Even the bonds to the hydrogen atoms at the pentacene's periphery can be seen
The detailed chemical structure of a single molecule has been imaged for the first time, say researchers.
The
physical shape of single carbon nanotubes has been outlined before,
using similar techniques - but the new method even shows up chemical
bonds.
Understanding structure on this scale could help in the
design of many things on the molecular scale, particularly electronics
or even drugs.
The IBM researchers report their findings in the journal Science.
It is the same group that in July reported the feat of measuring the charge on a single atom.
Fine tuning
In both cases, a team from IBM Research Zurich used what is known as an atomic force microscope or AFM.
Their
version of the device acts like a tiny tuning fork, with one of the
prongs of the fork passing incredibly close to the sample and the other
farther away.
When the fork is set vibrating, the prong nearest
the sample will experience a minuscule shift in the frequency of its
vibration, simply because it is getting close to the molecule.
Comparing
the frequencies of the two prongs gives a measure of just how close the
nearer prong is, effectively mapping out the molecule's structure.
The microscope must be kept under high vacuum and exceptionally cold
|
The measurement requires extremes of precision. In order to avoid
the effects of stray gas molecules bounding around, or the general
atomic-scale jiggling that room-temperature objects experience, the
whole setup has to be kept under high vacuum and at blisteringly cold
temperatures.
However, the tip of the AFM's prong is not
well-defined and isn't necessarily sharp on the scale of single atoms.
The effect of this bluntness is to blur the instrument's images.
The
researchers have now hit on the idea of deliberately picking up just
one small molecule - made of one atom of carbon and one of oxygen -
with the AFM tip, forming the sharpest, most well-defined tip possible.
Their measurement of a pentacene molecule using this carbon
monoxide tip shows the bonds between the carbon atoms in five linked
rings, and even suggests the bonds to the hydrogen atoms at the
molecule's periphery.
Tip of the iceberg
Lead
author of the research Leo Gross told BBC News that the group is aiming
to combine their ability to measure individual charges with the new
technique, characterising molecules at a truly unprecedented level of
detail.
That will help in particular in the field of "molecular
electronics", a potential future for electronics in which individual
molecules serve as switches and transistors.
Although the
approach can trace out the ethereal bonds that connect atoms, it cannot
distinguish between atoms of different types.
The team aims to
use the new technique in tandem with a similar one known as scanning
tunnelling microscopy - in which a tiny voltage is applied accross the
sample - to determine if the two methods in combination can deduce the
nature of each atom in the AFM images.
That would help the entire field of chemistry, in particular the synthetic chemistry used for drug design.
The
results are of wide interest to others who study the nano-world with
similar instruments. For them, implementing the same approach is as
simple as picking up one of these carbon monoxide molecules with their
AFM before taking a measurement.
Source - BBC,2009
Source: NY Times
Source: MTV