Controlling chemical modification of chlorinated silicon surfaces via wet-chemistry approaches and morphology-preserving functionalization of metal oxide nanomaterials through two-step click reaction
Date
2020
Authors
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Publisher
University of Delaware
Abstract
Functionalization of semiconductor surfaces has a wide range of applications in numerous fields including sensing, catalysis, photo-electro chemistry, and energy conversion. The controlled and tunable covalent bonding is required to introduce designated functionality onto the surfaces bringing unique physical and chemical properties for the specific applications. Therefore, developing novel functionalization approaches is always necessary to make the controlled and tunable functionalization of semiconductor surfaces attainable as well as to achieve better understanding of the bonding processes and reaction mechanisms. ☐ The work outlined in this dissertation expounds novel chemical approaches to the functionalization of silicon and metal oxide surfaces. Firstly, direct covalent attachment of dye molecules to silicon surface was achieved based on the stable Si-N bond formation through the reaction between protonated nitrogen atoms from the pyrrole structure of dye molecules and chlorine modified silicon surface. Furthermore, it was demonstrated that the physical and chemical properties of resulting dye-functionalized silicon surface can be tuned by self-metalation, thus making the wide range of applications possible by design. Secondly, a novel approach utilizing a two-step chemical procedure was developed to introduce desired organic functionality onto the surfaces of metal oxide nanomaterials with morphology preservation of brittle nano-features. Gas-phase exposure of prop-2-ynoic acid was carried out onto surfaces of different metal oxide nanomaterials (ZnO nanorods, CuO nanowires, TiO2 nanoparticles, and CeO2 nanoparticles) to achieve the morphology-preserving functionalization of metal oxide nanomaterials in the first step. The second step utilizes the created alkyne functional group for post-modification that introduces any pre-designed functionality to the surface via “click” chemistry with azides (R-N3). ☐ The combined spectroscopic, microscopic and theoretical investigations were performed to study the surface functionalization processes. X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), time-of-flight secondary ion mass spectrometry (ToF-SIMS), solid-state nuclear magnetic resonance spectroscopy (ss-NMR) and X-ray diffraction (XRD) were employed to comprehend the chemical reaction during the surface functionalization processes. Atomic force microscopy (AFM and scanning electron microscopy (SEM) were utilized to monitor the surface morphological information. Density functional theory (DFT) calculations were applied to stimulate the surface functionalization supporting the experimental results and to suggest plausible reaction mechanisms.
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Keywords
Click reaction, Metal oxides, Semiconductor surfaces, Sensitization, Silicon