For centuries, lens-based microscopy, such as light, phase-contrast, fluorescence, confocal and electron microscopy, has played an important role in the evolution of modern science and technology. In 1999, a novel form of microscopy, which is known as coherent diffractive imaging (CDI) or lensless imaging, was developed and transformed our traditional view of microscopy, in which the diffraction pattern of a non-crystalline object or a nanocrystal was first measured and then directly phased to obtain an image. The well-known phase problem was solved by combining the oversampling method with iterative algorithms. In the first part of the talk, I will present the principle of CDI and illustrate some applications using synchrotron radiation, X-ray free electron lasers and high harmonic generation.
In the second part of the talk, I will present a general tomographic method for determining the 3D local structure of materials at atomic resolution. By combining scanning transmission electron microscopy with a novel data acquisition and image reconstruction method known as equally sloped tomography, we achieve electron tomography at 2.4 Å resolution and observe nearly all the atoms in a multiply-twinned Pt nanoparticle. We find the existence of atomic steps at 3D twin boundaries of the Pt nanoparticle and, for the first time, image the 3D core structure of edge and screw dislocations in materials at atomic resolution. We expect this atomic resolution electron tomography method to find broad applications in solid state physics, materials sciences, nanoscience, chemistry and biology.
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2. M. C. Scott, C.-C. Chen, M. Mecklenburg, C. Zhu, R. Xu, P. Ercius, U. Dahmen, B. C. Regan and J. Miao, “Electron tomography at 2.4-ångström resolution”, Nature 483, 444–447 (2012).
3. C.-C. Chen, C. Zhu, E. R. White, C.-Y. Chiu, M. C. Scott, B. C. Regan, L. D. Marks, Y. Huang and J. Miao, “Three-dimensional imaging of dislocations in nanoparticles at atomic resolution”, Nature 496, 74–77 (2013).