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

Abstract

Understanding the assembly of nanoparticles into superlattices with well-defined morphology and structure is technologically important but challenging as it requires novel combinations of in-situ methods with suitable spatial and temporal resolution. In this study, we have followed evaporation-induced assembly during drop casting of superparamagnetic, oleate-capped γ-Fe2O3 nanospheres dispersed in toluene in real time with Grazing Incidence Small Angle X-ray Scattering (GISAXS) in combination with droplet height measurements and direct observation of the dispersion. The scattering data was evaluated with a novel method that yielded time-dependent information of the relative ratio of ordered (coherent) and disordered particles (incoherent scattering intensities), superlattice tilt angles, lattice constants, and lattice constant distributions. We find that the onset of superlattice growth in the drying drop is associated with the movement of a drying front across the surface of the droplet. We couple the rapid formation of large, highly ordered superlattices to the capillary-induced fluid flow. Further evaporation of interstitital solvent results in a slow contraction of the superlattice. The distribution of lattice parameters and tilt angles was significantly larger for superlattices prepared by fast evaporation compared to slow evaporation of the solvent.

Liquid‐Phase Transmission Electron Microscopy for Studying Colloidal Inorganic Nanoparticles

“…Lassemberg et al found a prenucleate state prior to nanoparticle nucleation by combining form‐factor and Porod analysis of SAXS spectra . On the other hand, structure factors depend on the distance and arrangement of many nanoparticles; thus structural information on the self‐assembly of nanoparticles has been provided . For example, Kim et al tracked the self‐assembly of Au nanoprisms through liquid‐cell TEM, and confirmed that the interparticle distance was similar to that measured by SAXS (Figure f–h) …”

“…The structure factor is from X‐ray diffraction between ordered nanoparticles, and the form factor is related to the shape and size of the nanoparticles. As the particle sizes can be tracked by form‐factor analysis, it can be used to investigate the growth processes of nanoparticles in real time . Polte et al studied the size increase of nanoparticles by analyzing the form factor of SAXS spectra during the growth of the Au nanoparticles .…”

Monitoring Nanocrystal Self‐Assembly in Real Time Using In Situ Small‐Angle X‐Ray Scattering

“…Recently, in situ scattering methods have emerged as a powerful characterization tool to study the nucleation and growth of nanoparticle superlattices . Small‐angle X‐ray scattering (SAXS) allows for monitoring the self‐assembly dynamics with subsecond temporal resolution over large sample volumes under controlled conditions (e.g., controlled solvent vapor environment and temperature) and provides real‐time information on long range order in the assembled structures.…”

Micro-scale 2D quasi-nanosheets formed by 0D nanocrystals: from single to multicomponent building blocks

“…The NCs retain the morphology in the colloidal solution with excellent stability for at least half a year, which are reactive enough to self-assemble into 2D superstructures. The solvent evaporation-induced interfacial self-assembly is a facile and versatile method to fabricate large-scale 2D superstructures [42,43]. The selfassembly process was observed upon dropwise adding 30 μL of NC suspension in toluene on the surface of EG confined in a glass container (π×1 2 ×2 cm 3 ), as depicted in Fig.…”