Center for Functional Nanomaterials Seminar

In the previous two decades, important technological advancements have expanded the range of temporal resolution in transmission electron microscopes (TEM). Commercial direct-counting and single-electron detectors have revealed dynamics in the ms-timescale. Laser-actuated photoemission microscopes [1, 2] combined with beam scanning, spatially-parsed large area detectors [3], and sparse-sensing algorithms [4], can now unlock phenomena at the ?s to sub-ps timescales. Further optimization of the photoemission stage [5] and beam bunching technologies could potentially extend the temporal resolution into the deep fs-regime. The laser-actuated photoemission microscope however, almost always required new instrument and detector purchases or drastic microscope modifications, in addition to expertise in laser. In practice, this level of investment places time-domain electron microscopy beyond the reach for most research groups.

Following our earlier concept paper [6], I will be presenting modest modifications to a pair of commercial instruments – one Schottky (200 keV located here at BNL) [7] and one thermionic (300 keV located at NIST) [8] that can confer temporal information spanning the ns and ps range with MHz to GHz repetition rates, in the stroboscopic mode without an excitation laser. The key enabling technology is a pair of broadband phase-matched modulating and demodulating RF pulsers. We have demonstrated 11 ps and 30 ps on the 200 keV and 300 keV microscopes respectively. The placement of the pulsers, mounted immediately below the gun, allows for the preservation of all optical configurations otherwise available to the unmodified instrument, and therefore makes these instruments dual-mode, both stroboscopic time-resolved (strobe) and conventional continuous waveform (CW) capable.

In the stroboscopic mode, we recently demonstrated direct visualization of electromagnetic waves moving through a MEMS device [9]. In addition to its time-resolving capabilities, this technology is showing promise for beam damage reduction in soft matter and biomaterials by gating the electrons arriving at the sample [10]. This award-winning (2019 R&D 100 Award, 2020 Microscopy Today Innovation Awards) innovative approach to modifying in-service microscopes has already begun to alter the landscape of ultrafast electron microscopy and has the potential to greatly reduce the access barrier to nanoscale time- and frequency-domain physics.


[1] VA Lobastov, R Srinivasan, AH. Zewail, Proc. Natl. Acad. Sci. 102 (2005) 7069−7073. https://doi.org/10.1073/pnas.0502607102
[2] T LaGrange, et. al., Appl. Phys. Lett. 89 (2006) 044105. https://aip.scitation.org/doi/10.1063/1.2236263
[3] T LaGrange, BW Reed, DJ. Masiel, MRS Bulletin 40 (2015) 22-28. https://doi.org/10.1557/mrs.2014.282
[4] A Stevens, et al., Advanced Structural and Chemical Imaging 1 (2015). https://doi.org/10.1186/s40679-015-0009-3
[5] DA Plemmons and DJ Flannigan, Chemical Physics Letters 683 (2017) 186–192. https://doi.org/10.1016/j.cplett.2017.01.055
[6] J Qiu, et. al., Ultramicroscopy 161 (2016) 130. https://doi.org/10.1016/j.ultramic.2015.11.006
[7] C Jing, et al., Ultramicroscopy, 207 (2019) 112829. https://doi.org/10.1016/j.ultramic.2019.112829
[8] JW Lau, et. al., Rev. Sci. Instr. 91 (2020) 021301. https://doi.org/10.1063/1.5131758
[9] X Fu, et. al., Science Advances (accepted)
[10] H Choe, et. al., bioRxiv. https://doi.org/10.1101/2020.05.15.099036