Switch narrows molecular-macroscopic gapBy Eric Smalley, Technology Research News
Researchers at the University of Liverpool have harnessed the electrical properties of a molecule to trigger a nanoscale electrical switch.
The development narrows the gap between the bottom-up approach of chemistry and the top-down approach of engineering in the drive to produce ever smaller machines and ever faster computers.
Two potential applications for the switch are chemical sensing and computer memory. Further advances are required, however, before it could be used in any application.
The switch consists of a gold nanoparticle linked by strands of polymethylene to a gold surface. Bipyridinium, which serves as a reduction-oxidation (redox) gate is embedded in the polymethylene connectors. When a molecule is in reduction it attracts electrons and in oxidation it sheds electrons.
A separate electrode adds or removes electrons from the redox gate. In its oxidized state, the bipyridinium blocks the flow of electrons between the surface and the nanoparticle. In its reduced state, electrons flow freely.
"We demonstrated a principle: it is possible to attach metal particles on to self-[assembled] linkers containing redox groups and observe their behavior as... switches," said Richard J. Nichols, a lecturer in the chemistry department at the University of Liverpool.
Self-assembly is a simple, inexpensive chemical process in which a substance is applied to a surface either in solution or a vapor and the substance adheres to the surface in a particular pattern, structure or orientation.
"Special features [of the switch] are the simplicity of the self-assembly procedure and the precision of the control of the [flow electrons] across the device," Nichols said.
The gold nanoparticle is six nanometers in diameter and stands three nanometers above the gold surface. The linking molecules have a footprint of .46 nanometers on the gold surface. A nanometer is one millionth of a millimeter, or about 10 carbon atoms long.
The small scale of the switch means it could make very dense memory. The switch may also prove useful in sensors where monitoring minute quantities of substances is important.
Using the switch in a sensor would require attaching molecules that bind to a particular target substance to the redox gate, said Nichols. "The electronic properties of the redox gate would be made to be sensitive to the binding of the [substance]," he said.
Though the chemical synthesis techniques used to produce the switch have come a long way, nanotechnology engineering will be required to integrate the switches into devices and allow them to communicate to the external world, Nichols said.
"This is a very interesting piece of work and is one of the most plausible that I have seen addressing the fundamental gap between the molecular and macroscopic worlds," said Jonathan W. Steed, a reader in inorganic and supramolecular chemistry at King's College London.
"This switching architecture is assembled on an ordered surface and has input/output functionality," he said. "It has long been established that we can make individual molecular machines but this is one of the few pieces of work to place them within an interrogateable framework. I hope we will see much more of this kind of science."
Nichols' colleagues were David I. Gittins, Donald Bethell and David J. Schiffrin. They published their work in the November 2, 2000 issue of the journal Nature. Gittins' participation was funded by the Engineering and Physical Sciences Research Council.
TRN Categories: Semiconductors and Materials; Nanotechnology
Story Type: News
Related Elements: Technical paper "A nanometer-scale electronic switch consisting of a metal cluster and redox-addressable groups" in the November 2, 2000 Nature
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