Advancements in UltraFast Electron Microscopy

<b>Abstract: </b>With the growing applications of temporally-resolved electron microscopy for probing basic chemical and electronic phenomena as well as reducing beam-induced damage, a multifaceted approach to ultrafast transmission electron microscopy is provided in this presentation. Traditionally accepted laser techniques with fixed image acquisition times have been complemented by ultrafast rf and microwave-driven techniques that can be synchronized with any sample excitation (laser, rf, thermal) with much faster image acquisition times (from days to minutes), thereby enabling more reliable data and microscope efficiency.<br/><br/>Keywords: ultrafast electron microscopy, stroboscopic, time-resolved imaging, high resolution transmission electron microscopy, beam damage.<br/><br/>Originally a basic research tool for materials science, transmission electron microscopes (TEMs) have seen a renaissance, as they have been applied in nearly every technology-based field. They have become the gold standard of high spatial resolution techniques and the ever-increasing applications from quantum dots to cellular 3D tomography and holography demand a much wider range of imaging capabilities. TEMs are used to connect photonics, nanodevice architecture, and biophysics, each with their individual intrinsic response times on the nanoscale. The continued evolution of applications and maturation of basic TEM instruments have not only created additional sectors in the TEM industry (life sciences, nanotechnology, and semiconductor), but have fostered significant growth in these areas that the new market sectors are comparable in size to the once dominant materials science market [1].<br/><br/>Generally, the picosecond regime is common for interrogating basic material phenomena, then longer time scales are generally necessary as material systems get larger physically. Ultrafast TEM (UTEM) was developed using lasers and photocathodes in the mid-2000s to interrogate time-resolved responses to optical stimuli [2]. While ultrafast lasers were a natural enabler for early research in UTEM, the explosive growth of these new applications based on large molecules (proteins, cells) and new 2D/3D architectures (NEMS/MEMS, nanosheets, spintronics) requires broader temporal capabilities due to their widely varying response times. If we include research focused on the mitigation of radiation damage from the microscope’s probe beam, an entirely new set of requirements and process space becomes critical. The material recovery time from beam induced damage between probe pulses, process temperature, sample area, etc., may all become variables to the imaging process. Especially in these cases, complementary enabling technologies (rf, microwave) have been used with simplified and typically improved imaging performance.<br/><br/>This presentation will also present the challenges for growing ultrafast techniques [3,4] and compares these complementary methods to laser UTEM techniques [3,4], for electron microscope users to consider when trying to expand their research capabilities. An update on UEM applications supported by recently developed techniques and extraordinary electron beam characteristics [7] as well as implementation perspectives will also be provided.<br/><br/><br/>References:<br/><br/>[1] Technavio. (2020). Transmission Electron Microscope Market by Applications, End-user, and Geography – Forecast and Analysis 2020-2024, Infiniti Research Limited.<br/>[2] A. H. Zewail, Annu Rev Phys Chem. <b>57 </b>(2006), p. 65. https://doi.org/10.1146/annurev.physchem.57.032905.104748<br/>[3] C. Jing, et al., Ultramicroscopy <b>207</b> (2019), p. 112829. https://doi.org/10.1016/j.ultramic.2019.<br/>[4] X. Fu, et al., Sci. Adv. <b>6</b> (2020), eabc3456. https://doi.org/10.1126/sciadv.abc3456<br/>[5] A. Arbouet, et al., in “Advances in Imaging and Electron Physics,” ed. P. W. Hawkes (Academic Press, New York) p. 1.<br/>[6] D. Flannigan and A. Zewail, Acc Chem Res <b>45</b> (2012), p. 1828. https://doi.org/10.1021/ar3001684<br/>[7] S. Reisbeck, et al., Ultramicroscopy <b>235</b> (2022), 113497.