Chiral twisted van der Waals nanowires
Chiral twisted van der Waals nanowires
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DOI：
10.1038/s41586-019-1147-x
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发表时间：
2019-06-20
期刊：
影响因子：
64.8
通讯作者：
Sutter, Eli
中科院分区：
文献类型：
--
作者：
Sutter, Peter;Wimer, Shawn;Sutter, Eli
相邻层之间具有小偏差（“层间扭曲”）的范德华异质结构引起了人们的兴趣，因为电子结构和相关现象（例如超导性）是由层间莫尔图案中出现的原子晶格和长程超晶格势决定的 (1-7)。以前，这种扭曲的异质结构涉及通过剥离隔离的层之间的单个平面界面，并以所需的相对方向以微机械方式堆叠(1,8-12)。在这里，我们展示了一类材料——层状晶体的范德华纳米线——其中可调节的层间扭曲在合成过程中自然演化。在气-液-固生长中，硫化锗(ii)纳米线（一种各向异性层状半导体）沿线轴分层结晶(13)，并且具有形成轴向螺位错的强烈倾向。纳米分辨电子衍射表明，由于轴向位错 (14,15) 的应力场，圆柱形固体两端的扭矩引起埃谢尔比扭曲，从而在范德华纳米线中产生手性结构。面内硫化锗晶轴沿着导线逐渐旋转，螺旋线相邻匝中的硫化锗层由于其层间扭曲而自然地形成莫尔图案。通过改变纳米线的厚度可以调节轴向旋转和扭转。结合电子衍射和阴极发光光谱显示了层间扭曲和局部激发光发射之间的相关性，这是由于沿纳米线的晶格取向和层间莫尔图案的逐渐变化所致。研究结果表明，朝着可扩展制造具有限定扭转角的范德华结构迈出了一步，其中层间莫尔图案是沿着纳米线上的螺旋路径而不是平面界面实现的。
Van der Waals heterostructures with small misalignment between adjacent layers ('interlayer twist') are of interest because of electronic structure and correlation phenomena (such as superconductivity) that are determined by both the atomic lattice and long-range superlattice potentials arising in interlayer moire patterns(1-7). Previously, such twisted heterostructures have involved a single planar interface between layers isolated by exfoliation and micromechanically stacked in the desired relative orientation(1,8-12). Here we demonstrate a class of materials-van der Waals nanowires of layered crystals-in which a tunable interlayer twist evolves naturally during synthesis. In vapour-liquid-solid growth, nanowires of germanium(ii) sulfide, an anisotropic layered semiconductor, crystallize with layering along the wire axis(13) and have a strong propensity for forming axial screw dislocations. Nanometre-resolved electron diffraction shows that Eshelby twist, induced by a torque on the ends of a cylindrical solid due to the stress field of an axial dislocation(14,15), causes a chiral structure in the van der Waals nanowires. The in-plane germanium sulfide crystal axes progressively rotate along the wire, and germanium sulfide layers in adjacent turns of the helix naturally form a moire pattern because of their interlayer twist. The axial rotation and the twist are tunable by varying the nanowire thickness. Combined electron diffraction and cathodoluminescence spectroscopy show the correlation between the interlayer twist and locally excited light emission that is due to progressive changes in the lattice orientation and in the interlayer moire registry along the nanowires. The findings demonstrate a step towards scalable fabrication of van der Waals structures with defined twist angles, in which interlayer moire patterns are realized along a helical path on a nanowire instead of a planar interface.