PULLMAN, Wash. — An article about building sophisticated electronic devices from individual molecules by Washington State University materials scientist Kerry W. Hipps was published in the Oct. 19 issue of Science magazine.
Hipps finds that the ability to measure the conductivity of a single molecule is the key to many problems facing molecular electronic designers.
“To do so, we must connect a macroscopic current source and volt meter to each end of a single molecule,” he said. “Molecular electronics is thus very much about contacts.” In addition, controlling the conductivity and properly insulating the molecules that act as attachment wires are crucial to obtaining accurate measurements.
In the article, titled “It’s All About Contacts,” Hipps surveys the work of four research groups that measured the electrical conduction of DNA molecules. The groups’ findings varied widely. One group described DNA as an insulator, the second as a semiconductor, the third as a conductor and the fourth as a superconductor, under certain circumstances. Hipps concludes that the inconsistent findings result from researchers making more or less successful electrical contacts.
Hipps poses the question, “If simply making physical contact between a metal and a molecule is not enough to guarantee good electrical contact, what is?” In response he rejects increasing the pressure on the contact because this tends to either move, deform or change the electronic structure of the molecule being measured, thus rendering any results inaccurate or irrelevant. He instead endorses the idea of creating reliable contacts by using direct chemical bonds, such as sulfur or selenium atoms bound to gold or silver. Hipps goes on to describe the construction of tiny gold particles, called nanostructures, that can act as the solder connecting a molecular circuit element to gold-coated electrodes. The structures are now providing reproducible results for measuring the conductivity of both rigid and flexible molecules.
He cites the work of X.D. Cui and others, also published in the same issue of Science, as finally giving “a tool to begin in earnest the study of single-molecule devises.”
Hipps, a professor in the Department of Chemistry and the Program in Materials Science, is an authority on the spectroscopic and microscopic characterization of solid surfaces.