Influence of Prestress Fields on the Phonon Thermal Conductivity of GaN Nanostructures

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
Linli Zhu ◽  
Haihui Ruan
Keyword(s):  
Thermal Conductivity ◽  
Phonon Dispersion ◽  
Electronic Devices ◽  
Phonon Modes ◽  
Phonon Thermal Conductivity ◽  
Phonon Group Velocity ◽  
Strain Stress ◽  
Theoretical Results ◽  
Phonon Properties ◽  
Phonon Dispersion Relations

The phonon thermal conductivity of Gallium nitride (GaN) nanofilms and nanowires under prestress fields are investigated theoretically. In the framework of elasticity theory, the phonon dispersion relations of spatially confined GaN nanostructures are achieved for different phonon modes. The acoustoelastic effects stemmed from the preexisting stresses are taken into account in simulating the phonon properties and thermal conductivity. Our theoretical results show that the prestress fields can alter the phonon properties such as the phonon dispersion relation and phonon group velocity dramatically, leading to the change of thermal conductivity in GaN nanostructures. The phonon thermal conductivity is able to be enhanced or reduced through controlling the directions of prestress fields operated on the GaN nanofilms and nanowires. In addition, the temperature and size-dependence of thermal conductivity of GaN nanostructures will be sensitive to the direction and strength of those prestress fields. This work will be helpful in controlling the phonon thermal conductivity based on the strain/stress engineering in GaN nanostructures-based electronic devices and systems.

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.

Impact of surface bond-order loss on phonon dispersion relations and thermal conductivity of cylindrical Si nanowires

2006 ◽  
Vol 74 (15) ◽  
Author(s):  
T. C. Au Yeung ◽  
M. X. Gu ◽  
Chang Q. Sun ◽  
George C. K. Chen ◽  
D. W. K. Wong ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Bond Order ◽  
Phonon Dispersion ◽  
Dispersion Relations ◽  
Si Nanowires ◽  
Surface Bond ◽  
Phonon Dispersion Relations

Strain engineering of phonon thermal transport properties in monolayer 2H-MoTe2

2017 ◽  
Vol 19 (47) ◽  
pp. 32072-32078 ◽  
Author(s):  
Aamir Shafique ◽  
Young-Han Shin
Keyword(s):  
Thermal Conductivity ◽  
First Principles ◽  
Lattice Thermal Conductivity ◽  
Boltzmann Transport Equation ◽  
Strain Engineering ◽  
First Principles Calculations ◽  
Boltzmann Transport ◽  
Phonon Group Velocity ◽  
Phonon Lifetime ◽  
Phonon Properties

The effect of strain on the phonon properties such as phonon group velocity, phonon anharmonicity, phonon lifetime, and lattice thermal conductivity of monolayer 2H-MoTe2is studied by solving the Boltzmann transport equation based on first principles calculations.

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.

Numerical Calculation for Phonon Properties of a Nano-Porous Si

2009 ◽  
Author(s):  
Koji Miyazaki ◽  
Daisuke Nagai ◽  
Yohei Kido ◽  
Hiroshi Tsukamoto
Keyword(s):  
Thermal Conductivity ◽  
Fourier Transform ◽  
Dispersion Curve ◽  
Phonon Dispersion ◽  
Mean Free Path ◽  
Atomic Scale ◽  
Phonon Modes ◽  
Velocity Correlation ◽  
Nano Structure ◽  
Time Space

We carried out molecular dynamics simulations (MD) of heat conduction in Si with a nano-hole to represent the nano-structure, in order to investigate the mechanism of the thermal conductivity reduction of nano-structured materials. The Stillinger-Weber potential is used in this study. The temperature is kept constant at 300K by velocity scaling. Periodic boundary conditions are applied in the x, y and z directions. Phonon dispersion curves are calculated by using the time-space 2D Fourier transform. The phonon group velocity is calculated from the slope of the dispersion curve. The velocity is reduced by nano-holes, even if those are random. Phonon mean free path can be evaluated from the width of dispersion curve, and the long waves are clearly scattered by nano-holes. Phonon density of states (DOS) is also calculated by the Fourier transform of a velocity correlation. The DOS of Si with periodic nano-holes are slightly smaller than that of a single crystal Si. In other words, the specific heat is reduced by periodic nano-holes due to the reduced phonon modes. We discuss the mechanism of the reduction of the thermal conductivity of nano-porous material on the atomic scale.

Micro- and Nanoscale Phonon Heat Transport in Silicon

Volume 4 ◽  
2004 ◽  
Author(s):  
Y. Ju
Keyword(s):  
Thermal Conductivity ◽  
Silicon Nanowires ◽  
Phonon Dispersion ◽  
Transport Model ◽  
Phonon Transport ◽  
Conductivity Data ◽  
Phonon Modes ◽  
Conductivity Model ◽  
Thermal Conductivity Data ◽  
Thermal Conductivity Model

Micro- and nanoscale energy transport in semiconductors is one of the critical research areas for emerging nano-electronics. Key features of phonon dispersion curves are re-examined, which motivates the use of phonon density of states obtained from ab initio calculations as a basis for constructing a semi-phenomenological thermal conductivity model. Thermal conductivity data on silicon nanowires are analyzed to identify dominant phonon modes. The consistency of the present thermal conductivity model is examined by comparing its prediction with the thermal conductivity data from bulk germanium samples with controlled amount of point defects. The thermal conductivity modeling study provides input parameters for a two-fluid phonon transport model for silicon and related semiconductors, which can play an important role in computer aided design of nanoelectronic devices and simulation of ultra-fast phenomena.

Phononic Engineering for Hot Carrier Solar Cells

2012 ◽  
pp. 214-242
Author(s):  
Sana Laribi ◽  
Arthur Le Bris ◽  
Lun Mei Huang ◽  
Par Olsson ◽  
Jean Francois Guillemoles
Keyword(s):  
Solar Cells ◽  
Solar Cell ◽  
Phonon Dispersion ◽  
Dispersion Relations ◽  
Phonon Modes ◽  
Nano Structure ◽  
Hot Carrier ◽  
Phonon Bottleneck ◽  
Nano Structures ◽  
Phonon Dispersion Relations

In this chapter, the authors first analyse the operation of a hot carrier solar cell and lay down the general principles. They then discuss the opportunity of phonon engineering to improve the phonon bottleneck. Finally, they present how these can be modeled in nanostuctures comprising several thousand atoms, where true 3D phonon dispersion relations for Si-Ge nano-structures are obtained using first principles methods. The effects of the nano-structure size and geometry on the phonon dispersion relations are investigated. The possible phonon decay processes in the nano-structures are discussed and compared with the bulk crystal materials. The performance of calculated nano-structures on the hot carrier solar cell is evaluated with the acquired knowledge of phonon modes.

The Phonon Thermal Conductivity of a Single-Layer Graphene From Complete Phonon Dispersion Relations

2010 ◽  
Author(s):  
Yunfeng Gu ◽  
Zhonghua Ni ◽  
Minhua Chen ◽  
Kedong Bi ◽  
Yunfei Chen
Keyword(s):  
Thermal Conductivity ◽  
Acoustic Phonon ◽  
Phonon Scattering ◽  
Phonon Dispersion ◽  
Single Layer ◽  
Single Layer Graphene ◽  
Optical Phonons ◽  
Relaxation Rates ◽  
Phonon Thermal Conductivity ◽  
Transverse Acoustic

In this paper, the phonon scattering mechanisms of a single layer graphene are investigated based on the complete phonon dispersion relations. According to the selection rules that a phonon scattering process should obey the energy and momentum conservation conditions, the relaxation rates of combing and splitting Umklapp processes can be calculated by integrating the intersection lines between different phonon mode surfaces in the phonon dispersion relation space. The dependence of the relaxation rates on the wave vector directions is presented with a three dimensional surfaces over the first Brillion zone. It is found that the reason for the optical phonons contributing a little to heat transfer is attributed to the strong Umklapp processes but not to their low group velocities. The combing Umklapp scattering processes involved by the optical phonons mainly decrease the acoustic phonon thermal conductivity, while the splitting Umklapp scattering processes of the optical phonons mainly restrict heat conduction by the optical phonons themselves. Neglecting the splitting processes, the optical phonons can contribute more energy than that carried by the acoustic phonons. Based on the calculated phonon relaxation time, the thermal conductivities contributed from different mode phonons can be evaluated. At low temperatures, both longitudinal and in-plane transverse acoustic phonon thermal conductivities have T2 temperature dependence, and the out-of-plane transverse acoustic phonon thermal conductivity is proportion to T3/2. At room temperature, the calculated thermal conductivity is on the order of a few thousands W/m.K depending on the sample size and the edge roughness, which is in agreement with the recently measured data.

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