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    Interface Effects Enabling New Applications of Two-Dimensional Materials

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    Name:
    thesis_sattar.pdf
    Size:
    5.002Mb
    Format:
    PDF
    Description:
    Shahid Sattar - Final Paper
    Embargo End Date:
    2019-06-01
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    Type
    Dissertation
    Authors
    Sattar, Shahid cc
    Advisors
    Schwingenschlögl, Udo cc
    Committee Members
    Alshareef, Husam N. cc
    Hussain, Muhammad Mustafa cc
    Chroneos, Alexander
    Program
    Materials Science and Engineering
    KAUST Department
    Physical Sciences and Engineering (PSE) Division
    Date
    2018-05
    Permanent link to this record
    http://hdl.handle.net/10754/628025
    
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    Abstract
    Interface effects in two-dimensional (2D) materials play a critical role for the electronic properties and device characteristics. Here we use first-principles calculations to investigate interface effects in 2D materials enabling new applications. We first show that graphene in contact with monolayer and bilayer PtSe2 experiences weak van der Waals interaction. Analysis of the work functions and band bending at the interface reveals that graphene forms an n-type Schottky contact with monolayer PtSe2 and a p-type Schottky contact with bilayer PtSe2, whereas a small biaxial tensile strain makes the contact Ohmic in the latter case as required for transistor operation. For silicene, which is a 2D Dirac relative of graphene, structural buckling complicates the experimental synthesis and strong interaction with the substrate perturbs the characteristic linear dispersion. To remove this obstacle, we propose solid argon as a possible substrate for realizing quasi-freestanding silicene and argue that a weak van der Waals interaction and small binding energy indicate the possibility to separate silicene from the substrate. For the silicene-PtSe2 interface, we demonstrate much stronger interlayer interaction than previously reported for silicene on other semiconducting substrates. Due to the inversion symmetry breaking and proximity to PtSe2, a band gap opening and spin splittings in the valence and conduction bands of silicene are observed. It is also shown that the strong interlayer interaction can be effectively reduced by intercalating NH3 molecules between silicene and PtSe2, and a small NH3 discussion barrier makes intercalation a viable experimental approach. Silicene/germanene are categorized as key materials for the field of valleytronics due to stronger spin-orbit coupling as compared to graphene. However, no viable route exists so far to experimental realization. We propose F-doped WS2 as substrate that avoids detrimental effects and at the same time induces the required valley polarization. The behavior is explained by proximity effects on silicene/germanene due to the underlying substrate. Broken inversion symmetry in the presence of WS2 opens a substantial band gap in silicene/germanene. F doping of WS2 results in spin polarization, which, in conjunction with proximity-enhanced spin orbit coupling, creates sizable spin-valley polarization. For heterostructures of silicene and hexagonal boron nitride, we show that the stacking is fundamental for the details of the dispersion relation in the vicinity of the Fermi energy (gapped, non-gapped, linear, parabolic) despite small differences in the total energy. We also demonstrate that the tightbinding model of bilayer graphene is able to capture most of these features and we identify the limitations of the model.
    DOI
    10.25781/KAUST-7P235
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-7P235
    Scopus Count
    Collections
    Dissertations; Dissertations; Physical Sciences and Engineering (PSE) Division; Materials Science and Engineering Program

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