Order/disorder dynamics in a dodecanethiol-capped gold nanoparticles supracrystal by small-angle ultrafast electron diffraction

TL;DR

This study introduces a novel ultrafast electron diffraction method to analyze the local order and dynamics of ligand molecules in gold nanoparticle supracrystals, revealing transient structural changes upon light excitation.

Contribution

The paper develops a new methodology combining small-angle ultrafast electron diffraction with angular cross-correlation analysis for atomic-scale characterization of ligand dynamics in nanoparticle assemblies.

Findings

Ligands order in a preferential orientation at equilibrium.

Light excitation induces positional disorder but increases overall homogeneity.

Transient annealing occurs within a few picoseconds after excitation.

Abstract

In metal nanoparticles (NPs) supracrystals, the metallic core provides some key properties, e.g. magnetization, plasmonic response or conductivity, with the ligand molecules giving rise to others like solubility, assembly or interaction with biomolecules. The formation of these supracrystals depends on a complex interplay between many forces, some stemming from the core, some from the ligands. At present, there is no known approach to characterize the local order of ligand molecules or their dynamics with atomic spatial resolution. Here, we develop a methodology based on small-angle ultrafast electron diffraction combined with angular cross-correlation analysis to characterize a two-dimensional supracrystal of dodecanethiol-coated gold NPs. We retrieve the static arrangement of the ligands, showing that at equilibrium they order in a preferential orientation on the NPs surface and throughout the two-dimensional supracrystal. Upon light excitation, positional disorder is induced in the supracrystal, while its overall homogeneity is surprisingly found to transiently increase. This suggests that transient annealing of the supracrystal takes place within few picoseconds (ps). This methodology will enable the systematic investigation of the dynamical structural properties of nano-assembled materials containing light elements, relevant for biological applications.