Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Nanoscale. 2018 Jan 18;10(3):1474-1480. doi: 10.1039/c7nr07607j.
Modifying the strain state of solids allows control over a plethora of functional properties. The weak interlayer bonding in van der Waals (vdWaals) materials such as graphene, hBN, MoS, and BiTe might seem to exclude strain engineering, since strain would immediately relax at the vdWaals interfaces. Here we present direct observations of the contrary by showing growth of vdWaals heterostructures with persistent in-plane strains up to 5% and we show that strain relaxation follows a not yet reported process distinctly different from strain relaxation in three-dimensionally bonded (3D) materials. For this, 2D bonded BiTe-SbTe and 2D/3D bonded BiTe-GeTe multilayered films are grown using Pulsed Laser Deposition (PLD) and their structure is monitored in situ using Reflective High Energy Electron Diffraction (RHEED) and post situ analysis is performed using Transmission Electron Microscopy (TEM). Strain relaxation is modeled and found to solely depend on the layer being grown and its initial strain. This insight demonstrates that strain engineering of 2D bonded heterostructures obeys different rules than hold for epitaxial 3D materials and opens the door to precise tuning of the strain state of the individual layers to optimize functional performance of vdWaals heterostructures.
改变固体的应变状态可以控制大量的功能特性。范德华（vdW）材料（如石墨烯、hBN、MoS 和 BiTe）的弱层间键合似乎排除了应变工程，因为应变会立即在 vdW 界面处松弛。在这里，我们通过展示具有高达 5%的持续面内应变的 vdW 异质结构的生长，直接观察到了相反的情况，并且表明应变松弛遵循一种尚未报道的过程，与三维键合（3D）材料中的应变松弛明显不同。为此，使用脉冲激光沉积（PLD）生长二维键合的 BiTe-SbTe 和二维/三维键合的 BiTe-GeTe 多层膜，并使用反射高能电子衍射（RHEED）原位监测其结构，使用透射电子显微镜（TEM）进行原位分析。对应变松弛进行了建模并发现其仅取决于正在生长的层及其初始应变。这一见解表明，二维键合异质结构的应变工程遵循与外延 3D 材料不同的规则，并为精确调整各层的应变状态以优化 vdW 异质结构的功能性能开辟了道路。
