Tesis:

1

Iskandar, Abdo. "Phonon Heat Transport and Photon-phonon Interaction in Nanostructures". Thesis, Troyes, 2018. http://www.theses.fr/2018TROY0010.

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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 surface
In 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

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2

Yatsui, T. y M. Ohtsu. "Dressed Photon-phonon Technology for Ultra Flat Surface". Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35264.

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A reduction of the surface roughness, Ra, is required in various applications including electronic devic-es and / or optical devices. Although chemical-mechanical polishing (CMP) has been used to flatten the sur-faces, it is generally limited to reducing Ra to about 2 Å because the polishing pad roughness is as large as 10 m, and the polishing-particle diameters in the slurry are as large as 100 nm. We therefore developed a new polishing method, dressed-photon and phonon etching (DPP etching), that uses dressed photon based on an autonomous phonon-assisted process. DPP etching does not use any polishing pad, with which we obtained ultra-flat silica surface with angstrom-scale average roughness as small as Ra of 0.1 nm. Addi-tionally, we succeeded in reduction of the Ra for the three-dimensional structures. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35264

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3

Fung, Tsz Cheong. "Phonon magnonics". Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:a36d494d-73c5-410a-82df-abd0117884e6.

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This thesis reports on some recent results in the field of acoustics and magnonics. Chapter 1 reviews the literature on magnonics and GHz frequency transducers, and highlights the lack of understanding of the growth mechanism of magnetron sputtered ZnO thin films. A novel configuration for exciting magnetostatic spinwaves using ZnO transducers is proposed. Chapter 2 is an introduction to piezoelectricity and how it can be used to generate GHz acoustic waves. A detailed formulation of the Mason model is presented in chapter 3 for predicting the performance of ZnO transducers. In chapter 4, the fabrication protocol of ZnO transducers in the custom-built sputtering plant is discussed and the transducer characterisation techniques including X-ray and pulse echo measurement are described. In chapter 5, the characterised properties of the film are compared with modelling prediction. It is found that the piezoelectric and structural properties of the fabricated ZnO films are strongly correlated and are critically dependent on the sputtering conditions and thicknesses. Chapter 6 is dedicated to plasma characterisation of the sputtering conditions using Langmuir probe diagnostics. The making of the Langmuir probe system and its development are discussed. Chapter 7 examines the various possible growth mechanisms of the ZnO films with a view to understanding how the c-axis texture forms during sputtering. The results from the Langmuir probe diagnostics and X-ray characterization indicate the detrimental in uence of ion bombardment on the film qualities. It is deduced that the c-axis self texturing of ZnO films is driven dominantly by the 'survival of the fastest' mechanism. Chapter 8 describes the theoretical formulation of magnetostatic spin-wave modes and the mechanism for which the laterally propagating magnetostatic modes are coupled to local elastic standing waves. The experimental evidence (using time resolved spectroscopy) of the acoustic excitation of magnetostatic spin-waves in a YIG film waveguide is then presented in chapter 9; the excitation efficiencies at various magnetic field configurations and carrier frequencies are investigated. Finally, chapter 10 ends the thesis with the summary of results and outlooks.

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4

KOMIRENKO, SERGIY MYKHAYLOVYCH. "Phonons and phonon-related effects in prospective nanoscale semiconductor devices". NCSU, 2000. http://www.lib.ncsu.edu/theses/available/etd-20001030-145518.

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The research was devoted to the theoretical investigation of lattice vibrations in low-dimensional heterostructures and bulk materials with strong polaronic coupling. The purpose of the research has been to develop the phonon theory for technologically-important materials such as nitrides of Ga and Al as well as to locate new phonon-related effects which can be utilized in artificially-created heterostructures. The electron-phonon interaction has been considered quantum mechanically.The main findings can be summarized briefly as follows: 1. Consideration of carrier-induced renormalization of acoustic phonon spectra in quantum wires revealed the possibility for the Peierls phase transition into a state with periodic lattice distortion and charge-density waves of macroscopic period in artificially-prepared structures. The phase diagram for this transition has been determined. An analytical dispersion relation for the coupled electron-phonon excitation has been derived.2. It is found that the drift of two-dimensional electrons in quantum wells can lead to efficient amplification (generation) of sub-THz coherent confined acoustic vibrations due to the Cerenkov effect when the velocity of the drifted electrons exceeds the sound velocity in the given medium. A theory has been developed to describe the confinement of acoustic modes propagating along the high-symmetry directions in cubic quantum wells.3. A theory of confinement of optical phonon modes in wurtzite quantum wells has been developed. A formalism has been derived for calculation of electron scattering rates in optically anisotropic (uniaxial) crystals and quantum wells. 4. From the comparison of the energy losses to the lattice as function of the carrier velocity obtained in frameworks of perturbative model and path-integral Thornber-Feynman approach it is found that perturbation theory can be applied for materials with intermediate polaronic coupling such a GaN and AlN. Moreover, the theoretical possibility of unique low-field runaway transport in these materials has been demonstrated.

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5

Lehmann, Dietmar. "Phonon Spectroscopy and Low-Dimensional Electron Systems". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2006. http://nbn-resolving.de/urn:nbn:de:swb:14-1138734990743-55381.

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The generation and propagation of pulses of nonequilibrium acoustic phonons and their interaction with semiconductor nanostructures are investigated. Such studies can give unique information about the properties of low-dimensional electron systems, but in order to interpret the experiments and to understand the underlying physics, a comparison with theoretical models is absolutely necessary. A central point of this work is therefore a universal theoretical approach allowing the simulation and the analysis of phonon spectroscopy measurements on low-dimensional semiconductor structures. The model takes into account the characteristic properties of the considered systems. These properties are the elastic anisotropy of the substrate material leading to focusing effects and highly anisotropic phonon propagation, the anisotropic nature of the different electron-phonon coupling mechanisms, which depend manifestly on phonon wavevector direction and polarization vector, and the sensitivity to the confinement parameters of the low-dimensional electron systems. We show that screening of the electron-phonon interaction can have a much stronger influence on the results of angle-resolved phonon spectroscopy than expected from transport measurements. Since we compare theoretical simulations with real experiments, the geometrical arrangement and the spatial extension of phonon source and detector are also included in the approach enabling a quantitative analysis of the data this way. To illustrate the influence of acoustic anisotropy and carrier confinement on the results of phonon spectroscopy in detail we analyse two different applications. In the first case the low-dimensional electron system acts as the phonon detector and the phonon induced drag current is measured. Our theoretical model enables us to calculate the electric current induced in low-dimensional electron systems by pulses of (ballistic) nonequilibrium phonons. The theoretical drag patterns reproduce the main features of the experimental images very well. The sensitivity of the results to variations of the confining potential of quasi-2D and quasi-1D electrons is demonstrated. This provides the opportunity to use phonon-drag imaging as unique experimental tool for determining the confinement lengths of low-dimensional electron systems. By comparing the experimental and theoretical images it is also possible to estimate the relative strength of the different electron-phonon coupling mechanisms.In the second application the low-dimensional electron system acts as the phonon pulse source and the angle and mode dependence of the acoustic phonon emission by hot 2D electrons is investigated. The results exhibit strong variations in the phonon signal as a function of the detector position and depend markedly on the coupling mechanism, the phonon polarization and the electron confinement width. We demonstrate that the ratio of the strengths of the emitted longitudinal (LA) and transverse (TA) acoustic phonon modes is predicted correctly only by a theoretical model that properly includes the effects of acoustic anisotropy on the electron-phonon matrix elements, the screening, and the form of the confining potential. A simple adoption of widely used theoretical assumptions, like the isotropic approximation for the phonons in the electron-phonon matrix elements or the use of simple variational envelope wavefunctions for the carrier confinement, can corrupt or even falsify theoretical predictions.We explain the `mystery of the missing longitudinal mode' in heat-pulse experiments with hot 2D electrons in GaAs/AlGaAs heterojunctions. We demonstrate that screening prevents a strong peak in the phonon emission of deformation potential coupled LA phonons in a direction nearly normal to the 2D electron system and that deformation potential coupled TA phonons give a significant contribution to the phonon signal in certain emission directions
Die vorliegende Arbeit beschäftigt sich mit der Ausbreitung von akustischen Nichtgleichgewichtsphononen und deren Wechselwirkung mit Halbleiter-Nanostrukturen. Güte und Effizienz moderner Halbleiter-Bauelemente hängen wesentlich vom Verständnis der Wechselwirkung akustischer Phononen mit niederdimensionalen Elektronensystemen ab. Traditionelle Untersuchungsmethoden, wie die Messung der elektrischen Leitfähigkeit oder der Thermospannung, erlauben nur eingeschränkte Aussagen. Sie mitteln über die beteiligten Phononenmoden und eine Trennung der einzelnen Wechselwirkungsmechanismen ist nur näherungsweise möglich ist. Demgegenüber erlaubt die in der Arbeit diskutierte Methode der winkel- und zeitaufgelösten Phononen-Spektroskopie ein direktes Studium des Beitrags einzelner Phononenmoden, d.h. in Abhängigkeit von Wellenzahlvektor und Polarisation der Phononen. Im Mittelpunkt der Arbeit steht die Fragestellung, wie akustische Anisotropie und Ladungsträger-Confinement die Ergebnisse der winkel- und zeitaufgelösten Phononen-Spektroskopie beeinflussen und prägen. Dazu wird ein umfassendes theoretisches Modell zur Simulation von Phononen-Spektroskopie-Experimenten an niederdimensionalen Halbleitersystemen vorgestellt. Dieses erlaubt sowohl ein qualitatives Verständnis der ablaufenden physikalischen Prozesse als auch eine quantitative Analyse der Messergebnisse. Die Vorteile gegenüber anderen Modellen und Rechnungen liegen dabei in dem konsequenten Einbeziehen der akustischen Anisotropie, nicht nur für die Ausbreitung der Phononen, sondern auch für die Matrixelemente der Wechselwirkung, sowie eine saubere Behandlung des Confinements der Elektronen in den niederdimensionalen Systemen. Dabei werden die Grenzen weit verbreiteter Näherungsansätze für die Elektron-Phonon-Matrixelemente und das Elektronen-Confinement deutlich aufgezeigt. Für den quantitativen Vergleich mit realen Experimenten werden aber auch solche Größen, wie die endliche räumliche Ausdehnung von Phononenquelle und Detektor, die Streuung der Phononen an Verunreinigungen oder die Abschirmung der Elektron-Phonon-Kopplung durch die Elektron-Elektron-Wechselwirkung berücksichtigt.Im zweiten Teil der Arbeit wird der theoretische Apparat auf typische experimentelle Fragestellungen angewandt. Im Falle der Phonon-Drag-Experimente an GaAs/AlGaAs Heterostrukturen wird der durch akustische Nichtgleichgewichtsphononen in zwei- und eindimensionalen Elektronensystemen induzierte elektrische Strom (Phonon-Drag-Strom) als Funktion des Ortes der Phononenquelle bestimmt. Das in der Arbeit hergeleitete theoretische Modell kann die experimentellen Resultate für die Winkelabhängigkeit des Drag-Stromes sowohl für Messungen mit und ohne Magnetfeld qualitativ gut beschreiben. Außerdem wird der Einfluss unterschiedlicher Confinementmodelle und unterschiedlicher Wechselwirkungsmechanismen studiert. Dadurch ist es möglich, aus Phonon-Drag-Messungen Rückschlüsse auf die elektronischen und strukturellen Eigenschaften der niederdimensionalen Elektronensysteme zu ziehen (Fermivektor, effektive Masse, Elektron-Phonon-Kopplungskonstanten, Form des Confinementpotentials). Als weiteres Anwendungsbeispiel wird das Problem der Energierelaxation (aufgeheizter)zweidimensionaler Elektronensysteme in GaAs Heterostrukturen und Quantentrögen untersucht. Für Elektronentemperaturen unterhalb 50 K werden die Gesamtemissionsrate als Funktion der Temperatur und die winkelaufgelöste Emissionsrate (als Funktion der Detektorposition) berechnet. Für beide Größen wird erstmals eine gute Übereinstimmung zwischen Theorie und Experiment gefunden. Es zeigt sich, dass akustische Anisotropie und Abschirmungseffekte zu überraschenden neuen Ergebnissen führen können. Ein Beispiel dafür ist der unerwartet große Beitrag der mittels Deformationspotential-Wechselwirkung emittierten transversalen akustischen Phononen, der bei einer Emission der Phononen näherungsweise senkrecht zum zweidimensionalen System beobachtet werden kann

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6

Chamberlain, Martyn Paul. "Electrons, phonons, coupled phonon-plasmons and their interactions in semiconductor heterostructures". Thesis, University of Essex, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254491.

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7

Moreira, Leandro Malard. "Raman spectroscopy of graphene:: probing phonons, electrons and electron-phonon interactions". Universidade Federal de Minas Gerais, 2009. http://hdl.handle.net/1843/ESCZ-7ZFGDY.

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Since the identification of mono and few graphene layers in a substrate in 2004, intensive work has been devoted to characterize this new material. In particular, Raman spectroscopy played an important role in unraveling the properties of graphene systems. Moreover resonant Raman scattering (RRS) in graphene systems was shown to be an important tool to probe phonons, electrons and electronphononinteractions. In this thesis, by using different laser excitation energies, we obtain important electronic and vibrational properties of mono- and bi-layer graphene. For monolayer graphene, we determine the phonon dispersion near the Dirac point for the in-plane transverse optical (iTO) mode and the in-plane longitudinal acoustic (iLA) mode. These results are compared with recent theoretical calculations for the phonon dispersion around the K point. For bilayer graphene we obtain the Slonczewski-Weiss-McClure band parameters. These results show that bilayer graphene has a strong electron-hole asymmetry, which is larger than in graphite. In a gating experiment, we observe that the change in Fermi level of bilayer graphene gives rise to a symmetry breaking, allowing the observation of both the symmetric (S) and anti- symmetric (AS) phonon modes. The dependence of the energy and damping of these phonons modes on the Fermi level position is explained in terms of distinct couplings of the S and AS phonons with intraand inter-band electron-hole transitions. Our experimental results confirm the theoretical predictions for the electron-phonon interactions in bilayer graphene. We also study the symmetry properties of electrons and phonons in graphene systems as a function of the number of layers, by a group theory approach. We derive the selection rules for the electron-radiation and for the electron-phonon interactions at all points in the Brillouin zone. By considering these selection rules, we address the double resonance Raman scattering process. The selection rules for monolayer and bilayer graphene in the presence of an applied electric field perpendicular to the sample plane are also discussed.
Desde a identificação de uma ou poucas camadas de grafeno em um substrato em 2004, trabalhos intensivos tem sido feitos para se caracterizar esse novo material. Em particular, a Espectroscopia Raman Ressonante tem sido muito importante para elucidar propriedades físicas e químicas em sistemas de grafeno. A Espectroscopia Raman Ressonante também tem se mostrado como uma ferramenta importante para se estudar fônons, elétrons e interações elétron-fônon em grafeno. Nesta tese, ao usarmos diferentes energias de laser de excitação, nós obtivemos propriedades importantes sobre as estruturas eletrônicas e vibracionais para uma e duas camadas de grafeno. Para uma monocamada de grafeno, nós determinamos a dispersão de fônons perto do ponto de Dirac para o modo óptico transversal no plano (iTO) e para o modo acústico longitudinal no plano (iLA). Comparamos nossos resultados experimentais como cálculos teóricos recentes para a dispersao de fônons nas proximidades do ponto K. Para a bicamada de grafeno, nós obtivemos os parâmetros de estrutura eletrônica do modelo de Slonczewski-Weiss-McClure. Nossos resultados mostram que a bicamada de grafeno possue uma forte assimetria elétron-buraco, que por sua vez é mais forte que no grafite. Em experimentos aplicando uma tensão de porta, variamos o nível de Fermi em uma bicamada de grafeno, o que levou uma quebra de simetria, deixando assim ambos os modos de vibração simétricos (S) e anti-simétricos (AS) ativos em Raman. A dependência da energia e do amortecimento desses modos de fônons com a energia de Fermi é explicada através do acoplamento elétron-buraco intra- ou inter- banca. Nossos resultados experimentais deram suporte às previsões teóricas para interações elétron-fónon em uma bicamada de grafeno.

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8

Persson, Jacob. "Magnon-Phonon Coupling". Thesis, Uppsala universitet, Materialteori, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-377297.

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Recent experimental and theoretical studies have found evidence of coupled interactions between magnons and phonons. The aim of this study is to construct a model of coupled magnons and phonons, as well as analysing their frequency spectrum. The model is derived by quantizing spin and lattice degrees of freedom, and the frequency spectrum is derived by solving the equations of motion. We found that both the strength and the composition of the coupled interactions affect the frequencies of magnons and phonons, with emphasis on the magnons. Their frequencies are imaginary close to the center of the Brillouin zone, which opens questions for future research.

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9

Levard, Hugo. "Ingénierie phononique pour les cellules solaires à porteurs chauds". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066013/document.

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Cette thèse traite des problématiques fondamentales liées aux phonons dans le cadre des cellules solaires à porteurs chauds. Ce concept appartient aux technologies photo-voltaïques dites de troisième génération, et vise à l’extraction des porteurs de chargesphotogénérés non-encore à l’équilibre thermique avec le réseau cristallin, conduisant àun rendement théorique maximum de l’ordre de la limite thermodynamique. Un des enjeuxmajeurs est ainsi le ralentissement du refroidissement des porteurs, refroidissement qui setraduit principalement par l’émission de phonon LO via l’interactions électron-phonon.En plus de l’idée d’écranter ce dernier processus, une approche consiste à concevoir unmatériau absorbeur dans lequel le phonon LO présente un temps de vie intrinsèque pluslong qu’il ne l’est dans les matériaux classiques, favorisant ainsi sa réabsorption par lesporteurs. Dans une première partie, et utilisant la théorie de la fonctionnelle densité per-turbée, la décoposition du phonon LO est étudiée en terme d'états finaux disponibles. Suit une discussion sur le calcul du temps de vie de ces phonons, et sur la possibilité d’atteindre les critères phononiques définis comme suffisants. Dans une deuxième partie, une étude de l’interaction électron-phonon est menée dans les super-réseaux. La constante de couplage est reliée au champ électriquemacroscopique induit par le phonon LO, de sorte à pourvoir précisément rendre compte deson anisotropie. Il apparaît que la dimensionalité des populations électroniques et phononiques est différemment affectée. Cette étude appelle à développer l’analyse de ce type de structure dans le cadre des cellules à porteurs chauds
This thesis deals with fundamental issues related to phonons in hot-carrier solar cells, athird generation photovoltaic technology. This concept aims at extracting photogeneratedcharge carriers before their reach a thermal equilibrium with the lattice, and exhibits a the-oretical efficiency close to thermodynamic limit. One of the main issue is to hinder carriercooling, which occurs through LO-phonon emission. In addition to the idea of screeningthe electron-phonon interaction, one approach consists in designing an absorber in which theLO-phonon has an intrinsic lifetime longer than what it is in conventional materials, en-hancing the rate of its reabsorption by the carriers. The LO-phonon decay and lifetimeis first investigated in semiconductors within density functional perturbation theory. Spe-cific criteria for relevant absorbing materials choosing, from a phonon point of view, arederived. A full study of the LO-phonon lifetime is performed on a singular material, andthe possibility to achieve the sufficient phononic requierements is discussed. Secondly, theabove-mentioned electron-phonon interaction is modelled in superlattices. The couplingstrength is related to the LO-phonon induced macroscopic electric field, which allows tostudy the directional dependence of the phonon emission. The latter reveals to differentlyaffect the dimensionality of the electronic and phononic interacting populations. Thisstudy calls for development of these structure in the framewok of hot-carrier solar cells

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10

Wu, Yunhui. "Experimental Investigation of Size Effects on Surface Phonon Polaritons and Phonon Transport". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLC012/document.

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La conduction thermique devient moins efficace à mesure que la taille des struc-tures diminuent en desous du micron, car la diffusion de surface des phononsdevient prédominante et limite plus efficacement les phonons que la diffusionphonon-phonon Umklapp. Des études récentes ont indiqué que les phonon po-laritons de surface (SPhPs), qui sont les ondes électromagnétiques évanescentesgénérées par l’hybridation des phonons optiques et des photons et se propageantà la surface d’une surface diélectrique polaire, pourraient servir de nouveauxvecteurs de chaleur pour améliorer les performances thermiques dans des dis-positifs micro- et nano-métriques. Nous étudions l’état des SPhPs existantdans un film submicronique diélectrique dans une large gamme de fréquences.Le calcul de la conductivité thermique des SPhPs basé sur l’équation de trans-port de Boltzmann (BTE) montre que le flux de chaleur transporté par lesSPhPs est supérieur à celui des phonons. Nous effectuons également une mesurede réflectance thermique dans le domaine temporel (TDTR) de films submi-croniques deSiNet démontrons que la conductivité thermique due aux SPhPsà haute température augmente lorsque l’épaisseur du film dimine. Les résultatsprésentés dans cette thèse ont des applications potentielles dans le domaine dutransfert de chaleur, de la gestion thermique, du rayonnement en champ proche et de la polaritoniques
Thermal conduction becomes less efficient as structures scale down into submicron sizes since phonon-boundary scattering becomes predominant and impede phonons more efficiently than Umklapp scattering. Recent studies indicated that the surface phonon polaritons (SPhPs), which are the evanescent electromagnetic waves generated by the hybridation of the optical phonons and the photons and propagating at the surface of a polar dielectric material surface, potentially serve as novel heat carriers to enhance the thermal performance in micro- and nanoscale devices. We study the condition of SPhPs existing in a dielectric submicron film with a broad frequency range. The calculaton of SPhPs thermal conductivity based on Boltzmann transport equation (BTE) demonstrates that the heat flux carried by SPhPs exceeds the one carried by phonons. We also conduct a time-domain-thermal-reflectance (TDTR) measurement of $SiN$ submicron films and demonstrate that the thermal conductivity due to the SPhPs at high temperatures increases by decreasing the film thickness. The results presented in this thesis have potential applications in the field of heat transfer, thermal management, near-field radiation and polaritonics

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11

Han, Haoxue. "Effect of phonon interference on the thermal conductivity and heat carriers". Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLC002.

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L'interférence des ondes de phonon peut modifier le spectre de phonon et ainsi la vitesse de groupe et la population de phonon. Ces interférences permettent de manipuler le flux d'énergie thermique en contrôlant la conductivité thermique et en utilisant les miroirs pour réfléchir les phonons. L'application technologique d'interférence de phonons dans les matériaux, par exemple la conversion renforcée thermoélectrique d'énergie et l'isolation améliorée thermique, a propulsé l'exploration des matériaux avec les interférences de phonons plus efficace.Dans un premier temps, nous proposons une nouvelle approche pour démontrer que la chaleur dans les solides peut être manipuler comme la lumière. Nous contrôlons avec précision le flux thermique par un métamatériau à l'échelle atomique qui comporte des défauts dans le réseau cristallin. L'interférence destructive entre les ondes de chaleur en suivant différents chemins mène à la réflexion totale de phonon et à une réduction remarquable de la conductance thermique. En exploitant cette interférence, nous modélisons une possibilité contre-intuitif de transport thermique: plus de chaleur est bloquée par l'ouverture des chaînes additionnelles de phonon. Le métamateriau thermique est un bon candidat de miroir atomique thermique de haute finesse. Nous renforçons la compréhension sur le contrôle cohérente des phonons qui peuvent être appliquée à la fois au son et à la propagation de chaleur.Dans un deuxième temps, nous introduisons un nano condensateur ultra-compacte de phonons cohérents formé par les miroirs d'interférence de haute finesse basée sur le métamatériau semi-conducteur à l'échelle atomique.Nos simulations de dynamique moléculaire montrent que le nano condensateur stocke les ondes monochromatiques térahertz, qui peuvent être utilisés pour un laser de phonon - l'émission de phonons cohérents. Un laser de phonon soit d'une ou de deux couleurs peut être réalisé en fonction de la géométrie du nano dispositif. Le stockage des phonons cohérents peut être réalisé par le refroidissement de la nano condensateur initialement thermalisé à la température ambiante ou par la technique pump-sonde. Le rétrécissement de la largeur de raie et de le nombre relatif de participation de phonon confirme un confinement dans la nanocavité par une quantité extrêmement faible de défauts de résonance. L'émission des faisceaux acoustiques cohérents en térahertz de la nano condensateur peuvent être réalisés en appliquant une contrainte réversible accordable qui décale les fréquences d'antirésonance.Enfin, nous étudions l'effet d'interférences destructrice de phonon à deux-chemin induite par les forces interatomiques de longue portée sur la conductance thermique et la conductivité d'un alliage silicium-germanium par des calculs atomiques. La conductance thermique à travers un plan atomique de germanium dans le réseau de silicium est sensiblement réduit par l'interférence destructrice du chemin de phonon entre les voisins les plus proches avec l'interaction directe contournant les atomes de défauts. Une réduction quintuple dans la conductivité thermique dans un alliage SiGe à la température ambiante a été observée en introduisant les forces de longue portée. Nous démontrons le rôle prédominant des interférences de phonons harmoniques régissant la conductivité thermique de matières solides en supprimant la diffusion inélastique de phonon à basse température. De telles interférences fournissent un mécanisme résistif harmonique pour contrôler la conduction de chaleur à travers les comportements cohérents de phonons dans les solides
Wave interference of phonons can modify the phonon spectrum and thereby the group velocity and phonon population. These wave interferences allow the flow of thermal energy to be manipulated by controlling the materials lattice thermal conductivity and using thermal mirrors to reflect thermal phonons.The technological application of the phonon interference in materials, such as enhanced thermoelectric energy conversion and improved thermal insulation,has thrusted the exploration for highly efficient wave interference materials. First, we provide a new approach to demonstrate that heat in solids can be manipulated like light. We precisely control the heat flow by the atomic-scale phononic metamaterial, which contains deliberate flaws in the crystalline atomic lattice,channeling the heat through different phonon paths. Destructive interference between heat waves following different paths leads to the total reflection of the heat current and thus to the remarkable reduction in the material ability to conduct heat. By exploiting this destructive phonon interference, we model a very counter-intuitive possibility of thermal transport: more heat flow is blocked by the opening of the additional phonon channels. Our thermal metamaterial is a good candidate for high-fi nesse atomic-scale heat mirrors. We provide an important further insight into the coherent control of phonons which can be applied both to sound and heat propagation.Secondly, we introduce a novel ultra-compact nanocapacitor of coherent phonons formed by high-finesse interference mirrors based on atomic-scale semiconducto rmetamaterials. Our molecular dynamics simulations show that the nanocapacitor stores monochromatic terahertz lattice waves, which can be used for phonon lasing - the emission of coherent phonons. Either one- or two-color phonon lasing can be realized depending on the geometry of the nanodevice. The two-color regime of the interference cavity originates from different incidence-angle dependence of phonon wave packet transmission for two wave polarizations at the respective antiresonances. Coherent phonon storage can be achieved by cooling the nanocapacitor initially thermalized at room temperature or by the pump-probe technique. The line width narrowing and the computed relative phonon participation number confirm strong phonon confinement in the interference cavity by an extremely small amount of resonance defects. The emission of coherent terahertz acoustic beams from the nanocapacitor can be realized by applying tunable reversible stress which shifts the antiresonance frequencies.Finally, we investigate the role of two-path destructive phonon interference induced by long-range interatomic forces on the thermal conductance and conductivityof a silicon-germanium alloy by atomistic calculations. The thermal conductance across a germanium atomic plane in the silicon lattice is substantially reduced by the destructive interference of the nearest-neighbour phononpath with a direct path bypassing the defect atoms. Such an interference causes a fivefold reduction in the lattice thermal conductivity in a SiGe alloy at room temperature. We demonstrate the predominant role of harmonic phonon interferences in governing the thermal conductivity of solids by suppressing the inelastic scattering processes at low temperature. Such interferences provide a harmonic resistive mechanism to explain and control heat conduction through the coherent behaviours of phonons in solids

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12

Sidorova, Mariia. "Timing Jitter and Electron-Phonon Interaction in Superconducting Nanowire Single-Photon Detectors (SNSPDs)". Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/22296.

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Die vorliegende Doktorarbeit beschäftigt sich mit der experimentellen Studie zweier miteinander verbundener Phänomene: Dem intrinsischen Timing-Jitter in einem supraleitendenden Nanodraht-Einzelphotonen-Detektor (SNSPD) und der Relaxation der Elektronenenergie in supraleitenden Filmen. Supraleitende Nanodrähte auf einem dielektrischen Substrat als mikroskopische Grundbausteine jeglicher SNSPDs stellen sowohl für theoretische als auch für experimentelle Studien komplexe Objekte dar. Die Komplexität ergibt sich aus der Tatsache, dass SNSPDs in der Praxis stark ungeordnete und ultradünne supraleitende Filme verwenden, die eine akustische Fehlanpassung zu dem zugrundeliegenden Substrat aufweisen und einen Nichtgleichgewichts-Zustand implizieren. Die Arbeit untersucht die Komplexität des am weitesten in der SNSPD Technologie verbreiteten Materials, Niobnitrid (NbN), indem verschiedene experimentelle Methoden angewandt werden. Als eine mögliche Anwendung der SNSPD-Technologie wird ein Prototyp eines dispersiven Raman-Spektrometers mit Einzelphotonen-Sensitivität demonstriert.
This Ph.D. thesis is based on the experimental study of two mutually interconnected phenomena: intrinsic timing jitter in superconducting nanowire single-photon detectors (SNSPDs) and relaxation of the electron energy in superconducting films. Microscopically, a building element of any SNSPD device, a superconducting nanowire on top of a dielectric substrate, represents a complex object for both experimental and theoretical studies. The complexity arises because, in practice, the SNSPD utilizes strongly disordered and ultrathin superconducting films, which acoustically mismatch with the underlying substrate, and implies a non-equilibrium state. This thesis addresses the complexity of the most conventional superconducting material used in SNSPD technology, niobium nitride (NbN), by applying several distinct experimental techniques. As an emerging application of the SNSPD technology, we demonstrate a prototype of the dispersive Raman spectrometer with single-photon sensitivity.

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13

Coudert, Stéphane. "Modélisation de la dynamique électron-photon-phonon dans des nano-structures métalliques confinantes". Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0044.

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Nous présentons un travail théorique en forte adéquation avec des résultats d’expériences qui a pour but de mieux comprendre la nature des processus de génération et de relaxation ultrarapides de porteurs chauds dans les métaux. Nous avons développé un code basé sur la résolution de l’équation de Boltzmann pour les électrons et les phonons, qui prend en compte,la diffusion des électrons par les phonons et l’absorption de photons assistée par phonons. Nous montrons l’importance des processus de diffusion Umklapp dans les processus d’absorption tant via les collisions électron-électron que les collisions électron-phonon. La non linéarité du signal de thermoréflectance avec l’énergie déposée nous permet de relier de manière quantitative les signaux de thermoréflectance à la modélisation. À l’aide d’une approche de type Pn, nous résolvons numériquement l’équation de Boltzmann à une dimension spatiale pour les électrons, ce qui nous permet de traiter le transport ultra-rapide sur des dimensions spatiales allant du régime balistique ( 10 nm) à des dimensions de plusieurs centaines de nanomètres tout en mettant en évidence l’effet des porteurs chauds photo-induits sur la dynamique du transport ultrarapide. Ce travail de modélisation nous permet de modéliser les résultats expérimentaux obtenus au LOMA ainsi que des résultats expérimentaux de la littérature
In the present work, we present a theoretical study aiming at understanding ultra-fast generation, elaxation and transport processes of hot carriers in metals. We have developed a numerical code solving the Boltzmann equation for both phonons and electrons which enables to model these ultrafast out of equilibrium processes. The importance of Umklapp processes in absorption mechanisms for electron-electron and electron-phonon scattering is shown. By using the Rosei model, experimental observable are extracted from microscopic calculations as the thermoreflectance signal. Numerical results are compared to experimental data. In general a good agreement is obtained. By coupling the present approach to experimental data, absolute thermoreflectance measurements can be carried out. Finally, Boltzmann equation for electrons with one spatial dimensions and three dimensions in momentum space is numerically solved. This enables to model ultrafast transport from ballistic spatial ( 10 nm) and temporal time scale ( 10 fs), beyond Fourier transport where the temperature is no longer defined, to macrocopic scales. The importance of describing the ultrafast transport of hot carriers is highlighted. The numerical predictions have been compared successfully with experimental results obtained in LOMA and in the litterature

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14

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.

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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
This 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

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15

Lehmann, Dietmar. "Phonon Spectroscopy and Low-Dimensional Electron Systems: The Effect of Acoustic Anisotropy and Carrier Confinement". Doctoral thesis, Technische Universität Dresden, 2004. https://tud.qucosa.de/id/qucosa%3A24636.

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The generation and propagation of pulses of nonequilibrium acoustic phonons and their interaction with semiconductor nanostructures are investigated. Such studies can give unique information about the properties of low-dimensional electron systems, but in order to interpret the experiments and to understand the underlying physics, a comparison with theoretical models is absolutely necessary. A central point of this work is therefore a universal theoretical approach allowing the simulation and the analysis of phonon spectroscopy measurements on low-dimensional semiconductor structures. The model takes into account the characteristic properties of the considered systems. These properties are the elastic anisotropy of the substrate material leading to focusing effects and highly anisotropic phonon propagation, the anisotropic nature of the different electron-phonon coupling mechanisms, which depend manifestly on phonon wavevector direction and polarization vector, and the sensitivity to the confinement parameters of the low-dimensional electron systems. We show that screening of the electron-phonon interaction can have a much stronger influence on the results of angle-resolved phonon spectroscopy than expected from transport measurements. Since we compare theoretical simulations with real experiments, the geometrical arrangement and the spatial extension of phonon source and detector are also included in the approach enabling a quantitative analysis of the data this way. To illustrate the influence of acoustic anisotropy and carrier confinement on the results of phonon spectroscopy in detail we analyse two different applications. In the first case the low-dimensional electron system acts as the phonon detector and the phonon induced drag current is measured. Our theoretical model enables us to calculate the electric current induced in low-dimensional electron systems by pulses of (ballistic) nonequilibrium phonons. The theoretical drag patterns reproduce the main features of the experimental images very well. The sensitivity of the results to variations of the confining potential of quasi-2D and quasi-1D electrons is demonstrated. This provides the opportunity to use phonon-drag imaging as unique experimental tool for determining the confinement lengths of low-dimensional electron systems. By comparing the experimental and theoretical images it is also possible to estimate the relative strength of the different electron-phonon coupling mechanisms.In the second application the low-dimensional electron system acts as the phonon pulse source and the angle and mode dependence of the acoustic phonon emission by hot 2D electrons is investigated. The results exhibit strong variations in the phonon signal as a function of the detector position and depend markedly on the coupling mechanism, the phonon polarization and the electron confinement width. We demonstrate that the ratio of the strengths of the emitted longitudinal (LA) and transverse (TA) acoustic phonon modes is predicted correctly only by a theoretical model that properly includes the effects of acoustic anisotropy on the electron-phonon matrix elements, the screening, and the form of the confining potential. A simple adoption of widely used theoretical assumptions, like the isotropic approximation for the phonons in the electron-phonon matrix elements or the use of simple variational envelope wavefunctions for the carrier confinement, can corrupt or even falsify theoretical predictions.We explain the `mystery of the missing longitudinal mode' in heat-pulse experiments with hot 2D electrons in GaAs/AlGaAs heterojunctions. We demonstrate that screening prevents a strong peak in the phonon emission of deformation potential coupled LA phonons in a direction nearly normal to the 2D electron system and that deformation potential coupled TA phonons give a significant contribution to the phonon signal in certain emission directions.
Die vorliegende Arbeit beschäftigt sich mit der Ausbreitung von akustischen Nichtgleichgewichtsphononen und deren Wechselwirkung mit Halbleiter-Nanostrukturen. Güte und Effizienz moderner Halbleiter-Bauelemente hängen wesentlich vom Verständnis der Wechselwirkung akustischer Phononen mit niederdimensionalen Elektronensystemen ab. Traditionelle Untersuchungsmethoden, wie die Messung der elektrischen Leitfähigkeit oder der Thermospannung, erlauben nur eingeschränkte Aussagen. Sie mitteln über die beteiligten Phononenmoden und eine Trennung der einzelnen Wechselwirkungsmechanismen ist nur näherungsweise möglich ist. Demgegenüber erlaubt die in der Arbeit diskutierte Methode der winkel- und zeitaufgelösten Phononen-Spektroskopie ein direktes Studium des Beitrags einzelner Phononenmoden, d.h. in Abhängigkeit von Wellenzahlvektor und Polarisation der Phononen. Im Mittelpunkt der Arbeit steht die Fragestellung, wie akustische Anisotropie und Ladungsträger-Confinement die Ergebnisse der winkel- und zeitaufgelösten Phononen-Spektroskopie beeinflussen und prägen. Dazu wird ein umfassendes theoretisches Modell zur Simulation von Phononen-Spektroskopie-Experimenten an niederdimensionalen Halbleitersystemen vorgestellt. Dieses erlaubt sowohl ein qualitatives Verständnis der ablaufenden physikalischen Prozesse als auch eine quantitative Analyse der Messergebnisse. Die Vorteile gegenüber anderen Modellen und Rechnungen liegen dabei in dem konsequenten Einbeziehen der akustischen Anisotropie, nicht nur für die Ausbreitung der Phononen, sondern auch für die Matrixelemente der Wechselwirkung, sowie eine saubere Behandlung des Confinements der Elektronen in den niederdimensionalen Systemen. Dabei werden die Grenzen weit verbreiteter Näherungsansätze für die Elektron-Phonon-Matrixelemente und das Elektronen-Confinement deutlich aufgezeigt. Für den quantitativen Vergleich mit realen Experimenten werden aber auch solche Größen, wie die endliche räumliche Ausdehnung von Phononenquelle und Detektor, die Streuung der Phononen an Verunreinigungen oder die Abschirmung der Elektron-Phonon-Kopplung durch die Elektron-Elektron-Wechselwirkung berücksichtigt.Im zweiten Teil der Arbeit wird der theoretische Apparat auf typische experimentelle Fragestellungen angewandt. Im Falle der Phonon-Drag-Experimente an GaAs/AlGaAs Heterostrukturen wird der durch akustische Nichtgleichgewichtsphononen in zwei- und eindimensionalen Elektronensystemen induzierte elektrische Strom (Phonon-Drag-Strom) als Funktion des Ortes der Phononenquelle bestimmt. Das in der Arbeit hergeleitete theoretische Modell kann die experimentellen Resultate für die Winkelabhängigkeit des Drag-Stromes sowohl für Messungen mit und ohne Magnetfeld qualitativ gut beschreiben. Außerdem wird der Einfluss unterschiedlicher Confinementmodelle und unterschiedlicher Wechselwirkungsmechanismen studiert. Dadurch ist es möglich, aus Phonon-Drag-Messungen Rückschlüsse auf die elektronischen und strukturellen Eigenschaften der niederdimensionalen Elektronensysteme zu ziehen (Fermivektor, effektive Masse, Elektron-Phonon-Kopplungskonstanten, Form des Confinementpotentials). Als weiteres Anwendungsbeispiel wird das Problem der Energierelaxation (aufgeheizter)zweidimensionaler Elektronensysteme in GaAs Heterostrukturen und Quantentrögen untersucht. Für Elektronentemperaturen unterhalb 50 K werden die Gesamtemissionsrate als Funktion der Temperatur und die winkelaufgelöste Emissionsrate (als Funktion der Detektorposition) berechnet. Für beide Größen wird erstmals eine gute Übereinstimmung zwischen Theorie und Experiment gefunden. Es zeigt sich, dass akustische Anisotropie und Abschirmungseffekte zu überraschenden neuen Ergebnissen führen können. Ein Beispiel dafür ist der unerwartet große Beitrag der mittels Deformationspotential-Wechselwirkung emittierten transversalen akustischen Phononen, der bei einer Emission der Phononen näherungsweise senkrecht zum zweidimensionalen System beobachtet werden kann.

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16

Geondzhian, Andrey. "Resonant inelastic X-ray scattering as a probe of exciton-phonon coupling". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY077/document.

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Les phonons contribuent à la diffusion inélastique résonante des rayons X (RIXS) du fait du couplage entre les degrés de liberté électronique et ceux du réseau. Contrairement à d'autres techniques sensibles aux interactions électron-phonon, la technique RIXS peut donner accès aux constantes de couplage dépendantes du moment. Des informations sur la dispersion de l'interaction électron-phonon sont très précieuses dans le contexte de la supraconductivité anisotrope conventionnelle et non conventionnelle.Nous avons considéré la contribution des phonons sur la diffusion RIXS d’un point de vue théorique. Contrairement aux études précédentes nous soulignons le rôle du couplage du réseau avec les trous de cœur. Notre modèle, avec les paramètres obtenus ab-initio, montre que même dans le cas d'un trou de coeur profond, la technique RIXS sonde le couplage exciton-phonon plutôt qu’un couplage direct électron-phonon.Cette différence conduit à des écarts quantitatifs et qualitatifs pour le couplage électron-phonon implicite par rapport à l'interprétation standard dans la littérature. Ainsi, notre objectif est de développer une approche rigoureuse pour quantifier le couplage électron-phonon dans le contexte des mesures de diffusion RIXS. La possibilité de reproduire avec précision les résultats expérimentaux à partir des calculs ab-initio, sans recourir à des paramètres ajustés, doit être considérée comme le test ultime d'une compréhension correcte de la contribution des phonons sur la diffusion RIXS.Nous commençons notre travail en considérant uniquement l’interaction trou de coeur-phonon dans le contexte de la spectroscopie par photoémission de rayons X. Nous combinons un calcul ab-initio de la fonction de réponse en espace réel avec des techniques de fonctions de Green à plusieurs corps pour reproduire les bandes latérales vibrationnelles dans les molécules SiX4 (X = H, F). L'approche que nous avons développée peut être appliquée aux matériaux cristallins.Nous examinons ensuite la contribution des phonons aux spectres d'absorption des rayons X. Contrairement aux excitations chargées générées par la photoémission par rayons X, l'absorption des rayons X crée une excitation neutre que nous approchons en tant que trou de cœur et électron excité. Nous résolvons d’abord la partie électronique du problème au niveau de l’équation de Bethe-Salpeter, puis nous habillons la quasi-particule excitonique à 2 particules résultante avec les interactions exciton-phonon en utilisant l’Ansatz des cumulants. La viabilité de cette méthode a été testée en calculant le seuil K XAS de la molécule N2 et le seuil K d’Oxygène de l’acétone. Les spectres vibrationnels obtenus concordent avec les résultats expérimentaux.Enfin, nous construisons une formulation hybride de la section transversale RIXS qui préserve la sommation explicite sur un petit nombre d'états finals, mais remplace la sommation sur les états intermédiaires, ce qui pourrait être extrêmement coûteux, par une fonction de Green. Nous avons obtenu un développement de la fonction de Green et dérivé des solutions analytiques exactes (dans la limite de non-recul) et approximatives. Le formalisme a de nouveau été testé sur le seuil K de l'acétone et est bien en accord avec l'expérience. En perspectives des travaux futurs, nous discutons de l’applicabilité de notre formalisme aux matériaux cristallins
Phonons contribute to resonant inelastic X-ray scattering (RIXS) as a consequence of the coupling between electronic and lattice degrees of freedom. Unlike other techniques that are sensitive to electron-phonon interactions, RIXS can give access to momentum dependent coupling constants. Information about the dispersion of the electron-phonon interaction is highly desirable in the context of understanding anisotropic conventional and unconventional superconductivity.We considered the phonon contribution to RIXS from the theoretical point of view. In contrast to previous studies, we emphasize the role of the core-hole lattice coupling. Our model, with parameters obtained from first principles, shows that even in the case of a deep core-hole, RIXS probes exciton-phonon coupling rather than a direct electron-phonon coupling.This difference leads to quantitative and qualitative deviations from the interpretation of the implied electron-phonon coupling from the standard view expressed in the literature. Thus, our objective is to develop a rigorous approach to quantify electron-phonon coupling within the context of RIXS measurements. The ability to accurately reproduce experimental results from first-principles calculations, without recourse to adjustable parameters, should be viewed as the ultimate test of a proper understanding of the phonon contribution to RIXS.We start by considering only the core-hole--phonon interaction within the context of X-ray photoemission spectroscopy. We combine an ab initio calculation of the real-space response function with many-body Green's functions techniques to reproduce the vibrational side-bands in SiX4 (X=H, F) molecules. The approach we developed is suitable for application to crystalline materials.We next consider the phonon contribution to X-ray absorption spectra. Unlike the charged excitations generated by X-ray photoemission, X-ray absorption creates a neutral excitation that we approximate as a core-hole and an excited electron. We first solved the electronic part of the problem on the level of the Bethe-Salpeter equation and then dressed the resulting 2-particle excitonic quasiparticle with the exciton-phonon interactions using the cumulant ansatz. The viability of this methodology was tested by calculating the N K-edge XAS of the N2 molecule and the O K-edge of acetone. The resulting vibronic spectra agreed favorably with experimental results.Finally, we construct a hybrid formulation of the RIXS cross section that preserves explicit summation over a small number of final states, but replaces the summation over intermediate states, which might be enormously expensive, with a Green's function. We develop an expansion of the Green's function and derive both analytically exact (in the no-recoil limit) and approximate solutions. The formalism was again tested on the O K-edge of acetone and agrees well with the experiment. To provide an outlook towards future work, we discuss application of the developed formalism to crystalline materials

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17

Levard, Hugo. "Ingénierie phononique pour les cellules solaires à porteurs chauds". Electronic Thesis or Diss., Paris 6, 2015. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2015PA066013.pdf.

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Cette thèse traite des problématiques fondamentales liées aux phonons dans le cadre des cellules solaires à porteurs chauds. Ce concept appartient aux technologies photo-voltaïques dites de troisième génération, et vise à l’extraction des porteurs de chargesphotogénérés non-encore à l’équilibre thermique avec le réseau cristallin, conduisant àun rendement théorique maximum de l’ordre de la limite thermodynamique. Un des enjeuxmajeurs est ainsi le ralentissement du refroidissement des porteurs, refroidissement qui setraduit principalement par l’émission de phonon LO via l’interactions électron-phonon.En plus de l’idée d’écranter ce dernier processus, une approche consiste à concevoir unmatériau absorbeur dans lequel le phonon LO présente un temps de vie intrinsèque pluslong qu’il ne l’est dans les matériaux classiques, favorisant ainsi sa réabsorption par lesporteurs. Dans une première partie, et utilisant la théorie de la fonctionnelle densité per-turbée, la décoposition du phonon LO est étudiée en terme d'états finaux disponibles. Suit une discussion sur le calcul du temps de vie de ces phonons, et sur la possibilité d’atteindre les critères phononiques définis comme suffisants. Dans une deuxième partie, une étude de l’interaction électron-phonon est menée dans les super-réseaux. La constante de couplage est reliée au champ électriquemacroscopique induit par le phonon LO, de sorte à pourvoir précisément rendre compte deson anisotropie. Il apparaît que la dimensionalité des populations électroniques et phononiques est différemment affectée. Cette étude appelle à développer l’analyse de ce type de structure dans le cadre des cellules à porteurs chauds
This thesis deals with fundamental issues related to phonons in hot-carrier solar cells, athird generation photovoltaic technology. This concept aims at extracting photogeneratedcharge carriers before their reach a thermal equilibrium with the lattice, and exhibits a the-oretical efficiency close to thermodynamic limit. One of the main issue is to hinder carriercooling, which occurs through LO-phonon emission. In addition to the idea of screeningthe electron-phonon interaction, one approach consists in designing an absorber in which theLO-phonon has an intrinsic lifetime longer than what it is in conventional materials, en-hancing the rate of its reabsorption by the carriers. The LO-phonon decay and lifetimeis first investigated in semiconductors within density functional perturbation theory. Spe-cific criteria for relevant absorbing materials choosing, from a phonon point of view, arederived. A full study of the LO-phonon lifetime is performed on a singular material, andthe possibility to achieve the sufficient phononic requierements is discussed. Secondly, theabove-mentioned electron-phonon interaction is modelled in superlattices. The couplingstrength is related to the LO-phonon induced macroscopic electric field, which allows tostudy the directional dependence of the phonon emission. The latter reveals to differentlyaffect the dimensionality of the electronic and phononic interacting populations. Thisstudy calls for development of these structure in the framewok of hot-carrier solar cells

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18

Sidorova, Mariia [Verfasser]. "Timing Jitter and Electron-Phonon Interaction in Superconducting Nanowire Single-Photon Detectors (SNSPDs) / Mariia Sidorova". Berlin : Humboldt-Universität zu Berlin, 2021. http://d-nb.info/1226153380/34.

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19

Roca, Vich Isabel. "How the ground state in a material will be affected by the spin-phonon interactions between nuclei in diatomic molecular structures". Thesis, Uppsala universitet, Materialteori, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-297712.

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Wave-like phonons are often used to describe the heat capacity in materials. In this report the spin-phonon interaction between nuclei in a diatomic molecular structure is introduced by looking at the Hamiltonian in its ground state. The corresponding Green's functions are computed in order to investigate how this interaction affects the phonons. When calculating the spin, pseudo fermions and tensor products are introduced to make the calculation easier because the spin statistics could be a bit tricky to deal with. Three different cases of how the total interaction Hamiltonian behaves are investigated i.e. when the phonon is coupled to the spin. It turns out that in two of these cases an effect on the phonons can be seen but not in the other case.

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20

Maire, Jérémie. "Thermal phonon transport in silicon nanostructures". Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0044/document.

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Lors de deux dernières décennies, la nano-structuration a permis une augmentation conséquente des performances thermoélectriques. Bien qu’à l’ origine le silicium (Si) ait une faible efficacité thermoélectrique, son efficacité sous forme de nanostructure, et notamment de nanofils, a provoqué un regain d’intérêt envers la conduction thermique au sein de ces nanostructures de Si. Bien que la conductivité thermique y ait été réduite de deux ordres de grandeur, les mécanismes de conduction thermique y demeurent flous. Une meilleure compréhension de ces mécanismes permettrait non seulement d’augmenter l’efficacité thermoélectrique mais aussi d’ouvrir la voie à un contrôle des phonons thermiques, de manière similaire à ce qui se fait pour les photons. L’objectif de ce travail de thèse était donc de développer une plateforme de caractérisation, d’étudier le transport thermique au sein de différentes nanostructures de Si et enfin de mettre en exergue la contribution du transport cohérent de phonons à la conduction thermique. Dans un premier temps, nous avons développé un système de mesure allant de pair avec une procédure de fabrication en salle blanche. La fabrication se déroule sur le site de l’institut de Sciences Industrielles et combine des manipulations chimiques, de la lithographie électronique, de la gravure plasma et du dépôt métallique. Le système de mesure est base sur la thermoreflectance : un changement de réflectivité d’un métal a une longueur d’onde particulière traduit un changement de température proportionnel. Nous avons dans un premier temps étudié le transport thermique au sein de simples membranes suspendues, suivi par des nanofils, le tout étant en accord avec les valeurs obtenues dans la littérature. Le transport thermique au sein des nanofils est bien diffus, à l’exception de fils de moins de 4 μm de long a la température de 4 K ou un régime partiellement balistique apparait. Une étude similaire au sein de structures périodiques 1D a démontré l’impact de la géométrie et l’aspect partiellement spéculaire des réflexions de phonons a basse température. Une étude sur des cristaux phononiques (PnCs) 2D a ensuite montré que même si la conduction est dominée par le rapport surface sur vole (S/V), la distance inter-trous devient cruciale lorsqu’elle est suffisamment petite. Enfin, il nous a été possible d’observer dans des PnCs 2D un ajustement de la conductivité thermique base entièrement sur la nature ondulatoire des phonons, réalisant par-là l’objectif de ce travail
In the last two decades, nano-structuration has allowed thermoelectric efficiency to rise dramatically. Silicon (Si), originally a poor thermoelectric material, when scaled down, to form nanowires for example, has seen its efficiency improve enough to be accompanied by a renewed interest towards thermal transport in Si nanostructures. Although it is already possible to reduce thermal conductivity in Si nanostructures by nearly two orders of magnitude, thermal transport mechanisms remain unclear. A better understanding of these mechanisms could not only help to improve thermoelectric efficiency but also open up the path towards high-frequency thermal phonon control in similar ways that have been achieved with photons. The objective of this work was thus to develop a characterization platform, study thermal transport in various Si nanostructures, and ultimately highlight the contribution of the coherent phonon transport to thermal conductivity. First, we developed an optical characterization system alongside the fabrication process. Fabrication of the structures is realized on-site in clean rooms, using a combination of wet processes, electron-beam lithography, plasma etching and metal deposition. The characterization system is based on the thermoreflectance principle: the change in reflectivity of a metal at a certain wavelength is linked to its change in temperature. Based on this, we built a system specifically designed to measure suspended nanostructures. Then we studied the thermal properties of various kinds of nanostructures. Suspended unpatterned thin films served as a reference and were shown to be in good agreement with the literature as well as Si nanowires, in which thermal transport has been confirmed to be diffusive. Only at very low temperature and for short nanowires does a partially ballistic transport regime appear. While studying 1D periodic fishbone nanostructures, it was found that thermal conductivity could be adjusted by varying the shape which in turn impacts surface scattering. Furthermore, low temperature measurements confirmed once more the specularity of phonon scattering at the surfaces. Shifting the study towards 2D phononic crystals (PnCs), it was found that although thermal conductivity is mostly dominated by the surface-to-volume (S/V) ratio for most structures, when the limiting dimension, i.e. the inter-hole spacing, becomes small enough, thermal conductivity depends solely on this parameter, being independent of the S/V ratio. Lastly, we were able to observe, at low temperature in 2D PnCs, i.e. arrays of holes, thermal conduction tuning based on the wave nature of phonons, thus achieving the objective of this work

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21

Carreto, Francisco Javier. "Optical phonon modes of PbSe nanoparticles". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2007. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.

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22

Graham, Stephen Charles. "Electron-phonon coupling in conjugated systems". Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387610.

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Giltrow, M. "Phonon study of vertical resonant structures". Thesis, Lancaster University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337346.

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Hahn, Andreas. "Particle detection with superconducting phonon sensors". Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259881.

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Beardsley, Ryan. "Coherent phonon processes in semiconductor superlattices". Thesis, University of Nottingham, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.546547.

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Stokes, Michael Keith. "Phonon absorption in superconducting tunnel junctions". Thesis, Lancaster University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.497770.

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27

MartiÌnez, Charles E. "Phonon interactions in gallium nitride nanostructures". Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430567.

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Hanna, Ann Catrina. "Energy resolved phonon scattering in glasses". Thesis, University of Glasgow, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280020.

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29

Statz, Eric R. (Eric Robert). "Phonon polariton interaction with patterned materials". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43770.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008.
Vita.
Includes bibliographical references (p. 139-144).
The generation, propagation and detection of THz phonon polaritons are studied through both femtosecond pump-probe techniques, and Finite Difference Time Domain (FDTD) simulations in this thesis. The theory surrounding the driving, propagation and detection of these modes is treated in a consistent notational system for both analytical solutions and approximate simulated responses. FDTD simulations in one, two and three dimensions are designed to best mimic lab experimental parameters, with various approximations of both THz pumping and probing developed. Various improvements on the FDTD method with the goal of more rapid simulations and more accurately described simulations of lab experiments from generation to detection are considered and developed. Experiments on phonon-polaritons interacting with periodicity and confinement in one, two, and three dimensions are all considered, and methods of data processing developed. By comparing FDTD simulation results to experimental results, the full three dimensional fields within these crystals can be investigated, and in many cases fully defined. The methods demonstrated open up new possibilities for THz spectroscopy in waveguides, microfluidics, and related platforms that include THz generation, propagation, interaction with the sample material, and detection in a compact, integrated structure. The methods also enable the proper description of large-amplitude THz generation and applications in nonlinear THz spectroscopy. Finally, linear and nonlinear THz signal processing applications my exploit the experimental and modeling methods described in this thesis.
by Eric R. Statz.
Ph.D.

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30

Metzler, Florian. "Experiments to investigate phonon-nuclear interactions". Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/121824.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2019
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 103-107).
This thesis presents a series of experiments conducted by the author between 2016 and 2018 that were designed to test for and investigate a proposed phonon-nuclear coupling interaction and an associated nuclear excitation transfer mechanism. Electric and magnetic interactions of phonons with atomic nuclei have been studied for several decades. However, such second-order interactions are too weak to induce nuclear state changes. Hagelstein and Chaudhary recently identified the possibility of a stronger, first-order phonon-nuclear interaction, based on the boost correction associated with the nucleon-nucleon potential for nuclei embedded in a condensed matter environment. Because the newly proposed interaction follows from the relativistic (Dirac) treatment of nucleons, Hagelstein and Chaudhary refer to this interaction as relativistic phonon-nuclear coupling.
Relativistic phonon-nuclear coupling implies the possibility of phonon-mediated nuclear excitation transfer where in the process of absorbing and emitting phonons, energy can transfer from excited state nuclei to nearby ground state nuclei, analogous to widely studied excitation transfer at the atomic and molecular level. To test for and investigate these theoretical conjectures, we prepared samples with a combination of ground state and excited state Fe-57 nuclei (from beta-decaying Co-57) attached to a steel substrate. Samples then underwent treatment by inducing vibrations via ultrasound or mechanical stress. Simultaneously, time histories of radioactive emission were recorded at different locations. Early experiments with vibrations induced at the MHz level via ultrasound transducers yielded negative results and no variations in radioactive emission were observed. However, in conjunction with mechanical stress, deviations from expected emission were observed.
After applying mechanical stress to a sample, we observed a 19% enhancement above expected levels of 14.4 keV gamma emission from Fe-57 and a 17% enhancement above expected levels of Fe K-alpha emission (which to a large extent is driven by internal conversion from the 14.4 keV nuclear transition). The enhancements decayed away with a time constant of about 2.5 days. At the same time, emission on the Sn K-alpha line (driven by fluorescence of Sn in the steel) was consistent with the expected exponential decay of Co-57 at the 1% level, suggesting detector integrity. Similar deviations from expected emission were observed by two additional detectors in different locations. Further experimentation exhibited a high level of reproducibility of the observed effects. By now, evidence for the effects have been seen in seven different detectors and in six different experimental configurations. In some experiments, reductions instead of enhancements can be observed.
Moreover, we observe differences in the ratio of 14.4 keV gamma and Fe K-alpha emissions across experiments. To explain reported observations, we propose that the temporary enhancements and reductions of emission originate from phonon-mediated nuclear excitation transfer and are caused by resulting delocalization and angular anisotropy effects. Delocalization can result from excitation transferring into the steel substrate and across the Co-57/Fe-57 residue. Angular anisotropy can follow from phase coherence at neighboring sites as a result of resonant excitation transfer. Furthermore, observed differences in the incremental emission of 14.4 keV gamma and Fe K-alpha emission suggests that a new channel for internal conversion is opened in off-resonant states present in excitation transfer. We motivate and discuss the conjectured mechanisms as well as alternative candidate explanations and conclude that the latter do not suffice to account for the reported observations.
Finally, we present limitations of this work to date and point at avenues for further research and clarification. Relativistic phonon-nuclear coupling and nuclear excitation transfer have the potential to form new tools in the toolbox of nuclear engineers. The further pursuit of research in this area could lead to the use of phonons in a wide range of applications: for mixing nuclear states; for generating angular anisotropy or inducing beam formation; and potentially for exciting or de-exciting atomic nuclei in applications otherwise reliant on photons. This, in turn, could lead to many nuclear engineering applications becoming more economical as well as less hazardous.
by Florian Metzler.
S.M.
S.M. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering

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31

Swinteck, Nichlas Z. "Phase-Space Properties of Two-Dimensional Elastic Phononic Crystals and Anharmonic Effects in Nano-Phononic Crystals". Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/228156.

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This dissertation contains research directed at investigating the behavior and properties of a class of composite materials known as phononic crystals. Two categories of phononic crystals are explicitly investigated: (I) elastic phononic crystals and (II) nano-scale phononic crystals. For elastic phononic crystals, attention is directed at two-dimensional structures. Two specific structures are evaluated (1) a two-dimensional configuration consisting of a square array of cylindrical Polyvinylchloride inclusions in air and (2) a two-dimensional configuration consisting of a square array of steel cylindrical inclusions in epoxy. For the first configuration, a theoretical model is developed to ascertain the necessary band structure and equi-frequency contour features for the realization of phase control between propagating acoustic waves. In contrasting this phononic crystal with a reference system, it is shown that phononic crystals with equifrequency contours showing non-collinear wave and group velocity vectors are ideal systems for controlling the phase between propagating acoustic waves. For the second configuration, it is demonstrated that multiple functions can be realized of a solid/solid phononic crystal. The epoxy/steel phononic crystal is shown to behave as (1) an acoustic wave collimator, (2) a defect-less wave guide, (3) a directional source for elastic waves, (4) an acoustic beam splitter, (5) a phase-control device and (6) a k-space multiplexer. To transition between macro-scale systems (elastic phononic crystals) and nano-scale systems (nano-phononic crystals), a toy model of a one-dimensional chain of masses connected with non-linear, anharmonic springs is utilized. The implementation of this model introduces critical ideas unique to nano-scale systems, particularly the concept of phonon mode lifetime. The nano-scale phononic crystal of interest is a graphene sheet with periodically spaced holes in a triangular array. It is found through equilibrium molecular dynamics simulation techniques, that phonon-boundary collision effects and coherent phononic effects (band-folding) are two competing scattering mechanisms responsible for the reduction of acoustic and optical phonon lifetimes. Conclusions drawn about the lifetime of thermal phonons in phononic crystal patterned graphene are linked with the anharmonic, one-dimensional crystal model.

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32

Lakehal, Massil. "Out of Equilibrium Lattice Dynamics in Pump Probe Setups". Thesis, Université de Paris (2019-....), 2020. http://www.theses.fr/2020UNIP7039.

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L'étude de la dynamique hors équilibre des systèmes fortement corrélés, à l'aide de laser femtoseconde, a révélé une variété de phénomènes sans analogue en physique d'équilibre. Dans cette thèse, nous étudions théoriquement la dynamique hors équilibre des degrés de liberté du réseau et leur signature en spectroscopie pompe-sonde. Nous développons une description microscopique des phonons cohérents displacive excité par le laser. La théorie capture la rétroaction de l'excitation des phonons sur le fluide électronique, qui manque dans la formulation phénoménologique actuelle. Nous montrons que cette rétroaction conduit à une oscillation avec une fréquence qui dépend du temps aux temps courts, même si le mouvement des phonons est harmonique. Pour les temps longs, cette rétroaction apparaît comme une phase résiduelle dans le signal oscillatoire. Nous appliquons la théorie au BaFe2As2, nous expliquons l'origine de la phase du signal oscillatoire rapporté dans des expériences récentes, et nous prédisons que le système oscille avec une fréquence décalé vers le rouge pour les grandes fluences. Notre théorie ouvre également la possibilité d'extraire des informations d'équilibre à partir la dynamique des phonons cohérents. Un autre phénomène intéressant qui a été observé en spectroscopie pompe-sonde est l'oscillation des fluctuations du réseau au double de la fréquence d’un phonon du système étudié. Ces oscillations sont interprétées comme une signature d'états de phonons squeezé macroscopique. Dans ce travail, nous identifions d'autres mécanismes d'oscillations à une fréquence double autre que le squeezing. Nous montrons qu'un quench de la température du bain thermique induite par la pompe, à laquelle le phonon est couplé, ou l'excitation d'un phonon cohérent pour lequel l'anharmonicité cubique est permise par symétrie peut également produire de telles oscillations en spectroscopie sans que le phonon soit dans un état squeezé. Nous concluons que, contrairement à ce qui est communément admis, les oscillations à double fréquence phononique en spectroscopie de bruit ne sont pas nécessairement une signature des phonons squeezés. Nous soulignons ce qui peut être un critère fiable pour identifier un phonon squeezé en utilisant la spectroscopie pompe-sonde
The study of the out of equilibrium dynamics of strongly correlated systems, using ultrafast pulses, uncovered a plethora of phenomena with no analog in equilibrium physics. In this thesis, we theoretically investigate the out of equilibrium dynamics of the lattice degrees of freedom and their signature in pump-probe spectroscopy. We develop a Hamiltonian-based microscopic description of laser pump induced displacive coherent phonons. The theory captures the feedback of the phonon excitation upon the electronic fluid, which is missing in the state-of-the-art phenomenological formulation. We show that this feedback leads to chirping at short timescales, even if the phonon motion is harmonic. At long times, this feedback appears as a finite phase in the oscillatory signal. We apply the theory to BaFe2As2, explain the origin of the phase in the oscillatory signal reported in recent experiments, and we predict that the system will exhibit redshifted chirping at larger fluence. Our theory also opens the possibility to extract equilibrium information from coherent phonon dynamics. Another interesting phenomenon that have been reported in pump-probe spectroscopy is the oscillation of the lattice fluctuations at double phonon frequency. These oscillations are invariably interpreted as a signature of macroscopic squeezed phonon states. In this work, we identify other mechanisms of double phonon frequency oscillations that do not involve squeezing. We show that a pump induced temperature quench of the bath, to which the phonon is coupled to, or exciting a coherent phonon for which cubic anharmonicity is allowed by symmetry can also produce such oscillations in noise spectroscopy without squeezing the phonon state. We conclude that, in contrast with what is commonly believed, double phonon frequency oscillations in noise spectroscopy are not necessarily a signature of macroscopic phonon squeezing. We point out what can be a reliable criterion to identify a squeezed phonon using pump-probe spectroscopy

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33

Dufåker, Daniel, Karlsson Fredrik, L. O. Mereni, V. Dimastrodonato, G. Juska, E. Pelucchi y Per-Olof Holtz. "Evidence of nonadiabatic exciton-phonon interaction probed by second-order LO-phonon replicas of single quantum dots". Linköpings universitet, Halvledarmaterial, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-90677.

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In this experimental study of single InGaAs/GaAs quantum dots (QDs) the photoluminescence intensity of the second order LO-phonon replica of the excitonic interband recombination was measured along with the intensities of the first and zeroth orders. The results show that the intensity of the second-order replica is three to four times stronger than expected from the adiabatic Huang-Rhys theory, indicating that the neglected nonadiabaticity plays an important role for the understanding of the exciton-phonon coupling in QDs.

Funding Agencies|Science Foundation Ireland|05/IN.1/I2510/IN.1/I3000|Swedish Research Council (VR)||K. A. Wallenberg Foundation||Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU)|2009-00971|

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34

Sundaresan, Sasi Sekaran. "ATOMISTIC MODELING OF PHONON BANDSTRUCTURE AND TRANSPORT FOR OPTIMAL THERMAL MANAGEMENT IN NANOSCALE DEVICES". OpenSIUC, 2014. https://opensiuc.lib.siu.edu/dissertations/854.

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Monte Carlo based statistical approach to solve Boltzmann Transport Equation (BTE) has become a norm to investigate heat transport in semiconductors at sub-micron regime, owing mainly to its ability to characterize realistically sized device geometries qualitatively. One of the primary issues with this technique is that the approach predominantly uses empirically fitted phonon dispersion relations as input to determine the properties of phonons so as to predict the thermal conductivity of specified material geometry. The empirically fitted dispersion relations assume harmonic approximation thereby failing to account for thermal expansion, interaction of lattice waves, effect of strain on spring stiffness, and accurate phonon-phonon interaction. To circumvent this problem, in this work, a coupled molecular mechanics-Monte Carlo (MM-MC) platform has been developed and used to solve the phonon Boltzmann Transport Equation (BTE) for the calculation of thermal conductivity of several novel and emerging nanostructures. The use of the quasi-anharmonic MM approach (as implemented in the open source NEMO 3-D software toolkit) not only allows one to capture the true atomicity of the underlying lattice but also enables the simulation of realistically-sized structures containing millions of atoms. As compared to the approach using an empirically fitted phonon dispersion relation, here, a 17% increase in the thermal conductivity for a silicon nanowire due to the incorporation of atomistic corrections in the LA (longitudinal acoustic) branch alone has been reported. The atomistically derived thermal conductivity as calculated from the MM-MC framework is then used in the modular design and analysis of (i) a silicon nanowire based thermoelectric cooler (TEC) unit, and (ii) a GaN/InN based nanostructured light emitting device (LED). It is demonstrated that the use of empirically fitted phonon bandstructure parameters overestimates the temperature difference between the hot and the cold sides and the overall cooling efficiency of the system, thereby, demanding the use of the BTE derived thermal conductivity in the calculation of thermal conductivity. In case of the light-emitting device, the microscopically derived material parameters, as compared to their bulk and fitted counterparts, yielded ~3% correction (increase) in optical efficiency. A non-deterministic approach adopted in this work, therefore, provides satisfactory results in what concerns phonons transport in both ballistic and diffusive regimes to understand and/predict the heat transport phenomena in nanostructures.

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35

Bright, Trevor James. "Non-fourier heat equations in solids analyzed from phonon statistics". Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29710.

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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Zhang, Zhuomin; Committee Member: Kumar, Satish; Committee Member: Peterson, G. P. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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36

Albrecht, Klaus Ferdinand [Verfasser] y Lothar [Akademischer Betreuer] Mühlbacher. "Nonequilibrium charge transport through quantum dots with electron-phonon interaction = Nichtgleichgewichts-Ladungstransport durch Quantenpunkte mit Elektron-Phonon Wechselwirkung". Freiburg : Universität, 2014. http://d-nb.info/1123478678/34.

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37

Parrish, Kevin D. "Phonon Scattering and Confinement in Crystalline Films". Thesis, Carnegie Mellon University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10622930.

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The operating temperature of energy conversion and electronic devices affects their efficiency and efficacy. In many devices, however, the reference values of the thermal properties of the materials used are no longer applicable due to processing techniques performed. This leads to challenges in thermal management and thermal engineering that demand accurate predictive tools and high fidelity measurements. The thermal conductivity of strained, nanostructured, and ultra-thin dielectrics are predicted computationally using solutions to the Boltzmann transport equation. Experimental measurements of thermal diffusivity are performed using transient grating spectroscopy.

The thermal conductivities of argon, modeled using the Lennard-Jones potential, and silicon, modeled using density functional theory, are predicted under compressive and tensile strain from lattice dynamics calculations. The thermal conductivity of silicon is found to be invariant with compression, a result that is in disagreement with previous computational efforts. This difference is attributed to the more accurate force constants calculated from density functional theory. The invariance is found to be a result of competing effects of increased phonon group velocities and decreased phonon lifetimes, demonstrating how the anharmonic contribution of the atomic potential can scale differently than the harmonic contribution.

Using three Monte Carlo techniques, the phonon-boundary scattering and the subsequent thermal conductivity reduction are predicted for nanoporous silicon thin films. The Monte Carlo techniques used are free path sampling, isotropic ray-tracing, and a new technique, modal ray-tracing. The thermal conductivity predictions from all three techniques are observed to be comparable to previous experimental measurements on nanoporous silicon films. The phonon mean free paths predicted from isotropic ray-tracing, however, are unphysical as compared to those predicted by free path sampling. Removing the isotropic assumption, leading to the formulation of modal ray-tracing, corrects the mean free path distribution. The effect of phonon line-of-sight is investigated in nanoporous silicon films using free path sampling. When the line-of-sight is cut off there is a distinct change in thermal conductivity versus porosity. By analyzing the free paths of an obstructed phonon mode, it is concluded that the trend change is due to a hard upper limit on the free paths that can exist due to the nanopore geometry in the material.

The transient grating technique is an optical contact-less laser based experiment for measuring the in-plane thermal diffusivity of thin films and membranes. The theory of operation and physical setup of a transient grating experiment is detailed. The procedure for extracting the thermal diffusivity from the raw experimental signal is improved upon by removing arbitrary user choice in the fitting parameters used and constructing a parameterless error minimizing procedure.

The thermal conductivity of ultra-thin argon films modeled with the Lennard-Jones potential is calculated from both the Monte Carlo free path sampling technique and from explicit reduced dimensionality lattice dynamics calculations. In these ultra-thin films, the phonon properties are altered in more than a perturbative manner, referred to as the confinement regime. The free path sampling technique, which is a perturbative method, is compared to a reduced dimensionality lattice dynamics calculation where the entire film thickness is taken as the unit cell. Divergence in thermal conductivity magnitude and trend is found at few unit cell thick argon films. Although the phonon group velocities and lifetimes are affected, it is found that alterations to the phonon density of states are the primary cause of the deviation in thermal conductivity in the confinement regime.

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38

Sergueev, Nikolai. "Electron-phonon interactions in molecular electronic devices". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102171.

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Over the past several decades, semiconductor electronic devices have been miniaturized following the remarkable "Moores law". If this trend is to continue, devices will reach physical size limit in the not too distance future. There is therefore an urgent need to understand the physics of electronic devices at nano-meter scale, and to predict how such nanoelectronics will work. In nanoelectronics theory, one of the most important and difficult problems concerns electron-phonon interactions under nonequilibrium transport conditions. Calculating phonon spectrum, electron-phonon interaction, and their effects to charge transport for nanoelectronic devices including all atomic microscopic details, is a very difficult and unsolved problem. It is the purpose of this thesis to develop a theoretical formalism and associated numerical tools for solving this problem.
In our formalism, we calculate electronic Hamiltonian via density functional theory (DFT) within the nonequilibrium Green's functions (NEGF) which takes care of nonequilibrium transport conditions and open device boundaries for the devices. From the total energy of the device scattering region, we derive the dynamic matrix in analytical form within DFT-NEGF and it gives the vibrational spectrum of the relevant atoms. The vibrational spectrum together with the vibrational eigenvector gives the electron-phonon coupling strength at nonequilibrium for various scattering states. A self-consistent Born approximation (SCBA) allows one to determine the phonon self-energy, the electron Green's function, the electronic density matrix and the electronic Hamiltonian, all self-consistently within equal footing. The main technical development of this work is the DFT-NEGF-SCBA formalism and its associated codes.
A number of important physics issues are studied in this work. We start with a detailed analysis of transport properties of C60 molecular tunnel junction. We find that charge transport is mediated by resonances due to an alignment of the Fermi level of the electrodes and the lowest unoccupied C60 molecular orbital. We then make a first step toward the problem of analyzing phonon modes of the C60 by examining the rotational and the center-of-mass motions by calculating the total energy. We obtain the characteristic frequencies of the libration and the center-of-mass modes, the latter is quantitatively consistent with recent experimental measurements. Next, we developed a DFT-NEGF theory for the general purpose of calculating any vibrational modes in molecular tunnel junctions. We derive an analytical expression for dynamic matrix within the framework of DFT-NEGF. Diagonalizing the dynamic matrix we obtain the vibrational (phonon) spectrum of the device. Using this technique we calculate the vibrational spectrum of benzenedithiolate molecule in a tunnel junction and we investigate electron-phonon coupling under an applied bias voltage during current flow. We find that the electron-phonon coupling strength for this molecular device changes drastically as the bias voltage increases, due to dominant contributions from the center-of-mass vibrational modes of the molecule. Finally, we have investigated the reverse problem, namely the effect of molecular vibrations on the tunneling current. For this purpose we developed the DFT-NEGF-SCBA formalism, and an example is given illustrating the power of this formalism.

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39

Erol, Mustafa. "Phonon studies in two dimensional electron gases". Thesis, Lancaster University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317611.

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40

Ari, Mehmet. "Phonon pulse studies of GaAlAs/GaAs heterostructures". Thesis, Lancaster University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239820.

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41

Stauffert, Oliver [Verfasser] y Michael [Akademischer Betreuer] Walter. "Electron-phonon coupling with density functional theory". Freiburg : Universität, 2019. http://d-nb.info/1191689328/34.

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42

Leadley, David Romwald. "Electron-phonon interactions in low dimensional structures". Thesis, University of Oxford, 1989. http://ora.ox.ac.uk/objects/uuid:3e8fe3de-4c61-48ac-a475-050b76901a6f.

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Transport properties of the two-dimensional electron gas (2DEG) in high magnetic fields are used to investigate scattering processes affecting the resistivity of GaAs-GaAlAs and GaInAs-InP heterojunctions and quantum wells: especially coupling of electrons to acoustic and optic phonons; and transitions between electric subbands. The experiments fall into two groups: A systematic study of magnetophonon resonance (MPR) between 30K and 300K. Resonance positions indicate a coupling substantially below the LO phonon energy, expected from 3D measurements. GaAs-GaAlAs hetero junctions show amplitudes varying smoothly with electron density (n_s) and closely related to the 4K mobility. On rotation in magnetic field they decrease rapidly as the resonance position returns to the LO value. In modulation doped structures the damping factor is determined by remote impurity scattering. As n_s is increased in GaInAs-InP the coupling frequency decreases dramatically from the GaAs-like LO at 272cm^-1 to the InAs-like TO at 226cm^-1. At higher electric fields the 'normal' MPR maxima invert, starting at low magnetic fields, to form 'hot electron' MPR minima, with maximum amplitude at ~60K. This is the first direct observation of HEMPR in 2D and is explained in a diffusion picture. At lower electric fields, additional resonances are identified with resonant cooling by inter-subband scattering. Comparisons are made with calculations and explanations sought including consideration of interface phonons; coupled plasmon-phonon modes; and shifts of the resonance positions due to the shape of the density of states. Low temperature magnetoresistance measurements in GaAs-GaAlAs heterojunctions with more than one occupied electric subband. Shubnikov-de Haas oscillations in perpendicular magnetic fields contain non-additive terms at electron temperatures > 2K where acoustic phonon mediated inter-subband scattering is comparable to intra-subband scattering. Subband separations and greatly enhanced g-factors [largest for electrons in the upper subband ] are deduced from the oscillations. Damping of the oscillations in field, gives values for quantum lifetimes (τ_s), much smaller than τ_tʼ, deduced from mobility. With two subbands occupied τ_s is always largest for the upper subband, while relative sizes of τ_t depend on sample quality. Study of electron energy loss rates, from thermal damping of the oscillations, shows enhancement in the region kT_e ~ ħω_cʼ, which is evidence for cyclotron phonon emission. Depopulating subbands in parallel fields causes the resistance to drop, by up to 60%, due to suppression of inter-subband scattering. Systematic studies show this scattering rate is independent of n_s.

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43

Montgomery, M. J. "Ineleastic electron-phonon interactions in atomic wires". Thesis, Queen's University Belfast, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411758.

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44

Cavill, Stuart Alan. "A phonon study of semiconductor tunnelling devices". Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325724.

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45

Williams, S. R. "Theoretical investigations of phonon transport in insulators". Thesis, University of Nottingham, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373345.

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46

Heraud, A. P. "Resonant phonon scattering in silicon and sapphire". Thesis, University of Nottingham, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353549.

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47

Strickland, Rosalind Elizabeth. "Phonon studies of two-dimensional hole gases". Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320793.

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48

Stoyanov, Nikolay Staykov 1979. "Phonon-polaritons in bulk and patterned materials". Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29954.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2003.
Vita.
This thesis explores the spectroscopic properties of phonon-polaritons, which are admixtures of coupled electromagnetic and mechanical vibrations in polar crystals. An in-depth theoretical treatment supplemented with simulations of experimental results of a four-wave mixing impulsive stimulated Raman scattering (ISRS) method to generate and probe polaritons with arbitrary wavevectors is developed. A novel method to generate phonon-polaritons with high amplitudes via focusing is also presented. The motivation for this work is ultimately the generation of lattice oscillations with high amplitude that will permit exploration of the potential energy surface of collective vibrational motion beyond its linear regime. Femtosecond laser machining has been used to fabricate microstructures in lithium niobate and lithium tantalate. Phonon-polaritons propagation has been extensively characterized in a number of functional elements, including waveguides, resonators, and various diffractive, reflective, and focusing elements. The experimental results are supplemented by two-dimensional finite-difference time-domain simulations of polariton generation and propagation in arbitrary two-dimensional patterned structures. The phonon-polaritons studied have THz frequencies and propagate at lightlike speeds. The motivation for this research is the development of a versatile terahertz spectroscopy platform, in which phonon-polaritons are used as a source of THz radiation. Furthermore, these fabricated microstructures can serve as the basic building blocks of an intergrated platform in a single crystal where phonon-polaritons are used for ultrafast signal processing.
by Nikolay Staykov Stoyanov.
Ph.D.

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49

Marcus, Stålhammar. "Band Structures in Magnon-Phonon Coupled Systems". Thesis, Uppsala universitet, Materialteori, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-304823.

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50

Yang, Xiaodong. "Effects of Electron-Phonon Interaction in Metals". Diss., Temple University Libraries, 2010. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/83903.

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Physics
Ph.D.
Phonons and electrons are two types of excitations which are responsible for many properties of condensed matter materials. The interaction between them plays an important role in condensed matter physics. In this thesis we present some theoretical investigations of the effects due to the interactions between phonons and electrons interactions. We show evidence that a structural martensitic transition is related to significant changes in the electronic structure, as revealed in thermodynamic measurements made in high magnetic fields. The effect of the magnetic field is considered unusual, as many influential investigations of martensitic transitions have emphasized that the structural transitions are primarily lattice dynamical and are driven by the entropy due to the phonons. We provide a theoretical frame-work which can be used to describe the effect of a magnetic field on the lattice dynamics in which the field dependence originates from the dielectric constant. The temperature-dependence of the phonon spectrum of alpha-uranium has recently been measured by Manley et al. using inelastic neutron scattering and x-ray scattering techniques. Although there is scant evidence of anharmonic interactions, the phonons were reported to show some softening of the optic modes at the zone boundary. The same group of authors later reported that an extra vibrational mode was observed to form at a temperature above 450 K. The existence of the proposed new mode is inconsistent with the usual theory of harmonic phonons, as applied to a structure composed of a monoclinic Bravais lattice with a two-atom basis. We investigate the effect that the f electron-phonon interaction has on the phonon spectrum and its role on the possible formation of a breathing mode of mixed electronic and phonon character. We examine the model by using Green’s function techniques to obtain the phonon spectral density. Some materials undergo phase transitions from a high temperature state with periodic translational invariance to a state in which the electronic charge density is modulated periodically. The wave vector of the modulation may be either commensurate or incommensurate with the reciprocal lattice vectors of the high temperature structure. In the case of an incommensurate charge density wave, the system supports phason excitation. For an incommensurate state, the new ground state has a lower symmetry than the high temperature state since the charge density does not have long-ranged periodic translational order. If the metal is ideal (with no impurities), a charge density wave should be able to slide throughout the crystal without resistance, resulting in current flow similar to that of a superconductor. The phason is an excitation of the charge density wave which is related to the collective motion of electrons. We estimate the phason density of states, and the phason contribution to the specific heat. Angle-resolved photoemission experiments have been performed on USb2, and very narrow quasiparticle peaks have been observed in a band which local spin-density approximation (LSDA) predicts to osculate the Fermi energy. The observed band is found to be depressed by 17 meV below the Fermi energy. The experimentally observed quasiparticle dispersion relation for this band exhibits a kink at an energy of about 23 meV below the Fermi energy. The kink is not found in LSDA calculations and, therefore, is attributable to a change in the quasiparticle mass renormalization by a factor of approximately 2. The existence of a kink in the quasiparticle dispersion relation of a band which does not cross the Fermi energy is unprecedented. The kink in the quasiparticle dispersion relation is attributed to the effect of the interband self-energy involving transitions from the osculating band into a band that does cross the Fermi energy.
Temple University--Theses

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Tesis sobre el tema "Phonon"

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