Revealing Grain Boundaries and Defect Formation in Nanocrystal Superlattices by Nanodiffraction

Abstract

X‐ray nanodiffraction is applied to study the formation and correlation of domain boundaries in mesocrystalline superlattices of PbS nanocrystals with face‐centered cubic structure. Each domain of the superlattice can be described with one of two mesocrystalline polymorphs with different orientational orders. Close to a grain boundary, the lattice constant decreases and the superlattice undergoes an out‐of‐plane rotation, while the orientation of the nanocrystals with respect to the superlattice remains unchanged. These findings are explained with the release of stress on the expense of specific nanocrystal–substrate interactions. The fact that correlations between adjacent nanocrystals are found to survive the structural changes at most grain boundaries implies that the key to nanocrystal superlattices with macroscopic domain sizes are strengthened interactions with the substrate.

Structure–Transport Correlation Reveals Anisotropic Charge Transport in Coupled PbS Nanocrystal Superlattices

“…AXCCA was applied and two‐point cross‐correlation functions (CCFs) for all channels were calculated, according to Equation () where and I ( q SL ,φ) is an intensity value taken at the point ( q SL ,φ) which are polar coordinates in the detector plane. [ 8,20,21 ] ⟨…⟩ φ denotes averaging over all azimuthal φ angles. q SL correspond to SAXS peaks and q AL to WAXS peaks.…”

“…Here, we address these questions by a direct correlation of the structural and electronic properties of SLs composed of electronically coupled lead sulfide (PbS) NCs. We perform X‐ray nanodiffraction and apply angular X‐ray cross‐correlation analysis (AXCCA) [ 8,20,21 ] to characterize the structure of the SLs, which are correlated with electric transport measurements of the same microdomains. By that, we reveal anisotropic charge transport in highly ordered monocrystalline hexagonal‐close‐packed (hcp) PbS NC SLs and find strong evidence for the effect of SL crystallinity on charge transport.…”

“…This defines individually addressable microchannels with L ≈ 1 µm, W ≈ 4 µm, and thickness h ( Figure a–e). Since this area is comparable to the typical grain size of PbS NC SLs, [ 21 ] these microchannels enable transport measurements in single‐crystalline PbS SLs.…”

Plasmonic Supercrystals with a Layered Structure Studied by a Combined TEM‐SAXS‐XCCA Approach

“…Orientational order can be quantified by the Fourier coefficients of C of order l with respect to the angle difference Δ [11,12] which is connected by the Wiener-Khinchin theorem to the Fourier coefficients of the intensity In this way, domain size of few µm are reported for self-assembled films of gold nanoparticles [8] and PbS nanocrystals. [14] The orientation of the sixfold symmetry in the scattering pattern and thus the probed sample area is given by ω = Ω 6 6 6 (6)…”

“…In the case of plasmonic nanoparticles (e.g., Ag, Au) (XCCA). [8][9][10][11][12] Recently, the use of XCCA in structural studies of self-assembled nanoparticles has increased, [8,[13][14][15] including insitu experiments of phase transitions. [16] Form factor measurements in solution provide statistically robust data for particle diameter, shape and dispersity.…”