The growth process of gold nanoplates formed by a thermal aqueous solution approach was investigated by withdrawing drops of a heated solution containing HAuCl_4, cetyltrimethylammonium bromide (CTAB), and trisodium citrate and examined the intermediate products formed by a transmission electron microscopy analysis. The formation process proceeds extremely rapidly within seconds of reaction to form large aggregated structures, which are composed of wormlike structures just several nanometers in diameter. These tiny nanostructures are fused extensively toward the central region to form a thicker mass. The central core grows in size via incorporating the exterior wormlike nanostructures and eventually evolves into the plate morphology. Appropriate amounts of CTAB and trisodium citrate were also found to be critical to the formation of nanoplates. This synthesis approach has been extended to prepare ultrasmall triangular gold nanoplates with average widths of 40 ± 7 and 58 ± 10 nm. Because of their relatively uniform sizes, these tiny nanoplates can spontaneously self-assemble into some ordered 2-dimensional structures such as the hexagonally arranged pattern. UV-vis absorption spectroscopy showed that these nanoplates exhibit a strong absorption band at 590-602 nm and a weak and broadband centered at ～775-900 nm.
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