报告时间：2017年6月15日上午10点(10:00 am, 15th June)
地点：教十一318会议室
Imaging Dynamic Chemical Processes by Transmission Electron Microscopy (TEM)
Nigel D. Browning1,2
1Physical and Computational Science Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA Nigel.browning@pnnl.gov
2Materials Science and Engineering, University of Washington, Seattle, WA 99194, USA
Many processes in materials chemistry take place in a liquid environment – such as chemical conversions, the synthesis of nanoparticles, the operation of Li-ion or next generation batteries, and biological cellular functions. In many of these cases, the final desired outcome is a result of a series of complicated transients, where a change in the order, magnitude or location in each of the steps in the process can lead to a radically different result. Understanding and subsequently controlling the final outcome of the process therefore requires the ability to directly observe the transients as they happen. Aberration Corrected (Scanning) Transmission Electron Microscopy ((S)TEM) has the spatial resolution to directly visualize these transient processes on the atomic scale. However, the increased current densities caused by the correctors have made beam damage more prevalent and the limitation to imaging in many cases is now the sample rather than microscope. Similar constraints are implicit during in-situ or operando TEM experiments involving liquids, where the goal of the experiment is to observe a transient phenomenon without the beam altering the process. The aim now is therefore to more efficiently use the dose that is supplied to the sample and to extract the most information from each image. Optimizing the dose/data content in non-traditional ways (i.e. not just simply lowering the beam current) involves two main strategies to achieve dose fractionation – reducing the number of pixels being sampled in STEM mode, or increasing the speed of the images in TEM mode. For the case of the STEM, inpainting methods allow a dose reduction of an order of magnitude or more, allowing data to be automatically recorded in a compressed form. For the TEM mode of operation, an increase in speed increases the number of images and means that compressive sensing and automated methods of tracking changes in the structure need to be developed so that only the important changes need to recorded. In this presentation, results from conventional microscopes showing the use of in-situ liquid stages to study dynamic processes will be presented and the potential insights gained by increasing the image acquisition speed and/or decreasing the electron dose will be described. The benefits of acquiring images with a pulsed photo-emission source in the Dynamic TEM (DTEM) will also be discussed.
This work was supported in part by the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by DOE, Office of Science, Basic Energy Sciences. The work was also supported by the Chemical Imaging Initiative under the Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory (PNNL). PNNL is a multi-program national laboratory operated by Battelle for the U.S. Department of Energy (DOE) under Contract DE-AC05-76RL01830. A portion of the research was performed using the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research and located at PNNL.
Nigel Browning is currently a Laboratory Fellow and Chemical Imaging Initiative Lead at Pacific Northwest National Laboratory (PNNL) – having joined PNNL in September 2011. He received his undergraduate degree in Physics from the University of Reading, U. K. and his Ph. D. in Physics from the University of Cambridge, U. K. After completing his Ph. D. in 1992, he joined the Solid State Division at Oak Ridge National Laboratory (ORNL) as a postdoctoral research associate before taking a faculty position in the Department of Physics at the University of Illinois at Chicago (UIC) in 1995. In 2002, he moved to the Department of Chemical Engineering and Materials Science at the University of California-Davis (UCD) and also held a joint appointment in the National Center for Electron Microscopy (NCEM) at Lawrence Berkeley National Laboratory (LBNL). In 2005 he moved the joint appointment from LBNL to Lawrence Livermore National Laboratory (LLNL) to become project leader for the Dynamic Transmission Electron Microscope (DTEM). In 2009, he also joined the Department of Molecular and Cellular Biology at UCD to focus on the development of the DTEM to study live biological structures. He has over 25 years of experience in the development of new methods in electron microscopy for high spatial, temporal and spectroscopic resolution analysis of engineering and biological structures. His research has been supported by DOE, NSF, NIH, DOD and by industry, leading to research projects for over 30 graduate students and 29 postdoctoral research fellows. He is a Fellow of the American Association for the Advancement of Science (AAAS) and the Microscopy Society of America (MSA). He received the Burton Award from the Microscopy Society of America in 2002 and the Coble Award from the American Ceramic Society in 2003 for the development of atomic resolution methods in scanning transmission electron microscopy (STEM). With his collaborators at LLNL he also received R&D 100 and Nano 50 Awards in 2008, and a Microscopy Today Innovation Award in 2010 for the development of the dynamic transmission electron microscope (DTEM). He has over 350 publications (h-index 65) and has given over 300 invited presentations on the development and application of advanced TEM methods.
