Controlling the structure and properties of 2D materials

Livermore’s Joel Berry (MSD) has coauthored a pair of papers describing promising methods for controlling the structure and properties of 2D materials. In one paper, Berry and his colleagues at the University of Pennsylvania and University of Chicago propose a new atomic-scale approach to form nano- to macro-patterned thin films with tailored properties (mechanical, electronic, optical, thermal, chemical) as well as exceptionally small, shape-programmed 3D objects. The approach is based on 3-atomic-layer-thick transition metal dicalchogenide (TMD) monolayers.

The team constructed and applied a theoretical modeling framework to show that nano- to macro-scale compositional patterns self-assemble when TMD alloy monolayers are annealed on non-flat substrates, that these patterns can be designed to generate a wide variety of material properties and/or 3D shapes upon removal from the substrate, and that the resultant 3D shapes can be dynamically manipulated using applied electric fields. They argue that this concept and material platform has the potential to impact a wide range of disciplines and technologies, including flexible electronics, catalysis, optical devices, responsive coatings, and soft robotics.

The other paper describes work by Berry and collaborators at 11 other institutions. This study focused on stacked 2D materials, which are being intensely studied as platforms for novel physics and for application in advanced optoelectronics, quantum transport devices, etc. The researchers identified a new physical mechanism that enables control of the atomic stacking order of layered 2D materials and used it to synthesize the elusive ABC stacking configuration in trilayer graphene (TLG).

In this mechanism, which they named curvature-based stacking selection (CBSS), nanoscale curvature of the growth substrate surface imparts geometrically necessary defects between the layers of 2D material, and these defects can be tailored to favor particular stacking configurations. Using a newly formulated theoretical model for CBSS, applied to TLG, the team predicted a range of curvatures over which ABC stacking (a semiconductor with a tunable bandgap and several other novel properties that is challenging to grow on large scales) was preferred over ABA stacking (a relatively uninteresting semimetal that is typically dominant in synthesized TLG). The scientists verified that chemical vapor deposition synthesis at these curvature levels results in a greatly enhanced fraction of ABC stacking compared to other approaches. They posit that the identification and exploitation of CBSS is a fundamental advance in the understanding of 2D materials synthesis towards the ultimate goal of wafer-scale synthesis of 2D materials with controlled atomic stacking order.

[J. Berry, S. Ristić, S. Zhou, J. Park, and D.J. Srolovitz, The MoSeS dynamic omnigami paradigm for smart shape and composition programmable 2D materials, Nature Communications 10, 5210 (2019), doi: 10.1038/s41467-019-12945-5. Z. Gao, S. Wang, J. Berry, Q. Zhang, J. Gebhardt, W.M. Parkin, J. Avila, H. Yi, C. Chen, S. Hurtado-Parra, M. Drndić, A.M. Rappe, D.J. Srolovitz, J.M. Kikkawa, Z. Luo, M.C. Asensio, F. Wang, and A.T.C. Johnson, Large-area epitaxial growth of curvature-stabilized ABC trilayer graphene, Nature Communications 11, 546 (2020), doi: 10.1038/s41467-019-14022-3.]