Institute of Physics, Montanuniversitaet Leoben, 8700, Leoben, Austria.
Institute for Inorganic Chemistry, Graz University of Technology, 8010, Graz, Austria.
Adv Mater. 2018 Aug;30(32):e1802078. doi: 10.1002/adma.201802078. Epub 2018 Jun 26.
When nanocrystals self assemble into ordered superstructures they form functional solids that may inherit the electronical properties of the single nanocrystals. To what extent these properties are enhanced depends on the positional and orientational order of the nanocrystals within the superstructure. Here, the formation of micrometer-sized free-standing supercrystals of faceted 20 nm Bi nanocrystals is investigated. The self-assembly process, induced by nonsolvent into solvent diffusion, is probed in situ by synchrotron X-ray scattering. The diffusion-gradient is identified as the critical parameter for controlling the supercrystal-structure as well as the alignment of the supercrystals with respect to the substrate. Monte Carlo simulations confirm the positional order of the nanocrystals within these superstructures and reveal a unique orientation phase: the nanocrystal shape, determined by the atomic Bi crystal structure, induces a total of 6 global orientations based on facet-to-facet alignment. This parallel alignment of facets is a prerequisite for optimized electronic and optical properties within designed nanocrystal solids.
当纳米晶体自组装成有序的超结构时，它们会形成具有功能性的固体，这些固体可能会继承单个纳米晶体的电子特性。这些特性在多大程度上得到增强取决于超结构中纳米晶体的位置和取向有序性。在这里，研究了具有面心 20nmBi 纳米晶体的微米级自由-standing 超晶体的形成。通过非溶剂向溶剂扩散的诱导，通过同步加速器 X 射线散射进行原位探测。扩散梯度被确定为控制超晶体结构以及超晶体相对于衬底取向的关键参数。蒙特卡罗模拟证实了这些超结构中纳米晶体的位置有序性，并揭示了一种独特的取向相：纳米晶体的形状由原子 Bi 晶体结构决定，基于面对面的排列总共诱导出 6 种全局取向。这种面的平行排列是在设计的纳米晶体固体中优化电子和光学性质的前提。
