AmericanChemicalSociety.com

We have produced vertically aligned glass microspikes using fiber drawing method. In order to make hierarchically ordered arrays of nanoelectrodes on the microspikes, we have grow vertically aligned ZnO nanowires using vapor deposition method. In this method, Zn powder is heated in a flow of nitrogen on the upstream of a receiving substrate, and oxygen is supplied over the receiving substrate through a smaller diameter tube. Both tubes are heated in a tube furnace at 560°C. At this temperature, solid zinc powder is molten and zinc vapor is delivered onto the receiving substrate, where oxidization reaction occurs and ZnO nanowires are produced. Fig. A shows an SEM image of vertically aligned nanowires grown on a 1 cm² glass substrate. EDX spectra confirm that the compositions of nanowires are zinc and oxygen. The nanowires are attached strongly on a glass surface; we have shown that the nanowires are fixed on surface even after boiling in hot water for over 2 hours. The nanowires can be grown on glass microspikes, thus forming hierarchal nanoelectrodes for solar energy conversion. In addition, ZnO nanowires can form three dimensional (3D) structures as shown in Fig. B. Such 3D structures show interesting optical properties. Under strong light excitation, 3D structures show weak fluorescent properties. Meanwhile, vertical nanowires can be used as wicks in heat pipe to enhance heat transfer. The water vapor condenses on the wick structure, and flow back to hot source. The tilt angles of nanowires can be controlled to have porous structures, which allow fast return of condensed water. The project has supported a graduate (Mr. Jerry Ma) and an undergraduate (Michelle Garcia). The hierarchically ordered nanowires will be used as nano-electrodes for dye sensitized solar cells, or organic solar cells. We are now working with Dr. Andre Gesqueire on the optical emission of ZnO nanowires and their 3D structures.