IMI Interdisciplinary Mathematics InstituteCollege of Arts and Sciences

Imaging the behavior of atoms, clusters and nanoparticles during elevated temperature experiments in an aberration-corrected electron microscope

  • March 17, 2009
  • 3:30 p.m.
  • Sumwalt 102


The advent of the modern aberration-corrected electron microscope began with the first prototype being demonstrated in Germany about a decade ago. Several commercial manufacturers now offer this technology, based on correctors manufactured by the German company CEOS GmbH (Heidelberg), and the American company Nion (Kirkland, WA). There are currently more than 50 instruments in the field that offer the capability to image the structure of materials at a resolution of 1Å (0.1nm) or better, both in direct transmission mode with a corrector placed after the microscope’s objective lens, and in scanning transmission mode, with a corrector placed in the probe-forming lens system. The latter arrangement offers the potential to record, simultaneously, both bright field (BF) and high-angle annular dark-field (HA-ADF) images of, for example, catalytic materials that comprise heavy metal species on light-element supports with dispersions at the single-atom level. The HA-ADF images show contrast relative roughly to the ratio of atomic numbers squared, so higher atomic numbers appear in bright contrast relative to lower atomic number elements. These features of the “STEM-corrected” microscope are ideal for studies of not only the structure of as-prepared catalysts, or catalysts that have undergone specific treatments external to the microscope, but also catalytic materials heated (and ultimately reacted) in-situ. We are working with the company Protochips (Raleigh, NC) to develop and test holders that retain MEMS-based heater chips that are remarkably stable at high temperature, and allow a number of new modes of study of materials behavior at elevated temperatures without compromising the sub-Ångström imaging performance of the aberration-corrected electron microscope. In this talk, these new technologies will be described, and the application to imaging of atoms, clusters and nanocatalysts at elevated temperature will be described. The need for image processing, enhancement and analysis to extract better and more reliable information from the high-resolution imaging experiments will also be discussed.

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