The influence of crystal thickness on scattering and radiation of high-energy electrons in oriented crystals

Reducing Radiation Damage in Soft Matter with Femtosecond Timed Single-Electron Packets

“…Further, under such finely-controlled conditions, no direct comparisons have been made to conventional lowdose methods for precisely the same dose rate and the same total dose. 15 Here, we report our observations of a repeatable reduction in damage when using pulsed electron packets generated via fs laser excitation of a photocathode in a modified TEM as compared to a conventional thermionic beam for precisely the same dose rate and accumulated dose. By using fs laser excitation to precisely control the electron-emission process, we confine the probability of emission to a temporal range of 300 fs (full-width at half-maximum, FWHM) 20 for extremely regular peak-to-peak emission times.…”

“…Relative arrival times of 5,20, and 100 µs were tested for electron packets comprised of, on average, 1, 5, and 20 electrons. In general, damage increased with decreasing time 15 between electrons and with increasing electron number. Further, we find that improvements relative to conventional methods vanish once a threshold number of electrons per packet is reached.…”

“…10 Though the factors and the mechanisms associated with beam damage are numerous and multi-faceted, a number of practical approaches have been shown to significantly reduce negative effects (2). For example, cryogenic methods operate by holding the specimen at reduced temperatures during exposure in order to lower diffusion and kinetic reaction rates, to reduce mass loss, and to minimize the impact of beam-induced thermal effects, especially for 15 poorly-conducting materials (3,4). This has led to significant advances in the ability to study highly-sensitive specimens, such as soft matter and biological structures, at sub-nanometer spatial scales (5)(6)(7)(8).…”

“…Minimizing exposure of the specimen to electron irradiation via low-dose and low-dose-rate methods and the use of conductive coatings and substrates have also proven beneficial (9)(10)(11)(12)(13). Further related to controlling damage through dose, the method of dose 20 fractionation, which is based on the acquisition of fast, multi-frame scans or brief, stroboscopic multi-image series, has been shown to be a viable approach for minimizing beam-induced artifacts (14)(15)(16).…”

“…Further, though not attempting to leverage relaxation and self-healing, proposals for extending the concept of diffract-before-destroy to TEM have also been discussed (26)(27)(28)(29). In this approach, sufficient information would be acquired before any damage has occurred by using a 15 single, brief, large number-density electron packet. Unlike X-ray photons, however, electrons in such a dense packet will experience significant Coulomb repulsion, which will degrade coherence and limit resolutions (30, 31).…”