Hydrothermal synthesis of Bi2Te3 nanowires through the solid-state interdiffusion of Bi and Te atoms on the surface of Te nanowires

Polycrystalline Bi₂Te₃ nanowires were prepared by a hydrothermal method that involved inducing the nucleation of Bi atoms reduced from BiCl₃ on the surface of Te nanowires, which served as sacrificial templates. A Bi–Te alloy is formed by the interdiffusion of Bi and Te atoms at the boundary between the two metals. The Bi₂Te₃ nanowires synthesized in this study had a length of 3–5 μm, which is the same length as that of the Te nanowires, and a diameter of 300–500 nm, which is greater than that of the Te nanowires. The experimental results indicated that volume expansion of the Bi₂Te₃ nanowires was a result of the interdiffusion of Bi and Te atoms when Bi was alloyed on the surface of the Te nanowires. The morphologies of Bi₂Te₃ are strongly dependent on the reaction conditions such as the temperature and the type and concentration of the reducing agent. The morphologies, crystalline structure and physical properties of the product were analyzed by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS).     

Facile synthesis and assembly of CuS nano-flakes to novel hexagonal prism structures

Highly ordered hexagonal prism microstructures of copper sulfide (CuS) by assembling nano-flakes have been synthesized with high yield via a facile one-step route. We synthesized CuS microstructures using low cost beginning materials CuSO₄·5H₂O and Na₂S₂O₃·5H₂O under lower reaction temperature (60 °C). Hexamethylinetetramin (C₆H₁₂N₄, HMT) was introduced into the reaction system as a capped agent. The influence of reaction time and capping agent (HMT) on the final structure of products was studied systematically. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopes (EDS), and transmission electron microscopy (TEM). The possible mechanism for the formation of the interesting highly ordered hexagonal prism microstructures CuS was also proposed.     

Effect of oxygen partial pressure on the growth of zinc micro and nanostructures

Zinc micro and nanostructures were synthesized in vacuum by condensing evaporated zinc on Si substrate at different gas pressures. The morphology of the grown Zn structures was found to be dependent on the oxygen partial pressure. Depending on oxygen partial pressure it varied from two-dimensional microdisks to one-dimensional nanowire. The morphology and structural properties of the grown micro and nanostructures were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Transmission electron microscopy (TEM) studies on the grown Zn nanowires have shown that they exhibit core/shell-like structures, where a thin ZnO layer forms the shell. A possible growth mechanism behind the formation of different micro and nanostructures has been proposed. In addition, we have synthesized ZnO nanocanal-like structures by annealing Zn nanowires in vacuum at 350 °C for 30 min.     

Growth of hexagonal and cubic InN nanowires using MOCVD with different growth temperatures

We have performed a detailed investigation of the metal-organic chemical vapor deposition (MOCVD) growth and characterization of InN nanowires formed on Si(1 1 1) substrates under nitrogen rich conditions. The growth of InN nanowires has been demonstrated by using an ion beam sputtered (∼10 nm) Au seeding layer prior to the initiation of growth. We tried to vary the growth temperature and pressure in order to obtain an optimum growth condition for InN nanowires. The InN nanowires were grown on the Au+In solid solution droplets caused by annealing in a nitrogen ambient at 700 °C. By applying this technique, we have achieved the formation of InN nanowires that are relatively free of dislocations and stacking faults. Scanning electron microscopy (SEM) showed wires with diameters of 90–200 nm and lengths varying between 3 and 5 μm. Hexagonal and cubic structure is verified by high resolution X-ray diffraction (HR-XRD) spectrum. Raman measurements show that these wurtzite InN nanowires have sharp peaks E₂ (high) at 491 cm⁻¹ and A₁ (LO) at 591 cm⁻¹.     

Ordered arrays of high-quality single-crystalline α-Si3N4 nanowires: Synthesis,properties and applications

Ordered arrays of high-quality single-crystalline α-Si₃N₄ nanowires (NWs) have been synthesized via thermal evaporation and detailed characteristics of the NWs have been analyzed by employing scanning electron microscope (SEM) along with energy dispersive spectroscopy (EDS), high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photospectroscopy (XPS), infrared (IR), photoluminescence (PL) and in situ I–V measurements by STM/TEM holder. The microscopic results revealed that the NWs having diameter in the range of ~30–100 nm and length in microns. Furthermore, the NWs are found to be single crystalline grown along [0 0 1] direction. The elemental composition and valence states of elements are analyzed by EDS and XPS. The room temperature PL spectra exhibit a broad range visible emission band. The electron transport property of a single NW illustrates the symmetric I–V curve of a semiconductor. The possible growth mechanism is also briefly discussed.     

A simple synthesis of large-scale SiC–SiO2 nanocables by using thermal decomposition of methanol: Structure, FTIR, Raman and PL characterization

Large-scale SiC nanocables were synthesized on a Ni(NO₃)₂-catalyzed Si substrate by using a simple and cheap method based on thermal decomposition of methanol. Based on X-ray diffraction and high-magnification transmission electron microscopy, the as-grown nanocables consisted of crystalline SiC cores and amorphous SiO₂ shells. The diameters of SiC cores were 5.7–10 nm and the thicknesses of SiO₂ shells were 9–20 nm. Dividing of nanocables was observed and its origin was investigated. An asymmetric feature of SiC TO band with a shoulder at the high-frequency side was attributed to the contribution of SiC TO mode. The nanocables displayed strong violet–blue emission. A possible growth mechanism was proposed.     

The effect of polyacrylamide on the crystallization of calcium carbonate: Synthesis of aragonite single-crystal nanorods and hollow vatarite hexagons

CaCO₃ nanorods were synthesized via a facile solution route by polymer-controlled crystallization in the presence of polyacrylamide (PAM). The morphology, size and crystal structure were characterized by means of scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results suggest that the as-synthesized product was CaCO₃ (aragonite) nanorods with diameter ca. 50 nm and length ca. 1 μm. Selected area electron diffraction (SAED) pattern shows the single-crystal nature of CaCO₃ nanorods. The reaction time, temperature, pH and reactant concentration were systemically investigated. With the increase in the reaction time, hollow vaterite hexagonal disks can be obtained.     

Template free-solvothermaly synthesized copper selenide (CuSe,Cu2−xSe, β-Cu2Se and Cu2Se) hexagonal nanoplates from different precursors at low temperature

Nonstoichiometric (Cu_2−xSe) and stoichiometric (CuSe, β-Cu₂Se and Cu₂Se) copper selenide hexagonal nanoplates have been synthesized using different general and convenient copper sources, e.g. copper chloride, copper sulphate, copper nitrate, copper acetate, elemental copper with elemental selenium, friendly ethylene glycol and hydrazine hydrate in a defined amount of water at 100 °C within 12 h adopting the solvothermal method. Phase analysis, purity and morphology of the product have been well studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray diffraction (EDAX) techniques. The structural and compositional analysis revealed that the products were of pure phase with corresponding atomic ratios. SEM, TEM and HRTEM analyses revealed that the nanoplates were in the range 200–450 nm and the as-prepared products were uniform and highly crystallized. The nanoplates consisted of {0 0 1} facets of top–bottom surfaces and {1 1 0} facets of the other six side surfaces. This new approach encompasses many advantages over the conventional solvothermal method in terms of product quality (better morphology control with high yield) and reaction conditions (lower temperatures). Copper selenide hexagonal nanoplates obtained by the described method could be potential building blocks to construct functional devices and solar cell. This work may open up a new rationale on designing the solution synthesis of nanostructures for materials possessing similar intrinsic crystal symmetry. On the basis of the carefully controlled experiments mentioned herein, a plausible formation mechanism of the hexagonal nanoplates was suggested and discussed. To the best of our knowledge, this is the first report on nonstoichiometric (Cu_2−xSe) as well as stoichiometric (CuSe, β-Cu₂Se and Cu₂Se) copper selenide hexagonal nanoplates with such full control of morphologies and phases by this method under mild conditions.     

Crystal growth, characterization and spectroscopic study of europium-doped NaY(PO3)4

Europium-doped NaY(PO₃)₄ single crystals have been synthesized by the flux method with sizes around 1 mm³. The unit cell parameters at room temperature refined by X-ray powder diffraction are a=7.1510(4) Å; b=13.0070(8) Å; c=9.6973(2) Å; β=90.606(3)°, Z=4 with the space group P2₁/n in monoclinic system. The present single crystals have a needle shape, they are elongated along the a crystallographic direction, and their size is in the 500 μm–1 mm range. The linear thermal expansion tensor parameters were determined, being the maximum value along the b direction, 16.1×10⁻⁶ K⁻¹ and the minimum along the a direction being 11.7×10⁻⁶ K⁻¹. The IR vibration modes attributed to the group P–O are consistent with the crystallographic data concerning the chain aspect of the phosphate anion. This material melts incongruently at 1141 K. Intense visible emissions attributed to Eu^{3+ 5}D₀→⁷F₁, ⁵D₀→⁷F₂ and ⁵D₀→⁷F₄, electronic transitions have been observed after pumping at 355 nm at room temperature.     

Structural and optical properties of CdO nanowires synthesized from Cd(OH)2 precursors by calcination

CdO nanowires were produced by calcination process using Cd(OH)₂nanowires as precursors. The Cd(OH)₂ nanowires were synthesized via arc discharge method submerged in de‐ionized water. Transmission electron microscopy (TEM) analysis of the as‐synthesized Cd(OH)₂ nanowires revealed that nanowire morphology was abundant form with the diameters range from 5 to 40 nm. In addition to the nanowire morphology, Cd(OH)₂ nanospheres and hexagonal shaped nanoparticles were also displayed. The Cd(OH)₂ nanostructures were used as precursors to produce CdO nanowires and calcinated in air at 400 °C for four hours. After calcination, the structural, morphological and optical properties of the as‐synthesized CdO nanowires were characterized by means of TEM, selected area electron diffraction (SAED), X‐ray diffraction (XRD) and UV‐vis spectroscopy. The XRD and SAED techniques showed that the as‐synthesized Cd(OH)₂ nanostructures could be transformed into CdO nanostructures after the calcination process. TEM results revealed that the as‐synthesized CdO nanowires were 5–30 nm in diameter and shorter than corresponding Cd(OH)₂ nanowires. In addition, the diameters of the spherical or irregular CdO nanoparticles ranged from 20 nm to 50 nm. UV‐vis spectroscopy analysis was showed that the direct gap of the CdO nanowires were found to be 2.60 eV which is slightly higher than the earlier reported values of the bulk CdO for direct band gaps (2.3 eV) due to quantum size effect. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tetragonal tungsten oxide nanobelts synthesized by chemical vapor deposition

Tungsten trioxide (WO₃) nanobelts in tetragonal structure were grown on Si substrates by a hot-wall chemical vapor deposition (CVD) method without using catalysts. The products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence (PL) spectrum. The width of the nanobelts is in the range of 50–100 nm with width-to-thickness ratios of 5–10 and lengths of up to tens of micrometers. These nanobelts grew along the [0 0 1] direction and can be identified as the tetragonal WO₃ structures. Raman and PL measurements indicate the high quality of the nanobelts. The vapor–solid growth mechanism could be applicable in our experiment.     

A catalyst-free method to silicon nanowires at relative low temperature

Well-crystallized straight Si nanowires (SiNWs) were successfully prepared in large scale via a facile reaction between NaN₃ and Na₂SiF₆ at 600 °C without using any catalyst. Characterization by X-ray powder diffraction and transmission electron microscopy demonstrates that the as-obtained product is pure-phase cubic SiNWs with diameters of 40 nm or so, and lengths of several micrometers. And the SiNWs with spherical tips can be obtained at a temperature as low as 300 °C. Heating temperature and holding time have crucial influence on the synthesis and morphology of the SiNWs. An oxide-assisted growth mechanism is responsible for the formation of the SiNWs.     

Simple hydrothermal preparation of -MnOOH nanowires and their low-temperature thermal conversion to β-MnO2 nanowires

Without the use of any extra surfactant or template, γ-MnOOH single crystalline nanowires were synthesized directly through the hydrothermal reaction between KMnO₄ and toluene in distilled water at 180 °C for 24 h; and β-MnO₂ single crystalline nanowires could be obtained just by calcination of the γ-MnOOH nanowires in air at 280 °C for 5 h. The as-prepared γ-MnOOH and β-MnO₂ nanowires were characterized by X-ray powder diffraction, atomic absorption spectroscopy, Fourier transformed infrared spectroscopy, scanning electron microscope, transmission electron microscope, high-resolution transmission electron microscope and selected area electron diffraction.     

A room temperature solution-phase process to synthesize pure phase single-crystalline hexagonal cobalt hydroxide nanoplates

A simple room temperature solution-phase method has been developed to synthesize pure phase single-crystalline hexagonal β-Co(OH)₂ nanoplates. The chemical composition and morphology of the as-prepared β-Co(OH)₂ nanoplates were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The results indicated that the as-prepared β-Co(OH)₂ nanoplates were composed of pure brucite-like β-Co(OH)₂ phase with single-crystalline feature. The effect of polyethylene glycol (PEG), NH₄OH, and NaOH on the morphology and size of β-Co(OH)₂ nanocrystals were discussed in detail. The growth mechanism of the as-synthesized nanoplates was also discussed in detail based on the experimental results.     

Preparation of CdS nanowires by the decomposition of the complex in the presence of microwave irradiation

A novel synthetic route for the preparation of CdS nanowires has been developed. CdS nanowires with a diameter of ca. 4 nm have been successfully prepared by the microwave irradiation of a complex of cadmium-1-pyrrlidine dithio carboxylic acid ammonium (C₅H₁₂N₂S₂, APDTC) [Cd(APDTC)₂]₂ in an ethylenediamine solution. The CdS nanowires were characterized by powder X-ray diffraction pattern, transmission electron microscopy (TEM), UV-Vis spectroscopy, diffuse reflection spectroscopy and PL spectroscopy.     

Low-temperature growth of tetragonal tungsten nanowire arrays on tungsten substrate using Ni solid catalysts

Tetragonal tungsten nanowire arrays were successfully fabricated on tungsten substrate using Ni catalysts by chemical vapor deposition (CVD) at 950 °C. The synthesized tungsten nanowires grew along [100] direction, with a high aspect ratio more than 50 and sharp tips. The Ni catalyst was found to be located at the wire's bottom and assisted the nucleation of the tungsten nanowire. Samples were characterized in detail by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) technologies. Based on the analysis of the experimental results, the possible formation mechanism of nanowires was proposed as well.     

Growth and characterization of the nonlinear optical single crystal: l-lysine acetate

Single crystals of l-lysine acetate, an organic nonlinear optical (NLO) material, were grown by the controlled evaporation of its aqueous solutions. Its solubility in aqueous solution was determined gravimetrically. The grown crystals were characterized by the single-crystal diffraction, X-ray powder diffraction, Fourier transform infrared and Raman spectra. The structure analysis reveals that it belongs to the monoclinic crystallographic system, space group P2₁, with cell parameters: a=5.420(2) Å, b=7.542(4) Å, c=12.653(1) Å, β=91.73(1)°, Z=2 and V=516.8 Å³. Experiments of thermogravimetric (TG) and differential thermal analysis (DTA) were carried out to study its thermal properties. The optical behaviours, including transmission spectrum and second harmonic generation (SHG), were investigated to study its linear and NLO properties.     

Facile synthesis and luminescence properties of octahedral YVO4:Eu microcrystals

Uniform octahedral YVO₄:Eu³⁺ microcrystals have been successfully prepared through a designed two-step hydrothermal conversion method. One-dimensional precursor Y₄O(OH)₉NO₃ was first prepared through a simple hydrothermal process without using any surfactant, catalyst or template. Subsequently, well-defined octahedral YVO₄ was synthesized at the expense of the precursor during a hydrothermal conversion process. XRD results demonstrate that the diffraction peaks of the final product can be well indexed to the pure tetragonal phase of YVO₄. The SEM and TEM images indicate that the as-prepared YVO₄ sample has regular octahedral shape with sharp corners and well-defined edges. The as-obtained YVO₄:Eu³⁺ phosphor shows strong red emission under ultraviolet excitation or low-voltage electron beam excitation. Furthermore, this facile and general conversion method may be of much significance in the synthesis of many other lanthanide compounds with uniform morphology.     

Size-controlled synthesis of LaAlO3 by reverse micelle method: Investigation of the effect of water-to-surfactant ratio on the particle size

Lanthanum monoaluminate (LaAlO₃) nanoparticles have been synthesized using microreactors made of poly(oxyethylene) nonylphenyl ether (Igepal CO-520)/water/cyclohexane microemulsions. The control of particle size was achieved by varying the water-to-surfactant molar ratio. The synthesized and calcined powders were characterized by thermogravimetry–differential thermal analysis (TGA-DTA), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Differential thermal analysis showed that LaAlO₃ phase transformation decreases with increase in water/surfactant (R) value. Pure LaAlO₃ phase was synthesized by annealing at 800 °C for 2 h in air directly from amorphous precursors, without formation of intermediate phase. The average particle size was found to increase with increase in water-to-surfactant ratio (R). FTIR analysis was carried to monitor the elimination of residual oil and surfactant phases from the microemulsion-derived precursor and calcined powder.