Title page for etd-0623113-160745


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URN etd-0623113-160745
Author Hua-rong Chang
Author's Email Address No Public.
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Department Physics
Year 2012
Semester 2
Degree Master
Type of Document
Language zh-TW.Big5 Chinese
Title First-principles studies of atomic structures and electronic properties of Bi ultrathin films on Si(111) and Ge(111)
Date of Defense 2013-06-07
Page Count 83
Keyword
  • Kohn-Sham
  • Ge(111)
  • Si(111)
  • topological insulator
  • first-principles
  • ultrathin bismuth films
  • Chern number
  • Abstract The atomic and electronic structures of ultrathin bismuth films on Si(111) and Ge(111) surface were investigated using first-principles calculations at Bi coverages ranging from 1/3 ML to 5 MLs. The free standing bismuth bilayer is in buckled honeycomb structure and has been previously identified as is a two dimensional topological insulator. On the other hand, at 1 ML, the reconstructed Si(111) and Ge(111) have been previously studied and exhibits strong Rashba splitting at the M point. Thus, it is very interesting and important to study the Bi ultrathin films on substrates. On Ge(111), we found that at the bismuth coverages of 3 MLs and 5 MLs the topmost 2MLs of Bi atoms form a buckled honeycomb structures and were hoped to exhibit the topological non-trivial phase. However, in the band structure calculations, the beneath Bi atoms play an important role in p-type doping to the topmost 2D topological insulator. The p-type doping results in shifts of Fermi level and changes of parity at the time-reversal symmetry points of the system, thus the topological non-trivial characteristic is broken. In the contrast, at 3 ML and 5 ML the buckled bismuth bilayer was unable to form on Si(111) substructure due to the a larger compressive strain compared to Ge(111).
    Advisory Committee
  • Chien-Cheng Kuo - chair
  • Ya-Ping Chiu - co-chair
  • Yi-Chun Chen - co-chair
  • Feng-Chuan Chuang - advisor
  • Files
  • etd-0623113-160745.pdf
  • Indicate in-campus at 3 year and off-campus access at 3 year.
    Date of Submission 2013-07-23

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