Strain-Driven and Layer-Number-Dependent Crossover of Growth Mode in van der Waals Heterostructures: 2D/2D Layer-By-Layer Horizontal Epitaxy to 2D/3D Vertical Reorientation
Strain-Driven and Layer-Number-Dependent Crossover of Growth Mode in van der Waals Heterostructures: 2D/2D Layer-By-Layer Horizontal Epitaxy to 2D/3D Vertical Reorientation
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DOI：
10.1002/admi.201800382
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发表时间：
2018-07-23
影响因子：
5.4
通讯作者：
Jung, Yeonwoong
中科院分区：
文献类型：
--
作者：
Choudhary, Nitin;Chung, Hee-Suk;Jung, Yeonwoong
由成分不同的原子层组成的异质集成二维范德华（vdW）固体预计将表现出单组分同类产品无法达到的奇异电/光学特性。然而，其形貌控制化学气相沉积（CVD）生长的基本原理及其相关的生长变量尚未阐明，使得其预计的技术机会远未实现。在此，通过采用三氧化钨 (WO3) 纳米线作为模型系统，独特地实现了 2D/2D 界面的详细原子级检查，研究了 2D 钼/二硫化钨 vdW 垂直堆叠的 CVD 生长机制。通过使用广泛的透射电子显微镜 (TEM) 表征，在这些材料中发现了有趣的生长模式转变，即 2D/2D 逐层水平外延到 2D/3D 垂直层重新取向，并证实它是由不同的 2D 层数驱动的。证实的分子动力学模拟表明，二维层生长过程中积累的内部应变决定了最终的生长模式，TEM 应变图分析进一步支持了这一点。这项研究不仅为更好地理解 2D vdW 异质结构的生长原理提供了新的见解，而且还为定制其功能以探索 2D/2D 异质结器件提供了重要的技术指导。
Heterogeneously integrated 2D van der Waals (vdW) solids composed of compositionally distinct atomic layers are envisioned to exhibit exotic electrical/optical properties unattainable with their monocomponent counterparts. However, the underlying principle for their morphology-controlled chemical vapor deposition (CVD) growth and its associated growth variables have not been clarified, leaving their projected technological opportunities far from being realized. Herein, by employing tungsten trioxide (WO3) nanowires as a model system that uniquely enables the detailed atomic-scale inspections of 2D/2D interfaces, the CVD growth mechanism of 2D molybdenum/tungsten disulfide vdW vertical stacks is studied. By employing extensive transmission electron microscopy (TEM) characterization, an intriguing growth mode transition is identified in these materials, i.e., 2D/2D layer-by-layer horizontal epitaxy to 2D/3D vertical layer reorientation, and it is confirmed that it is driven by varying 2D layer numbers. Corroborating molecular dynamics simulations clarify that the internal strain accumulated during the course of 2D layers growth dictates the final growth mode, further supported by TEM strain map analysis. This study not only sheds a new insight on better understanding the growth principles for 2D vdW heterostructures but also offers important technical guidance on tailoring their functionalities toward exploring 2D/2D heterojunction devices.