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1.
X.H. Li  Y.C. Liu  X.T. Zhang 《Materials Letters》2008,62(14):2088-2091
SiO2/ZnO nanocables were prepared by the combination of electrospinning technology and vapor transport deposition procedure. X-ray diffraction patterns indicated that ZnO with wurtzite structure was deposited on SiO2 nanofibers templates successfully. Field emission scanning electron microscopy and transmission electron microscopy showed that the products were core/shell nanocables with a narrow distribution of the core/shell diameters. The nanocables showed a strong near band edge emission in ultraviolet region and a weak deep level emission at room temperature in their photoluminescence (PL) spectra. The anomalous temperature characteristic of integrated PL intensity in temperature-dependent PL spectra was discussed by considering carrier injection across the interface of SiO2/ZnO nanocables.  相似文献   

2.
The nanocables with a single crystal ZnS core and a thin amorphous SiO2 shell were successfully synthesized by a simple thermal evaporation method with the mechanism of Vapor-Solid growth. Its morphology and microstructure were determined by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and photoluminescence spectroscopy (PL). The ZnS/SiO2 nanocables have diameters in the range of 20 nm-250 nm, lengths of several tens of micrometers. The core of the nanocable has a cubic sphalerite structure with the coexistence of periodically alternating twins along the [111] growth direction and stacking fault. The nanocables show strong room-temperature photoluminescence with four emission bands centering at 548 nm, 614 nm, 649 nm and 670 nm that may originate to the impurity of ZnS, existence of Si and oxide-related defects.  相似文献   

3.
In this paper, we reported the preparation of ZnO/ZnS core/shell nanocomposites by sulfidation of ZnO nanostructures via a simple hydrothermal method. The precursors of bare ZnO nanoparticles and ZnO nanorods were synthesized by a surfactant-assisted hydrothermal growth. The structural, morphological, and element compositional analysis of bare ZnO nanostructures and ZnO/ZnS core/shell nanocomposites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy techniques. The XRD results indicated that the phase of bare ZnO nanoparticles and ZnO nanorods was wurtzite structure, and the phase of coated ZnS nanoparticles on the surface of bare ZnO nanostructures was sphalerite structure with the size of about 8 nm. Photoluminescence measurement was carried out, and the PL spectra of ZnO/ZnS core/shell nanocomposites revealed an enhanced UV emission and a passivated orange emission compared to that of bare ZnO nanostructures. In addition, the growth mechanism of ZnO/ZnS core/shell nanostructures through hydrothermal method was preliminarily discussed.  相似文献   

4.
SiO2/Al2O3 composite microspheres with SiO2 core/Al2O3 shell structure and high surface area were prepared by depositing Al2O3 colloid particles on the surface of monodispersed microporous silica microspheres using a simple electrostatic attraction and heterogeneous nucleation strategy, and then calcined at 600 °C for 4 h. The prepared products were characterized with differential thermal analysis and thermogravimetric analysis (DTA/TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption and X-ray photoelectron spectroscopy (XPS). It was found that uniform alumina coating could be deposited on the surface of silica microspheres by adjusting the pH values of the reaction solution to an optimal pH value of about 6.0. The specific surface area and pore volume of the SiO2/Al2O3 composite microspheres calcined at 600 °C were 653 m2 g−1 and 0.34 ml g−1, respectively.  相似文献   

5.
A novel and rapid microwave method was used to prepare TiO2 coated ZnO nanocomposite particles. The resulted particles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Results show that ZnO nanoparticles were coated with 6-10 nm amorphous TiO2 layers. In addition, zeta potential analysis demonstrated the presence of TiO2 layer on the surface of ZnO nanoparticles. Photoluminescence (PL) spectroscopy and UV-visible spectroscopy were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnO nanoparticles, the TiO2 coated ZnO nanoparticles showed enhanced UV emission. The UV-visible diffuse reflectance study revealed the significant UV shielding characteristics of the nanocomposite particles. Moreover, amorphous TiO2 coating effectively reduced the photocatalytic activity of ZnO nanoparticles as evidenced by the photodegradation of Orange G with uncoated and TiO2 coated ZnO nanoparticles under UV radiation.  相似文献   

6.
The assembly of silica coated magnetite nanoparticles into chainlike nanostructures is reported in the presence of applied magnetic field. The coating of SiO2 onto the surface of magnetite nanoparticles was successfully conducted with the hydrolysis and condensation of tetraethyl orthosilicate. X-ray diffraction and transmission electron microscopy were used to characterize the microstructure and morphology. Vibrating sample magnetometry reveals that the coercivity is dependent on the coating thickness and can be controlled to a certain extent.  相似文献   

7.
ZnO:SiO2 films are intensively investigated for optical and electronic applications. Additionally, porous ZnO:SiO2 films are of great interest as catalyst and gas-sensing materials. The sol-gel method is an efficient and low-cost process for the deposition of meso- and microporous silica-based films. The present paper studies the effect of the withdrawal speed on the microstructure and optical properties of mesoporous ZnO:SiO2 films obtained by the sol-gel method. The morphology of the films was investigated by atomic force microscopy and the overall structure was studied by X-ray diffraction. The structure and size of the zinc oxide nanoparticles embedded in the silica matrix were investigated in more detail by transmission electron microscopy. These techniques showed ZnO:SiO2 films with crack-free mesoporous morphology and highly efficient embedding of ZnO nanoparticles with (100) preferred orientation. Furthermore, the optical transmittance (in the visible and near infrared regions) and the optical band gap value were observed to vary with withdrawal speed. It is shown that ZnO:SiO2 nanocomposites films which possess ZnO particles exhibiting a (100) orientation, with possible special applications in non-linear optics, could be prepared by the low-temperature crystallization sol-gel method.  相似文献   

8.
This paper reports on the luminescence and microstructural features of oxide nano-crystalline (Y2O3:Eu3+) and submicron-sized (Y2SiO5:Ce3+,Tb3+) phosphor cores, produced by two different synthesis techniques, and subsequently coated by an inert shell of SiO2 using a sol-gel process. The shells mitigate the detrimental effect of the phosphor particle surfaces on the photoluminescence emission properties, thereby increasing luminous output by 20-90%, depending on the core composition and shell thickness. For Y2O3:Eu3+, uniformly shaped, narrow particle size distribution core/shell particles were successfully fabricated. The photoluminescence emission intensity of core nanoparticles increased with increasing Eu3+ activator concentration and the luminescence emission intensity of the core/shell particles was 20-50% higher than that of the core particles alone. For Y2SiO5:Ce3+,Tb3+, the core/shell particles showed enhancement of the luminescence emission intensity of 35-90% that of the core particles, depending on the SiO2 shell thickness.  相似文献   

9.
The Cu2O particles or clusters dispersed mesoporous SiO2 composite films were prepared by a new method: First the matrix SiO2 films were prepared by sol-gel process combined with the dip-coating technique, and then they were soaked in Cu(NO3)2 solutions followed by γ-ray irradiation at room temperature and in ambient pressure. Thus prepared Cu2O/SiO2 composite films were examined by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and optical absorption spectroscopy. Compared with the pure Cu2O nanoparticles, an obvious blue shift existed in the obtained Cu2O/SiO2 composite films.  相似文献   

10.
This study was aimed to systematically investigate the luminescence response of SiO2:Ce3+ nanophosphors with different excitation sources. The powders were synthesized by using an urea assisted combustion method. SiO2:Ce1m% samples were also annealed at 1000 °C for 1 h in a charcoal environment to reduce incidental Ce4+ to partial Ce3+ ions. High resolution transmission electron microscopy (HRTEM) images of the as synthesized and annealed powder samples confirmed that the particles were spherical and in the size range of 3-8 nm in diameter. X-ray diffraction (XRD) and electron dispersion spectroscopy (EDS) results showed that the SiO2 was crystalline and pure. Diffused reflectance, photoluminescence (PL) and cathodoluminescence (CL) results of the SiO2:Ce3+ samples were obtained and compared with each other. The CL degradation and the surface reactions on the surface of the SiO2:Ce3+ were studied with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). A clear improvement in the chemical stability of the SiO2:Ce3+ annealed at 1000 °C were obtained.  相似文献   

11.
The umbrella-like ZnO nanostructures have been prepared by the morphological tailoring in the aqueous solution at 95 °C in the addition of heterogeneous seeds such as MnO2 and CdS nanoparticles. The morphology and structure of as-synthesized umbrella-like ZnO nanostructures have been characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscope (HRTEM), electron energy loss spectroscopy (EELS), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The heterogeneous seeds play the critical role for the formation of umbrella-like ZnO nanostructures. Furthermore, the formation mechanism of the umbrella-like nanostructures has been phenomenally presented.  相似文献   

12.
ZnO films with c-axis (0002) orientation have been grown on SiO2/Si substrates with an Al2O3 buffer layer by radio frequency magnetron sputtering. Crystalline structures of the films were investigated by X-ray diffraction, atomic force microscopy and scanning electron microscopy. The center frequency of the surface acoustic wave (SAW) device with a 4.8 μm thick Al2O3 buffer layer was measured to be about 408 MHz, which was much higher than that (265 MHz) of ZnO/SiO2/Si structure and approaches that (435 MHz) of ZnO/sapphire. It is a possible way as an alternative for the sapphire substrate for the high frequency SAW device applications, and is also useful to integrate the semiconductor and high frequency SAW devices on the same Si substrate.  相似文献   

13.
A novel two-step process was developed to synthesize and deposit SiO2/TiO2 multilayer films onto the cotton fibers. In the first step, SiO2 particles on cotton fiber surface were synthesized via tetraethoxysilane hydrolysis in the presence of cotton fibers, in order to protect the fibers against photo-catalytic decomposition by TiO2 nanoparticles. In the second step, the growth of TiO2 nanoparticles into the modified cotton fiber surface was carried out via a sol-gel method at the temperature as low as 100 °C. The as-obtained SiO2/TiO2 multilayer films coated on cotton fibers were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy and X-ray diffraction, respectively.  相似文献   

14.
A facile precipitation route was developed for the synthesis of cobalt hexacyanoferrate (CoHCF) as a thin shell around cores of nanoparticles of iron(III) oxide, forming nanoparticles of iron(III) oxide@CoHCF (n-Fe2O3@NaCo[Fe(CN)6]). The morphology and structure of the as-prepared n-Fe2O3@NaCo[Fe(CN)6] were characterized by the techniques of electron microscopies, X-ray diffraction measurements, X-ray photoelectron spectroscopy, infrared spectroscopy and thermogravimetry. Carbon composite electrodes of n-Fe2O3@NaCo[Fe(CN)6] were prepared and the electrochemical behavior of the nanoparticles was evaluated using cyclic voltammetry. The redox couples of n-Fe2O3@NaCo[Fe(CN)6] were investigated and the diffusion coefficients of counter cation in the shell of CoHCF were obtained. The effect of size of particles and the structure of CoHCF was also evaluated. n-Fe2O3@NaCo[Fe(CN)6] represented prominent electrocatalytic activity toward the oxidation of some biologically active compounds.  相似文献   

15.
Small Ag particles or clusters dispersed mesoporous SiO2 composite films were prepared by a new method: First the matrix SiO2 films were prepared by sol-gel process combined with the dip-coating technique, then they were soaked in AgNO3 solutions followed by irradiation of γ-ray at room temperature and in ambient pressure. The structures of these films were examined by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and optical absorption spectroscopy. It has been shown that the Ag particles grown within the porous SiO2 films are very small, and they are isolated and dispersed from each other with very narrow size distributions. With increasing the soaking concentration and an additional annealing, an opposite peakshift effect of the surface plasmon resonance (SPR) was observed in the optical absorption measurements.  相似文献   

16.
Multi-pods Au/FeOOH nanostructures were synthesized by a hydrothermal treatment of an aqueous solution of mixed micellar formed by gold nanoparticles, hexadecyltrimethyl ammonium bromide (CTAB), and (NH4)3[FeF6] at 160 °C for 48 h and sequential calcined at 290 °C for 1.5 h, resulting in the formation of multi-pods Au/Fe2O3 nanostructures. The as-obtained products were characterized by powder X-ray diffraction, transmission electron microscopy, selected area electron diffraction, field emission scanning electron microscopy, and UV-vis spectroscopy. Surface plasmon resonance band of gold nanoparticles was observed in the multi-pods Au/FeOOH nanostructures. However, a similar behavior was not seen with multi-pods Au/Fe2O3 nanostructures. The critical role of F ions and CTAB molecules in the formation of FeO(OH) multipods and the probable mechanism of the formation of multi-pods Au/FeOOH and Au/Fe2O3 nanostructures were discussed.  相似文献   

17.
Large-scale ear-like Si3N4 dendrites were prepared by the reaction of SiO2/Fe composites and Si powders in N2 atmosphere. The product was characterized by field emission scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The results reveal that the product mainly consists of ear-like Si3N4 dendrites with crystal structures, which have a length of several microns and a diameter of 100-200 nm. Nanosized ladder-like Si3N4 was also obtained when changing the Fe content in the SiO2/Fe composites. The Si3N4 nanoladders have a length of hundreds nanometers to several microns and a width of 100-300 nm. The ear-like Si3N4 dendrites are formed from a two-step growth process, the formation of inner stem structures followed by the epitaxial growth of secondary branches.  相似文献   

18.
The present study reports the synthesis and formation process of mesoporous core-shell TiO2 nanostructures by employing a glucose-assisted solvothermal process using water-ethanol mixture as solvent and subsequent calcination process at 550 °C for 4 h. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption analysis were used to investigate the structural properties of these nanostructures. By optimizing the preparation conditions, especially the contents of water and ethanol in the mixture solvent, mesoporous core-shell TiO2 nanostructures were obtained. These mesoporous nanostructures have anatase phase and exhibit the superior photocatalytic activity. This synthesis route is facile due to the usage of stable and low-cost Ti precursor such as TiCl3 and is thus applicable for large-scale production.  相似文献   

19.
SiO2 hollow spheres with movable Fe3O4 core were obtained by exposing the pre-synthesized Fe3O4\SiO2 particles (with an adsorption interlayer of ethylene glycol) under the irradiation of electron beam inside transmission electron micrograph (TEM). In the formation process, the evaporation of adsorbed ethylene glycol and the evolution of amorphous SiO2 layer played important roles, and that should be attributed to the high temperature and trapped charges induced by the irradiation of electron beam. This work provided a new route to obtain particles with movable core structure and extended the applications of electron beam.  相似文献   

20.
We report on the synthesis, morphology and magnetic properties of a novel NiO/SiO2 nanostructure. The NiO/SiO2 nanostructure was synthesized by a method based on the contribution of sol-gel and combustion processes. X-ray powder diffraction (XRPD) showed the formation of the nanocrystalline NiO phase. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) revealed perfectly spherical NiO nanoparticles with diameter of about 5 nm. Amorphous silica shell around the NiO nanoparticles was also observed by HRTEM showing NiO/SiO2 core-shell nanostructure. Magnetic measurements show hysteretic behavior at 2 K with coercivity HC = 700 Oe, remanent magnetization Mr = 3.9 emu/g, saturation magnetization MS = 28.2 emu/g and huge magnetic moment mp ≈ 1300 μB of the nanoparticles.  相似文献   

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