Strategies, Status, and Challenges in Wafer Scale Single Crystalline Two-Dimensional Materials Synthesis

Abstract

The successful exfoliation of graphene has given a tremendous boost to research on various two-dimensional (2D) materials in the last 15 years. Different from traditional thin films, a 2D material is composed of one to a few atomic layers. While atoms within a layer are chemically bonded, interactions between layers are generally weak van der Waals (vdW) interactions. Due to their particular dimensionality, 2D materials exhibit special electronic, magnetic, mechanical, and thermal properties, not found in their 3D counterparts, and therefore they have great potential in various applications, such as 2D materials-based devices. To fully realize their large-scale practical applications, especially in devices, wafer scale single crystalline (WSSC) 2D materials are indispensable. In this review, we present a detailed overview on strategies toward the synthesis of WSSC 2D materials while highlighting the recent progress on WSSC graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenide (TMDC) synthesis. The challenges that need to be addressed in future studies have also been described. In general, there have been two distinct routes to synthesize WSSC 2D materials: (i) allowing only one nucleus on a wafer scale substrate to be formed and developed into a large single crystal and (ii) seamlessly stitching a large number of unidirectionally aligned 2D islands on a wafer scale substrate, which is generally single crystalline. Currently, the synthesis of WSSC graphene has been realized by both routes, and WSSC hBN and MoS 2 have been synthesized by route (ii). On the other hand, the growth of other WSSC 2D materials and WSSC multilayer 2D materials still remains a big challenge. In the last section, we wrap up this review by summarizing the future challenges and opportunities in the synthesis of various WSSC 2D materials.

Recent Progress on Two-Dimensional Materials

“…In contrast to the relatively simple top-down approaches, achieving growth of high quality 2D materials by the bottom-up synthesis requires the reactions of various precursors on a suitable substrate at an appropriate experiential condition, and thus many tunable experimental parameters determine the quality of the product 1624,1625 . To optimize the bottom-up experimental synthesis of 2D materials, a deep understanding on the growth mechanisms of various 2D materials is essential.…”

Reducing Contact Resistance and Boosting Device Performance of Monolayer MoS2 by In Situ Fe Doping

“…[4][5][6] To realize the large-scale applications of 2D materials in the semiconductor industry, three aspects should be considered, including wafer-scale synthesis, contact engineering, and controllable doping.The wafer-scale synthesis of 2D single crystals has fueled vigorous scientific inquiry, and fruitful achievements have been attained. [7,8] For example, inch-sized single-crystal graphene was chemical vapor deposition (CVD) synthesized on Cu-Ni alloys by controlling the nucleation. [9] Through the seamless stitching of unidirectional domains, wafer-scale single crystals were obtained, such as monolayer graphene on Ge(110), [10] monolayer h-BN on vicinal Cu(110), [11] Cu(111)/sapphire, [12] and liquid Au substrate.…”

Single-crystal two-dimensional material epitaxy on tailored non-single-crystal substrates

“…Besides Cu substrates, the alignment maps (shown in Fig. 1b, c ) are also applicable for graphene and hBN grown on other twin FCC metal substrates if the epitaxial relationship of a zigzag direction of a 2D material aligning along a high symmetric <110> direction of a substrate stands 32 , 33 . For example, Au substrates are promising for the epitaxial growth of transition metal dichalcogenides (TMDCs) 34 , 35 , sharing the same epitaxial relationship as that of hBN on Cu surface.…”