Correlation between structural and optical properties of 30 nm and 60 nm lead sulfide nanowires

PbS nanowires with 30 nm and 60 nm diameter fabricated under the same condition of electrochemical deposition with sulfuric and oxalic anodic alumina membranes (AAM), respectively, have been successfully prepared in order to study their optical properties in relation to their size. Scanning electron microscopy indicates that the 60 nm PbS nanowire arrays have the same shape with the 30 nm. X-ray diffraction result shows that 60 nm PbS nanowires are crystalline and have a highly (200) preferential orientation like 30 nm ones. UV spectrum considers the nanowire size decrease as the absorption peak shifts to the blue. The quantum confinement effects compared between 30 nm and 60 nm PbS nanowire arrays were observed by the measurements of ultraviolet-visible absorption spectroscopy (UV-vis).     

Controlled synthesis and characterization of 10 nm thick Al2O3 nanowires

α-Al₂O₃ nanowires, with diameter around 10 nm, were synthesized in bulk quantity by heating the mixture of pure aluminum and graphite powders at 900 °C. Scarcity of oxygen is regarded as the reason for the growth of the small diameter α-Al₂O₃ nanowires at relatively low temperature. The product was characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence. The Oxygen vacancies in the nanowires lead to the strong photoluminescence in the wavelength range of 400-700 nm with its peak at 527 nm.     

Template-free synthesis of nickel nanowires by magnetic field

Nickel nanowires were prepared by a template free method combined with chemical reduction and magnetic field. The application of an external magnetic field resulted in the formation of self-aligned metallic nickel nanowires of about 50 nm in diameter. Nickel particles were prepared in the absence of a magnetic field to better illustrate the structure directing role of the magnetic field. Physical properties of the nickel nanochains were examined by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-Ray diffraction (XRD), and thermogravimetric analysis (TGA) methods. This study provides a simple method to prepare Ni nanowires in large scale which broads their practical applications.     

Synthesis of Cd1 − xMnxS nanoclusters by surfactant-assisted method: Structural, optical and magnetic properties

Cd_1 − xMn_xS nanoclusters were synthesized by surfactant-assisted chemical method for different Manganese (Mn) concentration (0.40 ≤ x ≥ 0.10) at 60 °C in argon atmosphere. Incorporation of magnetic ions (Mn) results a decrease in band gap of Cd_1 − xMn_xS nanoclusters. The room temperature ferromagnetic behaviour is demonstrated first time in Cd_0.60Mn_0.40S nanoclusters by vibrating sample magneto (VSM) measurements and the origin of magnetization has been discussed.     

Raman optical properties of Cu(OH)2 nanowires

We have for the first time investigated Raman optical properties of polycrystalline Cu(OH)₂ nanowires with an average diameter of ca. 9 nm and lengths of up to hundreds of micrometers that were synthesized by a simple surfactant-free solution-phase route at ambient temperature. The result indicated that the Raman peak of the as-prepared polycrystalline Cu(OH)₂ nanowires was obviously broadened, and red-shifted 16 cm^− 1 compared with that of bulk Cu(OH)₂ crystals. Based on the microstructure analysis and phonon confinement model of a crystal, we have proposed a rational explanation for the red-shift and broadening of Raman peak.     

Structural and optical properties of Al-doped SnO2 nanowires

We report a facile thermal evaporation method for the syntheses of Al-doped SnO₂ nanowires using Al-doped SnO₂ nanoparticles as precursors. High-density, single-crystalline Al-doped SnO₂ nanowires were directly grown on the 6H-SiC substrates without any catalyst. X-ray diffraction patterns show that the Al dopants are incorporated into the rutile SnO₂ nanowires. The X-ray photoelectron spectra confirm the SnO₂ nanowires doped with 5 at.% Al. The photoluminescence spectra of the Al-doped SnO₂ nanowires exhibit that the large blue shift of the emission band can be observed in the Al-doped SnO₂ nanowires compared with undoped nanowires. The distortion of the crystal lattices caused by incorporation of Al atoms at the interstitials should be responsible for the large blue shift of the emission band.     

Synthesis, characterization and magnetic properties of nanocrystalline Ni-Zn-Co ferrites

Nanocrystalline magnetic particles of Ni_0.7−xZn_0.3Co_xFe₂O₄ with x lying between 0.0 and 0.3 were synthesized by combustion method using metal nitrates, sucrose and polyvinyl alcohol (PVA). The synthesized powders where characterized by X-ray diffraction and Transmission electron microscopy (TEM). The average crystallite size determined from XRD data using Scherrer formula lie in the range of 20-30 nm. TEM micrographs show a well defined nano-crystallite state with an average particle size of around ~ 10 nm. The electron diffraction patterns confirm the spinel crystal structure of the ferrite. Magnetic properties measured at room temperature by vibrating sample magnetometer (VSM) reveal an increase in saturation magnetization with increase in cobalt concentration. Non-linear increase in saturation magnetization is related to surface effects and method of preparation.     

The effect of magnetic layer thickness on magnetic properties of Fe/Cu multilayer nanowires

Fe/Cu multilayer nanowires were ac-pulse electrodeposited into the anodic aluminum oxide templates prepared by a two-step mild anodization technique. Transmission electron microscopy images showed the distinct layers with a relatively high contrast. A highly pure layer (∼99%) was achieved by tuning the proper ions ratio and optimizing the off-time between pulses of each layer in the single electrodeposition bath. Fe/Cu multilayer nanowires with 38 nm diameter were obtained. The effect of reducing the Fe layer thickness on the magnetic properties of Fe/Cu multilayer nanowires was investigated. It was seen that reducing the Fe layer thickness, thereby variation of rode- to disc-like multilayer nanowires, caused to rotate the magnetic easy axis from parallel to perpendicular to the wires axis.     

Synthesis of Ni nanoparticles by reduction of NiCl2 ionic clusters in the confined space of AOT reversed micelles

Stable Nickel nanoparticles have been synthesized by a novel synthetic route based on the reduction of NiCl₂ ionic clusters in the confined space of reversed micelles. The reaction was carried out by adding anhydrous NaBH₄/ethanol solution to a solution of NiCl₂ ionic clusters nanoencapsulated in bis(2-ethylhexyl)sulfosuccinate (AOT) reversed micelles in the presence of n-dodecylmercaptane as capping agent. As highlighted by FT-IR, an extraction with water eliminates surfactant and side products leaving lipophilic Nickel nanoparticles to be dispersed in the organic solvent. UV-Vis investigation ascertained the formation of stable metal Nickel nanoparticles exhibiting novel optical properties.     

Synthesis, luminescent, and magnetic properties of LaVO4:Eu nanorods

The LaVO₄:Eu nanorods were synthesized successfully by an ethylenediaminetetraacetic acid (EDTA)-mediated hydrothermal method. The resulting products were characterized using XRD, TEM, HRTEM, Fluorescence Spectrometer and SQUID magnetometer. It was found that Eu³⁺ entered into the LaVO₄ crystalline host lattice and it replaced La³⁺. Consequently the unit cell parameters of LaVO₄:Eu nanorods became smaller. Further studies indicated that the rare earth ions Eu³⁺ improved the properties of the LaVO₄:Eu nanorods evidently. The Eu³⁺ ions doping in LaVO₄ nanorods led to better luminescent properties and magnetic properties than that of pure LaVO₄ nanorods.     

Synthesis and luminescence properties of YVO4:Eu nanocrystals grown in nanoporous glass

We report on a feasible method to synthesize luminescence nanocrystals in porous glass in this paper. Well dispersed YVO₄:Eu nanocrystals were proved being grown in nanoporous glass by XRD, micro-Raman spectra and HRTEM equipped with EDS. The YVO₄:Eu³⁺ nanocrystal grown in porous glass herein shows very different luminescence properties compared with single Eu-doped sample. By this method, intense red emission from high silica glass due to energy transfers VO₄³⁻ → Eu³⁺ was obtained. The results show that the reduction from Eu³⁺ to Eu²⁺ in porous glass impregnated with Eu³⁺ ions was avoided effectively.     

不同结构镍纳米线阵列的制备及其磁性

采用直流电沉积在多孔有序氧化铝模板中制备了不同结构的有序镍纳米线阵列。采用SEM和TEM对所制备的镍纳米线的形貌和结构进行了表征。研究了镍纳米线不同结构对镍纳米线阵列磁性性能的影响规律．当电沉积电压为2．5V时制备的镍纳米线为多晶结构；电沉积电压4V时，镍纳米线为沿[220]择优取向的单晶结构；电沉积电压＞5V时，择优取向由[220]转为[111]方向．磁滞回线结果表明，单晶镍纳米线阵列与多晶纳米线阵列相比具有更高的矩形度，沿[111]择优取向的单晶纳米线相比沿[220]取向的单晶镍纳米线具有更大的矩形度，表现出显著的磁各向异性。     

Simple air oxidation synthesis and optical properties of S-doped ZnO microspheres

The S-doped ZnO microspheres with average diameter of 3 micrometers (μm) have been successfully synthesized by a simple air oxidation process of ZnS precursor. X-ray diffractometer (XRD) pattern indicates that the as-obtained sample is composed of ZnO and ZnS. The scanning electron microscopy (SEM) image shows that the exterior surfaces of the microspheres are composed of many nanoparticles with an average grain size of 100 nanometers (nm). The photoluminescence (PL) spectra show the broad excitation region with the main peak at 370 nm and strong green emission centered at 500 nm, which can be attributed to the oxygen vacancies caused by S replacement of O.     

Magnetic behavior of arrays of nickel nanowires: Effect of microstructure and aspect ratio

Arrays of nickel nanowires with aspect ratio of ∼1200 and diameters ranging between 25 and 100 nm have been fabricated by electrodeposition in etched ion track templates. Samples with different areal densities ranging from 1 × 10⁶ cm⁻² to 1 × 10⁸ cm⁻² have been prepared for this study. Magnetic measurements were performed at room temperature for different aspect ratios and diameters of the wires. Coercivity of the wires showed a strong dependence on aspect ratio (l/d), diameter and microstructure. In the case of parallel applied field coercivity of the wires has maximum value at ∼40 nm diameter. The wires with high areal densities showed relatively lower coercivities as compared to the low density samples. The results have been discussed by taking into account various magnetic anisotropies originating from the shape and crystalline nature of the wires, and the magnetostatic interactions among the wires.     

Nonlinear optical and optical limiting properties of phthalocyanines in solution and thin films of PMMA at 633 nm studied using a cw laser

We present our results on nonlinear optical (NLO) and optical limiting properties of Tetra tert-butyl phthalocyanine and Zinc tetra tert-butyl phthalocyanine studied at 633 nm using a continuous wave laser. We have evaluated the sign and magnitude of the third-order nonlinearity from the closed aperture Z-scan data while the nonlinear absorption properties were assessed using the open aperture data. We have observed low power optical limiting, with low limiting thresholds, based on nonlinear refraction in both the samples. We also present results on the NLO properties of the same dyes doped in Polymethylmethacrylate (PMMA). These studies indicate that both the phthalocyanines are potential candidates for low power optical limiting applications.     

Synthesis and magnetic properties of Mn-doped ZnO nanorods via radio frequency plasma deposition

Well-aligned Mn-doped ZnO nanorods were synthesized by simple radio frequency (RF) plasma deposition in the absence of extra catalysts. The synthesized nanorods having a typical average diameter of about 25 nm, were about 310 nm in length and well-aligned along the normal direction of the substrate. Magnetic measurements indicate that the nanorods are ferromagnetic at room temperature (RT). The presence of considerable shallow donor defects in the nanorods does allow possible defect mediated mechanisms (e.g., bound magnetic polarons) for mediating exchange coupling of the dopant Mn ions resulting in RT ferromagnetism.     

Catalytic-free growth of ZnGa2O4 nanowires on amorphous carbon layers

Zinc gallate (ZnGa₂O₄) nanowires were directly grown on the amorphous carbon-coated silicon substrates using a facile chemical vapor deposition method without any metal catalysts. The growth mechanism can be attributed to a self-organization vapor-liquid-solid (VLS) process. The amorphous carbon layer plays an important role in the nucleation and growth process of the ZnGa₂O₄ nanowires. The photoluminescence (PL) of the nanowires shows a broad, strong green emission band centered at 532 nm and a weak UV emission band at 381 nm, which can be attributed to a large amount of ionized oxygen vacancies and the combination of Ga³⁺ ions with free electrons in coordinated oxygen vacancies, respectively.     

Optical and photocatalytic properties of sulfide semiconductor quantum dots (QDs) synthesized by silk fibroin template

Bio-template method is a simple, controllable and environmental friendly strategy to synthesize nanomaterials. It also avails the formation of bioactive and biocompatible nanoparticle–biomolecule hybrid for biotechnical applications. In this paper, silk fibroin was first successfully used as biomolecule template for the biomimic synthesis of CdS and ZnS quantum dots (QDs). The QDs showed promising applications as fluorescence probes and nanocatalysts. The effect of preparation situation to their optical and photocatalytic properties was well researched and CdS QDs with satisfying catalytic activities could be achieved by adjusting the protein matrix. It offers us a low-cost and effective way to synthesize series of sulfide semiconductor nanomaterials using silk fibroin.