Growth of tungsten disulfide bilayers featuring Moiré superlattices: A surface energy perspective

• Published in: Applied surface science Vol. 661; p. 160029
• Main Authors: Liu, Min, Zhang, Teng, Xia, Yuanzheng, Zhou, Jiangpeng, Liu, Mengyu, Zhang, Yuxiang, Xu, Feiya, Cao, Yiyan, Zhang, Chunmiao, Zheng, Xuanli, Wu, Yaping, Wu, Zhiming, Li, Xu, Kang, Junyong
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.07.2024
• Subjects: Chemical vapor deposition; Surface energy; Tungsten disulfide; Chemical vapor deposition; Tungsten disulfide; Surface energy
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2024.160029

[Display omitted] •Acetic acid treatment introduces micrometer-sized micropits on the sapphire substrate.•The micropits promote the formation of nucleation sites.•The micropits reduce surface energy and facilitate the transition to vertical growth mode.•WS2 bilayers and Moiré superlattices were obtained on acid-pretreated substrates.•WS2 bilayers have higher valley polarization and carrier mobility than monolayers. The bilayer (BL) transition metal dichalcogenides (TMDs), with their elevated carrier mobility and narrowed bandgap, are advantageous for future electronic applications in comparison with their monolayer (ML) counterparts. Here, we introduce a facile and efficient approach for the chemical vapor deposition synthesis of BL WS2. The method involves an acetic acid sonication treatment to modify the substrate surface morphology and the surface energy, which regulates the nucleation processes and shapes the growth mode of WS2 crystals. Further modifications to the growth conditions yield high-quality ML and BL WS2 films. A comparative study confirms the superior valley polarization and higher carrier mobility of BL WS2 compared with its ML counterpart. Additionally, a minor twist angle existed between the upper and lower layers, featuring a Moiré superlattice. This work reveals the role of surface morphology and surface energy in the growth of TMDs. Simultaneously, it offers insights into the controlled preparation of vertically stacked homo- and heterojunctions.