Modelling the formation of high aspect CdSe quantum wires: axial-growth versus oriented-attachment mechanisms

Following the recent low temperature synthesis of high quality and single crystal CdSe quantum nanowires, we have used a thermodynamic model to investigate the plausibility of axial-growth and oriented-attachment formation mechanisms. Using surface energies for clean and alkylamine-passivated CdSe surfaces reported elsewhere by Manna et al (2005 J. Phys. Chem. B 109 6183), we have compared equilibrium and metastable shapes of CdSe nanowires as a function of aspect ratio and axial orientation for different degrees of surface passivation. In general, the theoretical results support the oriented-attachment of low aspect quantum dots or nanorods, followed by coalescence to form high aspect [Formula: see text] quantum wires.     

A facile single-source route to CdS nanorods

CdS nanorods were synthesized on a large scale by thermolyzing a single-source precursor, (Me(4)N)(4)[S(4)Cd(10)(SPh)(16)], in a single surfactant system. Transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and x-ray powder diffraction (XRD) have been used to characterize the morphology and crystal structure of the sample. The TEM images show that the CdS nanorods are uniform with an aspect ratio of about 9:1. The XRD result demonstrates that the nanorods are in a wurtzite structure. The nanorods exhibit quantum size effects from the optical absorption spectrum. The influence of reaction conditions on the growth of CdS nanorods demonstrates that high precursor concentration and high reaction temperature (>190?°C) are favorable for the formation of CdS nanorods.     

种子生长法制备长径比为2-5的金纳米棒

报道了种子生长法合成金纳米棒.以氯金酸(HAuCl4)为原料,以硼氢化钠(NaBH4)为还原剂,首先还原金离子(Au3 )得到直径为3-4nm的金种子.以银离子(Ag )为辅助离子,以十六烷基溴化铵(CTAB)为表面活性剂,以抗坏血酸为弱还原剂,加入金种子溶液之后可以获得纳米棒.研究表明,通过改变银离子的用量可以控制金纳米棒长径比为2-5.TEM和UV-vis光谱的表征证实了金纳米棒的形貌和光谱特征,并深入探讨了金纳米棒的生长机理.     

Synthesis and optical properties of CdS nanorods and CdSe nanocrystals using oleylamine as both solvent and stabilizer

CdS nanorods and CdSe nanocrystals were prepared via the one-pot synthesis approach in oleylamine (OLA) system. The OLA used in this process as both the solvent and stabilizer is favorable for probing capping mechanism and simplifying experimental steps. The growth process and characterization of cadmium chalcogenide nanocrystals were determined by X-ray diffraction (XRD), transmission electron microscopy (TEM), Ultraviolet-visible (UV-vis) spectroscopy and photoluminescence (PL) spectroscopy. Results demonstrated OLA-capped CdS nanorods and CdSe nanocrystals were highly crystalline and had good optical properties.     

小型金纳米棒的制备

用种子生长法合成小型金纳米棒,改变合成参数可调控其形貌和性能。使用紫外-可见-近红外分光光度计和透射电子显微镜(TEM)测试和观察了金纳米棒的消光特性和形貌,研究了AgNO₃、十六烷基三甲基溴化铵(CTAB)和籽晶的用量对金纳米棒的形貌和性能的影响。结果表明：在不同条件下制备的金纳米棒具有良好的重现性。在(0.01 mol/L) AgNO3用量为0.035 mL、(0.1 mol/L) CTAB用量为11 mL、籽晶用量为1.1 mL的最佳条件下合成的金纳米棒,其长径比约为3.8,平均长度约为34 nm,形貌均匀性和分散性良好。这种小型金纳米棒可用于检测残留物福美双(Thiram)。     

Facile route to the synthesis of porous α-Fe2O3 nanorods

The requirements of simple and reliable protocols for the synthesis of anisotropic structures with controlled morphology continue to be a major challenge in nanoscience. In this paper we describe the facile synthesis of porous hematite (α-Fe₂O₃) nanorods using anionic surfactant as a rod-like template. α-FeOOH nanorods with diameters of 170–210 nm and lengths up to 3–5 μm were synthesized in high yield via hydrothermal method using sodium dodecyl sulphate as a template. The porous α-Fe₂O₃ was obtained after solvent extraction and calcining the as-obtained α-FeOOH nanorods at 500 °C for 6 h. Even after removal of template by solvent extraction and calcination the shape of the nanorods was intact except the generation of pores on the nanorods. The porous nanorods were analysed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission and high-resolution transmission electron microscopy (TEM & HRTEM), scanning electron microscopy (SEM) and superconducting quantum interference device (SQUID) measurements. SEM and TEM images showed that the morphology of hematite nanostructure is homogeneous in the shape of rods and full of porosity and magnetization measurements of the porous α-Fe₂O₃ nanorods showed weak ferromagnetic behavior. The surfactant SDS (sodium dodecyl sulphate) plays a key role in controlling the nucleation and growth of the nanorods and their use as a new class of inorganic scaffolds for the synthesis of nanomaterials are salient features of the work with implications in crystal engineering and nanocomposites design for various applications.     

Characterization of cadmium sulfide nanorods prepared by the solvothermal process

Cadmium sulfide nanorods were successfully prepared from cadmium nitrate tetrahydrate and thiourea in ethylenediamine by 200 °C solvothermal reactions using hydroxyethyl cellulose (HEC) as a capping material. X-ray diffraction (XRD), selected area electron diffraction (SAED), and Raman spectroscopy showed that the products were hexagonal wurtzite CdS with the 1st and 2nd harmonic modes at 303.5 and 593.0 cm^− 1, respectively. The intensity ratios of the 2nd to 1st harmonic modes were increased with their aspect ratios, due to the great strength of exciton-phonon coupling. By using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM) and fast Fourier transformation (FFT), the products were in the shape of nanoparticles in the HEC-free solution, and became nanorods with higher aspect ratios in the HEC-added solutions — especially with longer reaction time. These nanorods were single crystals with growth in the [001] direction.     

Colloidal synthesis and air-annealing of CdSe nanorods for the applications in hybrid bulk hetero-junction solar cells

TOP/TOPO-capped CdSe nanorods were synthesized by colloidal route process using hexylphosphonic acid as a ligand and CdO as a Cd precursor, and the influence of thermal annealing in air on the morphology, crystal structure and optical properties of CdSe nanorods has been elucidated by XRD, TEM and PL analysis. It was observed that as-synthesized CdSe nanorods of ∼ 4-5 nm diameters and ∼ 20 nm lengths go through solid state morphology transformation upon annealing at 350 °C in air atmosphere, forming the nanorods with bullet shape with one side pointed and the other side having a blunt hexagon with the average diameter of ∼ 12 nm and length of ∼ 25 nm. The annealed CdSe nanorods showed improved PL emissions without the shift of peak positions, indicating significant improvement of the crystallinity and optoelectronic properties of nanorods caused by reduction of defects.     

Role of aqueous ammonia on the growth of ZnO nanostructures and its influence on solid-state dye sensitized solar cells

Synthesis of various ZnO nanostructures for different zinc to ammonia concentration ratios by a single-step aqueous chemical method at relatively low temperature is reported here. These nanostructures show preferential growth along (002) direction as observed in XRD. Morphological characterization by SEM, TEM, HRTEM, and SAED patterns reveal the formation of nanostructures of different shape, size, aspect ratio, and the crystal lattice orientations, which are mainly influenced by zinc to ammonia concentration. These materials when used as photo anodes in dye sensitized solar cells, the sample with the mixture of pyramidal, short nanorods, and spherical nanoparticle exhibits maximum conversion efficiency of 0.123 % due to better dye loading and direct conduction pathway for electron transport.     

Correlation Between Structure and Ferromagnetism in Cobalt-Doped CdSe Nanorods

The present study deals with the investigation on structural and magnetic properties of pure and Co-doped CdSe nanorods synthesized by solvothermal route. The effects of Co-doping on structural, optical, and magnetic properties of nanorods have been explored using X-ray diffraction (XRD), transmission electron microscopy (TEM), High-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), Raman spectroscopy, energy dispersive spectroscopy (EDS), diffuse reflectance spectroscopy, electron spin resonance (ESR), and vibrating sample magnetometer (VSM), at room temperature. TEM images show that the synthesized nanorods having length in range of 80–150 nm and diameter of 10–20 nm. No ferromagnetic resonance signal has been observed in ESR spectra, indicating the absence of exchange interactions in pure and doped nanorods. The lattice contraction, increase in band gap, and ferromagnetic behavior have been observed with Co-doping concentration up to 5 %. However, at 10 % Co-doping concentration, reverse trend in above properties has been observed. The study reveals that there is a strong correlation between structural and magnetic properties of Co-doped CdSe nanorods.     

A novel solution method for selective synthesis of pure t-LaVO4

Tetragonal phase LaVO₄ (t-LaVO₄) was successfully selectively synthesized through a simple solution method with La(NO₃)₃ and NaVO₄ as starting materials without any templates or catalysts. The products were characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). XRD patterns showed that pure t-LaVO₄ could be obtained in wide ranges of pH value and crystallization temperature. TEM images revealed that nanorods with different aspect ratios were obtained in different synthesis conditions. The shorter nanorods had mean diameters of about 18-25 nm and lengths of 40-60 nm. However, the longer nanorods had uniform sizes with an average aspect ratio about 10. It was interesting to discover that t-LaVO₄ could be formed even at room temperature (RT), which might be beneficial for a large scale production. Different luminescence performances of the samples doped 5% Eu³⁺ were also investigated.     

Gelation effect on the synthesis of high-aspect-ratio gold nanorods

The growth process of high-aspect-ratio gold nanorods in gelled surfactant solution was studied. As for the application of gold nanorods, the surface plasmon is quite useful, whose absorption depends on their aspect ratio. Hence it is important to synthesize gold nanorods with favorable aspect ratio in high yield. For shorter nanorods (aspect ratio < -10), the synthesis and the growth mechanism have been studied well. For the longer nanorods (aspect ratio > -30), however, the growth mechanism has not yet been understood well, although it has been known that the high-aspect-ratio gold nanorods could be synthesized in high yield in gelled surfactant solution. In this paper, we studied the relationship between the growth process of high-aspect-ratio gold nanorods and the gelation of surfactant growth-solution. Small angle X-ray scattering (SAXS) revealed the microscopic feature of gelation as the structural transition of self-assembly of surfactant molecules from micellar to lamellar. These results will be helpful for better understanding on the growth mechanism of high-aspect-ratio gold nanorods.     

Synthesis and characterization of Mn2O3 nanorods using a novel manganese precursor

The Mn₂O₃ nanorods have been prepared using [Mn(sal)₂] complex as a novel precursor in the presence of sodium dodecyl sulfate (SDS) as surfactant. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectroscopy. Manganese oxide nanocrystals have been prepared under different condition. The controlled experimental results showed that the ultrasonic irradiation and the use of SDS as the surfactant in the chemical process play important role in the formation of the final products.     

水溶液法制备CdSe和ZnSe纳米棒

用水溶液法直接合成了水溶性、发荧光的ZnSe和CdSe纳米棒。ZnSe纳米棒的直径约20～30nm,长度可达60～70nm;CdSe纳米棒的直径约30～60nm,长度可达150～450nm。用X射线衍射仪(XRD)、透射电镜(TEM)、高分辨透射电镜(HR-TEM)、荧光仪等仪器对纳米棒进行了表征。XRD和HRTEM的结果显示纳米棒具有立方结构,结晶度较高。讨论了纳米棒的形成机理以及pH对纳米棒发光强度的影响。合成的纳米棒在水溶液中至少稳定半年,表面被氨基和羧基化,在生物分析中具有广泛的应用前景。     

Coalescence and interface diffusion in linear CdTe/CdSe/CdTe heterojunction nanorods

Colloidal nanorods with linear CdTe/CdSe/CdTe heterojunctions were synthesized by sequential reactant injection. After CdTe deposition at the ends of initially formed CdSe nanorods, continued heating in solution leads to Se-Te interdiffusion across the heterojunctions and coalescence to decreased aspect ratio. The Se-Te interdiffusion rates were measured by mapping the composition profile using nanobeam energy dispersive X-ray spectroscopy (EDS) along the lengths of individual nanorods aged in hot solvent for different amounts of time. The rate of nanorod coalescence was also measured and compared to model predictions using a continuum viscous flow model, which appears to provide a reasonable estimate of the coalescence rate.     

Shape and size control of barium chromate nanoparticles using reverse micelle

The shape and size of barium chromate nanoparticles formed using a water-in-oil microemulsion prepared from the anionic surfactant AOT were examined. As a result, nanowires, nanorods, and nanodots could be synthesized by changing the raw ion concentration and by adding ethanol as a poor solvent. The nanowires and nanorods were self-assembled. It has been shown that the aspect ratio of the generated nanoparticles decreased with increasing chromate ion concentration or due to the addition of ethanol. By contrast, the aspect ratio was almost constant even when the barium ion concentration was changed. The surfactant AOT was selectively adsorbed on the crystal faces of the barium chromate nanoparticles along the a-axis, where it suppressed the growth of their crystal face. Furthermore, the generated nanoparticles were self-assembled through hydrophobic interactions between the surface-anchored AOT molecules. In conclusion, it was clarified that the supersaturation ratio and the particle–surfactant interaction were important factors for controlling the shape and size of these inorganic nanoparticles using the microemulsion method.     

Controlled synthesis of LaPO(4) and CePO(4) nanorods/nanowires

LaPO(4) and CePO(4) nanorods/nanowires with controlled aspect ratios have been successfully synthesized using a hydrothermal microemulsion method under mild conditions. It has been shown that the obtained LaPO(4) has a monoclinic structure, while CePO(4) exists in the hexagonal structure. Uniform nanorods/nanowires with diameters of 20-60?nm and lengths ranging from several hundreds of nanometres to several micrometres were obtained. The aspect ratios of the obtained 1D nanostructures can be fine-tuned by simply changing the [H(2)O ]/[surfactant] molar ratios. The possible growth mechanism of LaPO(4) and CePO(4) nanorods/nanowires was explored in detail.     

A simple route to lanthanum hydroxide nanorods

This letter first describes a facile, low-cost, solution-phase approach to the large-scale preparation of lanthanum hydroxide single crystal nanorods at 60 °C without any template and surfactant. X-ray diffraction (XRD) shows that the nanorods are of pure hexagonal structure. The size and morphology of the products were examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Lanthanum hydroxide single crystal nanorods are with diameters of approximately 20 nm and lengths of 150-200 nm. The processes of formation and decomposition for the as-prepared lanthanum hydroxide nanorods were discussed.     

Facile sonochemical synthesis of CePO(4):Tb/LaPO(4) core/shell nanorods with highly improved photoluminescent properties

A simple, efficient and quick method has been established for the synthesis of CePO(4):Tb nanorods and CePO(4):Tb/LaPO(4) core/shell nanorods via ultrasound irradiation of inorganic salt aqueous solution under ambient conditions for 2?h. The as-prepared products were characterized by means of powder x-ray diffraction (PXRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectra and lifetimes. TEM micrographs show that all of the as-prepared cerium phosphate products have rod-like shape, and have a relatively high degree of crystallinity and uniformity. HRTEM micrographs and SAED results prove that these nanorods are single crystalline in nature. The emission intensity and lifetime of the CePO(4):Tb/LaPO(4) core/shell nanorods increased significantly with respect to those of CePO(4):Tb core nanorods under the same conditions. A substantial reduction in reaction time as well as reaction temperature is observed compared with the hydrothermal process.     

表面活性剂辅助低温固相合成CuS纳米棒

用表面活性剂聚乙二醇400为形貌控制剂,通过低温固相反应成功制备出CuS纳米棒.纳米棒的直径为10～60 nm、长度为100～600 nm.研究结果表明,在反应过程中,表面活性剂所形成的结构对最终纳米晶的形貌起着决定性的作用.用X射线粉末衍射和透射显微镜技术对所制备纳米晶的成分、形状和尺寸进行了表征分析.对CuS纳米棒的形成机理作了深入的讨论,提出了CuS纳米棒的表面活性剂软模板诱导自组装生长机理.