The Science of Scattering

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Murray Hill, N.J. (May, 1997) -- As is evident from the condition of his office, Phil Platzman is a theoretical physicist who likes to scatter things. Papers, publications, and periodicals of all sorts are scattered over virtually every surface, including much of the floor. Some might call it a mess, yet Platzman's propensity for scattering has paid off handsomely in scientific revelations, some practical products, and most recently in receipt of the prestigious Compton Award. Platzman shared the award, presented by the Argonne National Laboratory, with Peter Eisenberger, now vice provost of the Earth Institute at Columbia University, for their work in the scattering of X-rays.

Platzman came to Bell Labs from Caltech, where he had been working on quantum electrodynamics with the noted physicist, the late Richard Feynman. When he arrived here in 1960 as a post-doctoral fellow, or as he says, "a refugee from high-energy physics," Platzman's plan was to stay for two years and then move on. But plans do sometimes change. "I've been here for 37 years," he says, "the reason being...I'm a big Bell Labs fan."

X-Ray Scattering Microscope

It was about eight years after joining Bell Labs that Platzman became the head of the Scattering and Low Energy Physics Department where scientists were already scattering light. Bob Birgeneau, now dean of science and a professor at the Massachusetts Institute of Technology, had just arrived and was planning to scatter neutrons. Platzman, whose high-energy physics work was closely related to scattering, felt that X-rays should be scattered as well. To do so he hired Eisenberger from Harvard University where he had been working on electron magnetic resonance, and convinced him to turn his attention to X-rays.

In the physics sense, scattering is a method of investigating the properties of matter. Microscopes allow you to look at matter optically, but to study matter at the atomic level requires getting down into the X-ray range.

"X-rays are just a shorter wavelength version of light, but they allow you to look at things on a much finer scale, so you can learn things you can't learn with light," says Platzman.

[ Phil Platzman at work ]

Physicist Phil Platzman looks through a diffractometer, which is connected to a rotating anode X-ray machine. The diffractometer rotates a sample in extremely small increments, allowing scientists to study the energy level of X-rays as they bounce off the sample.

As the name implies, X-ray scattering involves firing X-rays at an object -- be it a semiconductor, a metal, an organic polymer or fluids such as water -- and observing the way they scatter.

Two Types of Scattering X-rays

There are two types of scattering: elastic and inelastic. Elastic scattering occurs when X-rays bounce off an object without any loss of energy. The angle at which they bounce provides information about the makeup of the object being studied. It is as though you bounce a ball and watch the direction of its rebound. If the ground is flat, the ball will come straight up, but if it strikes an uneven surface, the ball will veer off in a different direction, telling you something about the nature of the ground.

Conversely, inelastic scattering, involves observing how much energy an object absorbs from the X-rays.

"If you just want to see how things sit in the structure then you do elastic scattering," explains Platzman. "If you want to learn about the excitations you do inelastic scattering. And it is the excitations which determine most of the physical properties of condensed [solid] matter. That is, how it behaves when you heat it, pass current through it, or shine light on it. Understanding these properties is very important to the design of most of the products Lucent produces."

And it was largely for their pioneering work in the field of inelastic scattering that Platzman and Eisenberger received the Compton Prize.

Watching Flying X-rays

Of course, watching for the trajectories of flying X-rays, which are not visible to the human eye, and taking the appropriate measurements to understand the secrets they may reveal is no small task.

Measuring the energy of scattered X-rays, for example, involves the use of perfectly cut silicon crystals as detectors. As they are bombarded by X-rays bouncing off the object being tested, these crystals are rotated in excruciating small increments -- down to one hundred-thousandth of one degree. The X-rays are absorbed by the crystal at all but one angle, and it is the specific angle at which they are reflected rather than absorbed that reveals the energy of the X-rays.

The precision and uniqueness of many of the experiments conducted by Platzman and Eisenberger required that they literally invent some of the laboratory equipment they needed to make such observations. Some of these innovations have subsequently found their way into the commercial market.

One innovation born of pure research in X-ray science that has found its way into the commercial world is Lucent's recently announced microprobe, used to examine the structure of small, complex electronic devices such as lasers that go into various products.

This "real world" application was no accident, since lurking behind Platzman's and Eisenberger's research was the hope that it "would have a big impact on the company's long-term business, which is making devices," says Platzman. "But in order to make those devices you need to understand the materials from which they are made."

In addition to doing the science, Platzman has, over the years, served as a vigorous proponent of X-ray scattering, even when at one point it was falling out of favor.

"His impact over the long term was to make X-ray science important at Bell Labs, and he continues to do that," says Eric Isaacs, who Platzman hired nine years ago, and who continues to work with him on scattering. "Even through tough times when people were questioning it deeply, he was out there holding the flame high."

Advantages of Being a Dreamer

The satisfaction Platzman derives from his work is apparent. "Mostly," he says with exuberance, "we were having fun in the lab. And that sense of fun was contagious."

"Phil is a dreamer," adds Isaacs. "That's probably why I've had more fun with him than anyone I've ever worked with. He is really a good manager from a physicist's point of view. He would argue with you for a day, but if you could convince him you had good physics, you would get funded to do it."

In addition to his scientific accomplishments, Platzman takes great pride and pleasure in the people he has hired and mentored at Bell Labs, and in his ability to "tag along" with their work.

"One of the things I feel best about at Bell Labs is the fact that over the years I have been in research I hired a large number of people who have been very successful in the scientific world, and at Bell labs," he said. In fact, a list of Platzman's hires reads like a Who's Who in the rarefied upper echelons of the world of physics.