Current Status of Single Particle Imaging Project & 3D Visualization of Phase-Ordering with X-ray Sources
일 시 : 2020년 12월 28일 월요일 11:00
연 사 : 김 찬 박사 (European X-ray Free-Electron Laser (XFEL) Facility)
장 소 : 자연과학관 747호
Single particle imaging (SPI) project with X-ray sources has triggered development of hard X-ray Free-Electron Laser (XFEL) facilities in worldwide. In 2009, the world first angstromwavelength XFEL facility named Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory was up and running . A few years later, the world’s second and third hard XFELs (SCALA  in Japan and PAL-XFEL  in the Republic of Korea) started their operations. Since 2017, a world best performance XFEL facility, named European XFEL (EuXFEL), has been operational with extreme operating conditions, e.g., a high pulse energy (close to 4mJ/pulse: limited by a radiation safety limit) and a high repetition rate (up to 4.5MHz) . The SPI project has made tremendous progress thanks to the worldwide XFEL facilities although achievable resolution of SPI experiment is still far away from atomic resolution.
In the first part of this seminar, current status and future perspectives of SPI project will be addressed. In the second part of the seminar, 3D visualization of phase-ordering in an Fe-Al alloy by coherent X-ray Bragg ptychography [5,6] will be discussed. This experimental scheme offers the possibility of imaging the phase shift of the radiation scattered by the sample, which is related to the atomic structure such as ordering and lattice strain. Atomic ordering on a sublattice result in the emergence of superlattice reflections that otherwise are forbidden in the bcc structure. The degeneracy of the ordered structures results in domain boundaries that, in addition to the general strain of the lattice, will give a phase shift depending on which reflection is probed. We investigated the lattice strain associated with phase ordered domains by imaging the (002) fundamental and the (001) superlattice reflections of FeAl in the B2 phase . Using the (002) data, the (001) images could be normalized for lattice strain and APDs visualized in 3D for the first time.