Heteroepitaxy between transition-metal dichalcogenide (TMDC) monolayers can fabricate atomically thin semiconductor heterojunctions without interfacial contamination, which are essential for next-generation electronics and optoelectronics. Here we report a controllable two-step chemical vapor deposition (CVD) process for lateral and vertical heteroepitaxy between monolayer WS2 and MoS2 on a c-cut sapphire substrate. Lateral and vertical heteroepitaxy can be selectively achieved by carefully controlling the growth of MoS2 monolayers that are used as two-dimensional (2D) seed crystals. Using hydrogen as a carrier gas, we synthesize ultraclean MoS2 monolayers, which enable lateral heteroepitaxial growth of monolayer WS2 from the MoS2 edges to create atomically coherent and sharp in-plane WS2/MoS2 heterojunctions. When no hydrogen is used, we obtain MoS2 monolayers decorated with small particles along the edges, inducing vertical heteroepitaxial growth of monolayer WS2 on top of the MoS2 to form vertical WS2/MoS2 heterojunctions. Our lateral and vertical atomic layer heteroepitaxy steered by seed defect engineering opens up a new route toward atomically controlled fabrication of 2D heterojunction architectures.

中文翻译：

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晶种均匀性控制单层 MoS2 和 WS2 的横向和纵向异质外延

过渡金属二硫属化物 (TMDC) 单层之间的异质外延可以制造原子级薄的半导体异质结，而不会产生界面污染，这对于下一代电子产品和光电子产品至关重要。在这里，我们报告了一种可控的两步化学气相沉积 (CVD) 工艺，用于在 c 切割蓝宝石衬底上的单层 WS2 和 MoS2 之间进行横向和垂直异质外延。通过仔细控制用作二维 (2D) 晶种的 MoS2 单层的生长，可以选择性地实现横向和垂直异质外延。使用氢气作为载气，我们合成了超洁净的 MoS2 单层，这使得单层 WS2 从 MoS2 边缘横向异质外延生长，以创建原子相干且尖锐的面内 WS2/MoS2 异质结。当不使用氢气时，我们获得了沿边缘装饰有小颗粒的 MoS2 单层，诱导单层 WS2 在 MoS2 顶部垂直异质外延生长，形成垂直的 WS2/MoS2 异质结。我们由种子缺陷工程引导的横向和垂直原子层异质外延开辟了一条通往二维异质结结构的原子控制制造的新途径。