1D single‐crystalline zinc oxide nanostructures are promising for nanoscale optoelectronic applications. Here a simple chemical vapor deposition method for the growth of well‐aligned ZnO nanorods (see Figure) at low temperature is demonstrated. The nanorods, which grow on fused silica and are preferentially oriented in the c‐axis direction, are strongly UV light emitting, peaking at around 386 nm at room temperature.

Highly oriented ZnO nanorods have been grown on various substrates, such as fused silica, Si(100), and sapphire (110), using a simple catalyst-free CVD method at low temperatures. TEM analyses indicate that epitaxial ZnO nanorods have been grown on sapphire (110) with the ZnO/sapphire orientational relationship [001]|| [110] and [110]||[001]. In the Si(100) substrate, an amorphous SiO x interfacial layer exists between ZnO nanorods and Si(100). The well-aligned ZnO nanorods on fused silica substrates exhibit a strong UV emission and absorption at around 386 nm under room temperature. Photoluminescence and Raman spectra indicate that there is a very low concentration of oxygen vacancies in the highly oriented ZnO nanorods. Diameter control of the well-oriented and high-quality ZnO nanorods is achievable by variation of the growth conditions.

The preparation of high-purity and -quality gallium nitride nanowires is accomplished by a catalytic growth using gallium and ammonium. A series of catalysts and different reaction parameters were applied to systematically optimize and control the vapor-liquid-solid (VLS) growth of the nanowires. The resulting nanowires show predominantly wurtzite phase; they were up to several micrometers in length, typically with diameters of 10-50 nm. A minimum nanowire diameter of 6 nm has been achieved. Temperature dependence of photoluminescence spectra of the nanowires revealed that the emission mainly comes from wurtzite GaN with little contribution from the cubic phase. Moreover, the thermal quenching of photoluminescence was much reduced in the GaN nanowires. The Raman spectra showed five first-order phonon modes. The frequencies of these peaks were close to those of the bulk GaN, but the modes were significantly broadened, which is indicative of the phonon confinement effects associated with the nanoscale dimensions of the system. Additional Raman modes, not observed in the bulk GaN, were found in the nanowires. The field emission study showing notable emission current with low turn-on field suggests potential of the GaN nanowires in field emission applications. This work opens a wide route toward detailed studies of the fundamental properties and potential applications of semiconductor nanowires.

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Well-aligned rutlie and anatase TiO 2 nanorods as well as anatase TiO 2 nanowalls have been synthesized using a template-and catalyst-free metalorganic chemical vapor deposition (MOCVD) method. Structural analyses indicate that single-crystalline rutile and anatase TiO 2 nanorods were formed at 630 °C and 560 °C, respectively, while anatase TiO 2 nanowalls composed of well-aligned nanorods were formed at 535 °C. Optical characterizations of these TiO 2 nanostructures show that the band gap energies for indirect transistion of the rutile TiO 2 nanorods and anatase TiO 2 nanorods as well as nanowalls are at 3.0 and 3.2 eV, respectively.

A significant improvement of the efficiency of the ZnO nanowire ͑NW͒ dye-sensitized solar cell ͑DSSC͒ has been achieved by the chemical bath deposition of the dense nanoparticles ͑NPs͒ within the interstices of the vertical ZnO-NW anode. Impedance analyses of the electron transports in DSSCs reveal that the effective diffusion coefficient of an electron in the ZnO-NW array/NP composite anode falls between those in the ZnO-NW and TiO 2 -NP anodes. The superior performance of the ZnO-NW array/NP composite DSSC to the ZnO-NW cell is mainly ascribed to the enrichment of the light harvesting without significantly sacrificing the electron transport efficiency.

Mercurochrome and N3 dyes are employed to be the sensitizers in the ZnO-nanowire ͑NW͒ dye-sensitized solar cells ͑DSSCs͒. A lower fill factor is obtained in the N3-sensitized cell which results in comparable efficiencies in both ZnO-NW DSSCs although the N3 molecules possess a wider absorptive range for light harvesting. Electrochemical impedance spectroscopy and open-circuit photovoltage decay measurements are employed to investigate the electron transport properties in both ZnO-NW DSSCs. The results indicate that more abundant electron interfacial recombination occurs in the N3-sensitized ZnO-NW DSSC due to the higher surface trap density in the ZnO-NW photoanode after N3 dye adsorption.

Cathodoluminescence ͑CL͒ spectroscopy has been employed to study the electronic and optical properties of well-aligned ZnO nanorods with diameters ranging from 50 to 180 nm. Single-nanorod CL studies reveal that the emission peak moves toward higher energy as the diameter of the ZnO nanorod decreases, despite that their sizes are far beyond the quantum confinement regime. Blueshift of several tens of meV in the CL peak of these nanorods has been observed. Moreover, this anomalous energy shift shows a linear relation with the inverse of the rod diameter. Possible existence of a surface resonance band is suggested and an empirical formula for this surface effect is proposed to explain the size dependence of the CL data.