Two-dimensional heterostructures composed of different, vertically stacked transition-metal dichalcogenide (TMDC) layers are useful materials with optoelectronic applications. SeungNam Cha, Sungkyunkwan University (SKKU) Suwon, Gyeonggi-do, Republic of Korea, Jung Inn Sohn, University of Oxford, UK, and Dongguk University, Seoul, Republic of Korea, and colleagues have synthesized lateral heterostructures made from different TMDCs (pictured schematically). They are composed of MoS₂, WS₂, or Mo_1–xW_xS₂ alloys, with one material in the central triangle and another in the outer region.

The team combined chemical vapor deposition (CVD) with solution-processed precursor deposition to fabricate these monolayers. The solution processing was used to deposit an extremely small amount of transition-metal-oxide precursor (MoO₃ or WO₃) onto SiO₂ substrates. CVD was then used to add sulfur and form the desired structures. This process led to the growth of large and highly crystalline TMDC monolayers.

Thes resulting crystals have a clear heterogeneous junction and sizes of up to 160 μm. The formation of alloys instead of pure MoS₂ and WS₂ can be controlled by changing the growth parameters. The main factors that change the product are the temperature and the timing of the sulfur introduction.

• Direct Epitaxial Synthesis of Selective Two-Dimensional Lateral Heterostructures,
  Juwon Lee, Sangyeon Pak, Young-Woo Lee, Youngsin Park, A-Rang Jang, John Hong, Yuljae Cho, Bo Hou, Sanghyo Lee, Hu Young Jeong, Hyeon Suk Shin, Stephen M. Morris, SeungNam Cha, Jung Inn Sohn, Jong Min Kim,
  ACS Nano 2019.
  https://doi.org/10.1021/acsnano.9b05722