Abstract
Many attempts has been made to make nucleation kinetics clear so far, but many issues remain to be unknown. Here, focusing on the relationship between incubation period which can be seen before the formation and growth kinetics of particles, we investigate formation kinetics of gold nanoparticles. Based on the in-situ observation of laser-photo reduction of gold complex, AuCl4-, using UV-Vis spectroscopy and transmission electron microscopy (TEM), we propose simple model for reduction, formation and growth kinetics of gold particles, and discuss how metal nanoparticles form in aqueous solution. Gold nanoparticles, which consist of zero-valence gold atoms, are mainly produced after incubation period. During incubation period, reduction of gold complex to zero-valence gold atoms is dominant, particle formation is not dominant due to the lack of the source materials, zero-valence gold atoms. On the other hand, at the end of the incubation period, the concentration of zero-valence gold atoms in solution is high enough to cause the particle formation of gold. After that, reduction of gold complex, formation and growth of gold nanoparticles occur at the same time. Thus, the whole reduction process can be practically divided into two periods, 1) from the beginning of the irradiation of laser pulses to the end of incubation period, 2) after incubation period. Reduction process of gold complex is discussed in 1st period, and nucleation and particle growth processes are treated in 2nd period. Irradiated laser fluence is important factors in both periods.
