Gold Deposits: Scientists design nanoparticle films

In a step toward a cheaper, easier way to connect computer chips to computers, scientists have patterned semiconductors with a film of extremely small gold particles. The nanoscale detailing might also lead to other applications: new sensors for detecting chemical weapons, novel chemical catalysts, and better ways of delivering medicines.

The contacts that connect tiny components of a computer chip to a much larger wire are often made of gold because it doesn’t react with air easily. The metal is expensive, however.

In the new work, Jillian Buriak, Lon Porter Jr., and their colleagues at Purdue University in West Lafayette, Ind., use gold leftovers from coin-making factories. This so-called gold salt is inexpensive and can be converted into relatively pure gold particles, says Buriak.

In simple bench-top experiments, the researchers dipped pieces of semiconductor materials, such as germanium or gallium arsenide, into a solution containing gold salt. A gold layer spontaneously formed on the semiconductors’ surfaces. “You take a test tube [of gold salt] that’s worth pennies, and you’re able to get a very high-purity gold layer on top of your chip,” says Porter.

Scanning electron microscopy and atomic force microscopy revealed that the film is actually made of nanoscale gold particles. The same process worked for palladium and platinum, precious metals well known for catalyzing chemical reactions.

Simply forming nanoparticle films is just a start. To move toward practical applications, the researchers used several chip-patterning techniques to deposit the nanoparticle films as lines or grids. The team also learned to control the size of the films’ particles–from about 10 nanometers to 1 micrometer–by adjusting the temperature, deposition times, and gold-salt concentrations, says Porter, who with his coworkers reports the work in the Dec. 11 Nano Letters.

This work is “a very good example . . . of a generalizable method to fabricate nanoscale structures,” comments Jie Liu of Duke University in Durham, N.C.

The scientists also bonded a dense layer of organic molecules to the large surface area created by the films’ nanostructure, says Buriak. Researchers might be able to tailor such a top layer to detect certain molecules–say, those of a chemical warfare agent–to create a portable chemical sensor the size of a PalmPilot, adds Porter.

The new precious-metal films might also find use as catalysts since their nooks and crannies could promote chemical reactions, Porter suggests. Or, the small pockets could hold molecules for drug delivery.

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