|
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 materialscorrecting
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 |