Synthesis and characterization of two dimensional materials for electronic and thermoelectric applications
- The family of two-dimensional (2D) materials has been demonstrated to possess unique characteristics that make them appealing for scaled electronic applications. However, this versatile class of materials comes with its own unique challenges for fabrication and integration into widespread adoption. Therefore, in this work, we investigate the synthesis and properties of selected 2D materials, working to understand how their unique characteristics may impact their utility. First, we develop and refine processes for large-area chemical vapor deposition (CVD) of hexagonal boron nitride (h-BN) onto carbon nanotube (CNT) and metal substrates. We report one of the first demonstrations of direct deposition of multilayer h-BN on CNTs, resulting in a thin capping layer on the CNTs without the use of a transfer process. Additionally, we elucidate some effects of substrate crystallinity on the resultant h-BN film by characterizing films deposited on both polycrystalline and single crystal Pt substrates. Finally, we demonstrate the use of monolayer h-BN as an ultra-thin protective barrier layer, protecting monolayer MoS2 from degradation at elevated temperatures, and we discuss additional applications for this material. In addition, we investigate fundamental thermoelectric properties of thin WSe2, fabricating on-chip heater and thermometer structures and quantifiably demonstrating the benefits of using a low-thermal conductivity substrate to maintain a larger temperature gradient along the channel. Using our measurement platform, we measure the highest Seebeck coefficients for thin WSe2 reported in literature to date, demonstrating its promise for temperature sensing and energy harvesting applications. We conduct measurements on multiple WSe2 samples, studying the effect of film thickness on the thermoelectric properties, and electrostatically gate the channels using an ion gel, which enables us to sweep over a wide range of electron and hole carrier densities. Finally, we explore the effects of edge contributions to narrow MoS2 and WSe2 channels, fabricating back-gated devices on exfoliated nanoribbons. The exfoliation process to deposit these nanoribbons is promising for maintaining "pristine" edges, which are ideally in the armchair or zigzag configuration. This can allow for the impact of these edges on the electronic transport properties to be studied, and we measure numerous transistors with parallel nanoribbon channels to consider these effects. We observe some trends with the maximum and minimum currents vs. the average ribbon width of these channels, and outline the next steps for this project to further understand the edge contributions. This work explores the deposition as well as fundamental electronic and thermoelectric properties of 2D materials, aiming to incrementally advance this family of materials towards viability in larger-scale applications.
|Type of resource
|electronic resource; remote; computer; online resource
|1 online resource.
|Chen, Victoria Li Chien
|Degree committee member
|Degree committee member
|Stanford University, Department of Electrical Engineering
|Statement of responsibility
|Submitted to the Department of Electrical Engineering.
|Thesis Ph.D. Stanford University 2022.
- © 2022 by Victoria Li Chien Chen
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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