Revealing the Role of Gold in the Growth of Two‐Dimensional Molybdenum Disulfide by Surface Alloy Formation

Abstract

The formation of Mo/Au surface alloy during Au‐assisted chemical vapor deposition (CVD) of MoS2 is confirmed by a series of control experiments. A metal–organic chemical vapor deposition (MOCVD) system is adapted to conduct two‐dimensional MoS2 growth in a controlled environment. Sequential injection of Mo and S precursors, which does not yield any MoS2 on SiO2/Si, grows atomically thin MoS2 on Au, indicating the formation of an alloy phase. Transmission electron microscopy of a cross‐section of the specimen confirms the confinement of the alloy phase near the surface only. These results show that the reaction intermediate is the surface alloy, and that the role of Au in the Au‐assisted CVD is the formation of an atomically thin reservoir of Mo near the surface. This mechanism is clearly distinguished from that of MOCVD, which does not involve the formation of any alloy phases.

Selective Antisite Defect Formation in WS2 Monolayers via Reactive Growth on Dilute W‐Au Alloy Substrates

“…The use of gold as a catalyst for growing 2D TMD layers by CVD has been previously reported. [35][36][37][38] However, previous growth methods used either WO 3 [36,37] or metal-organic vapors [39] as precursors for growing TMDs on Au substrate [37] or SiO 2 substrate [40] which usually are hard to regulate to form metal-poor growth environments. Therefore, S vacancies are the most commonly observed defects in WS 2 grown by those methods.…”

Tabletop Fabrication of High-Performance MoS2 Field-Effect Transistors

“…MoS 2 was prepared by chemical vapor deposition after the recommendation of Kang et al 17 and Song et al 31 ( Figure 1 a). A SiO 2 (300 nm)/Si substrate (p-type, Namkang Hi-tech) or a quartz substrate was loaded into a one-inch quartz tube.…”

Controllable growth of two-dimensional materials on noble metal substrates

“…On the other hand, Au can also grow few-layer MoS 2 by combining surface alloying and sulfurization, as shown in Figures 6 D–6F ( Song et al., 2014 ). A Mo-Au surface alloy formed after sufficiently feeding Mo source under atmospheric pressure and then turned into MoS 2 on the top of Au by sulfidation ( Song and Choi, 2019 ). Bilayer to trilayer MoS 2 continuous films ( Figure 6 F) or desired patterns can be feasibly obtained over a large area.…”

“…Precisely speaking, this method is classified as thermally assisted conversion (TAC), but with an extra step, i.e., the diffusion of source-metal atoms before conversion, compared with conventional TAC from Mo ( Kong et al., 2013 ; Zhan et al., 2012 ) or MoO 3 ( Lin et al., 2012 ) films into MoS 2 . The role of Au substrates, in this case, is to reserve a limited amount of Mo atoms for the formation of atomically thin MoS 2 films rather than bulks ( Song and Choi, 2019 ). However, whether Au had the catalytic activity involved in the chemical reaction during the 2D TMDC growth remained elusive.…”

“…In the two-step growth of few-layer MoS 2 films, the direct exposure of Au in Mo(CO) 6 vapor causes the formation of the Mo-Au surface alloy ( Song et al., 2014 ). As a result, the highest Mo concentration exits in the topmost Au layer ( Song and Choi, 2019 ). However, if the location of Mo supply is shifted away from the top surface of the Au layer ( Song et al., 2014 ) to its bottom surface ( Shivayogimath et al., 2019 ), the Mo concentration in the topmost Au layer still keeps very low due to the presence of a concentration gradient.…”