Softness-driven complexity in supercrystals of gold nanoparticles.

Area of Science:

• Soft matter physics
• Materials science
• Nanotechnology

Background:

• Soft matter systems often involve self-assembling spherical objects.
• Unlike hard spheres, soft spheres deform, necessitating new models for space-filling at high concentrations.
• Gold nanocrystals with soft coatings offer a model system to study these phenomena.

Purpose of the Study:

• To investigate the self-assembly structures of soft gold nanocrystals.
• To explore the intermediate structural phases beyond simple FCC and BCC.
• To establish a structure diagram based on experimental data for varying core and ligand dimensions.

Main Methods:

• Experimental synthesis and characterization of hydrophobically coated gold nanocrystals.
• Systematic variation of gold core radius (R) and ligand length (L).
• Analysis of resulting supercrystal structures using a large experimental dataset.

Main Results:

• Observed FCC structure for thin soft coatings, similar to hard spheres.
• Observed BCC structure for thick soft coatings.
• Identified the hexagonal Frank-Kasper C14 structure in the intermediate region, coexisting with FCC.
• Established a structure diagram based on R and L, showing C14 phase stability.

Conclusions:

• The hexagonal Frank-Kasper C14 phase is a viable solution for space-filling with soft particles, even those with rigid cores.
• Experimental findings support the C14 phase's role in superlattice formation.
• Results will aid in developing predictive models for nanoparticle superlattice structures.