Direct Subangstrom Resolution Demonstrated

A team of scientists from Oak Ridge National Laboratory in Tennessee and Nion Co. in Kirkland, Wash., has used an aberration-corrected scanning transmission electron microscope to directly resolve subangstrom features in a silicon crystal lattice. The achievement, reported in the Sept. 17 issue of Science, suggests the potential of the technology to offer greater insights into the atomic-scale origins of material properties.

Subangstrom imaging has been achieved indirectly in a transmission electron microscope by processing a series of images to correct for spherical aberration, but the method can introduce artifacts. The new work, which used a 300-kV instrument fitted with a Nion spherical aberration corrector, imaged such atomic-scale features directly, with no evidence of distortion.

To demonstrate the approach, the scientists collected annular dark-field images of a silicon crystal in the [112] orientation, presenting the instrument with pairs of silicon columns 78 pm apart. Without aberration correction, the microscope has a resolution limit of 130 pm in this mode. With correction, 78-pm column spacing was apparent, and a Fourier transform of the image displayed 61-pm spacings.