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

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

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 (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 f? Nichtlineare Optik und Kurzzeitspektroskopie, 12489 Berlin, Germany.
2 School of Physics, Seoul National University, Seoul 151-742, Korea.