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Phonon Frequencies (phonon + frequency)
Selected AbstractsAdiabatic bond charge model for lattice dynamics of ternary chalcopyrite semiconductorsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 1 2006T. Gürel Abstract The adiabatic bond charge model of Rustagi and Weber is extended to study lattice dynamical properties of ternary chalcopyrite semiconductors AgGaS2, AgGaSe2, CuInS2, CuInSe2, CuGaS2, CuGaSe2, CuAlS2 and CuAlSe2. The new model calculations agree well with the results of Raman/IR and neutron measurements of Brillouin zone center phonon frequencies for both low and high frequency modes which was difficult for other phenomenological lattice dynamical models. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Revealing the Electron,Phonon Coupling in a Conjugated Polymer by Single-Molecule Spectroscopy,ADVANCED MATERIALS, Issue 15 2007R. Hildner Electron,phonon coupling in a ,-conjugated polymer is revealed by single-molecule spectroscopy in combination with statistical pattern recognition techniques. The technique allows to reveal the phonon-side band in the spectra of methyl-substituted ladder-type poly(para-phenylene) (see figure). For this polymer a weak electron,phonon coupling strength is found at low temperatures. The distribution of the phonon frequencies provides strong evidence that the low-energy vibrational modes, which couple to the electronic transitions, stem from vibrations of the host matrix. [source] Efficient Near-Infrared Emission from Sodalite Derivatives,ADVANCED MATERIALS, Issue 3 2006M. Lezhnina The use of nanoporous host materials for luminescent guests has been extended into the near-infrared (NIR) regime using sodalite derivatives containing rare earth ions and the tungstate group (see Figure). The emission intensities obtained for Nd3+ meet or even surpass commercial Nd glasses. While Nd3+ -tungstate-modified zeolites do not yield significant luminescence, NIR emission occurs in the sodalites due to the low phonon frequencies involved and the exclusion of water in particular. [source] Polarized Raman scattering studies of nonpolar a -plane GaN films grown on r -plane sapphire substrates by MOCVDPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 15 2006Haiyong Gao Abstract Nonpolar (110) a -plane GaN thin films were grown on r -plane (102) sapphire substrates by low-pressure metal organic chemical vapor deposition (MOCVD). The stress characteristics of the a -plane GaN films were investigated by means of polarized Raman scattering spectra in backscattering configurations. The experimental results show that there are strong anisotropic in-plane stresses within the epitaxial a -plane GaN films by calculating the corresponding stress tensors. The temperature dependence of Raman scattering spectra was studied in the range from 100 K to 550 K. The measurements reveal that the Raman phonon frequencies decrease with increasing temperature. The temperature at which nonpolar a -plane GaN films are strain free is discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Elasticity, electronic structure, and dielectric property of cubic SrHfO3 from first-principlesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009Z. F. Hou Abstract Recently, SrHfO3 compound was proposed as a potential gate dielectric to fabricate metal,oxide,semiconductor field-effect transistors (MOSFET) with equivalent oxide thickness (EOT) below 1 nm. Here we report the elasticity, electronic structure, and dielectric property of cubic SrHfO3 from first-principle study based on the plane-wave pseudopotential method within the local density approximation (LDA). The independent elastic constants of cubic SrHfO3 are derived from the derivative of total energy as a function of lattice strain. The elastic modulus is predicted from Voight-Hill bounds. The Born effective charges, electronic dielectric tensors, long wavelength phonon frequencies, and LO,TO splitting of cubic SrHfO3 are computed by linear response with density functional perturbation theory (DFPT). The calculated lattice constant and bulk modulus of cubic SrHfO3 are in good agreement with the available experimental data and other theoretical results. Our results show cubic SrHfO3 is a ductile insulator with an indirect band gap of 3.74 eV (LDA value) and electric dielectric tensor of 4.43, Hf 5d states and O 2p states exhibit a strong hybridization, and cubic SrHfO3 can be mechanically stable. In addition, the phonon frequency of ,soft mode' at zone-center also agrees well with previous theoretical value. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Surface phonons in CdS1,xSex nanoparticles embedded in a dielectric mediumPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2009Yu. M. Azhniuk Abstract Raman scattering by surface phonons in CdS1,xSex nanocrystals grown in a borosilicate glass matrix, is studied. CdSe-like and CdS-like surface phonon frequencies are shown to increase with the relevant component content in the nanocrystal composition. No clear size dependence of the surface phonon frequencies has been observed. On the other hand, surface phonons in CdS1,xSex nanocrystals exhibit resonant dependence on the Raman excitation wavelength. It is emphasized that measurements of Raman scattering by surface phonons in CdS1,xSex nanocrystals give no reason to judge upon the nanocrystal shape. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dispersion relation of the optical phonon frequencies in AlN/GaN superlatticesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005S.K. Medeiros Abstract In this work we study the dispersion relation of the phonon frequencies in heterojunctions composed by III-V nitride materials (GaN and AlN). We are concerned with the superlattice structure, namely /substrate /AlN /AlxGa1,xN/GaN/AlxGa1,xN/,, where the substrate is here considered to be a transparent dielectric medium like sapphire. We make use of a model based on the Fröhlich Hamiltonian, taking into account the macroscopic theory known as the continuum dielectric model. The optical phonon modes are modelled considering only the electromagnetic boundary conditions, in the absence of charge transfer between ions. Numerical results of the confined optical phonon dispersion are presented, characterizing three distinct optical phonon classes designated as interface (IF), half-space (HS) and propagating (PR) modes. Furthermore, due to the dielectric anisotropy presented in the nitride, some additional peculiarities will be presented, like dispersive confined modes. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Strain-induced correlations between the phonon frequencies of indium nitridePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2004O. Briot Abstract Using measurements of phonons frequencies in large size InN quantum dots deposited by Metal-organic vapor phase epitaxy, we found these frequencies to experience a blue shift with increasing compression. Next we show that all the phonon frequencies reported in the literature are correlated to the strain state of InN and are, within the experimental uncertainty, consistent with each other. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical and Structural Analysis of GaN Grown by Remote Plasma Enhanced Laser Induced Chemical Vapour DepositionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003Afifuddin Abstract High quality polycrystalline gallium nitride (GaN) films have been grown by remote plasma enhanced laser induced chemical vapour deposition (RPE-LICVD) on sapphire, silicon, and quartz substrates at temperatures below 600 °C. Transmission spectra of the films indicate excellent properties with band gap 3.38 ± 0.02 eV. A yellow band-to-band transition at 2.2 eV is observed. X-ray diffraction patterns reveal the (0002) wurtzite reflection at 2, = 34.6° is dominant. Raman spectra of the films are discussed with respect to the phonon frequencies and strain-related phenomena. Compositional analysis with heavy ion Elastic Recoil Detection shows stoichiometric nitrogen to gallium ratios and relatively small amounts of incorporated oxygen. [source] Spectroscopic and Thermal Properties of Ga2S3,Na2S,CsCl GlassesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006Luiz C. Barbosa The synthesis and properties of the vitreous system (0.75,x)Ga2S3,0.25Na2S,xCsCl, with x varying from 0.1 to 0.2, are presented. Thermal, optical, and structural properties such as density, viscosity, thermal expansion coefficient, glass transition temperature, softening point temperature, refractive index, and absorption coefficient were measured using several techniques: X-ray diffraction, Raman scattering, differential thermal analysis, thermal mechanical analysis, and absorption spectroscopy. This glass system presents a high third-order non-linear optical susceptibility that can be significantly increased by increasing the CsCl content without affecting the low phonon frequency. [source] Resonant Raman scattering in spherical quantum dots: II,VI versus III,V semiconductor nanocrystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2010Mikhail I. Vasilevskiy Abstract Resonant Raman scattering (RRS) in nearly-spherical nanocrystal (NC) quantum dots (QDs) is discussed with respect to the underlying (Fröhlich-type and optical deformation potential, ODP) mechanisms of the exciton,phonon interaction. Their relative contribution for different QD materials, both II,VI and III,V is compared. It is shown that the (usually overlooked) ODP interaction is entirely responsible for an additional peak in the RRS spectra, situated near the transverse-optical (TO) phonon frequency, which has been observed for InP, InAs and, recently, CdTe QDs. RRS spectra calculated using continuum models for confined phonons and excitons and taking into account both interaction mechanisms are in excellent agreement with these experimental data. [source] Quantum phase transition between antiferromagnetic and charge order in the Hubbard,Holstein modelPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2010Johannes Bauer Abstract We explore the quantum phase transitions between two ordered states in the infinite dimensional Hubbard,Holstein model at half filling. Our study is based on the dynamical mean field theory (DMFT) combined with the numerical renormalization group (NRG), which allows us to handle both strong electron,electron and strong electron,phonon interactions. The transition line is characterized by an effective electron,electron interaction. Depending on this effective interaction and the phonon frequency ,0 one finds either a continuous transition or discontinuous transition. Here, the analysis focuses on the behavior of the system when the electron,electron repulsion U and the phonon-mediated attraction , are equal. We first discuss the adiabatic and antiadiabatic limiting cases. For finite ,0 we study the differences between the antiferromagnetic (AFM) and charge order, and find that when present the AFM state has a lower energy on the line. [source] Elasticity, electronic structure, and dielectric property of cubic SrHfO3 from first-principlesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009Z. F. Hou Abstract Recently, SrHfO3 compound was proposed as a potential gate dielectric to fabricate metal,oxide,semiconductor field-effect transistors (MOSFET) with equivalent oxide thickness (EOT) below 1 nm. Here we report the elasticity, electronic structure, and dielectric property of cubic SrHfO3 from first-principle study based on the plane-wave pseudopotential method within the local density approximation (LDA). The independent elastic constants of cubic SrHfO3 are derived from the derivative of total energy as a function of lattice strain. The elastic modulus is predicted from Voight-Hill bounds. The Born effective charges, electronic dielectric tensors, long wavelength phonon frequencies, and LO,TO splitting of cubic SrHfO3 are computed by linear response with density functional perturbation theory (DFPT). The calculated lattice constant and bulk modulus of cubic SrHfO3 are in good agreement with the available experimental data and other theoretical results. Our results show cubic SrHfO3 is a ductile insulator with an indirect band gap of 3.74 eV (LDA value) and electric dielectric tensor of 4.43, Hf 5d states and O 2p states exhibit a strong hybridization, and cubic SrHfO3 can be mechanically stable. In addition, the phonon frequency of ,soft mode' at zone-center also agrees well with previous theoretical value. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Raman scattering analysis of GaN with various dislocation densitiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008T. Kitamura Abstract We characterized GaN crystals with various dislocation densities by micro-Raman spectroscopy. Defects and Strain for the GaN layer were examined through measurements of the Raman shift and the width of the TO phonon bands. The broadening of Raman bands in GaN crystals occurred as the dislocation density increased. The up-shift of the peak frequencies corresponding to compressive strain was observed for the heteroepitaxial samples grown by MOCVD and MBE. The in-plane distribution of defects and strain in epilayers with various dislocation densities was also examined by Raman mapping. The Raman maps showed that the examined phonon frequency and band width in samples fluctuated spatially. The increase of dislocation density in GaN epilayers induced not only the broadening of Raman bands but also increase of fluctuation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Strain-induced correlations between the phonon frequencies of indium nitridePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2004O. Briot Abstract Using measurements of phonons frequencies in large size InN quantum dots deposited by Metal-organic vapor phase epitaxy, we found these frequencies to experience a blue shift with increasing compression. Next we show that all the phonon frequencies reported in the literature are correlated to the strain state of InN and are, within the experimental uncertainty, consistent with each other. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||