Synthesis and optical properties of co-doped ZnO submicrometer tubes from electrospun fiber templates.

Submicrometer ZnO tubes have been synthesized by a polymer based template approach using sol-gel deposition. Zinc acetate, a precursor to ZnO, was deposited on catalytically active electrospun polycarbonate fibers approximately 250+/-100 nm in diameter. Thermal degradation of the core fibers resulted in the oxidation of zinc acetate to produce ZnO nanotubes with diameters of approximately 500+/-100 nm and an average wall thickness of approximately 100+/-50 nm. Scanning electron microscopy (SEM), Energy dispersive spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and UV-visible spectroscopy were used to characterize the composition, structure, and morphology of the tubes. Powder X-ray diffraction results showed that a wurtzite crystalline phase was obtained. The UV-visible absorption spectrum was red-shifted by 25 nm due to narrowing of the ZnO band gap (approximately 3.22 eV) as a result of Co doping. Similarly, green band emission was not observed in the emission spectrum, while emission lifetime was determined to be 620 ps from photoluminescence studies.

Fabrication and thermal analysis of submicron silver tubes prepared from electrospun fiber templates.

Submicron silver tubes have been synthesized by a polymer-based template approach. Two different approaches to metallization, electroless deposition and exchange plating, were evaluated within the template approach. Silver films with average thickness approximately 50-100 nm were deposited on polycarbonate fibers approximately 400 nm in diameter by each technique, resulting in tubes with a diameter between 450 and 500 nm after thermal degradation of core fibers. These nanomaterials were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and scanning thermal microscopy. The thermal conductivity of the silver submicron tubes was found to differ depending on the method of preparation, with tubes from electroless plating possessing relative thermal conductivity values that were 1 order of magnitude higher than that from exchange plating, 3000 W/m x K and 660 W/m x K, respectively. Interestingly, these results indicate that silver submicron tubes possess higher thermal conductivity than the bulk metal. This observation is discussed in the context of the continuous conduction path of the tubes and their high surface area-to-volume ratio.

Sub-micrometer-sized metal tubes from electrospun fiber templates.

Metallic tubes have been synthesized by a polymer-based template approach using electroless deposition. Gold, copper, and nickel were deposited as thin films on sub-micrometer polymer fibers which ranged in diameter from approximately 160 to 400 nm. After thermal degradation of the template fibers at 300 and 650 degrees C, tubes between 450 and 730 nm were obtained with wall thicknesses of 50-150 nm. Characterization by scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and powder X-ray diffraction indicate that the tubes have a face-centered cubic structure with [111] preferred orientation for all of the metals investigated and that the tube walls are polycrystalline, composed of nanoparticles, ranging in size from 5.0 to 25.0 nm.