New Microscope Technology Breaks Smallness Barrier

Researchers obtained the improved resolution with a 200-kilovolt Z-contrast scanning transmission electron microscope (STEM), aided by a new technology called aberration correction. The direct images have been seen as verification of atom-scale resolution below one angstrom, and provide researchers with an important tool for creating advanced materials.

Scientists from the Oak Ridge [U.S.] National Laboratory (ORNL; Oak Ridge, TN, USA) described their results in the September 17, 2004, issue of the journal Science. "Looking down on a silicon crystal, we can see atoms that are only 0.78 angstroms apart, which is the first unequivocal proof that we're getting sub-angstrom resolution. The same image shows that we're getting resolution in the 0.6 angstrom range,” stated Dr. Stephen Pennycook, a researcher in the ORNL condensed matter sciences division. An angstrom is an atomic scale unit of measure of one-billionth of a meter, about the diameter of an atom.

The researchers worked with Nion Co. (Kirkland, WA, USA) to produce images of pairs of silicon atom columns in a crystal. Nion provided the aberration-correction technology that corrects errors introduced to the images by defects in the electron lenses. Even though the concept is not new, this technology was only recently made workable by improvements in computation methods and image-analysis algorithms.

Aberration-corrected microscopy provides a direct image with fewer chances for artifacts. Uncorrected microscopy can achieve sub-angstrom resolution by combining a group of many images to achieve one image, but it also increases the introduction of artifacts into the images.

By demonstrating columns of atoms and the position of introduced "dopant” atoms, the atom-scale images provide a new understanding of materials' characteristics, according to Dr. Pennycook. The enhanced images also enable scientists to more accurately model and predict the behavior of materials on computers before time-consuming and costly bench tests are performed.

"With aberration correction you can see everything better, basically. It's always better to see what's what. For the material, chemical, and nanosciences, you want to see what is going on at the atomic scale--how atoms bond and how things work,” said Dr. Pennycook.


Related Links:
Oak Ridge National Laboratory