265 lines
13 KiB
Plaintext
265 lines
13 KiB
Plaintext
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(word processor parameters LM=8, RM=75, TM=2, BM=2)
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Taken from KeelyNet BBS (214) 324-3501
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Sponsored by Vangard Sciences
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PO BOX 1031
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Mesquite, TX 75150
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There are ABSOLUTELY NO RESTRICTIONS
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on duplicating, publishing or distributing the
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files on KeelyNet except where noted!
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October 30, 1993
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SCOPE.ASC
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This file shared with KeelyNet courtesy of Bert Pool.
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02-22-1993
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New optical microscopes transcend limits of visible light
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By John Markoff
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New York Times News Service
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A new generation of optical microscopes is emerging, capable of
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resolving images far beyond the conventional limits imposed by
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visible light.
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These microscopes are known as near-field scanning optical
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microscopes, or NSOM, and they may soon offer a wide variety of
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remarkable applications ranging from detailed movies of the inner
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workings of cells to vast increases in data storage capacity for the
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computer industry. In theory the technique could pack information so
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densely that two copies of "War and Peace" could be transcribed in
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the area of a pinhead.
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The renaissance of optical microscopy is a striking reversal of
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recent trends in this three-century-old technology. Since the 1930s
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conventional lens-based optical microscopes have increasingly lagged
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behind two other kinds. One is the electron and X-ray microscopes
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which resolve at far shorter wavelengths than optical systems; the
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other is scanning probe instruments which, in the case of the
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scanning tunneling microscope, can now routinely resolve objects as
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tiny as individual atoms.
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Yet despite the razor-sharp imaging ability of nonoptical systems
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they have failed to replace traditional optical microscopy for many
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applications because of what researchers call a Faustian bargain
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struck by each technology. In both cases compromises must be made.
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There are shortcomings in these powerful technologies ranging from
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lack of viewing contrast to the destructiveness of techniques that
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destroy biological material.
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Despite its great promise, the new optical technique has been
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developing slowly because of a variety of hurdles that are only now
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being overcome.
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Until now near-field scanning optical microscopes have been the
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laggards of the field, said Eric Betzig, a physicist at AT&T Bell
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Laboratories who is one of the leading developers of the
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Page 1
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instruments.
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That is now changing quickly based on technical advances made in
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Betzig's laboratory and by researchers at Cornell University and IBM
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scientists in Zurich, Switzerland. Their hope is that the near-field
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optical instruments now being perfected will take advantage of the
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decades of experience gained with improving conventional optical
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microscopes. Betzig said advantages like speed and the ease of
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preparing specimens would enable scientists to adapt quickly to the
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new technique.
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Betzig's belief in the field's promise is echoed by some of the
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leading figures in microscope research.
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"Near-field optical extends the limits to a degree that is
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unprecedented," said Calvin Quate, a Stanford University physicist
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who is a pioneer in developing advanced microscope technologies. "If
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you have two microscopes of similar resolution, the optical would
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win out because of the power of photons."
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Bell Laboratories researchers have already perfected near-field
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scanning optical microscopes capable of resolving images down to
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approximately 12 nanometers, or less than one 1,700,000-millionth of
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an inch. This makes it easy to view objects like bacterial viruses
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which are in the range of 70 nanometers across or about one
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360,000th of an inch.
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At the heart of the new technique is an ultra-fine fiber-optic probe
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that can be steered over the surface of a sample with remarkable
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accuracy while staying within several nanometers of the object's
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surface.
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The probe itself is created by heating and drawing a fiber-optic
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wire and then sheering its tip. The probe is coated with aluminum
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and a light is shined through it. As the probe is scanned over the
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surface of an object, an image is built up line by line, much as a
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television image is created.
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The great advantage of the new technique is that it evades a basic
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physics principle known as the diffraction limit, which holds that
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details that are smaller than half the wavelength of light cannot be
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resolved. The microscope can in fact resolve objects that are
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dwarfed by the wavelength of light, which is around 500 nanometers.
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To get around the diffraction barrier, the new instruments exploit
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the fact that a light wave can be defined as the sum of a series of
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waves with far shorter wavelengths. Because of the probe's extreme
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proximity to the surface it is measuring, it can detect these
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"evanescent" waves that are lost at greater distances.
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Several applications for the new breed of optical microscopes are
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now being explored. At Bell Laboratories Betzig and his co-workers
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have used the instrument to view extremely thin tissue samples taken
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from the hippocampus of a monkey's brain.
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When it is used together with a conventional optical microscope, the
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viewer can jump back and forth from a wide viewing area to focusing
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in on extremely fine features that have traditionally only been
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accessible to transmission electron microscopes. The Bell research
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Page 2
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suggests that the new instrument could become a cost-effective tool
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for clinical pathology. MORE (Optional 2ndtake follows.)
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In the laboratory of Michael S. Isaacson, a Cornell physicist who
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led one of the three groups that originally developed the near-field
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optical microscopes in the late 1970s and early 1980s, researchers
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are using the devices as diagnose semiconductor lasers. With the
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instrument's power, they can understand more precisely problems that
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develop in the process of growing the lasers.
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Despite early promise, some significant hurdles remain. In
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biological fields, Isaacson said that the instrument's usefulness is
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narrow so far.
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"The technique may be restricted to a certain class of biological
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objects," he said. Because the optical probe functions so close to
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the surface of an object, it may be impossible to navigate across
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cell surfaces that have many protruding receptors. But Isaacson said
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that researchers at the University of Washington had already begun
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using a near-field microscope to explore the structure of muscle
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cells, which generally have smooth surfaces.
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Indeed, the Bell Laboratories researchers, working with scientists
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at the Center for Light Microscope Imaging and Biotechnology at
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Carnegie Mellon University, have already demonstrated that the near-
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field technique can obtain more detailed images of cell structures
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than can other microscopic methods. The detailed cell images are
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providing new insights into the mechanisms of wound repair, they
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said.
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They have also recently begun to view cells under water, a first
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step toward creating images of living cells. It currently takes
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about 45 minutes to obtain a 512 by 512 pixel image, far slower than
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some of the living cell processes. In the future, however, Betzig
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said the researchers believe that modifications to the current
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system may make it possible to create several images per second.
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There are also several research projects under way in nonbiological
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areas. The Cornell Laboratory, in conjunction with IBM, is exploring
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use of the NSOM to write ultra-thin circuit lines on silicon wafers
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by scanning the probe tip over a light-sensitive semiconducting
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material.
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At present electronic circuits are etched on semiconductors by
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shining ultraviolet light through masks that make it possible to
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expose as many as 30 wafers an hour. Using a single NSOM probe would
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take a prohibitive amount of time even to write the circuitry for a
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single chip.
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To overcome this barrier scientists are discussing the possibility
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of creating arrays of tens of thousands of probes that could scan
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across the surface of a wafer writing ultra-dense semiconductor
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circuits.
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"You can fabricate silicon structures that are almost comparable
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with what you can do with electron beams," said Isaacson. "But in
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order for it to be realistic in a manufacturing sense you would have
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to do it in parallel."
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Page 3
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There may be intermediate applications in the semiconductor
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manufacturing process, however. The Bell Laboratories researchers
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are studying using the NSOM tools as an inexpensive means for
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correcting defects in the masks that are used in the lithographic
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process needed to make microchips. Potentially it will be possible
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to microscopically "weld" defects in the delicate semiconductor
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circuit pattern masks.
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The Bell Laboratories researchers are also exploring the possibility
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of using the NSOM as a device for storing and retrieving computer
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data. Currently they have been able to read and write information at
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densities of 45 billion bits per inch.
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If that much information were in the form of recorded music, it
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would take a disk the size of a quarter as much as eight days to
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play it all. If it took the form of compressed high-density
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television programming, a palm-sized disk could hold 17 hours'
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worth.
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Yet while such densities are more than 40 times greater than those
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attained with state-of-the-art magnetic recording techniques, there
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are competing technologies that may be even more promising. Last
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year IBM scientists at the company's Almaden Research Center in San
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Jose used an atomic force microscope probe in conjunction with a
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laser to store and retrieve data at even higher storage densities.
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It is still early but researchers are beginning to talk about the
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advent of a golden age in the Lilliputian world of high-technology
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microscopes.
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"It's a fantastic time, its the golden age of microscopy," said
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Kumar Wickramasinghe, manager of physical measurements at IBM's
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Thomas J. Watson Research Center in Yorktown Heights, N.Y. "The
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scanning tunneling microscope has taught me and a lot of others in
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this field that by scanning probes around you can overcome the
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limits to resolution. Now you're really limited only by the
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ingenuity of the scientist designing the probe. We're all having
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lots of fun."
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If you have comments or other information relating to such topics
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as this paper covers, please upload to KeelyNet or send to the
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Vangard Sciences address as listed on the first page.
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Thank you for your consideration, interest and support.
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Jerry W. Decker.........Ron Barker...........Chuck Henderson
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Vangard Sciences/KeelyNet
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If we can be of service, you may contact
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Jerry at (214) 324-8741 or Ron at (214) 242-9346
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Page 4
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