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Phonon Densities (phonon + density)
Selected AbstractsThermal conductance of the AlN/Si and AlN/SiC interfaces calculated with taking into account the detailed phonon spectra of the materials and the interface conditionsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2010M. Kazan Abstract We present a calculation of the thermal conductance (TC) of the interface between aluminium nitride (AlN) and silicon (Si) and that between AlN and silicon carbide (SiC) with taking into account the detailed phonon spectra of the materials, as obtained from first principles calculations, and the interface conditions. On the basis of the results obtained, we discuss the relation between the interface TC, the interface conditions, and the mismatches between the acoustic waves velocities and the phonon densities of states of the materials in contact. Our calculation method is expected to provide a reliable tool for thermal management strategy, independently from the substrate choice (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature-dependent Debye,Waller factors for semiconductors with the wurtzite-type structureACTA CRYSTALLOGRAPHICA SECTION A, Issue 3 2009M. Schowalter We computed Debye,Waller factors in the temperature range from 0.1 to 1000,K for AlN, GaN, InN, ZnO and CdO with the wurtzite-type structure. The Debye,Waller factors were derived from phonon densities of states obtained from Hellmann,Feynman forces computed within the density-functional-theory formalism. The temperature dependences of the Debye,Waller factors were fitted and fit parameters are given. [source] Computation and parametrization of the temperature dependence of Debye,Waller factors for group IV, III,V and II,VI semiconductorsACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2009M. Schowalter We calculated the temperature dependence of the Debye,Waller factors for a variety of group IV, III,V and II,VI semiconductors from 0.1 to 1000,K. The approach used to fit the temperature dependence is described and resulting fit parameters are tabulated for each material. The Debye,Waller factors are deduced from generalized phonon densities of states which were derived from first principles using the WIEN2k and the ABINIT codes. [source] Effects of Phonon Confinement on Anomalous Thermalization, Energy Transfer, and Upconversion in Ln3+ -Doped Gd2O3 NanotubesADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Andreia G. Macedo Abstract There is a growing interest in understanding how size-dependent quantum confinement affects the photoluminescence efficiency, excited-state dynamics, energy-transfer and thermalization phenomena in nanophosphors. For lanthanide (Ln3+)-doped nanocrystals, despite the localized 4f states, confinement effects are induced mostly via electron,phonon interactions. In particular, the anomalous thermalization reported so far for a handful of Ln3+ -doped nanocrystals has been rationalized by the absence of low-frequency phonon modes. This nanoconfinement may further impact on the Ln3+ luminescence dynamics, such as phonon-assisted energy transfer or upconversion processes. Here, intriguing and unprecedented anomalous thermalization in Gd2O3:Eu3+ and Gd2O3:Yb3+,Er3+ nanotubes, exhibiting up to one order of magnitude larger than previously reported for similar materials, is reported. This anomalous thermalization induces unexpected energy transfer from Eu3+C2 to S6 crystallographic sites, at 11,K, and 2H11/2,,,4I15/2 Er3+ upconversion emission; it is interpreted on the basis of the discretization of the phonon density of states, easily tuned by varying the annealing temperature (923,1123,K) in the synthesis procedure, and/or the Ln3+ concentration (0.16,6.60%). [source] Moments of phonon density of states spectra and characteristic phonon temperatures of wide band gap materialsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2006Roland Pässler Abstract We have re-digitized a variety of phonon density of states (PDOS) spectra, that have been published by different researchers for the wide band gap materials diamond, SiC, BN, AlN, GaN, ZnO, ZnS, and ZnSe, including calculations of the respective first- and second-order moments. Notwithstanding the obvious differences in concrete shapes of spectra presented for one and the same material by different authors, the respective magnitudes of estimated moments have been found in most cases to be nearly the same (to within uncertainties of some few%). Anticipated differences between phonon temperatures, ,eff, that are effective in controlling the observable temperature dependences of fundamental energy gaps and the respective average phonon temperatures, ,P, are seen to be throughout smaller than ±10%. The estimated high-temperature limits of Debye temperatures, ,D(,), are found to be significantly higher (by factors of order 1.4) than ,P. As a remarkable heuristic finding revealed by our numerical and analytical studies we can further state that, for SiC, AlN, GaN, ZnO, ZnS, and ZnSe, the individual ,D(,) values are nearly equal (within ±5%) to the respective average optical (LO/TO) phonon temperatures pertaining to the upper sections of the corresponding PDOS spectra. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||