Accurate quantification of lattice temperature dynamics from ultrafast electron diffraction of single-crystal films using dynamical scattering simulations

TL;DR

This paper develops and applies dynamical scattering models for ultrafast electron diffraction of single-crystal films, significantly improving the accuracy of lattice temperature measurements compared to traditional kinematical models.

Contribution

It introduces dynamical scattering models tailored for quantitative UED analysis, demonstrating their effectiveness on ultrafast laser-heated gold films and highlighting their importance for accurate structural parameter retrieval.

Findings

Dynamical models outperform kinematical models by tenfold in fitting UED patterns.

Lattice temperature rise matches predictions based on optical constants.

Fitting Debye-Waller factors yields underestimated temperature values.

Abstract

In ultrafast electron diffraction (UED) experiments, accurate retrieval of time-resolved structural parameters, such as atomic coordinates and thermal displacement parameters, requires an accurate scattering model. Unfortunately, kinematical models are often inaccurate even for relativistic electron probes, especially for dense, oriented single crystals where strong channeling and multiple scattering effects are present. This article introduces and demonstrates dynamical scattering models tailored for quantitative analysis of UED experiments performed on single-crystal films. As a case study, we examine ultrafast laser heating of single-crystal gold films. Comparison of kinematical and dynamical models reveals the strong effects of dynamical scattering within nm-scale films and their dependence on sample topography and probe kinetic energy. Applying to UED experiments on an 11 nm thick film using 750 keV electron probe pulses, the dynamical models provide a tenfold improvement over a comparable kinematical model in matching the measured UED patterns. Also, the retrieved lattice temperature rise is in very good agreement with predictions based on previously measured optical constants of gold, whereas fitting the Debye-Waller factor retrieves values that are more than three times lower. Altogether, these results show the importance of dynamical scattering theory for quantitative analysis of UED and demonstrate models that can be practically applied to single-crystal materials and heterostructures.