Large contribution of quasi-acoustic shear phonon modes to thermal conductivity in novel monolayer Ga2O3

Acoustic phonons play a critical role in energy transport in nanostructures. The dispersion of acoustic phonons strongly influences thermal conductivity. Recent observations show lower values of thermal conductivity in finite dimensional nanostructures than in the bulk material. In this work, we will present results for guided acoustic phonon modes in (a) a bilayered GaAs-Nb nanowire of rectangular cross section and (b) a trapezoidal Si nanowire. The former has been used for phonon counting in a nanocalorimeter for measuring thermal conductivity and the latter is commonly used in MEMS applications. A semi-analytical finite element (SAFE) analysis technique has been used to investigate the effects of layering, anisotropy, and boundaries on the dispersion of modes of propagation. Many interesting features of group velocities are found that show confinements around the corners, in the low velocity layer, and coupling of the longitudinal and flexural modes. These would strongly influence thermal conductivity and might provide means of nondestrutive evaluation of mechanical properties.

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Study of Thermometry in Two-Dimensional Sb2Te3 from Temperature-Dependent Raman Spectroscopy

Nanoscale Research Letters ◽

10.1186/s11671-020-03463-1 ◽

2021 ◽

Vol 16 (1) ◽

Cited By ~ 1

Author(s):

Manavendra P. Singh ◽

Manab Mandal ◽

K. Sethupathi ◽

M. S. Ramachandra Rao ◽

Pramoda K. Nayak

Keyword(s):

Thermal Conductivity ◽

Raman Spectroscopy ◽

Temperature Coefficient ◽

Heat Dissipation ◽

Peak Position ◽

Two Dimensional ◽

Phonon Modes ◽

Temperature Dependent ◽

Excellent Candidate ◽

High Figure

AbstractDiscovery of two-dimensional (2D) topological insulators (TIs) demonstrates tremendous potential in the field of thermoelectric since the last decade. Here, we have synthesized 2D TI, Sb2Te3 of various thicknesses in the range 65–400 nm using mechanical exfoliation and studied temperature coefficient in the range 100–300 K using micro-Raman spectroscopy. The temperature dependence of the peak position and line width of phonon modes have been analyzed to determine the temperature coefficient, which is found to be in the order of 10–2 cm−1/K, and it decreases with a decrease in Sb2Te3 thickness. Such low-temperature coefficient would favor to achieve a high figure of merit (ZT) and pave the way to use this material as an excellent candidate for thermoelectric materials. We have estimated the thermal conductivity of Sb2Te3 flake with the thickness of 115 nm supported on 300-nm SiO2/Si substrate which is found to be ~ 10 W/m–K. The slightly higher thermal conductivity value suggests that the supporting substrate significantly affects the heat dissipation of the Sb2Te3 flake.

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(Invited) Reduced Thermal Conductivity of Tcnq and F4-TCNQ Infiltrated HKUST-1 Due to Suppression of Linker Flexural Phonon Modes

ECS Meeting Abstracts ◽

10.1149/ma2020-02302021mtgabs ◽

2020 ◽

Vol MA2020-02 (30) ◽

pp. 2021-2021

Author(s):

Mallory E DeCoster ◽

Sangeun S Jung ◽

Zeinab Mohamed Hassan ◽

Hasan Babaei ◽

Emma M. Tiernan ◽

...

Keyword(s):

Thermal Conductivity ◽

Phonon Modes

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Anomalous strain effect on the thermal conductivity of low-buckled two-dimensional silicene

National Science Review ◽

10.1093/nsr/nwaa220 ◽

2020 ◽

Cited By ~ 1

Author(s):

Bin Ding ◽

Xiaoyan Li ◽

Wuxing Zhou ◽

Gang Zhang ◽

Huajian Gao

Keyword(s):

Thermal Conductivity ◽

Strain Effect ◽

Two Dimensional ◽

Phonon Modes ◽

Heat Management ◽

Anomalous Effect ◽

Long Wavelength ◽

Two Dimensional Materials ◽

Dynamics Simulations ◽

Energy Conversion Devices

Abstract The thermal conductivity of two-dimensional materials, such as graphene, typically decreases when tensile strain is applied, which softens their phonon modes. Here, we report an anomalous strain effect on the thermal conductivity of monolayer silicene, a representative low-buckled two-dimensional (LB-2D) material. ReaxFF-based molecular dynamics simulations are performed to show that biaxially stretched monolayer silicene exhibits a remarkable increase in the thermal conductivity, by as much as 10 times the freestanding value, with increasing applied strain in the range of [0, 0.1], which is attributed to increased contributions from long-wavelength phonons. A further increase in strain in the range of [0.11, 0.18] results in a plateau of the thermal conductivity in an oscillatory manner, governed by a unique dynamic bonding behavior under extreme loading. This anomalous effect reveals new physical insights into the thermal properties of LB-2D materials and may provide some guidelines for designing heat management and energy conversion devices based on such materials.

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Reduction of Lattice Thermal Conductivity in PbTe Induced by Artificially Generated Pores

Advances in Condensed Matter Physics ◽

10.1155/2015/496739 ◽

2015 ◽

Vol 2015 ◽

pp. 1-6 ◽

Cited By ~ 4

Author(s):

Jae-Yeol Hwang ◽

Eun Sung Kim ◽

Syed Waqar Hasan ◽

Soon-Mok Choi ◽

Kyu Hyoung Lee ◽

...

Keyword(s):

Thermal Conductivity ◽

Pore Structure ◽

Transport Properties ◽

Thermoelectric Materials ◽

Thermal Transport ◽

Lattice Thermal Conductivity ◽

Phonon Scattering ◽

Phonon Modes ◽

Thermal Transport Properties

Highly dense pore structure was generated by simple sequential routes using NaCl and PVA as porogens in conventional PbTe thermoelectric materials, and the effect of pores on thermal transport properties was investigated. Compared with the pristine PbTe, the lattice thermal conductivity values of pore-generated PbTe polycrystalline bulks were significantly reduced due to the enhanced phonon scattering by mismatched phonon modes in the presence of pores (200 nm–2 μm) in the PbTe matrix. We obtained extremely low lattice thermal conductivity (~0.56 W m−1 K−1at 773 K) in pore-embedded PbTe bulk after sonication for the elimination of NaCl residue.

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Monte Carlo Study of Phonon Heat Conduction in Silicon Thin Films Including Contributions of Optical Phonons

Journal of Heat Transfer ◽

10.1115/1.4000447 ◽

2010 ◽

Vol 132 (5) ◽

Cited By ~ 67

Author(s):

Arpit Mittal ◽

Sandip Mazumder

Keyword(s):

Thin Films ◽

Thermal Conductivity ◽

Monte Carlo ◽

Heat Conduction ◽

Phonon Scattering ◽

Computational Domain ◽

Optical Phonons ◽

Phonon Modes ◽

Silicon Thin Film ◽

Silicon Thin Films

Abstract The Monte Carlo method has found prolific use in the solution of the Boltzmann transport equation for phonons for the prediction of nonequilibrium heat conduction in crystalline thin films. This paper contributes to the state-of-the-art by performing a systematic study of the role of the various phonon modes on thermal conductivity predictions, in particular, optical phonons. A procedure to calculate three-phonon scattering time-scales with the inclusion of optical phonons is described and implemented. The roles of various phonon modes are assessed. It is found that transverse acoustic (TA) phonons are the primary carriers of energy at low temperatures. At high temperatures (T>200 K), longitudinal acoustic (LA) phonons carry more energy than TA phonons. When optical phonons are included, there is a significant change in the amount of energy carried by various phonons modes, especially at room temperature, where optical modes are found to carry about 25% of the energy at steady state in silicon thin films. Most importantly, it is found that inclusion of optical phonons results in better match with experimental observations for silicon thin-film thermal conductivity. The inclusion of optical phonons is found to decrease the thermal conductivity at intermediate temperatures (50–200 K) and to increase it at high temperature (>200 K), especially when the film is thin. The effect of number of stochastic samples, the dimensionality of the computational domain (two-dimensional versus three-dimensional), and the lateral (in-plane) dimension of the film on the statistical accuracy and computational efficiency is systematically studied and elucidated for all temperatures.

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Mechanism of Thermal Conductivity Reduction From Suspended to Supported Graphene: A Quantitative Spectral Analysis of Phonon Scattering

Volume 10: Heat and Mass Transport Processes, Parts A and B ◽

10.1115/imece2011-62963 ◽

2011 ◽

Cited By ~ 1

Author(s):

Bo Qiu ◽

Xiulin Ruan

Keyword(s):

Thermal Conductivity ◽

Spectral Analysis ◽

Phonon Scattering ◽

Md Simulations ◽

Mean Free Path ◽

Spectral Energy ◽

Phonon Modes ◽

Suspended Graphene ◽

Out Of Plane ◽

Predicted Values

In this work, we perform molecular dynamics (MD) simulations together with phonon spectral analysis to predict the thermal conductivity of both suspended and supported graphene. We quantitatively address the relative importance of different types of phonon in thermal transport and explain why thermal conductivity is significantly reduced in supported graphene compared to that in suspended graphene. Within the framework of equilibrium MD, we perform spectral energy density analysis to obtain the phonon mean free path of each individual phonon mode. The contribution of each mode to thermal conductivity is then calculated and summed to obtain the lattice thermal conductivity in the temperature range 300–650 K. Our predicted values and temperature dependence for both suspended and supported graphene agree with experimental data well. In contrast to prior studies, our results suggest that the contribution from out-of-plane acoustic (ZA) branch to thermal conductivity is around 25–30% in suspended graphene at room temperature. The thermal conductivity of supported graphene is predicted to be largely reduced, which is consistent with experimental observations. Such reduction is shown to be due to stronger scattering of all phonon modes rather than only the ZA mode in the presence of the substrate.

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Coupling Between Phonons and Fluid Particles in Water/Carbon Nanotube Systems

ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 3 ◽

10.1115/mnhmt2009-18305 ◽

2009 ◽

Author(s):

A. J. H. McGaughey ◽

J. A. Thomas ◽

J. Turney ◽

R. M. Iutzi

Keyword(s):

Thermal Conductivity ◽

Molecular Dynamics ◽

Carbon Nanotube ◽

Relaxation Times ◽

Mean Free Path ◽

Phonon Transport ◽

Dynamics Simulation ◽

Spectral Energy ◽

Total Thermal Conductivity ◽

Phonon Modes

We investigate thermal transport in water/carbon nanotube (CNT) composite systems using molecular dynamics simulations. Carbon-carbon interactions are modeled using the second-generation REBO potential, water-water interactions are modeled using the TIP4P potential, and carbon-water interactions are modeled using a Lennard-Jones potential. The thermal conductivities of empty and water-filled CNTs with diameters between 0.83 nm and 1.66 nm are predicted using molecular dynamics simulation and a direct application of the Fourier law. For empty CNTs, the thermal conductivity decreases with increasing CNT diameter. As the CNT length approaches 1 micron, a length-independent thermal conductivity is obtained, indicative of diffusive phonon transport. When the CNTs are filled with water, the thermal conductivity decreases compared to the empty CNTs and transitions to diffusive phonon transport at shorter lengths. To understand this behavior, we calculate the spectral energy density of the empty and water-filled CNTs and calculate the mode-specific group velocities, relaxation times, and thermal conductivity. For the empty 1.10 nm diameter CNT, we show that the acoustic phonon modes account for 65 percent of the total thermal conductivity. This behavior is attributed to their long mean-free paths. When the CNT is filled with water, interactions with the water molecules shorten the acoustic mode mean-free path and lower the overall CNT thermal conductivity.

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Role of Edge Chirality and Isotope Doping in Thermal Transport and Thermal Rectification in Graphene Nanoribbons

Volume 10: Heat and Mass Transport Processes, Parts A and B ◽

10.1115/imece2011-63169 ◽

2011 ◽

Author(s):

Yan Wang ◽

Xiulin Ruan

Keyword(s):

Thermal Conductivity ◽

Thermal Transport ◽

Graphene Nanoribbons ◽

Mass Density ◽

Transport Processes ◽

Phonon Modes ◽

Cross Sectional ◽

Thermal Rectification ◽

The Difference ◽

Dynamics Simulations

Thermal transport processes in graphene nanoribbons (GNRs) within and beyond the linear response regime has been studied using classical molecular dynamics simulations. Zigzag-edged GNRs have higher thermal conductivities than armchair-edged ones, and the difference diminishes with increasing width. Analysis on the cross-sectional distribution of heat flux reveals that edge atoms cannot transport thermal energy as efficiently as interior ones. Edge localization of phonon modes reduces thermal transport through edge carbon atoms, especially on armchair edges, which results in a lower thermal conductivity. Isotope (13C) doping can reduce the thermal conductivity of GNRs by 30%–40% by an addition of only ∼20% isotope atoms. The significant reduction in thermal conductivity is partially attributed to phonon localization induced by isotope defects, which is confirmed by phonon mode participation ratio analysis. We also demonstrate that a GNR asymmetric in edge chirality or mass density can generate considerable thermal rectification, which is essential for developing GNR-based thermal management devices.

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Mode-Wise Thermal Conductivity of Bismuth Telluride

Journal of Heat Transfer ◽

10.1115/1.4024356 ◽

2013 ◽

Vol 135 (9) ◽

Cited By ~ 36

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.

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