报告题目：Imaging ferroelastic domain dynamics with nanoscale X-ray diffraction at the MAX IV synchrotron
报告人：Prof. Jesper Wallentin, Lund University, Sweden
Metal halide perovskites (MHPs) have shown impressive results in solar cells, light emitting devices, and scintillator applications, but basic questions regarding its complex structure are still open . The low symmetry of MHP crystal structures allows the formation of ferroelastic domains, whose ferroelectric nature is debated. Ferroelastic and ferroelectric materials show nanoscale domains with typical sizes ranging from 10 to 1000 nm. Imaging dynamics of ferroic domains require an experimentally challenging combination of high spatial resolution, strain sensitivity and long penetration depth. Here, I will give a brief introduction to nanoscale synchrotron X-ray diffraction methods, and an update of the status of the 4th-generation synchrotron MAX IV in Lund, Sweden (https://www.maxiv.lu.se/).
We have developed nanoscale X-ray diffraction methods to study the dynamics of ferroelastic domains within MHP nanostructures, made available by recent developments in X-ray optics and synchrotron sources. CsPbBr3 nanowires were imaged across the orthorhombic to tetragonal crystal phase transition using in situ temperature-dependent nanofocused scanning X-ray diffraction, with the 60 nm beam at the NanoMAX beamline, MAX IV . The formation of highly organized domain pattern near 80 °C revealed the ferroelastic nature of the domains. To achieve improved temporal resolution, we used the newly developed Full-Field Diffraction X-ray Microscopy technique, available at the ID01 beamline, ESRF, France, to probe the domain evolution at 6 s time resolutions  . Twinned ferroelastic domains in single 500 nm CsPbBr3 particles were studied with 3D Bragg coherent x-ray diffraction imaging . A preferential double-domain structure was revealed, with one domain oriented along the  and the other along the  direction. These results demonstrate that X-ray methods now offer sufficient spatial resolution to image ferroic domains, allowing for in situ studies of their formation and dynamics in realistic conditions.
Jesper Wallentin is an Associate Professor at the division for Synchrotron Radiation Research at Lund University, Sweden. He did his PhD in Lund, and then a postdoc at the University of Göttingen in Germany. His research concerns the intersection of nanoscience and X-ray science, both developing X-ray methods to investigate nanostructured devices, and developing nanostructured X-ray detectors. His group has a strong collaboration with the NanoMAX beamline at MAX IV, but also visits many other synchrotrons for experiments. Recently, his group has synthesized single crystal MHP nanowires for X-ray scintillation detection.
Home page: https://www.sljus.lu.se/staff/jesper-wallentin/