Sinusoidal Displacement Describes Disorder in CsPbBr₃ Nanocrystal Superlattices

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Disorder is inherent in solids, including nanocrystal superlattices.
• Collective particle displacement in nanocrystal superlattices can lead to cumulative disorder, impacting structural properties.
• Understanding disorder propagation is crucial for controlling the properties of mesocrystalline systems.

Purpose of the Study:

• To investigate the propagation and accumulation of disorder in cesium lead bromide (CsPbBr₃) nanocrystal superlattices.
• To rationalize the anisotropic nature of disorder and its dependence on nanocrystal softness.
• To develop a model explaining structural coherence in relation to superlattice softness.

Main Methods:

• Synchrotron grazing incidence small- and wide-angle X-ray scattering (GISAXS/GIWAXS) were employed.
• CsPbBr₃ nanocrystals with varying colloidal softness (S = 0.3-0.7) were synthesized using different sizes and ligand mixtures.
• Diffraction patterns were analyzed to assess structural coherence and disorder characteristics.

Main Results:

• Anisotropic disorder was observed, with high structural coherence primarily along {100} axial directions.
• Decreasing nanocrystal softness led to a more ordered regime with resolution-limited diffraction peaks.
• Superlattice multilayer diffraction was observed for {110} diagonal reflections as softness decreased.
• A sinusoidal displacement model was proposed and validated against experimental data.

Conclusions:

• The sinusoidal displacement model effectively explains the observed anisotropies in structural coherence and disorder.
• Superlattice softness is a key parameter influencing disorder accumulation and propagation.
• This research advances the understanding of disorder in mesocrystalline systems, particularly near structural perfection.