Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, 1098XH, Amsterdam, The Netherlands.
Physical Chemistry and Soft Matter, Wageningen University and Research, Stippeneng 4, 6708WE, Wageningen, The Netherlands.
Adv Mater. 2018 Oct;30(43):e1803433. doi: 10.1002/adma.201803433. Epub 2018 Aug 21.
The assembly of semiconductor nanoparticles, quantum dots (QDs), into dense crystalline nanostructures holds great promise for future optoelectronic devices. However, knowledge of the sub-nanometer scale driving forces underlying the kinetic processes of nucleation, growth, and final densification during QD assembly remains poor. Emulsion-templated assembly has recently been shown to provide good control over the bulk condensation of QDs into highly ordered 3D supercrystals. Here, emulsion-templated assembly is combined with in situ small-angle X-ray scattering to obtain direct insight into the nanoscale interactions underlying the nucleation, growth, and densification of QD supercrystals. At the point of supercrystal nucleation, nanoparticles undergo a hard-sphere-like crystallization into a hexagonal-close-packed lattice, slowly transforming into a face-centered-cubic lattice. The ligands play a crucial role in balancing steric repulsion against attractive van der Waals forces to mediate the initial equilibrium assembly, but cause the QDs to be progressively destabilized upon densification. The rich detail of this kinetic study elucidates the assembly and thermodynamic properties that define QD supercrystal fabrication approaching single-crystal quality, paving the way toward their use in optoelectronic devices.
半导体纳米粒子（量子点，QDs）组装成密集的结晶纳米结构，为未来的光电设备带来了巨大的希望。然而，对于在 QD 组装过程中引发、生长和最终致密化的动力学过程背后的亚纳米尺度驱动力的了解仍然很差。最近的研究表明，乳液模板组装可以很好地控制 QD 大量凝聚成高度有序的 3D 超晶体。在这里，乳液模板组装与原位小角 X 射线散射相结合，直接深入了解 QD 超晶体成核、生长和致密化的纳米尺度相互作用。在超晶体成核点，纳米颗粒经历了类似于硬球的结晶过程，形成六方密堆积晶格，然后缓慢转变为面心立方晶格。配体在平衡空间排斥和范德华吸引力方面起着至关重要的作用，以介导初始平衡组装，但在致密化过程中导致 QD 逐渐失稳。这项动力学研究的丰富细节阐明了组装和热力学性质，这些性质定义了 QD 超晶体的制造接近单晶质量，为它们在光电设备中的应用铺平了道路。
