Fig. 1

Time-resolved mega-eV electron diffraction. Snapshots of electron diffraction of MoSe₂ bilayer for Debye–Waller factor (DWF) measurements. Several families of diffraction planes are labeled in the last diffraction image for clarity (i.e., {100}, {110}, {200}, {210}, {300}, and {220}). A time-resolved kinetic plot that illustrates the suppression of diffraction intensity at {110} family is shown, where I ₀ and I denote the Bragg peak diffraction intensities at negative and positive delay times from the fit of experimental results. Each image is accumulated over ~7000 pulses from multiple scans with effective charge of ~20 fC per pulse at the sample target. The mean-square displacements, \(\left\langle {\Delta u^{\mathrm{2}}} \right\rangle _{\Delta T}\), are obtained by plotting \({\mathrm{ln}}\left( {\frac{{I_0}}{I}} \right)\) vs. Q ², where Q is 2π over interplanar spacing d