Transient lattice contraction in the solid-to-plasma transition

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Science Advances  29 Jan 2016:
Vol. 2, no. 1, e1500837
DOI: 10.1126/sciadv.1500837
  • Fig. 1 Experimental scheme for the solid-to-plasma transition in xenon nanoclusters.

    (A) An initial 10-fs hard x-ray pulse ionizes the Xe cluster and forms a nanoplasma. A second 10-fs x-ray pulse at slightly lower photon energy measures geometrical and electronic properties of the plasma. Bragg peaks are recorded on an x-ray detector placed behind a nickel filter that absorbs photons from the initial x-ray pulse but is transparent to photons from the probe pulse. Coincident ion spectra are recorded with a TOF spectrometer. (B) Electrons are highly localized in the initial van der Waals cluster, forming an ordered crystal lattice with a well-defined neutral atomic spacing (dn). (C) During the nanoplasma transition, the highly excited electrons become delocalized in the deep Coulomb potential, affecting the overall lattice geometry with a new plasma spacing (dp).

  • Fig. 2 Evidence for atomic motion on the few-femtosecond time scale.

    (A) Bragg peaks from the (220) fcc reflection plane shift to higher scattering vector q with increasing pump-probe delay (0-, 60-, and 80-fs delays pictured here). (B) The average unit cell lengths measured from the q value for the (111) and (220) fcc reflection planes show a consistent decrease with increasing delay. (C) Apparent lattice disorder is calculated from the DWF. Two distinct regimes show a fast disorder (region a) on the same time scale as electronic responses, and a slower change (region b) indicative of lattice distortion. The teal marker is for the 50-fs delay average data set where single-shot data could not be filtered on single-grain clusters.

  • Fig. 3 TOF spectra from Xe clusters and atomic Xe.

    The TOF spectrum from Xe clusters shows high charge state ions with high kinetic energies, indicative of a hot nanoplasma. Kinetic energy distributions are simulated and fit with an ion optics Monte-Carlo software package. The Xe20+ peak corresponds to a maximum kinetic energy of 45 keV and an average kinetic energy of 10 keV. (Inset) Atomic Xe reference data show a most probable charge state of Q = 9+. A maximum charge state of Q = 25+ is observed, with more than 98% of collected ions having a charge state of 20+ or less.

Supplementary Materials

  • Supplementary Materials

    This PDF file includes:

    • Materials and Methods
    • Fig. S1. Transmission of the 30-μm nickel filter around the nickel K-edge.
    • References (25–30)

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