Size-dependent assembly of ligated gold nanocrystals in two dimensions

XP Liu and Y Ni and LH He, JOURNAL OF PHYSICS-CONDENSED MATTER, 28, 445201 (2016).

DOI: 10.1088/0953-8984/28/44/445201

Brownian dynamics (BD) simulation based on a coarse-grained model is performed to study the assembly of dodecanethiol-ligated Au nanocrystals (NCs) at a toluene-air interface. With increasing diameter from 3 nm to 9 nm, the NCs are found to form three different phases-a dispersed phase without aggregation, a mixture of dispersed NCs and rounded clusters, and a compactly packed solid phase of the fractal structure. Such size dependence of the assembled phase is attributed to the variation in the well depth Phi(c) of the interaction potential between NCs, and the value of Phi(c) = -3.5K(B)T for 6 nm NCs turns out to be most suitable to form monolayers with hexagonal packing. The result is of universal importance for assembling complete monolayers, because the valley of the interaction potential can be well tailored by properly choosing the NC size, ligand length and solvent.

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