In Situ Constructing the Kinetic Roadmap of Octahedral Nanocrystal Assembly Toward Controlled Superlattice Fabrication

Abstract

Crystallization and growth of anisotropic nanocrystals (NCs) into distinct superlattices were studied in real time, yielding kinetic details and designer parameters for scale-up fabrication of functional materials. Using octahedral PbS NC blocks, we discovered that NC assembly involves a primary lamellar ordering of NC-detached Pb­(OA)2 molecules on the front-spreading solvent surfaces. Upon a spontaneous increase of NC concentration during solvent processing, PbS NCs preferentially self-assembled into an orientation-disordered face-centered cubic (fcc) superlattice, which subsequently transformed into a body-centered cubic (bcc) superlattice with single NC-orientational ordering across individual domains. Unlike the deformation-based transformation route claimed previously, this solid–solid phase transformation involved a hidden intermediate formation of a lamellar-confined liquid interface at cost of the disassembly (melting) of small fcc grains. Such highly condensed and liquidized NCs recrystallized into the stable bcc phase with an energy reduction of 1.16 k B T. This energy-favorable and high NC-fraction-driven bcc phase grew as a 2D film at a propagation rate of 0.74 μm/min, smaller than the 1.23 μm/min observed in the early nucleated fcc phase under a dilute NC environment. Taking such insights and defined parameters, we designed experiments to manipulate the NC assembly pathway and achieved scalable fabrication of a large/single bcc supercrystal with coherent ordering of NC translation and atomic plane orientation. This study not only provides a design avenue for controllable fabrication of a large supercrystal with desired superlattices for application but also sheds new light on the nature of crystal nucleation/growth and phase transformation by extending the lengths from the nanoscale into the atomic scale, molecular scale, and microscale levels.

Ordering of ZnS Nanorods at the Air–Liquid Interface: An In Situ X-ray Scattering Study

“…A detailed model of the obtained structure at various phases of the monolayer and after annealing the monolayer at 48 °C has been presented. Similar studies on the self-assembled superstructures with the anisotropic nanorods/nanoparticles have been reported earlier − by ex-situ electron microscopy, which probe mainly the local structural information of a system. On the contrary, monitoring the in situ self-assembly process and real time observation with anisotropic nanorods at the air–liquid interfaces has remained almost unexplored.…”

Branchless Colloidal PbSe Nanorods: Implications for Solution-Processed Optoelectronic and Thermoelectric Devices

“…In the literature, more fundamental studies of the interaction between the surface ligands and the nanocrystals (e.g., PbS nanocrystals) show that the interaction affects the nanocrystal shape as well as the superlattice structure made up of the nanocrystals. 29,30 The reaction temperature affects the morphology of the nanorods in both syntheses with and without AA. The diameter of the nanorod increases as the reaction temperature increases in both cases.…”

“…More AA increases the growth rate further, causing more branching and aggregation. In the literature, more fundamental studies of the interaction between the surface ligands and the nanocrystals (e.g., PbS nanocrystals) show that the interaction affects the nanocrystal shape as well as the superlattice structure made up of the nanocrystals. , …”

Simple cubic self-assembly of PbS quantum dots by finely controlled ligand removal through gel permeation chromatography

“…It is noted that bcc packing as a common PbS QD assembly structure cannot be observed in GPC samples. Because of its lower packing density compared to fcc lattice, the self-assembly of bcc superlattice usually requires the adjustment of suitable external environment according to the bcc-related literatures, 48,49 for example, the proper QD concentration, solvent type, evaporation rate and ligand coverage. However, all GPC samples here maintain the same self-assembly conditions.…”