清华大学材料科学与工程研究院《材料科学论坛》学术报告
报告时间：2025年8月29日上午10:00-11:30
报告人：吴明健研究员（德国埃尔兰根-纽伦堡大学）
报告地点：清华大学逸夫技术科学楼A205学术报告厅
邀请人：于荣老师
报告题目：Unravel the structure of molecular crystals in organic semiconductors using analytical TEM, 3D electron diffraction and 4D-STEM
报告简介：
Harnessing the complex nano-scale structure in organic semiconductors is essential to tailor their functionality and performance. For example, the orientation of π-stacking domains and grain boundaries are essential to their electric transport properties in organic field-effect transistors (OFET); in bulk hetero-junction (BHJ) organic solar cells (OSCs) it determines exciton dissociation and charge carrier pathways thus dictate performance of the cells. These structural properties at different length scales are highly sensitive to processing conditions and protocols. Unravel the structure of organic semiconductors from molecular to device scale is essential to establish the processing-structure-properties relationship. Fast electrons interact strongly with matter and can deliver a multitude of structural and analytical signals to study the structure, chemistry and composition of materials at high spatial resolution. Modern electron microscopes, as “a synchrotron in a microscope” , hold the potential for such studies. However, direct observation of structures of organic semiconductors using electron microscopy face certain challenges including radiation damage, limitations due to sample geometry and yet-to-established workflows etc.
In this talk, I will report our efforts toward systematically and correlatively characterize the structure of OSCs and organic semiconductor thin films using TEM: from nano-morphology of OSC using analytical methods (with energy-filtered TEM or spatially resolved electron energy-loss spectroscopy), to evaluating their texture with EF-SAED (energy-filtered selection area electron diffraction) and 3D electron diffraction. The results are compared to that from identical sample using established X-ray based method using lab and synchrotron sources. Finally I will showcase probing local structure information with our recently proposed, dose-efficient method 4D-scanning confocal electron diffraction (4D-SCED) technique . Furthermore, I will discuss the merit when this technique is coupled to a state-of-the-art hybrid-pixel direct electron detector [6]. The unique combination of imaging, diffraction and spectroscopy methods in a single instrument of TEM enables straightforward, correlative study of organic semiconductors.
报告人简介：
Dr. Mingjian Wu is a staff scientist at the Institute of Micro- and Nanostructure Research at Friedrich-Alexander-Universitaet Erlangen-Nuernberg in Germany. He obtained Bachelor’s and Master’s degrees in Materials Science from Hunan University, China, and Doctor degree (summa cum laude) in Experimental Physics from Humboldt-Universitaet zu Berlin in 2014.
He is an enthusiastic “nano-photographer” with over 15 years of experience in electron microscopy. His expertise lies in developing and applying advanced microscopy, diffraction, and spectroscopy techniques—integrated with in situ, operando, and data science approaches—to gain unique insights into modern functional materials. His research interest lie in the investigation of organic semiconductors, in particular, developing methods and techniques to unravel structures that are difficult to study. He has published ~80 peer reviewed articles. In 2023, he received the “Outstanding Paper Award” from European Microscopy Society for contribution of developing 4D-STEM method for organic solar cell materials.