Making Gold in a Polyvinyl Alcohol Film

Anne L. Fischer

Fabricating gold nanoparticles in a polymer film by laser excitation is not new, but the problem has been that the high energy of the laser can damage the thin film. Researchers at Osaka University in Japan were interested in this method, however, because it could produce nanoparticles with a resolution of about half the wavelength of the irradiation.

Figure 1. The polyvinyl alcohol films, which contain HAuCl₄ (1 mM) in the presence of benzophenone, exhibit absorbance spectra at 30 minutes after the irradiation with the single laser (black line) and the two two-color lasers (red line).

Based on this, they knew that micron-size optical and electronic devices can be constructed in a specific region of the film. They modified the fabrication method, using two-color, two-laser flash photolysis to generate benzophenone ketyl excited radicals.

To produce the radicals, which serve as a reducing agent, they used two Nd:YAG lasers sequentially at two wavelengths. The first, nanosecond laser, from Quantel SA of Les Ulis, France, generated radicals in the ground state, which were then excited by the second, picosecond laser, from Continuum Inc. of Santa Clara, Calif.

Figure 2. This schematic shows the process for two-color, two-laser fabrication of gold nanoparticles. The inset photo shows polyvinyl alcohol films containing HAuCl₄ and benzophenone after irradiation with a single laser and the two-color lasers.

The damage to the polyvinyl alcohol film was inhibited because it cannot absorb the longer wavelength of the second laser until the radicals have been generated, and the irradiation of the first laser generates the radicals with relatively lower power.

According to professor Tetsuro Majima, these metal nanoparticles-polymer thin films are attractive for use in optics and electronic devices. The group is working to apply the two-color, two-laser method for micropatterning to small optics and electronic devices.

Journal of the American Chemical Society, July 4, 2006, pp. 6361-6366.