Fabrication and microstructure analysis of SeO<Subscript>2</Subscript> nanowires

Selenium dioxide nanowires were fabricated as the co-products of ZnSe nanostructures. The SeO₂ nanowires have diameters between 2070 nm and lengths up to several hundred micrometers. The morphology and microstructure of the nanowires were analyzed using TEM, and the growth mechanism of the SeO₂ nanowires was explained under the framework of a vapor-solid model, in which structure defects may play a very important role in the nanowire growth. The nanostructured SeO₂ materials may find application in both catalytic and biological fields. PACS 81.07.-b; 81.16.-c; 81.07.Nb; 81.05.-t; 68.37.Lp     

Catalyst-free growth of single-crystalline alumina nanowire arrays

Alumina nanowires were synthesized on a large-area silicon substrate via simple thermal evaporation of a mixture of aluminum and alumina powders. The microstructure of the as-grown alumina nanowires was characterized using X-ray diffraction and transmission electron microscopy techniques. These nanowires usually have a straight morphology and are single crystalline with the wire axis parallel to the (001) direction. Arrays of the alumina nanowires were also observed grown on the surface of many large particles. The catalyst-free growth of the alumina nanowires was explained in the framework of vapor–solid growth. PACS 81.07.-b; 81.16.-c; 81.07.Bc     

Functional nanowires of tin oxide

Quasi-one-dimensional nanostructures of tin oxide were produced in controlled conditions through condensation from the vapor phase. The preparation was assisted by noble metal catalysts and uniform single-crystalline nanowires were produced. The nucleation of nanowires was achieved at 470 °C, owing to the vapor–liquid–solid growth mechanism activated by the catalytic Pt clusters. The peculiar microstructural properties of these semiconducting metal oxide nanostructures will be summarized. The high aspect ratio and the high degree of crystallinity achieved for the nanowires foresee their functional exploitation. PACS 61.46.Hk; 81.07.Bc; 81.16.Hc; 68.37.Lp     

Thermal evaporation synthesis of zinc oxide nanowires

High quality ZnO nanowires were synthesized at high temperature without using heterogenous catalysts. The nanowires had a uniform prismatic shape and were grown in a cacti-like morphology. Characterizations of the products by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy showed that the ZnO nanowires were single crystalline and of high purity. An intensive exciton emission was observed around 3.25 eV from the ZnO nanowires at room temperature. The growth mechanism was discussed based on the experimental conditions and the ZnO crystal growth habits. This growth method can be used to prepare other metal oxide nanowires. PACS 61.46.+w; 81.16.-c; 81.07.De, 81.05.Hd     

Electrochemical deposition and characterization of Cu2O nanowires

Cu₂O nanowires were successfully synthesized by an electrochemical method using an alumina membrane as template through precise control of the pH value of the electrolyte. The deposition process was monitored by the time–current curve. Characterization was performed by means of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The growth directions of the Cu₂O nanowires were determined and the possible growth mechanism is discussed. PACS 68.37.Lp; 81.07.-b; 81.16.Be     

Fabrication and characterization of Zn-doped CdTe nanowires

At 850 °C, Zn-doped CdTe nanowires with an average diameter of about 40 nm and lengths up to several tens of micrometers were fabricated by a CVD approach. The nanowires were detected by SEM, XRD, TEM, HRTEM, EDS, SAED, and XPS, where the as-synthesized CdZnTe nanowires have high-quality crystalline structure and grow along the 〈001〉 direction and the Cd/Zn ratios of these nanowires are close to those expected from the starting compositions. The corresponding growth mechanism of the nanowires is also explained. PACS 81.05.Dz; 81.07.-b; 68.37.Lp; 79.60.-i; 78.67.-n     

Large-scale fast production of amorphous Si-Al-O nanowires under ambient conditions

A novel approach to the large-scale and fast production of free-standing nanowires and microwires under ambient conditions is reported. The method is based on the interaction of a high power laser beam with a commercial ceramic substrate under a high-pressure gas jet under ambient conditions. Large quantities of amorphous Si-Al oxide nanowires were produced and characterized. An explanation for the growth of the nanowires based in the vapor–liquid–solid (VLS) mechanism is proposed . PACS 81.05.Je; 81.07.b     

One-dimensional gallium nitride micro/nanostructures synthesized by a space-confined growth technique

Hexagonal GaN prismatic sub-micro rods and cone nanowires have been synthesized in a large scale by a novel and controllable space-confined growth method. The as-synthesized GaN products are highly crystalline with a wurtzite structure. The prismatic rods have lengths of 15∼20 μm and diameters of 400∼500 nm enclosed by hexagonal smooth side surfaces and a pyramidal end. And the cone nanowires have average diameters of 150∼200 nm and lengths up to several tens of μm with a cone tip. The photoluminescence (PL) studies reveal prominent band-gap UV emission properties of GaN products and narrow FWHM, indicating the excellent luminescent performance and high crystal quality. For field emission characteristic of GaN nanowires, the turn-on field is about 9.5 V/μm and the current density reaches 1.0 mA/cm² at an electric field of 18 V/ μm. The contrast experiments indicate a novel growth control can be achieved by using a graphite tube as reaction vessel. The sealed graphite tube combined with metallic initiator is greatly responsible for large-scale and uniform preparation of GaN prismatic rods and cone nanowires. Highly symmetric GaN hexagonal micropyramids are grown on a bare Si substrate. The growth mechanism and the control function of the graphite tube are demonstrated. These low-dimensional structures not only enrich semiconducting GaN family, but also are good building blocks for optoelectronic devices. PACS 81.10.Bk; 81.07.-b; 81.05.Ea     

One step solution synthesis towards ultra-thin and uniform single-crystalline ZnO nanowires

Bundles of high-aspect-ratio single-crystalline ZnO nanowires were fabricated by a single-step mild hydrothermal condition without the use of a seeding layer, thus eliminating an annealing step. The growth yields nanowires of high aspect ratio (>200). No significant lateral growth takes place with prolonged reaction time. The morphology and aspect ratio of the final products depend on the concentration of the precursors; a highly water-soluble tetradentate cyclic tertiary amine and zinc nitrate system. The nanowires grow along the [0001] direction and have an average width of <10 nm and a narrow distribution of ±5 nm. Photoluminescence measurements of the ultra-thin nanowires exhibit a strong band-edge emission at room temperature. The highly crystalline sub tens of nanometer scale diameter nanowires can, in combination, be a good one-dimensional candidate to study optical and electronic properties. PACS 81.16.Be; 81.07.Bc     

Spinel-type ZnSb<Subscript>2</Subscript>O<Subscript>4</Subscript> nanowires and nanobelts synthesized by an indirect thermal evaporation

Uniform zinc antimoniate (ZnSb₂O₄) nanowires and nanobelts with a spinel structure were synthesized by an indirect thermal evaporation method in air. The as-synthesized ZnSb₂O₄ nanowires and nanobelts are single crystalline, usually several tens of microns in length. The diameter of the nanowires is about 20 nm; the thickness and the width of the nanobelts are about 15 nm and 60 nm, respectively. Most of the nanowires and nanobelts grow along the [001] direction. A possible formation mechanism is also proposed to account for the growth of these ZnSb₂O₄ nanobelts and nanowires. PACS 61.46.+w; 81.07.-b     

Catalytic synthesis and photoluminescence of silicon oxide nanowires and nanotubes

A large quantity of nanowires and nanotubes of silicon oxide are produced by using Fe–Co–Ni alloy nanoparticles as catalyst. The products have a uniform diameter of around 100 nm. The nanowires have a smooth surface and the lengths are up to 100 μm or more. A new morphology called a serrated joint nanotube was found. The alloy catalyst plays a key role in the synthesis process. Room-temperature photoluminescence measurement under excitation at 360 nm showed that the silicon oxide had a strong blue-green emission at 525 nm (about 2.36 eV), which may be related to oxygen defects. PACS 81.15.Gh; 81.07.Vb; 81.07.De; 42.70.Nq; 78.55.-m     

Controlled synthesis and characterization of layered manganese oxide nanostructures with different morphologies

Layered manganese oxide nanostructures with different morphologies, such as nanowire bundles, cotton agglomerates, and platelikes were successfully fabricated by a simple and template-free hydrothermal method based on a reaction of KMnO₄ and KOH solutions with different concentrations. The obtained nanowire bundles were assembled by nanowires with diameters of 10 to 200 nm and lengths up to 5–10 μm. The cotton agglomerates were composed of manganese oxide layers with a thickness of about 10 nm. Both the concentration of KOH solutions and the reaction temperature played an important role in the formation of layered manganese oxide nanostructures with different morphologies. XRD, SEM, TEM, HRTEM, SAED, TG-DTA, and chemical analysis were employed to characterize these materials. On the basis of the experimental results, a possible formation mechanism of layered manganese oxide nanostructures with different morphologies was presented. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structural characterization of long ZnSe nanowires

ZnSe nanowires have been synthesized by vapor transport in an Ar atmosphere. The synthesized ZnSe nanowires have a thickness of 20 to 120 nm and a length of tens of micrometers. The nanowires are single crystals with a cubic zinc-blende structure growing along the [111] direction. The as-synthesized nanowires display rich Raman modes and one photoluminescence band peaking at around 450 nm. PACS 78.67.Bf; 81.07.Bc; 61.46.+w     

Hydrothermal synthesis of single-crystal ZnS nanowires

Wurtzite ZnS nanowires were prepared through a hydrothermal synthesis route with a low-temperature (180 °C) in the presence of ethylenediamine (en). The structure and morphology of the samples are studied and the growth mechanism is discussed. Room-temperature photoluminescence properties and the thermal gravimetric characteristics of the as-synthesized ZnS nanostructures are also studied. PACS 61.46.Hk; 78.67.Bf; 81.07.Vb     

Synthesis of βGa2O3 nanowires by an MOCVD approach

We have synthesized monoclinic gallium oxide (βGa₂O₃) nanowires on Au-coated Si substrates by a reaction of a trimethylgallium and oxygen mixture. The βGa₂O₃ nanowires became progressively thinner from bottom to top, with diameters ranging from 10 to 200 nm and lengths of several micrometers. We found that Au-containing nanoparticles were attached to the tips of the βGa₂O₃ nanowires and thus the nanowire growth could be a vapor–liquid–solid process .PACS 81.07.-b; 81.15.Gh     

A simple route to large scale synthesis of crystalline αSi3N4 nanowires

Crystalline Si₃N₄ nanowires were simply prepared by heating a silicon wafer at 1250 °C in a flowing NH₃ and N₂ atmosphere. The obtained nanowires are straight and uniform with diameters of 30–100 nm and of lengths up to tens of microns. The possible reactions in the synthesis process are discussed. The growth mechanism of the nanowires is vapor-solid (VS) process. PACS 81.05.Je; 81.07.Bc; 81.10.Bk; 81.16.Be; 81.20.Ka     

Fabrication and structural characterization of Mg<Subscript>2</Subscript>SiO<Subscript>4</Subscript> nanowires

This article demonstrates the first reported successful synthesis of Mg₂SiO₄ nanowires. We have thermally heated Au-coated Si substrates, using a quartz tube with its inner surface pre-coated with MgO nanostructures. We have characterized the sample morphologies by using scanning electron microscopy and transmission electron microscopy (TEM). X-ray diffraction analysis and high-resolution TEM observation coincidentally revealed that the nanowires were crystalline with an orthorhombic Mg₂SiO₄ structure. We have discussed the possible growth mechanism of Mg₂SiO₄ nanowires. PACS 81.07.-b; 81.05.Zx; 61.10.Nz; 68.37.Hk; 68.37.Lp     

Structure and properties of a pulp fibre-reinforced composite with regenerated cellulose matrix

In this article we report the synthesis of molybdenum trioxide nanoribbons assembled into self-standing films. The molybdenum oxide crystals are prepared by acid decomposition of sodium molybdate under hydrothermal conditions. The set of conditions to obtain well-aligned single crystalline, single-phase products was determined; under these conditions it is possible to obtain assemblies of crystals of several centimeters, aligned along a single crystalline direction. These crystals are also suitable precursors to other molybdenum chalcogenides, as we present a nanostructured molybdenum sulfide obtained by the sulfidation of these molybdenum oxide nanoribbons. A considerable amount of single nanowires and nanoplatelets of molybdenum sulfide were observed in this material. PACS 81.07.BC; 81.05.Je; 81.20.Ka     

Synthesis of highly aligned silicon oxide nanowires and their novel patterns

Highly aligned amorphous SiO_x nanowires with lengths of up to several hundred microns were synthesized by using a millimeter-sized droplet of elemental gallium as a catalyst. Gallium displays highly catalytic activity for the growth of SiO_x nanowires. Some novel patterns of aligned SiO_x nanowires, including honeycomb-like and spindle-like structures, were observed. These SiO_x nanowires are expected to be used in nanooptics and reinforcing composites. PACS 61.46.+w; 81.07.Vb; 81.16.Be     

Chemical tension and global equilibrium in VLS nanostructure growth process: from nanohillocks to nanowires

We formulate a global equilibrium model to describe the growth of one-dimensional nanostructures in the VLS process by including also the chemical tension in addition to the physical tensions, i.e. surface energies. The chemical tension derives from the Gibbs free energy change due to the growth of a crystal layer of an elementary thickness. The system global equilibrium is arrived at via the balance of the static physical tensions and the dynamic chemical tension. The model predicts and provides conditions for the growth of nanowires of all sizes exceeding a lower thermodynamic limit. The model also predicts the conditions distinguishing the growth of nanohillocks from nanowires. These predictions will allow the verification of the model by future experiments specifically designed for this purpose. PACS 81.07.-b; 82.60.-s; 05.70.Np; 68.35.Md; 68.03.Cd