Paper

Tracking the surface atomic motion in a coherent phonon oscillation

Agustsson, Steinn Ymir, Kutnyakhov, Dmytro, Pressacco, Federico, Hofmann, Philip, Demsar, Jure, Sanders, Charlotte E, Bühlmann, Kevin, Wurth, Wilfried, Curcio, Davide, Heber, Michael, Volckaert, Klara, Dziarzhytski, Siarhei, Acremann, Yves

2022

Overview

X-ray photoelectron diffraction is a powerful tool for determining the structure of clean and adsorbate-covered surfaces. Extending the technique into the ultrafast time domain will open the door to studies as diverse as the direct determination of the electron-phonon coupling strength in solids and the mapping of atomic motion in surface chemical reactions. Here we demonstrate time-resolved photoelectron diffraction using ultrashort soft X-ray pulses from the free electron laser FLASH. We collect Se 3d photoelectron diffraction patterns over a wide angular range from optically excited Bi\\(_2\\)Se\\(_3\\) with a time resolution of 140 fs. Combining these with multiple scattering simulations allows us to track the motion of near-surface atoms within the first 3 ps after triggering a coherent vibration of the A\\(_{1g}\\) optical phonons. Using a fluence of 4.2 mJ/cm\\(^2\\) from a 1.55 eV pump laser, we find the resulting coherent vibrational amplitude in the first two interlayer spacings to be on the order of 1 pm.

• Publisher: Cornell University Library, arXiv.org
• Subject: Adsorbates / Chemical reactions / Coherence / Diffraction patterns / Electrons / Fluence / Free electron lasers / Interlayers / Phonons / Photoelectrons / Soft x rays