Heating Experiments in the Electron Microscope: A 60-year ORNL Retrospective

Описание: In the past 15 years or so, electron microscopists have seen a remarkable improvement in the capability to conduct both heating and gas-reaction experiments in situ...inside the transmission electron microscope (TEM) due primarily to the introduction of unique heating devices called “E-chips.” These devices are “MEMS-based” elements (microelectromechanical systems) that are fabricated using semiconductor manufacturing methods and have the remarkable feature that a thin ceramic heating membrane can cycle from room temperature to 1000°C in a millisecond. The E-chips can be combined to form a minicell with a narrow gap that can contain a gas at up to atmospheric pressure, in a special holder that allows controlled flow thru the cell while the specimen on the chip is being heated. These new capabilities have initiated a resurgence in the field of in situ studies, that first originated in the early ‘60s in a few laboratories in the world, including the new electron microscopy facility in the Department of Chemical and Metallurgical Engineering at the University of Michigan, headed by Prof. Wilbur Bigelow. One of the microscopes was equipped with a cine camera that allowed 16-mm film recording of dynamic changes in samples during observations. Prof. Bigelow and his thesis advisor Michigan Chemistry Prof. Lawrence Brockway built a gas-handling system and a special furnace for the specimen holder, to study the initiation and growth of copper oxide grains in thin Cu single crystals beginning in the summer of 1965...and this study was inspired by earlier work that Prof. Brockway was familiar with, as a consultant at ORNL. The ORNL work, led by Dr. John Cathcart, involved the oxidation of highly polished Cu spheres studied at the optical microscope level; when he was appraised of that work on a visit to ORNL, Prof. Brockway had the inspiration that the early details of the development of oxide films might be revealed by in situ single crystal thin film studies. I was at the time (1963) just beginning to learn electron microscopy from Prof. Bigelow (still active today at age 99!), and I became the principal microscopist on the project. The work was actually funded by the microscopy group at the Oak Ridge K-25 plant, who were interested in adapting our methods to the study of oxidation of Ni single crystal films, giving a second connection to Oak Ridge. The talk today will span the history of those “early days” of in situ TEM studies and contrast them to the present-day technology with examples of studies of catalysts (e.g., for treating automotive exhausts) and aluminum alloys for automotive applications that are possible with today’s aberration-corrected, atomic-level imaging capabilities.

Biographical Sketch:
Dr. Lawrence F. Allard
Distinguished Research Staff Member
Oak Ridge National Laboratory
Oak Ridge, TN 37831

Dr. Larry Allard obtained all three of his degrees at the University of Michigan in (what is now the) Materials Science and Engineering Dept. He started his electron microscopy career in 1963 as a sophomore, learning theory and practice under Prof. Wilbur Bigelow. He is currently a Distinguished Research Staff Member in the Materials Science & Technology Division at Oak Ridge National Laboratory. His research involves ultra-high-resolution imaging and microanalysis in studies of precipitation processes in aluminum alloys and superalloys, catalytic materials (e.g. single-atom catalysts) for automotive exhaust after-treatment and other chemical processes, and instrumental developments involving in situ heating and operando gas-reactions electron microscopy used in those studies. He is the chief scientist in charge of the Aberration-Corrected Electron Microscope (ACEM) project at the High Temperature Materials Lab at ORNL; his JEOL 2200FS instrument at ORNL was one of the first of two new STEM/TEM instruments with sub-Ångström resolution that had been installed in 2004 in the United States. He is also the principal technical designer of ORNL’s new Advanced Microscopy Laboratory, a facility currently housing 7 aberration-corrected microscopes. Dr. Allard has more than 350 cited scientific publications that have garnered more than 23,000 citations. He is an elected Fellow of both the Microscopy Society of America and the Microanalysis Society. He is still collaborating closely with Prof. Bigelow, who at age 99 continues to contribute to the scientific capabilities provided by the microscopy group at ORNL and other institutions.