Liquid Phase Edge Epitaxy of Transition-Metal Dichalcogenide Monolayers

Abstract

Precise monolayer epitaxy is important for two-dimensional (2D) semiconductors toward future electronics. Here, we report a new self-limited epitaxy approach, liquid phase edge epitaxy (LPEE), for precise-monolayer epitaxy of transition-metal dichalcogenides. In this method, the liquid solution contacts 2D grains only at the edges, which confines the epitaxy only at the grain edges and then precise monolayer epitaxy can be achieved. High-temperature in situ imaging of the epitaxy progress directly supports this edge-contact epitaxy mechanism. Typical transition-metal dichalcogenide monolayers (MX2, M = Mo, W, and Re; X = S or Se) have been obtained by LPEE with a proper choice of molten alkali halide solvents (AL, A = Li, Na, K, and Cs; L = Cl, Br, or I). Furthermore, alloying and magnetic-element doping have also been realized by taking advantage of the liquid phase epitaxy approach. This LPEE method provides a precise and highly versatile approach for 2D monolayer epitaxy and can revolutionize the growth of 2D materials toward electronic applications.

Progress on the in situ imaging of growth dynamics of two-dimensional materials

“…As for optical microscopy, the advent of high temperature optical microscope made it possible to monitor the CVD process in furnace. 78,79 Secondly, with the development of in situ techniques, more in situ investigations are needed to quantify the growth parameters such as nucleation rate, growth rate, diffusion rate, kink density, energy barriers, and so on.…”

“…The most straightforward information obtained via in situ techniques is the growth rate and its dependence on the temperature, gas flow rate, precursor, substrate, and so on. 47,[59][60][61][71][72][73][74][75][76][77][78] In 2015, the growth and etching of graphene on Cu substrate were observed by the radiation-mode optical microscopy (Rad-OM). Bright patches of graphene grains were clearly recognized (Fig.…”

Synthesis of millimeter-sized MoxW(1−x) S2ySe2(1−y)monolayer alloys with adjustable optical and electrical properties and their magnetic doping

“…In previous work, we developed a more universal self-limiting growth method for high-quality 2D monolayers: liquid-phase edge epitaxy (LPEE). 50 In this LPEE method, MoS 2 and WSe 2 are used as the precursors, and CsCl with high surface tension is selected as the flux. According to the previous achievement of our group, the growth of monolayers is preferable for the solvent with higher surface tension.…”

“…According to the previous achievement of our group, the growth of monolayers is preferable for the solvent with higher surface tension. 50 The solution contacts the 2D grains only at the grain edges, which limits the epitaxy along the in-plane direction, thus achieving monolayer growth of quaternary monolayer Mo 1- x W x S 2 y Se 2(1− y ) alloys. STEM examined the quality of the prepared alloys, indicating high-quality single-crystal domains.…”

Synthesis of component-controllable monolayer MoxW(1−x)S2ySe2(1−y) alloys with continuously tunable band gap and carrier type

“…According to the liquid phase edge epitaxy (LPEE) growth mechanism previously proposed by our research group, 39 25 monolayer Mo x W (1− x ) S 2 y Se 2(1− y ) alloys with different atomic ratios can be obtained on sapphire substrates. In LPEE, the solution only contacts the edges of the two-dimensional grains, restricting epitaxy in the in-plane direction.…”