Decelerated lattice excitation and absence of bulk phonon modes at surfaces: Ultra-fast electron diffraction from Bi(111) surface upon fs-laser excitation

V Tinnemann; C Streubühr; B Hafke; T Witte; A Kalus; A Hanisch-Blicharski; M Ligges; P Zhou; D von der Linde; U Bovensiepen; M Horn-von Hoegen

doi:10.1063/1.5128275

Decelerated lattice excitation and absence of bulk phonon modes at surfaces: Ultra-fast electron diffraction from Bi(111) surface upon fs-laser excitation

Struct Dyn. 2019 Nov 5;6(6):065101. doi: 10.1063/1.5128275. eCollection 2019 Nov.

Authors

Affiliation

¹ Department of Physics and Center for Nanointegration (CENIDE), University of Duisburg-Essen, 47048 Duisburg, Germany.

Abstract

Ultrafast reflection high-energy electron diffraction is employed to follow the lattice excitation of a Bi(111) surface upon irradiation with a femtosecond laser pulse. The thermal motion of the atoms is analyzed through the Debye-Waller effect. While the Bi bulk is heated on time scales of 2 to 4 ps, we observe that the excitation of vibrational motion of the surface atoms occurs much slower with a time constant of 12 ps. This transient nonequilibrium situation is attributed to the weak coupling between bulk and surface phonon modes which hampers the energy flow between the two subsystems. From the absence of a fast component in the transient diffraction intensity, it is in addition concluded that truncated bulk phonon modes are absent at the surface.