October 11, 2001 11:55 AM PDT

Researchers see promise in plastic chips

By Dietmar Mueller

They're neighbors on the periodic table of elements, but carbon and silicon are pretty much strangers in the worlds of physics and technology. Carbon is the main building block of life, while silicon is the foundation for semiconductors.

But several promising research efforts are under way to combine the two realms, using organic polymers as material for the production of microelectronics, including transistors and displays.

Organic polymers are molecules that contain a long string of carbon atoms and make versatile plastics. Organic polymers that conduct electricity have been around since the 1970s--last year's Nobel Prize for chemistry, for instance, went to the researchers who discovered plastic conductors, organic materials that have some resistance to the flow of electricity. But creating a superconducting organic polymer has proved to be far more difficult.

On Monday, the research team of Bertram Batlogg of the Swiss Federal Institute for Technology from the ETH in Zurich, Switzerland, was honored with one of the most notable awards in the scientific world of Europe, the German Braunschweig Prize, for work on leading plastics.

The work of Batlogg, Christian Kloc and Hendrik Schon started at Bell Labs in Murray Hill, N.J., where in 1947 the transistor was invented. There Batlogg and his team have more than doubled the temperature at which carbon-60--also known as the "buckyball"--can behave as a superconductor. Batlogg, a native of Austria, is known as the scientist who created the world's first plastic material in which resistance to the flow of electricity vanishes below a certain temperature, making it a superconductor.

Batlogg achieved the "transition temperature" of 117 degrees Kelvin (-248 degrees Fahrenheit) by adding a methane-based compound to the material. It's believed that the increased transition temperature is due to an expansion of the crystal structure and that it could exceed 150 degrees Kelvin if the crystal can be stretched just 1 percent further. The temperature below which a material loses its resistance to electricity is known as its superconducting transition temperature.

In an earlier experiment, Batlogg and colleagues eliminated electrical resistance from carbon-60 at 54 degrees Kelvin (-362 degrees Fahrenheit) by adding positive "holes" to it. But when they added tribromomethane, the resistance disappeared at the much higher temperature of 117 Kelvin.

Carbon-60 molecules form a crystal with a face-centered cubic structure. Its lattice constant--the separation of the centers of two adjacent molecules--is 1.417 nanometers. When trichloromethane was added to the molecule, this stretched to 1.428 nanometers and the transition temperature reached about 70 degrees Kelvin. But when tribromomethane was added, the lattice constant grew to 1.443 nanometres and superconductivity persisted up to 117 degrees Kelvin.

As these results show, the transition temperature of carbon-60 increases linearly with lattice constant, and Batlogg's team believes that boosting this constant is the key to achieving superconductivity at higher temperatures. The challenge: The weak electrostatic attractions that bind the carbon-60 crystal lattice--known as van der Waals forces--will rapidly weaken even further as the carbon-60 molecules accept larger neutral molecules.

From September 2000 on Batlogg went on with his research at the Swiss Federal Technical University in Zurich but still kept the connections to his colleagues at Bell Labs alive. "We in general worry about the basic research. To use this thing for production is a thing others should do," Batlogg said.

"It's not about to replace conventional electronics," he said. "It's meant to complete it."

Batlogg is unsure of the full implications of his work, but he is confident that inexpensive electronics with organic materials will create new products, media and services. His work has proven that organic materials like plastic could be used for the manufacturing of semiconductors, lasers and even superconductors. This may lead to flat screens consumers can fold, intelligent labels, cheap solar cells, and even quantum computing devices.

Staff writer Dietmar Mueller reported from Munich.

 

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