Ultrathin single crystal ZnS nanowires

A facile synthesis of ultrathin single crystal ZnS nanowires with an average diameter of 4.4 nm in high yield (close to 100%) was firstly reported through the pyrolysis of a single-source precursor (zinc diethyldithiocarbamate). The obtained ultrathin ZnS nanowires exhibit good optical properties and hold promise for future applications in nanodevices.     

Controlled synthesis and photoluminescence properties of ZnS nanowires and nanoribbons

Rapid synthesis of wurtzite ZnS nanowires and nanoribbons has been achieved by a simple thermal evaporation of ZnS powder onto Si substrate in the presence of Au catalyst. A vapor-liquid-solid process is proposed for the formation of the ZnS nanostructures. The flow rate of the inert carrier Ar gas along with the temperature play an important role in defining the morphology of the ZnS nanostructures. The morphological change of the ZnS nanostructures and their growth sequence were studied through scanning electron microscopy. Room-temperature photoluminescence measurements showed intense blue emission at approximately 398 nm from both the nanowires and the nanoribbons.     

Ultrathin Au nanowires and their transport properties

This paper presents a facile synthesis of single-crystalline Au nanowires by reduction of HAuCl4 in oleic acid and oleylamine. The diameter of these micron-meter-long Au nanowires is controlled to be 3 and 9 nm by volume ratio of oleylamine and oleic acid. When linked between two gold electrodes, the 9 nm Au nanowire shows good electron conductivity with its breakdown current density reaching 3.5 x 10(12) A/m2. This demonstrates that the chemically made ultrathin Au nanowires can be used as a molecular-scale interconnect for nanoelectronic applications.     

Solvothermal synthesis and photoluminescent properties of ZnS/cyclohexylamine: inorganic-organic hybrid semiconductor nanowires

An inorganic-organic hybrid semiconductor, ZnS/CHA (CHA = cyclohexylamine) nanocomposites was successfully synthesized via a solvothermal method using CHA as solvent, which yielded uniform and ultralong nanowires with widths of 100-1000 nm and lengths of 5-20 microm. Changing the reaction conditions could alter the morphology and optical properties of the nanocomposites. The periodic layer subnanometer structures were identified by high-resolution transmission electron microscopy (HR-TEM) images, with thickness of approximately 2 nm. The composites exhibited a very large blue-shift in their optical absorption edge as well as an exciton excitation band due to a strong quantum confinement effect caused by the internal subnanometer-scale structures. The pure hexagonal wurtzite ZnS nanowires were also obtained by extracting the ZnS/CHA nanocomposites with dimethyl formamide (DMF). In addition, the luminescent properties of exciton and defect-related transitions in different samples of ZnS/CHA were discussed in detail.     

Selected-control hydrothermal synthesis of alpha- and beta-MnO(2) single crystal nanowires

A selective-control hydrothermal method has been developed in the preparation of alpha- and beta-MnO(2) single-crystal nanowires. The crystal structure and morphology of the final products can be influenced by the concentration of NH(4)(+) and SO(4)(2-).     

ZnS nanosheets: Egg albumin and microwave-assisted synthesis and optical properties

ZnS nanosheets were prepared via egg albumin and microwave-assisted method. The phases, crystalline lattice structures, morphologies, chemical and optical properties were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscope(FE-SEM), selected area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy and fluorescence(FL) spectrometer and growth mechanism of ZnS nanosheets was investigated. The results showed that all samples were pure cubic zinc blende with polycrystalline structure. The width of ZnS nanosheets with a rectangular nanostructure was in the range of 450–750 nm. The chemical interaction existed between egg albumin molecules and ZnS nanoparticles via the amide/carboxylate group. The band gap value calculated was 3.72 eV. The band at around 440 nm was attributed to the sulfur vacancies of the ZnS nanosheets. With increasing volumes of egg albumin, the photoluminescence (PL) intensity of ZnS samples firstly increased and then decreased, attributed to concentration quenching.     

CdS:Mn nanocrystals passivated by ZnS: synthesis and luminescent properties

Synthesis and characterization of highly luminescent ZnS-passivated CdS:Mn (CdS:Mn/ZnS) core/shell structured nanocrystals are reported. Mn-doped CdS core nanocrystals are produced ranging from 1.5 to 2.3 nm in diameter with epitaxial ZnS shell of wider band gap via a reverse micelle process. UV irradiation-stimulated photo-oxidation of the ZnS shell results in formation of sulfate (ZnSO(4)) as determined by x-ray photoelectron spectroscopy, which increases the photoluminescence emission intensity and subsequent photostability. Luminescent relaxation lifetime data present two different decay components, consisting of slow decay emission from the Mn center and a fast decay emission from a defect-related center. The impact of the density of surface defect states upon the emission spectra is discussed.     

Facile controlled synthesis of MnO2 nanowires for supercapacitors

In this report, a simple and facile method was developed for preparation of MnO₂ nanowires by calcinations of MnOOH nanowires previously synthesized under hydrothermal conditions, using hexamethylenetetramine as a reducing agent, without any template. The as-prepared MnO₂ nanowires displayed an enhanced specific capacitance (262.7 F g^?1) and good cycling stability (e.g., no loss within 1,500 cycles), showing good electrochemical performances as electrode material for supercapacitors.     

Metal-free phthalocyanine single crystal: Solvothermal synthesis and near-infrared electroluminescence

A metal-free purple H₂Pc single crystal was synthesized by a facile solvothermal method, and its solubility and near-infrared (NIR) optical properties were also investigated due to its potential applications as a light-emitting layer for OLEDs. The H₂Pc single crystal is insoluble in 1-chlorine naphthalene and other organic solvents. It gives a wide absorption in the range from 620 nm to 679 nm and a wide emission in near 922 nm. As an active light-emitting layer, H₂Pc was employed to fabricate electroluminescent (EL) devices with a structure of ITO/NPB (30 nm)/Alq₃:H₂Pc (30 nm)/BCP (20 nm)/Alq₃ (20 nm)/Al. The emission center is at 936 nm when the H₂Pc doping concentration is 20 wt%. The doping concentration strongly governs the emission intensity. When doping concentration decreases from 10 wt% to 1 wt%, the emission intensity remarkably fades, and simultaneously the emission center undergoes a blue shift.     

Nuclearity controlled cyanide-bridged bimetallic CrIII-MnII compounds: synthesis, crystal structures, magnetic properties and theoretical calculations

The preparation, X-ray crystallography and magnetic investigation of the compounds PPh4[Cr(bipy)(CN)4].2 CH3CN.H2O (1) (mononuclear), [[Cr(bipy)(CN)4]2Mn-(H2O)4].4H2O (2) (trinuclear), [[Cr(bipy)(CN)4]2Mn(H2O)2] (3) (chain) and [[Cr(bipy)(CN)4]2Mn(H2O)].H2O.CH3CN (4) (double chain) [bipy=2,2'-bipyridine; PPh4 (+)=tetraphenylphosphonium] are described herein. The [Cr(bipy)(CN)4]- unit act either as a monodentate (2) or bis-monodentate (3) ligand toward the manganese atom through one (2) or two (3) of its four cyanide groups. The manganese atom is six-coordinate with two (2) or four (3) cyanide nitrogens and four (2) or two (3) water molecules building a distorted octahedral environment. In 4, two chains of 3 are pillared through interchain Mn-N-C-Cr links which replace one of the two trans-coordinated water molecules at the manganese atom to afford a double chain structure where bis- and tris-monodenate coordination modes of [Cr(bipy)(CN)4]- coexist. The magnetic properties of 1-4 were investigated in the temperature range 1.9-300 K. A Curie law behaviour for a magnetically isolated spin quartet is observed for 1. A significant antiferromagnetic interaction between CrIII and MnII through the single cyanide bridge [J=-6.2 cm(-1), the Hamiltonian being defined as H=-J(SCr1.SMn+SCr2.SMn] occurs in 2 leading to a low-lying spin doublet which is fully populated at T <5 K. A metamagnetic behaviour is observed for 3 and 4 [the values of the critical field Hc being ca. 3000 (3) and 1500 Oe (4)] which is associated to the occurrence of weak interchain antiferromagnetic interactions between ferrimagnetic Cr2III MnII chains. The analysis of the exchange pathways in 2-4 through DFT type calculations together with the magnetic bevaviour simulation using the quantum Monte Carlo methodology provided a good understanding of their magnetic properties.     

Synthesis of single crystal BaWO4 nanowires in catanionic reverse micelles

High aspect-ratio, single crystal BaWO4 nanowires with diameters as small as 3.5 nm and lengths up to more than 50 microns were synthesized in catanionic reverse micelles formed by an equimolar mixture of two surfactants: undecylic acid and decylamine.     

Novel synthesis of organic nanowires and their optical properties

Aligned nanowires of organic luminescent material were prepared by introducing the organic luminants into nanochannels of variable size in an anodic aluminum oxide (AAO) membrane, and the emission spectra from these nanowire arrays exhibited novel size-dependent luminescent properties.     

Hydrothermal synthesis and their catalytic properties of manganite nanowires

La_0.5Sr_0.5MnO₃ nanowires and nanoparticles were synthesized by the hydrothermal and citrate methods, respectively. The samples were characterized by TEM, HRTEM, XRD, ICP and N₂ adsorption, etc. The formation mechanism of the nanowires was proposed and discussed. Further, the stabilities and catalytic activities of La_0.5Sr_0.5MnO₃ nanowires for CH₄ combustion were evaluated and compared with those of the nanoparticles. The results showed that the particle morphology had a significant effect on the properties of the catalysts. After running at a high temperature for a long duration, the nanowires showed a higher stability and a higher activity, compared with the nanoparticles. Their different stabilities were ascribed to the different surface energies (particle sizes), as well as to the different geometric packing models.     

Hydrothermal synthesis and magnetic properties of single-crystalline BiFeO3 nanowires

One-dimensional, single-crystalline BiFeO(3) nanowires presenting a diameter of 45-200 nm and a length from hundreds of nanometres to several microns have been prepared using an improved hydrothermal method. The characterization results of ZFC and FC magnetizations at different temperatures indicate that single-crystalline BiFeO(3) nanowires show a spin-glass transition below the freezing temperature of 55 K.     

Single-walled carbon nanotube-based coaxial nanowires: synthesis, characterization, and electrical properties

We report herein the template-directed synthesis, characterization, and electric properties of single-walled carbon nanotube- (SWNT-) based coaxial nanowires, that is, core (SWNT)-shell (conducting polypyrrole and polyaniline) nanowires. The SWNTs were first dispersed in aqueous solutions containing cationic surfactant cetyltrimethylammonium bromide (CTAB) or nonionic surfactant poly(ethylene glycol) mono-p-nonyl phenyl ether (O pi-10). Each individual nanotube (or small bundle) was then encased in its own micellelike envelope with hydrophobic surfactant groups orientated toward the nanotube and hydrophilic groups orientated toward the solution. And thus a hydrophobic region within the micelle/SWNT (called a micelle/SWNT hybrid template) was formed. Insertion and growth of pyrrole or aniline monomers in this hybrid template, upon removal of the surfactant, produce coaxial structures with a SWNT center and conducting polypyrrole or polyaniline coating. Raman and Fourier transform infrared (FTIR) spectroscopy and scanning (SEM) and transmission (TEM) electron microscopy were used to characterize the composition and the structures of these coaxial nanowires. The results revealed that the micellar molecules used could affect the surface morphologies of the resulting coaxial nanowires but not the molecular structures of the corresponding conducting polymers. Electric properties testing indicated that the SWNTs played the key roles in the conducting polymer/SWNT composites during electron transfer in the temperature range 77 K to room temperature. Compared with the SWNT network embedded in the conducting polymers, the composites within which SWNTs were coated perfectly by the identical conducting polymers exhibited higher barrier heights during electron transfer.     

New metallomesogens derived from unsymmetric 1,3,4-thiodiazoles: synthesis, single crystal structure, mesomorphism, and optical properties

A series of copper(II) complexes 1 derived from unsymmetric 1,3,4-thiadiazoles 2 exhibiting mesogenic properties are reported. All the precursors 2 and 3 exhibited smectic A or/and smectic C phases, whereas, copper complexes formed nematic, SmA or SmC phases. The mesophases formed by derivatives 2 and 3 were probably attributed to the H-bondings induced both intramolecularly or/and intermolecularly between amide (-NH) and phenolic (-OH) groups. The crystal and molecular structures of mesogenic 2-(5-(2-(hexyloxy)naphthalene-6-yl)-1,3,4-oxadiazole-2-yl)phenol (2; n=6, m=6) were determined by means of X-ray structural analysis. It crystallizes in the monoclinic space group P-1, with a=7.4255(18) Å, b=8.209(2) Å, c=17.315(5) Å, and Z=2. An intermolecular H-bond (d=1.89 Å) between N2 and H1A atoms with an angle of 161.5° was observed. All molecules were packed as tilted layer arrangement and a π-π interaction (ca. 3.56 Å) was observed. Variable temperature FTIR and ¹H NMR spectroscopies were also used to probe the possible H-bondings formed in compound 2 (m=0, n=6). The fluorescent properties of these compounds 2 were examined. All λ_max peaks of the absorption and photoluminescence spectra occurred at ca. 359-363 nm and 519-537 nm, respectively. Excited state intramolecular proton transfer (ESIPT) reaction in this type of ortho-hydroxy-1,3,4-thiadiazole was also observed.     

Chelating ligand-mediated synthesis of hollow ZnS microspheres and its optical properties

Monodispersed hollow ZnS microspheres have been successfully synthesized by a facile ethylenediamine tetraacetic acid (EDTA) mediated hydrothermal route. The sizes of the hollow spheres vary from 1.5 to 3.5 microm when the reaction temperature varied from 130 to 230 degrees C. The formation of these hollow spheres is attributed to the oriented aggregation of ZnS nanocrystals around the gas-liquid interface between H(2)S and water. EDTA plays important role as chelating ligand and capping reagent, which regulates the release of Zn(2+) ions for the formation of ZnS hollow spheres. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis spectroscopy, photoluminescence, and Raman spectroscopy. The obtained ZnS hollow spheres show a sharp and photostable UV emission approximately 370 nm, which is attributed to the recombination process associated with interstitial sulfur vacancy.     

Oxadiazole-based unsymmetrical chiral liquid crystal dimers: synthesis and mesomorphic properties

The synthesis and liquid crystalline properties of novel chiral Schiff's base dimers containing the 1,3,4-oxadiazole ring are reported. The length of the terminal S-alkyl chain has been varied. All the compounds synthesised were thermally stable and exhibited enantiotropic mesomorphism, showing either SmC*–SmA–TGB–N*–BP or SmC*–SmA phase sequence.     

溶胶-凝胶模板法制备BaTiO3纳米线及其光催化性能

纳米线为准一维纳米材料[1],因其具有优异的光学、电学及力学性能而引起人们的极大关注.它的制备方法有许多种,如分子束外延法、光刻法、CVD法、模板法[2]等.其中模板法由于具有实验装置简单,操作容易,形态可控,适用面广等特点而成为纳米材料合成领域的一大焦点.常用的模板有:有序空洞阵列氧化铝模板、含有孔洞无序分布的高分子模板、纳米洞孔玻璃模板.其中阳极氧化铝(AAO)模板具有孔径均一、排列有序、孔密度高、热稳定性好且孔径大小可控等优点,成为模板合成法中最常用模板之一[3].