Researchers at McGill University have succeeded in simultaneously observing the reorganizations of atomic positions and electron distribution during the transformation of the "smart material" vanadium dioxide (VO2) from a semiconductor into a metal -- in a time frame a trillion times faster than the blink of an eye.
The results, reported Oct. 24 in Science, mark the first time that experiments have been able to distinguish changes in a material's atomic-lattice structure from the relocation of the electrons in such a blazingly fast process.
The measurements were achieved thanks to the McGill team's development of instrumentation that could be used by scientists in a variety of disciplines: to examine the fleeting but crucial transformations during chemical reactions, for example, or to enable biologists to obtain an atomic-level understanding of protein function. This ultrafast instrumentation combines tools and techniques of electron microscopy with those of laser spectroscopy in novel ways.
"We've developed instruments and approaches that allow us to actually look into the microscopic structure of matter, on femtosecond time scales (one millionth of a billionth of a second) that are fundamental to processes in chemistry, materials science, condensed-matter physics, and biology," says Bradley Siwick, the Canada Research Chair in Ultrafast Science at McGill.
"We're able to both watch where nuclei go, and separate that from what's happening with the electrons," says Siwick, an associate professor in the departments of Chemistry and Physics. "And, on top of that, we are able to say what impact those structural changes have on the property of the material. That's what's really important technologically."
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