Zinc Oxide Nanotubes Research Articles

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Vertically aligned single-crystal zinc oxide nanotubes can be grown using a traditional metal–organic chemical vapour deposition technique

First principles study of the band structure and dielectric function of (6,6) single-walled zinc oxide nanotube

The band structure and dielectric function of a (6,6) single-walled zinc oxide nanotube (SWZONT) have been studied using the first-principles method within the pseudopotential density functional theory (DFT). We find that the (6,6) SWZONT has a direct band gap with an energy gap of 1.91 eV. The valence bands (VBs) are composed of two parts, namely, the low-energy part and the high-energy part. The dielectric function indicates a moderate optical anisotropy in the SWZONT. The magnitude of the peaks in the ε 2( ω) spectrum of dielectric function for the [1 0 0] direction is about half of the magnitude of the corresponding ones for the [0 0 1] direction, which is similar to the case found in single-walled boron nitrogen nanotubes (SWBNNTs). However, the character of dielectric function is different with that of single-walled carbon nanotubes (SWCNTs).

Photocatalytic formation of porous CdS/ZnO nanospheres and CdS nanotubes

It was found that ZnO nanocrystals have photocatalytic activity in the formation of CdS during the reduction of sulfur in the presence of cadmium acetate. It was shown that mesoporous spheres measuring 150–170 nm and consisting of CdS/ZnO particles measuring 5–8 nm are formed during the irradiation of ZnO particles measuring 5.5 nm. During the photodeposition of CdS by the action of light on nanorods produced by ultrasonic treatment of microcrystalline zinc oxide nanotubes of CdS 0.5–0.8 µm in length and 15–110 nm in internal diameter are formed. A mechanism, in which they appear at the ends of the ZnO nanorods and grow on the surface of the CdS/ZnO heterojunction, is proposed for the formation of the CdS nanotubes.

Fabrication of arrays of zinc oxide nanorods and nanotubes in aqueous solution under an external voltage

Arrays of zinc oxide (ZnO) nanorods have been synthesized on silicon substrates by a solution route under an external voltage. They were ∼10 2 nm in diameter and grew along the c-axis. Meanwhile, ZnO nanotubes were also obtained. Some comparative experiments showed that applying the external voltage effectively improved the alignment of the ZnO nanorods and enhanced their adherence to the substrates. The role of the external voltage is discussed in terms of the electric field established in the solution and the electrochemical reaction at the cathode. The formation of the nanotubes is attributed to the decrease of the precursor concentration and the disparity between the field strengths at different parts of the ZnO nanorods.

Elasticity and piezoelectricity of zinc oxide crystals, single layers, and possible single-walled nanotubes

The elasticity and piezoelectricity of zinc oxide (ZnO) crystals and single layers are investigated from the first-principles calculations. It is found that a ZnO thin film less than three Zn-O layers prefers a planar graphite-like structure to the wurtzite structure. ZnO single layers are much more flexible than graphite single layers in the elasticity and stronger than boron nitride single layers in the piezoelectricity. Single-walled ZnO nanotubes (SWZONTs) can exist in principle because of their negative binding energy. The piezoelectricity of SWZONTs depends on their chirality. For most ZnO nanotubes except the zigzag type, twists around the tube axis will induce axial polarizations. A possible scheme is proposed to achieve the SWZONTs from the solid-vapor phase process with carbon nanotubes as templates.

Stable field emission from hydrothermally grown ZnO nanotubes

Zinc oxide nanotube arrays were prepared by hydrothermal reaction in ammonia and zinc chloride solutions, and the field emission properties were tested. The turn-on field of the field emission was extrapolated to be about 7.0V∕μm at a current density of 0.1μA∕cm2. Meanwhile, the emission current densities reached 1mA∕cm2 at a bias field of 17.8V∕μm. The field enhancement factor β was estimated to be 910. The field emission of the zinc oxide nanotubes showed good stability. The variation of emission current density was less than 10% during a 24h test under a field of 15V∕μm.

Large-scale synthesis of single-crystalline ZnO nanotubes based on polymer-inducement

Single-crystalline zinc oxide nanotubes were synthesized in large scale through a simple polymer-induced growth method. Morphology and structural characterizations reveal that the zinc oxide nanotubes are uniform with outer diameters of about 80 nm, and in a hexagonal crystalline structure. Photoluminescence measurement shows a strong near-band ultraviolet emission at about 385 nm. This synthesis route is easily controllable, well repeatable, mild, and feasible to apply for the fabrication of other oxides nanotubes.

Synthesis of hierarchical zinc oxide nanotubes

In this paper, we report on the synthesis and structure of hierarchical zinc oxide nanotubes. Hierarchical nanotubes grown by physical vaporization of zinc in the presence of a catalyst were decorated with many secondary zinc oxide nanorods on the outer surface. The axis of these nanotubes with an average diameter of 65 nm was aligned along the c axis of wurtzite zinc oxide. The hierarchical zinc oxide nanotubes, many of which were single crystals, were transparent or opaque, depending on whether they had a zinc layer inside. The opaque nanotubes showed an abrupt change in electronic transmittance during investigation with transmission electron microscopy. The unique structure of the hierarchical ZnO nanotubes and the quantum effect resulting from the reduced dimension will modify the original properties of ZnO, leading to novel applications.

Fabrication and microstructure analysis on zinc oxide nanotubes

Well crystallized aligned zinc oxide nanoscale tubular structures have been fabricated viavapour phase growth on large area substrates. The ZnO nanotubes have regular polyhedralshapes, hollow cores with diameters of 30–100 nm, lengths over a few tens of micrometresand wall thicknesses of 4–10 nm. In morphology, the nanotubes were either straight ortwisted with several straight parts. The microstructure of the tubular material wasinvestigated in detail by using high-resolution transmission electron microscopy (HRTEM),Z-contrastimaging and compositional line profile analysis. The chemical composition ofindividual tubular structures was found to be stoichiometric ZnO using selected areaenergy dispersive x-ray spectroscopy and electron energy loss spectroscopy. X-raydiffraction (XRD) and selected area electron diffraction results indicated thatthe ZnO nanotubes had wurtzite crystal structure. XRD analysis and HRTEMinvestigations indicated the ZnO nanotubes were grown along the [001] direction.The growth of the tubular ZnO nanostructures was found to be closely relatedto the hexagonal nature of the ZnO crystal and the peculiar growth conditionsused.