Probing the Physical and Chemical Properties of Zinc Oxide Nanorods Using Confocal Raman Spectroscopy
Hansen, Matthew Niles
Zinc Oxide (ZnO) is a known waveguiding material whose bulk properties have widely been studied using Raman spectroscopy. Confining the material to the nanometer size domain affects the light-matter interaction of the material, leading to many interesting and useful phenomena which make ZnO nanomaterials promising candidates for development of nanometer sized probes for a variety of spectroscopic techniques. Raman spectroscopy is a powerful vibrational spectroscopic tool which can provide both concentration and structural data for a variety of molecules and is especially useful in biological matrices where water interference is problematic for other vibrational techniques. In developing ZnO nanorods (NRs) as miniature Raman probes, it is paramount to understand how the physical and chemical properties of this material are affected by nanometer size constraints to fully exploit their potential as substrates.Spatially resolved Raman spectroscopy was used to probe the unique light-matter and chemical properties of ZnO NRs. The position-resolved Raman scattering revealed behaviors both consistent and inconsistent with selection rules. More specifically, I observed the appearance of geometrically forbidden modes exclusively at the ends of the NRs. This was accompanied by an increase in the intensity of the allowed modes at the ends of the NRs. Building on these findings, ZnO NRs were reacted with hydrogen sulfide (H2S) in order to understand facet specific reactivity of the ZnO NRs. I demonstrated that the end facets of the NRs are more reactive than the side facets towards sulfidation, owing to their chemically unique surface. Finally, I demonstrate that the inclusion of copper into the ZnO crystal lattice alters the Raman properties of the ZnO NRs in two different ways. First, incorporation of Cu in the crystal lattice leads to a shift in the E2H mode and secondly, the copper leads to symmetry breaking allowing for the appearance of non-Raman active peaks. These insights should prove to be an important base of knowledge for further development of ZnO NR probes.
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Investigating the Fundamental Optical Properties of Single Zinc Oxide Nanorods as an Optical Waveguide for Biomedical Applications Truong, Johnson Thanh (Georgetown University, 2020)The superior optical properties of zinc oxide nanorods (ZnO NRs) have continued to promote their broad use in photonics, light detecting, and biosensing applications due to their waveguiding properties. One particularly ...