2D Materials

Two Dimensional Materials

2D materials such as graphene and MoS2 are being intensely studied for fundamental scientific purposes and with the aim of developing new technologies such as next generation energy production systems and ultrathin, flexible, nanoelectronic and optoelectronic devices. I have recently been exploring the concept of dynamically programmable 2D electromechanical materials. These materials are capable of rapid local switching between crystal structures with qualitatively different transport properties, enabling, e.g., dynamic “drawing” of localized conducting regions in an otherwise semiconducting monolayer. This opens several interesting device-relevant functionalities such as the ability to dynamically “rewire” a device in real time or to create nanoelectromechanical devices with no moving parts.

J. Berry, S. Zhou, J. Han, D. J. Srolovitz, and M. P. Haataja. “Domain Morphology and Mechanics of the H/T' Transition Metal Dichalcogenide Monolayers”, Physical Review Materials 2, 114002 (2018). [PDF]

C. H. Naylor, W. M. Parkin, Z. Gao, J. Berry, S. Zhou, Q. Zhang, B. McClimon, L. Z. Tan, C. E. Kehayias, M. Zhao, R. S. Gona, R. W. Carpick, A. Rappe, D. J. Srolovitz, M. Drndic, and A. T. C. Johnson. “Synthesis and Physical Properties of Phase-Engineered Transition Metal Dichalcogenide Monolayer Heterostructures”, ACS Nano, 11 (9), 8619 (2017). [PDF]

J. Berry, S. Zhou, J. Han, D. J. Srolovitz, and M. P. Haataja. “Dynamic Phase Engineering of Bendable Transition Metal Dichalcogenide Monolayers”, Nano Letters 17 (4), 2473 (2017). [PDF]

The figure above outlines basic elements of the dynamic phase engineering concept. On the left, the three TMD crystal structures and the 12 crystallographic ‘variants’ of the T' structure are shown. The H phase is semiconducting, while the T and T' phases are semimetallic. On the right, a simulated indentation-induced structural phase transition in monolayer MoTe2 is shown. The schematic plot of conductance versus indenter deflection shows the jump in conductance upon fully transforming the monolayer to the conducting T' phase. Domains are colored according to local crystal structure and orientation, as indicated to the left.

We have developed and implemented a multi-scale, first-principles-informed modeling framework that describes the evolution of microstructural crystal domain morphologies in elastically bendable 2D monolayers. This approach has allowed us to identify several ways in which TMD monolayers can be dynamically strain-engineered and patterned for specific functionalities and device applications. Morphology and mechanical response can be controlled by applying strain either uniformly or through local probes, as demonstrated in the animations below.