Computational Methods for Elucidating Phase Transitions in 2-D Materials

Aditi Krishnapriyan, Stanford University

Two-dimensional materials have received great attention in recent years for their strength and ability to withstand tensile strain up to 20 percent, as well as for their outstanding electronic and heat-transport properties. Some of these 2-D materials also show emergent properties that do not appear in the three-dimensional bulk materials from which they come. Here, we study transition metal dichalcogenides, which consist of transition metals such as molybdenum, tungsten, tantalum and niobium, paired with a chalcogenide element such as sulfur, selenium and tellurium. These materials are particularly noted for having the potential to exist in several different crystal structures, including a metallic 1T or 1T’ broken symmetry phase and a semiconductor 2H phase. These phase changes may provide new opportunities for energy-efficient applications, such as in electronic and optical devices. However, almost nothing is known about the mechanisms, kinetics and microstructural effects of these phase changes.

We employ and develop atomistic techniques to make the first studies of these phase transitions. We use density functional theory to calculate the ground-state energies of the different phase-boundary interfaces of these materials, as well as to calculate the various different energy barriers. We aim to identify and predict atomistic mechanisms that describe the phase transition of these materials, thus enabling us to predict the kinetics of the phase transitions.

Abstract Author(s): A. Krishnapriyan, E. Reed