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, MoS₂, and Bi₂Te₃ 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 Bi₂Te₃–Sb₂Te₃ and 2D/3D bonded Bi₂Te₃–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.

中文翻译：

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范德华力异质结构的应变工程†

改变固体的应变状态可以控制过多的功能特性。范德华（vdWaals）材料（例如石墨烯，hBN，MoS ₂和Bi ₂ Te ₃）中的弱层间键合似乎可以排除应变工程，因为应变会立即在vdWaals界面上松弛。在这里，我们通过显示vdWaals异质结构的持续面内应变高达5％的增长，提出了相反的直接观察结果，并且我们显示了应变弛豫遵循的是尚未报告的过程，与三维键合（3D）材料中的应变弛豫明显不同。为此，2D键合的Bi ₂ Te ₃ –Sb ₂ Te ₃和2D / 3D键合的Bi使用脉冲激光沉积（PLD）生长₂ Te ₃ -GeTe多层膜，并使用反射高能电子衍射（RHEED）原位监测其结构，并使用透射电子显微镜（TEM）进行原位分析。对应变松弛进行建模，发现其仅取决于生长的层及其初始应变。该见解表明，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，并为精确调整各个层的应变状态以优化vdWaals异质结构的功能打开了大门。