Atomic-resolution visualization and doping effects of complex structures in intercalated bilayer graphene

Abstract

Molecules intercalating two-dimensional (2D) materials form complex structures that have been mostly characterized by spatially averaged techniques. Here we use aberration-corrected scanning transmission electron microscopy and densityfunctional-theory (DFT) calculations to study the atomic structure of bilayer graphene (BLG) and few-layer graphene (FLG) intercalated with FeCl3. In BLG we discover two distinct intercalated structures that we identify as monolayer-FeCl3 and monolayer-FeCl2. The two structures are separated by atomically sharp boundaries and induce large but different free-carrier densities in the graphene layers, 7.1 × 10 cm -2 and 7.8 × 10 cm -2 respectively. In FLG, we observe multiple FeCl3 layers stacked in a variety of possible configurations with respect to one another. Finally, we find that the microscope's electron beam can convert the FeCl3 monolayer into FeOCl monolayers in a rectangular lattice. These results reveal the need for a combination of atomically-resolved microscopy, spectroscopy, and DFT calculations to identify intercalated structures and study their properties.

Polymorphic Phases of Metal Chlorides in the Confined 2D Space of Bilayer Graphene

“…Thanks to the recent developments in transmission electron microscopy, obtaining the atomic-resolution images of the intercalants inside the graphene layers became recently possible. [34,35] As the intercalation chemistry in BLG and in graphite is still not fully understood yet, the scanning transmission electron microscopy (STEM) data may be extremely useful in that context.…”

Emerging field of few-layered intercalated 2D materials

“…Studying the intercalation at the 2D level allows to follow the electrochemical intercalation process by various techniques in situ such as XRD, 161 Hall measurements 22,93 and also to follow the process by optical microscopy 89,162 and even transmission electron microscopy at atomic resolution. 15,93,163 TEM imaging not only allows to optically follow the intercalation and deintercalation of the ions into the few-layered 2DM, but also identies areas of varying crystallinity and grain sizes (Fig. 22).…”

Detection of defects in atomic-resolution images of materials using cycle analysis

“…At each pixel, a subimage is defined, centered at the pixel and encompassing an area roughly equal to the area per atomic column. These subimages are filtered using PCA to remove noise and surface contamination [21,22]. The subimages are then passed through a 2D correlation [23] with an ideal atomic column (a 2D Gaussian) defined by:…”