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March 26th, 2010

High-res Z-contrast photos can distinguish atoms

Published on March 26th, 2010 | By: pwray@ceramics.org
Individual boron and nitrogen atoms are clearly distinguished by their intensity in this Z-contrast scanning electron transmission microscope image from Oak Ridge National Laboratory. Each single hexagonal ring of the boron-nitrogen structure, for instance the one marked by the green circle in the figure a, consists of three brighter nitrogen atoms and three darker boron atoms. The lower (b) image is corrected for distortion. (Credit: ORNL.)

Individual boron and nitrogen atoms are clearly distinguished by their intensity in this Z-contrast STEM image. Each single hexagonal ring of the boron-nitrogen structure consists of three brighter nitrogen atoms and three darker boron atoms. The lower (b) image is corrected for distortion. (Credit: ORNL.)

According to a press release, using a special Z-contrast scanning transmission electron microscope, researchers at Oak Ridge National Laboratory took the first picture detailed enough to differentiate different atoms within a chemical compound. This super-high resolution scanning may play an important role in the future of materials chemistry, where tiny atomic differences can have profound effects on the properties of different chemical compounds.

This is not the first picture of an atom, nor is it the first picture of atoms from different elements. However, in those older photos, the atoms were arranged beforehand by scientists. But in the Oak Ridge pic, the material was created chemically, and the picture was still able to identify individual atoms.

“This research marks the first instance in which every atom in a significant part of a non-periodic material has been imaged and chemically identified,” says Materials Science and Technology Division researcher Stephen Pennycook. “It represents another accomplishment of the combined technologies of Z-contrast STEM and aberration correction.”

The material in the photo, boron nitride, consists of boron, nitrogen, and oxygen, with some carbon atoms inserted in place of boron to serve as a control in the image. The STEM that took the picture used a 60 kilovolt beam. That’s a very low energy for this kind of microscope, because if the beam were any more powerful, it would displace some of the atoms in the compound.

Right now, scientists can only determine the chemical arrangements in a material through chemistry. By developing a technique for taking pictures like this, material chemists and engineers of the future will be able to simple look at the chemical compound to see its geometry and composition.

The team’s Z-contrast STEM analysis is described in an article published today in the journal Nature.

 


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