Low-Temperature Growth of 2D-MoS₂ Thin Films by Plasma-Enhanced Atomic Layer Deposition Using a New Molybdenum Precursor and Applicability to Gas Sensors

Abstract

Two-dimensional transition-metal dichalcogenides (2D TMDs) such as molybdenum disulfide (MoS 2 ) have received great attention for various applications. However, large-scale synthesis of high-quality 2D TMDs remains a challenge. Atomic layer deposition (ALD) is a promising deposition method for synthesizing large-area 2D TMDs, but it shows poor film quality due to the narrow process temperature window caused by the low thermal stability of conventional precursors. In this study, a plasma-enhanced atomic layer deposition (PEALD) process utilizing a new cyclopentadienyl-based Mo precursor (r-cyclopentadienyl dicarbonyl nitrosyl molybdenum, IM-02) was presented for synthesizing crystalline MoS 2 at a low growth temperature. IM-02 exhibited excellent thermal stability and suitability as an ALD precursor. The resulting MoS 2 thin films showed good uniformity and crystallinity without additional thermal treatment. Interestingly, the quality of the MoS 2 film was further improved by exposure to H 2 S plasma, which increased crystallinity and reduced grain boundaries and surface defects, suppressing surface contamination by carbon and oxygen in air. The resulting MoS 2 thin films were highly selective for NO 2 gas, with a response rate of about 50% at 100 ppm NO 2 even at room temperature, indicating their potential for use in gas sensors. These results suggest the PEALD process using IM-02 and H 2 S plasma as a promising approach for synthesizing high-quality MoS 2 thin films, with potential applications in various fields.

Atomic vs. sub-atomic layer deposition: impact of growth rate on the optical and structural properties of MoS2 and WS2

“…Amorphous, optically inactive MoS 2 can be grown by ALD at temperatures as low as 100 • C [15,16]. Most of the ALD-grown MoS 2 layers are reported to not show photoluminescence (PL) [17,18], need subsequent annealing at high temperature to obtain PL [19] or no information on the PL properties is given [20][21][22][23][24][25]. It is expected that the growth temperature is the limiting factor responsible for the PL inactivity of ALD grown MoS 2 .…”

Defects and Defect Engineering of Two-Dimensional Transition Metal Dichalcogenide (2D TMDC) Materials

“…Moreover, the properties of the TMDC materials depend on the layers’ thickness, making these TMDC materials promising ones for electronics and optoelectronics applications. The various synthesis techniques of TMDC materials have been applied, such as mechanical exfoliation, liquid exfoliation, chemical vapor deposition (CVD), physical vapor deposition (PVD) [ 9 ], atomic layered deposition (ALD) [ 10 ], chemical vapor transport (CVT) [ 11 ], molecular beam epitaxy (MBE) [ 12 ], and metal–organic chemical vapor deposition (MOCVD) [ 13 , 14 ]. Indeed, each synthesis process generates different types of defects in these materials [ 9 ].…”