Sutter Eli, Sutter Peter
Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA.
Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE, 68588, USA.
Small. 2021 Dec;17(51):e2104784. doi: 10.1002/smll.202104784. Epub 2021 Oct 16.
1D nanowires of 2D layered crystals are emerging nanostructures synthesized by combining van der Waals (vdW) epitaxy and vapor-liquid-solid (VLS) growth. Nanowires of the group IV monochalcogenide germanium sulfide (GeS) are of particular interest for twistronics due to axial screw dislocations giving rise to Eshelby twist and precision interlayer twist at helical vdW interfaces. Ultrathin vdW nanowires have not been realized, and it is not clear if confining layered crystals into extremely thin wires is even possible. If axial screw dislocations are still stable, ultrathin vdW nanowires can reach large twists and should display significant quantum confinement. Here it is shown that VLS growth over Bi catalysts yields vdW nanowires down to ≈15 nm diameter while maintaining tens of µm length. Combined electron microscopy and diffraction demonstrate that ultrathin GeS nanowires crystallize in the orthorhombic bulk structure but can realize nonequilibrium stacking that may lead to 1D ferroelectricity. Ultrathin nanowires carry screw dislocations, remain chiral, and achieve very high twist rates. Whenever the dislocation extends to the nanowire tip, it continues into the Bi catalyst. Eshelby twist analysis demonstrates that the ultrathin nanowires follow continuum predictions. Cathodoluminescence on individual nanowires, finally, shows pronounced emission blue shifts consistent with quantum confinement.
二维层状晶体的一维纳米线是通过结合范德华（vdW）外延生长和气-液-固（VLS）生长合成的新兴纳米结构。由于轴向螺旋位错会导致埃舍尔比扭转以及在螺旋范德华界面处产生精确的层间扭转，因此IV族单硫属化物硫化锗（GeS）的纳米线在扭曲电子学方面具有特别的研究价值。超薄范德华纳米线尚未实现，而且将层状晶体限制在极细的线中是否可行尚不清楚。如果轴向螺旋位错仍然稳定，超薄范德华纳米线可以达到大的扭转角度，并且应该会表现出显著的量子限制效应。在此研究中表明，在铋催化剂上进行VLS生长可得到直径低至约15纳米的范德华纳米线，同时保持数十微米的长度。结合电子显微镜和衍射分析表明，超薄硫化锗纳米线以正交晶系体结构结晶，但可以实现非平衡堆积，这可能会导致一维铁电性。超薄纳米线携带螺旋位错，保持手性，并实现非常高的扭转率。每当位错延伸到纳米线尖端时，它会继续延伸到铋催化剂中。埃舍尔比扭转分析表明，超薄纳米线符合连续介质理论预测。最后，对单个纳米线的阴极发光显示出明显的发射蓝移，这与量子限制效应一致。
