Local orientational order in self-assembled nanoparticle films: the role of ligand composition and salt

Abstract

An X-ray cross-correlation study of the local orientational order in selfassembled films made from PEGylated gold nanoparticles is presented. The local structure of this model system is dominated by four-and sixfold order. Coadsorption of shorter ligands in the particle's ligand layer and variation of salt concentration in the suspension prior to self-assembly result in a change of local orientational order. The degree of sixfold order is reduced after salt addition. This decrease of order is less pronounced for the fourfold symmetry. The results presented here suggest complex symmetry-selective order formation upon ligand exchange and salt addition and demonstrate the versatility of X-ray crosscorrelation methods for nanoparticle superlattices. research papers J. Appl. Cryst. (2019). 52, 777-782 Felix Lehmkü hler et al. Local orientational order in self-assembled nanoparticle films 781

Coexistence of hcp and bct Phases during In Situ Superlattice Assembly from Faceted Colloidal Nanocrystals

“…In order to resolve the superlattice structure in detail, we performed the X-ray cross correlation analysis (XCCA), 49,50 which has been recently demonstrated to be a valuable tool to access structural information of crystalline materials beyond convectional pair correlation SAXS analysis. 36,[51][52][53][54][55]22 The details of the XCCA method are described in Ref. 56.…”

Recent Notable Approaches to Study Self‐Assembly of Nanoparticles with X‐Ray Scattering and Electron Microscopy

“…In a follow‐up study, the authors reported a dependence of the local orientational order of the assembled films on the ligand composition. [ 132 ] Moreover, the addition of salt further reduced the order of the films due to screening of the charged particles during the assembly, suggesting a complex symmetry‐selective assembly process.…”

“…[ 120 ] Order formation upon drying is thermodynamically favored for nearly any NP shapes, so it should be kept in mind that even dried NP films and materials that would not be considered “crystalline” but rather heterogenous and disordered at first sight, often feature some degree of local, sometimes hidden, order. [ 130–132 ] For many shapes, formation of crystalline superstructures can be thermodynamically even more favorable than for spheres, [ 133–135 ] e.g., perovskite nanocrystals with a cubic structure are known to crystallize readily. [ 109 ]…”

“…[120] Order formation upon drying is thermodynamically favored for nearly any NP shapes, so it should be kept in mind that even dried NP films and materials that would not be considered "crystalline" but rather heterogenous and disordered at first sight, often feature some degree of local, sometimes hidden, order. [130][131][132] For many shapes, formation of crystalline superstructures can be thermodynamically even more favorable than for spheres, [133][134][135] e.g., perovskite nanocrystals with a cubic structure are known to crystallize readily. [109] The whole range of available NP materials, sizes, and shapes can potentially crystallize into self-assembled structures and the ligand chemistry allows for a wide range of interparticle gaps within the superstructures, so the structural diversity and complexity of crystalline superstructures is practically unlimited and the interest in new intriguing structures is ong oing.…”

Kinetics of pressure-induced nanocrystal superlattice formation

“…The particle concentration was 500 nM corresponding to a volume fraction of about 1 vol% AuNC. This system is known to selfassemble after solvent evaporation 26,27 and is supposed to form a superlattice around p ≈ 3000 bar 22 .…”