排序方式: 共有157条查询结果,搜索用时 15 毫秒
61.
D. K. T. Ng M. H. Hong L. S. Tan Y. W. Zhu C. H. Sow 《Applied Physics A: Materials Science & Processing》2008,93(3):685-689
Patterned gallium nitride nanowires and nanodots have been grown on n-Si (100) substrates by pulsed laser deposition. The
nanostructures are patterned using a physical mask, resulting in regions of nanowire growth of different densities. The field
emission (FE) characteristics of the patterned gallium nitride nanowires show a turn-on field of 9.06 V/μm to achieve a current
density of 0.01 mA/cm2 and an enhanced field emission current density as high as 0.156 mA/cm2 at an applied field of 11 V/μm. Comparing the peak FE current densities of both the nanowires and nanodots, the peak FE current
density of nanowires is around 700 times higher than that of the peak FE current density of nanodots since nanodots have a
lower aspect ratio compared to nanowires. The field emission results indicate that, besides density difference, crystalline
quality as well as the low electron affinity of gallium nitride, high aspect ratio of gallium nitride nanostructures will
greatly enhance their field emission properties. 相似文献
62.
Nitrogen-doped ZnO (ZnO:N) films are prepared by thermal oxidation of sputtered Zn3N2 layers on A1203 substrates. The correlation between the structural and optical properties of ZnO:N films and annealing temperatures is investigated. X-ray diffraction result demonstrates that the as-sputtered Zn3N2 films are transformed into ZnO:N films after annealing above 600℃. X-ray photoelectron spectroscopy reveals that nitrogen has two chemical states in the ZnO:N films: the No acceptor and the double donor (N2)o. Due to the No acceptor, the hole concentration in the film annealed at 700℃ is predicted to be highest, which is also confirmed by Hall effect measurement. In addition, the temperature dependent photoluminescence spectra allow to calculate the nitrogen acceptor binding energy. 相似文献
63.
Martin O. Berendt Anders Bjarklev Lars Gruner-Nielsen Carl E. Soccolich 《Fiber and Integrated Optics》1999,18(4):255-272
We discuss fiber designs that have been suggested for the reduction of Bragg-grating-induced coupling to cladding modes. The discussion is based on a theoretical approach that includes the effect of asymmetry in the UV-induced index grating, made by UV-side writing. Experimental results from gratings in a depressed-cladding fiber are compared with simulations. The model gives good agreement with the measured transmission spectrum and accounts for the pronounced coupling to asymmetrical cladding modes, even when the grating is written with smallest possible blaze. The asymmetry causing this is accounted for by the unavoidable attenuation of the UV light. It is found for the considered fiber designs that a high numerical-aperture fiber increases the spectral separation between the Bragg resonance and the onset of cladding-mode losses. A depressed-cladding fiber reduces the coupling strength to the lower order cladding modes, and the UV-sensitive cladding design reduces the cladding-mode coupling loss. The analysis suggests that the UV-sensitive cladding design is the most effective in reducing the cladding-mode-coupling losses. 相似文献
64.
L. A. Kappers O. R. Gilliam R. H. Bartram A. Watterich I. Földvári 《辐射效应与固体损伤》2013,168(6-12):671-676
Electron spin resonance (ESR) studies show that electron irradiation of an f -TeO 2 single crystal followed by 330-nm UV illumination at ~10 v K generates a new spin-1/2 paramagnetic center having C 2 symmetry, like the Te lattice sites, that is attributed to a self-trapped charge on a Te. Identification is facilitated by a strong hyperfine interaction with 125 Te at a central Te site and weaker 125 Te superhyperfine interactions with three different equivalent pairs of neighboring Te cations. The irradiations also produce the diamagnetic V_{O}^{\times} center and the paramagnetic V_{O}^{\bullet} and V_{O}^{\prime} centers. From measurements of concentration changes of the paramagnetic centers due to thermal annealing of the new center it is deduced that the self-trapped charge is a self-trapped electron. It is designated as a \hbox{TeO}_{2}^{\prime} center. This assignment is consistent with its low thermal stability since it anneals quickly at temperatures above 40 v K. ESR characteristics of this new center are described. 相似文献
65.
The lifetime of the surface plasmon in sputtered Ag ultrathin films on Cu(111) was investigated by high‐resolution electron energy loss spectroscopy measurements. The linewidth of the surface plasmon was found to follow a square‐root dependence on the fluence. Such finding allows the tuning of the lifetime of the plasmonic excitation upon sputtering and has general implications in plasmon‐based spectroscopies and in plasmon‐mediated processes across the films and at their surfaces. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
66.
A. A. Klyukanov A. V. Catanoi 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(3):275-281
Microscopic many-body theory for electronic properties
of solid states is developed with an emphasis on the role of correlation
memory effects. Heisenberg equation of motion, fluctuation-dissipation
theorem and operators of commutation have been used to calculate
multiplasmon transmission electron energy loss spectra. Multiquantum
integral kinetic equation for the longitudinal complex dielectric function
is derived. Strong interaction between high-energy probe beam electrons penetrating the
solid state and plasma of valence electrons is taken into account. It is
shown that average number of high-frequency plasmons generated in every
collision process is more than one for typical values of metal parameters.
It is obtained that excitation of a good few plasmons is simultaneous event.
Calculated multiplasmon structure of electron energy loss spectra coincides
with experimental. 相似文献
67.
High efficient green light emitting diodes (LED) on the basis of GaN/InGaN exhibit indium-rich nanoclusters inside the quantum wells (QW) due to InN-GaN phase decomposition. By direct measurements of the variations in the electronic structure, we show for the first time a correlation between indium-rich nanoclusters and local energy band gap minima. Our investigations reveal the presence of 1-3 nm wide indium rich clusters in these devices with indium concentrations x as large as x∼0.30-0.40 that narrow the band gap locally to energies as small as 2.65 eV. These clusters are able to act as local traps for migrating photon-emitting carriers and seem to boost the overall device performance. 相似文献
68.
A room temperature sphere-to-rod transition of the polyethylene oxide-polypropylene oxide-polyethylene oxide-based triblock
copolymer, (PEO)20(PPO)70 (PEO)20 micelles have been observed in aqueous medium under the influence of ethanol and sodium chloride. Addition of 5–10% ethanol
induces a high temperature sphere-to-rod transition of the micelles, which is brought to room temperature upon addition of
NaCl. The inference about the change in the shape of the micelles has been drawn from small-angle neutron scattering (SANS)
and viscosity studies. 相似文献
69.
We have undertaken a detailed experimental and numerical investigation of fibre Bragg grating growth rates over relatively long timescales, in which we consider the influence of zero-order UV irradiation, jitter and drift. In contrast to other studies, our results show that measurements of grating growth dynamics are in good agreement with numerical expressions describing exponential decay of a population of defect sites if the influence of small lateral displacements between the optical fibre and the modulated UV beam (jitter) are accounted for. 相似文献
70.