|
Discovery of molecular wheel offers promise for design of nanoscale
devices
 Rüschlikon/Switzerland,
July 24, 1999 -- 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's Zurich Research
Laboratory, 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 states—rotating 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's Zurich Research Laboratory.
"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's Zurich Research Laboratory
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's Zurich Research Laboratory; 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.
|
