Browsing by Author "Zhao, Yuming"

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    Nanoimprinted conducting nanopillar arrays made of MWCNT/polymer nanocomposites: a study by electrochemical impedance spectroscopy
    Xiao, Chuan; Zhao, Yuming; Zhou, Wei (2021-01-21)
    Conducting vertical nanopillar arrays can serve as three-dimensional nanostructured electrodes with improved electrical recording and electrochemical sensing performance in bio-electronics applications. However, vertical nanopillar-array electrodes made of inorganic conducting materials by the conventional nanofabrication approach still face challenges in terms of high manufacturing costs, poor scalability, and limited carrier substrates. Here, we report a new type of conducting nanopillar array composed of multi-walled carbon nanotube (MWCNT) doped polymeric nanocomposites, which are manufactured on the wafer-scale on both rigid and flexible substrates by direct nanoimprinting of perfluoropolyether nanowell-array templates into uncured MWCNT/polymer mixtures. By controlling the MWCNT ratios and the annealing temperatures during the fabrication process, MWCNT/polymer nanopillar arrays can be endowed with outstanding electrical properties with high DC conductivity (similar to 4 S m(-1)) and low AC electrochemical impedance (similar to 10(4) omega at 1000 Hz). Moreover, by electrochemical impedance spectroscopy (EIS) measurements and equivalent circuit modeling analysis, we can decompose the overall impedance of the MWCNT/polymer nanopillar arrays in the electrolyte into multiple bulk and interfacial circuit components, and can thus illustrate their different dependences on the MWCNT ratios and the annealing temperatures. In particular, we find that an appropriate annealing process can significantly reduce the anomalous ion diffusion impedance and improve the MWCNT/polymer nanopillars' impedance properties in the electrolyte.
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    Sensing Interfacial Non-Faradaic and Faradaic Processes via Plasmonic-Enhanced Metallic Luminescence in Nano-Optoelectrodes
    Zhao, Yuming (Virginia Tech, 2024-01-03)
    Metallic nanostructures supporting surface plasmon modes can concentrate optical fields, and enhance luminescence processes from the metal surface at plasmonic hotspots. Such nanoplasmonic metal luminescence contributes to the spectral background in surface-enhanced Raman spectroscopy (SERS) measurements and is helpful in bioimaging, nano-thermometry, and chemical reaction monitoring applications. Despite increasing interest in nanoplasmonic metal luminescence, little attention has been paid to investigating its dependence on voltage modulation. Also, the hyphenated electrochemical surface-enhanced Raman spectroscopy (EC-SERS) technique typically ignores voltage-dependent spectral background information associated with nanoplasmonic metal luminescence due to limited mechanistic understanding and poor measurement reproducibility. In this thesis, we combine the experimental observations and theoretical study on dynamic Faradaic & non-Faradaic modulated nanoplasmonic metallic luminescence and molecular vibrational Raman from hotspots at the electrode-electrolyte interfaces using multiple novel nano-optoelectrodes. Our work represents a critical step toward the general application of nanoplasmonic metal luminescence signals in optical voltage biosensing, hybrid optical-electrical signal transduction, and interfacial electrochemical monitoring.