Search results for "Raman scattering"
showing 10 items of 284 documents
An interface effect in c-oriented (Y/Pr)Ba2Cu3O7 Superlattices: Raman scattering by ‘Forbidden’ phonons
1997
Abstract Raman results of ultrathin layer high Tc superlattices ( Y m Pr 1 )Ba2Cu3O7 (m = 2, 3, 4) exhibit a common feature: new peaks, absent in the bulk compounds. These peaks are attributed to oxygen B1u symmetry modes confined in the YBa2Cu3O7 layers. To explain their Raman activity a mechanism based on the asymmetry of crystal field at Y-Pr layer interfaces is proposed.
Raman scattering study of the anharmonic effects in CeO2−ynanocrystals
2007
We have studied the temperature dependence of the F2g Raman mode phonon frequency and broadening in CeO2−y nanocrystals. The phonon softening and phonon linewidth are calculated using a model which takes into account the three-and four-phonon anharmonic processes. A detailed comparison of the experimental data with theoretical calculations revealed the predominance of four-phonon anharmonic processes in the temperature dependence of the phonon energy and broadening of the nanocrystals. On the other hand, three-phonon processes dominate the temperature behavior of phonons in polycrystalline samples. The anti-Stokes/Stokes peak intensity ratio was also investigated and found to be smaller for…
Time resolved CARS measurements of I2 in solid Kr
2006
Dephasing is a central concept in condensed phase spectroscopy. It determines how long a system will maintain its coherence. The dephasing time of a system is determined by dynamic intermolecular interactions, and therefore measurements of dephasing time can provide information on interactions and couplings between a molecule and its environment. This chapter illustrates the application of the femtosecond coherent anti-Stokes Raman scattering (CARS) method to investigate the vibrational dephasing of I 2 in solid krypton. Dephasing of vibrational states between v = 2 and v = 16 is studied in the temperature range T = 2.6–32 K. The low vibrational states show dephasing times on the order of a…
Two-phonon magneto-Raman scattering in quantum wells: Fröhlich interaction
1996
We have developed a theoretical model of two-phonon resonant magneto-Raman scattering in a semiconductor quantum well (QW). Frohlich electron-phonon interaction has been considered and the corresponding selection rules are derived for Faraday geometry and backscattering configuration. The resonant profiles are analyzed as a function of magnetic field and laser energy. To simplify the discussion a three-band model with parabolic masses has been used as a first approach, studying later the role of heavy-hole light-hole admixture in the scattering process. It is shown that, due to mixing effects, Frohlich interaction contributes to the two-phonon Raman spectra in the parallel (z(σ ± , σ ± ) z)…
Two-LO-Phonon Resonant Raman Scattering in II-VI Semiconductors
1996
Recently, absolute values of socond-order Raman scattering efficiency have been measured around the E 0 and E 0 + Δ 0 critical points of several II-VI semiconductor compounds. The measurements were perfomed in the z(x,x)z backscattering configuration on (001) (ZnSe and ZnTe) and (110) (CdTe) surfaces. They show strong incoming and outgoing resonances around the baud gap and larger scattering efficiencies as compaered to III-V compounds. A theoretical model which includes excitons as intermediate states in the Raman process is shown to give a very good quantitative agreement between theory and experiment. Only a small discrepancy exists, while III-V compounds the discrepancies were close to …
Long-Range and Short-Range Structure of Proton-Conducting Y:BaZrO3
2011
Yttrium-doped barium zirconate (BZY) is the most promising candidate for proton-conducting ceramics and has been extensively studied in recent years. The detailed features of the crystal structure, both short-range and long-range, as well as the crystal chemistry driving the doping process, are largely unknown. We use very high resolution X-ray diffraction (HR-XRD) to resolve the crystal structure, which is very slightly tetragonally distorted in BZY, while the local environment around Zr4+ and Y3+ is probed with extended X-ray absorption fine structure (EXAFS), and the symmetry and vibrations are investigated by using Raman spectroscopy. It is found that barium zirconate shows some degree …
Femtosecond coherent anti-Stokes Raman-scattering polarization beat spectroscopy of I2–Xe complex in solid krypton
2006
Time-resolved coherent anti-Stokes Raman-scattering (CARS) measurements are carried out to study the interaction between xenon atom and iodine molecule in a solid krypton matrix. Interference between the CARS polarizations of the "free" and complexed iodine molecules is observed, while the quantum beats of the complex are not detected due to low concentration. Vibrational analysis based on the polarization beats yields accurate molecular constants for the I2-Xe complex. The harmonic frequency of the I2-Xe complex is found to be redshifted by 0.90 cm-1 when compared to the free I2, whereas the anharmonicity is approximately the same. The dephasing rate of the complex is found to be somewhat …
Thermodynamic approach of supercontinuum generation
2009
International audience; This paper is aimed at providing an overview on recent theoretical and experimental works in which a thermodynamic description of the incoherent regime of supercontinuum generation has been formulated. On the basis of the wave turbulence theory, we show that this highly nonlinear and quasi-continuous-wave regime of supercontinuum generation is characterized by two different phenomena. (i) A process of optical wave thermalization ruled by the four-wave mixing effects: The spectral broadening inherent to supercontinuum generation is shown to result from the natural tendency of the optical field to reach its thermodynamic equilibrium state, i. e., the state of maximum n…
Vibrational Properties of InSe under Pressure: Experiment and Theory
1996
The pressure dependence of the phonon modes in the layered semiconductor γ-InSe has been investigated experimentally and theoretically for pressures up to 11 GPa. The mode Gruneisen parameters of all Raman-active zone-center phonons have been determined by Raman scattering under pressure. In addition, features corresponding to second and third-order scattering processes are apparent in the Raman spectra under resonance conditions, from which information about zone-edge modes can be obtained. For the assignment of the observed Raman features to vibrational modes we have calculated the phonon dispersion curves using a rigid-ion model including couplings to first-nearest neighbors and long-ran…
Structural, vibrational and electrical study of compressed BiTeBr
2016
Compresed BiTeBr has been studied from a joint experimental and theoretical perspective. Room-temperature x-ray diffraction, Raman scattering, and transport measurements at high pressures have been performed in this layered semiconductor and interpreted with the help of ab initio calculations. A reversible first-order phase transition has been observed above 6–7 GPa, but changes in structural, vibrational, and electrical properties have also been noted near 2 GPa. Structural and vibrational changes are likely due to the hardening of interlayer forces rather than to a second-order isostructural phase transition while electrical changes are mainly attributed to changes in the electron mobilit…