Ultrafast Transmission Electron Microscopy
images (Figures 6a and 6b) have indistinguishable resolution between the native (continuous) and pulsed beam. Similarly, the ultrafast diffraction image (Figure 6c) is indistinguishable from the continuous beam image. Pulsed images in Figure 6 were acquired using a 2.6 GHz pulse train, resulting in a pulse duration of ∼3 ps (∼1 e-
/pulse). Details of the TEM are given in
the caption. For samples sensitive to high beam energies, the wide repetition range of the UFPTM
H74 has been shown to extend and
predict the onset of radiation damage at various ultrafast imaging conditions. Figure 7 contains the changes in the diffraction fading curves for paraffin (C36
) and purple
membrane (a plasma membrane of Halobacterium halobium), as the continuous electron beam is modulated using the UFPTM [28,29]. At 20% duty factor the accumulated dose was nearly doubled at the 1/e point, confirming the dose rate dependence versus a total fluence dependence on the lattice structure. Tis is an intriguing capability for biological samples, providing a route to reduce beam-induced damage at room temperature. Furthermore, due to the GHz-level frequencies of the RF UTEM techniques, these stroboscopic studies can be completed in a small fraction of the time of the complementary laser-UTEM technique.
Summary While most of
this article has been focused on the Figure 5: Ultrafast Pulser (UFPTM ) integration into TEM. UFPTM main column
elements: kicker (K1, K2) and aperture shown in inset. Reprinted from [26], with permission from American Association for the Advancement of Science.
to the native electron beam, losing negligible coherence when enabled. Excellent spatial resolution was achieved as the con- tinuous and pulsed beam are almost indistinguishable for the gold nanoparticle images shown in Figure 6. Te brightfield
introduction and application of the various UTEM techniques available, this section will summarize the capabilities of the techniques and address some of the pertinent implementation details for each of them. Table 1 lists the four UTEM techniques discussed and compares key characteristics of beam operation, sample excitation and overall performance. For the operation modes, DTEM is only a single-shot
technique that can be extended into the powerful movie mode, whereas a stroboscopic or single-electron regime is achievable with the other three techniques. For the RF UTEM techniques, the microscope may be operated in a continuous or native mode simply by turning off the RF; in a matter of seconds
Figure 6: Brightfield image and diffraction images comparing imaging capabilities of UFPTM 2021 September •
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(pulsed) and native instrument (continuous). Native instrument is JEOL JEM-2100F, UFPTM repetition rate of 2.6 GHz. Courtesy of Dr. Spencer Reisbick, Brookhaven National Laboratory. 51
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