Review

Imaging Atomic Structure and Dynamics with Ultrafast X-ray Scattering

Science  08 Jun 2007:
Vol. 316, Issue 5830, pp. 1444-1448
DOI: 10.1126/science.1135923

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  1. Fig. 1.

    (A) Schematic representation of photogenerated softening of the interatomic potential in InSb (25). (B) Time-dependent distribution of atomic positions following bond softening. The initial Gaussian distribution broadens linearly with time and with a velocity determined by the root mean square atomic velocities before laser excitation. (C) Schematic representation of a photogenerated shift in the equilibrium bond length in a bismuth crystal (30, 34). (D) Time-dependent distribution of atomic positions after displacive vibrational excitation. The frequency of the coherently excited vibration determines the period of the oscillation in average atomic position, whereas the magnitude of the shift in equilibrium position determines the amplitude of the oscillation.

  2. Fig. 2.

    Schematic depiction of single-particle coherent diffractive imaging with an XFEL pulse. (A) The intensity pattern formed from the intense x-ray pulse (incident from left) scattering off the object is recorded on a pixellated detector. The pulse also photo-ionizes the sample. This leads to plasma formation and Coulomb explosion of the highly ionized particle, so only one diffraction pattern [a single two-dimensional (2D) view] can be recorded from the particle. Many individual diffraction patterns are recorded from single particles in a jet (traveling from top to bottom). The particles travel fast enough to clear the beam by the time the next pulse (and particle) arrives. The data must be read out from the detector just as quickly. (B) The full 3D diffraction data set is assembled from noisy diffraction patterns of identical particles in random and unknown orientations. Patterns are classified to group patterns of like orientation, averaged within the groups to increase signal to noise, oriented with respect to one another, and combined into a 3D reciprocal space. The image is then obtained by phase retrieval.

  3. Fig. 3.

    (A) Diffraction pattern recorded with a single FEL pulse from a test object placed in the 20-μm focus of the beam (8). (B) The diffraction pattern recorded with a second FEL pulse selected with a fast shutter, showing diffraction from the hole in the sample created by the first pulse. (C) Scanning electron microscope image of the test object, which was fabricated by ion-beam milling a 20-nm-thick silicon nitride membrane. The scale bar denotes 1 μm. (D) The image reconstructed from the single-shot diffraction pattern shown in (A).