Multi-scale time-resolved electron diffraction enabled by high repetition rate, high dynamic range direct electron detection

Ultrafast-optical-pump -- structural-probe measurements, including ultrafast electron and x-ray scattering, provide direct experimental access to the fundamental timescales of atomic motion, and are thus foundational techniques for studying matter out of equilibrium. High-performance detectors are needed in scattering experiments to obtain maximum scientific value from every probe particle. We present the first ultrafast electron diffraction experiments to deploy a hybrid pixel array direct electron detector, and we show that its single-particle sensitivity, high dynamic range and 1 kHz frame rate enable new probe modalities in electron-based structural dynamics. Specifically, we perform measurements on a WSe$_2$/MoSe$_2$ 2D heterobilayer that resolve the weak features of diffuse scattering and moir\'e superlattice structure without saturating the zero order peak. Enabled by the detector's high frame rate, we show that a lock-in technique provides diffraction difference images with signal-to-noise at the shot noise limit. Finally, we demonstrate that a fast detector frame rate coupled with a high repetition rate probe can provide continuous time resolution from femtoseconds to seconds, enabling us to perform a scanning ultrafast electron diffraction experiment that maps thermal transport in WSe$_2$/MoSe$_2$ and resolves distinct diffusion mechanisms in space and time.