排序方式: 共有98条查询结果,搜索用时 31 毫秒
11.
Ibrahim Avgin 《Journal of luminescence》2008,128(10):1623-1628
We report the amplitude scaling behavior of Frenkel exciton chains with nearest-neighbor correlated off-diagonal random interactions. The band center spectrum and its localization properties are investigated through the integrated density of states and the inverse localization length. The correlated random interactions are produced through a binary sequence similar to the interactions in spin glass chains. We produced sets of data with different interaction strength and “wrong” sign concentrations that collapsed after scaling to the predictions of a theory developed earlier for Dirac fermions with random-varying mass. We found good agreement as the energy approaches the band center for a wide range of concentrations. We have also established the concentration dependence of the lowest order expansion coefficient of the scaling amplitudes for the correlated case. The correlation causes unusual behavior of the spectra, i.e., deviations from the Dyson-type singularity. 相似文献
12.
13.
The MgO (2 0 0) surface is widely used as a substrate for epitaxial growth of superconducting and ferro-electric films. Highly oriented, single crystalline, extremely flat and transparent MgO films have been successfully deposited on quartz substrates by the chemical spray pyrolysis technique using economically viable metal organic and inorganic precursors under optimized conditions at the substrate temperature of 600 °C. Thermal analysis (TGA/DTA) in the temperature range 30-600 °C with the heating rate of 10 °C/min revealed the decomposition behavior of the precursors and confirmed the suitable substrate temperature range for film processing. The heat of reaction, ΔH due to decomposition of metal organic precursor contributed additional heat energy to the substrate for better crystallization. The intensity of the (2 0 0) peak in X-ray diffraction (XRD) measurements and the smooth surface profiles revealed the dependency of precursor on film formation. The compositional purity and the metal-oxide bond formation were tested for all the films. UV-Vis-NIR optical absorption in the 200-1500 nm range revealed an optical transmittance above 80% and the absorption edge at about 238 nm corresponding to an optical band gap Eg = 5.25 eV. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) micrographs of MgO films confirmed better crystallinity with larger grain size (0.85 μm) and reduced surface roughness (26 nm), respectively. 相似文献
14.
Krzysztof Ziewiec 《Journal of Non》2008,354(33):4019-4023
The Cu68.5Ni12P19.5 alloy was cast into the ribbons using melt spinning (23 m/s). The amorphous ribbon in the as-cast state was investigated by differential thermal analysis (DTA), dynamic mechanical analysis (DMA), resistivity measurements and X-ray diffraction ‘in situ’ at different temperatures. The work presents attempts to find correlation between the changes of the mechanical properties presented by DMA cycles and during the other tests. The measurements of the relative resistivity R/R0 versus temperature for repeated heating and cooling cycles to different temperatures show changes of the temperature coefficient of resistivity (TCR) indicating reversible and irreversible transformations in the studied alloy. 相似文献
15.
G. Seifert M. Kaempfe K.-J. Berg H. Graener 《Applied physics. B, Lasers and optics》2000,71(6):795-800
Single-color femtosecond pump-probe experiments were performed to investigate the time dependence of laser-induced ultrafast
desorption and deformation processes of silver nanoparticles in glass. After laser excitation at wavelengths close to the
surface plasmon resonance, transient extinction changes were found to exhibit dynamics on quite different time scales ranging
from sub-picoseconds to some hundred ps. The slowest observed decay component is identified as characteristic for the deformation/desorption
processes. Possible mechanisms for these processes are discussed.
Received: 3 April 2000 / Revised version: 3 July 2000 / Published online: 20 September 2000 相似文献
16.
The characteristics of a BaO–Al2O3–B2O3–SiO2–La2O3 glass ceramic prepared by spray pyrolysis were studied. Glass powders with spherical shape and amorphous phase were prepared
by complete melting at a preparation temperature of 1 500°C. The mean size and geometric standard deviation of the powders
prepared at the temperature of 1 500°C were 0.6 μm and 1.3. The glass powders had similar composition to that of the spray
solution. The glass transition temperature (T
g) of the glass powders was 600.3°C. Two crystallization exothermic peaks were observed at 769.3 and 837.8°C. Densification
of the specimen started at a sintering temperature of 600°C, in which Ba4La6O(SiO4)6 as main crystal structure was observed. Complete densification of the specimen occurred at a sintering temperature of 800°C.
The specimens sintered at temperatures above 800°C had main crystal structure of BaAl2Si2O8. 相似文献
17.
Pure and urea-doped gamma-glycine (γ-glycine) single crystals were grown by solution method with slow evaporation technique. When urea was added as dopant, morphological alterations were noticed in γ-glycine crystals. Structural characterization of the grown crystals was carried out by single and powder X-ray diffraction (XRD) methods and it is observed that the samples crystallize in non-centrosymmetric space groups. UV-visible transmittance studies were performed to analyse optical transparency of pure and urea-doped γ-glycine crystals and found that the crystals were transparent in the entire visible-NIR region. Density and melting point of the grown crystals were measured. Second harmonic generation (SHG) for the grown crystals of this work was confirmed using Nd:YAG laser. Thermogravimetric and differential thermal analyses (TG/DTA) thermograms reveal that the materials have good thermal stability. From Microhardness studies, it is observed that urea-doped γ-glycine crystal is harder than pure (undoped) sample. 相似文献
18.
G. Seifert M. Kaempfe K.-J. Berg H. Graener 《Applied physics. B, Lasers and optics》2001,73(4):355-359
By repetitive irradiation of pico- or femtosecond laser pulses on glasses containing silver nanoparticles, dichroitic areas
can be produced with different optical properties depending on the actual irradiation parameters. This effect, which is nanoscopically
caused by permanent deformation of the initially spherical particles to non-spherical shapes and an additional formation of
a halo of very small particles, is studied as a function of polarization and number of the applied pulses using two different
laser systems (Ti:sapphire, λ=400 nm, tp=150 fs; Nd:YLF, λ=523.5 nm, tp=4 ps). A very special diffraction grating produced by this local deformation, which has strongly polarization- and wavelength-dependent
features, is introduced and discussed.
Received: 20 July 2001 / Published online: 10 October 2001 相似文献
19.
The low-temperature dynamics of two different varieties of a low-molecular glass—protonated toluene (C6H5CH3) and perdeuterated toluene (C6D5CD3)—weakly doped with tetra-tert-butylterrylene (TBT) molecules was investigated with single-molecule spectroscopy. In both glassy matrices the distributions of the spectral widths were measured for a large number of single TBT molecules at T=2 K. The marked shift of the distribution upon deuteration of matrix was observed and attributed to an isotope effect which is qualitatively analyzed. It was found that at this temperature the tunneling dynamics of the matrix dominates the broadening behavior and hydrogen/deuterium atoms are involved in the tunneling motions. 相似文献
20.
Viscosity of (GeSe2)x(Sb2Se3)1−x undercooled melts (x = 0.4-0.8) was measured using parallel-plate method and penetration method. By using these two techniques viscosity of the whole measurable region of undercooled melt and of the part of glass region can be measured. In this relatively broad viscosity interval (seven orders of magnitude) all measured samples show Newtonian behavior and the dependence of their viscosity on temperature can be described by a simple Arrhenius equation. The kinetic fragilities calculated from these dependencies show similar compositional dependence as heat capacity changes at glass transition measured by DSC. 相似文献