Letteratura scientifica selezionata sul tema "Phonons – Transport"
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Articoli di riviste sul tema "Phonons – Transport":
1
Liu, Yizhou, Yong Xu e Wenhui Duan. "Three-Dimensional Topological States of Phonons with Tunable Pseudospin Physics". Research 2019 (31 luglio 2019): 1–8. http://dx.doi.org/10.34133/2019/5173580.
Abstract (sommario):
Efficient control of phonons is crucial to energy-information technology, but limited by the lacking of tunable degrees of freedom like charge or spin. Here we suggest to utilize crystalline symmetry-protected pseudospins as new quantum degrees of freedom to manipulate phonons. Remarkably, we reveal a duality between phonon pseudospins and electron spins by presenting Kramers-like degeneracy and pseudospin counterparts of spin-orbit coupling, which lays the foundation for “pseudospin phononics”. Furthermore, we report two types of three-dimensional phononic topological insulators, which give topologically protected, gapless surface states with linear and quadratic band degeneracies, respectively. These topological surface states display unconventional phonon transport behaviors attributed to the unique pseudospin-momentum locking, which are useful for phononic circuits, transistors, antennas, etc. The emerging pseudospin physics offers new opportunities to develop future phononics.
2
Manuel, Cristina, e Laura Tolos. "Transport Properties of Superfluid Phonons in Neutron Stars". Universe 7, n. 3 (5 marzo 2021): 59. http://dx.doi.org/10.3390/universe7030059.
Abstract (sommario):
We review the effective field theory associated with the superfluid phonons that we use for the study of transport properties in the core of superfluid neutrons stars in their low temperature regime. We then discuss the shear and bulk viscosities together with the thermal conductivity coming from the collisions of superfluid phonons in neutron stars. With regard to shear, bulk, and thermal transport coefficients, the phonon collisional processes are obtained in terms of the equation of state and the superfluid gap. We compare the shear coefficient due to the interaction among superfluid phonons with other dominant processes in neutron stars, such as electron collisions. We also analyze the possible consequences for the r-mode instability in neutron stars. As for the bulk viscosities, we determine that phonon collisions contribute decisively to the bulk viscosities inside neutron stars. For the thermal conductivity resulting from phonon collisions, we find that it is temperature independent well below the transition temperature. We also obtain that the thermal conductivity due to superfluid phonons dominates over the one resulting from electron-muon interactions once phonons are in the hydrodynamic regime. As the phonons couple to the Z electroweak gauge boson, we estimate the associated neutrino emissivity. We also briefly comment on how the superfluid phonon interactions are modified in the presence of a gravitational field or in a moving background.
3
Prasher, Ravi. "Thermal Transport Due to Phonons in Random Nano-particulate Media in the Multiple and Dependent (Correlated) Elastic Scattering Regime". Journal of Heat Transfer 128, n. 7 (4 gennaio 2006): 627–37. http://dx.doi.org/10.1115/1.2194036.
Abstract (sommario):
Effects of multiple and dependent or correlated elastic scattering of phonons due to nanoparticles on thermal transport in random nano-particulate media (random phononic crystals) are investigated in this paper under various approximations. Multiple scattering means that the scattered wave from one particle is incident on another particle to be scattered again. Dependent scattering means far-field interference of the scattered waves due to phase difference, which is ignored in the independent scattering regime. Multiple and dependent scattering effects become important when the interparticle distance is comparable to the wavelength of phonons. Results show that multiple scattering primarily affects the velocity and density of states of phonons and dependent scattering primarily affects the mean free path of phonons. Effects of both multiple and dependent scattering increases with increasing volume fraction of nanoparticles. Modification of these parameters affects the equilibrium phonon intensity and the thermal conductivity of phonons.
4
Bin Mansoor, Saad, e Bekir Sami Yilbas. "Nonequilibrium cross-plane energy transport in aluminum–silicon–aluminum wafer". International Journal of Modern Physics B 29, n. 17 (23 giugno 2015): 1550112. http://dx.doi.org/10.1142/s021797921550112x.
Abstract (sommario):
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.
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Lax, M., e W. Cai. "EFFECT OF NONEQUILIBRIUM PHONONS ON THE ELECTRON RELAXATION AND TRANSPORT". International Journal of Modern Physics B 06, n. 07 (10 aprile 1992): 975–1006. http://dx.doi.org/10.1142/s0217979292000529.
Abstract (sommario):
We review the recent theoretical study of the effect of nonequilibrium phonons on hot-carrier relaxation and transport. In a quantum well, the proper treatment of the electron-phonon coupling between electrons confined to two dimensions (2-D) by phonons traveling freely in three dimensions (3D) requires special care because phonon heating produces a bottleneck in the rate of transfer of energy from the carriers to the phonons. Because the carriers interact with phonons primarily when the latter are close to the quantum well, the latter should be described, not by plane waves, but by packets adapted to the shape of the carrier confinement. A quasi-equilibrium technique that retains off-diagonal elements in the phonon wave-vector permits an unrestricted treatment of the density operator equation. That in turn leads to a choice of wave packet that comes from solving the integrodifferential equations rather than by imposition. Moreover, if the carrier distribution is assumed in quasi-equilibrium with a given drift and temperature, the coupled partial differential equations are reduced to coupled ordinary differential equations that can be solved with modest computer power. Comparison with experimental results for steady flow of energy from carriers to phonons, and for time-dependent relaxation yields quantitative agreement.
6
Bao, Bengang, Fei Li e Xin Zhou. "Characteristics of acoustic phonon transport and thermal conductance in multi-frame graphene nanoribbons". Modern Physics Letters B 32, n. 26 (20 settembre 2018): 1850307. http://dx.doi.org/10.1142/s0217984918503074.
Abstract (sommario):
Using non-equilibrium Green’s function method and maintaining the zigzag carbon chains unchanged, we investigate the transmission rate of acoustic phonon and the reduced thermal conductance through multi-frame graphene nanoribbons (GNRs). The results show that the reduced thermal conductance approaches [Formula: see text] in the limit [Formula: see text]. Due to the fact that only long wavelength acoustic phonons with zero cutoff frequency are excited at such low temperatures, the scattering influence on the long wavelength acoustic phonons by the multi-frame in GNRs can be ignored and these phonons can go through the scattering region perfectly. As the temperature goes up, the reduced thermal conductance decreases. This is because the high-frequency phonons are excited and these high-frequency phonons are scattered easily by the scattering structures. With the further rise in temperature, acoustic phonon modes with the cutoff frequency greater than zero are excited, which leads to a rapid increase of the reduced thermal conductance. This study shows that changing the frame structure by a small length can lead to a significant change of transmission probability. In the higher frequency region, the transmission spectra display complex peak-dip structures, which results from the fact that in higher frequency region more phonon modes are excited and scattered in the middle scattering region with multi-frames, and the scattering phonons are coupled with the incident phonons, with the increase of the length of frame structure, the scattering of the phonon is also enhanced, which leads to the decrease in the phonon transmission; by changing the frame structure, the parameters can effectively adjust the position of low-frequency phonon transmission valley. The frame structure can induce high-frequency phonon blocking effect and the blocking effect depending on the structure parameter of the frame. When the single frame and double frame GNRs are narrowest, the scattering from low-frequency phonons by the scattering structure is largest, which leads to the fact that the reduced thermal conductance is smallest at low temperatures; however, at high temperature, the reduced thermal conductance is biggest when the single frame and double frame GNRs are narrowest. This is because the scattering from high-frequency phonons by the scattering structure is the smallest. When the length of the frame structure is unchanged, a graphite chain is inserted in which the reduced thermal conductance is always reduced. These results provide an effective theoretical basis for designing the thermal transport quantum devices based on GNRs.
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Bannov, N. A., V. V. Mitin e F. T. Vasko. "Modelling of Hot Acoustic Phonon Propagation in Two Dimensional Layers". VLSI Design 6, n. 1-4 (1 gennaio 1998): 197–200. http://dx.doi.org/10.1155/1998/79658.
Abstract (sommario):
The transport of confined acoustic phonons in a flee-standing quantum well has been studied by solving the quantum kinetic equation for phonons. The phonon decay rate has been numerically calculated for GaAs flee-standing quantum well. Phonon interaction with electrons through the deformation potential makes the major contribution to the acoustic phonon decay.
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Chen, J., e Y. Liu. "Effect of out-of-plane acoustic phonons on the thermal transport properties of graphene". Condensed Matter Physics 26, n. 4 (2023): 43603. http://dx.doi.org/10.5488/cmp.26.43603.
Abstract (sommario):
The lattice thermal conductivity of graphene is evaluated using a microscopic model that takes into account the lattice's discrete nature and the phonon dispersion relation within the Brillouin zone. The Boltzmann transport equation is solved iteratively within the framework of three-phonon interactions without taking into account the four-phonon scattering process. The Umklapp and normal collisions are treated rigorously, thereby avoiding relaxation-time and long-wavelength approximations. The mechanisms of the failures of these approximations in predicting the thermal transport properties are discussed. Evaluation of the thermal conductivity is performed at different temperatures and frequencies and in different crystallite sizes. Reasonably good agreement with the experimental data is obtained. The calculation reveals a critical role of out-of-plane acoustic phonons in determining the thermal conductivity. The out-of-plane acoustic phonons contribute greatly and the longitudinal and transverse acoustic phonons make small contributions over a wide range of temperatures and frequencies. The out-of-plane acoustic phonons dominate the thermal conductivity due to their high density of states and restrictions governing the anharmonic phonon scattering. The selection rule severely restricts the phase space for out-of-plane phonon scattering due to reflection symmetry. The optical phonon contribution cannot be neglected at higher temperatures. Both Umklapp and normal processes must be taken into account in order to predict the phonon transport properties accurately.
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Luckyanova, M. N., J. Mendoza, H. Lu, B. Song, S. Huang, J. Zhou, M. Li et al. "Phonon localization in heat conduction". Science Advances 4, n. 12 (dicembre 2018): eaat9460. http://dx.doi.org/10.1126/sciadv.aat9460.
Abstract (sommario):
Nondiffusive phonon thermal transport, extensively observed in nanostructures, has largely been attributed to classical size effects, ignoring the wave nature of phonons. We report localization behavior in phonon heat conduction due to multiple scattering and interference events of broadband phonons, by measuring the thermal conductivities of GaAs/AlAs superlattices with ErAs nanodots randomly distributed at the interfaces. With an increasing number of superlattice periods, the measured thermal conductivities near room temperature increased and eventually saturated, indicating a transition from ballistic to diffusive transport. In contrast, at cryogenic temperatures the thermal conductivities first increased but then decreased, signaling phonon wave localization, as supported by atomistic Greenșs function simulations. The discovery of phonon localization suggests a new path forward for engineering phonon thermal transport.
10
Prasher, Ravi S. "Mie Scattering Theory for Phonon Transport in Particulate Media". Journal of Heat Transfer 126, n. 5 (1 ottobre 2004): 793–804. http://dx.doi.org/10.1115/1.1795243.
Abstract (sommario):
Scattering theory for the scattering of phonons by particulate scatterers is developed in this paper. Recently the author introduced the generalized equation of phonon radiative transport (GEPRT) in particulate media, which included a phase function to account for the anisotropic scattering of phonons by particulate scatterer. Solution of the GEPRT showed that scattering cross section is different from the thermal transport cross-section. In this paper formulations for the scattering and transport cross section for horizontally shear (SH) wave phonon or transverse wave phonon without mode conversion is developed. The development of the theory of scattering and the transport cross section is exactly analogous to the Mie scattering theory for photon transport in particulate media. Results show that transport cross section is very different from the scattering cross section. The theory of phonon scattering developed in this paper will be useful for the predictive modeling of thermal conductivity of practical systems, such as nanocomposites, nano-micro-particle-laden systems, etc.
Tesi sul tema "Phonons – Transport":
1
Davaasambuu, Jav, Friedrich Güthoff, Klaudia Hradil e Götz Eckold. "Phonons in demixing systems". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-188279.
2
Davaasambuu, Jav, Friedrich Güthoff, Klaudia Hradil e Götz Eckold. "Phonons in demixing systems". Diffusion fundamentals 12 (2010) 109, 2010. https://ul.qucosa.de/id/qucosa%3A13916.
3
Tavakoli-Ghinani, Adib. "Transport de phonons dans le régime quantique". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY090/document.
Abstract (sommario):
Ce travail de thèse est consacré à la mesure de transport de chaleur par les phonons dans le régime quantique dans des systèmes confinés à très basse température.Le contexte de ce sujet est de soumettre ces systèmes à deux conditions extrêmes : basse température et faibles dimensions et de comprendre les propriétés thermiques fondamentales issues de ces limites.Les échantillons étudiés au cours de cette thèse sont des structures suspendues (membrane ou nanofil) ; elles sont élaborées à partir de nitrure de silicium amorphe (SiN).En abaissant la température, les longueurs caractéristiques des phonons comme le libre parcours moyen ou la longueur d'onde dominante des phonons augmentent. Lorsque ces longueurs caractéristiques dépassent les dimensions latérales du système, la diffusion sur les surfaces (boundary scattering) régira les propriétés thermiques. Dans cette limite de diffusion, le transport des phonons va de la diffusion aux surfaces (régime de Casimir) au régime balistique (limite quantique). Dans ce régime balistique, le courant de chaleur peut être exprimé en utilisant le modèle de Landauer. La conductance thermique est alors exprimée par: K=N_α q T où, N_α est le nombre de modes vibratoires peuplés, q=((π²k_B^2)T)⁄3h est la valeur universelle du quantum de conductance thermique et T est le coefficient de transmission.Dans ce travail, les mesures de conductance thermique de nanofils suspendus ont été effectuées jusqu'à très basse température. Une plate-forme de mesure ayant une sensibilité sans précédent a été développée pour mesurer la variation d'énergie inférieure à l'attojoule. Ces nouveaux capteurs permettent de mesurer les propriétés thermiques du guide d'onde de phonon 1D dans le régime quantique du transport de chaleur. Nous montrons que le coefficient de transmission est le facteur dominant qui définit la valeur de conductance thermique. Ce coefficent dépend de la dimension et de la forme des réservoirs ainsi que de la nature du matériau utilisé ce qui rend difficile la mesure du quantum de conductance thermique. Nous montrons que dans toutes les structures de SiN mesurées, le transport thermique pourrait être dominé par des excitations de faible énergie qui existent dans les solides amorphes (a-solides).Le deuxième ensemble important d'expériences concerne la chaleur spécifique. Nous avons étudié les propriétés thermiques de membranes suspendues de SiN très minces que l'on pense être des cavités de phonon 2D. Nous montrons que la dépendance en température de la chaleur spécifique s'écarte du comportement quadratique comme prévu à très basse température. Les modèles pertinents donnant une explication quantitative des résultats sont encore à l'étude. La présence de systèmes à deux niveaux dans les matériaux amorphes pourrait être une explication possible de la valeur absolue élevée de la chaleur spécifique observéeThis PhD entitles Phonon heat transport in the quantum regime is based on the analysis of the thermal properties of confined systems at very low temperature.The context of this subject is putting the systems in two extreme conditions (low temperature and low dimensions) and understand the fundamental thermal properties coming from these limits.The studied samples during this PhD that are suspended structures (membrane or nanowire) are elaborated from amorphous silicon nitride.By lowering the temperature, the phonon characteristic lengths like the mean free path or the phonon dominant wavelength increase. When these characteristic lengths exceed lateral dimensions of the system, the boundary scattering will govern the thermal properties. In the boundary scattering, phonon transport goes from boundary limited scattering (Casimir regime) to ballistics regime (quantum limit). In this ballistic regime, the heat current can be expressed using the Landauer model. The thermal conductance is then expressed as: K=N_α q T where N_α is the number of populated vibrational modes, q=((π²k_B^2)T)⁄3h is the universal value of quantum of thermal conductance, and T is the transmission coefficient.In this work, thermal conductance measurements of suspended nanowires have been performed down to very low temperature. A measurement platform having an unprecedented sensitivity have been developed that can measure a variation of energy smaller than the attojoule. These new sensors allow the measurement of thermal properties of 1D phonon waveguide in the quantum regime of heat transport. We show that the transmission coefficient is the dominant factor that set the thermal conductance value. It depends on the dimension and the shape of the reservoirs, and the nature of the material in use rendering difficult the measurement of the quantum of thermal conductance. We show that in all of the SiN structures, the thermal transport could be dominated by low energy excitations that exist in amorphous solids (a-solids).The second important set of experiments concerns the specific heat. We have studied suspended the thermal properties of very thin SiN membranes that are thought to be 2D phonon cavities. We show that the temperature dependence of the specific heat departs from the quadratic behavior as expected at very low temperature. The true models giving a quantitative explanation of the results is still under consideration. The presence of tunneling two-level systems in amorphous materials could be one possible explanation for the high absolute value of specific heat that has been measured
4
Heron, Jean-Savin. "Transport des phonons à l'échelle du nanomètre". Phd thesis, Grenoble 1, 2009. http://www.theses.fr/2009GRE10183.
Abstract (sommario):
Pour comprendre les mécanismes du transport de la chaleur à l'échelle du nanomètre, nous avons fabriqué des dispositifs suspendus nanostructurés complexes et mesuré leur conductance thermique aux températures cryogéniques, notamment via la méthode 3 oméga. Nous avons pu ainsi démontrer la dépendance du transport des phonons aux dimensions et à la géométrie des nanostructures. Pour des nanofils de silicium d'une longueur comprise entre 8 et 10 µm, et d'une section de 200x100 nm^2, nous observons une déviation au régime diffusif de Casimir sous 5K, que nous pouvons expliquer en tenant compte de la rugosité en surface des nanofils. Quand la température décroit, la longueur d'onde des phonons augmente et des collisions balistiques en surface surviennent, impliquant une augmentation du libre parcours moyen des phonons, considéré comme constant jusque là. D'importants effets mésoscopiques sur le transport des phonons induits par la géométrie des nanofils ont pu être mesurés pour la première fois. La présence de zig-zag sur la longueur des fils bloquent le courant de phonons sur une large gamme de température, ayant pour conséquence une importante réduction de l'ordre de 40% de la conductance thermique en comparaison avec des nanofils droits. En parallèle, des expériences ont été menées sur des NEMS de silicium à basse température, et comparées avec des résultats antérieurs sur des MEMS de même géométrie. Le comportement mécanique des structures de silicium aux petites échelles est également abordé. A la fin de ce manuscrit, sont présentés les premiers prototypes de nano-calorimètres zepto-Joules (10^-21 J), qui vont permettre des caractérisations thermiques extrêmes d'objets uniques mésoscopiquesTo understand the mechanisms of the heat transport at small length scales, we are fabricating complex nano-devices and measuring the thermal conductance of suspended silicon nanowires at cryogenic temperatures, principally by the 3 omega method. We demonstrate the dependance of the phonon transport to the dimensions and the geometry of these nanostructures. For nanowires with a length between 8 and 10 µm, and a section of 200x100 nm^2, we observe a deviation of the diffusive regime of Casimir below 5K, which can be explained by taking account the roughness of the surface of the nanowires. When the temperature decreases, the wave length of the phonons increases and ballistic collisions at the surface occur, implying an increase of the mean free path of the phonons, considered before as constant. Important mesoscopic effects on the phonons transport induced by the geometry of the nanowires have been measured for the first time. The presence of zigzag on the length of the wires blocks the current of phonons on a wide range of temperature, with as consequence an important decrease in the order of 40 % of the thermal conductance in comparison with straight nanowires. Experiments in parrallel on silcon NEMS have been performed at low temperatures, and compared with MEMS of same geometries. The mechanical behavior of silcon nanostructures at low scale is also aborded. At the end, first prototypes of zeptoJoules nanocalorimeters (10^-21 J) are presented, which allow thermal characterization of single mesoscopic object
5
Heron, Jean-Savin. "Transport des phonons à l'échelle du nanomètre". Phd thesis, Grenoble 1, 2009. http://tel.archives-ouvertes.fr/tel-00461703.
Abstract (sommario):
Pour comprendre les mécanismes du transport de la chaleur à l'échelle du nanomètre, nous avons fabriqué des dispositifs suspendus nanostructurés complexes et mesuré leur conductance thermique aux températures cryogéniques, notamment via la méthode 3 oméga. Nous avons pu ainsi démontrer la dépendance du transport des phonons aux dimensions et à la géométrie des nanostructures. Pour des nanofils de silicium d'une longueur comprise entre 8 et 10 µm, et d'une section de 200x100 nm^2, nous observons une déviation au régime diffusif de Casimir sous 5K, que nous pouvons expliquer en tenant compte de la rugosité en surface des nanofils. Quand la température décroit, la longueur d'onde des phonons augmente et des collisions balistiques en surface surviennent, impliquant une augmentation du libre parcours moyen des phonons, considéré comme constant jusque là. D'importants effets mésoscopiques sur le transport des phonons induits par la géométrie des nanofils ont pu être mesurés pour la première fois. La présence de zig-zag sur la longueur des fils bloquent le courant de phonons sur une large gamme de température, ayant pour conséquence une importante réduction de l'ordre de 40% de la conductance thermique en comparaison avec des nanofils droits. En parallèle, des expériences ont été menées sur des NEMS de silicium à basse température, et comparées avec des résultats antérieurs sur des MEMS de même géométrie. Le comportement mécanique des structures de silicium aux petites échelles est également abordé. A la fin de ce manuscrit, sont présentés les premiers prototypes de nano-calorimètres zepto-Joules (10^-21 J), qui vont permettre des caractérisations thermiques extrêmes d'objets uniques mésoscopiques.
6
Hamzeh, Hani. "Résolution de l’équation de transport de Boltzmann pour les phonons et applications". Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112371/document.
Abstract (sommario):
Cette thèse est consacrée à l’étude de la dynamique et du transport des phonons via la résolution de l’équation de transport de Boltzmann (ETB) pour les Phonons. Un ‘solveur’ Monte Carlo dédié à la résolution de l’ETB des phonons dans l’espace réciproque, prenant en compte tous les processus d’interactions Normaux et Umklapp à trois-phonons, est proposé. Une prise en compte rigoureuse des lois de conservation de l’énergie et de la quantité de mouvement est entreprise. Des relations de dispersion réalistes, intégrant tous les modes de polarisations, sont considérées. Le calcul des taux d’interactions à trois-phonons de tous les processus Normaux et Umklapp est effectué en utilisant l’approche théorique due à Ridley qui ne nécessite qu’un unique paramètre semi-ajustable pour chaque mode de polarisation, nommément : le coefficient de couplage anharmonique représenté par les constantes de Grüneisen. Les taux d’interactions ainsi calculés ne servent pas uniquement à la résolution de l’ETB des phonons, mais ont permis aussi une analyse complète des canaux de relaxation des phonons longitudinaux optiques de centre de zone. Cette analyse a montré que le canal de Vallée-Bogani est négligeable dans le GaAs, et que vraisemblablement les temps de vie des phonons LO de centre de zone dans l’InAs et le GaSb rapportés dans la littérature sont fortement sous-estimés. Pour la première fois à notre connaissance, un couplage de deux solveurs Monte Carlo indépendants l’un dédié aux porteurs de charges (Thèse E. Tea) et l’autre dédié aux phonons, est effectué. Cela permet d’étudier l’effet des phonons chauds sur le transport des porteurs de charges. Cette étude a montré que l’approximation de temps de relaxation surestime souvent l’effet bottleneck des phonons. Le ‘solveur’ Monte Carlo est étendu pour résoudre l’ETB des phonons dans l’espace réel (en plus de l’espace réciproque), cela a permet d’étudier le transport des phonons et ainsi de la chaleur. La théorie généralisée de Ridley est toujours utilisée avec des particules de simulations qui interagissent les unes avec les autres directement. Les règles de conservation de l’énergie et de la quantité de mouvement sont rigoureusement respectées. L’effet des processus Umklapp sur la quantité de mouvement totale des phonons est fidèlement traduit; tout comme l’effet des interactions sur les directions des phonons, grâce à une procédure prenant en compte les directions vectorielles respectives lors d’une interaction, au lieu, de la distribution aléatoire usuellement utilisée. Les résultats préliminaires montrent la limite de l’équation analytique de conduction de la chaleurThis work is dedicated to the study of phonon transport and dynamics via the solution of Boltzmann Transport Equation (BTE) for phonons. The Monte Carlo stochastic method is used to solve the phonon BTE. A solution scheme taking into account all the different individual types of Normal and Umklapp processes which respect energy and momentum conservation rules is presented. The use of the common relaxation time approximation is thus avoided. A generalized Ridley theoretical scheme is used instead to calculate three-phonon scattering rates, with the Grüneisen constant as the only adjustable parameter. A method for deriving adequate adjustable anharmonic coupling coefficients is presented. Polarization branches with real nonlinear dispersion relations for transverse or longitudinal optical and acoustic phonons are considered. Zone-center longitudinal optical (LO) phonon lifetimes are extracted from the MC simulations for GaAs, InP, InAs, and GaSb. Decay channels contributions to zone-center LO phonon lifetimes are investigated using the calculated scattering rates. Vallée-Bogani’s channel is found to have a negligible contribution in all studied materials, notably GaAs. A comparison of phonons behavior between the different materials indicates that the previously reported LO phonon lifetimes in InAs and GaSb were quite underestimated in the literature. For the first time, to our knowledge, a coupling of two independent Monte Carlo solvers, one for charge carriers [PhD manuscript, E. TEA], and one for phonons, is undertaken. Hot phonon effect on charge carrier dynamics is studied. It is shown that the relaxation time approximation overestimates the phonon bottleneck effect. The phonon MC solver is extended to solve the phonon’s BTE in real space simultaneously with the reciprocal space, to study phonon and heat transport. Ridley’s generalized theoretical scheme is utilized again with simulation particles interacting directly together. Energy and momentum conservation laws are rigorously implemented. Umklapp processes effect on the total phonon momentum is thoroughly reproduced, as for the anharmonic interactions effect on resulting phonon directions. This is thanks to a procedure taking in consideration the respective vector directions during an interaction, instead of the randomization procedure usually used in literature. Our preliminary results show the limit of the analytic macroscopic heat conduction equation
7
Iskandar, Abdo. "Phonon Heat Transport and Photon-phonon Interaction in Nanostructures". Thesis, Troyes, 2018. http://www.theses.fr/2018TROY0010.
Abstract (sommario):
Cette thèse avait pour cadre, le contrôle du transport thermique via les phonons et leur interaction avec des photons dans des nanostructures. Le manuscrit comprend cinq chapitres. Dans le premier, nous introduisons la physique des phonons et excitations élémentaires optiques de la matière. Le deuxième chapitre fournit une description des procédés de croissance, techniques de structuration et techniques de caractérisation utilisées. Dans le troisième chapitre, nous démontrons qu’à la fois, phonons et photons peuvent être confinés et interagir dans une même nanostructure. Dans le quatrième chapitre, nous montrons expérimentalement que le spectre de phonons d'un matériau peut être modifié par des mécanismes d'hybridation entre des modes de surface introduits par une nanostructuration et les modes normaux du matériau massif. Nous montrons que la forme et la taille des nanostructures sur la surface du matériau ont des effets sur le spectre de phonons du substrat. Dans le cinquième chapitre, nous montrons qu'à basse température (inférieure à 4 K), la chaleur spécifique des nanofils est équivalente à celle d'un cristal essentiellement bidimensionnel. Encore plus étonnant à l'interface entre les nanofils et le substrat, nous avons mis en évidence une transition entre une transmission élastique spéculaire et une transmission élastique diffuse. Lorsque la température augmente on observe alors une transition entre une diffusion élastique et une diffusion inélastique. L’ensemble de ces résultats laisse entrevoir des perspectives intéressantes pour le contrôle des propriétés thermiques de matériaux massifs par nanostructuration de surfaceIn this dissertation, we investigate phonon heat transport and phonon interaction with optical elementary excitations in nanostructures. In the first chapter, we present an introduction to the physics of phonons and optical elementary excitations in nanostructured materials. The second chapter provides a detailed description of the samples growth and fabrication procedures and the various characterization techniques used. In the third chapter, we demonstrate that phonons and photons of different momenta can be confined and interact with each other within the same nanostructure. In the fourth chapter, we present experimental evidence on the change of the phonon spectrum and vibrational properties of a bulk material through phonon hybridization mechanisms. We demonstrate that the phonon spectrum of a bulk material can be altered by hybridization between confined phonon modes in nanostructures introduced on the surface of the material and the underlying bulk phonon modes. Shape and size of the nanostructures made on the surface of the substrate have strong effects on the phonon spectrum of the bulk material itself. In the fifth chapter, we demonstrate that at low temperatures (below 4 K) the nanowire specific heat exhibits a clear contribution from an essentially two-dimensional crystal. We also demonstrate that transitions from specular to diffusive elastic transmission and then from diffusive elastic to diffusive inelastic transmission occur at the interface between nanowires and a bulk substrate as temperature increases. Perspectives include the control of bulk material thermal properties via surface nanostructuring
8
France-Lanord, Arthur. "Transport électronique et thermique dans des nanostructures". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS566/document.
Abstract (sommario):
La miniaturisation continue des composants électroniques rend indispensable la connaissance des mécanismes de transport à l’échelle nanométrique. Alors que les processus simples de conduction dans les matériaux homogènes sont bien assimilés, la compréhension du transport à l’échelle nanométrique dans les systèmes hétérogènes reste à améliorer. Par exemple, le couplage entre courant, résistance et flux de chaleur dans des nanostructures doit être clarifié. Dans ce contexte, le sujet de thèse est centré autour du développement et de l’application de méthodes de calcul avancées pour la prédiction des propriétés de transport électronique et thermique à l’échelle nanométrique. Dans une première partie, nous avons paramétré un modèle de potentiel inter-atomique classique adapté à la description de systèmes multicomposants, afin de modéliser les propriétés structurelles, vibratoires et de transport de chaleur de la silice, ainsi que du silicium. Pour ce faire, une approche d’optimisation automatisée et reproductible a été mise en place. En guise d’exemple, nous avons calculé la dépendance en température de la résistance de Kapitza pour le système silice amorphe - silicium cristallin, ce qui a permis de souligner l’importance d’une description structurelle précise de l’interface. Dans une seconde partie, nous avons étudié la décomposition modale de la conductivité thermique du graphène supporté par un substrat de silice amorphe. Plus précisément, l’influence de l’état de surface (hydroxilation, etc) sur le transport thermique a été quantifiée. Le rôle déterminant des excitations collectives de phonons a été mis au jour. Finalement, dans une dernière partie, les propriétés de transport électronique du graphène supporté par une bi-couche de silice, système récemment observé expérimentalement, ont été étudiées. L’influence d’ondulations dans la couche de graphène ou dans le substrat, souvent présentes dans les échantillons réels et dont l’amplitude et la longueur d’onde peuvent être contrôlées, a été dégagée. Nous avons également modélisé le champ électrique généré par une grille, et déterminé son incidence sur le transport électroniqueThe perpetual shrinking of microelectronic devices makes it crucial to have a proper understanding of transport mechanisms at the nanoscale. While simple effects are now well understood in homogeneous materials, the understanding of nanoscale transport in heterosystems needs to be improved. For instance, the relationship between current, resistance, and heat flux in nanostructures remains to be clarified. In this context, the subject of the thesis is centered around the development and application of advanced numerical methods used to predict electronic and thermal conductivities of nanomaterials. This manuscript is divided into three parts. We begin with the parameterization of a classical interatomic potential, suitable for the description of multicomponent systems, in order to model the structural, vibrational, and thermal transport properties of both silica and silicon. A well-defined, reproducible, and automated optimization procedure is derived. As an example, we evaluate the temperature dependence of the Kapitza resistance between amorphous silica and crystalline silicon, and highlight the importance of an accurate description of the structure of the interface. Then, we have studied thermal transport in graphene supported on amorphous silica, by evaluating the mode-wise decomposition of thermal conductivity. The influence of hydroxylation on heat transport, as well as the significant role played by collective excitations of phonons, have come to light. Finally, electronic transport properties of graphene supported on quasi-two-dimensional silica, a system recently observed experimentally, have been investigated. The influence on transport properties of ripples in the graphene sheet or in the substrate, which often occur in samples and whose amplitude and wavelength can be controlled, has been evaluated. We have also modeled electrostatic gating, and its impact on electronic transport
9
Hamzeh, Hani. "Résolution de l'équation de transport de Boltzmann pour les phonons et applications". Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00778705.
Abstract (sommario):
Cette thèse est consacrée à l'étude de la dynamique et du transport des phonons via la résolution de l'équation de transport de Boltzmann (ETB) pour les Phonons. Un 'solveur' Monte Carlo dédié à la résolution de l'ETB des phonons dans l'espace réciproque, prenant en compte tous les processus d'interactions Normaux et Umklapp à trois-phonons, est proposé. Une prise en compte rigoureuse des lois de conservation de l'énergie et de la quantité de mouvement est entreprise. Des relations de dispersion réalistes, intégrant tous les modes de polarisations, sont considérées. Le calcul des taux d'interactions à trois-phonons de tous les processus Normaux et Umklapp est effectué en utilisant l'approche théorique due à Ridley qui ne nécessite qu'un unique paramètre semi-ajustable pour chaque mode de polarisation, nommément : le coefficient de couplage anharmonique représenté par les constantes de Grüneisen. Les taux d'interactions ainsi calculés ne servent pas uniquement à la résolution de l'ETB des phonons, mais ont permis aussi une analyse complète des canaux de relaxation des phonons longitudinaux optiques de centre de zone. Cette analyse a montré que le canal de Vallée-Bogani est négligeable dans le GaAs, et que vraisemblablement les temps de vie des phonons LO de centre de zone dans l'InAs et le GaSb rapportés dans la littérature sont fortement sous-estimés. Pour la première fois à notre connaissance, un couplage de deux solveurs Monte Carlo indépendants l'un dédié aux porteurs de charges (Thèse E. Tea) et l'autre dédié aux phonons, est effectué. Cela permet d'étudier l'effet des phonons chauds sur le transport des porteurs de charges. Cette étude a montré que l'approximation de temps de relaxation surestime souvent l'effet bottleneck des phonons. Le 'solveur' Monte Carlo est étendu pour résoudre l'ETB des phonons dans l'espace réel (en plus de l'espace réciproque), cela a permet d'étudier le transport des phonons et ainsi de la chaleur. La théorie généralisée de Ridley est toujours utilisée avec des particules de simulations qui interagissent les unes avec les autres directement. Les règles de conservation de l'énergie et de la quantité de mouvement sont rigoureusement respectées. L'effet des processus Umklapp sur la quantité de mouvement totale des phonons est fidèlement traduit; tout comme l'effet des interactions sur les directions des phonons, grâce à une procédure prenant en compte les directions vectorielles respectives lors d'une interaction, au lieu, de la distribution aléatoire usuellement utilisée. Les résultats préliminaires montrent la limite de l'équation analytique de conduction de la chaleur.
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Santamore, Deborah Hannah Cross Michael Clifford. "Quantum transport and dynamics of phonons in mesoscopic systems /". Diss., Pasadena, Calif. : California Institute of Technology, 2003. http://resolver.caltech.edu/CaltechETD:etd-05272003-152136.
Libri sul tema "Phonons – Transport":
1
Gurevich, Vadim Lʹvovich. Transport in phonon systems. Amsterdam: North-Holland, 1986.
2
Gurevich, V. L. Transport in phonon systems. Amsterdam: North-Holland, 1986.
3
L̕ubomír, Hrivnák, a cura di. Teória tuhých látok. 2a ed. Bratislava: Veda, vydavatel̕stvo Slovenskej akadémie vied, 1985.
4
Ziman, J. M. Electrons and phonons: The theory of transport phenomena in solids. Oxford: Clarendon Press, 2001.
5
Chen, Gang. Nanoscale energy transport and conversion: A parallel treatment of electrons, molecules, phonons, and photons. New York, NY: Oxford, 2004.
6
Gang, Chen. Nanoscale energy transport and conversion: A parallel treatment of electrons, molecules, phonons, and photons. Oxford: Oxford University Press, 2005.
7
Frey, Martin. Scattering in nanoscale devices. Konstanz: Hartung-Gorre, 2010.
8
Li, Hai-Peng, e Rui-Qin Zhang. Phonon Thermal Transport in Silicon-Based Nanomaterials. Singapore: Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-13-2637-0.
9
Neophytou, Neophytos. Theory and Simulation Methods for Electronic and Phononic Transport in Thermoelectric Materials. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-38681-8.
10
Yamamoto, Takahiro, Kazuyuki Watanabe e Satoshi Watanabe. Thermal transport of small systems. A cura di A. V. Narlikar e Y. Y. Fu. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780199533046.013.6.
Abstract (sommario):
This article focuses on the phonon transport or thermal transport of small systems, including quasi-one-dimensional systems such as carbon nanotubes. The Fourier law well describes the thermal transport phenomena in normal bulk materials. However, it is no longer valid when the sample dimension reduces down to below the mean-free path of phonons. In such a small system, the phonons propagate coherently without interference with other phonons. The article first considers the Boltzmann–Peierls formula of diffusive phonon transport before discussing coherent phonon transport, with emphasis on the Landauer formulation of phonon transport, ballistic phonon transport and quantized thermal conductance, numerical calculation of the phonon-transmission function, and length dependence of the thermal conductance.
Capitoli di libri sul tema "Phonons – Transport":
1
Jacoboni, Carlo. "Phonons". In Theory of Electron Transport in Semiconductors, 49–68. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-10586-9_5.
2
Srivastava, Gyaneshwar P. "Phonons and Thermal Transport in Nanocomposites". In The Physics of Phonons, 259–94. 2a ed. Boca Raton: CRC Press, 2022. http://dx.doi.org/10.1201/9781003141273-9.
3
Sols, F. "Dissipative Transport in Nanostructures: A Many-Electron Approach". In Phonons in Semiconductor Nanostructures, 479–87. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-1683-1_46.
4
Srivastava, Gyaneshwar P. "Phonons and Thermal Transport in Impure and Mixed Crystals". In The Physics of Phonons, 319–42. 2a ed. Boca Raton: CRC Press, 2022. http://dx.doi.org/10.1201/9781003141273-11.
5
Noguchi, H., T. Takamasu, N. Miura, J. P. Leburton e H. Sakaki. "Theoretical and Experimental Study of Electron Transport in One-Dimensional Coupled Quantum Boxes". In Phonons in Semiconductor Nanostructures, 471–78. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-1683-1_45.
6
Bannov, N. A., V. V. Mitin e M. A. Stroscio. "Localized Acoustic Phonons in Low Dimensional Structures". In Quantum Transport in Ultrasmall Devices, 191–200. Boston, MA: Springer US, 1995. http://dx.doi.org/10.1007/978-1-4615-1967-6_9.
7
Lukkarinen, Jani. "Kinetic Theory of Phonons in Weakly Anharmonic Particle Chains". In Thermal Transport in Low Dimensions, 159–214. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-29261-8_4.
8
Stock, B., M. Fieseler e R. G. Ulbrich. "Transport Properties of Tera-Hertz Phonons in Galliumarsenide". In Proceedings of the 17th International Conference on the Physics of Semiconductors, 1177–80. New York, NY: Springer New York, 1985. http://dx.doi.org/10.1007/978-1-4615-7682-2_266.
9
Vast, Nathalie, Jelena Sjakste, Gaston Kané e Virginie Trinité. "Electronic Transport: Electrons, Phonons and Their Coupling within the Density Functional Theory". In Simulation of Transport in Nanodevices, 31–96. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2016. http://dx.doi.org/10.1002/9781118761793.ch2.
10
Ruckh, R., e E. Sigmund. "Quasi Resonant Transport Behaviour of Nonequilibrium Phonons in Insulating Crystals". In Phonon Scattering in Condensed Matter V, 278–80. Berlin, Heidelberg: Springer Berlin Heidelberg, 1986. http://dx.doi.org/10.1007/978-3-642-82912-3_81.
Atti di convegni sul tema "Phonons – Transport":
1
Roberts, N. A., e D. G. Walker. "Phonon Transport in Asymmetric Sawtooth Nanowires". In ASME/JSME 2011 8th Thermal Engineering Joint Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajtec2011-44341.
Abstract (sommario):
Thermal transport in asymmetric sawtooth nanowires was investigated. The boundaries reflect phonons differently depending on the frequency and momentum of the phonon. These systems show thermally rectifying behavior when the boundary reflections are a function of both the direction the phonon is traveling and the frequency of the phonon. This rectifying effect could be useful for thermal management applications at all size scales, but would have to be built up from the nanoscale because of a strong dependence on the device aspect ratio and the Knudsen number of the system. Monte Carlo simulations show an accumulation of phonons at the boundary which emits phonons in a perceived rough direction where those phonons have some probability of diffuse reflections at the boundary while phonons emitted in the smooth direction only experience specular reflections at the boundary and are eventually thermalized at the opposite boundary. In this study the level of rectification of the system was linearly dependent on the device aspect ratio as long as the length of the device was near or below the phonon mean free path of the phonons.
2
Dechaumphai, Edward, e Renkun Chen. "Modeling of Thermal Transport in Phononic Crystals Using Finite Difference Time Domain Method". In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-65477.
Abstract (sommario):
Phonon transport in two dimensional nano-membranes with periodic variations in acoustic properties, a.k.a. phononic crystals, has drawn tremendous interests recently due to their novel properties and potential applications in thermal energy conversion. Recent experiments have demonstrated drastically lower thermal conductivity than what one would expect from the Boltzmann transport equations (BTE) that describe phonon transport as particle diffusion. To understand the intriguing behavior, we used a partially coherent picture to model thermal transport in 2D phononic crystals. In this model, phonons with mean free paths longer than the characteristic size of the phononic crystals are treated as coherent waves. The finite difference time domain method is utilized to simulate the wave behavior and to obtain the phonon dispersion relations in phononic crystals. On the other hand, phonons with mean free paths shorter than the characteristic size are considered particles and are treated by BTE after taking the diffusive boundary scattering into account. Our result shows that the thermal conductivity reduces as the characteristic sizes decrease due to both the zone folding effect and the diffusive boundary scattering, which is consistent with the recent experimental results.
3
Sinha, S., E. Pop e K. E. Goodson. "A Split-Flux Model for Phonon Transport Near Hotspots". In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-61949.
Abstract (sommario):
Intense electron-phonon scattering near the peak electric field in a semiconductor device results in nanometer-scale phonon hotspots with power densities on the order of 1 W/μm3. To study the impact of the hotspot on phonon transport, we solve the phonon Boltzmann transport equation under the relaxation time approximation to yield the departure from equilibrium amongst phonon modes. The departure function is split into two contributions: one arising from the far-from-equilibrium emitted phonons and the other from the near-equilibrium thermal phonons. The model predictions are compared with existing data on ballistic phonon transport in silicon. Computations of transient and steady state phonon occupation numbers for a device geometry show the predominance of longitudinal optical phonons for electric fields on the order of 1 MV/m. Due to the low group velocity of these modes, there is an energy stagnation at the hotspot which results in an excess temperature rise of about 13% for a 90 nm bulk silicon device. During device switching, emitted phonons have sufficient time to relax completely when the duty cycle is 30% on a period of 100 ps.
4
Zuckerman, Neil, e Jennifer R. Lukes. "Atomistic Visualization of Ballistic Phonon Transport". In ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference collocated with the ASME 2007 InterPACK Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ht2007-32674.
Abstract (sommario):
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.
5
Masao, Yusuke, e Mitsuhiro Matsumoto. "Direct Simulation of the Nonlinear Boltzmann Transport Equation for Phonons". In ASME/JSME 2011 8th Thermal Engineering Joint Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajtec2011-44060.
Abstract (sommario):
In order to solve a Boltzmann transport equation (BTE) of phonons for investigating heat conduction in non-metallic solids, we propose to employ a DSMC (direct simulation Monte Carlo) scheme to simulate dynamics of phonons in analogy with rarefied gas. In this paper, we describe the DSMC scheme for phonon dynamics and present some results with our prototype codes for a face-centered cubic model. The dynamics of phonons with two branches of acoustic modes is discussed, in the case where the distribution of phonons in strong nonequilibrium situation is driven into equilibrium.
6
Miller, John, Wanyoung Jang e Chris Dames. "Thermal Rectification by Ballistic Phonons". In ASME 2008 3rd Energy Nanotechnology International Conference collocated with the Heat Transfer, Fluids Engineering, and Energy Sustainability Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/enic2008-53064.
Abstract (sommario):
In analogy to the asymmetric transport of electricity in a familiar electrical diode, a thermal rectifier transports heat more favorably in one direction than in the reverse direction. One approach to thermal rectification is asymmetric scattering of phonons and/or electrons, similar to suggestions in the literature for a sawtooth nanowire [1] or 2-dimensional electron gas with triangular scatterers [2]. To model the asymmetric heat transport in such nanostructures, we have used phonon ray-tracing, focusing on characteristic lengths that are small compared to the mean free path of phonons in bulk. To calculate the heat transfer we use a transmission-based (Landauer-Buttiker) method. The system geometry is described by a four-dimensional transfer function that depends on the position and angle of phonon emission and absorption from each of two contacts. At small temperature gradients, the phonon distribution function is very close to the usual isotropic equilibrium (Bose-Einstein) distribution, and there is no thermal rectification. In contrast, at large temperature gradients, the anisotropy in the phonon distribution function becomes significant, and the resulting heat flux vs. temperature curve (analogous to I-V curve of a diode) reveals large thermal rectification.
7
Singh, Dhruv, Jayathi Y. Murthy e Timothy S. Fisher. "Frequency Resolved Phonon Transport in Si/Ge Nanocomposites". In ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems. ASMEDC, 2011. http://dx.doi.org/10.1115/ipack2011-52244.
Abstract (sommario):
In this paper, we analyze cross plane phonon transport and thermal conductivity in two-dimensional Si/Ge nanocomposites. A non-gray BTE model that includes full details of phonon dispersion, the spread in phonon mean free paths and the frequency dependent transmissivity is used to simulate thermal transport. The general conclusions inferred from gray BTE simulations that the thermal conductivity of the nanocomposite is much lower than its constituent materials and interfacial density as the parameter determining thermal conductivity remain the same. However, it is found that the gray BTE significantly overpredicts thermal conductivity in the length scales of interest and quantitatively reliable results are obtained only upon inclusion of the details of phonon dispersion. The transition of phonon transport from ballistic regime to near diffusive regime is observed by looking at a large range of length scales. Non-equilibrium energy exchange between optical and acoustic phonons and the granularity in phonon mean free paths are found to significantly affect thermal conductivity leading to departures from the frequently employed gray approximation. It is also found that the frequency content of thermal conductivity in the nanocomposite extends out to a much larger frequency range unlike bulk Si and Ge. Scattering against heterogeneous interfaces is very effective in suppressing thermal conductivity contribution from the low frequency acoustic phonons but less so for high frequency phonons, which have much smaller mean free paths.
8
Prasher, Ravi S. "Scattering of Phonons by Nano and Micro Particles". In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-59347.
Abstract (sommario):
Scattering theory for the scattering of phonons by particulate scatterers is developed in this paper. Recently the author introduced the generalized equation of phonon radiative transport (GEPRT) in particulate media which included a phase function to account for the anisotropic scattering of phonons by particulate scatterer. Solution of the GEPRT showed that scattering cross section is different than the thermal transport cross section. In this paper formulations for the scattering and transport cross section for horizontally shear (SH) wave phonon or transverse wave phonon without mode conversion is developed. The development of the theory of scattering and the transport cross section is exactly analogous to the Mie scattering theory for photon transport in particulate media. Results show that transport cross section is very different than the scattering cross section. It is also shown that for SH (horizontally shear) phonons the scattering and transport cross sections are proportional to ω8 rather than the well accepted value of ω4 in the Rayleigh regime where ω is the frequency of the SH phonons. The theory of phonon scattering developed in this paper will be useful for the predictive modeling of thermal conductivity of practical systems such as nano composites, nano-micro particle laden systems and etc.
9
Shi, Li, Sergei Plyasunov, Adrian Bachtold, Paul L. McEuen e Arunava Majumdar. "Scanning Thermal Microscopy of Carbon Nanotubes". In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1453.
Abstract (sommario):
Abstract This paper reports the use of scanning thermal microscopy (SThM) for studying heat dissipation and phonon transport in nanoelectronic circuits consisting of carbon nanotubes (CNs). Thermally designed and batch fabricated SThM probes were used to resolve the phonon temperature distribution in the CN circuits with a spatial resolution of 50 nm. Heat dissipation at poor metal-CN contacts could be readily found by the thermal imaging technique. Important questions regarding energy transport in nanoelectronic circuits, such as where is heat dissipated, whether the electrons and phonons are in equilibrium, how phonons are transported, and what are the effects of mechanical deformation on the transport and dissipation properties, are addressed in this work.
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Park, Jungkyu, Eduardo B. Farfán, Christian Enriquez, Nicholas Kinder e Matthew Greeson. "Thermal Transport in Thorium Dioxide". In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-71614.
Abstract (sommario):
Thorium is more abundant in nature than uranium and thorium fuels can breed fissile U-233 fuel that can be used in various types of nuclear reactors. Moreover, thorium dioxide has drawn interest from researchers due to its relatively superior thermal properties when compared to conventional uranium dioxide fuel pellets. In this study, thermal transport in thorium dioxide is investigated using reverse non-equilibrium molecular dynamics. The thermal conductivity of bulk thorium dioxide was measured to be 20.8 W/m-K and the phonon mean free path was estimated to be between 7 ∼ 8.5 nm at 300 K. It was also observed that the thermal conductivity of thorium dioxide has a strong dependency on temperature; the thermal conductivity decreases with an increase in the temperature. Moreover, by simulating thorium dioxide structures with different lengths at different temperatures, it was also identified that short wavelength phonons dominate thermal transport in thorium dioxide at high temperatures, resulting in decreased intrinsic phonon mean free paths and minimal effect of boundary scattering while long wavelength phonons dominate the thermal transport in thorium dioxide at low temperatures.
Rapporti di organizzazioni sul tema "Phonons – Transport":
1
Baowen, Li. Managing Phonon Transport by Core/Shell Nanowires. Fort Belvoir, VA: Defense Technical Information Center, novembre 2012. http://dx.doi.org/10.21236/ada570448.
2
Ziade, Elbara, Elbara Ziade, Khalid Hattar e Khalid Hattar. Tunable Thermal Transport across Interfaces via Phonon Engineering. Office of Scientific and Technical Information (OSTI), novembre 2019. http://dx.doi.org/10.2172/1763287.
3
Sarma, Sankar D. Electron-Phonon Interaction, Transport and Ultrafast Processes in Semiconductor Microstructures. Fort Belvoir, VA: Defense Technical Information Center, agosto 1992. http://dx.doi.org/10.21236/ada255297.
4
Das Sarma, Sankar. Electron-Phonon Interaction, Transport and Ultrafast Processes in Semiconductor Microstructures. Fort Belvoir, VA: Defense Technical Information Center, agosto 1992. http://dx.doi.org/10.21236/ada255723.