A variety of novel hierarchical nanostructures with 6-, 4-, and 2-fold symmetries have been successfully grown by a vapor transport and condensation technique. It was found that the major core nanowires are single-crystal In2O3 with 6, 4, and 2 facets, and the secondary nanorods are single-crystal hexagonal ZnO and grow either perpendicular on or slanted to all the facets of the core In2O3 nanowires. The core In2O3 nanowires have diameters of about 50−500 nm, whereas the secondary ZnO nanorods have diameters of about 20−200 nm. Depending on the diameter of the core In2O3 nanowires, the secondary ZnO nanorods grow either as a single row or multiple rows. These hierarchical heteronanostructures may find applications in a variety of fields such as field emission, photovoltaics, transparent EMI shielding, supercapacitors, fuel cells, high strength and multifunctional nanocomposites, etc. that require not only high surface area but also structural integrity.

WurtziteZnO nanobridges and aligned nanonails have been synthesized by thermal vapor transport and condensation method. The nanobridges have two rows of c-axis ZnO nanorods epitaxailly grown on the edges of the {0001} plane of the ZnO nanobelt. Some variations of the nanobridges have also been observed. The ZnO nanonails, with crystalline cap and small diameter shafts, grow along the c-axis. The shape of the nanonail cap and shaft varies. The nanobridges have very low concentration of indium in the structure and the nanonails are pure ZnO. These materials have potential in applications such as optoelectronics, etc.

Studies on field emission (FE) from thin films of zinc oxide (ZnO) nanowires found that both the turn-on voltage and emission current density depend on the areal density of nanowires. The density of ZnO nanowires is controlled by the gold (Au) nanoparticle density deposited on the silicon substrates. The growth of ZnO nanowires was achieved by the thermal evaporation/condensation method. It is shown that the same screening effect observed on carbon nanotube field emitters also affects the FE from thin films of ZnO nanowires. Thin films with the lowest areal density of ZnO nanowires showed much better FE characteristics, comparable to that of carbon nanotubes. More importantly, the FE characteristics of ZnO nanowire thin film were further improved with annealing in hydrogen.

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were estimated by subtracting the optical energy gap from the measured I p .OLED devices were fabricated on ITO-coated glass substrates. The PEDT:PSS layer was deposited by spin coating. All other material layers in the devices, including the metal cathode, were deposited by thermal evaporation in a multiple-source vacuum chamber with a base pressure of < 10 ±6 torr. The deposition rate of organic layers was kept at about 0.2 nm s ±1 . The deposition system permits the fabrication of the complete device structure in a single vacuum pump-down without breaking vacuum. The active area of the device is 2 mm 2 mm, as defined by the shadow mask for cathode deposition. The current±voltage±brightness (I±V±L) characteristics of EL devices were measured using a source-measurement unit (SMU) and a Si photodiode calibrated with Photo Research PR-650 spectroradiometer. The EL spectra were taken with a calibrated CCD spectrograph