Observation on growth process of gold Y- and phi-shaped nanoparticles in solutions.

The morphological evolution of gold (Au) nanoparticles is demonstrated via TEM and UV-vis spectroscopy in a real-time basis. Y-shaped and phi-shaped Au nanoparticles were prepared by a seed mediated method at 0 degrees C. The evolution of shape ranging from spheres to Y- and phi-shapes was characterized by UV-vis spectroscopy. For the spherical particles, the corresponding transverse plasmon absorption (540 nm) was observed at the initial growth stage. As further growth proceeded, new peaks appeared at ca. 620 nm and ca. 700-1000 nm, which was to the characteristic peak of Y-shaped and phi-shaped nanoparticles, respectively. In addition, all intermediate steps were observed in the morphology change by TEM. At the initial step, spherical particles with 20 nm size were generated and the particles were gradually evolved from tiny triangular shape or I-shape to Y- and phi-shape. In this study, the growth mechanism of Au nanoparticles was investigated by the characterization of optical properties as well as morphologies with respect to reaction time.