Analytical electron microscopy studies of radiation damage
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I.
INTRODUCTION
THE power of AEM in the characterization of materials, both structurally and compositionally, is based on two physical conditions: (1) electrons can be focused by either magnetic or electrostatic lenses, thus providing fine probe, imaging, and analysis capabilities, and (2) electrons interact strongly with materials, providing a variety of signals, each of which contains some infbmaation about the material. It is the high spatial resolution characterization that makes AEM attractive for structure-property correlations in numerous areas of materials science. Such is the case in radiation damage studies, where the development of AEM has provided the needed tools for microstructural and compositional characterization of irradiated materials. This capability has made significant contributions to the understanding of such phenomena as radiation-induced segregation, phase instability, embrittlement, and sensitization under irradiation. This paper will initially discuss several of the more widely used AEM techniques, review several applications of AEM to radiation damage studies, and, finally, discuss a spin-off from AEM studies of radiation damage, namely, the development of advanced austenitic steels for hightemperature use, based on principles developed from the comparison of phase equilibria under irradiation and thermal aging. II.
ANALYTICAL ELECTRON MICROSCOPY
Figure 1 illustrates some of the signals produced by the interaction of electrons with matter. These signals include "transmitted" and diffracted electrons which provide structural characterization through imaging and crystallographic characterization through electron diffraction. Backscattered and secondary electrons familiar EDWARD A. KENIK, Research Staff Member, is with the Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6376. This paper is based on a presentation made in the symposium "Irradiation-Enhanced Materials Science and Engineering" presented as part of the ASM INTERNATIONAL 75th Anniversary celebration at the 1988 World Materials Congress in Chicago, IL, September 25-29, 1988, under the auspices of the Nuclear Materials Committee of TMS-AIME and ASM-MSD. METALLURGICAL TRANSACTIONS A
from scanning electron microscopy (SEM) provide complementary information to that supplied by transmitted electrons in scanning transmission electron microscopy (STEM). Auger electrons provide near-surface compositional information, whereas inelastically scattered electrons and X-rays provide compositional information from thicker regions. A state-of-the-art analytical electron microscope combines high-performance lenses and a highbrightness electron source (i.e., LaB6 thermionic emission or field emission source) to produce usable electron probes at the nanometer size range, with a variety of detectors appropriate for several of the signals mentioned above. There are two basic configurations for electron-optical columns used in AEM. The first is based on the conventional (static beam) transmission e
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