Scientists: Gold may play role in optical chips

Gold rods about one five-thousandth the thickness of a human hair could one day be used to make light sources for optical chips.

Gold is prized in chip manufacture for its excellent electrical conductivity, but it also has unusual properties that could give it a role in new optical chips, scientists have discovered.

In a typical electronic chip, tiny gold wires link microscopic connecting pads on the silicon wafer to the terminals of the chip packaging. The gold wires are about 50 micrometers in diameter, about half as thick as a human hair, and at that thickness the gold still behaves like the shiny metal we know. A micrometer is one millionth of a meter.

If you divide it into rods 2,500 times thinner, though, just 20 nanometers across, the gold glitters in an entirely different way, according to scientists at the U.S. Department of Energy's laboratory in Argonne, Illinois.

At the nanometer scale, where distances are measured in billionths of a meter, it's not just optical properties that change: many materials respond differently to variations in temperature, and to the effects of electric and magnet fields, when divided into such nanoparticles.

The nanoscale gold rods studied at Argonne National Laboratory emit light when electrons in them are stimulated, and the wavelength of the light depends on the length of the rod used, the scientists found. They tested gold rods with lengths between 70 nm and 300 nm.

Being able to control the wavelength of light, and to build light sources of a specific wavelength, is very important in optical communications. The discovery at Argonne could one day allow the fabrication of tuned light sources inside chips, leading to the creation of chips that can switch or route optical signals in fiber networks without having to convert them back to an electronic form first, the scientists said. However, they emphasized that they are only involved in basic research, not the development of products.

Researchers at the Nanotechnology and Optical Instrumentation Laboratory in Troyes, France, also participated in the research, which was published Dec. 23 in a paper in Physical Review Letters entitled "Surface Plasmon Characteristics of Tunable Photoluminescence in Single Gold Nanorods." It can be viewed here

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