Impacts of Hot Electron Diffusion, Electron-Phonon Coupling, and Surface Atoms on Metal Surface Dynamics Revealed by Reflection Ultrafast Electron Diffraction

Abstract

Metals exhibit nonequilibrium electron and lattice subsystems at transient times following femtosecond laser excitation. In the past four decades, various optical spectroscopy and time-resolved diffraction methods have been used to study electron-phonon coupling and the effects of underlying dynamical processes. Here, we take advantage of the surface specificity of reflection ultrafast electron diffraction (UED) to examine the structural dynamics of photoexcited metal surfaces, which are apparently slower in recovery than predicted by thermal diffusion from the profile of absorbed energy. Fast diffusion of hot electrons is found to critically reduce surface excitation and affect the temporal dependence of the increased atomic motions on not only the ultrashort but sub-nanosecond times. Whereas the two-temperature model with the accepted physical constants of platinum can reproduce the observed surface lattice dynamics, gold is found to exhibit appreciably larger-than-expected dynamic vibrational amplitudes of surface atoms while keeping the commonly used electron-phonon coupling constant. Such surface behavioral difference at transient times can be understood in the context of the different strengths of binding to surface atoms for the two metals. In addition, with the quantitative agreements between diffraction and theoretical results, we provide convincing evidence that surface structural dynamics can be reliably obtained by reflection UED even in the presence of laser-induced transient electric fields.

25 pages, 5 figures

References in corpus (11)

• Tracking ultrafast hot-electron diffusion in space and time by ultrafast thermo-modulation microscopy
• Electron-phonon coupling and energy flow in a simple metal beyond the two-temperature approximation
• Nonequilibrium Electron Interactions in Metal Films
• Ultrafast imaging of photoelectron packets generated from graphite surface
• Comment on "Structural Preablation Dynamics of Graphite Observed by Ultrafast Electron Crystallography"
• Ultrafast carrier-coupled interlayer contraction, coherent intralayer motions, and phonon thermalization dynamics of black phosphorus
• Accurate quantification of lattice temperature dynamics from ultrafast electron diffraction of single-crystal films using dynamical scattering simulations
• Strong Coupling of Self-Trapped Excitons to Acoustic Phonons in Bismuth Perovskite ${\text{Cs}}_3{\text{Bi}}_2{\text{I}}_9$
• Simultaneous Investigation of Ultrafast Structural Dynamics and Transient Electric Field by Sub-picosecond Electron Pulses
• Investigation of transient surface electric field induced by femtosecond laser irradiation of aluminum
• A brief review: Ultrafast electron diffractive voltammetry: General formalism and applications

Cited by in corpus (1)

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