Structural dynamics of laser-irradiated gold nanofilms

Szymon L. Daraszewicz, Yvelin Giret, Nobuyasu Naruse, Yoshie Murooka, Jinfeng Yang, Dorothy M. Duffy, Alexander L. Shluger, and Katsumi Tanimura
Phys. Rev. B 88, 184101 – Published 5 November 2013

Abstract

We performed relativistic ultrafast electron diffraction (UED) measurements of the structural dynamics of photoexcited gold nanofilms and developed an atomistic model, based on the two-temperature molecular dynamics (2T-MD) method, which allows us to make a direct comparison of the time evolutions of measured and calculated Bragg peaks. The quantitative agreement between the temporal evolutions of the experimental and theoretical Bragg peaks at all fluences suggests that the 2T-MD method provides a faithful atomistic representation of the structural evolution of photoexcited gold films. The results reveal the transition between slow heterogeneous melting at low absorbed photon fluence to rapid homogeneous melting at higher fluence and nonthermally driven melting at very high fluence. At high laser fluence, the time evolution of Bragg peaks calculated using the conventional 2T-MD model disagrees with experiment. We show that using an interatomic potential that directly depends on the electron temperature delivers a much better agreement with UED data. Finally, our ab initio calculations of phonon spectra suggest electronic bond softening, if the nanofilms can expand freely under electronic pressure, and bond hardening, if they are constrained in all three dimensions.

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  • Received 20 March 2013

DOI:https://doi.org/10.1103/PhysRevB.88.184101

©2013 American Physical Society

Authors & Affiliations

Szymon L. Daraszewicz1, Yvelin Giret1,2, Nobuyasu Naruse2, Yoshie Murooka2, Jinfeng Yang2, Dorothy M. Duffy1, Alexander L. Shluger1, and Katsumi Tanimura2

  • 1Department of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, United Kingdom
  • 2The Institute of Scientific and Industrial Research (ISIR), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan

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Issue

Vol. 88, Iss. 18 — 1 November 2013

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