posted on 2019-12-04, 13:09authored byYangjin Lee, Sol Lee, Jun-Yeong Yoon, Jinwoo Cheon, Hu Young Jeong, Kwanpyo Kim
Phosphorene, a monolayer of black phosphorus (BP), is
an elemental
two-dimensional material with interesting physical properties, such
as high charge carrier mobility and exotic anisotropic in-plane properties.
To fundamentally understand these various physical properties, it
is critically important to conduct an atomic-scale structural investigation
of phosphorene, particularly regarding various defects and preferred
edge configurations. However, it has been challenging to investigate
mono- and few-layer phosphorene because of technical difficulties
arising in the preparation of a high-quality sample and damages induced
during the characterization process. Here, we successfully fabricate
high-quality monolayer phosphorene using a controlled thinning process
with transmission electron microscopy and subsequently perform atomic-resolution
imaging. Graphene protection suppresses the e-beam-induced damage
to multilayer BP and one-side graphene protection facilitates the
layer-by-layer thinning of the samples, rendering high-quality monolayer
and bilayer regions. We also observe the formation of atomic-scale
crystalline edges predominantly aligned along the zigzag and (101)
terminations, which is originated from edge kinetics under e-beam-induced
sputtering process. Our study demonstrates a new method to image and
precisely manipulate the thickness and edge configurations of air-sensitive
two-dimensional materials.