Image of a strontium titanate grain boundary taken with Z-contrast TEM.

A microscope invented with Office of Science support is the first technique to produce a direct image of a complex atomic structure while also identifying the atoms involved. Steve Pennycook of Oak Ridge National Laboratory combined elements of three existing electron microscopes to make the Z-contrast microscope, which uses electrons bounced off (scattered from) a sample to form an image of the atoms. Because the scattered intensity depends on the atomic number (Z) of the chemical element being probed, the image intensity provides a means of identifying the atoms. The method improves on scanning electron microscopes (which produce clear images but cannot penetrate materials), transmission electron microscopes (which produces images that cannot be interpreted directly as atomic structure), and the hybrid scanning transmission electron microscope (which produces outstanding microanalysis but poor-quality images). Z-contrast microscopy is particularly suited to the viewing of interfaces, grain boundaries, and defects in materials-features that cannot be analyzed well using indirect means. The Z-contrast microscope won an R&D 100 award from R&D Magazine as a significant new technology. Pennycook also received the Materials Research Society Medal and the Kurt J. Heinrich Award of the Microbeam Analysis Society.

Scientific Impact: Z-contrast microscopy has had major impact on the study of materials structure. It has achieved the highest resolution of a crystal structure ever recorded in a microscope and provided new information on the atomic-scale structure and chemistry of a variety of materials—correcting previously published quasicrystal structures, for example.

Social Impact: Z-contrast microscopes are commercially manufactured. This tool is likely to lead to dramatic advances in structural materials, superconductors, and semiconductors, especially in the smoothness of interfaces where different materials join, and thereby pave the way for improved computers, fiber-optic communications, medical imaging, and laser-disc players.

Reference: M. F. Chisholm and S. J. Pennycook, "Z-Contrast Imaging of Grain-Boundary Core Structures in Semiconductors," MRS Bulletin 22, 53 (1997).

URL: http://www.ornl.gov/awards/cf/cfcitations/cfbios/pennycoo.htm
http://www.ornl.gov/reporter/no4/z_con.htm
http://www.ornl.gov/bes/BES/amis/amis.htm#highlights

Technical Contact: Don Freeburn, Office of Basic Energy Sciences, 301-903-3156

Press Contact: Jeff Sherwood, DOE Office of Public Affairs, 202-586-5806

SC-Funding Office: Office of Basic Energy Sciences