Space-charge effects in ultrafast electron diffraction patterns from single crystals
Ultramicroscopy 116 (2012) p. 86–94
Robert P.Chatelain, Vance Morrison, Chris Godbout, Bas van der Geer, Marieke de Loos, Bradley J.Siwick
The impact of electron–electron interactions in the post-specimen region of ultrafast electron diffraction and dynamic transmission electronmicroscopy instruments has been studied. Specifically, space-charge induced distortions of ultrafast electron diffraction patterns from single crystal specimens and their dependence on electron bunch-charge, beamenergy, energyspread, focusing conditions and speciment hickness have been investigated using the General Particle Tracer code. We have found that these space-charge interactions lead to significant broadening and displacement of the Bragg spots at currently realizable electron beam illumination conditions. These impacts increase in severity with beam brightness and are reduced with increasing (relativistic) beam energies. The primary mechanism for the distortions has been determined to bespace-charge interactions between the scattered beamlets and the main unscattered beam. Overall, these results suggest that creative post-specimen electron optical design, relativistic beam energies and post-processing of diffraction patterns to correct for space-charge distortions hould be explored as routes to make good use of any futuree nhancements to beam brightness in UED and DTEM instruments.Compression of subrelativistic space-charge-dominated electron bunches for single-shot femtosecond electron diffractionon
Physical Review Letters, 105 (26), art. no. 264801 (2010).
Van Oudheusden, T., Pasmans, P.L.E.M., Van Der Geer, S.B., De Loos, M.J., Van Der Wiel, M.J., Luiten, O.J.
We demonstrate the compression of 95 keV, space-charge-dominated electron bunches to sub-100 fs durations. These bunches have sufficient charge (200 fC) and are of sufficient quality to capture a diffraction pattern with a single shot, which we demonstrate by a diffraction experiment on a polycrystalline gold foil. Compression is realized by means of velocity bunching by inverting the positive spacecharge- induced velocity chirp. This inversion is induced by the oscillatory longitudinal electric field of a 3 GHz radio-frequency cavity. The arrival time jitter is measured to be 80 fs.