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報告人：Omar F. Mohammed教授

報告人單位：沙特阿卜杜拉國王科技大學

報告時間：2025年6月10日(星期二）10：00

會議地點：科技D樓1903會議室

舉辦單位：柔性電子（未來技術）學院、先進材料研究院

報告人簡介：Dr. Mohammed is Professor of Chemistry and Materials Science & Engineering; and the principal investigator of ultrafast laser spectroscopy and four-dimensional (4D) electron imaging laboratory at KAUST. He earned a Ph.D in Physical and Theoretical Chemistry from Humboldt University of Berlin, Germany. Prior to joining KAUST, Dr. Mohammed was a senior research associate at Caltech, where he worked with Professor Zewail, a Nobel laureate, on developing innovative laser spectroscopic and time-resolved electron imaging techniques. Dr. Mohammed has published over 370 articles in international peer-reviewed journals including Science, Nature, Nature Materials, Nature Energy and Nature Photonics, large number of these papers are currently highly cited (39 papers). Dr. Mohammed has more than 45,000 citations and 100h-index. Dr. Mohammed is the recipient of severalprestigiousawards, including the Distinguished Scholar Award from Arab Fund for Economic and Social Development, Kuwait; Long-term Fellowship, Germany, the Japan Society for the Promotion of Science (JSPS) fellowship, Japan, the State Prize in Basic Sciences, Egypt, Shoman Prize in Photochemistry, Shoman Foundation, Jordan, and Kuwait Prize in Physics, Kuwait Foundation, Kuwait.

報告摘要：The separation and collection of photo-generated charge carriers in light-harvesting devices are limited by the losses and ambiguous dynamical events at the surfaces and interfaces of the absorber layers. These events occur in ultrafast time scales and can only be visualized selectively in space and time by scanning ultrafast electron microscopy (the sole technique capable of surface-selective visualization of light-triggered carrier dynamics at nanometer and femtosecond scales). In this method, the surface of the photoactive materials is excited by a clocking optical pulse and the photo-induced changes will be directly imaged using a pulsed electron beam that generate secondary electrons with a couple of electron volts energy, which are emitted from the very top surface of the material in a manner that is extremely sensitive to the localization of the electron and hole on the photoactive material surfaces. This powerful technique along with ultrafast laser spectroscopy allow us to directly and precisely investigate and decipher the trajectory of charge carriers on materials surfaces and interfaces simultaneously in real space and real time. Through this work, we have optimized the properties of photoactive materials for applications in light-harvesting devices that led to the world-record solar cell devices based on perovskite crystals. Moreover, we have clearly demonstrated in space and time how the surface orientations, surface oxidation and passivation can significantly impact the overall dynamical processes of photogenerated carriers in solar materials. Moreover, I will talk about our recent ground-breaking work in X-ray imaging technology that include cutting-edge materials discovery, heavy-atom engineering, and efficient (nearly 100%) interfacial energy transfer between sensitizers and scintillators that has led to the development of novel X-ray imaging screens with outstanding sensitivity, ultralow detection limit, unprecedented spatial image resolution and low-cost fabrication. The talk also discusses a novel top-filter-bottom sandwich structure scintillator for high-performance dual-energy X-ray imaging within a single exposure. Finally, our recent innovation of true-color multi-energy X-ray imaging technology centered around multiple scintillator architecture with a six-layer ΔE-E telescope configuration to achieve powerful material-specific capability, surpassing what is offered by traditional X-ray imaging technologies will also be discussed in this talk. This breakthrough research enables clear resolution of different biological tissues and materials objects based on their corresponding colors and paves the way for the development of new imaging scintillator architectures with potential applications in medical imaging, industrial monitoring and security checks.

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