scholarly journals Nanotube heat conductors under tensile strain: Reducing the three-phonon scattering strength of acoustic phonons

2021 ◽  
Vol 104 (7) ◽  
Author(s):  
Daniel Bruns ◽  
Alireza Nojeh ◽  
A. Srikantha Phani ◽  
Jörg Rottler
Keyword(s):  
Tensile Strain ◽  
Phonon Scattering ◽  
Acoustic Phonons ◽  
Scattering Strength

Phonon Scattering in Bi2Te3/Sb2Te3 Superlattice

2011 ◽  
Author(s):  
Yaguo Wang ◽  
Xianfan Xu ◽  
Rama Venkatasubramanian
Keyword(s):  
Thermal Conductivity ◽  
Thermoelectric Materials ◽  
Phonon Scattering ◽  
Quantum Confinement Effect ◽  
Theoretical Models ◽  
Heat Transfer Process ◽  
Acoustic Phonons ◽  
Time Resolved ◽  
Hetero Structure ◽  
Phonon Velocity

Thermoelectric materials are characterized with the figure of merit, ZT = S2σT/κ, where T is the temperature, S the Seebeck coefficient, σ the electrical conductivity and κ the thermal conductivity. Many researches have been focused on reducing lattice thermal conductivity through increasing phonon scattering at interfaces. Thin-film superlattices are one of the promising candidates for high ZT thermoelectric materials. Several theoretical models have been used to explain the large ZT in superlattice. One comes from the extra scattering channels at interfaces introduced by the hetero-structure. Another is a result of quantum confinement effect which reduces the phonon group velocity propagating perpendicularly through the superlattice layers through flattening the dispersion curve of acoustic phonons. In this work, ultrafast time-resolved measurements were conducted on Bi2Te3, Sb2Te3 and Bi2Te3/Sb2Te3 superlattice (SL) films to detect coherent acoustic phonons in these materials. Scattering of these phonons is revealed in the Bi2Te3/Sb2Te3 SLs, which comes from the interfaces of the hetero-structure in SL. Also, a decrease of acoustic phonon velocity resulted from folding and flattening of phonons branches is observed. Results show that both interface scattering and the reduced phonon velocity contribute to suppressing the heat transfer process.

Phonon Scattering in Bi2Te3/Sb2Te3 Superlattice

2012 ◽  
Author(s):  
Yaguo Wang ◽  
Carl Liebig ◽  
Xianfan Xu ◽  
Rama Venkatasubramanian
Keyword(s):  
Heat Transport ◽  
Acoustic Phonon ◽  
Phonon Scattering ◽  
Scattering Mechanism ◽  
Acoustic Phonons ◽  
Time Resolved ◽  
Interface Scattering ◽  
Phonon Folding ◽  
Phonon Velocity ◽  
Time Resolved Measurements

Ultrafast time-resolved measurements were conducted to investigate scattering mechanism of coherent optical and acoustic phonons in Bi2Te3, Sb2Te3 and Bi2Te3/Sb2Te3 superlattice (SL) films. Strong phonon scatterings in the Bi2Te3/Sb2Te3 SLs are attributed to the interfaces of their hetero-structures. Moreover, decreases of acoustic phonon velocity are observed in SLs, coming from phonon folding and softening. Our results show that both the enhanced interface scattering and the reduced phonon velocity contribute to suppressing the heat transport in SLs.

Modeling of Strain-Induced Phonon Thermal Conductivity Reduction in Thermoelectric Nanocomposites

2008 ◽  
Author(s):  
Yaoyao Xu ◽  
Gang Li
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Lattice Dynamics ◽  
Tensile Strain ◽  
Phonon Scattering ◽  
Mean Free Path ◽  
Nanocomposite Material ◽  
Phonon Thermal Conductivity ◽  
Strain Effects ◽  
Strain Dependent

In this paper, we study strain effects on the phonon thermal conductivity of 2-D Si/Ge nanocomposites. Lattice dynamics is employed for the calculation of the phonon scattering properties as a function of strain. Cauchy-Born rule is used to model the deformed configuration of the atoms. The effective thermal conductivity of the nanocomposite material is modeled by using a modified effective medium approximation (EMA) approach. The strain effects are incorporated into the modified EMA through the strain dependent phonon mean free path. The effective thermal conductivity of the strained nanocomposite material is calculated for different characteristic lengths of the Si component. The results show that a 2% tensile strain can reduce the effective thermal conductivity by more than 10%.

scholarly journals Giant isotope effect on phonon dispersion and thermal conductivity in methylammonium lead iodide

2020 ◽  
Vol 6 (31) ◽  
pp. eaaz1842
Author(s):  
M. E. Manley ◽  
K. Hong ◽  
P. Yin ◽  
S. Chi ◽  
Y. Cai ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
High Performance ◽  
Phonon Scattering ◽  
Light Emission ◽  
Phonon Dispersion ◽  
Acoustic Phonons ◽  
Lead Iodide ◽  
Phonon Bottleneck ◽  
Optic Phonon ◽  
Methylammonium Lead Iodide

Lead halide perovskites are strong candidates for high-performance low-cost photovoltaics, light emission, and detection applications. A hot-phonon bottleneck effect significantly extends the cooling time of hot charge carriers, which thermalize through carrier–optic phonon scattering, followed by optic phonon decay to acoustic phonons and finally thermal conduction. To understand these processes, we adjust the lattice dynamics independently of electronics by changing isotopes. We show that doubling the mass of hydrogen in methylammonium lead iodide by replacing protons with deuterons causes a large 20 to 50% softening of the longitudinal acoustic phonons near zone boundaries, reduces thermal conductivity by ~50%, and slows carrier relaxation kinetics. Phonon softening is attributed to anticrossing with the slowed libration modes of the deuterated molecules and the reduced thermal conductivity to lowered phonon velocities. Our results reveal how tuning the organic molecule dynamics enables control of phonons important to thermal conductivity and the hot-phonon bottleneck.

Dependent Scattering of Acoustic Phonons From Particles Embedded in an Anisotropic Medium

2007 ◽  
Author(s):  
Neil Zuckerman ◽  
Jennifer R. Lukes
Keyword(s):  
Cross Sections ◽  
Phonon Scattering ◽  
Elastic Anisotropy ◽  
Mode Conversion ◽  
Three Dimensional ◽  
Atomic Scale ◽  
Dynamics Simulation ◽  
Nanometer Scale ◽  
Acoustic Phonons ◽  
Scale Granularity

Dependent scattering of acoustic phonons by multiple nanometer-scale inclusions in anisotropic media is investigated using a new molecular dynamics simulation technique. The spectral-directional characteristics of the scattering are found by calculation of three-dimensional scattering phase functions and cross sections for inclusions of varying sizes in various spatial arrangements. The technique enables computation of the effects of reflected wave interference and sequential scattering, mode conversion, lattice strain, elastic anisotropy, and atomic-scale granularity on acoustic phonon scattering from structured inclusions. The results will improve understanding and prediction of heat transfer in quantum-dot superlattices and other engineered thermal materials with nanometer-scale structures.

Thermal Conduction in Nonhomogeneous CVD Diamond Layers in Electronic Microstructures

1996 ◽  
Vol 118 (2) ◽  
pp. 279-286 ◽  
Author(s):  
K. E. Goodson
Keyword(s):  
Thermal Conduction ◽  
Room Temperature ◽  
Phonon Scattering ◽  
Chemical Vapor ◽  
Phonon Transport ◽  
Local Characteristic ◽  
Scattering Rate ◽  
Chemical Vapor Deposited ◽  
Conduction Cooling ◽  
Scattering Strength

Chemical-vapor-deposited diamond layers of thickness between 0.1 and 5 μm have the potential to improve conduction cooling in electronic microstructures. However, thermal conduction in these layers is strongly impeded by phonon scattering on defects, whose concentrations can be highly nonhomogeneous, and on layer boundaries. By assuming that defects are concentrated near grain boundaries, this work relates the internal phonon scattering rate to the local characteristic grain dimension and to the dimensionless grain-boundary scattering strength, a parameter defined here that varies little within a given layer. Solutions to the Peierls–Boltzmann phonon transport equation for conduction along and normal to layers account for the nonhomogeneous internal scattering rate. Predictions for conduction along and normal to layers as thin as 0.2 μm agree well with room-temperature data. This research helps optimize diamond layer thicknesses for specific microstructures, such as silicon-on-diamond (SOD) circuits.

Towards quantitative simulations of inelastic electron diffraction patterns and images

1992 ◽  
Vol 50 (2) ◽  
pp. 1170-1171
Author(s):  
Z. L. Wang
Keyword(s):  
Phonon Scattering ◽  
Incident Beam ◽  
Dynamical Theory ◽  
Inelastic Electron ◽  
Additional Advantage ◽  
Coupled Equations ◽  
Atomic Vibrations ◽  
Diffraction Patterns ◽  
Primary Advantage ◽  
The One

A new dynamical theory has been developed based on Yoshioka's coupled equations for describing inelastic electron scattering in thin crystals. Compared to existing theories, the primary advantage of this theory is that the incoherent summation of the diffracted intensities contributed by electrons after exciting vast numbers of different excited states has been evaluated before any numerical calculation. An additional advantage is that the phase correlations of atomic vibrations are considered, so that full lattice dynamics can be combined in the phonon scattering calculation. The new theory has been proven to be equivalent to the inelastic multislice theory, and has been applied to calculate energy-filtered diffraction patterns and images formed by phonon, single electron and valence scattered electrons.A calculated diffraction pattern of elastic and phonon scattered electrons for a parallel incident beam case is in agreement with the one observed (Fig. 1), showing thermal diffuse scattering (TDS) streaks and Kikuchi pattern.

ACOUSTIC PHONONS IN HEISENBERG PARAMAGNETS

1971 ◽  
Vol 32 (C1) ◽  
pp. C1-526-C1-527 ◽  
Author(s):  
H. S. BENNETT
Keyword(s):  
Acoustic Phonons
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