Movie-mode dynamic electron microscopy
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Introduction The rising prevalence of in situ techniques in transmission electron microscopy (TEM) highlights an important fact: Conventional microscopy on static samples captures only what the sample is (structure) and not what it does (dynamics). Modern applications, ranging from materials science to biology to nanotechnology, demand an understanding of microscale and nanoscale dynamics, and in situ TEM fills this need by revealing not just the start and end states of a process, but also the states in between. Such information is crucial for the development and testing of models for mesoscale (∼1 nm to ∼10 μm) dynamics and predictive capabilities for designing nanotechnological systems. Yet, many in situ TEM instruments are limited to conventional video frame rates (∼33 ms), often far too slow to catch the relevant dynamics. At such frame rates, 10 nm of motion blur corresponds to a feature moving at only ∼0.3 μm/s, an exceptionally slow speed compared to many dynamical processes such as microstructural evolution in phase transformation fronts, with characteristic speeds of some millimeters or meters per second.1 Capturing such processes requires nanosecondscale resolution. Many studies on condensed-matter physics require even higher time resolutions, at the picosecond level or lower.
These needs motivate today’s efforts to improve TEM time resolution by orders of magnitude through dynamic and ultrafast TEM (DTEM and UTEM, respectively). DTEM and UTEM, along with femtosecond lasers, free-electron x-ray lasers, high harmonic generation, and ultrafast electron diffraction, are part of an ongoing revolution in high-time-resolution studies in chemistry, materials science, biology, atomic physics, and condensed-matter physics. Although all of these fields benefit from recent developments in lasers, electron sources, and electronics, they also share a long history, with roots going back many decades, and time-resolved electron microscopy is no exception. In the mid-1960s, Spivak et al. developed a multishot accumulation (i.e., stroboscopic) system to study magnetic domain wall motion, achieving microsecond time resolution by gating the thermionic electron source in a scanning electron microscope.2 Enabled by the development of pulsed lasers in the 1970s, Bostanjoglo and co-workers improved the temporal resolution of in situ TEM observations to nanosecond time scales using pulsed lasers to generate short electron bunches through thermal emission and later by UV-stimulated photoemission.3–6 Bostanjoglo and Domer especially focused on the single-shot approach in which a single pulse contains enough electrons to form a complete image.6 More recently, Zewail and co-workers pushed the temporal resolution of the
Thomas LaGrange, Integrated Dynamic Electron Solutions, CA, USA; [email protected]. Bryan W. Reed, Integrated Dynamic Electron Solutions, CA, USA; [email protected] Daniel J. Masiel, Integrated Dynamic Electron Solutions, CA, USA; [email protected] DOI: 10.1557/mrs.2014.282
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MRS BULLETIN • VOLUME 40 • JANUA
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