atomic force microscope
In 1953, J. Robert Oppenheimer, the scientific leader of the Manhattan Project, had his security clearances revoked by President Dwight D. Eisenhower, ostensibly because of admitted violations of security procedures; however, it was generally believed that the action was taken because of Oppenheimer's opposition to the development of the even more destructive hydrogen bomb, which was vigorously pressed by the chairman of the Atomic Energy Commission, Adm. Lewis Strauss. During the security proceeding before the commission, Oppenheimer's colleague and close associate, the physicist Edward Teller, testified against him. As a result, Teller himself was ostracized by a large part of the atomic science community, symbolizing a fundamental division of opinion on nuclear weapons policy.
Other scientists prominent in the development of the atomic bomb included the physicists Hans Bethe and Enrico Fermi, the chemist George Kistiakowsky, and the mathematician John von Neumann, whose invention of the high‐speed computer was critical in the development process.
As the nuclear policy concerns of government policymakers have moved from building a nuclear arsenal to assuring that many atomic weapons could survive an attack and then retaliate (a “secure second strike capability”), to negotiating international agreements to reduce the likelihood of a nuclear exchange and control the spread of nuclear weapons, and now to the eventual abolition of nuclear weapons, atomic scientists have been involved at every stage. They served as technical experts but also as proponents of policy options. The creation of the office of science adviser to the president, and of the president's Science Advisory Committee, provided significant input on nuclear policy, particularly during the incumbency as science advisers of George Kistiakowsky under President Eisenhower, and Jerome Wiesner under President John F. Kennedy.
The atomic science community has tended to support more severe constraints on the use of nuclear weapons, somewhat in contrast to the attitudes of political scientists, who seem more willing, in Herman Kahn's phrase, to think about the unthinkable. Even before the end of the Cold War, and in the face of rigorous security arrangements, atomic scientists in the West were able to develop working relationships with Soviet colleagues concerned about avoiding nuclear holocaust. On the other hand, the scientists on the staff of the nuclear weapons laboratories have persisted, perhaps understandably, in arguing and lobbying for continued testing of nuclear weapons, even in the face of international agreement on the Comprehensive Test Ban Treaty.
With the parallel development of fissionable materials as a potential source of energy for peacetime use, atomic scientists have also been involved in discussions on how to minimize the production of weapons‐grade materials, as byproducts of nuclear reactors, and how to deal with the problem of nuclear waste.
The creation of the first atom bomb called for the highest levels of scientific creativity; but it is generally acknowledged that today, many well‐named scientists would be able to fabricate at least a crude nuclear device. The focus of concern within the atomic science community has therefore shifted to more sophisticated technical problems of delivery, reliability, and control, with a consequent splintering of scientific expertise. The dynamic that continues to exert most force on the community is the awareness of the destructive power that their science has unleashed.
[See also Bush, Vannevar; Cold War: Domestic Course.]
Charles P. Curtis , The Oppenheimer Case, 1955.
Gene M. Lyons and and Louis Morton , Schools for Strategy, 1965.
George Kistiakowsky , A Scientist in the White House, 1976.
Gregg Herken , The Winning Weapon, 1980.
Fred Kaplan , The Wizards of Armageddon, 1983.
Atomic Force Microscope
Atomic force microscope
In 1985, the development of the atomic force microscope (AFM) allowed scientists to visualize the surface of cellular structures during some physiological processes. Along with the use of field ion microscopes and powerful scanning tunneling microscopes (STM), these advances in microscopy represent the most fundamental greatest advances since the development of the electron microscope .
Invented by Gerd Binnig and Christoph Gerber in Zurich, Switzerland, and Calvin Quate (1923– ) in California, the AFM uses a tiny needle made of diamond, tungsten, or silicon, much like those used in the STM. While the STM relies upon a subject's ability to conduct electricity through its needle, the AFM scans its subjects by actually lightly touching them with the needle. Like that of a phonograph record, the AFM's needle reads the bumps on the subject's surface, rising as it hits the peaks and dipping as it traces the valleys. Of course, the topography read by the AFM varies by only a few molecules up or down, so a very sensitive device must be used to detect the needle's rising and falling. In the original model, Binnig and Gerber used an STM to sense these movements. Other AFM's later used a fine-tuned laser. The AFM has already been used to study the super-microscopic structures of living cells and other objects that could not be viewed with the STM.
American physicist Paul Hansma (1946– ) and his colleagues at the University of California, Santa Barbara, conduct various studies using AFM research. In 1989, this team succeeded in observing the blood-clotting process within blood cells. Hansma's team presented their findings in a 33–minute movie, assembled from AFM pictures taken every ten seconds. Other scientists are utilizing the AFM's ability to remove samples of cells without harming the cell structure. By adding a bit more force to the scanning needle, the AFM can scrape cells, making it the world's most delicate dissecting tool.
Scientists continue to apply this method to the study of living cells, particularly fragile structures on the cell surface, whose fragility makes them nearly impossible to view without distortion.
See also Bacterial membranes and cell wall; Bacterial surface layers; Bacterial ultrastructure; Microscope and microscopy
Atomic Force Microscope (AFM)
Atomic force microscope (AFM)
In recent years, tremendous advances have been made in the field of microscopy (the study of microscopes). The electron microscope (which uses a beam of electrons, or negatively charged particles, to form an enlarged image of an object) is found in most hospitals and medical laboratories. The research behind the electron microscope led to Erwin Wilhem Muller's field ion microscope and the powerful scanning tunneling microscope (STM; developed by Heinrich Rohrer and Gerd Binnig), two of the most powerful optical tools in the world. In 1985 a new microscope was added to this list: the atomic force microscope (AFM). The AFM was invented by Binnig, Christoph Gerber of Zurich, Switzerland, and Calvin Quate (1923-) from California.
How AFM Works
The AFM uses a tiny needle made of diamond, tungsten (a hard, heavy metallic element often used in steel production), or silicon (a non-metallic chemical element found in most natural things). The AFM scans its subjects by lightly touching them with the needle. In this respect, it uses the subjects like a phonograph record. The AFM's needle reads the bumps on the subject's surface, rising as it hits the peaks and dipping as it traces the valleys. Of course, the topography (map survey) read by the AFM varies by only a few molecules up or down, so a very sensitive device must be used to detect the needle's rising and falling. In the original model, Binnig and Gerber used a STM to sense these movements. Other AFM's use a fine-tuned laser.
The AFM has already been used to study the supermicroscopic structures of living cells. American physicist Paul Hansma (1946-) and his colleagues at the University of California, Santa Barbara, are quickly becoming experts in AFM research. In 1989, this team succeeded in observing the blood-clotting process within blood cells. Hansma's team presented their findings in a thirty-three-minute movie, assembled from AFM pictures taken every ten seconds.
Other scientists are utilizing the AFM's ability to remove samples of cells without harming the cell structure. By adding a bit more force to the scanning needle, the AFM can scrape cells, making it the world's most delicate dissecting (to take apart) tool. Scientists hope to apply this method to the study of living cells, particularly floppy protein cells. The fragility of these cells makes them nearly impossible to view without distortion.
atomic force microscope
atomic force microscope (AFM), device that uses a spring-mounted probe to image individual atoms on the surface of a material, first developed by Gerd Binnig in 1986. Unlike the scanning tunneling microscope, which is also a scanning probe microscope, the AFM can be used on materials that do not conduct electricity. In the original AFM, the probe traverses the surface, moving upward due to bumps and downward due to depressions; a laser beam reflected from the tip of the probe measures the up and down movements, and the pattern of reflected light creates an image of the surface. Another type of AFM measures the sideways deflection of the tip caused by friction as the probe moves across the surface; differences in friction can be used distinguish different atoms and molecules on the material. A third variation employs a magnetic probe; this probe does not touch the material but moves up and down in reaction to the magnetic forces between the tip and the surface. In a microchip-size AFM, the electronic circuitry and multiple probes are integrated on a sliver of silicon; although less sensitive than a full-size AFM, the device has applications in microelectronics where the multiple probes make it possible to record images very quickly.