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Investigation of Electro-Optical Properties of Heterostructures based on 2-D Layered Materials by Quantum Simulation

Saadat Somaeh Sofla, Zahra | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54081 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Simchi, Abdolreza; Shayeganfar, Farzaneh
  7. Abstract:
  8. Density Functional Theory is one of the most robust Ab-intio methods for describing the structural and electronic properties of a wide range of materials. The ability to predict the material properties changes due to targeted material manipulation at the atomic scale has reduced the cost of many empirical experiments. It has improved the knowledge and understanding of the investigation and producing new materials and devices. Tow dimensional heterostructures are highly regarded due to their unique optoelectronic properties, potential application in nanoelectronic devices, energy storage devices, solid-state devices, and photovoltaic devices. In this study, the two-dimensional materials individually and two-dimensional heterostructures of graphene and molybdenum disulfide were studied. Due to the importance of the heterostructure twist angle on its properties, the desired heterostructure was studied in different twist angles. Structural and electronic properties have been computed in terms of density functional theory using GGA approximation and PBE as exchange-correlation functional. For this purpose, the PWscf code of the Quantum ESPRESSO calculation package was used to perform the calculations. This computation is based on the pseudo-potential method in which plane waves are used as the basis for the expansion of the Cohen-Sham single-wave functions. The used pseudopotentials are optimized norm conserving Vanderbilt pseudopotential. The results show that in the GGA approximation, the heterostructure band structure could be considered as the overlap of the isolated band structures of each constituents. The nature of the electronic behavior of graphene will remain intact. However, with the change of the graphene twist angle, a change in the type and size of the MoS2 band gap was observed. The direct bandgap is converted to indirect bandgap (1.52 eV) at 30 ° twist angle due to the band gap's dependence on its thickness. Charge density calculations showed; charge transfer in the graphene/molybdenum disulfide heterostructure occurred from graphene to molybdenum disulfide monolayer
  9. Keywords:
  10. Density Functional Theory (DFT) ; Graphene ; Molybdenum Desulfide ; Transition Metals ; Two Dimentional Materials ; Transmission Metal Dichalcogenides (TMDs) ; Hybrid Nanostructures

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