Engineering Kinetics for Energy-Efficient Phase Change Materials: Application to Two-Dimensional MoS2
Aditi Krishnapriyan, Stanford University
Predictive capabilities for kinetic processes in materials are in their infancy, but kinetics are critical for a spectrum of energy applications, including phase-change materials, catalysis, materials synthesis and combustion. The structural phase transition between the metallic 1T or 1T' and semiconducting 2H structures in two-dimensional transition metal dichalcogenide materials is important to understand for synthesis and may provide exciting new opportunities for energy-efficient electronic and optical devices. However, little is known about the mechanisms of these phase changes or how to engineer the kinetics. We develop a novel density functional theory (DFT) method to determine the minimum energy critical nucleus and the resulting nucleation barrier of the 1T or 1T' metallic phases in a 2H semiconducting lattice. We determine multiple zigzag and armchair interfaces that dominate the metallic-to-semiconducting phase interfaces and predict that the lowest energy nanoparticle shape of 1T in a 2H lattice is a kite shape with both zigzag and armchair interfaces while for 1T' in a 2H lattice it is triangular with only zigzag interfaces, enabling distinction in transmission electron microscopy (TEM) studies. We also discover that due to the nature of the system's geometric constraints, the individual interface energies are mathematically ill-defined. Finally, we discuss the nucleation barriers, critical nucleus size and approximate nucleation times under a variety of conditions. In a collaboration with Los Alamos National Laboratory, we utilize our results to develop tight-binding models for these important systems that provide the first correct description of these phase-change kinetics. This work points to strategies for engineering kinetic properties in phase-change materials that will facilitate their future application.
Abstract Author(s): Aditi Krishnapriyan, Evan Reed, Marc Cawkwell