Structural dynamics of laser-irradiated gold nanofilms

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 o...

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Bibliographic Details
Published in:Physical review. B, Condensed matter and materials physics Condensed matter and materials physics, 2013-11, Vol.88 (18), Article 184101
Main Authors: Daraszewicz, Szymon L., Giret, Yvelin, Naruse, Nobuyasu, Murooka, Yoshie, Yang, Jinfeng, Duffy, Dorothy M., Shluger, Alexander L., Tanimura, Katsumi
Format: Article
Language:English
Subjects:
Dynamics
Electronics
Evolution
Fluence
Gold
Mathematical models
Melting
Nanostructure
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Summary: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 LIED 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.
ISSN:1098-0121
1550-235X
DOI:10.1103/PhysRevB.88.184101