Ordered semiconductor ZnO nanowire arrays embedded in anodic alumina membranes (AAM) were fabricated by generating alumina templates with nanochannels, electrodepositing Zn in them, and then oxidizing the Zn nanowire arrays. The polycrystalline ZnO nanowires with the diameters ranging from 15 to 90 nm were uniformly assembled into the hexagonally ordered nanochannels of the AAM. Photoluminescence (PL) measurements show a blue PL band in the wavelength range of 450–650 nm caused by the singly ionized oxygen vacancy in ZnO nanowires.

Here, we report a generic synthetic approach to rationally design multiply connected and hierarchically branched nanopores inside anodic aluminum oxide templates. By using these nanochannels, we controllably fabricate a large variety of branched nanostructures, far more complex than what exists today. These nanostructures include carbon nanotubes and metallic nanowires having several hierarchical levels of multiple branching. The number and frequency of branching, dimensions, and the overall architecture are controlled precisely through pore design and templated assembly. The technique provides a powerful approach to produce nanostructures of greater morphological complexity, which could have far-reaching implications in the design of future nanoscale systems.T he design and controlled synthesis of complex nanowire (1-5) and carbon nanotubes (CNTs) (6-8) will impact developments in nanotechnology applications. The present synthesis approaches, however, limit the degree of complexity that can be controllably configured into these structures. Fabrication inside rationally designed porous templates [such as anodic aluminum oxide (AAO) templates] is ideal to produce nanowire morphologies, but this feat has been accomplished controllably only for linear (9-15) and Y-shaped (6, 7) architectures. The creation of controlled pore structure, with various levels of complexity, inside these templates provides a powerful way to produce predesigned multiply connected and branched nanowires and nanotubes. We have developed a rational approach for creating hierarchically branched nanoporous AAO templates and have fabricated a whole generation of branched nanowires and nanotubes inside these templates. As a suitable example, we detail the case of CNT structures in this work, but other material systems can also be made into similar architectures, as highlighted for the case of metallic nanowires in Materials and Methods. Materials and MethodsPreparation of AAO Templates. AAO templates were prepared by using a modified two-step anodization process (6, 16). The first-step anodization was the same for all templates. High-purity Al foils were anodized in 0.3 M oxalic acid solution at 8-10°C under a constant voltage (in the range of 40-72 V dc ) for 8 h. Then, the formed anodic aluminum layer was removed. In the second-step anodization, templates with different pore architectures underwent different processes of anodization as follows. AAO Templates with Multiple Generations of Y-Branched Pores.We reduced the anodizing voltage multiple times in the second-step anodization. Initially, the anodization was performed under the same conditions as those in the first step to create the primary stem pores; then, the anodizing voltage was reduced by a factor of 1͞ ͌ 2 to form Y-branched pores. Two-, three-, and fourgeneration Y-branched pores can be obtained by further sequential reduction of anodizing voltages. It is noted that if a subsequent anodizing voltage is Յ25 V, after any prior anodization, the samples should be washed in deionized w...

In2O3 nanofibers have been prepared by using a thermal evaporation–oxidation method. The nanofibers generally show rectangular cross sections (see Figure) with different width‐to‐thickness ratios. The photoluminescence spectrum of these nanowires shows light emission in the blue‐green region. By doping with other elements potential applications in opto‐electronic nanodevices and nanosized gas sensors could be achieved.

There are two mass diffusion processes regarding the vapor-liquid-solid (VLS) growth of nanostructures: one is inside the catalyst droplet toward the liquid-solid interface; the other is along the side surface planes of the growing nanostructures. In this letter, microscale, modulated mass diffusion scenarios are exhibited through the synthesis of two types of ZnS nanostructures in an Au-catalyzed VLS process: periodically twinned nanowires originated from periodical fluctuation between diffusion rate inside the catalytic droplet and the growth rate on the liquid-solid interface; the formation of asymmetrically polytypic nanobelts is related to one certain side surface bounded by high surface-energy plane, which serves as a preferential diffusion direction of reactant adatoms. The results may have important impact on the understanding of the physical and chemical process of the VLS mechanism. These longitudinally and latitudinally tunable crystalline structures enrich the family of one-dimensional nano-building blocks, and may find potential applications in nanotechnology.