Fundamental studies on surface chemistry and interfacial interactions of nanoscale heterostructures for chemical sensing, photocatalysis, and thermal transport management
By combining carbon nanostructures (e.g., graphene, CNTs) with noble metal nanoparticles and further integration them with semiconducting nanowires or quantum dots, it is possible to achieve unique multifunctional hybrid nanoscale heterostructures. The heterostructures are anticipated to exhibit novel thermal, chemical, mechanical, electrical and optical performances. This dissertation mainly focused on fundamentally understanding of the processing, structure-property relationships and novel physical phenomenon related noble metal-carbon nano-systems and their heterostructuring with semiconducting nanowires or quantum dots. This leads to the generation of fundamental knowledge and effective control of their structure, morphology, surface and interface properties with novel processing methods, and thus further allows for modulating their electric, optical, chemical, thermal and mechanical performances. The main content of this dissertation was summarized as follows. (1) Carbon-base surface chemistry: fabrication (Chemical Vapor Deposition or CVD) and controlled patterning of graphene encapsulated gold nanoparticles (referred as graphene nanoparticles or GNPs) on silicon substrate and their surface functionalization with DNA, external nanoparticles, or semiconducting quantum dots; (2) metal oxide heterostructures for photocatalysis and electrocatalysis: cobalt oxide (Co3O4) nanowires were grown on the cobalt foil using a water vapor-assisted thermal oxidation method. These Co3O4 nanowires were further decorated with tungsten oxide nanostructure for the fabrication of p-n junction heterostructures with improved light-driven organic degradation efficiency; (3) Surface-enhanced Raman Spectroscopy (SERS): Vapor-Liquid-Solid (VLS) growth of silicon (Si) nanowires and their surface decoration with noble metal nanoparticles or graphene nanoparticles (GNPs) for precise and controlled Raman sensing of trace-amount organics; (4) thermal management on carbon nanomaterials: Design of thermal conductivity measurement set-up based on the Raman spectroscopy. The thermal conductivity of carbon nanotube films (pristine and/or after plasma/acid treatment) was measured using the self-designed Raman set-up. A multilayer CNT/polymer nanocomposite film with gradient thermal transport property was designed and fabricated. Their isotropic thermal conduction was further studied and simulated.
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