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

OPTICAL diffraction; FEMTOCHEMISTRY; X-rays; NANOSTRUCTURES; ARSENIDES; SUPERLATTICES

Reversible structural changes of a nanostructure were measured non-destructively 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 (ΔR/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. [ABSTRACT FROM AUTHOR]

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