Seeing is believing. Direct imaging of sample morphology and internal structure has been a key step in modern scientific research. In terms of microscopy, x-ray imaging techniques exhibit unique advantages in studying real materials under real conditions in real timebecause of the superb penetration power of high-energy photons. Into the twenty-first century, the advent of synchrotron and free-electron laser has stimulated a rapid development in x-ray imaging techniques. With highly coherent and intense x-ray beams, we are now capable of visualizing material microstructures and their dynamic evolution with extremely high spatial and temporal resolutions.

In this seminar, working principles and applications of multiple full-field x-ray imaging techniques will be introduced, including absorption/phase contrast imaging, computed tomography, transmission x-ray microcopy, and coherent diffractive imaging (CDI). These techniques allowin situ studies of a broad range of material systems by2-D and 3-D imaging sample structures with spatial resolutions ranging from a few nanometers to micrometers and temporal resolutions from a hundred of picoseconds to seconds. Two techniques will be particularly highlighted in the talk. One is coherent surface scattering imaging (CSSI), which is an optics-free hard x-ray imaging technique by synergistically combining coherent surface scattering and grazing incidence near the sample total external reflection. It is demonstrated that CSSI can reconstruct not only planar images of surface structures but also 3-D architectures with nanometer resolution along the surface normal direction. As a reflection-mode CDI, CSSI promises extensive applications in elucidating structures in substrate-supported and buried biological membranes and nano-electronics/photonics. The second technique that will be explicitly discussedis the simultaneous high-speed x-ray imaging and diffraction, which was recently developed and implemented at the 32-ID-B beamline of the Advanced Photron Source (APS). This ultrafast x-ray technique makes use of the unique time structures of the APS, withthe shortest exposure timeset by the natural width of the x-ray pulses (100 ps) and the maximum frame rate set by the bunch repetition frequency (6.5 MHz).Capable of collecting sample information in both real and reciprocal spaces in the sub-nanosecond timescale, this technique is ideal for probingthe behaviors of crystalline materials involved in a variety of dynamic processes, such as high-strain-rate loading, laser heating, quenching, and combustion.
 
Biography:
Tao Sun received his bachelor and master degrees from Tsinghua University in China, and his Ph.D. in Materials Science and Engineering from Northwestern University in 2009 (co-supervised by Prof. Vinayak Dravid and Dr. Jin Wang). After about three years’ postdoc research at Argonne (co-advised by Dr. Jin Wang and Dr. Murray Gibson), he was appointed to the staff scientist position in 2012. Tao is now an assistant physicist in the Imaging Group of X-ray Science Division, and cooperates in operating multiple x-ray imaging beamlines. Tao’s research covers a broad range of topics in materials science and x-ray physics. His current research focuses on developing novel synchrotron x-ray imaging and scattering techniques, and on achieving fundamental understanding of some interesting transient phenomena in hard and soft condensed matters.

Selected publications:
• Matt Hudspeth*, Tao Sun*, NiranjanParab, ZheruiGuo, KamelFezzaa, Shengnian Luo, Weinong Chen, "Simultaneous X-ray diffraction and phase-contrast imaging for investigating material deformation mechanisms during high-rate loading", Journal of Synchrotron Radiation, 22, (2015), 1

• Tao Sun, Michael Treacy, Tian Li, Nestor Zaluzec, and J. Murray Gibson, "The Importance of Averaging to Interpret Electron Correlographs of Disordered Materials", Microscopy and Microanalysis, 20, (2014) 627

• Tao Sun, Zhang Jiang, Joseph Strzalka, Leonidas Ocola, Jin Wang, “Three-dimensional coherent x-ray surface scattering imaging near total external reflection”, Nature Photonics, 6, (2012) 586

• J. Murray Gibson, Michael Treacy, Tao Sun, Nestor Zaluzec, “Substantial crystalline topology in amorphous silicon”, Physical Review Letters, 105, (2010) 125504

• Tao Sun, Suresh Donthu, Michael Sprung, Kenneth D'Aquila, Zhang Jiang, Arvind Srivastava, Jin Wang, Vinayak Dravid, “Effect of Pd doping on the microstructure and gas sensing performance of nanoporous tin oxide thin films”, ActaMaterialia, 57, (2009) 1095

• Tao Sun, Hao Hu, Zixiao Pan, Xuefa Li, Jin Wang, Vinayak Dravid, “In situ real-time investigation of kinetics of nucleation and growth of sol-gel-derived functional oxide thin films”, Physical Review B. 77, (2008) 205414