Understanding interactions between capped nanocrystals: three-body and chain packing effects.

Area of Science:

• Materials Science
• Nanotechnology
• Computational Chemistry

Background:

• Self-assembly of capped nanocrystals (NCs) is a key area in materials science.
• Understanding the mechanical and thermodynamic stability of NC superstructures is limited.
• Controlling interactions between NCs is crucial for advanced applications.

Purpose of the Study:

• To investigate the origin and magnitude of interactions in self-assembled gold NCs.
• To explore methods for rationally manipulating these interactions.
• To understand how ligand length and NC size affect self-assembly.

Main Methods:

• Molecular simulations of interacting gold NCs protected by capping molecules (ligands).
• Computation of the potential of mean force for pairs and triplets of NCs.
• Simulation of NCs with varying sizes (1.8-3.7 nm) and ligand lengths (ethanethiol-dodecanethiol) in vacuum.

Main Results:

• Pair interactions are strongly attractive due to van der Waals forces between ligands.
• Three-body interactions introduce an energy penalty upon ligand overlap, significant for short ligands.
• Longer ligands promote NC chain formation over close packing, aligning with experimental findings.

Conclusions:

• The overlap cone model accurately predicts equilibrium distances between NCs based on ligand packing.
• Equilibrium distance is consistently ~1.25 times the core diameter, independent of ligand length.
• Predictions are made for ligand choices favoring stable 3D structures versus high-quality monolayers.