a scanning
transmission electron microscope (STEM) can be used to remove atoms, enabling
milling, doping, and deposition. Utilization of a STEM as an atomic scale
fabrication platform is increasing; however, a detailed understanding of
beam-induced processes and the subsequent cascade of aftereffects is lacking.
Here, we examine the electron beam effects on atomically clean graphene at a
variety of temperatures ranging from 400 to 1000 C. We find that temperature
plays a significant role in the milling rate and moderates competing processes
of carbon adatom coalescence, graphene healing, and the diffusion (and
recombination) of defects. The results of this work can be applied to a wider
range of 2D materials and introduce better understanding of defect evolution in
graphite and other bulk layered materials.
