Direct growth of monolayer 1T–2H MoS₂ heterostructures using KCl-assisted CVD process

Abstract

Accessing the metastable phases in a controlled fashion can further expand the applications of atomically thin transition metal dichalcogenides (TMDs). Although top-down approaches based on ion intercalation exfoliation have shown to be an effective route to transform 2H phase into 1T and/or 1T′ polytype phases, a bottom-up growth strategy could be more suitable for device integration. Herein, we show that by assisting the atmospheric pressure chemical vapor deposition (APCVD) growth with a specific alkali metal halide (AMH), it possible to induce the direct synthesis of 1T phase domains coexisting with 2H phase structure in micrometer-sized MoS2 monolayer flakes. The photoluminescence emission and structural properties of three different AMH (NaCl, KBr and KCl) MoS2 crystals are compared. Both NaCl and KBr assisted MoS2 monolayers displayed the semiconducting 2H-phase. On the other hand, we demonstrate that KCl promotes the formation of a 1T–2H phase mixture. X-ray photoemission spectroscopy and resonant Raman studies performed on KCl–MoS2 monolayers show the emergence of a second chemical state and 1T Raman bands compared to the rest of the samples. High-resolution scanning transmission electron microscope imaging revealed important changes in the atomic arrangement between 2H and 1T domains, providing clear evidence of the presence of the 1T metastable phase in the lattice. Moreover, the growth 1T domains can also be controlled by modifying the deposition temperature. Our experiments show that the introduction of KCl during the APCVD growth result in stable 1T-MoS2 domains, providing a simple and reproducible route towards the polymorphism phase engineering of layered TMDs using a direct bottom-up approach.

Modulation of Schottky Barrier Height by Nitrogen Doping and Its Influence on Responsivity of Monolayer MoS2 Photodetector

“…Also, Raman analysis was done for monolayer MoS 2 as can be clearly seen in Figure 2b that the Raman spectroscopy had two distinct peaks centered at 384 cm −1 and 403 cm −1 , which corresponded to E 2g 1 and A 1g modes; where E 2g 1 signified in-plane vibration of M and S atoms and A 1g signified out-of-plane vibration and the frequency difference between in-plane and out-plane was observed to be 19 cm −1 confirming monolayer MoS 2 flakes. [31,32]…”

Electron-Injection and Atomic-Interface Engineering toward Stabilized Defected 1T-Rich MoS2 as High Rate Anode for Sodium Storage

“…Some approaches have been developed to obtain 1T-phase MoS 2 , such as chemical Li + intercalation/extraction exfoliation, , chemical vapor deposition (CVD), and solvothermal/hydrothermal method. , In spite of stunning developments in improving specific capacity of MoS 2 anodes, obvious capacity attenuation was accompanied for both cycling and rate performance. , It is ascribed to the habitual conversion of the metastable 1T-phase MoS 2 to the stable 2H phase via restacking in the charge–discharge process . In addition, the annealing process is usually required to improve the crystallinity of MoS 2 and form more active sites, but it also encounters the phase conversion from 1T to 2H. , Therefore, the formation of a stable 1T-phase MoS 2 that can withstand annealing and electrochemical cycling simultaneously is significant and challenging.…”

“…Some approaches have been developed to obtain 1T-phase MoS 2 , such as chemical Li + intercalation/extraction exfoliation, 9,10 chemical vapor deposition (CVD), 11 and solvothermal/ hydrothermal method. 12,13 In spite of stunning developments in improving specific capacity of MoS 2 anodes, obvious capacity attenuation was accompanied for both cycling and rate performance.…”

Dual Catalytic and Self‐Assembled Growth of Two‐Dimensional Transition Metal Dichalcogenides Through Simultaneous Predeposition Process

“…Although metal organic salts, such as perylene-3,4,9,10-tetracarboxylic acid tetrapotassium salts, were introduced in early CVD studies [9,25] remarkable improvements in growth have been demonstrated by the adoption of alkali metal halides (AMHs). [26][27][28][29][30][31][32][33][34][35][36][37][38] The versatility and practicality of AMH-assisted CVD are supported by the reduced process temperature, [26] millimeter-scaled large grains, [27] rapid growth, [27,28] and one-dimensional growth (TMD nanowire). [29] AMH-assisted CVD has evolved into a universal process capable of synthesizing more than 40 2D TMDs.…”