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The spatial distribution of surface plasmon scattering from a single nanoparticle, changes dramatically near a metal surface, as a result of interference from the direct scattered light and indirect light from the mirror reflection. The unique interference patterns are reproduced by simulations based on Huygens-Fresnel wave propagation theory.

The formation of either large nanocrystals or small clusters takes place during the cobalt carbonyl decomposition by using different concentrations of oleic acid ligand. It was demonstrated that by adding or removing free oleic acid ligand from the final reaction product, one can turn a nanocrystal colloid into a cluster complex solution and vice versa.

Self-assembly of Au nanoparticles (NPs) coated with positively charged cetyltrimethylammonium ions (CTA+) and negatively charged citrate ions in aqueous liquid cell was investigated by in situ transmission electron microscopy (TEM). Under electron illumination in TEM, the hydrated electrons will reduce the overall positive charges of the CTA+ covered Au NPs and decrease the repulsive electrostatic forces among NPs, leading to assembly of individual NPs into one-dimensional structures. On the contrary, the negatively charged Au NPs coated with citrate ions are steady in liquid cell regardless of electron beam intensity. [ABSTRACT FROM AUTHOR]

The assembly of nanoparticles into large, two-dimensional structures provides a route for the exploration of collective phenomena among mesoscopic building blocks. We characterize the structure of Langmuir monolayers of dodecanethiol-ligated gold nanoparticles with in situoptical microscopy and X-ray scattering. The interparticle spacing increases with thiol concentration and does not depend on surface pressure. The correlation lengths of the Langmuir monolayer crystalline domains are on the order of five to six particle diameters. Further compression of the monolayers causes wrinkling; however, we find that wrinkled monolayers with excess thiol can relax to an unwrinkled state following a reduction of surface pressure. A theoretical model based on van der Waals attraction and tunable steric repulsion is adopted to explain this reversibility. [ABSTRACT FROM AUTHOR]