Coupled electron-phonon transport and heat transfer pathways in graphene nanostructures

Carbon ◽  
2017 ◽  
Vol 123 ◽  
pp. 525-535 ◽  
Author(s):  
Liang Chen ◽  
Zhequan Yan ◽  
Satish Kumar
Keyword(s):  
Heat Transfer ◽  
Phonon Transport ◽  
Graphene Nanostructures

scholarly journals A Thermal Transport Study of Branched Carbon Nanotubes with Cross and T-Junctions

2021 ◽  
Vol 11 (13) ◽  
pp. 5933
Author(s):  
Wei-Jen Chen ◽  
I-Ling Chang
Keyword(s):  
Heat Transfer ◽  
Carbon Nanotubes ◽  
Thermal Management ◽  
Thermal Transport ◽  
Topological Defects ◽  
Branch Length ◽  
Phonon Transport ◽  
Heat Current ◽  
Transport Mechanisms ◽  
Non Equilibrium Molecular Dynamics

This study investigated the thermal transport behaviors of branched carbon nanotubes (CNTs) with cross and T-junctions through non-equilibrium molecular dynamics (NEMD) simulations. A hot region was created at the end of one branch, whereas cold regions were created at the ends of all other branches. The effects on thermal flow due to branch length, topological defects at junctions, and temperature were studied. The NEMD simulations at room temperature indicated that heat transfer tended to move sideways rather than straight in branched CNTs with cross-junctions, despite all branches being identical in chirality and length. However, straight heat transfer was preferred in branched CNTs with T-junctions, irrespective of the atomic configuration of the junction. As branches became longer, the heat current inside approached the values obtained through conventional prediction based on diffusive thermal transport. Moreover, directional thermal transport behaviors became prominent at a low temperature (50 K), which implied that ballistic phonon transport contributed greatly to directional thermal transport. Finally, the collective atomic velocity cross-correlation spectra between branches were used to analyze phonon transport mechanisms for different junctions. Our findings deeply elucidate the thermal transport mechanisms of branched CNTs, which aid in thermal management applications.

Analysis of heat transfer between solids at low temperatures

1976 ◽  
Vol 54 (17) ◽  
pp. 1749-1771 ◽  
Author(s):  
J. D. N. Cheeke ◽  
H. Ettinger ◽  
B. Hebral
Keyword(s):  
Heat Transfer ◽  
Thermal Contact ◽  
Impedance Matching ◽  
Debye Model ◽  
Phonon Transport ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Critical Cone ◽  
Acoustic Mismatch ◽  
The Heat Transfer Coefficient

A detailed analysis is given of the acoustic mismatch formulation first given by Little for the thermal contact resistance between solids for the case of phonon transport in a Debye model. Extrema in the heat transfer coefficients as a function of the refractive index of the interface are shown to be due to either impedance matching conditions or to the presence of the critical cone. Detailed numerical tables are presented which permit rapid evaluation of the heat transfer coefficient to an accuracy of 5% or better.

Modeling and Prediction of Sub-Micrometer Heat Transfer During Thermomechanical Data Storage

1999 ◽  
Author(s):  
William P. King ◽  
Juan G. Santiago ◽  
Thomas W. Kenny ◽  
Kenneth E. Goodson
Keyword(s):  
Heat Transfer ◽  
Data Storage ◽  
Phonon Scattering ◽  
Heat Rate ◽  
Phonon Transport ◽  
Polymer Layer ◽  
Spatial Density ◽  
Atomic Force ◽  
Data Layer ◽  
Gas Conduction

Abstract Heat transfer governs the bit size and writing rate during sub-micrometer thermomechanical data storage with Atomic Force Microscope (AFM) cantilevers. The present work predicts the temperature distribution and rates of heat flow in the AFM tip and the substrate as functions of the peak cantilever temperature, the diameter of the tip-substrate contact, and the thickness of the deforming polymer coating on the silicon substrate. The calculations consider increased phonon scattering, radiation losses, and gas conduction losses at the silicon tip boundaries. Nearly ballistic phonon transport in the tip augments the dependence of the heat rate into the polymer on the tip-polymer contact diameter. For a cantilever heater temperature of 700 K and a polymer layer thickness of 80 nm, the temperature at the tip-polymer interface is predicted for contact diameters from 4 nm to 50 nm. This work models the deformation of the polymer layer during data writing and predicts data bit size as a function of tip temperature and writing time. These simulations will help optimize the design of the cantilever and the polymer data layer, with the goal of increasing the spatial density and rate of bit formation.

Atomistic Visualization of Ballistic Phonon Transport

2007 ◽  
Author(s):  
Neil Zuckerman ◽  
Jennifer R. Lukes
Keyword(s):  
Heat Transfer ◽  
High Frequency ◽  
Energy Transport ◽  
Imaging Techniques ◽  
Phonon Transport ◽  
Dynamics Simulation ◽  
Short Time Scale ◽  
Ballistic Phonons ◽  
Short Time ◽  
Phonon Focusing

Heat transfer in solid materials at short time scales, short length scales, and low temperatures is governed by the transport of ballistic phonons. In anisotropic crystals, the energy carried by these phonons is strongly channeled into well-defined directions in a phenomenon known as phonon focusing. Presented here is a new molecular dynamics simulation approach for visualizing acoustic phonon focusing in anisotropic crystals. An advantage of this approach over experimental phonon imaging techniques is that it allows examination of phonon propagation at selected modes and frequencies. The spatial, mode, and frequency dependence of ballistic energy transport gained with this approach will be useful for understanding heat transfer issues in high frequency electronics and short time scale laser-material interactions.

Monte Carlo Simulation of Steady-State Microscale Phonon Heat Transport

2008 ◽  
Vol 130 (7) ◽  
Author(s):  
Jaona Randrianalisoa ◽  
Dominique Baillis
Keyword(s):  
Heat Transfer ◽  
Thin Films ◽  
Monte Carlo ◽  
Heat Conduction ◽  
Steady State ◽  
Monte Carlo Method ◽  
Silicon Nanowires ◽  
Silicon Film ◽  
Relaxation Times ◽  
Phonon Transport

Heat conduction in submicron crystalline materials can be well modeled by the Boltzmann transport equation (BTE). The Monte Carlo method is effective in computing the solution of the BTE. These past years, transient Monte Carlo simulations have been developed, but they are generally memory demanding. This paper presents an alternative Monte Carlo method for analyzing heat conduction in such materials. The numerical scheme is derived from past Monte Carlo algorithms for steady-state radiative heat transfer and enables us to understand well the steady-state nature of phonon transport. Moreover, this algorithm is not memory demanding and uses very few iteration to achieve convergence. It could be computationally more advantageous than transient Monte Carlo approaches in certain cases. Similar to the famous Mazumder and Majumdar’s transient algorithm (2001, “Monte Carlo Study of Phonon Transport in Solid Thin Films Including Dispersion and Polarization,” ASME J. Heat Transfer, 123, pp. 749–759), the dual polarizations of phonon propagation, the nonlinear dispersion relationships, the transition between the two polarization branches, and the nongray treatment of phonon relaxation times are accounted for. Scatterings by different mechanisms are treated individually, and the creation and/or destruction of phonons due to scattering is implicitly taken into account. The proposed method successfully predicts exact solutions of phonon transport across a gallium arsenide film in the ballistic regime and that across a silicon film in the diffusion regime. Its capability to model the phonon scattering by boundaries and impurities on the phonon transport has been verified. The current simulations agree well with the previous predictions and the measurement of thermal conductivity along silicon thin films and along silicon nanowires of widths greater than 22nm. This study confirms that the dispersion curves and relaxation times of bulk silicon are not appropriate to model phonon propagation along silicon nanowires of 22nm width.

Mode-Resolved Thermal Conductivity of Freestanding and Supported Bismuth Telluride Quintuple Layer

2016 ◽  
Author(s):  
Cheng Shao ◽  
Hua Bao
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Bismuth Telluride ◽  
Normal Mode Analysis ◽  
Relaxation Times ◽  
Phonon Transport ◽  
Mode Analysis ◽  
Underlying Mechanisms ◽  
Dynamics Simulations ◽  
Phonon Properties

The successful exfoliation of atomically-thin bismuth telluride quintuple layer (QL) attracts tremendous interest in investigating the electron and phonon transport properties in this quasi-two-dimensional material. While experimental results show that thermal conductivity is significantly reduced in Bi2Te3 QL compared to the bulk phase, the underlying mechanisms for the reduction is still unclear. Also in some measurements, the Bi2Te3 QL is usually supported on the substrate and the effect of the substrate on heat transfer in Bi2Te3 QL is unknown. In this work, we have performed molecular dynamics simulations and normal mode analysis to study the mode-wise phonon properties in freestanding and supported Bi2Te3 QL. We found that the existing of substrate will decrease the phonon relaxation times in Bi2Te3 QL in the full frequency range. Thermal conductivity accumulation function for both freestanding and supported Bi2Te3 QL are constructed and compared. We found that half of heat transfer in freestanding Bi2Te3 QL contributed from phonons with mean free paths larger than 16.5 nm, while in supported Bi2Te3 QL this value is reduced to 11 nm. In both cases phonons with MFPs in the range of 10–30 nm are the dominate heat carriers, which contribute to 55% and 53% of thermal conductivity in freestanding and supported cases.

scholarly journals Modeling of Subcontinuum Thermal Transport Across Semiconductor-Gas Interfaces

2008 ◽  
Author(s):  
Dhruv Singh ◽  
Xiaohui Guo ◽  
Alina Alexeenko ◽  
Jayathi Y. Murthy ◽  
Timothy S. Fisher
Keyword(s):  
Heat Transfer ◽  
Boltzmann Equation ◽  
Thermal Transport ◽  
Phonon Transport ◽  
Interface Temperature ◽  
Molecular Flow ◽  
Parallel Plates ◽  
Thermal Interface ◽  
The Boltzmann Equation ◽  
Gas Molecules

A physically rigorous computational algorithm is developed and applied to calculate sub-continuum thermal transport in structures containing semiconductor-gas interfaces. The solution is based on a finite volume discretization of the Boltzmann equation for gas molecules (in the gas phase) and phonons (in the semiconductor). A partial equilibrium is assumed between gas molecules and phonons at the interface of the two media, and the degree of this equilibrium is determined by the accommodation coefficients of gas molecules and phonons on either side of the interface. Energy balance is imposed to obtain a value of the interface temperature. The problem of heat transfer between two parallel plates is investigated. A range of transport regimes is studied, varying from ballistic phonon transport and free molecular flow to continuum heat transfer in both gas and solid. In particular, the thermal interface resistance (or temperature slip) at a gas-solid interface is extracted in the mesoscopic regime where a solution of the Boltzmann equation is necessary. This modeling approach is expected to find applications in the study of heat conduction through microparticle beds, gas flows in microchannel heat sinks and in determining gas gap conductance in thermal interface materials.

Validation of a Unified Nondiffusive-Diffusive Phonon Transport Model for Nanoscale Heat Transfer Simulations

2014 ◽  
Author(s):  
Ashok T. Ramu ◽  
Yanbao Ma
Keyword(s):  
Heat Transfer ◽  
Spatial Dependence ◽  
Hot Spots ◽  
Transport Model ◽  
Boltzmann Transport Equation ◽  
Phonon Transport ◽  
High Fidelity ◽  
Boltzmann Transport ◽  
Fourier Law ◽  
Limiting Case

Heat transfer in the vicinity of nanoscale hot-spots is qualitatively different from that in the macroscale, which effect stems from the breakdown of Fourier law due to phonon nondiffusive transport. In this work, we validate a recently proposed alternative, high-fidelity phonon transport model, the unified nondiffusive-diffusive (UND) model, which takes into account the mixed ballistic-diffusive nature of heat transport, as well as reduces to the Fourier law as a limiting case. In the UND model, the nondiffusive phonons are treated using the Boltzmann transport equation, while the diffusive phonon gas is treated by the Fourier law. The numerical results of Maznev et al. for the geometry and spatial dependence of variables corresponding to the transient gratings experiments of Johnson et al. are used for validation of the model.

Microscale Thermal Energy Transfer Between Thin Films with Vacuum Gap at Interface

2019 ◽  
Vol 44 (2) ◽  
pp. 123-142 ◽  
Author(s):  
Haider Ali ◽  
Bekir Sami Yilbas
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Thermal Conductivity ◽  
Energy Transfer ◽  
Radiative Heat ◽  
Near Field ◽  
Silicon Film ◽  
Phonon Transport ◽  
Ballistic Phonons ◽  
Vacuum Gap

Abstract Transfer of phonons through a silicon–diamond thin film pair with a nano-size gap at the interface is examined. The thin film pair is thermally disturbed by introducing 301 K at the silicon film left edge while keeping the other edges of the thin films at a low temperature (300 K). The radiative phonon transport equation is solved numerically to quantify the phonon intensity distribution in the combined films. The frequency dependent formulation of phonon transport is incorporated in the transient analysis. The thermal boundary resistance is adopted at the interface in the formulations. The near-field radiative heat transfer is also adopted at the gap interface, as the vacuum gap size falls within the Casimir limit. The predictions of thermal conductivity are validated through the thermocouple data. It is observed that predictions of thermal conductivity are in agreement with the experimental data. The ballistic phonons play a major role in energy transfer through the gap; their contribution is more significant than that of the near-field radiative heat transfer. Enlarging the size of the gap reduces the influence of the ballistic phonons on the energy transfer in the films. Increasing the silicon film thickness alters the energy transfer through the gap; in this case, the equivalent equilibrium temperature difference is increased at the interface.

Thermal transport in layered structure of YBa2Cu3O7−δ superconductors

2017 ◽  
Vol 31 (30) ◽  
pp. 1750225
Author(s):  
Rakhi Sharma ◽  
B. D. Indu
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Layered Structure ◽  
Thermal Conduction ◽  
Cuprate Superconductors ◽  
Phonon Transport ◽  
Numerical Estimation ◽  
Layered Superconductors ◽  
Area Of Interest ◽  
Transfer Study

The heat transfer study in YBa2Cu3O[Formula: see text] superconductors structures is focused on the influence of the effect of scattering events in cross-plane and in-plane references. Understanding the mechanism of controlling the thermal conductivity of layered superconductors is an area of interest for nano microelectronics and thermo-electronic technological applications. The model of the thermal conduction, and phonon transport perpendicular and parallel to the layers of YBa2Cu3O[Formula: see text] are developed. It has been justified via numerical estimation and found substantial diminution in thermal conductivities in both in-plane and cross-plane directions of layered cuprate superconductors.

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