Critical island size, scaling, and ordering in colloidal nanoparticle self-assembly

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Understanding nanoparticle (NP) interactions is crucial for controlling self-assembly processes.
• Dodecanethiol-coated gold NPs in toluene via drop drying present a model system for studying these interactions.

Purpose of the Study:

• Investigate the dependence of island density, scaled island-size distribution (ISD), and scaled capture-zone distribution (CZD) on coverage, deposition flux, and NP size.
• Elucidate the roles of short-range (SR) and long-range (LR) interactions in NP self-assembly.

Main Methods:

• Experimental investigation of island density, ISD, and CZD.
• Analysis of NP size, coverage, and deposition flux effects.
• Comparison with theoretical models of epitaxial growth and simulations incorporating dipole repulsion.

Main Results:

• Critical island size is >1 for all NP sizes. SR attraction strength increases with NP size, decreasing island density exponent and critical island size.
• ISD is sharply peaked, similar to epitaxial growth, despite cluster diffusion and coalescence.
• For large NPs, scaled ISD and CZD align well with epitaxial models. For smaller NPs, ISD is less peaked, suggesting enhanced coalescence or detachment.
• Observed ordering of NP islands indicates LR repulsive interactions, consistent with NP dipole moments arising from surface tension-driven thiol asymmetry.

Conclusions:

• NP size significantly impacts SR attraction and self-assembly dynamics.
• Dipole repulsion, potentially due to surface-induced asymmetry, explains the observed ordering of NP islands.
• The findings provide insights into controlling NP self-assembly through tailored interactions.