daSilva Jessica Cimada, Smeaton Michelle A, Dunbar Tyler A, Xu Yuanze, Balazs Daniel M, Kourkoutis Lena F, Hanrath Tobias
Nano Lett. 2020 Jul 8;20(7):5267-5274. doi: 10.1021/acs.nanolett.0c01579. Epub 2020 Jun 9.
Understanding the mechanism and ultimately directing nanocrystal (NC) superlattice assembly and attachment have important implications on future advances in this emerging field. Here, we use 4D-STEM to investigate a monolayer of PbS NCs at various stages of the transformation from a hexatic assembly to a nonconnected square-like superlattice over large fields of view. Maps of nanobeam electron diffraction patterns acquired with an electron microscope pixel array detector (EMPAD) offer unprecedented detail into the 3D crystallographic alignment of the polyhedral NCs. Our analysis reveals that superlattice transformation is dominated by translation of prealigned NCs strongly coupled along the <11> direction and occurs stochastically and gradually throughout single grains. We validate the generality of the proposed mechanism by examining the structure of analogous PbSe NC assemblies using conventional transmission electron microscopy and selected area electron diffraction. The experimental results presented here provide new mechanistic insights into NC self-assembly and oriented attachment.
理解其机制并最终指导纳米晶体（NC）超晶格的组装和附着，对这一新兴领域的未来发展具有重要意义。在这里，我们使用4D-STEM在大视野范围内研究单层PbS NCs从六方组装到非连接方形超晶格转变的各个阶段。用电子显微镜像素阵列探测器（EMPAD）获取的纳米束电子衍射图案图谱，为多面体NCs的三维晶体学取向提供了前所未有的详细信息。我们的分析表明，超晶格转变主要由沿<11>方向强烈耦合的预排列NCs的平移主导，并且在单个晶粒中随机且逐渐地发生。我们通过使用传统透射电子显微镜和选区电子衍射检查类似的PbSe NC组件的结构，验证了所提出机制的普遍性。这里展示的实验结果为NC自组装和定向附着提供了新的机理见解。
