Characterization of transverse electron pulse trains using RF powered traveling wave metallic comb striplines.

Advancements in ultrafast electron microscopy have allowed elucidation of spatially selective structural dynamics. However, as the spatial resolution and imaging capabilities have made progress, quantitative characterization of the electron pulse trains has not been reported at the same rate. In fact, inexperienced users have difficulty replicating the technique because only a few dedicated microscopes have been characterized thoroughly.

Stroboscopic ultrafast imaging using RF strip-lines in a commercial transmission electron microscope.

The development of ultrafast electron microscopy (UEM), specifically stroboscopic imaging, has brought the study of structural dynamics to a new level by overcoming the spatial limitations of ultrafast spectroscopy and the temporal restrictions of traditional TEM simultaneously. Combining the concepts governing both techniques has enabled direct visualization of dynamics with spatiotemporal resolutions in the picosecond-nanometer regime. Here, we push the limits of imaging using a pulsed electron beam via RF induced transverse deflection based on the newly developed 200 keV frequency-tunable strip-line pulser.

Coherent Phonon Disruption and Lock-In during a Photoinduced Charge-Density-Wave Phase Transition.

Ultrafast manipulation of phase domains in quantum materials is a promising approach to unraveling and harnessing interwoven charge and lattice degrees of freedom. Here we find evidence for coupling of displacively excited coherent acoustic phonons (CAPs) and periodic lattice distortions (PLDs) in the intensely studied charge-density-wave material, 1-TaS, using 4D ultrafast electron microscopy (UEM). Initial photoinduced Bragg-peak dynamics reveal partial CAP coherence and localized -axis dilations.

UEMtomaton: A Source-Available Platform to Aid in Start-up of Ultrafast Electron Microscopy Labs.

The steady rise in the number of ultrafast electron microscopy (UEM) labs, in addition to the opacity and lack of detailed descriptions of current approaches that would enable point-by-point construction, has created an opportunity for sharing common methods and instrumentation for (for example) automating data acquisition to assist in efficient lab start-up and to learn about common and robust protocols. In the spirit of open sharing of methods, we provide here a description of an entry-level method and user interface (UI) for automating UEM experiments, and we provide access to the source code and scripts (source-available) for ease of implementation or as a starting reference point for those entering or seeking to enter the field (https://github.com/CEMSFlannigan/UEMtomaton/releases/tag/v1.

Influence of Discrete Defects on Observed Acoustic-Phonon Dynamics in Layered Materials Probed with Ultrafast Electron Microscopy.

The structural anisotropy of layered materials leads to disparate lattice responses along different crystallographic directions following femtosecond photoexcitation. Ultrafast scattering methods are well-suited to resolving such responses, though probe size and specimen structure and morphology must be considered when interpreting results. Here we use ultrafast electron microscopy (UEM) imaging and diffraction to study the influence of individual multilayer terraces and few-layer step-edges on acoustic-phonon dynamics in 1T-TaS and 2H-MoS.