Synthesis of Gold Nanoparticles in Liquid Polyethylene Glycol by Sputter Deposition and Temperature Effects on their Size and Shape

Combining the use of liquid polyethylene glycol (PEG) as a capture medium with the sputter deposition technique, we developed the easy and simple preparation of gold nanoparticles (Au NPs) in liquid PEG with neither chemical reactions nor additional stabilizers. PEG was selected because of its ability to stabilize NPs and its environmental friendliness. We used PEG with an average molecular weight of 600 because it is in the liquid state at room temperature and has a vapor Pressure low enough to endure the sputtering operation. Structural characterizations were performed using transmission electron microscope (TEM) observations, small-angle X-ray scattering (SAXS) measurements, and UV-vis absorption measurements. It is revealed that the particle size and shape are strongly dependent on the preparation temperature of PEG. Close investigation of the temperature-dependent properties of PEG suggests that the collision frequency of sputtered Au particles (atoms and small clusters) is one of the most important factors for the determination of particle size and shape. We discuss the stabilization effects of the capture media from the viewpoint of the structures of the NPs and their formation processes by comparing the present NPs, with our recent results of Au NPs prepared in an ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate. We also investigated the heat treatment effect on NPs that were previously generated in PEG at 20 degrees C. It is established that the size of the NPs can be controlled by postheating and that this effect on the previously generated NPs is quite different from the temperature effect during initial preparation.