研究目的
Investigating the structural and electronic properties of 2D Transition Metal Dichalcogenides (TMDs) monolayers and the way these properties are affected upon formation of a bilayer, focusing on MoS2-based bilayers including MoS2/MoS2, WS2/MoS2, MoSe2/MoS2, and WSe2/MoS2 structures, and the impact of vacancies on the interlayer interactions.
研究成果
The study concludes that changes in the properties of 2D monolayers upon building a stack do occur and are driven by both strain effects and interfacial electronic processes. The actual energy level alignment in stacks of 2D monolayers cannot be reliably assessed by the sole consideration of the electronic properties of the isolated mono-sheets due to the role played by both strain and interfacial electronic effects.
研究不足
The study does not include the spin-orbit coupling in the calculations, which does not significantly affect the 2D direct bandgap of the materials under study. The computational approach becomes too computationally prohibitive to treat the large unit cells to be considered with bilayers when using the DFT/GW approach for more accurate quasi-particle gaps.
1：Experimental Design and Method Selection:
The study employs first-principles calculations based on density functional theory (DFT) with the projector augmented-wave (PAW) method and the local density approximation (LDA) for the exchange-correlation functional. The hybrid (HSE03) functional is used for more reliable electronic gaps and energy level alignment at interfaces.
2：Sample Selection and Data Sources:
The study focuses on model systems made of a bilayer structure built from widely investigated TMDs, systematically including MoS2 as one component.
3：List of Experimental Equipment and Materials:
The calculations were carried out using the VASP package, with a large cutoff energy of 550 eV and a supercell made of 3 x 3 primitive unit cells with a vacuum of at least 22 ? between adjacent bilayers.
4：Experimental Procedures and Operational Workflow:
The 2D Brillouin zone integration was sampled by a Γ-centered Monkhorst-Pack point scheme of 15x15x1 for geometry relaxations. Single-point calculations were performed to obtain electronic gaps and energy level alignment.
5：Data Analysis Methods:
The charge distribution was obtained via a Bader analysis. The spin-orbit coupling was not included in the calculations.
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