排序方式: 共有100条查询结果,搜索用时 15 毫秒
71.
Yanyan Shen Xu Li Zhuo Wang Lili Zhang Dacheng Zhang Mengkai Li Bing Yuan Zhaodong Li Changlong Liu 《Journal of Crystal Growth》2009,311(21):4605-4609
SiO2 samples were implanted with 45 keV Zn ions at doses ranging from 5×1015 to 1.0×1017 ions/cm2, and were then subjected to furnace annealing at different temperatures. Several techniques, such as ultra-violet–visible spectroscopy (UV–vis), grazing incidence X-ray diffraction spectroscopy (GXRD) and atomic force microscopy (AFM), have been used to investigate formation of nanoparticles and their thermal evolution. Our results clearly show that Zn nanoparticles could be effectively formed in SiO2 at doses higher than 5×1016 ions/cm2. The subsequent thermal annealing at oxygen ambient could induce the growth of Zn nanoparticles at intermediate annealing temperature range. While at temperature above 600 °C, Zn nanoparticles could be transformed into ZnO, or even Zn2SiO4 nanoparticles. The results have been tentatively discussed in combination with Zn diffusion and migration obtained by Rutherford backscattering spectroscopy (RBS) measurements. 相似文献
72.
Particle size effect on phase and magnetic properties of polymer-coated magnetic nanoparticles 总被引:1,自引:0,他引:1
Srinivasan Balakrishnan Michael J. Bonder George C. Hadjipanayis 《Journal of magnetism and magnetic materials》2009,321(2):117-122
Polymer-coated magnetic nanoparticles are hi-tech materials with ample applications in the field of biomedicine for the treatment of cancer and targeted drug delivery. In this study, magnetic nanoparticles were synthesized by chemical reduction of FeCl2 solution with sodium borohydride and coated with amine-terminated polyethylene glycol (aPEG). By varying the concentration of the reactants, the particle size and the crystallinity of the particles were varied. The particle size was found to increase from 6 to 20 nm and the structure becomes amorphous-like with increase in the molar concentration of the reactant. The magnetization at 1 T field (M1T) for all samples is > 45 emu/g while the coercivity is in the range of 100-350 Oe. When the ethanol-suspended particles are subjected to an alternating magnetic field of 4 Oe at 500 kHz, the temperature is increased to a maximum normalized temperature (3.8 °C/mg) with decreasing particle size. 相似文献
73.
The arms of CdSe nano-tetrapods can be greatly elongated with the core diameters and arm width unchanged by multiple injections. Room-temperature absorption and photoluminescence (PL) spectra of tetrapods with different arm lengths show that these tetrapods have almost the same core size, which is consistent with the high resolution TEM results. Field emission characteristics show that the onset field required drawing a current density of from CdSe nano-tetrapods with different arm lengths are , , and , respectively, and the field enhancement factors are determined to be about 218, 554, and 946, respectively. Results show that the longer is the arm of the tetrapods, the lower the turn-on field and the higher the field enhancement factor. 相似文献
74.
Temperature dependence of photoconductivity and persistent photoconductivity of single ZnO nanowires 总被引:1,自引:0,他引:1
Zhi-Min Liao Yi Lu Jun Xu Jing-Min Zhang Da-Peng Yu 《Applied Physics A: Materials Science & Processing》2009,95(2):363-366
Photoelectrical properties of single ZnO nanowires have been investigated using photocurrent–voltage characteristics measurements
varying with excitation photon energy and temperature. It is found that persistent photoconductivity (PPC) exists, and the
PPC decreases with decreasing temperature. The temperature dependence of the PPC effect indicates that thermally activated
return of electrons from shallow traps is responsible for the PPC phenomenon. The photosensitivity is found to be linear with
the applied voltage, and it increases with decreasing temperature. A temperature dependence of photoconductivity gain was
introduced to explain the experimental results. 相似文献
75.
F. Sánchez-Bajo A. L. Ortiz F. L. Cumbrera 《Applied Physics A: Materials Science & Processing》2009,94(1):189-194
An analytical model for the determination of crystallite size and crystal lattice microstrain distributions in nanocrystalline
(nc) materials by X-ray diffractometry (XRD) is presented. It entails generalizing the variance method to establish analytically
the connection between the variance coefficients of the physically broadened XRD peaks and the characteristic parameters of
explicit distributions of crystallite sizes and crystal lattice microstrains, which results in a more detailed characterization
of the nc-materials. The proposed model is generic in nature and has the potential to be used under the assumption of different
mathematical functions for the two distributions, which suggests that it may have an important role to play in the characterization
of nc-materials. Nevertheless, the specialization to the case of nc-materials with log-normal crystallite size distribution
and three typical types of lattice microstrains is used as an illustration and to formulate explicit analytical expressions
of interest. Finally, the usefulness of the proposed model is demonstrated on standard XRD profiles. 相似文献
76.
L. Tsybeskov E.-K. Lee H.-Y. Chang D. J. Lockwood J.-M. Baribeau X. Wu T. I. Kamins 《Applied Physics A: Materials Science & Processing》2009,95(4):1015-1027
Silicon–germanium epitaxially grown on silicon in the form of two-dimensional (quantum wells) and three-dimensional (quantum
dots) nanostructures exhibits photoluminescence and electroluminescence in the technologically important spectral range of
1.3–1.6 μm. Until recently, the major roadblocks for practical applications of these devices were strong thermal quenching
of the luminescence quantum efficiency, and a long carrier radiative lifetime. This paper summarizes recent progress in the
understanding of carrier recombination in Si/SiGe nanostructures and presents a potential new route toward CMOS compatible
light emitters for on-chip optical interconnects. 相似文献
77.
The mapping of marine habitats mainly relies on acoustic techniques and there is a clear need for reliable classification methods supplementing the interpreter with as much quantitative information as possible. This article presents textural analyses of multibeam sonar imagery from Stanton Banks, on the continental shelf off Northern Ireland. TexAn, originally developed for the textural analysis of sidescan sonar imagery, was tested over an area of ∼72 km2 surveyed in 2005 by the European MESH project. The multibeam imagery is affected by several artefacts, including strong uncorrected angular variations in some tracks, and the acquisition of some tracks with very different aspects. The results from unsupervised classification of the imagery, using K-Means, match well the interpretations that can be made using concurrent bathymetric data and visual observations acquired in a later cruise. Textural analyses successfully detect faint trawlmarks and distinguish between the different types of seafloor, including variations within sediments, rocky outcrops and gullied terrains. 相似文献
78.
Microwave Response of MgB2/A12O3 Superconducting Thin Films by Microstrip Resonator Technique
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Double-sided superconducting MgB2 thin films are deposited onto c-A120a substrates by the hybrid physical chemical vapour deposition method. The microwave response of MgB2/A12O3 is investigated by microstrip resonator technique. A grain-size model is introduced to the theory of microstrip resonators to analyse microwave properties of the films. We obtain effective penetration depth of the films at OK (λe0 = 463nm) and surface resistance (R8 = 1.52 mΩ at 11 K and 8. 73 GHz) by analysing the resonant frequency and unload quality factor of the microstrip resonator, which suggests that the impurities and disorders of grain boundaries of MgB2/A12 Oa result in increasing penetration depth and surface resistance of the films. 相似文献
79.
The power conversion efficiency of organic solar cells based on donor–acceptor blends is governed by an interplay of polaron pair dissociation and bimolecular polaron recombination. Both processes are strongly dependent on the charge carrier mobility, the dissociation increasing with faster charge transport, with raised recombination losses at the same time. Using a macroscopic effective medium simulation, we calculate the optimum charge carrier mobility for the highest power conversion efficiency, for the first time accounting for injection barriers and a reduced Langevin‐type recombination. An enhancement of the charge carrier mobility from 10–8 m2/V s for state of the art polymer–fullerene solar cells to about 10–6 m2/V s, which yields the maximum efficiency, corresponds to an improvement of only about 20% for the given parameter set. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
80.
T. E. Jackman G. C. Aers M. W. Denhoff P. J. Schultz 《Applied Physics A: Materials Science & Processing》1989,49(3):335-339
Silicon epilayers grown by molecular beam epitaxy and doped in-situ using low-energy implantation were examined using a variable-energy positron beam. The samples had been previously characterized using electrical measurements, ion channeling, SIMS, and electron microscopy. The positron results show that defects have been created in layers grown at 460°C and in the highly doped layers grown at 700°C. The assignment of defect structures is difficult at present, but is consistent with the formation of As clusters or Asvacancy complexes. 相似文献