Precession Electron Diffraction Scanning in Transmission Electron Microscopes
Robert Stroud, NanoMEGAS USA
July 16, 2019
BME Conference Room; Tech E311
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Schedule:
11:00 AM - 12:30 PM - Talk
2:00 PM - 3:00 PM - Roundtable Discussion
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ASTAR Orientation Mapping in a Cu Film |
There is growing interest in using nanobeam diffraction mapping techniques to characterize the structure of materials at the nanoscale. With this technique, a series of diffraction patterns are collected in a transmission electron microscope and stored while the focused beam scans the sample. One of the main advantages is that acquired data is available for off-line processing of essential properties, like the local crystallographic texture or the phase distribution, with limited beam time.
Diffraction scanning techniques benefit from precession electron diffraction (PED). This is because precession is known to increase the number of reflections and to decrease the dynamic effect on the Bragg reflection intensities, which, in turn, improves the quality of the diffraction patterns. Typically, orientation and phase identifications are greatly improved.
Several post-processing strategies will be presented, including standard template matching, that have proven to be efficient for orientation/phase identification, and strain mapping. It will be shown that specific structural entities may be highlighted by producing so-called virtual dark-field images and by the construction of electron diffraction correlation coefficient maps that have been shown to reveal 3D information.
Measurement of strain with high spatial resolution and high precision is critical to monitor designed and unintended strain distributions. In this regard, strain mapping using nano-beam spot diffraction patterns in the transmission electron microscope is particularly interesting due to its relative ease of implementation and high spatial resolution.
TEM based 3-D diffraction tomography consists of collecting a series of randomly oriented diffraction patterns, in precession mode, all from the same crystal across a large TEM angular range. The resulting set of hkl reflection intensities, i.e. - the reciprocal cell of the crystal, enable direct cell and structure determination.
Several application examples will be presented including metals, thin films, semiconductors, nanoparticles, and organic crystals.
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As Sales Director for NanoMEGAS USA, Robert has responsibility for sales and service within North and South America. Previous sales and marketing positions, over the past 24 years, have included US Country Manager for Cameca Instruments, and Asia Pacific Sales Manager for FEI Company.
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