Notre Dame researchers led by Ken Henderson have achieved a critical step in the search for rapid molecular-based computing. The group demonstrated the ability to move an electron within a neutral molecule, providing the binary switch necessary for computing. A key advance is that the molecule does not require the presence of a second molecule to generate the electron, which creates bias in the system. Their article on the discovery, “Solving the Counter Ion and Clocking Problems in Molecular QCA: Synthesis of a Neutral Mixed Valence Diferrocenyl Carborane,” was accepted by the prestigious journal Angewandte Chemie after peer reviewers ranked it among the top 10 percent of submissions, and as “highly important.”
Coauthors with Henderson are John A. Christie, Ryan P. Forrest Steven A. Corcelli, Natalie A. Wasio, Rebecca C. Quardokus, Ryan Brown, and S. Alex Kandel, all of the Department of Chemistry and Biochemistry at Notre Dame; Craig S. Lent of the Department of Electrical Engineering; and Yuhui Lu of the Department of Chemistry at Holy Cross College.
Technology to enhance computer speed with traditional silicon chips is approaching limits, where chips are so small that transistors don’t work and chips suffer heat damage. One potential alternative is quantum-dot cellular automata (QCA) that uses the movement of charge to provide the on-off signals of zeroes and ones needed in computing.
Craig Lent at Notre Dame first proposed QCA computing several years ago, and research groups across the world are searching for ways to make practical devices. Until this breakthrough, the use of molecules as electronic switches was problematic due to the bias imposed by the need for a second charged molecule as part of the system. The Notre Dame group makes the process entirely internal to a single molecule.
“That’s a big benefit because we overcome the issue of bias,” Henderson says. “You don’t want that in a computer as such bias may lead to incorrect transfer of data in the microprocessor.” The group designed and prepared a molecule which uses two differently charged iron atoms bridged by a negatively charged molecular cage made of boron. The molecule has successfully been placed on a surface and characterized at the atomic level using scanning tunneling microscopy. “This technology will hopefully allow us to see the individual charges as they move,” he says.
The next step is to demonstrate that information can be reliably transferred from one molecule to another in a sequence. “We’d like to be able to see the location of the electron influence a neighboring molecule,” Henderson says. “Then what we’re doing is pushing information. We want to take it to the point where we actually build a device that is analogous to a microprocessor.”