Interferometric 4D‐STEM for Lattice Distortion and Interlayer Spacing Measurements of Bilayer and Trilayer 2D Materials

Abstract

Van der Waals materials composed of stacks of individual atomic layers have attracted considerable attention due to their exotic electronic properties that can be altered by, e.g., manipulating the twist angle of bilayer materials or the stacking sequence of trilayer materials. To fully understand and control the unique properties of these few‐layer materials, a technique that can provide information about their local in‐plane structural deformations, twist direction, and out‐of‐plane structure is needed. In principle, interference in overlap regions of Bragg disks originating from separate layers of a material encodes 3D information about the relative positions of atoms in the corresponding layers. Here, an interferometric 4D scanning transmission electron microscopy technique is described that utilizes this phenomenon to extract precise structural information from few‐layer materials with nm‐scale resolution. It is demonstrated how this technique enables measurement of local pm‐scale in‐plane lattice distortions as well as twist direction and average interlayer spacings in bilayer and trilayer graphene, and therefore provides a means to better understand the interplay between electronic properties and precise structural arrangements of few‐layer 2D materials.

Disentangling multiple scattering with deep learning: application to strain mapping from electron diffraction patterns

“…4D-STEM experiments are gaining popularity among electron microscopists because they can collect atomicscale information from each probe over a nearly arbitrary field-of-view [10], and can measure a broad spectrum of quantities of physical interest including 3D structural determination [11], ferroelectric polarization [12], imaging of lithium in cathode materials [13], ptychographic atomic imaging [14], correlation of local strain with composition from x-ray ptychography [15], distinguishing between chemical and structural interfacial roughness [16], strain in 2D material bilayers [17,18], and many others. The ability to extract quantitative information with atomic-scale resolution is, however, frequently limited by the size and complexity of experimental 4D-STEM data.…”

Automated Experiment in 4D-STEM: Exploring Emergent Physics and Structural Behaviors

“…Originally, 4D-STEM was proposed by Rodenburg as a pathway to avoid intrinsic resolution limits in STEM. , Using this approach, atomic resolution imaging has been demonstrated along with imaging of the light elements . Similarly, 4D-STEM provides insights into the structure of electric and magnetic fields on the atomic level, allowing local chemistry analysis of defects, − mapping of lattice distortion and interlayer spacing in 2D materials, and even visualization of anionic electrons …”

Mapping pm-scale Lattice Distortions and Measuring Interlayer Separations in Stacked 2D Materials by Interferometric 4D-STEM

“…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][7][8], and four-dimensional STEM (4D-STEM) [9][10][11] have recently been developed to provide access to this type of structural information.…”

“…Here, we describe an interferometric 4D-STEM approach for mapping picometer-scale structural reconstructions with nanometer resolution and measuring interlayer separations of few-layer materials [11]. By using a defocused STEM probe, diffracted beams focus in the same plane as the transmitted beam, perpendicular to the beam direction, and propagate to the far field.…”

“…(f) From these distortions, properties such as local deviations in twist angle can also be mapped with nanometer resolution. Figure reproduced and condensed with permission from [11].…”