Sub-angstrom resolution

Sub-angstrom resolution for electron microscopes. A typical scanning transmission electron microscope (STEM) operates at 100–300 keV and has a spatial resolution limited by both spherical and chromatic aberration to about 1.5–2.0 Å, roughly 50 times the electron wavelength. Now, researchers at Nion R&D in Kirkland, Washington, and IBM Corp’s T. J. Watson Research Center have demonstrated aberration-corrected STEM operation. The corrector has four main quadrupoles, three main octupoles, and about 28 other windings; all can be separately excited in real time to control the electrons. Very stable, computer-controlled power supplies and feedback systems proved essential for successful operation. With the new STEM, Philip Batson (IBM) has obtained 0.75-Å resolution at 120 keV with no extensive after-the-fact computer processing. The figure shows uncorrected (left) and corrected images of the crystal structure of a germanium–silicon alloy. Batson says that the new technology can open the way to smaller, smarter instruments. (P. E. Batson, N. Dellby, O. L. Krivanek, Nature 418 , 617, 2002 http://dx.doi.org/10.1038/nature00972 .)