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Low-cost microscope to spur new surface studies
 Zurich,
Switzerland, and Chiba, Japan; July 15, 1998 -- Scientists
can now examine surfaces with greater precision, more convenience
and at less cost thanks to a cleverly designed atomic force microscope
developed by IBM Research - Zurich in Switzerland and
Seiko Instruments Inc., Chiba, Japan.
The new atomic force microscope (AFM) can inspect surfaces with
nearly atomic resolution without a special vibration-damping table.
The least expensive version, called Nanopics (TM), will cost less
than one-third of US$100,000 average price of today's basic, less-capable
AFMs.
The basic technology for this low-cost AFM was developed by scientists
at IBM Research - Zurich. Seiko Instruments Inc. (SII)
later licensed IBM's AFM patents and worked with the IBM scientists
to develop the product. SII is already selling the new instrument
in Japan. Worldwide availability has not been announced. SII estimates
that about 1,000 AFMs were purchased in 1997 worldwide with a sales
volume of about US$100 million.
"The dramatically reduced price of such a powerful AFM will
allow many small commercial and research laboratories and even schools
to begin to study surfaces on a nearly atomic scale," said
IBM Fellow Gerd Binnig. He is an IBM Zurich physicist who invented
the AFM in 1986, shortly before receiving the Nobel Prize in Physics
for his role in inventing, with Heinrich Rohrer, the scanning tunneling
microsope (STM) for imaging atoms on conducting surfaces.
Understanding the atomic-scale details of surfaces is increasingly
important in both science and industry. Among a myriad examples,
AFM examinations of surfaces have led to improved optical lenses,
magnetic hard disks and filters used in blood cleansing.
Like the STM, the AFM can detect the height profile of a sample
by scanning its surface with a fine tip—in the best cases with such high resolution that the position of
individual atoms can be recognized. An STM works by sending a "tunneling"
current between tip and sample, which must be electrically conductive.
The AFM, however, can be used to investigate any surface, even poorly
or nonconducting ones, which broadens its potential applications
significantly. Many companies and laboratories are using AFMs today.
The original AFM was developed by Binnig, IBM colleague Christoph
Gerber, and Calvin Quate of Stanford University in California. Its
heart is a fine tip formed at the end of a flexible silicon bar
called a cantilever. Forces between the tip and sample can cause
the cantilever to bend closer or farther away from the sample surface
or to change its resonant frequency, depending on the distance between
tip and sample. Such changes are detected and are used to image
the topography of the surface as it is scanned by the tip.
"We wanted to create a high-tech instrument that is accessible
to as many people as possible," says Binnig. "Our collaboration
with SII has produced a microscope that we believe will become standard
equipment in many laboratories. The microscope will also make it
possible for young people with yet a limited knowledge of microscopy
to gain their own insight into smallest features of nature."
Technical background The technical innovations that made the new
AFM cheaper to manufacture and simpler to operate include:
Sensors integrated into the cantilever itself measure its motion.
Conventional force microscopes use expensive laser beam reflection
or interferometry systems to measure the cantilever deflection.
Inexpensive voice coils from everyday loudspeakers position the
AFM tip more precisely and over a wider range than the costly piezoelectric
elements used in conventional scanning microscopes. An intricate
but inexpensive mechanism moves the tip precisely over a wide range
of distances: (1) rough vertical tip approach to a surface (4-5
millimeters), (2) fine vertical adjustment of the tip-sample distance
(20 micrometers, thousandths of a millimeter), and (3) scanning
surfaces from 0.5 to 800 micrometers square. Only the component
containing the AFM cantilever scans across the surface. In most
conventional force microscopes, the entire sample is moved. This
design makes the instrument less expensive to manufacture and also
permits looking at a specific area of a large sample. (To do this,
the measuring head is separated from the the sample holder and positionined
directly atop the sample.) The AFM was designed to be compact and
uses components with naturally high resonant frequencies, all of
which reduces the instrument's sensitivity to external vibrations.
This AFM can thus operate in many more types of locations than had
been possible before. The measurement electronics of the basic Nanopics
AFM produces a TV-quality color video image of 512-by-512 pixels.
Results can therefore be displayed on any TV screen and stored on
ordinary video tape. Color can also be added to illustrate sample
properties, such as topography or material structures, making expensive
digital image recording unnecessary for displaying results.
The finest Nanopics resolution of a few nanometers is achieved
with the relatively simple image-processing equipment at scanning
lengths of up to 500 nanometers. Optional features include higher
image resolution, programmable computer control of the instrument,
and digital recording to permit more sophisticated image display
and analysis. SII is also developing customized but still low-cost
AFMs for specific applications, such as for inspecting semiconductor
surfaces and for use in biology.
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