A simple method is proposed to control the size of alkanethiol-protected Au nanoparticles by heat treatment in the solid state. The mean diameter of the Au nanoparticles prepared by Brust's two-phase method (∼1.5 nm) was evolved to 3.4-9.7 nm by heating to 150-250 °C in air. The uniform growth of nanoparticles was not observed when tetraoctylammonium bromide (TOAB), which was used as a phase-transfer agent during the preparation of Au nanoparticles, was removed before the particle growth process. The crystal structures of Au nanoparticles and alkanethiol ligand structures on Au nanoparticles were characterized before and after the heat treatment. The size-evolution mechanism was discussed on the basis of the thermodynamic model. The heat-treated Au nanoparticles easily formed self-assembled 2D superlattices with hexagonal packing, where the alkanethiol protective agents with an all-trans conformation were estimated to interpenetrate each other.
A simple method to manipulate the size of gold nanoparticles—involving heat treatment in the solid state—is reported by these authors. It is demonstrated that the nanoparticle size can be controlled from 3 to 10 nm by changing the heat‐treatment temperature and/or the stabilizing agent in the presence of tetraoctylammonium bromide. The Figure shows 6.8 nm particles heat‐treated at 190 °C.
For fabrication of a planar array of 1D chains of gold nanoparticles prepared by a chemical process, the faceted (110) planes of sodium chloride crystals were used as templates to produce nanoscale ridge-and-valley structured carbon layers by a vacuum process. When these carbon layers loaded on copper grids were dipped in toluene solution of 3.4 nm gold nanoparticles followed by natural dry, a planar array of 1D chains of gold nanoparticles were formed on carbon layers, where the nanoparticles were immobilized predominantly in valleys and partly on ridges of carbon layers.
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