From Wikipedia,
the free encyclopedia.
Mechanochemistry,
sometimes also called "positional
synthesis" or "positional
assembly" is a technique for
forming
chemical bonds by direct
computer control of the position
of
molecules.
As of 2004, the typical
experimental arrangement is to
attach a molecule to the tip of an
atomic force microscope, and
then use the microscope's precise
positioning abilities to push the
molecule on the tip into another
on a substrate. Since the angles
and distances can be precisely
controlled, and the reaction
occurs in a vacuum, novel chemical
compounds and arrangements are
possible.
Much of the excitement
regarding mechanochemistry regards
its potential use in automated
assembly of
molecular-scale devices. Such
techniques appear to have many
applications in medicine,
aviation, resource extraction,
manufacturing and warfare.
Most theoretical explorations
of such machines have focused on
using
Carbon, because of the many
strong bonds it can form, the many
types of chemistry these bonds
permit, and utility of these bonds
in medical and mechanical
applications. Carbon forms
diamond, for example, which if
cheaply available, would be an
excellent material for many
machines.
In practice, getting exactly
one molecule to a known place on
the microscope's tip is possible,
but has proven difficult to
automate. Since practical products
require at least several hundred
million atoms, this technique has
not yet proven practical in
forming a real product.
The goal of mechanoassembly
research at this point focuses on
overcoming these problems by
calibration, and selection of
appropriate synthesis reactions.
The first product to be built by
these means will probably be a
specialized, very small (roughly
1,000 nanometers on a side)
machine tool that can build copies
of itself using mechanochemical
means, under the control of an
external computer. In the
literature, such a tool is called
an
assembler.
Once assemblers exist,
geometric growth (copies making
copies) could reduce the cost of
assemblers rapidly. Control by an
external computer should then
permit large groups of assemblers
to construct large, useful
projects to atomic precisions.
One such project would combine
molecular-level conveyor belts
with permanently-mounted
assemblers to produce a
factory.
History
The technique was first
proposed by
Eric Drexler in his
1986 book
The Engines of Creation.
In
1988, researchers at
IBM's Zurich Research
Institute successfully spelled the
letters "IBM" in Xenon atoms on a
cryogenic copper surface, grossly
validating the approach. Since
then, a number of research
projects have undertaken to use
similar techniques to store
computer data in a compact
fashion.
More recently the technique has
been used to explore novel
physical chemistries, sometimes
using lasers to excite the tips to
particular energy states, or
examine the quantum chemistry of
particular chemical bonds.
See also
molecular nanotechnology, a
more general explanation of the
possible products, and discussion
of other assembly techniques.
