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19 April 2005 (All day)
Physicists have found a way to bombard materials with extremely fast x-ray pulses--a technique that may provide a new method of studying transitions from solid to liquid at a very detailed level.
There are many ways of studying the atomic bonds and molecular interactions that give materials their strength and other fundamental properties. One of the most recently developed methods is to probe a material with ultra fast x-ray pulses--a technique that reveals how atomic bonds change over a very short time scale. To achieve a more detailed analysis of this process, scientists have struggled to increase the frequency and the intensity of these pulses.
Physicists at the Stanford Synchrotron Radiation Laboratory (SSRL) in Menlo Park, California, have now managed to produce such ultra fast pulses. The big challenge was to compress the electron bunches, sent out by the linear accelerator SLAC, to ultra short duration. Another challenge was to synchronize a laser with the x-ray source. The combination allows the x-ray pulses to be fast, accurate, and powerful enough to make almost any material reveal new properties.
The team tested the method on indium antimonide, a crystal suspected of rapidly changing its atomic structure while melting. When the x-ray source sent out pulses as short as 80 millions of billionths of a second, the researchers could see the first short period of the crystal melting, which occurred in an unexpected way: The atoms diverged from their initial energy equilibrium while the average crystalline structure remained--a rarely studied behavior that could not have been seen as clearly with other techniques.
The researchers say the method can be used to probe many materials in a more detailed way. It also helps answer a long-standing problem in condensed matter physics, concerning how solids transform into liquids on ultra fast time scales. "By using this technique, we open a new window into the atomic scale world," says physicist Aaron Lindenberg, lead author of the paper published 15 April in Science. "This is spectacular work," says Steve Yalisove, a materials scientist at the University of Michigan in Ann Arbor. He notes the new technique could someday be used on jet turbine blades, for example, to more accurately assess their integrity and durability.
More on the study from SLAC