Controlled synthesis of 2D MX2 (M = Mo, W; X = S, Se) heterostructures and alloys

Abstract

The advent of two-dimensional materials and van der Waals (vdW) heterostructures has been a boon for the nanoscience community, enabling the fabrication of nanostructures with atomic-scale precision, resulting in high performance opto-electronic devices. Yet, while vdW heterostructures have been widely studied, their fabrication remains rudimentary, relying upon physical stacking and ad hoc collections of recipes, rather than a rational framework. Here, we report our work on the synthesis of vdW heterostructures and monolayer alloys of MoS2-WS2 and MoSe2-WSe2 and the creation of a unifying, diagrammatic approach to heterostructure growth in these materials systems, which we call Time-Temperature-Architecture (TTA) diagrams. We demonstrate the temperature tunable synthesis of in-plane, vertical, and hybrid heterostructures, as well as monolayer alloys within the MoS2-WS2 and MoSe2-WSe2 systems. We use the TTA framework to add previously unexplored entries to this collection: the first ever single-step growth of MoSe2-WSe2 vertical heterostructures and Mo1-xWxSe2 alloys, and a new MoS2-WS2 hybrid architecture that combines the morphologies of both vertical and in-plane heterostructures. The TTA diagrams are a simple framework for vdW heterostructure and alloy growth, which we believe will be crucial, and enable further work on heterostructures and alloys of MoS2-WS2 and MoSe2-WSe2.