Local Probe Analysis of the Structural, Electronic, and Optical Properties of Nanomaterials
This dissertation is divided into two segments. The first segment focuses on the structural and electronic characterization of one-dimensional (1D) and two-dimensional (2D) nanostructures using scanning tunneling microscopy (STM) and spectroscopy (STS). The second segment focuses on the investigation of unique optical behavior in 1D-2D heterosystems using scattering-scanning near-field optical microscopy (s-SNOM).
Bottom-up synthesis from molecular precursors provides a useful methodology for designing and fabricating interesting nanomaterials. The first part describes application of bottom-up synthesis techniques to fabricate 1D nanostructures (graphene nanoribbons (GNRs)) and 2D networks (covalent organic frameworks (COF)). Following the synthesis, the structural and electronic properties of these nanomaterials were studied using STM and STS. In this dissertation, two specific GNR projects are discussed that provide in-detail investigation of the manipulation of the electronic properties of GNRs through the site-specific introduction of dopant atoms. The first project describes the detailed study of boron-doped N=7 AGNRs, where the AGNRs are substitutionally doped with boron atoms in their backbone. The second project focuses on the study of sulfur-doped N=13 GNRs, where the sulfur atoms substitutionally dope the edges of the GNRs. This dissertation also describes two COF projects that demonstrate the strong dependence of the electronic structure of single-layer COFs on the chemical bond arrangement within the covalent network. Specifically, the synthesis and characterization of two different porphyrin-based single-layer 2D COFs that exhibit symmetric (COF-366-OMe) and asymmetric (COF-420) bonding environments are studied.
The second part of the thesis describes investigation of the coupling between 1D plasmon polaritons in silver nanowires with 2D phonon polaritons of the silicon carbide (SiC) substrate. The silver nanowire-SiC hybrid structure was investigated using near-field infrared spectroscopy. A significant change in the 1D plasmon dispersion by the 2D phonon polaritons in SiC was observed upon approaching the SiC phonon polariton energies.