Synthesis and characterization of MSe (M=Zn, Cd) nanorods by a new solvothermal method

Array of bis-quaternary ammonium surfactant tailored Cu(2−x)Te quantum dots with amended functional assets

Copper telluride [Cu_(2−x)Te] nanoparticles stabilized by highly hydrophobic surfactants were synthesised and their structural, optical and electrical properties were examined.

Synthesis, Characterization and Photocatalytic Properties of Lithium Titanate Nanorods

Lithium titanate nanorods have been synthesized via the hydrothermal process using lithium acetate, titanium butoxide and ethylenediamine as raw materials. X-ray diffraction (XRD) analysis shows that lithium titanate nanorods are composed of orthorhombic Li 2 Ti 3 O 7 phase. Scanning electron microscopy (SEM) shows that the diameter and the length of lithium titanate nanorods are about 40–150 nm and 1 μm, respectively. UV-Vis diffuse reflectance spectrum indicates that the bandgap of the lithium titanate nanorods is 3.63 eV. Ethylenediamine plays an essential role in the formation of lithium titanate nanorods. Ethylenediamine-assisted nucleation and crystalline growth process have been proposed to explain the formation and growth of lithium titanate nanorods. Photocatalytic degradation of methylene blue (MB) dye over the lithium titanate nanorods has been investigated under UV-Vis light irradiation. MB solution with the initial concentration of 2.5 mgL-1 can be degraded totally using 10 mg lithium titanate nanorods in 10 mL MB solution.

INORGANIC SEMICONDUCTOR NANOWIRES

One-dimensional (1D) nanostructures are ideal systems for investigating the dependence of electrical transport, optical properties and mechanical properties on size and dimensionality. They are expected to play an important role as both interconnects and functional components in the fabrication of nanoscale electronic and optoelectronic devices. This article presents an overview of current research activities that center on nanowires whose lateral dimensions fall anywhere in the range of 1–200 nm. It is organized into three parts: The first part discusses various methods that have been developed for generating nanowires with tightly controlled dimensions, orientations, and well-defined properties. The second part highlights a number of strategies that are being developed for the hierarchical assembly of nanowire building blocks. The third part surveys some of the novel physical properties (e.g., optical, electrical, and mechanical) of these nanostructures. Finally, we conclude with some personal perspectives on the future research directions in this field.

SYNTHESIS, CHARACTERIZATION, AND ASSEMBLY OF CdSe QUANTUM DOT ARRAY

CdSe semiconducting nanoparticles in the range of 6–7 nm in size were synthesized by a soft chemical procedure at room temperature. The particles were characterized by powder X-ray diffraction, UV–visible optical spectroscopy revealing nanocrystallization, and quantum mechanical electron confinement. Photoluminescence and Raman spectroscopy of these nanocrystalline powders indicated optical phonon confinement. Asymmetric line shapes revealed occurrence of nonzone center phonons. The particles could be successfully deposited on ITO substrate by electrophoresis to obtain self-organized quantum dot array. Scanning electron microscopy, high-resolution scanning electron microscopy, confocal fluorescence microscopy, and atomic force microscopy investigations revealed self-similar deposits.

Synthesis, assembly, and optical properties of shape- and phase-controlled ZnSe nanostructures

Shape-, size-, and phase-controlled ZnSe nanostructures were synthesized by thermolysis of zinc acetate and selenourea using liganding solvents of octadecylamine (ODA) and trioctylphosphineoxide (TOPO) at different molar ratios. Materials synthesized in pure ODA resulted in uniform ultranarrow nanorods and nanowires of 1.3 nm in diameter. Morphological change from nanowire to spherical particle of larger diameter occurs with increasing TOPO/ODA ratio. Variation of the TOPO content in the mixed solvent also allows control of the crystallographic phase of ZnSe (wurtzite or zinc blende). The conditions and mechanisms of shape and phase control are discussed. Ultra-high-density networks of the ordered wires are achieved using the Langmuir-Blodgett technique in a single step as an essential stage on the route to ultra-high-density semiconductor nanocircuit fabrication.

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.

Shape control of II-VI semiconductor nanomaterials

Anisotropic II-VI semiconductor nanocrystals and nanoparticles have become important building blocks for (potential) nanotechnological applications. Even though a wide variety of differently shaped nanoparticles of this class can be prepared, the underlying mechanisms are mostly not fully understood. This Review article provides a brief overview of the currently studied shape-evolution mechanisms and the most prominent synthesis methods for such particles, with an aim to provide a fundamental understanding on how different morphologies evolve, and to function as a tool to aid in the preparation of specific nanocrystals.

Templated synthesis of ZnSe nanostructures using lyotropic liquid crystals

We report a technique for controlled synthesis of zero-, one-, and two-dimensional compound semiconductor nanostructures by using cubic, hexagonal, and lamellar lyotropic liquid crystals as templates, respectively. The liquid crystals were formed by self-assembly in a ternary system consisting of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) amphiphilic block copolymer as the surfactant, heptane as the non-polar dispersed phase, and formamide as the polar continuous phase. ZnSe quantum dots and nanowires with diameters smaller than 10 nm, as well as free-standing, disc-like quantum wells, were grown inside the spherical, cylindrical, and planar nanodomains, respectively, by reacting diethylzinc that was dissolved in the heptane domains with hydrogen selenide gas that was brought into contact with the liquid crystal in a sealed chamber at room temperature and atmospheric pressure. The shape and size of the resulting nanostructures can be manipulated by selecting the templating phase of the liquid crystal, the size of the dispersed nanodomains that is controlled by the composition of the template, and the concentration of diethylzinc in them.

One-step fabrication of uniform Si-core/CdSe-sheath nanocables

A simple one-step thermal evaporation of CdSe powder using Si substrate at controlled conditions results in ultrauniform Si-core/CdSe-sheath nanocables. These nanocables are approximately 80 nm in diameter and several tens of micrometers in length. Detailed microstructure and chemical composition analysis of the nanocables indicates that they are composed of a single crystalline Si (cubic) core and CdSe (hexagonal) sheath. The experimental evidence suggested that the Si nanowires can be directly grown from the Si substrate via an oxide-assisted growth mechanism and further served as templates for CdSe, resulting in nanocable heterostructures.

Kinetically controlled synthesis of wurtzite ZnS nanorods through mild thermolysis of a covalent organic-inorganic network

The high-temperature (over 1020 degrees C) polymorph of ZnS, wurtzite ZnS, has been successfully prepared through a low-temperature (180 degrees C) hydrothermal synthesis route in the presence of ethylenediamine (en). The effects of en concentrations, reactant concentrations, reaction temperatures, and reaction times on crystal structures and shapes of ZnS have been investigated. We have demonstrated that the wurtzite ZnS showing rodlike morphology can be kinetically stabilized in the presence of en, especially at a high reactant concentration under appropriate hydrothermal conditions. Besides phase evolution of ZnS from hexagonal to cubic, morphological transformation from nanorods to nanograins has also been observed in the present investigation. Nanograins of phase-pure cubic ZnS, the thermodynamically stable polymorph, are easily prepared, and no hexagonal ZnS nanorods are detected in "pure" water, i.e., in the absence of en molecules. The above investigations indicate that the controlled fabrication of wurtzite ZnS nanorods is due to a mediated generation of the lamellar phase, ZnS.0.5en, a covalent organic-inorganic network based on ZnS slabs, and to its subsequent thermolysis in aqueous solution. The controlled growth of wurtzite ZnS nanorods and sphalerite ZnS nanograins provides us an opportunity to structurally modulate physical properties. These wurtzite ZnS nanorods display narrower and stronger blue emission than sphalerite ZnS nanograins.

Shape control of CdSe nanocrystals

Nanometre-size inorganic dots, tubes and wires exhibit a wide range of electrical and optical properties that depend sensitively on both size and shape, and are of both fundamental and technological interest. In contrast to the syntheses of zero-dimensional systems, existing preparations of one-dimensional systems often yield networks of tubes or rods which are difficult to separate. And, in the case of optically active II-VI and III-V semiconductors, the resulting rod diameters are too large to exhibit quantum confinement effects. Thus, except for some metal nanocrystals, there are no methods of preparation that yield soluble and monodisperse particles that are quantum-confined in two of their dimensions. For semiconductors, a benchmark preparation is the growth of nearly spherical II-VI and III-V nanocrystals by injection of precursor molecules into a hot surfactant. Here we demonstrate that control of the growth kinetics of the II-VI semiconductor cadmium selenide can be used to vary the shapes of the resulting particles from a nearly spherical morphology to a rod-like one, with aspect ratios as large as ten to one. This method should be useful, not only for testing theories of quantum confinement, but also for obtaining particles with spectroscopic properties that could prove advantageous in biological labelling experiments and as chromophores in light-emitting diodes.