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Researchers develop a technique to measure defects in materials with unprecedented accuracy

DOE/Brookhaven National Laboratory : 13 March, 2005  (Technical Article)
Researchers at the U.S. Department of Energy's Brookhaven National Laboratory have developed a technique to detect defects in materials with picometer accuracy.
This is the highest accuracy ever achieved in such measurements, akin to finding a speck of dust in an area as big as the United States. A picometer is a trillionth of a meter. The research is reported in today's issue of the journal Physical Review Letters.

Yimei Zhu, a materials physicist from Brookhaven who was the lead researcher in this project, said, 'Defects are tiny deviations from the normal positions of atoms in materials, and they often control a material's function. For example, certain defects allow a larger current to be transported without resistance in superconductors, or improve the electronic, magnetic and optical properties of semiconductors used in computers or digital equipment. This new technique enables researchers to measure defects with unprecedented accuracy, which is important for designing advanced materials.'

The researchers developed the new technique, which they named interferometry in coherent electron diffraction, using a one-of-a-kind transmission electron microscope. The technique is complementary to neutron-scattering techniques, which require reactors or accelerators; and x-ray scattering techniques, which require a synchrotron. Because of its small probe size and high spatial resolution, electron microscopy is particularly suited for the investigation of an extremely tiny area of a material, making it indispensable for research in nanometer-scale science and technology. In this new form of interferometry developed at Brookhaven, electrons from a coherent source of light hit a sample from different directions and form particular 'interference' patterns, which can be viewed by a detector. This information is then interpreted by scientists to measure defects in materials.

Brookhaven researchers' expertise in materials science coupled with a transmission electron microscope made the new technique possible. Built by JEOL of Tokyo according to Brookhaven researchers' specifications, the microscope on which the research was performed can magnify samples up to 50 million times. At this magnification, an atom looks as big as a ping pong ball, and a ping pong ball would look as big as the earth. One of the best instruments of its kind in the world, the microscope is tailored for research in solid-state physics, chemistry and biology, as well as materials science.
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