Excitation of longitudinal and transverse coherent acoustic phonons in nanometer free-standing films of (001) Si

Maher Harb, Weina Peng, Germán Sciaini, Christoph T. Hebeisen, Ralph Ernstorfer, Mark A. Eriksson, Max G. Lagally, Sergei G. Kruglik, and R. J. Dwayne Miller
Phys. Rev. B 79, 094301 – Published 9 March 2009

Abstract

Transmission electron diffraction is naturally sensitive to the detection of shear-type deformations in single-crystalline structures due to the effective tilting of the lattice planes characteristic of shear, but in general is insensitive to longitudinal phonon propagation. Here, we report on the generation and detection of both transverse and longitudinal coherent acoustic phonons in 33 nm free-standing (001)-oriented single crystalline Si films using femtosecond electron diffraction (FED) to monitor these laser-induced atomic displacements. The mechanism for excitation of the shear mode that leads to coupling to the longitudinal phonon is attributed to the inhomogeneous lateral profile of the optical-pump pulse and the periodic boundary condition imposed by the supporting grid structure. In this application, the constructive interference in the diffraction process makes FED particularly sensitive to the detection of coherent phonon modes and offers an atomic perspective of the dynamics involving collective motions.

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  • Received 18 September 2008

DOI:https://doi.org/10.1103/PhysRevB.79.094301

©2009 American Physical Society

Authors & Affiliations

Maher Harb1, Weina Peng2, Germán Sciaini1, Christoph T. Hebeisen1, Ralph Ernstorfer1,*, Mark A. Eriksson2, Max G. Lagally2, Sergei G. Kruglik1, and R. J. Dwayne Miller1,†

  • 1Departments of Chemistry and Physics, and Institute for Optical Sciences, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6
  • 2University of Wisconsin-Madison, Madison, Wisconsin 53706, USA

  • *Present address: Max-Planck-Institute of Quantum Optics, D-85748 Garching, Germany.
  • dmiller@lphys.chem.utoronto.ca

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Vol. 79, Iss. 9 — 1 March 2009

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