Zurich, Switzerland, 24 July 1998—IBM scientists and a team of international collaborators reported today the discovery of "molecular wheels": propeller-shaped molecules that rotate rapidly in a bearing-like structure formed by surrounding molecules. The scientists believe this unexpected phenomenon shows great promise for the development of molecular mechanical devices and further demonstrates the validity of using single molecules to perform the various functions required in such devices.
In a paper published today in Science, IBM Research - Zurich, together with colleagues at the French National Center for Scientific Research (CNRS) in Toulouse, and the Risø National Laboratory in Roskilde, Denmark, report their design of the propeller-shaped molecules which can switch between two statesrotating and immobilized, and the high-speed molecular rotation, which they observed by using a scanning tunneling microscope (STM).
"Our discovery of the molecular wheel came about from recent molecular switch experiments in which we were investigating a reversible change in the shape of specifically designed molecules triggered by a voltage pulse from the STM tip," said James K. Gimzewski, who leads the nano-engineering effort at IBM Research - Zurich. "We believe that, compared to other proposed or synthetic molecular mechanisms, the molecular wheel, which works in a dry state and appears to be wearless, is advantageous for creating gears and motors at the nanoscale level."
In viewing the STM images, the researchers observed a ring-like object instead of the molecule that had been there before. The object, now in a slightly different position, had shifted its position by just one-fourth of a nanometer. It evidently jumped into a tiny space left vacant by an irregularity in the molecular layer and thus escaped the immobilizing grip of four molecules that surrounded it closely on one side. An adjacent molecule on the other side confined its further lateral motion and, in effect, contributed to forming a bearing for rotation of the central molecule. This rotation was responsible for the blurred, ring-like appearance of the molecule in the STM image.
Researchers at CNRS calculated the behavior of the molecular wheel. "Our calculations show that the thermal energy at room temperature is sufficient for the molecule to rotate in a bearing formed by an irregularity in the molecular layer as observed, whereas the proximity of molecules in a fully ordered lattice stops such movement," said Christian Joachim, who heads the theoretical effort at CNRS. Such wheels may someday become the smallest conceivable components of molecular engines.
In 1995, IBM Zurich scientists precisely positioned individual molecules at room temperature for the first time ever. This led in the following year to their creation of an abacus with "beads" made of single ball-shaped molecules to demonstrate new nano-engineering capabilities and, subsequently, to the realization of an amplifier having a single molecule as its active part. The enabling tool for this research is the STM, invented at IBM Research - Zurich in the early eighties. The STM's ultrafine tip can be used not only to image a surface with atomic resolution, but also to manipulate individual atoms and molecules.
The authors of the scientific report published in Science (July 24, 1998) are James K. Gimzewski, Reto R. Schlittler, and Veronique Langlais of IBM Research - Zurich; Christian Joachim and Hao Tang of CEMES (Center d'Elaboration de Materiaux et d'Etudes Structurales) at CNRS; and Ib Johannsen of the Condensed Matter Physics and Chemistry Department at Risø National Laboratory in Roskilde, Denmark. The project is supported by the European Union ESPRIT project "Nanowires", which is partially funded by the Swiss Federal Office for Education and Science.