Saudi Cultural Missions Theses & Dissertations
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Item Restricted Van der Waals Heterostructures and 2D Materials with Native Oxide for Emerging Electronic Applications(University of Cambridge, 2023-12-30) Almutairi, Abdulaziz; Hofmann, StephanThe rapid advancement of Artificial Intelligence (AI) and Machine Learning (ML) in various industries has created a significant energy demand. However, this demand poses a challenge as the world strives to shift towards sustainable energy sources. The current computational paradigms, reliant on complementary metal-oxide-semiconductor (CMOS) transistors, are becoming more inadequate for meeting these emerging demands due to limitations imposed by materials characteristics and device architecture. To address this computational paradigm shift, an innovative material platform is necessary. Two-dimensional (2D) layered materials and their heterostructures offer a promising solution to meet this demand, owing to their unique properties. In addition, oxidation processes of 2D materials, which are termed "morphotaxy", allow for precise control over the material thickness and the fabrication of complex heterostructures, opening the door for advanced computing architectures such as non-von Neumann neuromorphic computing. This thesis explores the critical role of interfaces in the performance and efficiency of devices based on 2D materials van der Waals (vdW) and semiconductor/native oxide heterostructures. The susceptibility of these materials to contamination is highlighted, especially in vdW heterostructures. Elemental analysis of chemical species present at the interfaces of hBN-encapsulated graphene is conducted to determine the origin of contaminants. The findings highlighted the difference between contaminants originating from the heterostructure stacking process and the ones from the device lithography process. Moreover, the impact of such interfaces on carrier transport across two 2D materials and the realisation of phenomena like moiré superlattices in vdW heterostructures based on twisted WSe2/MoS2 hetero-bilayer is discussed. The results showed that inhomogeneity across the heterostructure interface brought by strain and contamination has an impact on the formation of the interlayer exciton (ILX) by reducing the hybridisation of the electronic states between the two 2D layers. In addition, the interface between the semiconductor and oxide in oxidised HfS2 and GaS is probed using complementary characterisation techniques. The results clearly demonstrate the role of the oxidation method on the crystallinity, thickness and uniformity of the produced oxide. This level of control facilitated the production of highly uniform ultrathin oxide layers on top of their corresponding 2D semiconductor materials, which are used for the first demonstration of low-energy resistive switching.18 0Item Restricted Chemical and Mechanical Sensing of Graphene and MoS2 2D Materials(Saudi Digital Library, 2023-08-10) Alshammari, Majed Fahad; Dalton, AlanSensing technologies have garnered significant attention owing to their significance in both present-day and future contexts. Numerous industries, particularly the food and health- care sectors, are actively pursuing the development of high-performance sensors. These sensors are crucial in enhancing quality standards within these sectors. The miniaturiza- tion of sensor technologies utilizing conventional semiconductors is approaching its inher- ent limitations, wherein the ability to build them at increasingly smaller scales is becoming increasingly challenging while still ensuring optimal performance. Nanotechnologies have given rise to a novel discipline known as 2D material science, which involves the fabrication of nanoscale thin materials exhibiting distinctive structures and electrical properties. Graphene and MoS2, belonging to the TMDs group, are well recog- nized as prominent 2D materials. These materials exhibit distinctive mechanical, elec- trical, and thermal characteristics, rendering them highly suitable for the development of effective nanoscale sensors. This work employs graphene and MoS2 as sensors, with graphene balls serving as mech- anical sensors and MoS2 as chemical sensors. The paper elucidates the synthesis of these two-dimensional materials and outlines the procedure for evaluating the sensing capabil- ities of each material. I kindly request that you rewrite your text to adhere to academic standards. In this study, a two-dimensional (2D) MoS2 flake is employed as a chem- ical sensor to investigate its sensitivity towards ethanol and IPA compounds upon their introduction into the surface of MoS2. Ultimately, the objective is to evaluate the mech- anical sensing capabilities of the graphene ball by employing an Atomic Force Microscope (AFM) tip to induce strain in the graphene structure and measure the resulting electrical fluctuations.8 0