Kinetics of the self-assembly of nanocrystal superlattices measured by real-time in situ X-ray scattering

Abstract

On solvent evaporation, non-interacting monodisperse colloidal particles self-assemble into a close-packed superlattice. Although the initial and final states can be readily characterized, little is known about the dynamic transformation from colloid to superlattice. Here, by using in situ grazing-incidence X-ray scattering, we tracked the self-assembly of lead sulfide nanocrystals in real time. Following the first appearance of an ordered arrangement, the superlattice underwent uniaxial contraction and collective rotation as it approached its final body-centred cubic structure. The nanocrystals became crystallographically aligned early in the overall self-assembly process, showing that nanocrystal ordering occurs on a faster timescale than superlattice densification. Our findings demonstrate that synchrotron X-ray scattering is a viable method for studying self-assembly in its native environment, with ample time resolution to extract kinetic rates and observe intermediate configurations. The method could be used for real-time direction of self-assembly processes and to better understand the forces governing self-organization of soft materials.

Tuning colloidal quantum dot band edge positions through solution-phase surface chemistry modification

“…Ligand shell inter-digitization is commonly observed for QD films fabricated using aliphatic, monodentate ligands2526, and likely occurs with R-CA − ligands. However, we hypothesize that the extent of inter-QD ligand shell inter-digitization is mediated by the functional group on the aromatic ring.…”

Quantifying Angular Correlations between the Atomic Lattice and the Superlattice of Nanocrystals Assembled with Directional Linking

“…1,2 Colloidal NCs stabilized by organic surfactants have been shown to pose excellent building blocks for the design of synthetic MCs with tailored structural properties which are conveniently obtained by self-assembly of NCs from solution on a solid or liquid substrate by exploiting ligand-ligand 3 interactions. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Typically, the utilized ligands consist of wide-gap, bulky hydrocarbons which render the MCs insulating. [26][27][28][29][30][31][32][33] MCs obtained in this way exhibit average grain sizes of ~150 µm 2 , which enables a detailed characterization by electron and/or X-ray microscopy.…”

“…24,63 We anticipate that the progressive exploration of synthetic MCs with increasing complexity, e.g, binary NC superlattices, nanorod assemblies, honeycomb lattices, etc. will benefit strongly from the present study.…”

“…The fact that the shorter cubic directions of the SL ("a") exhibit collinearity with the AL, and the longer cubic direction ("c") does not, supports the view that ligand-ligand interactions from specific facets of neighboring NCs are responsible for the often observed tetragonal distortion in PbS MCs. 24,63 We anticipate that the progressive exploration of synthetic MCs with increasing complexity, e.g, binary NC superlattices, nanorod assemblies, honeycomb lattices, etc. will benefit strongly from the present study.…”

Superlattice growth and rearrangement during evaporation-induced nanoparticle self-assembly

“…Robust methods to produce nanoparticles with controlled compositions, sizes, and shapes 7–11 have enabled the production of nanoparticle superlattices with a wide range of structures and compositions 2, 12–15 . There are many methods to produce nanoparticle superlattices, but evaporation induced self-assembly on solid substrates (drop casting) is arguably the most widely used 16–20 . Self-assembly of nanoparticles from a dilute dispersion by drop casting is a complex process that is controlled by the particle interactions, packing constraints, mass and heat transfer during drying, together with kinetic and thermodynamic factors 21–24 .…”