We have performed first-principles calculations of the electronic structure ZnO, and applied them to determination structural lattice-dynamical properties their dependence on pressure. The dynamical matrices been obtained for wurtzite, zinc-blende, rocksalt modifications with several lattice parameters optimized pressures up 12 GPa. These are employed calculate one-phonon densities states (DOS) two-phonon DOS associated either sums or differences phonons. results provide essential tools...

Anomalous Raman modes have been reported in several recent papers dealing with doped- and undoped-ZnO layers grown by different methods. Most of these anomalous attributed to local vibrational impurities or defects. However, we will show that most the observed correspond wurtzite-ZnO silent allowed breakdown translational crystal symmetry induced defects impurities.

The five independent elastic moduli of single-crystalline hexagonal boron nitride ($h$-BN) are determined using inelastic x-ray scattering. At room temperature the in units GPa ${\mathrm{C}}_{11}=811$, ${\mathrm{C}}_{12}=169$, ${\mathrm{C}}_{13}=0$, ${\mathrm{C}}_{33}=27.0$, and ${\mathrm{C}}_{44}=7.7$. Our experimental results compared with predictions ab initio calculations previously reported incomplete datasets. These provide solid background for further theoretical advances quantitative...

The phonon dispersion relations of bulk hexagonal boron nitride have been determined from inelastic x-ray scattering measurements and analyzed by ab initio calculations. Experimental data calculations show an outstanding agreement reconcile the controversies raised recent experimental obtained electron-energy loss spectroscopy second-order Raman scattering.

We present the results of a first-principles theoretical study relative stability several structural phases group--III nitrides AlN, GaN, and InN that complements picture behavior under pressure these technologically important materials. Along with structures which have been previously considered in other studies materials (comprising those observed phases: wurtzite, zinc-blende, rocksalt; $d\ensuremath{-}\ensuremath{\beta}\ensuremath{-}\mathrm{Sn},$ NiAs, CsCl structures) we also assessed...

We studied the correlations among size, defects, and photoluminescence emissions in ZnO nanoparticles of sizes ranging from 25 to 73 nm. The impurities defects were characterized by Fourier-transform infrared spectroscopy Raman spectroscopy. Particles larger size revealed fewer surface enhanced E2 mode hexagonal crystals, while oxygen vacancy centers did not vary significantly with particle size. A simultaneous increase excitonic luminescence defect intensities is shown, indicating both are...

Ultrathin passive films effectively prevent the chemical attack of stainless steel grades in corrosive environments; their stability depends on interplay between structure and chemistry constituents iron, chromium, molybdenum (Fe-Cr-Mo). Carbon (C), eventually boron (B), are also important steels, although small quantities. In particular, nanoscale inhomogeneities along surface can have an impact material failure but still poorly understood. Addressing a stainless-type glass-forming...

We have investigated the lattice dynamics of a wurtzite GaN single crystal by inelastic x-ray scattering. Several dispersion branches and phonons at high-symmetry points been measured, including two zone-center Raman- infrared-inactive silent modes. The experiments complemented ab initio calculations. They are in very good agreement with our measurements, not only for phonon energies, but also scattering intensities, thus validating correctness eigenvectors. Other phenomenological theories...

Phonon linewidths can exhibit a large variation when either pressure or isotopic masses are changed. These effects yield detailed information about the mechanisms responsible for and lifetimes, e.g., anharmonicity disorder. We report Raman measurements of linewidth upper ${\mathrm{E}}_{2}$ phonons ZnO crystals with several compositions their dependence on pressure. Changes by factor 12 observed at given temperature. Comparison calculated densities one-phonon states, isotope scattering,...

The first- and second-order Raman spectra of cubic ZnS $(\ensuremath{\beta}$-ZnS, zinc-blende) are revisited. We consider measured with two laser lines for samples different isotopic compositions, aiming at a definitive assignment the observed features mechanisms which determine linewidth first order TO LO phonons. For this purpose, dependence on temperature pressure is investigated. phonons found to vary strongly masses. Pressure runs, up 15 GPa, were performed 16 K 300 K. Whereas...

Zinc oxide is a key material for optoelectronic applications, whose transport properties are typically dominated by the lattice vibrations. We report here phonon-dispersion relations of wurtzite ZnO at 10 K, as determined using inelastic neutron scattering. The experimental data analyzed with aid ab initio calculations based on density-functional perturbation theory. A complete picture dynamics drawn from present results, thus contributing to understanding mechanical, thermodynamical, and materials.

The two-dimensional mapping of the phonon dispersions around $K$ point graphite by inelastic x-ray scattering is provided. present work resolves longstanding issue related to correct assignment transverse and longitudinal branches at $K$. We observe an almost degeneracy three TO, LA LO derived a strong trigonal warping. Correlation effects renormalize Kohn anomaly TO mode, which exhibits warping effect opposite that electronic band structure. determined electron--phonon coupling constant be...

Raman spectra of aluminum nitride (AlN) under pressure have been measured up to $25\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, i.e., beyond the onset wurtzite-to-rocksalt phase transition around $20\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. The experimental coefficients for all Raman-active modes wurtzite are reported and compared those obtained from ab initio lattice dynamical calculations, as well previous theoretical results. in wurtzite-type semiconductors (AlN, GaN, InN, ZnO, BeO),...

We present a detailed investigation of the dynamic structure factor $S(\mathbf{Q},\ensuremath{\omega})$ as well dielectric function ${\ensuremath{\epsilon}}_{\text{M}}(\mathbf{Q},\ensuremath{\omega})$ prototypical semiconductor silicon for finite momentum transfer, combining inelastic x-ray scattering measurements and ab initio calculations. show that, in contrast to optical spectra, time-dependent density-functional theory adiabatic local-density approximation (TDLDA) together with...

We present an experimental and theoretical investigation of the phonon dispersion relations in zinc blende (3C) SiC. The data were obtained for entire Brillouin zone by inelastic x-ray scattering (IXS) using a synchrotron radiation source. Eigenvector analysis is performed with aid state-of-the-art linear response first principles calculations based on density functional theory. predictions reproduce remarkably well. These results are compared previously 〈111〉 direction Raman spectroscopy...

During the past five years low-temperature heat capacity of simple semiconductors and insulators has received renewed attention. Of particular interest is its dependence on isotopic masses effect spin-orbit coupling in ab initio calculations. Here we concentrate lead chalcogenides PbS, PbSe, PbTe. These materials, with rock salt structure, have different natural isotopes for both cations anions; a fact that allows systematic experimental theoretical study effects, e.g., specific heat. Also,...

Achieving comprehensive information on thin film lattice dynamics so far has eluded well established spectroscopic techniques. We demonstrate here the novel application of grazing incidence inelastic x-ray scattering combined with ab initio calculations to determine complete elastic stiffness tensor, acoustic and low-energy optic phonon dispersion relations wurtzite indium nitride films. Indium is an especially relevant example, due technological interest for optoelectronic solar cell...

We report evidence of a nonadiabatic Kohn anomaly in boron-doped diamond, using joint theoretical and experimental analysis the phonon dispersion relations. demonstrate that standard calculations phonons density-functional perturbation theory are unable to reproduce relations high-energy measured by high-resolution inelastic x-ray scattering. On contrary, taking into account effects within many-body field-theoretic framework, we obtain excellent agreement with our data. This result indicates...

Abstract Considerable attention has been devoted recently to the dependence of widths Raman phonons semiconductors on pressure and isotopic mass. The is usually small monotonic unless phonon happens be close a singularity two‐phonon density states (DOS) which determines its width. In latter case, strong nonmonotonic dependences width mass can appear. We have investigated E 2 high ZnO crystals with different isotopes observed wide range FWHM depending masses. Ab initio calculations DOS...

The transverse-optic (TO) phonons of zinc-blende-type CuCl $(\ensuremath{\gamma}$-CuCl) and the longitudinal-optic (LO) $\ensuremath{\gamma}$-CuBr exhibit striking anharmonic self-energy anomalies at center Brillouin zone. We investigate here by Raman spectroscopy dependence LO TO $\ensuremath{\gamma}$-CuI on pressure, temperature, isotopic mass copper, in search for related effects. find that pressure phonon linewidth is qualitatively different low temperature close to room temperature. A...

The high-pressure phases of group-VI elements sulfur and selenium in their spiral chain ring structures are examined by situ Raman x-ray diffraction techniques combined with first principles electronic structure calculations. S-II, S-III, Se-I, Se-VII having S-VI a molecular six-member studied wide P-T range. square S-III is characterized seven modes that harden increasing pressure. calculations reproduce the observed frequencies allow authors to make mode assignment. "p-S" "hplt" reported...

We demonstrate that the valence energy-loss function of hexagonal boron nitride (hBN) displays a strong anisotropy in shape, excitation energy and dispersion for momentum transfer q parallel or perpendicular to hBN layers. This is manifested by e.g. an shift 0.7 eV cannot be captured single-particle approaches demonstration two-body electron-hole interaction. Furthermore, in-plane directions we observe splitting -plasmon M direction absent K this can traced back band-structure effects.

We report here on a polyamorphic-phase transition upon application of pressure Ce-based metallic glass, Ce${}_{70}$Al${}_{10}$Ni${}_{10}$Cu${}_{10}$, investigated by x-ray diffraction and inelastic scattering. This alloy is found to display strong hysteresis in volume per atom subsequent release pressure. The observed structural changes are correlated with scattering the elastic constants, acoustic mode frequencies, sound speed. results reported point toward three different amorphous phases...

We present an investigation of the dynamic structure factor and dielectric function ${\ensuremath{\epsilon}}_{M}(\mathbf{Q},\ensuremath{\omega})$ prototypical semiconductor silicon for finite momentum transfer, combining inelastic x-ray scattering experiments ab initio calculations. In contrast with optical spectra, transfer time-dependent density-functional theory in adiabatic local-density approximation together lifetime broadening describes physics valence excitations correctly. Major...