In situ ultraviolet-visible absorbance measurement during and after solution plasma sputtering for preparation of colloidal gold nanoparticles

The absorption spectra of the HCl, NaCl, and NaOH solutions during and after the solution plasma sputtering for the preparation of gold nanoparticles are measured by in situ ultraviolet-visible (UV-vis) spectroscopy to determine the particle diameter and behavior. In the solution plasma sputtering, gold particles are directly formed from the plasma phase and not by the reduction of Au3+ ions dissolved from electrodes. The initial diameter and behavior differ according to the solution used. In HCl solution, gold nanoparticles are formed and dissolve into Au3+ ions. When the solution is saturated, the gold nanoparticles grow by the aggregation of Au3+ ions. Cluster-sized particles are formed in NaCl solution that constitute nanoparticles, which are very stable for several days. Gold nanoparticles of 3 nm diameter are formed in NaOH solution, which aggregate over several days. The contribution of chlorine ions to the day-order stability of gold nanoparticles is suggested.