Thermodynamically driven tilt grain boundaries of monolayer crystals using catalytic liquid alloys

TL;DR

This paper introduces a vapor-liquid-solid growth method using sodium molybdate alloys to control and optimize grain boundary defects in monolayer MoS2, enhancing its optical properties through thermodynamic stability.

Contribution

It presents a novel VLS growth technique with catalytic liquid alloys to precisely engineer grain boundary defects in monolayer MoS2, improving its photoluminescence.

Findings

Mo-rich alloys produce Mo-polar 5|7 defects with over 95% yield

Enhanced PL intensity correlates with suppression of non-radiative recombination

Na adsorption on defects reduces non-radiative pathways

Abstract

We report a method to precisely control the atomic defects at grain boundaries (GBs) of monolayer MoS2 by vapor-liquid-solid (VLS) growth using sodium molybdate liquid alloys, which serve as growth catalysts to guide the formations of the thermodynamically most stable GB structure. The Mo-rich chemical environment of the alloys results in Mo-polar 5|7 defects with a yield exceeding 95%. The photoluminescence (PL) intensity of VLS-grown polycrystalline MoS2 films markedly exceeds that of the films exhibiting abundant S 5|7 defects, which are kinetically driven by vapor-solid-solid growths. Density functional theory calculations indicate that the enhanced PL intensity is due to the suppression of non-radiative recombination of charged excitons with donor-type defects of adsorbed Na elements on S 5|7 defects. Catalytic liquid alloys can aid in determining a type of atomic defect even in various polycrystalline 2D films, which accordingly provides a technical clue to engineer their properties.