Geometry-Adaptive Coassembly of Binary Nanocrystal Superlattices with Tunable Translational and Orientational Order

Self-assembled colloidal nanocrystals form superlattices with programmable structures, yet achieving simultaneous control over both packing symmetry and orientational order, particularly in multicomponent systems, remains a significant challenge. Here, we report a geometry-adaptive coassembly approach using nanodumbbells (NDs) and nanospheres (NSs) to construct binary nanocrystal superlattices (BNSLs) with precisely tunable translational and orientational order. During coassembly, NSs selectively occupy the interstitial voids formed by the concave waists of vertically aligned NDs, while the ND hexagonal heads impose geometric constraints that regulate their orientations. By systematically increasing NS size─thereby weakening constraint strength─we observe a structural transition from hexagonal to tetragonal lattices, accompanied by a progressive shift in ND orientations from ordered to random within each phase. Interestingly, within an optimal NS size range, an unconventional tetragonal phase appears, where NDs adopt two distinct orientations rotated by 30°. We show that the formation of these orientationally ordered BNSLs is governed by a phase-specific threshold void size, which dictates the maximum NS size that can be accommodated without disrupting the close-packed arrangement of NDs. This work demonstrates a geometry-mediated approach to structural control in multicomponent superlattices, developing a predictive framework for designing BNSLs with tailored translational and orientational order.