Molecule Cascades

TLDR

Carbon monoxide molecules were arranged in atomically precise configurations—called molecule cascades—where the motion of one molecule triggers successive motion in a domino‑like cascade. The authors propose a cascade‑based computation scheme that provides all devices and interconnects needed for one‑time computation of any logic function. They assembled isotopically pure cascades on a Cu(111) surface using a low‑temperature STM and implemented logic gates by engineering molecular arrangements at cascade intersections. The hopping rate in cascades is temperature‑independent below 6 K with a strong isotope effect, indicating quantum tunneling, while at higher temperatures a thermally activated rate with a low Arrhenius prefactor suggests tunneling from excited vibrational states; the authors also demonstrate a three‑input sorter built from AND, OR, crossover, and fan‑out units.

Abstract

Carbon monoxide molecules were arranged in atomically precise configurations, which we call "molecule cascades," where the motion of one molecule causes the subsequent motion of another, and so on in a cascade of motion similar to a row of toppling dominoes. Isotopically pure cascades were assembled on a copper (111) surface with a low-temperature scanning tunneling microscope. The hopping rate of carbon monoxide molecules in cascades was found to be independent of temperature below 6 kelvin and to exhibit a pronounced isotope effect, hallmarks of a quantum tunneling process. At higher temperatures, we observed a thermally activated hopping rate with an anomalously low Arrhenius prefactor that we interpret as tunneling from excited vibrational states. We present a cascade-based computation scheme that has all of the devices and interconnects required for the one-time computation of an arbitrary logic function. Logic gates and other devices were implemented by engineered arrangements of molecules at the intersections of cascades. We demonstrate a three-input sorter that uses several AND gates and OR gates, as well as the crossover and fan-out units needed to connect them.