03 Aug 06:43
by Michael J. Zachman,
Jacob Madsen,
Xiang Zhang,
Pulickel M. Ajayan,
Toma Susi,
Miaofang Chi
The electronic properties of stacked few-layer 2D materials depend strongly on their precise structural arrangement. In this paper, a 4D scanning transmission electron microscopy technique is described that utilizes interference between Bragg disks from separate layers of bilayer and trilayer 2D materials, e.g., to enable measurement of average interlayer spacings and nanometer-scale mapping of local structural reconstructions.
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.
03 Aug 06:41
by Bei Jiang,
Shiwei Wang,
Jingyu Sun,
Zhongfan Liu
State-of-the-art progress in controllable synthesis of wafer-scale graphene films by chemical vapor deposition is summarized according to application requirements. Synthesis challenges of graphene on metal wafers deal with wrinkle formation, difficulties in few-layer growth and transfer-related issues, while those on insulating wafers are mainly concerned with massive grain boundaries, layer inhomogeneity, and low growth rates.
Abstract
The availability of high-quality, large-scale, and single-crystal wafer-scale graphene films is fundamental for key device applications in the field of electronics, optics, and sensors. Synthesis determines the future: unleashing the full potentials of such emerging materials relies heavily upon their tailored synthesis in a scalable fashion, which is by no means an easy task to date. This review covers the state-of-the-art progress in the synthesis of wafer-scale graphene films by virtue of chemical vapor deposition (CVD), with a focus on main challenges and present status. Particularly, prevailing synthetic strategies are highlighted on a basis of the discussion in the reaction kinetics and gas-phase dynamics during CVD process. Perspectives with respect to key opportunities and promising research directions are proposed to guide the future development of wafer-scale graphene films.
28 May 02:24
by Nathanael P. Kazmierczak
Nature Materials, Published online: 15 April 2021; doi:10.1038/s41563-021-00973-w
Complete strain tensor fields of twisted bilayer graphene are quantitatively mapped, revealing two-regime reconstruction mechanics depending on twist angle.
Open Access
