Small Gold Nanoparticles as Crystallization “Catalysts”: Effect of Seed Size and Concentration on Au-ZnO Hetero Nanoparticles

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This work reports the effect of seed nanoparticle size and concentration effects on heterogeneous crystal nucleation and growth in colloidal suspensions. We examined these effects in the Au nanoparticle-seeded growth of Au-ZnO heteronanocrystals under synthesis conditions that generate hexagonal, cone-shaped ZnO nanocrystals. It was observed that small (∼4 nm) Au seed nanoparticles form one-to-one Au-ZnO hetero dimers and that Au nanoparticle seeds of this size can also act as crystallization “catalysts” that readily promote the nucleation and growth of ZnO nanocrystals. Larger seed nanoparticles (∼9 and ∼11 nm) provided multiple, stable ZnO-nucleation sites, generating multicrystalline hetero trimers, tetramers, and oligomers.