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1.
Under the dielectric continuum model and Loudon’s uniaxial crystal model, the properties of the quasi-confined (QC) optical phonon dispersions and the electron-QC phonons coupling functions in a cylindrical wurtzite nanowire are deduced via the method of electrostatic potential expanding. Numerical computations on a GaN/Al0.15Ga0.85N wurtzite nanowire are performed. Results reveal that, for a definite axial wave number kz and a certain azimuthal quantum number m, there are infinite branches of QC modes. The frequencies of these QC modes fall into two regions, i.e. a high frequency region and a low frequency region. The dispersion of the QC modes are quite apparant only when kz and m are small. The lower-order QC modes in the higher frequency region play more important role in the electron-QC phonon interactions. Moreover, for the higher-order QC modes in the high frequency region, the electrostatic potentials “escaping” out of the well-layer material nearly could be ignored. 相似文献
2.
The rapidity and transverse momentum dependence of the nuclear modification ratio for dilepton production at RHIC and LHC is presented, calculated in the color glass condensate (CGC) framework. The transverse momentum ratio is compared for two distinct dilepton mass values and a suppression of the Cronin peak is verified even for large mass. The nuclear modification ratio suppression in the dilepton rapidity spectra, as obtained experimentally for hadrons at RHIC, is verified for LHC energies at large transverse momentum, although not present at RHIC energies. The ratio between LHC and RHIC nuclear modification ratios is evaluated in the CGC, showing the large saturation effects at LHC compared with the RHIC results. These results consolidate the dilepton as a most suitable observable to investigate the QCD high density approaches. 相似文献
3.
I. Ursu I. Apostol M. Dinescu I. N. Mihăilescu A. Popa A. M. Prokhorov V. I. Konov N. I. Chapliev 《Applied Physics A: Materials Science & Processing》1984,34(2):133-138
Progressive damage of aluminium mirrors subjected to microsecond pulsed TEA-CO2 laser irradiation in air, at incident intensity levels lower than the thresholds for melting induction and air breakdown ignition, was evidenced by electron microscopy investigations. A simple model was developed accounting for the results of our experimental studies. 相似文献
4.
P. Billaud J.-R. Huntzinger E. Cottancin J. Lermé M. Pellarin L. Arnaud M. Broyer N. Del Fatti F. Vallée 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):271-274
The extinction spectrum of single silver nanoparticles
with size ranging from 20 to 80 nm is investigated with the spatial
modulation spectroscopy technique using either a tunable laser or a white
lamp as the broadband source. Results are in good agreement with the
prediction of the Mie theory, permitting to extract the nanoparticle size
from the measured absolute value of the optical extinction cross-section. In
contrast, the deduced refractive index of the nanoparticle environment and
the reduction of the electron mean free path show a large dependence on the
precise value of the bulk silver dielectric function. 相似文献
5.
Within the framework of the dielectric-continuum model and Loudon's uniaxial crystal model, the equation of motion for p-polarization field in arbitrary wurtzite multilayer heterostructures are solved for the quasi-confined phonon (QC) modes. The polarization eigenvector, the dispersion relation, and the electron-QC interaction Fröhlich-like Hamiltonian are derived by using the transfer-matrix method. The dispersion relations and the electron-QC coupling strength are investigated for a wurtzite GaN/AlN single QW. The results show that there are infinite branches of dispersion curve with definite symmetry with respect to the center of the QW structure. The confinement of the quasi-confined phonons in the QW leads to a quantization of qz,j characterized by an integer m that defines the order of corresponding quasi-confined modes. The QC modes are more dispersive for decreasing m. The QC modes display an interface behavior in the barrier and a confined behavior in the well. The symmetric modes have more contribution to electron-QC interaction than the antisymmetric modes. The strains have more effect on symmetry modes, and can be ignored for symmetry modes. 相似文献
6.
G.E. Isted 《Applied Surface Science》2005,252(5):1883-1890
The preparation of metal surfaces that in ambient conditions are flat and smooth over micron length scales is desirable for a wide range of applications. Scanning probe microscopy (SPM) studies of biomolecular adsorption and cell attachment require such well-prepared substrates. Standard polishing finishes are often found to exhibit considerable roughness and damage including scratches when investigated by SPM. We have prepared by means of UHV technology Au(1 1 0) and Cu(1 1 0) surfaces that when in ambient air exhibit a more homogeneous morphology and are considerably smoother than conventional polished surfaces. SPM techniques and the optical technique of reflection anisotropy spectroscopy (RAS) are used to characterise the morphological and electronic properties of these surfaces, respectively. The RA response of both Au(1 1 0) and Cu(1 1 0) surfaces in ambient conditions can be interpreted in terms of optical transitions between surface-modified bulk bands. 相似文献
7.
H. Khosroabadi A. Tavana M. Akhavan 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(2):161-165
Ab initio total energy calculations have been performed for superconducting
GdBa2Cu3O7 and insulating PrBa2Cu3O7 using the
full-potential linear augmented plane-wave method in the local density
approximation (LDA) and generalized gradient approximation (GGA). The
comparison of the calculated unit cell volume and lattice parameters with
the experimental data indicates the improvement of these parameters in the
GGA relative to LDA. LDA and GGA give the equilibrium unit cell volume about
6% smaller and 1.25% larger than the experimental data, respectively
for both systems. Thus frozen phonon calculations have been performed to
determine the eigenvalues and eigenvectors of the k=0 Ag modes of the
two systems in equilibrium structure have been obtained in GGA. The
calculated frequencies in the GGA are in good agreement with the other LDA
calculations for similar systems. Comparison of computational data with
experimental data indicates that calculations determine the frequencies
about ten percent below the experimental data. Even by improving LDA to GGA
in these calculations, the calculated phonon frequencies have remained
almost ten percent below the experimental data, even though the calculated
unit cell volumes are nearly equal to the experimental data. So, applying
GGA has not considerably decreased the difference between the computational
and experimental data. The effect of Pr doping on the eigenvalues and
eigenvectors have also been investigated. 相似文献
8.
A. H. Moudden 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):173-183
Several structures for off-stoichiometric beryllium diboride dicarbide Be1−xB2C2 have been designed, and their properties studied from first-principles density functional methods. Among the most stable
phases examined, the layered hexagonal structures are shown to exhibit various features in the electronic properties and in
the lattice dynamics reminiscent of the superconducting magnesium diboride and alkaline earth-intercalated graphites. For
substoichiometric composition x ∼ 1/3, the system is found metallic with a moderately strong electron-phonon coupling through a predominant contribution
arising from high frequency streching modes modulating the σ-bonding of the B-C network, and a weaker contribution at medium frequency range of the phonon spectra, arising from the intercalent
motion coupled to the π-bonding states. Further, anharmonicities emerging from the proximity of the Fermi level to the σ-band edge, contributes to reduce the phonon softening hence stabilizing the structure. All these effects appear to combine
favourably to produce a high temperature phonon-superconductivity. 相似文献
9.
J. Dong J.L. Luo X.G. Luo R. Jin N.L. Wang 《Journal of Physics and Chemistry of Solids》2008,69(12):3052-3057
We study the charge dynamics and electronic structure by optical spectroscopy technique. Here we focus on the following four issues: (1) the evolution of optical spectra with Na content; (2) the spectral features specific to different regions in the phase diagram; (3) the c-axis optical response for crystal at the A-type antiferromagnetic region; (4) the optical response of misfit-layered Bi2M2Co2Oy (M=Ba, Sr, Ca) and Ca3Co4Oy single crystals. 相似文献
10.
E.S. Clementyev K. Conder A. Furrer I.L. Sashin 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):465-467
We provide here experimental data on the phonon density-of-states of MgB2 obtained by the inelastic neutron scattering technique. The measurements were performed for the natural boron-based magnesium
diboride with use of a time-of-flight neutron spectrometer. Several phonon bands were observed in the phonon spectrum at energies
of about 33, 55, 82 and 99 meV. We show that the cut-off energy of the density-of-states occurs at around 105 meV which is
much higher than expected so far from heat-capacity data and partially explains the high T
c
value observed for MgB2. The characteristic phonon energies are indicative of an intermediate coupling regime in this compound. We conclude that
a much needed neutron experiment aimed at the study of the isotopic effect in the phonon density-of-states of MgB2 is conceivable.
Received 19 March 2001 相似文献