In physics and chemistry, a plasma is typically an ionized gas, characterized by the phenomenon in which at least one electron is dissociated from the atoms or molecules. Artificial and engineered plasma has generally been generated in gas phase as in, for example, the well known semiconductor manufacturing processes employing plasma-enhanced chemical vapor deposition and surface treatment with atmospheric pressure plasma. In particular, low-temperature plasma is utilized in materials processing. On the other hand, the plasma phenomenon in liquid phase is not generally well known, although it has been partially utilized in water treatments. The fundamentals of plasma in liquid phase have not been established, including its generation techniques, its state, and activated chemical species. However, it would be reasonable to expect a higher reaction rate under lower-temperature conditions, and the greater chemical reaction variability since the molecular density of liquid is much higher than gas phase.
In this paper, we report on the synthesis of nanocolloidal gold by employing spark-streamer discharge in an aqueous solution under an open environment, and reveal fundamental characteristics of the synthesized nanocolloidal gold. Spark and streamer discharges in HAuCl4 (aq.) was generated by a DC pulse power supply. After this generation, the presence of nano particles was confirmed based on the color shift of the HAuCl4(aq.) solution. Observation of these nanoparticles by transmission electron microscope (TEM) with energy dispersive X-ray spectroscopy (EDS) proved them to be nano colloidal gold with an averaged diameter of ca. 10-20 nm by TEM observation and EDS analysis. A plasmon band around 530 nm was observed. This band with this wavelength originating from gold was observed.
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