CVD Synthesis of Twisted Bilayer WS₂ with Tunable Second Harmonic Generation

Abstract

The introduction of rotational freedom by twist angles in twisted bilayer (TB) transition metal dichalcogenides (TMDCs) can tailor the inherent properties of the TMDCs, which provides a promising platform to investigate the exotic physical properties. However, direct synthesis of high‐quality TB‐TMDCs with full twist angles is significantly challenging due to the substantial energy barriers during crystal growth. Here, we propose a modified chemical vapor deposition (CVD) strategy to synthesize TB‐WS2 with a wide twist angle range from 0 to 120°. Utilizing a tilted SiO2/Si substrate, a gas flow disturbance is generated in the furnace tube to create a heterogeneous concentration gradient of the metal precursor, which provides an extra driving force for the growth of TB‐WS2. The Raman and photoluminescence (PL) results confirm a weak interlayer coupling of the TB‐WS2. High‐quality periodic Moiré patterns are observed in the scanning transmission electron microscopy (STEM) images. Moreover, owing to the strong correlation between the nonlinear optical response and the twisted crystal structure, tunable second harmonic generation (SHG) behaviors are realized in the TB‐WS2. This approach opens up a new avenue for the direct growth of high‐crystalline‐quality and pristine TB‐TMDCs and their potential applications in nonlinear optical devices.This article is protected by copyright. All rights reserved

Atomic engineering of two-dimensional materials via liquid metals

“…This study offers a methodology for the in situ construction of 2D twisted materials and facilitating the employment of tBLGs in the field of electronics. In addition to the deep understanding of tBLG, the twisted TMDs have also been widely investigated, 266–269 but have not ever been achieved by liquid metals or alloys.…”