Two-dimensional (2D) materials possess a host of exotic properties, which can further be modified by stacking them into heterostructures. Since interactions between layers can alter their structural, electronic, and magnetic properties, these can be controlled for example through twist angles or stacking sequences [1]. A noteworthy example is bilayer graphene, which undergoes in-plane structural distortions and a corresponding restructuring of its electronic properties at low twist angles [2] that can result in correlated insulating states [3] and unconventional superconductivity [4]. The ability to map out structural distortions and their variations across materials with a range of twist angles and stacking sequences is therefore important for understanding and ultimately controlling both structural and electronic/magnetic properties of these materials. As a result, various transmission electron microscopy (TEM) techniques such as diffraction [5], dark-field and scanning TEM (STEM) imaging [6-8], and four-dimensional STEM (4D-STEM) [9-11] have recently been developed to provide access to this type of structural information.
[1]
Kenji Watanabe,et al.
Strain fields in twisted bilayer graphene
,
2020,
Nature Materials.
[2]
E. Kaxiras,et al.
Atomic and electronic reconstruction at the van der Waals interface in twisted bilayer graphene
,
2018,
Nature Materials.
[3]
Andreas Mittelberger,et al.
Unraveling the 3D Atomic Structure of a Suspended Graphene/hBN van der Waals Heterostructure
,
2017,
Nano letters.
[4]
K. Novoselov,et al.
2D materials and van der Waals heterostructures
,
2016,
Science.
[5]
Pinshane Y. Huang,et al.
Strain solitons and topological defects in bilayer graphene
,
2013,
Proceedings of the National Academy of Sciences.
[6]
Pinshane Y. Huang,et al.
Twinning and twisting of tri- and bilayer graphene.
,
2012,
Nano letters.