Multi-scale time-resolved electron diffraction: A case study in moir\'e materials

TL;DR

This paper demonstrates the use of a high-frame-rate hybrid pixel electron detector in ultrafast electron diffraction to study atomic motion and thermal transport in moiré heterobilayers, achieving high temporal and spatial resolution.

Contribution

It introduces a novel application of a high-performance hybrid pixel detector for ultrafast electron diffraction in moiré materials, enabling detailed time-resolved structural analysis.

Findings

Resolved diffuse scattering and moiré superlattice features.

Achieved shot-noise-limited diffraction difference imaging.

Mapped thermal transport and diffusion mechanisms in WSe₂/MoSe₂.

Abstract

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 deploy a hybrid pixel array direct electron detector to perform ultrafast electron diffraction experiments on a WSe$_2$/MoSe$_2$ 2D heterobilayer, resolving 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 chopping 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.