Thermal transport across a thin film composite due to laser short-pulse heating

2015 ◽  
Vol 40 (2) ◽  
Author(s):  
Saad Bin Mansoor ◽  
Bekir Sami Yilbas
Keyword(s):  
Energy Transport ◽  
Phonon Scattering ◽  
Short Pulse ◽  
Average Energy ◽  
Equilibrium Temperature ◽  
Aluminum Film ◽  
Boltzmann Transport ◽  
Incident Laser Radiation ◽  
Electron Phonon Coupling ◽  
Local Point

AbstractLaser short-pule irradiation of silicon-diamond-aluminum thin films is considered and energy transport across the films is modelled using the Boltzmann transport equation. Electron-phonon coupling is adopted to formulate energy transfer across the electron and lattice sub-systems in the aluminum film. Thermal boundary resistance is incorporated at the film interfaces. The transfer matrix method is used to account for the transmittance, reflection and absorption of the incident laser radiation across the films. Equivalent equilibrium temperature is introduced to access energy transport in the films, which represents the average energy of all phonons around a local point when they redistribute adiabatically to an equilibrium state. It is found that equivalent equilibrium temperature increases sharply in the electron sub-system due to electron excess energy gain from the irradiated field. Equivalent equilibrium temperature decays gradually in the lattice sub-system with increasing period due to phonon scattering in the film.

Nonequilibrium cross-plane energy transport in aluminum–silicon–aluminum wafer

2015 ◽  
Vol 29 (17) ◽  
pp. 1550112
Author(s):  
Saad Bin Mansoor ◽  
Bekir Sami Yilbas
Keyword(s):  
Boltzmann Equation ◽  
Energy Transport ◽  
Silicon Film ◽  
Equilibrium Temperature ◽  
Phonon Transport ◽  
Aluminum Film ◽  
Boltzmann Transport ◽  
Aluminum Films ◽  
The Boltzmann Equation ◽  
Aluminum Silicon

Transient phonon transport across cross-planes of aluminum–silicon–aluminum combined films is investigated and the Boltzmann transport equation is incorporated to formulate the energy transport in the combined films. Since electrons and phonons thermally separate in the thin aluminum film during heating, the Boltzmann equation is used separately in the electron and lattice subsystems to account for the energy transport in the aluminum film. Electron–phonon coupling is incorporated for the energy exchange between electron and lattice subsystems in the film. Thermal boundary resistance (TBR) is introduced at the interfaces of the silicon–aluminum films. In order to examine the ballistic contribution of phonons on the phonon intensity distribution in the silicon film, frequency-dependent solution of the Boltzmann equation is used in the silicon film and the film thickness is varied to investigate the size effect on the thermal conductivity in the film. It is found that equivalent equilibrium temperature of phonons remains high at silicon–aluminum interface because of the ballistic contribution of the phonons. Equivalent equilibrium temperature for the electron subsystem becomes higher than that corresponding to phonon temperature at the aluminum–silicon interface.

Energy Transport across the Thin Films Pair with Presence of Minute Vacuum Gap at Interface

2017 ◽  
Vol 42 (2) ◽  
Author(s):  
Haider Ali ◽  
Bekir Sami Yilbas
Keyword(s):  
Energy Transfer ◽  
Thermal Radiation ◽  
Energy Transport ◽  
Short Pulse ◽  
Silicon Film ◽  
Mean Free Path ◽  
Aluminum Film ◽  
Gap Size ◽  
Electron Phonon Coupling ◽  
Vacuum Gap

AbstractCross-plane energy transport in aluminum and silicon films pair with presence of minute vacuum gap in between them is investigated. Laser short-pulse heating is introduced in the aluminum film and energy transfer in the films pair is formulated using the Boltzmann equation. Energy exchange between the electron and lattice subsystems is expressed in terms of the electron–phonon coupling. The vacuum gap size is considered to be less than the mean-free path silicon and the Casimir limit is applied to incorporate the thermal radiation contribution to the overall energy transport across the vacuum gap. It is found that ballistic phonon contribution to energy transfer across the vacuum gap is significant and the contribution of the thermal radiation, due to Casimir limit, to energy transfer is small. The vacuum gap size has significant effect on the energy transfer from aluminum film to the silicon film; in which case, increasing vacuum gap size enhances temperature difference across the interface of the vacuum gap.

Contribution of Ballistic Electron Transport to Energy Transfer During Electron-Phonon Nonequilibrium in Thin Metal Films

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Patrick E. Hopkins ◽  
Pamela M. Norris
Keyword(s):  
Thin Films ◽  
Electron Transport ◽  
Phonon Scattering ◽  
High Energy ◽  
Boltzmann Transport ◽  
Phonon Coupling ◽  
Ballistic Electron ◽  
Ballistic Electron Transport ◽  
Interface Scattering ◽  
Electron Phonon Coupling

With the ever decreasing characteristic lengths of nanomaterials, nonequilibrium electron-phonon scattering can be affected by additional scattering processes at the interface of two materials. Electron-interface scattering would lead to another path of energy flow for the high-energy electrons other than electron-phonon coupling in a single material. Traditionally, electron-phonon coupling in transport is analyzed with a diffusion (Fourier) based model, such as the two temperature model (TTM). However, in thin films with thicknesses less than the electron mean free path, ballistic electron transport could lead to electron-interface scattering, which is not taken into account in the TTM. The ballistic component of electron transport, leading to electron-interface scattering during ultrashort pulsed laser heating, is studied here by a ballistic-diffusive approximation of the Boltzmann transport equation. The results for electron-phonon equilibration times are compared with calculations with TTM based approximations and experimental data on Au thin films.

Thermal Conductivity Reduction in Few-Layer Graphene

2011 ◽  
Author(s):  
Dhruv Singh ◽  
Jayathi Y. Murthy ◽  
Timothy S. Fisher
Keyword(s):  
Thermal Conductivity ◽  
Weak Coupling ◽  
Phonon Scattering ◽  
Single Layer ◽  
Acoustic Mode ◽  
Single Layer Graphene ◽  
Boltzmann Transport ◽  
Layer Graphene ◽  
Out Of Plane ◽  
Few Layer Graphene

Using the linearized Boltzmann transport equation and perturbation theory, we analyze the reduction in the intrinsic thermal conductivity of few-layer graphene sheets accounting for all possible three-phonon scattering events. Even with weak coupling between layers, a significant reduction in the thermal conductivity of the out-of-plane acoustic modes is apparent. The main effect of this weak coupling is to open many new three-phonon scattering channels that are otherwise absent in graphene. The highly restrictive selection rule that leads to a high thermal conductivity of ZA phonons in single-layer graphene is only weakly broken with the addition of multiple layers, and ZA phonons still dominate thermal conductivity. We also find that the decrease in thermal conductivity is mainly caused by decreased contributions of the higher-order overtones of the fundamental out-of-plane acoustic mode. Moreover, the extent of reduction is largest when going from single to bilayer graphene and saturates for four layers. The results compare remarkably well over the entire temperature range with measurements of of graphene and graphite.

Eddy-mediated Hadley cell expansion due to axisymmetric angular momentum adjustment to greenhouse gas forcings

2021 ◽  
Author(s):  
Nicholas A. Davis ◽  
Thomas Birner
Keyword(s):  
Angular Momentum ◽  
Greenhouse Gas ◽  
Cell Expansion ◽  
Energy Transport ◽  
Baroclinic Instability ◽  
Temperature Response ◽  
Equilibrium Temperature ◽  
Hadley Cell ◽  
Mean Flow ◽  
Fully Coupled

AbstractThe poleward expansion of the Hadley cells is one of the most robust modeled responses to increasing greenhouse gas concentrations. There are many proposed mechanisms for expansion, and most are consistent with modeled changes in thermodynamics, dynamics, and clouds. The adjustment of the eddies and the mean flow to greenhouse gas forcings, and to one another, complicates any effort toward a deeper understanding. Here we modify the Gray Radiation AND Moist Aquaplanet (GRANDMA) model to uncouple the eddy and mean flow responses to forcings. When eddy forcings are held constant, the purely axisymmetric response of the Hadley cell to a greenhouse gas-like forcing is an intensification and poleward tilting of the cell with height in response to an axisymmetric increase in angular momentum in the subtropics. The angular momentum increase drastically alters the circulation response compared to axisymmetric theories, which by nature neglect this adjustment. Model simulations and an eddy diffusivity framework demonstrate that the axisymmetric increase in subtropical angular momentum – the direct manifestation of the radiative-convective equilibrium temperature response – drives a poleward shift of the eddy stresses which leads to Hadley cell expansion. Prescribing the eddy response to the greenhouse gas-like forcing shows that eddies damp, rather than drive, changes in angular momentum, moist static energy transport, and momentum transport. Expansion is not driven by changes in baroclinic instability, as would otherwise be diagnosed from the fully-coupled simulation. These modeling results caution any assessment of mechanisms for circulation change within the fully-coupled wave-mean flow system.

Thermoelectrics by Computational Design: Progress and Opportunities

2021 ◽  
Vol 51 (1) ◽  
Author(s):  
Boris Kozinsky ◽  
David J. Singh
Keyword(s):  
First Principles ◽  
High Performance ◽  
Materials Science ◽  
Phonon Scattering ◽  
Transport Coefficients ◽  
Computational Design ◽  
Science Volume ◽  
Annual Review ◽  
Publication Date ◽  
Boltzmann Transport

The performance of thermoelectric materials is determined by their electrical and thermal transport properties that are very sensitive to small modifications of composition and microstructure. Discovery and design of next-generation materials are starting to be accelerated by computational guidance. We review progress and challenges in the development of accurate and efficient first-principles methods for computing transport coefficients and illustrate approaches for both rapid materials screening and focused optimization. Particularly important and challenging are computations of electron and phonon scattering rates that enter the Boltzmann transport equations, and this is where there are many opportunities for improving computational methods. We highlight the first successful examples of computation-driven discoveries of high-performance materials and discuss avenues for tightening the interaction between theoretical and experimental materials discovery and optimization. Expected final online publication date for the Annual Review of Materials Science, Volume 51 is August 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Raman scattering from impurities in semiconductors. II. Special cases

1978 ◽  
Vol 56 (5) ◽  
pp. 560-564
Author(s):  
Robert Barrie ◽  
H. -C. Chow
Keyword(s):  
Raman Scattering ◽  
General Result ◽  
Phonon Scattering ◽  
Phonon Coupling ◽  
Strong Electron ◽  
Impurities In Semiconductors ◽  
Electron Phonon Coupling ◽  
Special Cases ◽  
Weak Electron

Special cases of the general result for Raman scattering from an impurity in a semiconductor are discussed. For weak electron–phonon coupling the zero-phonon and one-phonon scattering intensities are derived. For strong electron–phonon coupling a comparison is made between two different approximations that have been previously used.

FREQUENCY DEPENDENT PHONON TRANSPORT IN TWO-DIMENSIONAL SILICON AND DIAMOND THIN FILMS

2012 ◽  
Vol 26 (17) ◽  
pp. 1250104 ◽  
Author(s):  
B. S. YILBAS ◽  
S. BIN MANSOOR
Keyword(s):  
Thin Films ◽  
Boltzmann Transport Equation ◽  
Diamond Films ◽  
Equilibrium Temperature ◽  
Phonon Transport ◽  
Two Dimensional ◽  
Boltzmann Transport ◽  
Frequency Dependent ◽  
Aluminum Films ◽  
The Difference

Phonon transport in two-dimensional silicon and aluminum films is investigated. The frequency dependent solution of Boltzmann transport equation is obtained numerically to account for the acoustic and optical phonon branches. The influence of film size on equivalent equilibrium temperature distribution in silicon and aluminum films is presented. It is found that increasing film width influences phonon transport in the film; in which case, the difference between the equivalent equilibrium temperature due to silicon and diamond films becomes smaller for wider films than that of the thinner films.

Transient Energy and Heat Transport in Metals

2009 ◽  
Author(s):  
Y. Ezzahri ◽  
A. Shakouri
Keyword(s):  
Heat Transport ◽  
Energy Transport ◽  
Phonon Scattering ◽  
Effect Of Temperature ◽  
New Formalism ◽  
Transient Energy ◽  
Scattering Time ◽  
Short Time ◽  
New Phenomena ◽  
Diffusive Part

A recently developed Shastry formalism for energy transport is used to analyze the temporal behavior of the energy and heat transport in metals. Comparison with Cattaneo’s equation is performed. Both models show the transition between ballistic and diffusive regimes. Furthermore, because the new model considers the discrete character of the lattice, it highlights some new phenomena such as oscillations in the energy transport at very short time scales. The energy relaxation of the conduction band electrons in metals is considered to be governed by the electron-phonon scattering, and the scattering time is taken to be averaged over the Fermi surface. Using the new formalism, one can quantify the transfer from ballistic modes to diffusive ones as energy propagates in the material and it is transformed into heat. While the diffusive contribution shows an almost exponentially decaying behavior with time, the non-diffusive part shows a damped oscillating behavior. The origin of this oscillation will be discussed as well as the effect of temperature on the dynamics of the energy modes transport.

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