First Plastic Superconductor Developed at Bell Labs
Peter Singer, Editor-in-Chief -- Semiconductor International, 4/1/2001
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Bell Labs says its breakthrough comes after a 20-year quest to find organic polymers that act as superconductors. Although 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, which are organic materials that have some resistance to the flow of electricity), creating a superconducting organic polymer proved to be far more difficult.
"This is stunning and truly beautiful work, and opens new vistas for coming studies," said Professor Olle Inganas of Linkoping University (Linkoping, Sweden), who is an authority in the field of organic materials.
The Bell Labs breakthrough was made possible by a multidisciplinary team of researchers whose backgrounds range from experimental low-temperature physics to materials science and organic chemistry. It "emphasizes that interdisciplinary work, involving both synthetic chemistry and condensed-matter physics, will advance the frontiers of both fields," said Denis Jérome at the Université Paris-Sud (Orsay, France), and Klaus Bechgaard at Risø National Laboratory (Roskilde, Denmark), in a commentary in the March 8 issue of Nature (the same issue in which the Bell Labs work appeared).
The challenge in creating a plastic superconductor was overcoming the inherent structural randomness of a polymer — similar to strands of cooked spaghetti — which prevented the electronic interactions necessary for superconductivity.
The Bell Labs scientists were able to overcome this by making a solution containing the plastic polythiophene. They then deposited thin films of it onto an underlying layer so that the polymer molecules stacked up against one another like uncooked spaghetti. Instead of adding chemical impurities to change the material's electrical properties, as is often done, the researchers used a novel technique in which they removed electrons from polythiophene.
The temperature below which polythiophene became superconducting was -455°F. Although this is extremely cold, scientists are optimistic that they can raise the temperature in the future by altering the molecular structure of the polymer.
Polythiophene, which can be a conductor at room temperatures and has been used previously in making optoelectronic components and smart pixels, may be the first of many superconducting plastics.
"With the method we used, many organic materials may potentially be made superconducting now," said Zhenan Bao, a Bell Labs chemist who was involved in the research. Bell Labs scientists plan in the coming months to study the interrelationships between semiconducting, superconducting and molecular electronics with materials such as polythiophene.
"A new window into nature has opened up," Ananth Dodabalapur, a device physicist at Bell Labs and member of the research team, said of the implications of the breakthrough.
In addition to Bao and Dodabalapur, the other Bell Labs scientists that were involved in the research were Hendrik Schon, Christian Kloc and Bertram Batlogg. Batlogg also is affiliated with the solid-state physics laboratory at ETH Honggerberg in Switzerland. Ortwin Schenker, a collaborator from the University of Konstanz (Konstanz, Germany), also participated in the research.
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