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Phonon Dispersion Curves (phonon + dispersion_curve)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

Raman spectroscopy of optical phonon confinement in nanostructured materials

JOURNAL OF RAMAN SPECTROSCOPY, Issue 6 2007
Akhilesh K. Arora
Abstract If the medium surrounding a nano-grain does not support the vibrational wavenumbers of a material, the optical and acoustic phonons get confined within the grain of the nanostructured material. This leads to interesting changes in the vibrational spectrum of the nanostructured material as compared to that of the bulk. Absence of periodicity beyond the particle dimension relaxes the zone-centre optical phonon selection rule, causing the Raman spectrum to have contributions also from phonons away from the Brillouin-zone centre. Theoretical models and calculations suggest that the confinement results in asymmetric broadening and shift of the optical phonon Raman line, the magnitude of which depends on the widths of the corresponding phonon dispersion curves. This has been confirmed for zinc oxide nanoparticles. Microscopic lattice dynamical calculations of the phonon amplitude and Raman spectra using the bond-polarizability model suggest a power-law dependence of the peak-shift on the particle size. This article reviews recent results on the Raman spectroscopic investigations of optical phonon confinement in several nanocrystalline semiconductor and ceramic/dielectric materials, including those in selenium, cadmium sulphide, zinc oxide, thorium oxide, and nano-diamond. Resonance Raman scattering from confined optical phonons is also discussed. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Lattice dynamics of CuAlO2 under high pressure from ab initio calculations

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007
P. Rodríguez-Hernández
Abstract The density functional perturbation theory is employed to study the vibrational properties of CuAlO2 under pressure. The calculations are preformed using the pseudopotential wave method and the local density approximation for the exchange-correlation (XC) potential. The d electrons of Cu are treated as valence states. We present the phonon dispersion curves. Our results are in good agreement with the available experimental Raman scattering experiments. Ab initio calculations show the presence of a dynamical instability, possibly related with the experimentally observed phase transition. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ab initio determination of structural and dynamical properties of the InP(110)-S interface

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004
H. M. Tütüncü
Abstract We have presented an ab initio pseudopotential study within the local density approximation of the structural properties of the S-treated InP(110) surface for an exchange model. The calculated structural parameters for this model are in good agreement with previous ab initio calculations. With these structural papameters, we have used an ab initio linear-response approach based on the density functional theory to investigate the dynamical properties of this surface. We discuss the similarities and contrast the differences in the phonon dispersion curves of the S-treated InP(110) and the clean InP(110) surfaces. We have found that the rotational phonon mode predicted for the clean surface can be also identified for the S-treated InP(110) surface. In addition to this, two new surface-localized phonon states appear in the acoustic-optical gap range due to the adsorption of S atoms. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Phonons in the Kondo insulator YbB12

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004
K. S. Nemkovski
Abstract We have studied the phonon excitations in the Kondo insulator YbB12 by means of inelastic neutron scattering. The excitation spectra extended up to the energy of 130 meV that is connected with boron "molecules" vibrations mainly. The specific shape of phonon dispersion curves for low frequency lattice vibration has been found. It could be explained by weak bounding of Yb ions in the lattice. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]