MeV Electron Time-Resolved Total Scattering for Material Dynamics

The MeV electrons produced by the photocathode RF gun made it feasible for MeV ultrafast electron scattering [1-2]. MeV ultrafast electron scattering became a new frontier in ultrafast science due to its capability of following dynamics on femtoseconds scale with the high spatial resolution and sensitivity [3-4]. Furthermore, MeV electrons experience less multiple-scattering, and possess “real” flat Ewald-sphere; MeV ultrafast electron diffraction (MeV-UED) is an ideal tool to explore both structure and dynamics using total scattering technique. Total scattering has been explored by X-ray and Neutron scattering communities to study energy materials, the time-resolved total scattering enabled by MeV-UED make it feasible to image strcture dynamics and energy transfer in 2-D heterostructure [3] and revealing the intricate relation between dynamics and function of 2-D perovskite [4].<br/><br/>I will discuss many advantages of MeV electron for total scattering. MeV electron total scattering not only produces stronger diffraction signal and sensitive to the structure change, but also has less background and no geometric correction. Furthermore, we have experimentally demonstrated that MeV electron total scattering is capable of probing both electronic and nuclear structure dynamic [5]. MeV-UED enabled the first ultrafast operando [6] and in-situ [7] experiments.<br/><br/>1. X.J. Wang et al, Phys. Rev. E , 54, No.4, R3121 -3124 (1996).<br/>2. X.J. Wang et al, Proceedings of the 2003 Particle Accelerator Conference, 2003, pp. 420-422 Vol.1, doi: 10.1109/PAC.2003.1288940.<br/>3. J. Sood, et al, “Bidirectional phonon emission in two-dimensional heterostructures triggered by ultrafast charge transfer”<b>,</b> Nat. Nanotechnol.18, 29–35 (2023).<br/>4. H. Zhang et al., “Ultrafast relaxation of lattice distortion in two-dimensional perovskites”, Nature Physics <b>volume 19</b>, pages 545–550 (2023).<br/>5. J. Yang et al, "Simultaneous observation of nuclear and electronic dynamics by ultrafast electron diffraction", Science 368, 885 (2020).<br/>6. A. Sood et al, "Universal phase dynamics in VO₂ switches revealed by ultrafast operando diffraction", <i>Science</i> <b>373</b>, 352 (2021).<br/>7. P. K. Muscher et al, "Highly Efficient Uniaxial In-Plane Stretching of a 2D Material via Ion Insertion", <i>Adv. Mater.</i> <b>33</b>, 2101875 (2021).