Ultrafast electron diffraction from a Bi(111) surface: Impulsive lattice excitation and Debye–Waller analysis at large momentum transfer

The lattice response of a Bi(111) surface upon impulsive femtosecond laser excitation is studied with time-resolved reflection high-energy electron diffraction. We employ a Debye–Waller analysis at large momentum transfer of 9.3 Å−1 ≤ Δ k ≤ 21.8 Å−1 in order to study the lattice excitation dynamics...

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Veröffentlicht in:Structural dynamics (Melville, N.Y.) N.Y.), 2019-05, Vol.6 (3), p.035101-035101
Hauptverfasser: Tinnemann, V., Streubühr, C., Hafke, B., Kalus, A., Hanisch-Blicharski, A., Ligges, M., Zhou, P., von der Linde, D., Bovensiepen, U., Horn-von Hoegen, M.
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Sprache:eng
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Zusammenfassung:The lattice response of a Bi(111) surface upon impulsive femtosecond laser excitation is studied with time-resolved reflection high-energy electron diffraction. We employ a Debye–Waller analysis at large momentum transfer of 9.3 Å−1 ≤ Δ k ≤ 21.8 Å−1 in order to study the lattice excitation dynamics of the Bi surface under conditions of weak optical excitation up to 2 mJ/cm2 incident pump fluence. The observed time constants τint of decay of diffraction spot intensity depend on the momentum transfer Δk and range from 5 to 12 ps. This large variation of τint is caused by the nonlinearity of the exponential function in the Debye–Waller factor and has to be taken into account for an intensity drop ΔI > 0.2. An analysis of more than 20 diffraction spots with a large variation in Δk gave a consistent value for the time constant τT of vibrational excitation of the surface lattice of 12 ± 1 ps independent on the excitation density. We found no evidence for a deviation from an isotropic Debye–Waller effect and conclude that the primary laser excitation leads to thermal lattice excitation, i.e., heating of the Bi surface.
ISSN:2329-7778
2329-7778
DOI:10.1063/1.5093637