See down to 0.6 Å

SURFACE SCIENCE

A milestone in electron microscopy--the first direct sub-angstrom imaging of a crystal lattice--has been reported by researchers at Oak Ridge National Laboratory and Nion, a company in Kirkland, Wash., that specializes in advanced electron-microscope optics [Science, 305, 1741 (2004)].

The researchers fitted a 300-kV scanning transmission electron microscope (STEM) at ORNL with a Nion aberration corrector and made a number of other technical enhancements to the system, producing what they believe to be the highest resolution electron microscope in the world.

In their images of a silicon crystal, they are able to distinguish columns of atoms that are 0.78 Å apart. The actual resolution limit of the microscope is 0.6 Å, according to team leader Stephen J. Pennycook, who heads ORNL's Electron Microscopy Group. This is a huge improvement over the resolution limit of 1.3 Å that they had before the aberration corrector was installed, he adds.

The team, which includes Peter D. Nellist at Nion and Matthew F. Chisholm at ORNL, also has imaged individual atoms in catalytic clusters. They expect their advance will allow single dopant or impurity atoms to be detected in various materials and nanostructures.

"This is an exciting result which shows that sub-angstrom imaging technology can now be applied to practical materials problems on a daily basis," says physicist Philip E. Batson of the IBM T. J. Watson Research Center in Yorktown Heights, N.Y.

Pennycook foresees the possibility of further improvements that will allow the group to achieve 0.3-Å resolution. He also hopes to achieve 3-D imaging of individual nanostructures.

At present, the ORNL STEM is a one-of-a-kind instrument, but Nion is planning to market a similar microscope with an even more advanced aberration corrector, according to Pennycook