Abstract: The transmission electron microscope (TEM) is a versatile instrument that combines imaging, diffraction and spectroscopy for characterizing the microstructure of a wide variety of materials. The fundamental principle of the TEM consists of forming an image with high spatial resolution that is coupled to an electron diffraction pattern, which is generated by the passage of a very high-energy electron beam through a suitably thin specimen that is amorphous or crystalline. Chemical analysis of the microstructure and features contained within, such as second phase precipitates, is accomplished in the TEM with appropriate analytical instruments such as X-ray energy dispersive spectroscopy (XEDS) and electron energy loss spectroscopy (EELS). However, understanding the relationship between the image and diffraction pattern that is generated in the TEM is paramount for analyzing the microstructure of materials. The generation and usefulness of: Selected area electron diffraction (SAED), Diffraction contrast, and convergent beam electron diffraction (CBED) will be discussed. Several examples based on the relationship between the crystal lattice and reciprocal lattice and corresponding image and diffraction pattern obtained by SAED and CBED will be given in order to gain an appreciation of the versatility that the TEM offers in materials science for characterizing amorphous or crystalline microstructures.
Speaker Bio: Dr. David Hoelzer has been a Research Staff Member in the Materials Science and Technology Division of Oak Ridge National Laboratory (ORNL) since May 2000. His research interests include the development of advanced high-temperature materials with emphasis on understanding the relationship between processing, microstructure and mechanical properties; the analysis of microstructures using analytical electron microscopy (AEM) focusing on understanding the crystallography of phases and the solid-state phase transformations; and the mechanical alloying processing. He was the principal investigator of several projects that led to successful development of the advanced oxide dispersion strengthened 14YWT ferritic alloy that contains a high concentration of nano-size Ti-, Y- and O-enriched clusters, or nanostructures. He also worked on investigating the relationship between microstructural texture and recrystallization behavior of Nb-1Zr and the investigation of the solute interactions between Ti and interstitial O, C and N impurities by studying the dynamic strain aging deformation behavior of V-4Cr-4Ti and vanadium. Prior to joining ORNL, Dr. Hoelzer was a TEM Technical Specialist and Adjunct Instructor at the New York State College of Ceramics at Alfred University (NYSCC), Alfred, NY for six years. He received his PhD, MS and BS from the University of Florida at Gainesville. He is presently a member of: ASM International, Materials Research Society (MRS), Electron Microscopy Society (EMSA) and Sigma Xi. (Source: https://www.ornl.gov/staff-profile/david-t-hoelzer)
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