Revealing Electron–Phonon Interactions and Lattice Dynamics in Nanocrystal Films by Combining in Situ Thermal Heating and Femtosecond Laser Excitations in 4D Transmission Electron Microscopy

We present a comparative investigation on static equilibrium and transient structural dynamics of nanocrystalline gold films on silicon nitride supports performed at various in situ temperatures and by ultrafast laser excitations in a four-dimensional ultrafast transmission electron microscope (4D-UTEM). The change of relative diffraction intensity and lattice spacing with rising temperatures was systematically measured for {220} Debye–Scherrer rings via the in situ heating technique, which leads to a precise determination of the actual Debye temperature and a finding of significant depression of lattice expansions in the films. The diffraction intensity/lattice spacing–temperature relationship calibrated by the static, thermally equilibrium observations was then employed for investigating ultrafast transient dynamics on the same specimen region. The electron–phonon coupling constant g was determined to be 7.2 × 1015 W/m3 K in combination with simple two-temperature model analysis. We found a marked varia...