Effects of Surface Stress on the Phonon Properties in GaN Nanofilms

2015 ◽  
Vol 82 (11) ◽  
Author(s):  
Haonan Luo ◽  
Linli Zhu
Keyword(s):  
Group Velocity ◽  
Surface Stress ◽  
Opposite Effect ◽  
Phonon Dispersion ◽  
Density Of State ◽  
Average Group ◽  
Calculation Results ◽  
Negative Surface ◽  
Phonon Properties ◽  
Confined Phonons

This work investigates the phonon properties such as phonon dispersion relation, average group velocity, and phonon density of state (DOS) theoretically in GaN nanofilm under various surface stress fields. By taking into account of the surface energy effects, the elasticity theory is presented to describe the confined phonons of nanofilms with different surface stresses. The calculation results show that the influence of surface stress on the phonon properties depends on the thickness of nanofilm. The negative surface stress leads to a higher average group velocity and corresponding lower phonon DOS. The positive surface stress has the opposite effect. The significant modification of thermal properties, e.g., phonon thermal conductivity, in GaN nanofilms is mostly stemmed from the change of phonon average group velocity and DOS by surface stress. These results suggest that the thermal or electrical properties in GaN nanofilms could be enhanced or reduced by tuning the surface stress acting on the films.

AB INITIO STUDY OF PHONON DISPERSION AND ELASTIC PROPERTIES OF L12 INTERMETALLICS Ti3Al AND Y3Al

2013 ◽  
Vol 27 (30) ◽  
pp. 1350224 ◽  
Author(s):  
N. ARIKAN ◽  
M. ERSEN ◽  
H. Y. OCAK ◽  
A. İYIGÖR ◽  
A. CANDAN ◽  
...  
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Phonon Dispersion ◽  
High Symmetry ◽  
Generalized Gradient ◽  
Pressure Derivative ◽  
Phonon Dispersion Curves ◽  
Lattice Constants ◽  
Density Functional Perturbation Theory ◽  
Phonon Properties

In this paper, the structural, elastic and phonon properties of Ti 3 Al and Y 3 Al in L1 2( Cu 3 Al ) phase are studied by performing first-principles calculations within the generalized gradient approximation. The calculated lattice constants, static bulk moduli, first-order pressure derivative of bulk moduli and elastic constants for both compounds are reported. The phonon dispersion curves along several high-symmetry lines at the Brillouin zone, together with the corresponding phonon density of states, are determined using the first-principles linear-response approach of the density functional perturbation theory. Temperature variations of specific heat in the range of 0–500 K are obtained using the quasi-harmonic model.

The Chemical Bonding of Organic-Inorganic in Hybrid Compounds

2004 ◽  
Vol 848 ◽  
Author(s):  
Yadong Dai ◽  
Liling Guo ◽  
Minjie Hu ◽  
Kunyu Shi ◽  
Xinmin Min ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Energy Density ◽  
Chemical Bonding ◽  
Fermi Energy ◽  
Energy Band Structure ◽  
Bond Orders ◽  
Density Of State ◽  
Hybrid Compound ◽  
Hybrid Compounds ◽  
Calculation Results

ABSTRACTAs has been discussed, research on the electronic structure between organic and inorganic atoms in hybrid compounds has become important. In our study, DV—Xα method was employed to calculate the electronic structure of the hybrid compound. The information obtained from the calculation included orbit charge, bonding order, Fermi energy, density of the state, etc. The influence of organic and inorganic parts on the energy band structure of the hybrid compound was discussed based on the calculation results of Fermi energy and density of state. The chemical bonding between organic and inorganic parts in the hybrid compound was also analyzed in detail according to the orbital charges and bond orders.

Mode-Wise Phonon Properties of Bismuth Telluride

2012 ◽  
Author(s):  
Yaguo Wang ◽  
Xianfan Xu
Keyword(s):  
Bismuth Telluride ◽  
Thermal Transport ◽  
Phonon Dispersion ◽  
Normal Mode Analysis ◽  
Relaxation Times ◽  
Mode Analysis ◽  
Phonon Modes ◽  
Time Resolved ◽  
Transport Control ◽  
Phonon Properties

Thermal transport properties and thermal transport control are important for many materials, for example, low thermal conductivity is desirable for thermoelectric materials. Knowledge of mode-wise phonon properties is crucial to identify dominant phonon modes for thermal transport and design effective phonon barriers for thermal transport control. In this paper, we adopt the normal mode analysis to investigate spectral phonon properties, and to calculate phonon dispersion relations and phonon relaxation times in bismuth telluride. Our results agree with previously reported data for long-wavelength longitudinal acoustic phonon and A1g optical phonon obtained from ultrafast time-resolved measurements. By combing the frequency dependent anharmonic phonon group velocities and lifetime, mode-wise thermal conductivities are predicted to reveal the contributions of heat carriers with different polarizations and wavelength.

LATTICE DYNAMICS OF MBa2Cu3O7(M=Y, Gd) and YBa2Cu3O6

1989 ◽  
Vol 03 (08) ◽  
pp. 1277-1286 ◽  
Author(s):  
JIE QIN ◽  
YIMIN JIANG
Keyword(s):  
Density Of States ◽  
Phonon Dispersion ◽  
Experimental Investigations ◽  
Phonon Density ◽  
Phonon Density Of States ◽  
Phonon Dispersion Curves ◽  
Rare Earth Atom ◽  
Range Overlap ◽  
Phonon Properties ◽  
Good Agreement

We have presented a lattice dynamical calculation of phonon dispersion curves and one-phonon density of states for the high-T c superconducting MBa 2 Cu 3 O x (M=Y, Gd : x=7, 6) compounds. The model we used is in the framework of a rigid-ion model which includes long-range Coulomb potential and a short-range overlap. The results of calculation give quite good agreement with the available Raman and infrared data, and the measurements of phonon density of states. These results therefore can serve as a guide for further experimental investigations of the phonon properties in M-Ba-Cu-O (M=rare earth atom) system.

Mode-Wise Thermal Conductivity of Bismuth Telluride

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Yaguo Wang ◽  
Bo Qiu ◽  
Alan J. H. McGaughey ◽  
Xiulin Ruan ◽  
Xianfan Xu
Keyword(s):  
Thermal Conductivity ◽  
Bismuth Telluride ◽  
Thermal Transport ◽  
Phonon Dispersion ◽  
Relaxation Times ◽  
Phonon Modes ◽  
Time Resolved ◽  
Transport Control ◽  
Reported Data ◽  
Phonon Properties

Thermal properties and transport control are important for many applications, for example, low thermal conductivity is desirable for thermoelectrics. Knowledge of mode-wise phonon properties is crucial to identify dominant phonon modes for thermal transport and to design effective phonon barriers for thermal transport control. In this paper, we adopt time-domain (TD) and frequency-domain (FD) normal-mode analyses to investigate mode-wise phonon properties and to calculate phonon dispersion relations and phonon relaxation times in bismuth telluride. Our simulation results agree with the previously reported data obtained from ultrafast time-resolved measurements. By combining frequency-dependent anharmonic phonon group velocities and lifetimes, mode-wise thermal conductivities are predicted to reveal the contributions of heat carriers with different wavelengths and polarizations.

Electron–Phonon Interaction Model and Prediction of Thermal Energy Transport in SOI Transistor

2007 ◽  
Vol 7 (11) ◽  
pp. 4094-4100 ◽  
Author(s):  
Jae Sik Jin ◽  
Joon Sik Lee
Keyword(s):  
Energy Density ◽  
Group Velocity ◽  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Dispersion Model ◽  
Hot Spot ◽  
Interaction Model ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Electron Phonon Scattering

An electron–phonon interaction model is proposed and applied to thermal transport in semiconductors at micro/nanoscales. The high electron energy induced by the electric field in a transistor is transferred to the phonon system through electron–phonon interaction in the high field region of the transistor. Due to this fact, a hot spot occurs, which is much smaller than the phonon mean free path in the Si-layer. The full phonon dispersion model based on the Boltzmann transport equation (BTE) with the relaxation time approximation is applied for the interactions among different phonon branches and different phonon frequencies. The Joule heating by the electron–phonon scattering is modeled through the intervalley and intravalley processes for silicon by introducing average electron energy. The simulation results are compared with those obtained by the full phonon dispersion model which treats the electron–phonon scattering as a volumetric heat source. The comparison shows that the peak temperature in the hot spot region is considerably higher and more localized than the previous results. The thermal characteristics of each phonon mode are useful to explain the above phenomena. The optical mode phonons of negligible group velocity obtain the highest energy density from electrons, and resides in the hot spot region without any contribution to heat transport, which results in a higher temperature in that region. Since the acoustic phonons with low group velocity show the higher energy density after electron–phonon scattering, they induce more localized heating near the hot spot region. The ballistic features are strongly observed when phonon–phonon scattering rates are lower than 4 × 1010 s−1.

Electron–Phonon Interaction Model and Prediction of Thermal Energy Transport in SOI Transistor

2007 ◽  
Vol 7 (11) ◽  
pp. 4094-4100
Author(s):  
Jae Sik Jin ◽  
Joon Sik Lee
Keyword(s):  
Energy Density ◽  
Group Velocity ◽  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Dispersion Model ◽  
Hot Spot ◽  
Interaction Model ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Electron Phonon Scattering

An electron–phonon interaction model is proposed and applied to thermal transport in semiconductors at micro/nanoscales. The high electron energy induced by the electric field in a transistor is transferred to the phonon system through electron–phonon interaction in the high field region of the transistor. Due to this fact, a hot spot occurs, which is much smaller than the phonon mean free path in the Si-layer. The full phonon dispersion model based on the Boltzmann transport equation (BTE) with the relaxation time approximation is applied for the interactions among different phonon branches and different phonon frequencies. The Joule heating by the electron–phonon scattering is modeled through the intervalley and intravalley processes for silicon by introducing average electron energy. The simulation results are compared with those obtained by the full phonon dispersion model which treats the electron–phonon scattering as a volumetric heat source. The comparison shows that the peak temperature in the hot spot region is considerably higher and more localized than the previous results. The thermal characteristics of each phonon mode are useful to explain the above phenomena. The optical mode phonons of negligible group velocity obtain the highest energy density from electrons, and resides in the hot spot region without any contribution to heat transport, which results in a higher temperature in that region. Since the acoustic phonons with low group velocity show the higher energy density after electron–phonon scattering, they induce more localized heating near the hot spot region. The ballistic features are strongly observed when phonon–phonon scattering rates are lower than 4 × 1010 s−1.

Phonons in SiC from INS, IXS, and Ab-Initio Calculations

2006 ◽  
Vol 527-529 ◽  
pp. 689-694 ◽  
Author(s):  
Dieter Strauch ◽  
B. Dorner ◽  
A.A. Ivanov ◽  
M. Krisch ◽  
J. Serrano ◽  
...  
Keyword(s):  
Density Functional ◽  
Phonon Dispersion ◽  
Inelastic Neutron ◽  
First Principles Calculations ◽  
Phonon Dispersion Curves ◽  
Functional Methods ◽  
X Ray Scattering ◽  
Density Functional Perturbation Theory ◽  
Phonon Properties

Preliminary results for the phonon dispersion curves of hexagonal 4H-SiC from experimental inelastic neutron (INS) and X-ray scattering (IXS) are reported and contrasted with those of cubic 3C-SiC and silicon. The experimental frequencies and scattering intensities are in excellent agreement with those from first-principles calculations using density-functional methods. The relative merits of the two experimental techniques and aspects of the density functional perturbation theory and the so-called frozen phonon method for the determination of the basic phonon properties are briefly outlined.

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