Argonne National Laboratory

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Aberration-Corrected Scanning Transmission Electron Microscopy: Including Light Elements

NST Nanoscience Seminar
Patrick Phillips, University of Illinois at Chicago
May 28, 2013 11:00AM to 12:00PM
Building 440, Room A105-106
Scanning transmission electron microscopy (STEM) offers a multitude of characterization techniques for a wide range of relevant materials, most commonly realized through chemical analysis combined with high angle annular dark field (HAADF) imaging. However, with the recent advent of annular bright field (ABF) STEM, it is now possible to image light and heavy elements simultaneously. By coupling ABF imaging to HAADF and chemical analyses, a full-scale materials characterization can be performed. The first part of this talk will focus on the STEM-based characterization of AlxGa1xN nanowires for UVLED applications.

To assist subsequent growth processes while striving for optimum efficiency, both structural and chemical characterization methods are necessary, which can be provided at sufficiently high resolutions by advanced STEM instruments. Specifically, structural characterization will focus on determining layer thicknesses and wire polarity, as well as visualizing any short-range ordering and/or stacking faults that may be present. Chemically, both energy dispersive X-ray (EDX)and electron energy loss (EEL) spectroscopies will be discussed in various capacities, ranging fromquantum well composition (EDX) to N K-edge fine structure of both GaN and AlN (EELS).

The second portion of the talk will present numerous example materials which required structural, chemical, and/or electronic characterization via aberration-corrected STEM methods. Additionally, the technique of ABF STEM (coupled with HAADF) will be discussed in terms of imaging very thin samples. Notably, preliminary research has indicated that some of the phenomenological theory of ABF breaks down in the limit of thin specimens. Where necessary, supporting STEM multislice image simulations will be presented.