Single-crystalline and uniform nanopolyhedra, nanorods, and nanocubes of cubic CeO2 were selectively prepared by a hydrothermal method at temperatures in the range of 100-180 degrees C under different NaOH concentrations, using Ce(NO3)3 as the cerium source. According to high-resolution transmission electron microscopy, they have different exposed crystal planes: {111} and {100} for polyhedra, {110} and {100} for rods, and {100} for cubes. During the synthesis, the formation of hexagonal Ce(OH)3 intermediate species and their transformation into CeO2 at elevated temperature, together with the base concentration, have been demonstrated as the key factors responsible for the shape evolution. Oxygen storage capacity (OSC) measurements at 400 degrees C revealed that the oxygen storage takes place both at the surface and in the bulk for the as-obtained CeO2 nanorods and nanocubes, but is restricted at the surface for the nanopolyhedra just like the bulk one, because the {100}/{110}-dominated surface structures are more reactive for CO oxidation than the {111}-dominated one. This result suggests that high OSC materials might be designed and obtained by shape-selective synthetic strategy.

By decomposing Zn(OH)4 2- or Zn(NH3)4 2+ precursor in various solvents at suitable reaction conditions, zinc oxide with a diversity of well-defined morphologies was synthesized. Flowerlike ZnO built up by nanorods was obtained by treating Zn(OH)4 2- precursor in water at 180 °C for 13 h. Whereas a replacement of the solvent by n-heptane yields snow flakelike ZnO. The prismlike and the prickly spherelike ZnO were also prepared, respectively, by decomposing Zn(NH3)4 2+ or Zn(OH)4 2- in ethanol at 100 °C for 13 h. The rodlike ZnO was produced at 180 °C under the same condition for preparing prickly spherelike product. Besides these typical samples, ZnO in other morphologies was studied manipulatively by changing the reaction conditions of our solution route. Systematical condition-dependent experiments were compared comprehensively to reveal the formation and detailed growth process of ZnO nanosized crystallites and aggregates. The experimental results studied by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy indicated that the solvent, precursor, solution basicity, and reaction temperature as well as time are responsible for the variations of ZnO morphologies.

Phosphate ions play a crucial role not only for the formation of the spindlelike precursors of the single‐crystalline hematite nanotubes that were synthesized by a facile hydrothermal method. They are also important for the adsorption and coordination effects. The mechanism of tube formation was deduced through EM observations as a coordination‐assisted dissolution process (see picture).

We present an innovative approach to the production of single-crystal iron oxide nanorings employing a solution-based route. Single-crystal hematite (alpha-Fe2O3) nanorings were synthesized using a double anion-assisted hydrothermal method (involving phosphate and sulfate ions), which can be divided into two stages: (1) formation of capsule-shaped alpha-Fe2O3 nanoparticles and (2) preferential dissolution along the long dimension of the elongated nanoparticles (the c axis of alpha-Fe2O3) to form nanorings. The shape of the nanorings is mainly regulated by the adsorption of phosphate ions on faces parallel to c axis of alpha-Fe2O3 during the nanocrystal growth, and the hollow structure is given by the preferential dissolution of the alpha-Fe2O3 along the c axis due to the strong coordination of the sulfate ions. By varying the ratios of phosphate and sulfate ions to ferric ions, we were able to control the size, morphology, and surface architecture to produce a variety of three-dimensional hollow nanostructures. These can then be converted to magnetite (Fe3O4) and maghemite (gamma-Fe2O3) by a reduction or reduction-oxidation process while preserving the same morphology. The structures and magnetic properties of these single-crystal alpha-Fe2O3, Fe3O4, and gamma-Fe2O3 nanorings were characterized by various analytical techniques. Employing off-axis electron holography, we observed the classical single-vortex magnetic state in the thin magnetite nanorings, while the thicker rings displayed an intriguing three-dimensional magnetic configuration. This work provides an easily scaled-up method for preparing tailor-made iron oxide nanorings that could meet the demands of a variety of applications ranging from medicine to magnetoelectronics.

though ALD is mainly applied to high-k dielectric ultra-thin films for gate oxides of field-effect transistors because of the low deposition rate, it is a useful tool for nanostructure fabrication as demonstrated in this study. ExperimentalAAO Fabrication: An ordered hole array of AAO, pore diameter~35 nm and pore density~10 10 cm ±2, was fabricated by aluminum anodization. Al thin film (500 nm) was sputtered on a silicon wafer and then oxidized in a 0.3 M oxalic acid solution at 16 C under a constant voltage of 40 V. The pore diameter of the AAO was increased in 0.1 M phosphoric acid solution.CNT Growth: For CNT growth on AAO by CVD, the AAO/Si substrate was first heated at 600 C in a nitrogen atmosphere. The CNTs were then grown inside the pores by catalytically pyrolyzing acetylene for 20 min using 10 % acetylene in nitrogen carrier gas (100 sccm). The resulting specimen was ionmilled to remove residual amorphous carbon from the template surface and the CNTs were partially exposed by etching the alumina matrix using a mixture of phosphoric acid and chromic acid.Ru ALD: Metallic Ru thin films (~6 nm) were coated on the CNT array by ALD using Ru(od) 3 /n-butylacetate solution (0.1 M) (od = octane-2,4-dionate) and oxygen gas. Ru(od) 3 solution was kept in a canister pressurized with argon fitted with a liquid injector. The injector was connected to a vaporizer, which was attached to a reaction chamber containing the CNT template. When the injector was turned on, about 0.01 mL Ru(od) 3 solution was injected and carried by Ar gas (150 sccm) to the vaporizer, which was kept at 200 C. The valves for Ru(od) 3 vapor and oxygen gas (100 sccm) were alternately opened for 2 s with an interval of 3 s to purge volatile byproducts and any excess reactants in the reaction chamber with Ar (300 sccm). The working pressure was regulated to about 1 torr in every step by an automatic valve for 70 cycles.Removal of CNT Templates: To remove carbon nanotube templates by ashing, the Ru-coated CNT array was heated at 500 C in an oxygen flow of 100 sccm (1 torr) for 1 h.Analytical Method: DFM images were obtained with a dynamic force microscope in non-contact mode (SPA 500, Seiko Instruments Inc.). All DFM experiments were performed in air at room temperature. The HR-TEM images, EDS spectra, and annular dark-field scanning transmission electron microscope (ADF-STEM) images were obtained by a TECNAI-UT30 microscope equipped with a Schottky-type field emission gun operating at 300 kV.

Thermal treatment of Zn(NH3)(4)2+ precursor in ethanol solvent led to the formation of the tubular ZnO which exhibited strong ultraviolet photoluminescence around 385 nm at room temperature; TEM images showed the hollow tubules with approximately 450 nm in diameter and approximately 4 microns in length were built up by ZnO polycrystals.

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