Lensless X-ray Microscopy Images Nanocrystals
Daniel S. Burgess
Scientists at the University of Illinois in Urbana have used coherent hard x-rays to produce 3-D images of 750-nm lead nanocrystals with a spatial resolution of 40 nm. With improved detectors and more powerful sources of coherent x-rays, they suggest, the lensless approach should achieve resolutions similar to those of electron microscopes but with greater penetration depths, enabling applications from basic research in materials science to the study of atomic-scale components for nanomachines.
Called coherent x-ray diffraction imaging, the approach circumvents the problems involved with the control and focusing of hard x-rays using components such as Fresnel zone plates and mirror optics. Instead, coherent x-rays simply are directed at the sample to yield so-called oversampled diffraction patterns. Iterative mathematical operations are then performed on the phase data embedded in the collected diffraction patterns to construct the images.
Using a beam line at the Advanced Photon Source synchrotron facility at Argonne National Laboratory in Illinois for illumination, the scientists collected diffraction patterns from the nanocrystals, which they grew on an SiO2 substrate in the vacuum chamber of the beam line. The images revealed deformations in the lattice of the hemispherical crystals, which they attributed to a surface defect at the site of nucleation on the substrate that resulted in a residual strain.
Nature, July 6, 2006, pp. 63-66.
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