Invited Paper MN-ThM1
Piezoelectric and Phase Change Properties of Two-Dimensional Materials

Thursday, October 22, 2015, 8:00 am, Room 210B

Some of the most dramatic accomplishments with 2D materials have been enabled by properties that emerge only at the single or few-layer limit and are not found in bulk forms. Using and developing a variety of atomistic modeling methods, we have predicted that many of the commonly studied single-layer and few-layer transition metal dichalcogenide (TMD) materials (e.g. MoS₂) exhibit substantive electromechanical coupling in the form of piezoelectric and flexoelectric-like effects, unlike their bulk parent crystals.¹ I will describe the first recent observations of some of these effects in the laboratory by several research groups.

Single-layers of two-dimensional Mo- and W-dichalcogenide compounds differ from graphene in an important respect: they can potentially exist in more than one crystal structure. Some of these monolayers exhibit hints of a poorly understood structural metal-to-semiconductor transition with the possibility of long metastable lifetimes. If controllable, such a transition could bring an exciting new application space to monolayer materials. We have discovered that mechanical deformations provide a route to switching thermodynamic stability between a semiconducting and a metallic crystal structure in some of these monolayer materials.² Our DFT-based calculations reveal that single-layer MoTe₂ exhibits a phase boundary at a few percent tensile strain. The potential application space for this work ranges from information and energy storage to electronic and optical electronic devices.

¹Karel-Alexander N. Duerloo, Mitchell T. Ong, and Evan J. Reed, Journal of Physical Chemistry Letters 3 (19), 2871 (2012); Karel-Alexander N. Duerloo and Evan J. Reed, Nano Letters (4), 1681 (2013).

²Karel-Alexander Duerloo, Y. Li, and E. J. Reed, Nature Communications 5, 4214 (2014).