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      EXAFS study of amorphous selenium

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      Date
      2010-04
      Author
      McLeod, John Anderson
      Type
      Thesis
      Degree Level
      Masters
      Metadata
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      Abstract
      An overview of synchrotrons and synchrotron radiation is presented, along with the theory and practical considerations behind several types of X-ray spectroscopy. The theory and practical considerations of density functional theory are also given, with direct reference to some specific software packages. Some synchrotron-excited X-ray spectroscopy measurements and density functional theory calculations of selenium and arsenic-doped selenium films are then outlined. The physical structure of crystalline and amorphous selenium and the electronic structure of amorphous selenium are discussed and comparison is made to the experimental results. A weak feature in the conduction band is identified as a "fingerprint" of the degree of crystallization in amorphous selenium from X-ray absorption measurements. Similarly, a weak feature corresponding to lone-pairs in the valence band is identified as a "fingerprint" of the arsenic concentration from X-ray emission measurements. Finally a detailed model of the structure of amorphous selenium is explained, and compared to experiment. This model is tested both by direct calculations and by a reverse Monte Carlo approach. The implications of this model with respect to the structure of amorphous and arsenic-doped amorphous selenium are discussed. Calculations suggest that simply randomizing the arrangement of "perfect" trigonal selenium is unable to reproduce the measurements of amorphous selenium; a moderate variation in the bond angle of "perfect" trigonal selenium is also necessary.
      Degree
      Master of Science (M.Sc.)
      Department
      Physics and Engineering Physics
      Program
      Physics and Engineering Physics
      Supervisor
      Moewes, Alex
      Committee
      Chang, Gap Soo; Tse, John; Xiao, Chijin; Pickering, Ingrid
      Copyright Date
      April 2010
      URI
      http://hdl.handle.net/10388/etd-04262010-193841
      Subject
      amorphous selenium
      EXAFS
      X-ray spectroscopy
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