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Geoffrey H. CAMPBELL (Lawrence Livermore National Laboratories)

“Crystal-Amorphous Phase Transition” taken with 20-ns TEM

Title: Time resolved electron microscopy for in situ experiments
Author: Geoffrey H. Campbell, Melissa K. Santala1, and Joseph T. McKeown
Affiliation: Materials Science Division, Lawrence Livermore National Laboratory, Livermore, CA 94550 USA
1Now at Oregon State University, Corvallis, OR 97331 USA
Email: ghcampbell[at]llnl.gov
URL: https://sc-programs.llnl.gov/html/bes/dtemSCW0974.html
Abstract:

False color images of the growth of crystalline germanium-telluride (yellow) into amorphous germanium-telluride (blue) in a series of 17.5-nsec electron images during crystallization induced by a 12-nsec laser pulse. The time signature in each frame is relative to the peak laser intensity on the specimen. Image: Lawrence Livermore National Laboratory

“Crystal-Amorphous Phase Transition” taken with 20-ns TEM
   by Dr. Campbell et al., Lawrence Livermore National Lab.
Transmission electron microscopy has functioned for decades as a platform for in situ observation of materials and processes with high spatial resolution. Yet the dynamics often remain elusive, as they unfold too fast to discern at these small spatial scales under traditional imaging conditions. Simply shortening the exposure time in hopes of capturing the action has limitations, as the number of electrons will eventually be reduced to the point where noise overtakes the signal in the image. Pulsed electron sources with high instantaneous current have successfully shortened exposure times (thus increasing the temporal resolution) by about six orders of magnitude over conventional sources while providing the necessary signal-to-noise ratio for dynamic imaging. We describe here the development of this new class of microscope and the principles of its operation, with examples of its application to problems in materials science.
This work performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.
Biographical Sketch: Geoffrey H. Campbell earned his BS in Materials Science from MIT in 1984, his MS at UC Berkeley in 1986 and his Ph.D. from UC Santa Barbara in 1990. As a student, Campbell developed an interest in the application of transmission electron microscopy to materials science topics. He took a post-doctoral position at the Max Planck Institute for Metals Research in Stuttgart, where he was an Alexander von Humboldt Foundation scholar, working on the determination of the atomic structure of grain boundaries in BCC metals by high resolution electron microscopy. Since 1991, Campbell has been at Lawrence Livermore National Laboratory and his interests have involved the behavior of grain boundaries and interfaces, fundamental aspects of plasticity, laser/material interactions, high strain-rate deformation, and fragmentation. Since 2004, he has worked on time resolved electron microscopy applied to dynamic response of materials. In 2006, he became group leader for the Ultrafast Materials Science group.

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