Growth and characterization of honeycomb SiC monolayer on a TaC(111) surface

Abstract

This thesis proves the successful synthesis of silicon carbide (SiC) monolayers on the tantalum carbide (TaC) (111) substrate through a novel bottom-up growth method, offering improved control over the supply of constituent materials for a more detailed study of the formation process. Initial examination of the clean TaC(111) surface revealed surface-induced states in its electronic band structure. Core level measurements of the Ta 4f core level distinguished its surface and bulk components, but the presence of two bulk peaks led to an investigation of the carbon concentration of the crystal. Analysis of carbon deposition dynamics on the TaC(111) surface revealed carbon diffusion into the bulk resulting in increased TaC stoichiometry. This stoichiometry enhancement was found to be essential to form a SiC monolayer. After silicon deposition, carbon diffused to the surface, bonding with silicon and forming 2D SiC, confirmed by comparing the measured band structure with DFT calculations. The ARPES measurements found that the 2D SiC interacts strongly with the TaC substrate through π band hybridization with the TaC surface states, resulting in a strongly spin-orbit split Dirac-like feature at the K points. Moreover, by depositing an excess amount of carbon, graphene forms on top of the TaC. After silicon deposition, 2D SiC forms underneath the graphene, making it more freestanding. Future research could examine the stability of the SiC monolayer in ambient environments and see whether graphene can provide any protective benefits. Additional next steps would be to explore proximity-induced superconductivity and intercalating layers beneath the SiC monolayer to decouple it from the substrate, allowing a more direct comparison with its theorized electronic properties. By demonstrating a novel and practical way of synthesizing large-area SiC monolayers, this thesis brings 2D SiC into the growing family of two-dimensional materials.

Popular Abstract

By adding carbon and silicon to a tantalum carbide surface, my thesis reveals a new method of creating two-dimensional silicon carbide, a material that could lead to more efficient electronic devices.

Today’s electronics rely heavily on silicon, as most people know. To improve our devices, these silicon electronics have been made smaller and smaller, but have now reached their limit. Imagine if instead of using bulky three-dimensional structures, we could use ultra-thin sheets of atoms stacked together. These sheets, known as two-dimensional (2D) materials, have sparked a new wave of research since the Nobel Prize-winning discovery of graphene in 2010. Graphene, a single layer of carbon atoms, showed us that 2D materials could revolutionize technology, but it has limitations.

For instance, graphene doesn't have a band gap — a property crucial for controlling the flow of electricity in devices like computers, where we need clear on/off states (like traffic lights managing the flow of cars). This band gap is essential for creating the binary ones (electric current) and zeros (no electric current) that are the foundation of computer logic. Materials with a band gap are called semiconductors, and those with a direct band gap are particularly useful for devices such as LEDs, lasers, and solar cells. A direct band gap is like a well-paved road that allows cars to accelerate smoothly and efficiently after stopping at a traffic light, while an indirect band gap is like a twisting road that makes cars take longer to reach full speed.

In my research, I focus on creating a new 2D material: silicon carbide (SiC), which combines silicon and carbon atoms in a single layer. Scientists believe that 2D SiC could be a game-changer because it has a direct band gap but making it has been very challenging. Recently, a breakthrough showed that heating a silicon carbide crystal with a thin layer of tantalum carbide (TaC) on top can help form 2D SiC.

Building on this discovery, my goal was to create 2D SiC directly on a TaC crystal. By adding carbon and silicon to a heated TaC surface, I successfully formed the 2D SiC. This method gave me better control over the formation process and deeper insights into how 2D SiC grows. Additionally, by adjusting the amount of carbon, I could create a graphene layer on top of the 2D SiC. Graphene's stability raised the exciting possibility of using it as a protective layer over the 2D SiC. Future research could explore this possibility.

Most importantly, my work showed a new and controlled way of creating 2D SiC, bringing it closer to being used in the next generation of electronic and optical devices. This could lead to faster, more efficient technology, continuing the progress we've made with silicon but taking it to the next level.

• author: Elvarsson, Audunn Orri
• supervisor: Balasubramanian Thiagarajan; Jan Knudsen
• organization: Department of Physics; Synchrotron Radiation Research
• course: FYSM63 20241
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy
• keywords: ARPES, angle-resolved photoemission spectroscopy, XPS, X-ray photoelectron spectroscopy, core level, core level fitting, electronic band structure, SiC monolayer, silicon carbide monolayer, 2D SiC, two-dimensional SiC, TaC, tantalum carbide, LEED, low-energy electron diffraction
• language: English
• id: 9167231
• date added to LUP: 2024-06-25 10:36:02
• date last changed: 2024-06-25 10:36:02