Scanning Probe Studies of One and Two Dimensional Organic Polymers
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Murali, Harshavardhan
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Abstract
This document explores the synthesis and characterization of one and two-dimensional organic materials through a combination of surface-assisted chemical synthesis and characterization techniques. The first part of the thesis focuses on the on-surface synthesis and characterization of a two-dimensional heterotriangulene based Covalent Organic Framework (COF). We characterize the incorporation of atomic hydrogen as a tool to modulate the in-situ growth in Ultra-High Vacuum (UHV), using the dimethylmethylene-bridged triphenylamine (DTPA) COF. Scanning Tunneling Microscopy (STM) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) revealed insights into the structural growth properties of these materials. Semiempirical calculations were performed to complement the experimental Scanning Tunneling Spectroscopy (STS) data and computational Density Functional Theory (DFT) calculations to further elucidate the electronic structure. We then describe the synthesis and characterization of donor-acceptor polymers based on a benzobisthiadiazole (BBT) acceptor and dithophene donors on Au(111), theorized to have a freestanding open shell electronic structure, using STM and STS to uncover their properties as synthesized on the surface. We do not observe features that suggest an open shell character, but low temperature STS measurements indicate the presence of a conductance peak near zero bias that appears when picking up monomer molecules. In the final part of the thesis, we present preliminary investigations into imaging porphenes, a class of two-dimensional materials composed of repeating porphyrin units, using STM.
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2024-12-13
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Dissertation