RESEARCHERS at International Business
Machines (IBM) claim to have overcome a fundamental obstacle to
the improvement of microscopes that work by using visible light. They can now
directly examine and study
very small fragments of
matter such as genes.
Developed at the company s Yorktown Heights,
New York centre, the new
microscope is said to be so
sharp-eyed that it is potentially capable of determining spectrums of individual atoms. Says Kumar
Wickramasinghe, leader of
the IBM research team that
developed the microscope,
"We hope to obtain the first single-atom
spectrums ever recorded before the year end."
Called a 'scanning interferometric
apertureless microscope', or Siam, the
device can also speedily scan ultracompact optical data storage items like compact disks. Officials at the IBM say the
new device opens the way for making
and using very small memory diskettes,
each capable of storing data equivalent
to 30 full length movies.
Visible light interacts with atoms
and molecules to produce characteristic
spectrums - patterns that reveal chemical composition. The developers of the
modern microscope, as well as its users,
have tried hard for more than three centuries to overcome a fundamental limitation imposed by the wivelength of visible light. Researchers using the traditional light-based microscope can examine small objects, as long as they
are larger than the wavelength of light
used to view them. But when studying
very minute particles of matter, the conventional microscope proves to be
redundant as the light waves are too
long to register ultra-fine details.
Some atomic particles such as electrons have a wavelength which is far
shorter than that of light, and in the
'30s, this fact was exploited while developing the electron microscope which
uses an electron beam to centre images
of sub-microscopic particles. Since
then, the scanning tunneling microscope - also invented by IBM scientists,
the atomic force microscope and other
devices which are not light-based have
helped study ultrasmall objects, including atoms imaged as bumps on highly
polished surface. But these devices do
not produce spectrums of atoms and
Now the Siam microscope can view
objects which are one-five hundredth-
times smaller than those which can be
seen through the conventional microscope. Wickramasinghe believes that
biologists can now identify patterns of
genes and other molecules at lightening
speed, by pinpointing them with light
and identifying their spectral patterns
that result from interaction with constituent atoms.
The hallmark of the Siam
device is that, it can be attached
to the conventional light
microscope. It uses ordinary
lenses to focus laser light to
the smallest possible spot on a
very thin slice of the sample.
Under the sample is a silicon
probe, its tip sharpened by
etching to a thickness of one
nanometre - one billionth
of a metre, and about five
times the width of one atom.
The probe is mounted on
a scanning device that vibrates
it towards and away from the
200,000 times a second.
As the vibration continues, the
scatters some of the light
which reaches the device after
passing through the sample.
Another device then combines
the scattered light with the
unscattered light to produce an
interference pattern that provides
insights into the chemical composition of the object. This means
that biologists will be able to see
where antibodies go on the surface
of antigens, map genes, or even
examine molecular structure of
viruses, Wickramasinghe points out.