Layer-Selective Synthesis of MoS₂ and WS₂ Structures under Ambient Conditions for Customized Electronics

Abstract

Transition metal dichalcogenides (TMDs) have attracted significant interest as one of the key materials in future electronics such as logic devices, optoelectrical devices, and wearable electronics. However, a complicated synthesis method and multistep processes for device fabrication pose major hurdles for their practical applications. Here, we introduce a direct and rapid method for layer-selective synthesis of MoS 2 and WS 2 structures in wafer-scale using a pulsed laser annealing system (λ = 1.06 μm, pulse duration ∼100 ps) in ambient conditions. The precursor layer of each TMD, which has at least 3 orders of magnitude higher absorption coefficient than those of neighboring layers, rigorously absorbed the incoming energy of the laser pulse and rapidly pyrolyzed in a few nanoseconds, enabling the generation of a MoS 2 or WS 2 layer without damaging the adjacent layers of SiO 2 or polymer substrate. Through experimental and theoretical studies, we establish the underlying principles of selective synthesis and optimize the laser annealing conditions, such as laser wavelength, output power, and scribing speed, under ambient condition. As a result, individual homostructures of patterned MoS 2 and WS 2 layers were directly synthesized on a 4 in. wafer. Moreover, a consecutive synthesis of the second layer on top of the first synthesized layer realized a vertically stacked WS 2 /MoS 2 heterojunction structure, which can be treated as a cornerstone of electronic devices. As a proof of concept, we demonstrated the behavior of a MoS 2 -based field-effect transistor, a skin-attachable motion sensor, and a MoS 2 /WS 2 -based heterojunction diode in this study. The ultrafast and selective synthesis of the TMDs suggests an approach to the large-area/mass production of functional heterostructure-based electronics.

Synthesis of two‐dimensional transition metal dichalcogenides for electronics and optoelectronics

“…More importantly, this method has excellent controllability and the obtained films scale is up to 1.412 cm. Subsequently, Park et al 69 reported an approach to induce a local photothermal decomposition reaction of ammonium tetrathiomolybdate and ammonium tetrathiotungstate precursor resulting in thermal deposited MoS 2 and WS 2 thin films utilizing photothermal effect of infrared laser, and then to prepare vdWHs in the substrate directly. Laser synthesis method has good advantages in controllable and selective synthesis, however, it is necessary to further study of larger size and monolayer materials growth due to the restrict of laser.…”

Synthesis of Large-Scale Transition Metal Dichalcogenides for Their Commercialization

“…3(a)]. The precursor nuclei in the solution continuously adhere to the SiO 2 /Si substrate; Park et al [23] have recently developed a novel process that can freely form TMDC patterns through a pulsed laser annealing method. Using the precursor deposition method of Yang et al [20], a precursor is initially deposited on a 4-inch TMDC thin film by spin coating.…”

“…The analyzed photo responsivity of the fabricated device is ~5.39 A W -1 , which is higher than that of the previously reported TMDC-based optoelectronic devices that are made up of monolayer homo-and heterojunctions. Park et al [23] demonstrated a p-n diode with vertically stacked solution-processed WS 2 /MoS 2 thin films prepared by irradiating (NH 4 ) 2 WS 4 /MoS 2 films with an ultra-short laser pulse (~100 ps) to cause selective thermolysis of (NH 4 ) 2 WS 4 , since it shows ~60 times higher absorbance than the MoS 2 film during the laser annealing (1.06 μm). The process converts (NH 4 ) 2 WS 4 to a WS 2 film with high crystallinity despite the instant formatting on the MoS 2 lattice.…”

“…The previously reported methods of TMDC-based strain sensor fabrication used thin films grown using CVD, with several subsequent photolithography steps to pattern the strain gauge [41,42]. Park et al [23] demonstrated the direct pattern formation of a MoS 2 -based strain gauge and proposed that a lithography-free approach can be applied to develop a three-axis strain gauge rosette. The application of an external force on the MoS 2 strain gauge causes strain-induced deformation of the conductive pathways, which changes the electrical conductivity of the material [ Fig.…”

Effect of the strain on spin-valley transport properties in MoS2 superlattice

“…Since monolayer graphene is a gapless semiconductor, it has no useful applications in the semiconductor industry, logic, and spintronic devices. Within the 2D materials, monolayer molybdenum disulfide (MoS 2 ) was successfully synthesized via several experimental techniques 3 – 7 . Unlike graphene, the monolayer MoS 2 is a direct bandgap semiconductor with a tunable bandgap 8 .…”