Magnetotransport Properties of AlxIn1-xAsySb1-y/GaSb and Optical Properties of GaAs1-xSbx Page: 17
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Transmission Electron Diffraction Measurements
Transmission electron microscopy (TEM) [62] and scanning transmission electron
microscopy (STEM) [63] are direct ways to observe the superstructures in an ordered
alloy. With transmission electron microscopy (TEM), a thin (<200 nm) sample is
bombarded by a highly focused beam of single-energy electrons. The beam has enough
energy for the electrons to be transmitted through the sample. The transmitted electron
signal is greatly magnified by a series of electromagnetic lenses. The magnified
transmitted signal may be observed in two ways, through electron diffraction or direct
electron imaging. Electron diffraction patterns are used to determine the crystallographic
structure of the material. A typical electron diffraction pattern due to zinc -blende
structure is shown in Fig. 5. Direct electron images yield information about the
microstructure of the material and about its defects. With scanning transmission electron
microscopy (STEM), the electron beam is raster-scanned across the material. This
produces a variety of electron and X-ray signals that may be used for compositional
analysis. However these two techniques only provide local structural information either
averaged through a thin section (TEM) or at the cross-section surface (STEM). The
general technique employed to observe the atomic ordering is transmission electron
diffraction (TED) because the structure of the ordered alloy will result in the extra
diffraction peaks (atomic ordering peaks) in addition to the fundamental diffraction peaks
in the diffraction pattern, which, upon analysis, yields the type of ordering. The other
advantage of TED is its strong intensity, which allows the prediction of the degree of
ordering from the relative intensities of regular ordered diffraction peaks.17
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Lukic- Zrnic, Reiko. Magnetotransport Properties of AlxIn1-xAsySb1-y/GaSb and Optical Properties of GaAs1-xSbx, dissertation, May 2003; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc5522/m1/27/: accessed May 14, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .