Author: Soraya Rahpeima
Rahpeima, Soraya, 2023 Integration of 2D materials to surfaces of electrodes, Flinders University, College of Science and Engineering
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Advances in design and development of nano/micro-scale electronic components such as transistors and integrated circuits have revolutionized consumer products as in computers and smartphones. 2D Materials are central for achieving further development of the electronics industry. However, to obtain the full potential of 2D materials, they need to be connected to electrodes. Indeed, connecting 2D materials with electrodes such as silicon (Si) will advance the existing semiconductor technology. The focus of this dissertation is covalently attaching thin 2D materials to Si electrodes to improve the electrical properties of semiconducting devices based on this element.
During the course of PhD, it was discovered that graphene oxide (GO) reacts with Si via a Si‒O‒C bonding. The contact is based on a direct and spontaneous covalent attachment between Si surface and the GO layer which is confirmed by no desorption after electrochemically reduction of GO to reduced graphene oxide (rGO). The Si‒rGO surface showed advantageous electrical responses such as reduction of the Schottky barrier at the interface of metal‒semiconductor (M‒S) contacts, which is an energy cost in the semiconducting industry. The GO layer was found to function as a protective layer for H‒terminated Si (Si‒H) electrode against oxidation due to its impermeability to gases and liquids. This property is also beneficial to the semiconducting and solar cells research. Direct covalent bonding between GO and Si led to the protection of Si against oxidation for up to 30 days. In an attempt to connect 2D materials with electrodes using radical reactions, the electrochemical reduction of aryl diazonium salts was used, which was found to be pivotal, not only for bridging in between 2D materials and electrodes, but also for functionalization of Si‒GO surfaces for further applications. During the course of this thesis, interesting fundamental understanding was found regarding how molecular film deposition on Si electrodes depends on the surface charge and on the crystal orientation of the surface. The kinetics of diazonium salts molecular grafting was found to be highly dependent on the crystallinity of the electrode substrate, due to differences in the potential of zero charge (PZC) of each crystal plane. These findings offer opportunities in understanding and controlling electro grafting of organic thin films on hybrid semiconducting devices for effective engineering 2D materials connection. The dissertation also explores new properties of 2D materials generated by the vortex fluidic device (VFD) and their properties when interfaced with electrodes, particularly Si. The VFD offers a simple and a versatile pathway for fabrication of new forms of 2D materials in the realm of clean technology. Investigation of electrochemical, electrical, and magnetic properties of VFD fabricated 2D materials, when deposited on the electrode, were carried out by Cyclic Voltammetry (CV), Conductive-Atomic Force Microscopy (C-AFM), and Magnetic Force Microscopy (MFM) characterization techniques.
Keywords: 2D materials, graphene oxide, reduced graphene oxide, diazonium salt, H-terminated silicon
Subject: Chemistry thesis
Thesis type: Doctor of Philosophy
Completed: 2023
School: College of Science and Engineering
Supervisor: Prof. Colin Raston