快猫短视频

COULD common gases do the number crunching in computers based on individual
molecules instead of transistors on a chip? The prospect of such superfast
molecular computers has come a step closer now a chemist in Berlin has developed
molecules that can be made to flip back and forth between two states by the
gases carbon dioxide and nitrogen.

James La Clair, an independent chemist formerly with the Scripps Research
Institute in California, has created a molecule that is fluorescent when
nitrogen is present, but becomes non-fluorescent when nitrogen is replaced by
CO₂ (Angewandte Chemie International Edition, vol 38, p 3045).
He says it is the first molecular switch that is driven by common atmospheric
gases. 鈥淭his finding provides a new cornerstone for future electronics,鈥� La
Clair says. 鈥淭his technology may some day lead to computers that only need gases
and light to think.鈥�

鈥淭he molecule looks like a line of wheels,鈥� he says. 鈥淎s they spin, they can
all align. When they鈥檙e aligned, they fluoresce.鈥� In the presence of nitrogen,
the molecule, known as SENSI, flips into the fluorescing or 鈥渙n鈥� state.
Replacing nitrogen with CO₂ switches it to the 鈥渙ff鈥� state in which it
cannot fluoresce (see Diagram).

To make the molecules fluoresce, La Clair uses a beam of laser light. This
stimulates molecules that are in the 鈥渙n鈥� state to emit a photon of light, which
he detects using a device called a single photon counting silicon avalanche
detector.

鈥淚t鈥檚 nice work,鈥� comments Fraser Stoddart, a chemist at the University of
California in Los Angeles. He says that La Clair鈥檚 experiments 鈥渆stablish some
fundamental concepts鈥� and should be capable of further development.

Molecular switches developed by other groups consist of large groups of
molecules, which can only be observed in bulk. La Clair鈥檚 key advance, says
Stoddart, is to have observed changes in a single molecule鈥攑otentially
allowing the creation of much smaller molecular computers.

There are, however, some big practical problems to be solved. For now, to
flip the molecular switch you have to fill a balloon with one gas, then evacuate
it and fill it with the other. But La Clair believes he could eventually develop
microscopic digital devices built from arrays of molecules that are individually
flipped on and off by tiny amounts of gases.

Molecular computing is attracting a great deal of interest because
conventional chips made of silicon-based transistors are thought to be
approaching their limit in terms of speed, since the processes used to etch
circuits on silicon are limited by the wavelength of light
(快猫短视频, 7 November 1998, p 42).
But molecular circuits could be just a
fraction of a nanometre wide. Researchers have already created molecular wires,
logic gates and switches, which may some day be hooked up to make a working
computer a fraction of the size of existing machines.