4D Electron Tomography

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Science  25 Jun 2010:
Vol. 328, Issue 5986, pp. 1668-1673
DOI: 10.1126/science.1190470

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  1. Fig. 1

    (A) Schematic representation of time-resolved 4D electron tomography. The heating pulse initiates (at t0) the structural change and acts as a clocking pulse, whereas the time-delayed electron packet (at tα), with respect to the clocking pulse, images the structure at a given tilt angle (α). (B) A series of 2D images at various projection angles and time steps are taken to construct the tomograms. In this work, increments of 1° and scannings from −58° to +58° were used to define α and its range; the time scale ranged from femtoseconds to microseconds. The number of total spatiotemporal projections made was near 4000, and these were used to construct the tomographic movies of the object in motion; see text.

  2. Fig. 2

    Tomograms and images resolved in time. (A) Representative time frames of 3D volume images taken at t = 50 ps and 25 ns for the MWNT specimen. The bracelet shape (radius 620 nm) and the detailed tubular morphology are displayed; from the 3D volume models, the length of the ring (L) was measured to be 4.4 μm. Around the anchored region of the ring, L1 and L2 are the lengths of the long and short segments, respectively. The 3D isosurface rendering was made with the Amira visualization program. (B) Cross section of tomographic images. Shown are 4.6-nm-thick 2D slices in the xy plane, perpendicular to the optical axis, at t = 50 ps (top) and 25 ns (bottom). The dark regions indicated by arrows represent nanometer-thick carbon walls; the light area is the vacant space in the tomograms. Tubular features with hollow channels of diameter ~10 nm are well resolved. (C) TEM image of a MWNT specimen. A typical projection image at α = 0° is given with the dimensions indicated. Despite the initial femtosecond excitation, all motions in the object begin on the picosecond time scale because of the nature of structural change (26).

  3. Fig. 3

    Dynamics of 2D image projections. (A) Snapshots of images recorded stroboscopically at different time delays, as indicated at the upper right of each image. (B) Difference images relative to the frame at t = −50 ns, showing projected motions of the MWNT specimen. In the difference images, the regions of white or black indicate the motions involved, whereas the gray regions indicate that the contrast is unchanged from that of the reference frame. Scale bars, 200 nm. (C) Oscillatory motions from the time-dependent displacements along three representative transverse cross sections of the MWNT specimen; they are indicated as arrows in the image at t = –50 ns, with the color code indicated. (D) FFTs of the displacements in the time regime of 0 to 4.9 μs with a sampling rate of 10 ns for each of the displacements shown. As such, the tomograms would decipher 4D dynamical structures from matrix-isolated conformational structures in cyroelectron microscopy (37).

  4. Fig. 4

    4D tomographic visualization of motion. (A) Representative 3D volume snapshots of the nanotubes at relatively early times. Each 3D rendered structure at different time delay (beige) is shown at two view angles. A reference volume model taken at t = 0 ns (black) is merged in each panel to highlight the resolved nanometer displacements. Arrows in each panel indicate the direction of motion. (B) The time-dependent structures visualized at later times and with various colors to indicate different temporal evolution. The wiggling motion of the whole bracelet is highlighted with arrows. From these tomograms, movies were constructed in the two different time domains (movies S2 and S3). Note that the time scale given here is chosen to display clearly the objects’ motions, as opposed to the early ultrashort time domain (see text).

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