Search results for "Phonon"
showing 10 items of 466 documents
Electronic cooling and hot electron effects in heavily doped silicon-on-insulator film
2004
The influence of carrier concentration in silicon-on-insulator film on the thermal characteristics of semiconductor and performance of the superconductor-semiconductor-superconductor micro-coolers have been investigated at sub kelvin temperatures. The overheating of the lattice in heavily doped silicon film must be taken into account in the analysis of electron-phonon coupling experiment and operation of the cooler device. The heat flow between electrons and phonons in heavily doped silicon films is found to be proportional to T6, which is in accordance with theoretical prediction for dirty limit. Increasing the doping level in the semiconductor considerably increases both the efficiency of…
Temperature-dependent resistivity and anomalous Hall effect in NiMnSb from first principles
2019
We present implementation of the alloy analogy model within fully relativistic density-functional theory with the coherent potential approximation for a treatment of nonzero temperatures. We calculate contributions of phonons and magnetic and chemical disorder to the temperature-dependent resistivity, anomalous Hall conductivity (AHC), and spin-resolved conductivity in ferromagnetic half-Heusler NiMnSb. Our electrical transport calculations with combined scattering effects agree well with experimental literature for Ni-rich NiMnSb with 1--2% Ni impurities on Mn sublattice. The calculated AHC is dominated by the Fermi surface term in the Kubo-Bastin formula. Moreover, the AHC as a function o…
Phonon dispersion in GaN/AlN non‐polar quantum wells: confinement and anisotropy
2007
We have calculated the phonon dispersion relations in a non-polar GaN/AlN quantum well within the dielectric continuum model and making use of Loudon's model of uniaxial crystals. Due to the strong in-plane anisotropy of this orientation, we have found that in general ordinary and extraordinary phonons are not decoupled. In this work we analyze the conditions for the occurrence of interface modes. In these novel heterostructures there is an added dependence of the phonon dispersion on the orientation of the in-plane phonon wavevector, which allows the existence of interface phonons at energies forbidden in the better known polar structures. Under particular circumstances the vibrations exci…
Fast Local Motion around T g in a Molecular Glass as Observed by Incoherent Neutron Scattering
1987
Incoherent quasi-elastic neutron scattering experiments on a molecular glass (1,3,5-tri-α-naphtylbenzene, C36H24) are reported. We find clear evidence for an anomalously strong decrease of the elastic and a corresponding increase of the inelastic scattering around the glass transition temperature. The line shape of this extra inelastic intensity gives evidence for a quasi-elastic scattering implying the existence of a localized and fast (τc ≈ 4.10-12s) molecular motion. From the elastic incoherent structure factor (EISF) a mean jump length ≤ 0.6 A is estimated. The significance of this motion as precursor of the glass instability is discussed within the framework of dynamic glass transition…
Phonon contribution to the absorption of ultrasound in amorphous solids at moderately low temperatures
1998
Abstract Sound absorbtion in amorphous solids is considered to be due to the scattering of sound waves from the thermal phonons. It is shown that the dependence of the absorption coefficient on the temperature displays a maximum in the interval 10≲T≲100 K . The frequency dependence of the absorption coefficient is investigated. Numerical calculations for amorphous Mg and Zn illustrate the theoretical results.
Amorphous polymorphis in ice investigated by inelastic neutron scattering
1997
Abstract High-density Ilda and low-density Ilda amorphous have been investigated by inelastic neutron scattering (INS) with emphasis on the energy window from 0.5 to 20 meV. At variance with earlier measurements the spectra in the Ilda phase show a simple ω2 behaviour in the acoustic region and the temperature dependence is found to be harmonic. Ilda converts with a strongly temperature-dependent rate towards Ilda ice. We have investigated in detail the time evolution of both the static and dynamic response functions at several temperatures. Elastic small-angle signals indicate the presence of strong heterogeneties at the early stages of the conversion process. At least two different time s…
Isotopic Effect In Extended X-Ray-Absorption Fine Structure of Germanium
2008
Extended x-ray absorption fine structure has been measured on two powdered samples of 70Ge and 76Ge as a function of temperature from 20 to 300 K. The effect of isotopic mass difference on the amplitude of relative atomic vibrations is neatly evidenced by the temperature dependence of the difference of Debye-Waller factors. The isotopic effect is also detected on the difference of nearest-neighbor average ineratomic distances, thanks to a resolution better than 10 fm. (DOI: 10.1103/PhysRevLett.100.055901)
Temperature Effects on the Phonon Spectrum in YBa2Cu3O7 Single Crystals and Thin Films
1989
We have performed a detailed investigation of the temperature dependence of the 385cm-1 phonon in single crystals and thin films of the YBa2Cu3O7 superconductor by means of Raman spectroscopy. In the single crystal the frequency of this phonon shows a downshift of about 5 cm-1 on passing the superconducting transition from above, which is referred to a strong electron-phonon interaction in the superconductor. The shift of the phonon in thin epitaxial films on MgO or SrTiO3 substrates is only about 2.5 cm-1. This difference may be a result of a structural transition in the single crystal which is possibly suppressed in the films because of the epitaxy. The electron-phonon interaction is also…
Pressure dependence of the refractive index in wurtzite and rocksalt indium nitride
2014
We have performed high-pressure Fourier transform infrared reflectance measurements on a freestanding InN thin film to determine the refractive index of wurtzite InN and its high-pressure rocksalt phase as a function of hydrostatic pressure. From a fit to the experimental refractive-index curves including the effect of the high-energy optical gaps, phonons, free carriers, and the direct (fundamental) band-gap in the case of wurtzite InN, we obtain pressure coefficients for the lowfrequency (electronic) dielectric constant e1 . Negative pressure coefficients of -8.8 × 10-2 GPa-1 and -14.8 × 10-2 GPa-1 are obtained for the wurtzite and rocksalt phases, respectively. The results are discussed …
Phonon Bridge Effect in Superlattices of Thermoelectric TiNiSn/HfNiSn With Controlled Interface Intermixing
2020
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