Preparation and characterization of lanthanum borate nanowires

Lanthanum borate nanowires had been fabricated by reacting lanthanum oxide and boron with carbon nanotubes at 1100 °C. Electron microscopy studies show that the nanowires have a single-crystal structure with uniform diameters of ∼ 15 nm and lengths up to several micrometers. The growth mechanism of LaBO₃ nanowires could be basically attributed to a CNTs template-confined reaction process; carbon nanotubes confine the reaction in a local space during the reaction. The morphology of lanthanum borate nanowires depends on the shape of the carbon nanotubes at high reaction temperatures.     

Metallic nickel nanorod arrays embedded into ordered block copolymer templates

We report on metallic Nickel nanorods prepared by utilizing a mask of ordered nanostructured hollow channels in a block copolymer matrix. These polymeric templates were formed by a self organized process in block copolymer supramolecular assemblies. Nickel was filled into with two different techniques, electrodeposition and washing in. We monitor the formation process of these nanorods by means of atomic force microscopy and synchrotron radiation soft X-ray based photoelectron emission microscopy. The oxidation state of the nickelrods is evaluated with X-ray absorption spectroscopy and X-ray photoelectron spectroscopy at the Ni L edges and lateral distributions of the Ni nanorods were detected with micrometer resolved X-ray absorption spectroscopy. The finding is that the Ni rods were metallic despite their preparation under ambient conditions, inside the particles no hints for NiO complexes were found. This indicates that the polymer protects Ni nanoparticles against oxidation.     

Preparation of Pt-Ru-Ni ternary nanoparticles by microemulsion and electrocatalytic activity for methanol oxidation

Ternary platinum-ruthenium-nickel nanoparticles are prepared by water-in-oil reverse microemulsions of water/Triton X-100/propanol-2/cyclohexane. Nanoparticles formed in the microemulsions are characterized by transmission electron microscopy (TEM), electron diffraction (ED), X-ray diffractometry (XRD), energy dispersive X-ray analysis (EDX). These resulting materials showed a homogenous alloy structure, the mono-dispersion and an average diameter of 2.6 ± 0.3 nm with a narrow particle size distribution. The composition and particle size of ternary Pt-Ru-Ni nanoparticles can be controlled by adjusting the initial metal salt solution and preparation conditions. Pt-Ru-Ni ternary metallic nanoparticles showed an enhanced catalytic activity towards methanol oxidation compared to Pt-Ru bimetallic nanoparticles.     

Hydrothermal routes to various controllable morphologies of nanostructural lithium aluminate

The α-LiAlO₂ powders have been successfully prepared by a hydrothermal route based on using the surfactant of heax-adecyltrimethyl ammonium bromide (CTAB) as the template. One-dimensional (1D) nanorods with higher and lower aspect ratio, 2D mesoporous microsheets were respectively observed with different concentration of the surfactants. A high specific surface area up to 151 m²/g was obtained by this method. The formation mechanism of the nanostructural lithium aluminate was proposed.     

Formation and control of mechanism for the preparation of ultra-fine barium strontium titanate powders by the citrate precursor method

A modified citrate precursor method, combining the advantages of the nitrate autocombustion method by introducing the nitric acid, was successfully used to synthesize ultrafine Ba_0.70Sr_0.30TiO₃ powders. Slight agglomerated and homogenized BST powders, with an average particle size of 20 nm, were obtained at 800 °C. Combining the results of TG/DTA and XRD, it can be concluded that the formation of BST powders takes place via two reaction mechanisms: decomposition of an intermediate oxycarbonate mechanism (DIOm) at low temperature, and solid-state reaction mechanism (SSRm) between nanocrystalline carbonates and amorphous TiO₂ at high temperature. TEM shows higher amount of CA led to BST powders of better quality in morphology. Based on results of chemical analysis, it is suggested that higher amount of CA drives the mechanism to tend to DIOm. By simply adjusting the ratio of reagents, the reaction mechanism can be dominated and we can greatly control the final morphology of the powders.     

Solvothermal synthesis of nanorods of ZnO, N-doped ZnO and CdO

ZnO nanorods with diameters in the 80-800 nm range are readily synthesized by the reaction of zinc acetate, ethanol and ethylenediamine under solvothermal conditions. The best products are obtained at 330 °C with a slow heating rate. Addition of the surfactant Triton^®-X 100 gave nanorods of uniform (300 nm) diameter. By adding a small amount of liquid NH₃ to the reaction mixture, N-doped ZnO nanorods, with distinct spectroscopic features are obtained. CdO nanorods of 80 nm diameter have been prepared under solvothermal conditions using a mixture of cadmium cupferronate, ethylenediamine and ethanol at 330 °C. Similarly, Zn_1−xCd_xO nanorods of a 70 nm diameter are obtained under solvothermal conditions starting with a mixture of zinc acetate, cadmium cupferronate, ethanol and ethylenediamine.     

Electrical conduction mechanisms of metal nanoclusters embedded in an amorphous Al2O3 matrix

We present the synthesis and electrical characterization of amorphous nanocomposite layers made of metallic nanoclusters embedded in an alumina matrix (nc-Co:Al₂O₃). The nanostructured materials were fabricated using a pulsed laser deposition (PLD)-derived method based on a nano-cluster generator coupled with a conventional PLD system for host medium co-deposition. The films were subjected to a detailed structural study carried out using high-resolution transmission electron microscopy and atomic force microscopy. The clusters inserted in the alumina matrix are metallic, well crystallized and possess an fcc structure with an average diameter centered at ∼ 2 nm. Dielectric constant and electrical conduction mechanisms of nc-Co:Al₂O₃ layers integrated in metal-insulator-metal capacitive structures were studied for different doping levels and for a broad temperature range (303-473 K). It was concluded that the dielectric constant in the films depends on the doping levels while the major electrical conduction mechanisms are best described by the space charge limited currents formalism, in which the current density J on an applied voltage V follow a power-law dependence (J ∼ Vⁿ) at applied voltages higher than ∼ 2 V. Such composite may find immediate applications as dielectric layers with controlled discharging conduction paths in Radio Frequency-Micro-Electro-Mechanical Systems capacitive structures.     

ZnO nanostructured film deposition using the separated pulsed laser deposition (SPLD) assisted by electric and magnetic drift motion

We have developed the separated pulsed laser deposition (SPLD) technique to prepare high quality ZnO based films exhibiting uniform and droplet-free properties. This SPLD consists of an ablation chamber and a deposition chamber which can be independently evacuated under different ambient gases.The gas species and the pressures in both chambers can be arbitrarily chosen for the specific deposition such as nanostructured films and nanoparticles. The ablation chamber is a stainless steel globe and the deposition chamber is a quartz tube connected to a metallic conic wall with an orifice. We used a KrF excimer laser with λ = 248 nm and 25 ns pulse duration. The different gas conditions in two chambers allow us to realize optimal control of the plasma plume, the gas phase reaction and the film growth by applying the bias voltage between the conic wall and the substrate under the magnetic field. We can expect that at appropriate pressures the electric and magnetic field motion (E × B azimuthal drift velocity) gives significant influences on film growth.We have deposited ZnO thin films at various pressures of ablation chamber (Pab) and deposition chamber (Pd). The deposition conditions used here were laser fluence of 3 J/cm², laser shot number of 30,000, Pab of 0.67-2.67 Pa (O₂ or Ar), Pd of 0.399-2.67 Pa (O₂), and substrate temperature of 400 °C. Particle-free and uniform ZnO films were obtained at Pab of 0.67 Pa (Ar) and Pd of 1.33 Pa (O₂). The ZnO film showed high preferential orientation of (002) plane, optical band gap of 2.7 eV, grain size of 42 nm and surface roughness of 1.2 nm.