Fig. 3: Evolution of branched cubic mesocrystals via OA of primary NPs.

a–e Representative cryo-TEM images at different reaction times showing the multi-step crystallization of Pt mesocrystals going from NPs to clusters (stage i), to core/shell structures (stage ii), to branched cubes (stage iii). f−j SAED patterns at the reaction time points; cluster at 15 min (f), core/shell structures with thick shell (g) and thin shell (h) at 27 min, cubes without branches at 43 min (i), and branched cubes at 66 min (j), respectively. Inset, corresponding cryo-TEM images of each single structure. Scale bars for the insets: 50 nm. k−n HR-cryo-TEM images observed at 13 min and corresponding FFT patterns showing \(\left\langle 100\right\rangle\) alignment (k, l) and \(\left\langle 111\right\rangle\) alignment (m, n) between NPs within a cluster. o−q HR-cryo-TEM image of a core/shell structure observed at 25 min (o) and corresponding FFT patterns of the core (p) and shell (q) marked by dashed lines in (o). Z.A., zone axis. r Schematic showing the evolution of branched cubic mesocrystals via OA involving a switch in the facet upon which attachment occurs.