Electron Source Needs for Dynamic Transmission Electron Microscopy (DTEM)
1 : Lawrence Livermore National Laboratory, Lawrence Livermore National Laboratory 7000 East Avenue • Livermore, CA 94550 - United States
(LLNL)
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Single-shot dynamic transmission electron microscopy (DTEM), which demands sufficient current density to capture a complete image or diffraction pattern in a single short exposure, presents unique technical challenges. The stringent requirements of real-space imaging on the nanosecond time scale demand a source with high current, high brightness, and a time-independent transverse phase-space profile. The performance can be expressed in terms of a dimensionless figure of merit, the coherent fluence, which is nearly invariant in a well-designed electron optical column. If the coherent fluence is poor at the source, then no amount of electron-optical engineering can rescue the performance. Because of this, the ultracold beam concept is an extremely promising avenue for the improvement of DTEM performance. Still, a high coherent fluence does not guarantee high performance of the entire system. The electron column needs to be properly engineered to minimize the effects of electron-electron interactions both before and after the sample. It remains an open question whether atomic-resolution electron microscopy will be possible with picosecond-scale single exposure times, but one thing is certain: It will not be possible if these very challenging issues are not addressed.
