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Science 3 December 2004:
Vol. 306. no. 5702, pp. 1771 - 1773
DOI: 10.1126/science.1104739
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Reports

Coherent Atomic Motions in a Nanostructure Studied by Femtosecond X-ray Diffraction

M. Bargheer,1 N. Zhavoronkov,1 Y. Gritsai,1 J. C. Woo,2 D. S. Kim,2 M. Woerner,1* T. Elsaesser1

Reversible structural changes of a nanostructure were measured nondestructively with subpicometer spatial and subpicosecond temporal resolution via x-ray diffraction (XRD). The spatially periodic femtosecond excitation of a gallium arsenide/aluminum gallium arsenide superlattice results in coherent lattice motions with a 3.5-picosecond period, which was directly monitored by femtosecond x-ray pulses at a 1-kilohertz repetition rate. Small changes ({Delta}R/R = 0.01) of weak Bragg reflexes (R = 0.005) were detected. The phase and amplitude of the oscillatory XRD signal around a new equilibrium demonstrate that displacive excitation of the zone-folded acoustic phonons is the dominant mechanism for strong excitation.

1 Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, 12489 Berlin, Germany.
2 School of Physics, Seoul National University, Seoul 151-742, Korea.

* To whom correspondence should be addressed. E-mail: woerner{at}mbi-berlin.de

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Science. ISSN 0036-8075 (print), 1095-9203 (online)