Preparation and characterization of CdS/Si coaxial nanowires

CdS/Si coaxial nanowires were fabricated via a simple one-step thermal evaporation of CdS powder in mass scale. Their crystallinities, general morphologies and detailed microstructures were characterized by using X-ray diffraction, scanning electron microscope, transmission electron microscope and Raman spectra. The CdS core crystallizes in a hexagonal wurtzite structure with lattice constants of a=0.4140 nm and c=0.6719 nm, and the Si shell is amorphous. Five Raman peaks from the CdS core were observed. They are 1LO at 305 cm⁻¹, 2LO at 601 cm⁻¹, A₁-TO at 212 cm⁻¹, E₁-TO at 234 cm⁻¹, and E₂ at 252 cm⁻¹. Photoluminescence measurements show that the nanowires have two emission bands around 510 and 590 nm, which originate from the intrinsic transitions of CdS cores and the amorphous Si shells, respectively.     

Preparation and characterization of poly(lactic acid)-grafted TiO2 nanoparticles with improved dispersions

Poly(lactic acid) (PLA)-grafted TiO₂ particles were prepared by in situ melt polycondensation of lactic acid onto the surface of TiO₂ nanoparticles. The resulting products were characterized by FTIR, XPS, TG-FTIR, XRD analysis and electron microscopy observation so as to have a better understanding of bonding between the graft polymer and nanoparticles. New characteristic peaks of Ti-carboxylic coordination bond, the changes in the relative intensities of the infrared absorption bands of graft polymer and the two decomposition stage of PLA-grafted TiO₂ confirmed that PLA was grafted on the surface of TiO₂ nanoparticles. By attachment of PLA, the PLA-grafted TiO₂ samples exhibited much better dispersion and a slightly larger particle size than bare TiO₂ particles. PLA-grafted TiO₂ nanoparticles will find wide applications in biomedical and eco-friendly materials, especially as fillers in PLA matrix.     

Preparation, characterization and study of optical properties of ZnS nanophosphor

In this work the preparation, characterization and photoluminescence studies of pure and copper-doped ZnS nanophosphors are reported, which are prepared by using solid-state reaction technique at a temperature of 100 °C. The as-obtained samples were characterized by X-ray diffraction (XRD) and UV-VIS Reflectance spectroscopy. The XRD analysis confirms the formation of cubic phase of undoped as well as Cu²⁺-doped ZnS nanoparticles. Furthermore it shows that the average size of pure as well as copper-doped samples ranges from 15 to 50 nm. The room-temperature PL spectra of the undoped ZnS sample showed two main peaks centered at around 421 and 450 nm, which are the characteristic emissions of interstitial zinc and sulfur vacancies, respectively. The PL of the doped sample showed a broad-band emission spectrum centered at 465 nm accompanied with shoulders at around 425, 450 and 510 nm, which are the characteristic emission peaks of interstitial zinc, sulfur vacancies and Cu²⁺ ions, respectively. Our experimental results indicate that the PL spectrum confirms the presence of Cu²⁺ ions in the ZnS nanoparticles as expected.     

Large-scale synthesis of SnO2 nanobelts

Tin dioxide (SnO₂) nanobelts have been successfully synthesized in bulk quantity by a simple and low-cost process based on the thermal evaporation of tin powders at 800 °C. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations reveal that the nanobelts are uniform, with lengths from several-hundred micrometers to a few millimeters, widths of 60 to 250 nm and thicknesses of 10 to 30 nm. X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and selected-area electron diffraction analysis (SAED) indicate that the nanobelts are tetragonal rutile structure of SnO₂. The SnO₂ nanobelts grow via a vapor–solid (VS) process. Received: 3 June 2002 / Accepted: 10 June 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-551/559-1434, E-mail: gwmeng@mail.issp.ac.cn     

Preparation, characterization and application of a nanostructured composite: Octakis(cyanopropyldimethylsiloxy)octasilsesquioxane

Octakis(cyanopropyldimethylsiloxy)octasilsesquioxane was prepared and characterized by ¹³C, ²⁹Si NMR (MAS), SEM, FT-IR, XRD and thermogravimetric techniques. The four groups α, β, γ, κ (to the terminal silicon atom), associated with an acrylonitrile, were clearly seen in the ¹³C NMR (α-CH₂ at 17.9; β-CH₂ at 31.3; γ-CH₂ at 50.4; κ-CN at 59.0 ppm). The ²⁹Si NMR spectrum of the final product, exhibits only Q type silicon signal, ascribed to Q⁴ (−118.0 ppm). The presence of acrylonitrile substituted for octameric cube confers a relative change phase and thermal stability to the material. With regard to the applications for this new material, it was intended, in this case, to react with Na₂[Fe(CN)₅NH₃] by chemical substitution. This composite was incorporated into a carbon paste electrode and the electrochemical studies were performed by cyclic voltammetry. The cyclic voltammogram of the modified graphite paste electrode, showed one redox couples with formal potential () = 0.24 V versus SCE.     

Model predictions and experimental characterization of Co-Pt alloy clusters

Model and real cobalt-platinum alloy clusters are compared in terms of structure, composition and segregation. Canonical and semi grand canonical Metropolis Monte Carlo simulations are performed to model these clusters, using embedded atom (EAM) and modified embedded atom (MEAM) potentials. All of them correctly predict the bulk L1₂ Co₃Pt and CoPt₃ structures as well as the L1₀ CoPt phase. However, the lattice parameters, phase stability and the L1₀-fcc order-disorder transition temperature are at variance. Segregation predictions with EAM and MEAM potentials are contradictory. Experimentally, mixed clusters with various compositions were deposited by Low Energy Cluster Beam on amorphous carbon at room temperature. Their size distribution, crystalline structure and composition were examined by Transmission Electron Microscopy (TEM). Clusters with the same size distributions were modelled. Both experiment and modelling show their crystallographic parameters to continuously correspond to the fcc CoPt chemically disordered phase. Diffraction measurements indicate surface segregation of the specie in excess, in agreement with EAM predictions for the Co-rich phase. The consequences on magnetic properties are discussed.     

Preparation and characterization of nitrogen-incorporated SnO2 films

Nitrogen-incorporated SnO₂ thin films have been grown on Si(100) and quartz substrates by reactive sputtering of a Sn target in gas mixtures of N₂–O₂. The structure of the nitrogen-incorporated SnO₂ thin films was studied by X-ray diffraction, and the changes in the chemical bonds and atomic binding states of the nitrogen-incorporated SnO₂ thin films were analyzed by X-ray photoelectron spectroscopy. It was found that the binding energy of Sn 3d and O 1s shifts 0.65 eV and 0.35 eV, respectively, toward the lower-energy side after nitrogen was incorporated into the SnO₂ thin films as a comparison with that of pure SnO₂ film. The indirect optical band gap gradually decreases from 3.42 eV to 3.23 eV, i.e. from the UV to the edge of the visible-light range, with increasing nitrogen flux content in the N₂–O₂ gas mixtures. PACS 81.15.Cd; 78.20.-e; 68.37.Xy; 81.05.Je     

Fabrication and characterization of a granular film consisting of size-selected silver nanoparticles: application to a SERS substrate

Uniform-sized silver nanoparticles with average diameter of 13.7 nm have been prepared in the gas-phase by combining a pulsed laser ablation method with a low pressure-differential mobility analyzer (LP-DMA). By depositing the silver nanoparticles onto a silicon substrate, a granular film consisting of size-selected silver nanoparticles has been fabricated and its morphology and electronic properties have been examined using transmission electron microscopy (TEM) and UV-visible absorption spectroscopy. This granular silver film serves as a highly active substrate for surface-enhanced Raman scattering (SERS).     

Preparation and structural characterization of nanocrystalline SnO2 powders

Nanocrystalline SnO₂ powders have been prepared by solid–liquid reaction and solid-state thermal oxidizing techniques. The microstructures and phase compositions of the product were characterized by thermogravimetry analysis, X-ray diffraction, and the Raman spectrum. It is shown that at least two phases, SnO₂ and SnO_x, coexist at 450 °C. However, only the tetragonal rutile structure SnO₂ phase is detected after the Sn powders were annealed at 550 °C. The Raman peaks of the nanocrystalline SnO₂ powders reveal remarkable red shift and broadening, which could be attributed to the phonon confinement effect, oxygen vacancies, and the stress effect. PACS 81.07.Wx; 81.10.Jt; 78.30.-j     

Controlled synthesis and phase characterization of Fe-based nanoparticles obtained by thermal decomposition

Iron oxide nanoparticles were synthesized by the thermal decomposition of Fe(acac)₃ and Fe(CO)₅. Three different homogeneous procedures were used for the controlled synthesis of Fe₃O₄, γ-Fe₂O₃ and Fe₃O₄/γ-Fe₂O₃ mixture nanocrystals. A combination of characterization techniques was used in order to distinguish these oxides. The controllable size, the narrow distribution and the rhombic self-assembly of the nanoparticles were revealed by the high-resolution transmission electron microscopy images and the X-ray powder diffraction results. For the quantitative analysis of the samples manganometry was used. Preliminary magnetic measurements indicated the size and composition dependence of saturation magnetization, a superparamagnetic behavior of the samples and some ferromagnetic features.     

Fabrication and characterization of amorphous silica nanostructures

Large-scale amorphous silica nanostructures, including nanowires, nanotubes and flowerlike nanowire bunches depending on the position, have been fabricated on silicon wafer through a cheap route under the assistance of gold and germanium. Accompanying the observation of blue-green light emission, comprehensive micro-structural characterization reveals that the growth of nanostructures is catalyzed only by gold whereas the final morphology of nanostructures depends on the location to germanium ball. Au₂Si, a compound of gold and silicon, is also disclosed as an intermediate state during the catalysis. Correspondingly, a growth scheme is proposed based on the experimental results and the vapor-liquid-solid mechanism.     

Synthesis and optical characterization of monodispersed Mn doped CdS nanoparticles

Monodispersed Mn²⁺ doped CdS nanoparticles with average size as small as 1.8 nm have been synthesized through chemical method. The nanostructures of the prepared nanoparticles have been confirmed through X-ray diffraction (XRD), ultraviolet-visible (UV-vis) absorption and transmission electron microscope (TEM) measurements. The photoluminescence emission covering 450-650 nm of the visible region is observed under ultraviolet light excitation, from Mn²⁺ doped CdS nanoparticles dispersed in dimethyl sulfoxide (DMSO).     

Synthesis and characterization of ZnO-Ag core-shell nanocomposites with uniform thin silver layers

This paper presents an investigation on the synthesis and characterization of ZnO-Ag core-shell nanocomposites. ZnO nanorods were employed as core material for Ag seeds, and subsequent nucleation and growth of reduced Ag by formaldehyde formed the ZnO-Ag core-shell nanocomposites. The ZnO-Ag nanocomposites were annealed at different temperature to improve the crystallinity and binding strength of Ag nanoparticles. The morphology, microstructure and optical properties of the ZnO-Ag core-shell nanocomposites were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, ultraviolet-visible (UV-vis) absorption and photoluminescence measurement. It was demonstrated that very small face-center-cubic Ag nanoparticles were coated on the surface of ZnO nanorods. The ultraviolet absorption and surface plasmon absorption band of ZnO-Ag core-shell nanocomposites exhibited some redshifts relative to pure ZnO nanorods and monometallic Ag nanoparticles. The coating of Ag nanocrystals onto the ZnO nanorods completely quenched the photoluminescence. These observations reflected the strong interfacial interaction between ZnO nanorods and Ag nanoparticles. The effect of Ag coating thickness on the morphology and optical properties of ZnO-Ag core-shell nanocomposites was also investigated. Moreover, the growth mechanism of ZnO-Ag core-shell nanocomposites was also proposed and discussed in detail.     

Preparation and characterization of nanosized (Y,Bi)VO4:Eu and Y(V,P)O4:Eu red phosphors

Nanosized luminescent (Y,Bi)VO₄:Eu³⁺ and Y(V,P)O₄:Eu³⁺ were synthesized at low temperatures either by a coprecipitation method or by a hydrothermal method from aqueous solutions. The effect of Bi³⁺ ion or P⁵⁺ ion content in the lattice, annealing temperature effects on the crystal structure and the particle size, and the luminescence property of (Y,Bi)VO₄:Eu³⁺ and Y(V,P)O₄:Eu³⁺ nanoparticles were examined with a field-enhanced scanning electron microscopy, XRD, and a spectrofluorometer. The pristine YVO₄:Eu³⁺, (Y,Bi)VO₄:Eu³⁺, or Y(V,P)O₄:Eu³⁺ nanoparticles are 35-50 nm in size. The luminescence spectrum of the Eu³⁺ ion was used to probe its position in the crystal lattice. The dopant ions enter the same lattice sites in the nanocrystalline as in the corresponding bulk material, resulting similar spectral features between them. Photoluminescence intensity is weak for the pristine nanoparticles. Annealing the nanoparticles at temperatures up to 1000 °C results in the increased luminescence intensity (>80% of micrometer-sized phosphors) with the minimal particle growth and the improved particle crystallinity.     

Preparation and reactivity of aluminum nanopowders coated by hydroxyl-terminated polybutadiene (HTPB)

HTPB-coated aluminum (Al) nanopowders were prepared by laser-induction complex heating. The characterization of the nanopowders was revealed using transmission electronic microscopy (TEM), high-resolution transmission electronic microscopy (HRTEM), X-ray diffraction analysis (XRD) and Fourier transform infrared (FTIR) spectrometry. Results showed that HTPB-coated Al nanopowders have a core-shell structure with size ranging from 30 to 100 nm and organic HTPB exists in HTPB-coated Al nanopowders. Differential scanning calorimeter (DSC) and thermal gravimeter (TG) analysis of the HTPB-coated Al nanopowders and Al₂O₃-passivated Al nanopowders stored for 2 years in ambient environment indicated that the reactivity and stability of HTPB-coated Al nanopowders outperform Al₂O₃-passivated Al nanopowders. These findings demonstrate that HTPB is a suitable surface coating material for Al nanopowders.     

Synthesis and characterization of zinc oxide nanoparticles by laser ablation of zinc in liquid

We report formation of colloidal suspension of zinc oxide nanoparticles by pulsed laser ablation of a zinc metal target at room temperature in different liquid environment. We have used photoluminescence, atomic force microscopy and X-ray diffraction to characterize the nanoparticles. The sample ablated in deionized water showed the photoluminescence peak at 384 nm (3.23 eV), whereas peaks at 370 nm (3.35 eV) were observed for sample prepared in isopropanol. The use of water and isopropanol as a solvent yielded spherical nanoparticles of 14-20 nm while in acetone we found two types of particles, one spherical nanoparticles with sizes around 100 nm and another platelet-like structure of 1 μm in diameter and 40 nm in width. The absorption peak of samples prepared in deionized water and isopropanol are seen to be substantially blue shifted relative to that of the bulk zinc oxide due to the strong confinement effect. The technique offers an alternative for preparing the nanoparticles of active metal.     

Polyoxometalates nanoparticles: synthesis, characterization and carbon nanotube modification

In this paper, we described a large-scale synthesis method of the polyoxometalates (POMs) nanoparticles and the modification of carbon nanotube (CNTs) through a chemical modified approach. Four types of POMs nanoparticles were prepared by a one-step solid-state reaction at room temperature and characterized by IR, elemental analyses, XRD and TEM. These uniform nanoparticles have an average size of 8-10 nm. Furthermore, based on chemical adsorption between POMs and carboxylic acid groups, which were introduced to the CNTs by adding dilute nitric acid, POMs nanoparticles were successfully located on the CNTs as the modifier.     

Laser-assisted growth of gold nanoparticles: Shaping and optical characterization

We demonstrate that supported gold nanoparticles with a given well-defined shape can be produced by laser-assisted growth. For this purpose, gold nanoparticles with average radii ranging from 1.5 to 13 nm, i.e., coverage between 0.45 × 10¹⁶ and 5.6 × 10¹⁶ atoms/cm², were prepared at room temperature by self-assembly of atoms deposited on quartz and sapphire substrates. For analysis of the samples, the optical spectra of the particles were measured with p-polarized light and photon energies in the range of 1.3 to 3.1 eV. Irradiating the particles during growth with laser light of different wavelengths to stimulate surface plasmon excitation made it possible to stabilize mean axial ratios between 0.19 and 0.98. The influence of the laser fluence on the shape of the nanoparticles was also investigated and shows that the position of the surface plasmon resonance shifts to higher energies as the fluence rises. Optimum growth conditions to shape gold nanoparticles with axial ratios close to unity (spheres) with a relatively low laser fluence of 60 ± 5 mJ/cm² have also been found. The results of our experiments show that laser-assisted growth is a powerfultechnique to control the shape of nanoparticles.     

Preparation and characterization of C54 TiSi2 nanoislands on Si (1 1 1) by laser deposition of TiO2

We present the preparation of C54 TiSi₂ nanoislands on Si (1 1 1) with a method of the pulsed laser deposition of titanium oxide thin films. The TiO₂ thin films with nominal thicknesses of 1 nm on Si (1 1 1) were annealed at 850 °C for about 4 h in situ. The X-ray diffraction patterns and the X-ray photoelectron spectra indicate that the nanoislands are in C54 TiSi₂ phase. The characterization using a scanning tunneling microscope shows that the nanoislands with triangular, polygonal and rod-like shapes on Si (1 1 1) exhibit the Volmer-Weber growth mode. The sizes of the polygonal islands distribute in two separated ranges. For the small islands, they have a narrow lateral size distribution centered at 4 nm and a height range in 0.6-3.6 nm, while for the large islands, their lateral sizes are in the range of 12-40 nm and the heights in the range of 4-9 nm. The sizes of the well-shaped triangular islands are intermediate with the lateral sizes in range of 5-20 nm and the heights of 2-3.5 nm. The rod-like islands are about 50-200 nm in length, 5 nm in height and about 15-20 nm in width. The origination of the various shapes of the nanoislands is attributed to the symmetry of Si (1 1 1) substrate and the lattice mismatch between the C54 TiSi₂ and the Si (1 1 1) surface.     

Synthesis and characterization of novel red emitting nanocrystal Gd6WO12:Eu phosphors

Novel nanosized Gd₆WO₁₂:Eu³⁺ phosphors were synthesized via a co-precipitation reaction. The crystal structure and morphology of the phosphors were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). It was found that the resultant powders show a regular and sphere-like shape with average particle size of 60 nm. Intrinsic red emission originating from Eu³⁺ was observed while excited at the W⁶⁺→O²⁻ and Eu³⁺→O²⁻ charge transfer bands or f-f absorption bands. The color coordinates of the phosphors were calculated to be x=0.625, y=0.375. The concentration dependence of the luminescence was studied, and optimum doping concentration for obtaining maximum emitting intensity was confirmed to be around 12 mol%. It was also found that the electric dipole-dipole interaction plays an important role for quenching luminescence of Eu³⁺.