Mixed-Salt Enhanced Chemical Vapor Deposition of Two-Dimensional Transition Metal Dichalcogenides

TL;DR

This study introduces a mixed-salt CVD technique that significantly improves the growth quality and size of 2D transition metal dichalcogenides like MoSe2 and WTe2, enabling scalable production of large monolayer crystals.

Contribution

The paper develops a novel mixed-salt CVD method that enhances the growth of large-area 2D TMDCs with improved reproducibility and scalability compared to previous salt-assisted techniques.

Findings

Achieved large grain sizes of 100-250 μm for MoSe2.

Produced isolated flakes up to ~450 μm.

Demonstrated the synergistic effect of Na+ and SeO32- in growth.

Abstract

The usage of molten salts, e.g., Na2MoO4 and Na2WO4, has shown great success in the growth of two-dimensional (2D) transition metal dichalcogenides (TMDCs) by chemical vapor deposition (CVD). In comparison with the halide salt (i.e., NaCl, NaBr, KI)-assisted growth (Salt 1.0), the molten salt-assisted vapor-liquid-solid (VLS) growth technique (Salt 2.0) has improved the reproducibility, efficiency and scalability of synthesizing 2D TMDCs. However, the growth of large-area MoSe2 and WTe2 is still quite challenging with the use Salt 2.0 technique. In this study, a renewed Salt 2.0 technique using mixed salts (e.g., Na2MoO4-Na2SeO3 and Na2WO4-Na2TeO3) is developed for the enhanced CVD growth of 2D MoSe2 and WTe2 crystals with large grain size and yield. Continuous monolayer MoSe2 film with grain size of 100-250 {\mu}m or isolated flakes up to ~ 450 {\mu}m is grown on a halved 2-inch SiO2/Si wafer. Our study further confirms the synergistic effect of Na+ and SeO32- in the enhanced CVD growth of wafer-scale monolayer MoSe2 film. And thus, the addition of Na2SeO3 and Na2TeO3 into the transition metal salts could be a general strategy for the enhanced CVD growth of many other 2D selenides and tellurides.