Fundamental Processes and Practical Considerations of Lead Chalcogenide Mesocrystals Formed via Self-Assembly and Directed Attachment of Nanocrystals at a Fluid Interface

Abstract

Significant advances in the synthesis and processing of colloidal nanocrystals have given scientists and engineers access to a vast library of building blocks with precisely defined size, shape, and composition. These materials have inspired exciting prospects to enable bottom-up fabrication of programmable materials with properties by design. Successfully assembling and connecting the building blocks into superstructures in which constituent nanocrystals can purposefully interact requires robust understanding of and control over a complex interplay of dynamic physicochemical processes. Fluid interfaces provide an advantageous experimental workbench to both probe and control these processes. Despite the ostensible simplicity of fabricating nanocrystal assemblies at a fluid interface, sensitivity to processing conditions and limited reproducibility have underscored the complexity of this process. In situ studies have provided mechanistic insights into the competing dynamics of key subprocesses including solvent spreading and evaporation, superlattice formation, ligand detachment kinetics, and nanocrystal attachment. Understanding how these subprocesses influence the complex choreography of self-assembly, structure transformation, and oriented attachment processes presents a rich research challenge. In this context, we present a detailed methodology for self-assembly and attachment of lead chalcogenide nanocrystals at a liquid–gas interface as a model system for the fabrication of mono- and multilayer cubic connected superlattices. We discuss key experimental parameters such as the characteristics of the building blocks and processing conditions and detailed steps from colloidal nanocrystal injection to superlattice transfer. We hope that this Methods/Protocols paper will provide guidance for future advances in the exciting path toward bringing the prospect of nanocrystal-based programmable materials to fruition.

Assembly, Properties, and Application of Ordered Group II–VI and IV–VI Colloidal Semiconductor Nanoparticle Films

“…As a best practice example, see the recent minireview of Cimada daSilva et al on the interfacial self‐assembly of lead chalcogenide QDs. [ 40 ]…”

“…For recent examples, see the reviews of Barad et al. [ 39 ] for an in‐depth summary on selected 2D‐assembly strategies with a focus on metallic, metal oxide, and polymer nanoparticles, Cimada daSilva et al [ 40 ] for the interfacial self‐assembly of lead chalcogenide QDs into 2D superstructures, or Guillemeney et al [ 41 ] for the assembly of semiconductor nanoplatelets. This stands in contrast to the high importance assigned to thin films consisting of colloidal semiconductor nanocrystals in many different applications like photovoltaics, (photo‐)sensing, or (opto‐)electronics.…”

Gold nanoparticle superlattices: conditions for long range order, Moiré patterns and binary phase from a single population

“…(3). A broad range of superlattices have been discovered from the self-assembly of metal (4), metal oxide (5), chalcogenide (6), core-shell (7), semiconductor NPs (8) and binary systems (9)(10)(11). Among these different materi-als, gold NPs can serve as a model system since they have original plasmonic properties that depend on their organization (12).…”

Temperature-Controlled Reversible Formation and Phase Transformation of 3D Nanocrystal Superlattices Through In Situ Small-Angle X-ray Scattering

“…Achieving structural modulation is challenging, since the high volume fraction of the SL hinders NC translation and rotation. Nevertheless, the ligand corona that coats the inorganic core of the NCs provides additional degrees of freedom. , Understanding these complex phenomena requires detailed in situ studies that capture the assembly of the NCSLs and their structural transformations . Such studies are rare and require a high degree of control over the synthesis of the NCs and their transformative assembly.…”