Viewing new subatomic worlds
Assembly has begun on an electron microscope expected to advance the state of the art to such an extent that its use may open previously unknown branches of science to study.
University of Chicago physicist Albert Crewe designed the new instrument and is supervising its construction at the university. Professor Crewe built the first microscope capable of observing a single atom.
With a projected ability to resolve objects as minute as one-half an angstrom (two billionths of an inch), the microscope will be the first capable of directly observing the atomic structure of almost any solid material. Since atoms in most substances are spaced about one angstrom apart, the most powerful existing microscopes, unable to resolve objects smaller than about two angstroms , can observe only certain larger atoms under special conditions.
The instrument's unprecedented resolution is due largely to Crewe's recent invention of a device that corrects the inherent distortions in an electron microscope's magnetic lenses.
Crewe says he sees this technology being applied to ''countless problems where a substance's structure at the atomic level is not known, and actually visualizing it would be taking a very substantial step forward.''
The microscope's power, specialists say, will make it an invaluable research tool for studies of ceramics, metallurgy, chemical catalysts, and certain biological science applications. The understanding of atomic structures in these areas may eventually lead to the development of lighter, stronger, metal alloys, improvements in the semiconductor components used throughout the entire electronics industry, and potential leaps in medical technology.
''It's going to be a tool that eventually all the big engineering corporations will have in their research labs,'' says Steven Sibener, a Chicago chemist studying catalysts. ''It will be a very viable, useful tool - not merely esoteric.''
Yet equally promising is the instrument's potential for introducing vital, although perhaps esoteric, scientific issues that have yet to be even thought of. ''When Galileo looked at the moon with his meager 10-power telescope,'' says ceramics Prof. David Kingery of the Massachusetts Institute of Technology, ''he couldn't imagine a lot of the questions that came up. Neither can we.''
''You're going to be opening all kinds of new properties when you're able to resolve on such a subatomic scale,'' adds Mr. Sibener.
Atoms are the basic units of all matter. Because atoms are several thousand times smaller than a light wave, it is impossible to reveal them with a conventional light microscope, no matter how powerful it may be.
Thus an electron microscope uses electrons - negatively charged subatomic particles of energy that spin about the atom's nucleus - instead of light to ''see'' objects.
Inside the Scanning Transmission Electron Microscope (STEM) Crewe invented, a stream of electrons roughly analagous to the light source of an optical microscope is generated at the tip of a tungsten wire. A bank of magnetic lenses focuses the beam to a width under half an angstrom. This precision beam scans the target area, probing the dimensions of electron clouds surrounding the atoms.
When the beam hits an atom, some of the electrons are deflected to form a characteristic pattern of that atom. Sensors are used to detect the deflected electrons, which are then amplified and displayed in a television-type screen.
Crewe's approach to improving the accuracy of the electron beam is to ''fine tune'' the magnetic lens. Earlier attempts had failed because the enormous complexity of this type of correcting device made it impossible to build. But his device is vastly simplified and, he feels, more effective.
Crewe's 200,000-volt microscope supposedly will have resolution abilities more than three times as powerful as the best 1 million-volt instruments that are currently considered the state of the art.
Will it work? Crewe says he is ''90 percent confident'' that the device will work up to theoretical predictions. But he emphasizes that it has yet to be actually built. ''There are some parts we're just figuring out how to make.'' But Crewe points to the confidence of others in the success of this project. ''The National Science Foundation thinks it will work. So does IBM.''
The National Science Foundation has given Crewe a grant of nearly $1 million to construct the microscope. IBM has provided a large computer system with which the instrument will be operated.
Crewe says even if the corrector does not operate up to expectations, the instrument would still represent a significant breakthrough in electron microscopy. ''Each time you improve resolution, you open a new window and there's a whole host of things to do,'' he says. ''What we have done is to try to open another window.''