Quantum nano-electronics in two-dimensional materials
Creators: name: Javaid, Maria
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 510403
subject: Condensed matter modelling and density functional theory
classificationCode: 510404
subject: Electronic and magnetic properties of condensed matter; superconductivity

description: Two-dimensional materials represent one of the most important frontiers of material science today. They hold this place at the forefront of science because of the unprecedented opportunities for atomically thin materials with controllable properties in fields as diverse as electronics, photonics, gas sensing, medicine, and catalysis. Among these two-dimensional materials, transition-metal dichalcogenides are an important class comprising a range of materials varying from conductors to insulators. In this thesis, our interest is to understand the fundamental physics of transition-metal dichalcogenides using density-functional theory and to explore their potential applications in modern electronics and photonics. Our approach allows the design of quantum-electronic devices that utilize the physics of two-dimensional materials in particular, transition-metal dichalcogenides, and we demonstrate that with the preliminary design of a single electron transistor in molybdenum disulfide incorporating all of the essential physics explored in this thesis. <br><br>Size-dependent effects can cause significant property variations in small-sized nanoflakes. We present the first investigation of the size-dependent structural, electronic, and optical properties of MoS2 monolayers using density-functional theory. Understanding the size-dependent properties will inform efforts to engineer the electronic structures at the nano-scale. Exploring the size-dependent properties in nanoflakes smaller than 2 nm, a regime not yet explored, is potentially promising in tunable fluorescent applications. <br><br>The ultrathin geometry and promising electronic properties make two-dimensional materials a potential candidate for device physics. Despite the growth in the number of identified two-dimensional materials, there is still a lack of cohesion in the field, as many of the landmark results appear to be difficult to reproduce, and trends between and within families of two-dimensional materials are often difficult to identify. Against this backdrop, we present a comprehensive study of the electronic structures of stable, layered, transition-metal dichalcogenides using density-functional theory in this thesis. The aim is to provide a catalogue of the known stable, layered, transition-metal dichalcogenides structures and their electronic properties to researchers which can help them in the selection of an appropriate material according to their applications. We investigate their band structure responses to transverse electric fields. Our results show that band gap engineering by applying electric fields can be an effective strategy to modulate the electronic properties of transition-metal dichalcogenides for next-generation device applications. <br><br>By modulating the local band structure of bilayer MoS2 -- a typical semiconducting transition-metal dichalcogenide, we present a multi-scale modelling and design of a gate-defined single-electron transistor in a MoS2 bilayer. By combining density-functional theory and finite-element analysis, we design a surface gate structure to electrostatically define and independently tune a quantum dot and its associated tunnel barriers in the MoS2 bilayer. The physics to date enables us to design more rationale devices in MoS2 bilayer by modifying its local band structure. Our surface-gate structure enables to obtain a more controllable design of a single-electron transistor as compared to conventional GaAs based devices. This approach suggests new pathways for the creation of novel quantum electronic devices in two-dimensional materials.<br>