A controllable synthesis of multi-armed CdTe nanorods

A simple, productive and low-cost route has been developed to synthesize multi-armed CdTe nanorods using myristic acid (MA) as a complex agent. The yield of this approach can reach 75%. The dimension of the multi-armed nanorods can be controlled by tuning the molar ratios of Cd/Te and Cd/MA; the diameter can be changed from 2 to?7?nm while the length from 15 to 60?nm. The hexagonal structure was confirmed in x-ray diffraction analysis. However, it was assumed that one crystal is composed of the dominant hexagonal structure along with a cubic structure in the core.     

Preparation of hexagonal WO3 from hexagonal ammonium tungsten bronze for sensing NH3

Hexagonal tungsten oxide (h-WO₃) was prepared by annealing hexagonal ammonium tungsten bronze, (NH₄)_0.07(NH₃)_0.04(H₂O)_0.09WO_2.95. The structure, composition and morphology of h-WO₃ were studied by XRD, XPS, Raman, ¹H MAS (magic angle spinning) NMR, scanning electron microscopy (SEM), and BET-N₂ specific surface area measurement, while its thermal stability was investigated by in situ XRD. The h-WO₃ sample was built up by 50-100 nm particles, had an average specific surface area of 8.3 m²/g and was thermally stable up to 450 °C. Gas sensing tests showed that h-WO₃ was sensitive to various levels (10-50 ppm) of NH₃, with the shortest response and recovery times (1.3 and 3.8 min, respectively) to 50 ppm NH₃. To this NH₃ concentration, the sensor had significantly higher sensitivity than h-WO₃ samples prepared by wet chemical methods.     

Hydrothermal synthesis of nanoplates assembled hierarchical h-WO3 microspheres and phase evolution in preparing cubic Zr(Y)O2-doped tungsten powders

Three-dimensional hierarchical h-WO₃ and doping tungsten powders have recently attracted considerable attention because of their superior sensing properties and refined grains, respectively. In this article, we report a facile hydrothermal hydrogen reduction process for preparing hierarchical h-WO₃ microspheres that self-assemble with nanoplates. Meanwhile, the phase evolution process and evolution mechanisms during the conversion of h-WO₃ to W are systemically investigated. Results indicate that the highly homogeneous h-WO₃ microspheres are uniformly covered with ultrafine ZrY₂(OH)₁₀ micelles, which fully transform into m-WO₃ and cubic Zr(Y)O₂ after calcination at 600?°C. Microspheres possessing different pore diameters and containing nanosized particles can be obtained by adjusting the hydrogen reduction process. These phase evolution process can provide reasonable guidance for preparing tungsten oxide with high electrochemical properties and ultrafine tungsten powders. The h-WO₃ microspheres with an average size of 3?μm consist of nanoplates and the tungsten powders doped with 1.0?wt% Zr(Y)O₂ have a mean particle size of approximately 1.4?μm. Comparative test results indicate that the addition of 1.0?wt% Zr(Y)O₂ can promote the formation of low-degree particle agglomerates.     

Luminescent properties of GdPO4:Eu nanorods

Highly luminescent GdPO₄:Eu³⁺ nanorods with hexagonal and monoclinic structures were successfully synthesized by a hydrothermal method. Results are shown that the prepared GdPO₄:Eu has a hexagonal or monoclinic structure under different synthetical process. The properties of the Eu³⁺-doped GdPO₄ nanorods were characterized by XRD, SEM and UV–vis spectroscopy. A study of the photoluminescence of Eu³⁺-doped GdPO₄ has revealed that the optical properties of these nanophosphors are strongly dependent on their crystal structures and morphologies.     

Photo-initiated growth of zinc oxide (ZnO) nanorods

A photo-initiated process via femtosecond pulse-induced heterogeneous nucleation in zinc ammine complex (Zn(NH₃)₄²⁺)-based aqueous solution without catalyst and surfactant, followed by hydrothermal treatments for crystal growth into zinc oxide (ZnO) nanorods, was investigated. Flat-top hexagonal ZnO nanorods with smooth planes of diameter ≥ 100 nm and length ≤ 1 μm were grown with laser irradiation, compared to porous rod-like structures without irradiation. The flat-top planes indicate slow growth rate, due to the intermediate step of Zn(NH₃)₄²⁺ decomposition to Zn(OH)₄²⁻, before dehydration to ZnO. Prolonged hydrothermal treatment produced nanotubes and lateral splits due to OH⁻ erosion of the crystal faces. XRD analysis showed a hexagonal crystal structure while photoluminescence study indicated a peak at about 380 nm.     

Template-free synthesis of high surface area single-crystalline lanthanum hydroxide nanorods via a low-temperature solution route

Under mild reaction conditions, uniform La(OH)₃ nanorods were fabricated in large scale by a facile template-free solution method. The as-prepared sample was characterized by a number of techniques. It is found that the La(OH)₃ nanorods are hexagonal in structure and single-crystalline, with the diameter and length of 6–30 and 45–200 nm, respectively. The surface area of the nanorods is up to 113 m²/g. We attribute the high surface area to the use of 1-propanol/H₂O mixed solvent and the rapid cooling of sample to 0 °C. A formation mechanism of the rodlike crystal is tentatively suggested. The reported solution-phase process may be a facile and low-cost approach for the generation of high surface area single-crystalline nanorods of other rare earth hydroxides.     

Synthesis of CuS nanorods grown at room temperature by electrodeposition method

CuS thin films were deposited on stainless steel substrates from an aqueous solution of CuSO₄, Na₂S₂O₃ and Triethanolamine. Deposited films were characterized by XRD, SEM, EDAX, Raman and Optical measurements. The electrodeposition bath concentration can be used to control the diameter of the electrodeposited nanorods within the range of 35–40 nm. The formation of complexes of copper ions and TEA was found to be a key factor in the nanorods growth process. Films are polycrystalline with hexagonal crystal structure. SEM images indicate that the film surfaces are smooth, homogeneous and well-covered. A new structure of CuS nanorods having length of 5–10 μm and diameter from 35 to 40 nm has been demonstrated. By changing bath concentration and keeping deposition time fixed the agglomeration of rods is enhanced due to the formation of large number of particles during growth process. Raman shifts of samples are detected at wave numbers 473 cm⁻¹. Typical film deposited with optimized bath concentration shows optical band gap of about 2.73 eV.     

Dopant-controlled synthesis of water-soluble hexagonal NaYF<Subscript>4</Subscript> nanorods with efficient upconversion fluorescence for multicolor bioimaging

A novel strategy is proposed to directly synthesize water-soluble hexagonal NaYF₄ nanorods by doping rare-earth ions with large ionic radius (such as La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, and Gd³⁺), and the dopantcontrolled growth mechanism is studied. Based on the doping effect, we fabricated water-soluble hexagonal NaYF₄:(Yb,Er)/La and NaYF₄:(Yb,Er)/Ce nanorods, which exhibited much brighter upconversion fluorescence than the corresponding cubic forms. The sizes of the nanorods can be adjusted over a broad range by changing the dopant concentration and reaction time. Furthermore, we successfully demonstrated a novel depth-sensitive multicolor bioimaging for in vivo use by employing the as-synthesized NaYF₄:(Yb,Er)/La nanorods as probes.      

In situ synthesis and characterization of GaN nanorods through thermal decomposition of pre-grown GaN films

Herein we describe a thermal treatment route to synthesize gallium nitride (GaN) nanorods. In this method, GaN nanorods were synthesized by thermal treatment of GaN films at a temperature of 800?°C. The morphology and structure of GaN nanorods were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that GaN nanorods have a hexagonal wurtzite structure with diameters ranging from 30 to 50?nm. Additionally, GaN nanoplates are also founded in the products. The growth process of GaN nanostructures was investigated and a thermal decomposition mechanism was proposed. Our method provides a cost-effective route to fabricate GaN nanorods, which will benefit the fabrication of one-dimensional nanomaterials and device applications.     

Evidence of hexagonal WO3 structure stabilization on mica substrate

WO₃ nanorods are grown by a simple vapor deposition method on a mica substrate and characterized by Selected Area Electron Diffraction and Energy Dispersive X-rays Spectroscopy. Experimental results show the clear evidence of an unexpected WO₃ hexagonal structure as well as an epitaxial growth on the mica substrate. Besides, potassium is evidenced inside the nanorods. It is thus deduced that a metastable WO₃ hexagonal phase is stabilized by epitaxy through a tungsten bronze interlayer having same hexagonal structure.     

Electrodeposition of template free hierarchical ZnO nanorod arrays via a chloride medium

We have successfully grown template and buffer free ZnO nanorod films via chloride medium by controlling bath temperature in a simple and cost effective electrochemical deposition method. Thin films of ZnO nano-rods were obtained by applying a potential of ?0.75 V by employing Ag/AgCl reference electrode for 4 h of deposition time. The CV measurements were carried out to determine potential required to deposit ZnO nanorod films whereas chronoamperometry studies were carried out to investigate current and time required to deposit ZnO nanorod films. The formation of ZnO nanorod has been confirmed by scanning electron microscopy (SEM) and Raman spectroscopy. Low angle XRD analysis confirms that ZnO nanorod films have preferred orientation along (101) direction with hexagonal wurtzite crystal structure. The SEM micrographs show nice surface morphology with uniform, dense and highly crystalline hexagonal ZnO nanorods formation. Bath temperature has a little influence on the orientation of nanorods but has a great impact on their aspect ratio. Increase in bath temperature show improvement in crystallinity, increase in diameter and uniform distribution of nanorods. Compositional analysis shows that the amount of oxygen is ~49.35 % and that of Zn is ~50.65 %. The optical band gap values were found to be 3.19 and 3.26 eV for ZnO nanorods prepared at bath temperature 70 and 80 °C respectively. These results indicate that by controlling the bath temperature band gap of ZnO nanorods can be tailored. The obtained results suggest that it is possible to synthesize ZnO nanorod films by a simple, cost effective electrodeposition process which can be useful for opto-electronic devices fabrication.     

Effects of exposed facets on photocatalytic properties of WO3

Hexagonal WO₃ (h-WO₃) was prepared by using Na₂SO₄ and (NH₄)₂·SO₄ as capping agents under different hydrothermal conditions. XRD, SEM and TEM results indicated that three types of morphologies, including h-WO₃ rods with exposed (2 0 0) facets, h-WO₃ nanosheets with exposed (0 0 2) facets and h-WO₃ with corn cob-like structure and no preferred direction, could be obtained by tuning the capping agents and pH. Specifically, h-WO₃ nanosheets with exposed (0 0 1) facets have the best visible photocatalytic properties due to its high specific surface area and charge separation nature on the (0 0 2) high energy facets.     

Synthesis of ultrafine lanthanum hydroxide nanorods by a simple hydrothermal process

Lanthanum hydroxide (La(OH)₃) nanorods with 6–15 nm in width and 200–400 nm in length have been prepared by a simple hydrothermal process. X-ray diffraction (XRD) shows that the nanorods are of hexagonal structure, and furthermore, high-resolution transmission electron microscopy (HRTEM) identifies that the lanthanum hydroxide nanorods are highly crystalline. Moreover, the mechanism for the hydrothermal synthesis of lanthanum hydroxide nanorods has been preliminarily presented.     

Fabrication and structure characterization of MnCO3/α-Fe2O3 nanocrystal heterostructures

Novel MnCO₃/α-Fe₂O₃ nanocrystal heterostructures, with MnCO₃ nanorods 5-10 nm in diameter and 15-50 nm in length, grown onto the surfaces of the α-Fe₂O₃ nanohexahedrons sized around 30-50 nm, were fabricated via a two-step solvothermal route. The coalescent planes of the heterostructure for the MnCO₃ nanorod and the α-Fe₂O₃ nanohexahedron were determined to be (01?4) and (110), respectively. The formation of the MnCO₃ nanorods from the Mn contained amorphous flakes was tracked by transmission electron microscopy observations at various reaction stages, which suggested a rolling-broken-growth process. Evidenced by the comparative experimental result, the α-Fe₂O₃ nanohexahedrons played an important role in inducing the nucleation and growth of the hexagonal MnCO₃ nanorods on their surfaces.     

Facile template-free hydrothermal synthesis and microstrain measurement of ZnO nanorods

ZnO nanorods were synthesized at low temperature by hydrothermally heating 0·1 M solution of ZnCl₂ for 5, 10 and 15 h at a pH of 10. No template, seeded substrate, catalyst and autoclave were employed for the synthesis of ZnO nanorods. The effect of heating durations on the morphology and crystal orientation of the structure were investigated by using scanning electron microscopy and X-ray diffraction, respectively. SEM images showed that the flower-like structures were formed in 5 h hydrothermally-heated sample, whereas the hexagonal zinc oxide nanorods were perfectly fabricated with the increase in growth time. XRD patterns showed that the preferred orientation in nanorods could be controlled by hydrothermal treatment time. The crystallite size and microstrain were analysed by Williamson–Hall and Halder–Wagner methods. These results revealed the presence of defects in ZnO nanorods. However, by increasing the hydrothermal treatment time, both defects in lattice and crystallite size are decreased.     

Catalytic synthesis of large-scale GaN nanorods

A novel rare earth metal seed was employed as the catalyst for the growth of GaN nanorods. Large-scale GaN nanorods were synthesized successfully through ammoniating Ga₂O₃/Tb films sputtered on Si(1 1 1) substrates. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy were used to characterize the structure, morphology, and composition of the samples. The results demonstrate that the nanorods are high-quality single-crystal GaN with hexagonal wurtzite structure. The growth mechanism of GaN nanorods is also discussed.     

Fabrication of GaN nanowires and nanorods catalyzed with tantalum

Single-crystalline GaN nanowires and nanorods have been fabricated through ammoniating Ga₂O₃ films catalyzed with tantalum (Ta) by RF magnetron sputtering, and microstructure, morphology and optical properties were investigated in particular. The results indicate that the nanowires have a hexagonal wurtzite structure with size about 50 nm in diameter and more than ten microns in length, however, the nanorods are rod-like structures with smooth surface and 100–300 nm in diameter. The growth direction of these nanostructures are perpendicular to the (100) crystal plane. The photoluminescence spectrum at room temperature exhibits a strong UV light emission band centered at 364 nm.     

Electrochemical performance of CdS nanomaterials synthesized by microemulsion techniques

Precursor cadmium compounds influence the electro-catalytic performance of CdS nanomaterials for sulphide/polysulphide redox couple reaction. CdS nanorods and nanoparticles were synthesized from different raw materials, namely Cd(NO₃)₂, CdCl₂ or CdO, by a room temperature microemulsion approach using CS₂ as a sulphur source. Cadmium salts (i.e. CdCl₂, Cd(NO₃)₂) result in single phase CdS crystals with hexagonal structure while CdO gives two crystal phases with majority of cubic structure. Nanorods, produced from CdCl₂, demonstrated the best catalytic performance for the enhancement of the polysulphide reaction.     

Effect of the ammoniating time on microstructure and morphology of one-dimensional Mg-doped GaN nanowires catalysed with Au

Mg-doped GaN nanowires have been successfully synthesised on Si(1?1?1) substrates by magnetron sputtering through ammoniating Ga₂O₃/Au thin films, and the effect of ammoniating time on microstructure and morphology were analysed in detail. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence spectrum were carried out to characterise the microstructure, morphology and optical properties of the GaN samples. The results demonstrate that the nanowires after ammonification at 900°C for 15?min are single crystal GaN with a hexagonal wurtzite structure and high crystalline quality, having the size of 50–80?nm in diameter, more than 10 microns in length and good emission properties. The growth direction of this nanowire is parallel to [0?0?1] direction of hexagonal unit cell. Ammoniating time has a great impact on the microstructure, morphology and optical properties of the GaN nanowires.     

Graphene/zinc bismuthate nanorods composites and their electrochemical sensing performance for ascorbic acid

Graphene/zinc bismuthate nanorods composites have been prepared using graphene and zinc bismuthate nanorods as the raw materials. The composites are composed of graphene nanosheets with folds and wrinkles and zinc bismuthate nanorods which possesses cubic ZnBi₃₈O₅₈ and hexagonal graphite phases. The zinc bismuthate nanorods are dispersed on the graphene nanosheets. A pair of quasi-reversible redox cyclic voltammogram (CV) peaks exist at the graphene/zinc bismuthate nanorods composites modified glassy carbon electrode. The CV peak current linearly increases with the scan rate from 25?mV?s^?1 to 200?mV?s^?1. The electrochemical response is linear in the ascorbic acid concentration range of 0.0001-2?mM and the detection limit is 0.07?μM. The graphene/zinc bismuthate nanorods composites can be considered as a promising electrode materials to be utilized as the electrochemical sensor.