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.
| Identifer | oai:union.ndltd.org:kaust.edu.sa/oai:repository.kaust.edu.sa:10754/628025 |
| Date | 05 1900 |
| Creators | Sattar, Shahid |
| Contributors | Schwingenschlögl, Udo, Physical Science and Engineering (PSE) Division, Alshareef, Husam N., Hussain, Muhammad Mustafa, Chroneos, Alexander |
| Source Sets | King Abdullah University of Science and Technology |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Rights | 2019-06-01, At the time of archiving, the student author of this dissertation opted to temporarily restrict access to it. The full text of this dissertation became available to the public after the expiration of the embargo on 2019-06-01. |
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