Synthesis of carbon and zinc oxide nanotubes and their applications in electronic devices

Nanostructured materials, including single and multiwalled carbon nanotubes (SWCNTs and MWCNTs), zinc oxide (ZnO) nanotubes (NTs) and graphene, have been successfully synthesized using chemical vapor deposition (CVD) or wet chemistry routines, and used to fabricate nanoelectronic and optoelectronic devices, including field effect transistors (FETs) and heterojunction solar cells. Both nanomaterials properties and devices performances have been characterized.;Vertically aligned multiwalled carbon nanotubes (VACNTs) have been synthesized using both the pre-deposited iron films and the continuous supply of catalytic species via gas flow in pyrolytic decomposition of hydrocarbons by CVD. High quality VACNTs have been obtained after the optimization of synthesis parameters.;Using metal nanoparticles as catalysts, centimeter-long SWCNTs have been synthesized on a silicon wafer with a thin thermal oxide layer. A series of FETs have been fabricated directly on a single SWCNT by inkjet printing of Pd nanoparticles to form both source and drain electrodes. The devices exhibit typical Schottky barrier p-type conductance characteristics. The line density and field mobility of charge carriers, as well as the effect of gate field modulation have been shown to strongly depend on thermal treatment of the SWCNT-FETs, implying the effect of carrier doping and interfacial reconstruction.;ZnO NTs have been synthesized in an aqueous solution of zinc nitrate at 60ºC. A novel core-shell growth mechanism was hypothesized to explain the synthesis of ZnO NTs. The crystalline microstructures and optical properties of ZnO NTs upon thermal annealing in air at various temperatures have been examined. Ultraviolet-Visible (UV-Vis) absorption spectra reveal a slightly redshift of the direct band gap upon annealing.;Solution structure of regioregular poly(3-hexylthiophene) (RR-P3HT) in toluene has been examined using optical spectroscopy in situ and atomic force microscopy upon casting films on a clean substrate. Time-resolved absorption and emission spectra indicate an increasing conjugation length with the storage time for an initially homogeneous solution. AFM micrographs show growing rod-like aggregates in solution over time.;Bulk heterojunction solar cells have been fabricated with a layered structure of glass-substrate/ graphene/ZnO NTs/P3HT/poly(3,4-ethylenedioxythiophene):poly(styrenesulfon ate)(PEDOT:PSS)/Au, in which vertically aligned ZnO NTs are electron donors, P3HT is the acceptor, and a highly conductive graphene film is the transparent electrode. The open-circuit voltage, short-circuit current density, fill factor, and power conversion efficiency have been measured to discuss the potential of such energy harvesting devices.