Screw-Dislocation-Driven Growth of Two-Dimensional Few-Layer and Pyramid-Like WSe2 by Sulfur-Assisted Chemical Vapor Deposition

TL;DR

This paper reports a novel sulfur-assisted CVD method to grow 2D WSe2 with screw-dislocation-driven spiral and pyramid-like structures, revealing new growth mechanisms and demonstrating promising electronic properties.

Contribution

It introduces a sulfur-assisted CVD process that enables the growth of complex 2D WSe2 structures via screw dislocations, advancing understanding of growth mechanisms and material properties.

Findings

Screw dislocations drive spiral growth of WSe2 flakes.

Sulfur aids in selenization, producing few-layer and pyramid-like WSe2.

Devices exhibit high on/off ratios and mobility.

Abstract

Two-dimensional (2D) layered tungsten diselenides (WSe2) material has recently drawn a lot of attention due to its unique optoelectronic properties and ambipolar transport behavior. However, direct chemical vapor deposition (CVD) synthesis of 2D WSe2 is not as straightforward as other 2D materials due to the low reactivity between reactants in WSe2 synthesis. In addition, the growth mechanism of WSe2 in such CVD process remains unclear. Here we report the observation of a screw-dislocation-driven (SDD) spiral growth of 2D WSe2 flakes and pyramid-like structures using a sulfur-assisted CVD method. Few-layer and pyramid-like WSe2 flakes instead of monolayer were synthesized by introducing a small amount of sulfur as a reducer to help the selenization of WO3, which is the precursor of tungsten. Clear observations of steps, helical fringes, and herring-bone contours under atomic force microscope characterization reveal the existence of screw dislocations in the as-grown WSe2. The generation and propagation mechanisms of screw dislocations during the growth of WSe2 were discussed. Back-gated field-effect transistors were made on these 2D WSe2 materials, which show on/off current ratios of 106 and mobility up to 44 cm2/Vs.