Dissertations / Theses on the topic 'Phonon energy'
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1
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.
2
Ong, Pang-Leen. "PHONON-ENERGY-COUPLING-ENHANCEMENT EFFECT AND ITS APPLICATIONS." UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_diss/652.
Abstract:
Silicon Oxide/Oxynitride (SiO2/SiON) has been the mainstream material used for gate dielectric for MOS transistors for the past 30 years. The aggressive scaling of the feature size of MOS transistor has limited the ability of SiO2/SiON to work effectively as the gate dielectric to modulate the conduction of current of MOS transistors due to excess leakage current dominated by direct quantum tunneling. Due to this constraint, alternative gate dielectric/high-k is being employed to reduce the leakage current in order to maintain the rate of scaling of MOS transistors. However, the cost involved in the implementation of these new gate dielectric materials are high due to the requirements of a change in the process flow for device fabrication. This work presents the results of a novel processing method implementing the use of rapid thermal processing (RTP) on conventional SiO2/SiON gate dielectric to reduce the gate leakage current by three to five orders of magnitude. Electrical properties of the effect were characterized on fabricated MOS capacitors using semiconductor parameter analyzer and LCR meter. Material characterization was performed using FT-IR to understand the mechanism involved in this novel processing method, named PECE (Phonon-Energy-Coupling-Enhancement). By implementing this novel process, the use of SiO2/SiON as gate dielectric can be scaled further in conventional process flow of device fabrication.
3
Damart, Tanguy. "Energy dissipation in oxide glasses." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1189/document.
Abstract:
L'atténuation d'ondes à basse et haute fréquences dans les verres n'est pas encore bien comprise en grande partie car les phénomènes à l'origine de cette dissipation varient grandement en fonction de la fréquence. L’existence de structures complexes et organisation multi échelle dans les verres favorise l'apparition de temps de relaxation allant de la seconde à la femtoseconde et de corrélation prenant place de l’Angström à la centaine de nanomètre. A basse fréquence, une meilleur compréhension de ces phénomènes de dissipation serait bénéfique à de nombreux domaines. Par exemple, les multi-couches recouvrants les miroirs des interféromètres servant à détecter les ondes gravitationnelles sont réalisées à partir de verres d'oxyde (SiO2 et Ta2O5) qui sont une source majeur de dissipation. A haute fréquence, l'étude de la dissipation pose des questions théoriques sur le lien entre asymétrie locale et atténuation acoustique.Durant cette étude, nous avons réalisé une analyse approfondie de l'interaction entre ondes mécaniques et structure des verres en utilisant des techniques de simulations telle que la dynamique moléculaire. En partant de la synthèse de verres de SiO2 et Ta2O5, nous nous sommes appliqués à trouver l'origine structurelle de la dissipation aux différentes échelles de fréquence. A basse fréquence nous avons été capable de catégoriser les déplacements atomiques à l'origine de la dissipation en utilisant la théorie des états à deux niveaux. A haute fréquence, nous avons utilisé une technique de spectroscopie mécanique appuyé par un développement analytique pour montrer l'importance du désordre local dans l’existence de dissipationThe origin of sound attenuation at low and high frequency in glasses stays elusive mainly because of the complex temperature and frequency dependence of the phenomena at its root. Indeed, the presence of complex structures and multi-scale organizations in glasses induce the existence of relaxation time ranging from the second to the femto-second and of spatial correlation ranging from the Angström to a hundred nanometers. At low-frequency, a better understanding of the phenomena at the origin of dissipation would be beneficial to several applications. For example, the multi-layers coating the mirrors of gravitational waves detectors consists of a superposition of two oxide glasses: silicate (SiO2) and tantalum pentoxide (Ta2O5), are an important source of dissipation. At high frequency, the study of dissipation raises theoretical questions about the link between attenuation and dissipation as well as between loclt asymmetry and dissipation. In the present study, we conducted an analysis of the interaction between mechanical waves and the structure of two oxide glasses using simulation techniques such as non-equilibrium molecular dynamics. At high-frequencies, we implemented and used mechanical spectroscopy to measure dissipation numerically and performed in parallel an analytical development based on the projection of the atomic motion on the vibrational eigenmodes. At low-frequencies, we used molecular dynamics to gather sets of thermally activated events that we classed in three categories based on topologically distinct atomic motions and from which we predicted dissipation numerically using a refreshed TLS model
4
Kulikowski, Anoushka. "Phonon studies of energy loss in vertical tunnelling structures." Thesis, Lancaster University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286990.
5
Giltrow, M. "Phonon study of vertical resonant structures." Thesis, Lancaster University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337346.
6
Sklan, Sophia Robin. "Dynamical tuning of phonon transport for information and energy control." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103231.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 145-164).
Controlled transport of energy and information is of paramount importance. It remains challenging, however, partially from the difficulty in controlling their physical carriers. Steering electrons and photons is now routine, yet atomic vibrations (quantized as phonons) are hard to control. This is partly due to the centrality of phonons in the disordered transport of energy as heat, but even in ordered sound waves problems persist. Phonons can readily couple to each other or to other degrees of freedom, degrading their energy or information content. Reversing these couplings, thereby regulating atomic motion, only recently became plausible. This increased control would reduce parasitic losses and turn phonons into information carriers. Dynamical effects are a crucial and under-examined aspect of this control as static devices are insufficient for changing external conditions. Dynamical control adds flexibility and versatility to phononic systems. Essentially, dynamical control requires tunable materials, materials whose physical properties depend on an external signal. Dynamical tuning is sensitive to the relative frequencies of the tuning signal and the controlled phonons. We develop an intuitive framework of the temporal modulation regimes. In low frequency tuning, phonons can adapt adiabatically to the material's changes. A variety of signals can be temporally and spatially modulated to tune phonon transport in this regime. We apply this adiabatic perspective to analyze dynamical effects in thermal cloaks. Tuning signals near the frequency of some phonon mode can produce resonant couplings. This hybridization can produce large changes in phonon properties. We apply this hybridization to develop a rigorously nonreciprocal phononic computer using magneto-acoustic materials that can outperform conventional computers in some tasks. At high frequencies, phonons can only respond perturbatively to the tuning signal's changes. This regime is generally limited to optical control but it opens up new avenues for control. Employing an alternative approach to optical coupling, we develop a model of inverse acousto-optics (tuning the speed of sound with optical intensity) and dynamical phonon localization.
by Sophia Robin Sklan.
Ph. D.
7
Chen, Dye-Zone A. (Dye-Zone Abraham) 1973. "Energy transmission through and along thin films mediated by surface phonon-polaritons." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42067.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 131-138).
Surface phonon-polaritons are hybrid electromagnetic modes that are the result of photons coupling to transverse optical phonons. Recently, these surface modes have received much renewed interest primarily due to the fact that micro-fabrication techniques can now routinely create structures at the length scales of interest (nanometers to microns). This thesis investigates the transmission of energy mediated by surface phonon-polaritons. First, the heat flux transported along the in-plane direction of a thin film is explored. A kinetic theory-based calculation is performed using a diffusion approximation. These results are further confirmed by simulations using fluctuational electrodynamics. It was found that for amorphous silicon dioxide films tens of nanometers thick, the in-plane heat flux carried by surface phonon-polaritons can exceed the heat flux carried by phonons in the film. The results also show that the effective thermal conductivity due to surface polaritons increases with decreasing film thickness, offering a method to potentially offset the reduction in thermal conductivity due to increased interface scattering of phonons in crystalline thin films. Both calculations point to the propagation length of the surface phonon-polariton as the source for the large heat flux. An experimental measurement of the surface phononpolariton propagation length on amorphous silicon dioxide is performed using attenuated total reflection and is found to agree well with the calculated value. The last part of this thesis examines the energy transmission in the direction normal to the plane of the film. Specifically, the transmission of light through an amorphous silicon dioxide film perforated by sub-wavelength holes is experimentally measured. A five-fold increase through the perforated film versus through a solid film is observed in discrete frequency ranges, which strongly suggests the involvement of surface phonon-polaritons.
by Dye-Zone A. Chen.
Ph.D.
8
Minnich, Austin Jerome. "Exploring electron and phonon transport at the nanoscale for thermoelectric energy conversion." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67593.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 147-155).
Thermoelectric materials are capable of solid-state direct heat to electricity energy conversion and are ideal for waste heat recovery applications due to their simplicity, reliability, and lack of environmentally harmful working fluids. Recently, nanostructured thermoelectrics have demonstrated remarkably enhanced energy conversion efficiencies, primarily due to a reduction in lattice thermal conductivity. Despite these advances, much remains unknown about heat transport in these materials, and further efficiency improvements will require a detailed understanding of how the heat carriers, electrons and phonons, are affected by nanostructures. To elucidate these processes, in this thesis we investigate nanoscale transport using both modeling and experiment. The first portion of the thesis studies how electrons and phonons are affected by grain boundaries in nanocomposite thermoelectric materials, where the grain sizes are smaller than mean free paths (MFPs). We use the Boltzmann transport equation (BTE) and a new grain boundary scattering model to understand how thermoelectric properties are affected in nanocomposites, as well as to identify strategies which could lead to more efficient materials. The second portion of the thesis focuses on determining how to more directly measure heat carrier properties like frequency-dependent MFPs. Knowledge of phonon MFPs is crucial to understanding and engineering nanoscale transport, yet MFPs are largely unknown even for bulk materials and few experimental techniques exist to measure them. We show that performing macroscopic measurements cannot reveal the MFPs; instead, we must study transport at the scales of the MFPs, in the quasi- ballistic transport regime. To investigate transport at these small length scales, we first numerically solve the frequency-dependent phonon BTE, which is valid even in the absence of local thermal equilibrium, unlike heat diffusion theory. Next, we introduce a novel thermal conductivity spectroscopy technique which can measure MFP distributions over a wide range of length scales and materials using observations of quasi-ballistic heat transfer in a pump-probe experiment. By observing the changes in thermal resistance as a heated area size is systematically varied, the thermal conductivity contributions from different MFP phonons can be determined. We present the first experimental measurements of the MFP distribution in silicon at cryogenic temperatures. Finally, we develop a modification of this technique which permits us to study transport at scales much smaller than the diffraction limit of approximately one micron. It is important to access these length scales as many technologically relevant materials like thermoelectrics have MFPs in the deep submicron regime. To beat the diffraction limit, we use electron-beam lithography to pattern metallic nano dot arrays with diameters in the hundreds of nanometers range. Because the effective length scale for heat transfer is the dot diameter rather than the optical beam diameter, we are able to study nanoscale heat transfer while still achieving ultrafast time resolution. We demonstrate the modified technique by measuring the MFP distribution in sapphire. Considering the crucial importance of the knowledge of MFPs to understanding and engineering nanoscale transport, we expect these newly developed techniques to be useful for a variety of energy applications, particularly for thermoelectrics, as well as for gaining a fundamental understanding of nanoscale heat transport.
by Austin Jerome Minnich.
Ph.D.
9
Mafra, Daniela Lopes. "Using inelastic scattering of light to understand the nature of electron-phonon interactions and phonon self-energy renormalizations in graphene materials." Universidade Federal de Minas Gerais, 2012. http://hdl.handle.net/1843/MPDZ-8Y4GEG.
Abstract:
In the last decade, many theoretical and experimental achievements have been made in the physics of graphene. In particular, Raman spectroscopy has been playing an important role in unraveling the properties of graphene systems. In this thesis we use the Raman spectroscopy to study some effects of the electron-phonon coupling in monolayer and bilayer graphene and to probe the electronic and vibrational structure of bilayer graphene. Phonon self-energy corrections have mostly been studied theoretically and experimentally for phonon modes with zone-center (q = 0) wavevectors. Here, we combine Raman spectroscopy and gate voltage to study phonons of monolayer graphene for the features originated from a double-resonant Raman (DRR) process with q .= 0 wavevectors. We observe phonon renormalization effects in which there is a softening of the frequency and a broadening of the decay width with increasing the gate voltage, that is opposite from what is observed for the zone-center q = 0 case. We show that this renormalization is a signature for the phonons with q . 2k wavevector that come from both intravalley and intervalley DRR processes. Within this framework, we resolve the identification of the phonon modes contributing to the G. Raman feature, at ¡ 2450 cm.1, and also for
five second order Raman combination modes in the frequency range of 1700 . 2300 cm.1 of monolayer graphene. By combining the DRR theory with the anomalous phonon renormalization effect, we show a new technique for using Raman spectroscopy to identify the proper phonon mode assignment for each combination mode. We also study the behavior of the optical phonon modes in bilayer graphene devices
by applying top gate voltage, using Raman scattering. We observe the splitting of the Raman G band as we tune the Fermi level of the sample, which is explained in terms of mixing of the Raman (Eg) and infrared (Eu) phonon modes, due to different doping in the two layers. We show that the comparison between the experiment and theoretical model not only gives information about the total charge concentration in the bilayer graphene device, but also allows to separately quantify the amount of unintentional charge coming from the top and the bottom of the system, and therefore to characterize the intrinsic charges of bilayer graphene with its surrounding environment. In the second part of this thesis, the dispersion of electrons and phonons near the K point of bilayer graphene was investigated in a resonant Raman study of the G¡Ç band using different laser excitation energies in the near-infrared and visible range.
The electronic structure was analyzed within the tight-binding approximation, and the Slonczewski-Weiss-McClure (SWM) parameters were obtained from the analysis of the dispersive behavior of the G¡Ç band considering both the inner and the outer DRR processes. We show that the SWM parameters obtained considering the inner process are in better agreement with those obtained from other experimental techniques, strongly suggesting that the inner process is the main responsible for the G¡Ç feature in graphene. Additionally, the dependence of the intensity of the four peaks that compose the G¡Ç band of bilayer graphene with laser excitation energy and laser power is explored and explained in terms of the electron-phonon coupling and the relaxation of the photon-excited electron. We show that the carrier relaxation occurs predominantly by emitting a lowenergy acoustic phonon and the different combinations of relaxation processes determine the relative intensities of the four peaks that give rise to the G¡Ç band. Some peaks show an increase of their intensity at the expense of others, thereby making the intensity of the peaks both different from each other and dependent on laser excitation energy and on power level. This effect gives important information about the electron and phonon dynamics and needs to be taken into account for certain applications of bilayer graphene in the field of nanotechnology.Na última década, muitos avanços teóricos e experimentais foram alcançados na física do grafeno. Em particular, a Espectroscopia Raman tem sido muito importante para elucidar propriedades físicas e químicas em sistemas de grafeno. Nessa tese nós usamos a Espectroscopia Raman para estudar alguns dos efeitos do acoplamento elétron-fônon no grafeno de camada única e de dupla camada e para obter informações sobre a estrutura eletrônica e vibracional do grafeno de camada dupla. As renormalizações das energias dos fônons tem sido estudadas basicamente para fônons com vetor de onda nulo (q=0). Aqui, nós combinamos a Espectroscopia Raman com aplicação de tensão de porta, para estudar, em grafeno de camada única, as bandas originadas do processo Raman com dupla ressonância (DDR) com etores de onda q0. Nós observamos os efeitos de decaimento dos fônons com o aumento da tensão de porta e esse efeito é o oposto do que é observado para os fônons com q=0. Nós mostramos que esse tipo de renormalização é uma assinatura dos fônons com vetor de onda q2K que vem de um processo de camada única, os modos de fônons que contribuem para a banda Raman G*, em ~2450cm-1 e para outros cinco picos provenientes de combinação de modos na região de frequência 1700-2300cm-1. Combinando a teoria do processo DRR com o efeito de renormalização de fônons, nós mostramos uma nova técnica para usar a Espectroscopia Raman para identificar cada modo Raman apropriadamente. Nó também estudamos o comportamento dos modos ópticos do grafeno de camada dupla combinando o espalhamento Raman e a aplicação de tensão de porta em dispositivos desse material. Nós observamos que a banda G se divide em duas quando o nível de Fermi da amostra é mudado e isso é explicado em termos da mistura dos modos de fônon Raman (Eg) e infravermelho (Eu) devido a diferença de concentração de carga nas duas camadas. Nós mostramos que a comparação entre os dados experimentais e o modelo teórico não dá apenas informação sobre a concentração de carga total no dispositivo de grafeno de camada dupla, mas também nos permite quantificar separadamente a quantidade de cargas não intencionais provenientes da camada de cima e de baixo do sistema e, portanto caracterizar a interação do grafeno de camada dupla com o ambiente a sua volta. Na segunda parte dessa tese, a dispersão de elétrons e fônons perto do ponto K do grafeno de camada dupla é investigada atravé do estudo da banda G' usando várias energias de excitação de laser na região do infravermelho e do visível. A estrutura eletrônica foi analisada dentro da aproximação de ligações-forte e os parâmetros Slonczewski-Weiss-McClure (SWM) foram obtidos através do comportamento dispersivo da banda G' considerando-se tanto o processo DRR interno, quanto o externo. Nós mostramos que os parâmetros SWM obtidos considerando-se que o processo DRR interno está em melhor acordo com os valores obtidos por outras técnicas experimentais, sugerindo fortemente que o processo interno é o principal responsável pela banda G' no grafeno. Além disso, a dependência da intensidade dos quatro picos que compõe a banda G' do grafeno de camada dupla com a energia de excitação de laser e com a potência do laser é explorada e explicada em termos do acoplamento elétron-fônon e do relaxamento dos elétrons foto-excitados. Nós mostramos que o relaxamento dos elétrons ocorre predominantemente pela emissão de fônons acústicos de baixa energia e as diferentes combinações dos processos de relaxamento determinam as intensidades relativas dos quatro picos que dão origem à banda G'. Esse efeito nos fornece informações importantes sobre a dinâmica dos elétrons e fônons e precisa ser levado em conta para aplicações do grafeno de camada dupla do campo nanotecnológico.
10
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.
Abstract:
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.
11
Stanton, Nicola Marie. "Experimental studies of electron-phonon interactions in gallium nitride." Thesis, University of Nottingham, 2001. http://eprints.nottingham.ac.uk/14212/.
Abstract:
This thesis presents an experimental investigation of the electron-phonon interaction in GaN. Bulk epilayers, grown by MBE, and AIGaN/GaN heterostructures, grown by MOCVD, have been studied. The energy relaxation rate for hot electrons has been measured over a wide range of temperatures, allowing both acoustic and optic phonon emission to be studied in GaN epilayers. Direct phonon measurements, both studying the emission and absorption processes, have been performed. Detection of phonons emitted when hot electrons relax their excess energy complements the measurements of relaxation rates. Absorption of acoustic phonons by the epilayers, using both fixed and extended metal film phonon sources, allowed investigation into the effectiveness of the 2kF cutoff in the low mobility layers. The experimental findings are compared with the predictions of theory. AIGaN/GaN heterostructures were characterised and measurements of the energy relaxation rate in the temperature range 4K-40K obtained. Excellent agreement with theory is observed. A preliminary study of phonon absorption by the 2DEG system is presented, which allowed experimental determination of the "thickness" of the 2DEG and demonstrated the applicability of the technique in the study of low dimensional systems.
12
Al-Jawhari, Hala A. "Study of energy loss by a hot two-dimensional electron gas." Thesis, Lancaster University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287252.
13
Cross, Andrew John. "The electron-phonon interaction in GaAs/(AlGa)As quantum wells." Thesis, University of Nottingham, 2001. http://eprints.nottingham.ac.uk/14316/.
Abstract:
This thesis presents a study of the electron-phonon interaction in two dimensional electron gases (2DEGs), by measuring of the acoustic phonon emission from a sequence of n-type doped GaAs/(AlGa)As quantum wells. Previous studies of emISSIon from 2DEGs confined in GaAs heterojunctions (Chin et al., 1984) have shown a surprising absence of longitudinal acoustic (LA) mode phonon emission, in contrast with theoretical studies (Vass, 1987) which predict that deformation potential coupled LA mode emission should dominate the energy relaxation processes. This may be attributed to the finite width of the quasi-2D sheet, which imposes a restriction on the maximum emitted phonon wavevector component perpendicular to the 2DEG, leading to a suppression of the emission (the "1Iao cutoff') at smaller phonon wavevectors than predicted by the earlier theory. By using the quantum well width w as a means of modulating the thickness of the 2DEG, the dependence of the 1Iao cutoff on the phonon emission can be directly measured. In the present work, significant LA phonon emission from the quantum well samples is observed. To complement the experimental measurements, the theory of emission from a 2DEG has been modelled in detail using computer simulation techniques. Calculations of the electron-phonon interaction, including matrix element anisotropy and dynamic screening, as well as phonon focusing effects, can be combined to produce accurate predictions of the experimentally detected phonon emission energy spectra.
14
Hardikar, Rahul Padmakar. "Dynamic electron-phonon interactions in one-dimensional models." Diss., Mississippi State : Mississippi State University, 2007. http://library.msstate.edu/etd/show.asp?etd=etd-11092007-143010.
15
Zhou, Jiawei. "Ab initio simulation and optimization of phonon drag effect for lower-temperature thermoelectric energy." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100088.
Abstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 81-85).
In recent years, extensive efforts have been devoted to searching for materials with high thermoelectric (TE) efficiency above room temperature for converting heat into electricity. These efforts have led to significant advances with a record-high zT above 2. However, the pursuit of higher TE performance at lower temperatures for cooling and refrigeration applications receives much less attention. Today's most widely-used thermoelectric materials below room temperature are still (Bi,Sb) 2(Te,Se)3 material system, discovered 60 years ago with a maximum zT around 1. This thesis develops the first-principles simulation tools to study the phonon drag effect - a coupling phenomenon between electrons and non-equilibrium phonons - that leads to a large Seebeck coefficient at low temperatures. Phonon drag effect is simulated successfully from first-principles for the first time and results compare well with experimental data on silicon. While the common wisdom always connects a significant phonon drag effect to a high thermal conductivity, a key insight revealed from the simulation is that phonons contributing to phonon drag and to thermal conductivity do not spectrally overlap. Even in a heavily-doped silicon sample with 1019 cm-3 doping concentration, phonon drag still contributes to -50% of the total Seebeck coefficient. By selectively scattering phonons contributing to heat conduction but not to phonon drag, a large improvement in thermoelectric figure of merit zT is possible. An ideal phonon filter is shown to tremendously enhance zT of n-type silicon at room temperature by a factor of 20 to ~0.25, and the enhancement reaches 70 times at lOOK. A practical phonon filtering method based on nanocluster scattering is shown to enhance zT due to reduced thermal conductivity and optimized phonon drag effect. This work opens up a new venue towards better themoelectrics by harnessing non-equilibrium phonons. More material systems can be systematically studied with the developed simulation tools.
by Jiawei Zhou.
S.M.
16
Pentland, Ian Alisdair. "A phonon emission study of quasi-1D electron gases." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325695.
17
Osborne, Daniel Josiah. "A Nanoengineering Approach to Oxide Thermoelectrics For Energy Harvesting Applications." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/36133.
Abstract:
The ability of uniquely functional thermoelectric materials to convert waste heat directly into electricity is critical considering the global energy economy. Profitable, energy-efficient thermoelectrics possess thermoelectric figures of merit ZT â ¥ 1. We examined the effect of metal nanoparticle â oxide film interfaces on the thermal conductivity κ and Seebeck coefficient α in bilayer and multilayer thin film oxide thermoelectrics in an effort to improve the dimensionless figure of merit ZT. Since a thermoelectricâ s figure of merit ZT is inversely proportional to κ and directly proportional to α, reducing κ and increasing α are key strategies to optimize ZT.
We aim to reduce κ by phonon scattering due to the inclusion of metal nanoparticles in the bulk of thermoelectric thin films deposited by Pulsed Laser Deposition. XRD, AFM, XPS, and TEM analyses were carried out for structural and compositional characterization. The electrical conductivities of the samples were measured by a four-point probe apparatus. The Seebeck coefficients were measured in-plane, varying the temperature from 100K to 310K. The thermal conductivities were measured at room temperature using Time Domain Thermoreflectance.Master of Science
18
Koster, Sophie Amelia. "Energy Levels and Dynamics of Tm²⁺ Doped into AMX₃ Salts." Thesis, University of Canterbury. Physics and Astronomy, 2014. http://hdl.handle.net/10092/9643.
Abstract:
Divalent thulium has been doped into CsCaI₃, CsCaBr₃, CsCaCl₃ and RbCaI₃- a series of AMX₃ salts. Using previously published optical spectra, a series of parameterised energy level calculations have been performed. The calculated energy levels, optimised crystal field parameters and simulated optical absorption spectra are presented. Theoretical predictions yield excellent approximation to the experimental data.
Temperature dependent fluorescent lifetimes from the (³F₄,t₂g) and (³H₆,t₂g) excited (emitting) states have been measured using a pulsed dye laser. For CsCaBr₃ and RbCaI₃ doped with Tm²⁺, visible emission for the (³F₄,t₂g) state yields 10 K and 28 K lifetimes of 1.7 μs and 0.40 μs respectively. In both cases no emission is observed at room temperature. Considering direct multiphonon relaxation to the lower lying (³H₆,t₂g) levels, a simple energy gap law well accounts for the measured data with effective phonon energies in the range 100-200 cm⁻¹ - consistent with the phonon density of states in these low phonon energy hosts. Monitoring infrared emission from the (³H₆,t₂g) states, 14 K and 10 K lifetimes of 301 μs and 250 μs are found for CsCaBr₃ and CsCaCl₃ respectively. For CsCaBr₃ this value reduces to 270 μs at 200 K and is not quenched until 300 K, whilst for CsCaCl₃ emission is quenched by 170 K. This temperature dependent behavior is interpreted in terms of internal conversion via configurational crossing between the excited and ground state potential energy surfaces. Fitting the fluorescence lifetime data to a modified Mott equation, it is inferred that the potential barrier for non-radiative relaxation is five times larger in CsCaBr₃ compared to CsCaCl₃. This explains the fact that emission is still observable in the bromide host at room temperature.
19
Devitt, Andrew Maurice. "Time and angle resolved phonon absorption in the fractional quantum hall regime." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342525.
20
Kaul, Pankaj B. "Thermal Transport in Tin-Capped Vertically Aligned Carbon Nanotube Composites for Thermal Energy Management." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1383515941.
21
Pfau, Charlotte [Verfasser], S. [Akademischer Betreuer] Schweizer, R. [Akademischer Betreuer] Wehrspohn, and U. [Akademischer Betreuer] Rogulis. "Low phonon energy glass ceramics for efficient rare-earth luminescence / Charlotte Pfau. Betreuer: S. Schweizer ; R. Wehrspohn ; U. Rogulis." Halle, Saale : Universitäts- und Landesbibliothek Sachsen-Anhalt, 2014. http://d-nb.info/1076503195/34.
22
Galparsoro, Larraza Oihana. "Phonon and electron excitations in diatom abstraction from metallic surfaces." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0417/document.
Abstract:
La rationalisation des processus chimiques élémentaires aux surfacesest d'intérêt primordial pour de nombreux phénomènes naturels ou d'intérêttechnologique. D'un point de vue fondamental, la façon dont l'énergie, concomitanteà toute réaction chimique, est distribuée parmi les degrés de liberté des moléculesformées et/ou transférée à la surface est loin d'être systématisée. Dans ce travail,des simulations, reposant sur la méthode des trajectoires quasi-classiques (QCT),sont réalisées pour examiner cette problématique lors de recombinaisons demolécules d'hydrogène (H2) et d'azote (N2) résultant de l'abstraction d'atomesadsorbés via collision par un atome provenant de la phase gazeuse sur des surfacesde Tungstène - W(100) et W(110) - à taux de couverture non nul. Ces processussont ici étudiés pour leur intérêt en physique des interactions plasma-paroi. Dessurfaces d'énergie potentielle, construites à partir de calculs de structure électroniquebasés sur la théorie de la fonctionnelle densité (DFT), sont utilisées pour simuler,dans le cadre de la mécanique classique - incluant les corrections semi-classiquespertinentes - les processus ultrarapides dit de "Eley-Rideal" et par "atomes-chauds"(sub-picoseconde). La mise en place de modèle effectifs, pour tenir compte de ladissipation de l'énergie aux phonons de la surface et aux excitations électroniques(paires électron-trou), permet de rationaliser la dynamique non-adiabatique del'abstraction atomique aux surfaces métalliquesThe rationalization of elementary processes at surfaces is of prime importance for numerous natural and technological areas. From a fundamental pointof view, the way the energy concomitant to any chemical reaction is distributed among the desorbing molecules degrees-of-freedom and the surface is far frombeing fully pictured. In this work, quasiclassical molecular dynamics (QCT)simulations have been carried out to investigate this issue for the recombination ofH2 and N2 resulting from atomic adsorbate abstraction by atom scattering off theW(100) and W(110) covered surfaces, these processes being of relevance inplasma-wall interactions. Potential energy surfaces, built from density functional(DFT) theory calculations, have been used to simulate, within the framework ofclassical dynamics (including semi-classical corrections), the subpicosecond Eley-Rideal and Hot-Atom processes. The implementation of effective models to accountfor energy dissipation to surface phonons and electron-hole pair excitations, have allowed to rationalize the non-adidabatic dynamics of atom abstraction at metalsurfaces
23
Vallerini, Barbosa Itália. "Nanocristaux oxydes luminescents pour le développement de nanosondes de température in vivo." Electronic Thesis or Diss., Université Grenoble Alpes, 2023. http://www.theses.fr/2023GRALI125.
Abstract:
Les changements thermiques biologiques sont des événements courants lors d'activités métaboliques cellulaires anormales. En effet, les aberrations thermiques – telles qu'une augmentation de la température locale des tissus – sont directement liées à la détection de zones enflammées, à la présence de tumeurs ou d'autres maladies. En plus de contribuer au diagnostic des maladies, la détermination de la température locale dans les systèmes biologiques peut également aider à leur traitement. Par exemple, dans l'hyperthermie, une élévation de température doit être induite dans les tissus tumoraux à des niveaux cytotoxiques afin de détruire les cellules cancéreuses et de fournir un traitement contre le cancer. Cependant, la montée en température doit être réalisée de manière contrôlée et bien localisée sur les cellules cibles cancéreuses, tout en évitant un échauffement des tissus sains environnants. De plus, pour déterminer de telles maladies, les variations de température doivent être déterminées avec précision. Des études antérieures en nanothermométrie luminescente montrent qu’il n’y a encore de sondes thermiques adéquates pour les environnements biologiques. Il est donc nécessaire de développer des nanothermomètres luminescents avec une morphologie et une taille adéquate, fonctionnant avec des longueurs d'onde d'excitation et d'émission dans le domaine de transparence des tissus. Pour répondre à cette demande, nous avons mené une étude de différents nanocristaux d'oxydes dopés avec des ions lanthanides afin de développer des nanothermomètres luminescents capables de déterminer la température dans des systèmes in vivo à haute résolution thermique. Les performances thermométriques ont été déterminées en calculant la sensibilité thermique relative (S_r) à l'aide de l'approche d'intensité de luminescence ratiométrique. Par ailleurs, notre étude a permis de soulever quelques hypothèses pouvant contribuer efficacement aux performances thermométriques. Nous avons mis en jeu la technique du rapport d’intensité de deux pics de luminescence pour laquelle les valeurs de S_r peuvent être optimisées en co-dopant les nanocristaux avec deux, ou plusieurs, ions Ln3+ et en utilisant des matrices oxydes présentant différentes énergies de phonons. Ainsi, du fait de sa nature générique et de sa souplesse de synthèse, la méthode Pechini a été choisie pour synthétiser plusieurs matrices oxydes, Y2O3, Y2Ge2O7, Y3Al5O12 (YAG), Y3BO6 et YBO3. Les nanocristaux ont tout d’abord été mono-dopés avec Nd3+, puis co-dopés avec Nd3+ -Yb3+ pour améliorer les propriétés de sonde thermiques dans les fenêtres biologiques du proche IR. De plus, nous avons optimisé les concentrations de dopage dans les matrices hôtes pour une plus grande efficacité dans la détection de la luminescence dans les organismes biologiques. Nous avons observé expérimentalement que les valeurs de Sr sont fortement impactées sur l'énergie des phonons de la matrice. Nous avons observé que par co-dopage Nd3+-Yb3+ les performances thermométriques des nanocristaux sont améliorées par rapport aux nanocristaux mono dopés Nd3+. Notre étude de ce différent oxyde a montré que le YAG et Y2O3 sont des matrices les plus prometteuses, pour l'application de la nanothermométrie luminescente in vivo. Enfin, des nanocristaux individuels (non agglomérés comme dans le cas des synthèses Péchini) de YAG de taille 60 nm et de morphologie contrôlée ont été obtenus en solution par la méthode solvothermale pour faire avancer les études dans les futures applications biologiques. Nous avons observé que les nanothermomètres YAG adaptés à cet objectif ont un Sr égal à 0,47 %·K-1 et une résolution thermique de 0,3 K. Des tests expérimentaux in vivo seront bien sûr nécessaires pour valider les résultats de cette étude; cependant, nos résultats obtenus sur les performances des nanocristaux YAG:Nd3+-Yb3+ démontrent dès à présent un fort potentiel pour des applications in vivo de nanothermométrie luminescente ratiométriqueBiological thermal modifications are common events during abnormal cellular metabolic activities. Indeed, thermal aberrations – such as an increase in local tissue temperature – are directly related to the detection of inflamed areas, the presence of tumors, or other diseases. In addition to contributing to the diagnosis of diseases, the determination of local temperature in biological systems can also help with their treatment. For instance, in hyperthermia, the increase in temperature must be induced in tumor tissues up to cytotoxic levels in order to kill cancer cells and therefore, it assists in the cancer treatment. However, the increase in temperature must be carried out in a controlled and well-localized manner to target cancer cells, while avoiding overheating of surrounding healthy tissue. Furthermore, to determine such biological aberrations, temperature variations must be accurately determined. The thermometric performance of the nanothermometers was determined by calculating the relative thermal sensitivity (S_r) using the ratiometric luminescence intensity approach. Furthermore, our study made it possible to raise some hypotheses that can effectively contribute to the thermometric performance of thermal probes. We use the technique of the intensity ratio of two luminescence peaks for which the values of S_r can be optimized by co-doping the nanocrystals with two, or more, Ln3+ ions and by using oxide matrices presenting different phonon energies. Thus, due to its generic nature and synthesis flexibility, the Pechini method was chosen to synthesize several oxide matrices, Y2O3, Y2Ge2O7, Y3Al5O12 (YAG), Y3BO6 and YBO3. The nanocrystals were firstly monodoped with Nd3+ and posteriorly, codoped with Nd3+ -Yb3+ to improve the thermal probe properties within the biological windows of near infrared. In addition, we optimized the doping concentrations in the host matrices for greater efficiency in luminescence detection in biological organisms. We experimentally observed that Sr values are strongly impacted to the phonon energy of the matrix. We analyzed that by Nd3+ -Yb3+ codoping the thermometric performance of nanocrystals is improved compared to nanocrystals mono doped with Nd3+. Our study of different oxides shows that the YAG and Y2O3 matrices are the most promising matrices for the luminescence nanothermometry in vivo application. Lastly, YAG individual nanocrystals (non-agglomerated as in the case of Pechini syntheses) of size 60 nm and controlled morphology were obtained in solution by the solvothermal method to advance in further studies in biological applications. We observed that the YAG nanothermometers suitable for the purpose have a S_r equal to 0.47 %·K-1 and a thermal resolution of 0.3 K. In vivo experimental tests are required to validate the findings of this study; however, our results obtained on the performance of YAG: Nd3+ -Yb3+ nanocrystals has been showing high potential for in vivo applications of ratiometric luminescence nanothermometry
24
Kennedy, Jermaine L. "Investigations of fiber optic temperature sensors based on Yb:Y3Al5O12." [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001566.
25
Swift, Angela Marion. "The development of a cryogenic phonon detector, based on the coupling of superconducting tunnel junctions to indium antimonide crystals : with applications in X-, #gamma#- and #beta#-ray spectroscopy antimonide." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294274.
26
Timrov, Iurii. "Ab initio study of plasmons and electron-phonon coupling in bismuth: from free-carrier absorption towards a new method for electron energy-loss spectroscopy." Palaiseau, Ecole polytechnique, 2013. http://pastel.archives-ouvertes.fr/docs/00/82/37/58/PDF/thesis.pdf.
Abstract:
Ce travail a été consacré à l'étude théorique du bismuth semi-métallique à l'aide de méthodes basées sur la théorie de la fonctionnelle de la densité (DFT). Les effets de couplage spin-orbite et d'échange et de corrélation dans l'approximation de densité locale (LDA) et de gradient généralisé (GGA) ont été approfondis de façon systématique. J'ai trouvé que les poches d'électrons et de trous au niveau de Fermi sont correctement décrites, ce qui m'a permis d'interpréter avec succés les expériences pompe-sonde dans le bismuth photoexcité menées au laboratoire des Solides Irradiés. Le calcul du couplage électron-phonon a montré la forte dépendance, par rapport au vecteur d'onde électronique, du couplage de la bande de valence la plus haute avec le phonon A1g LO de centre de zone, ce qui explique l'observation de la forte dépendance en k de l'amplitude d'oscillation de l'énergie de liaison de cette même bande en photoémission résolue en temps. J'ai aussi montré que la présence d'extréma dans les bandes de valence et de conduction, où la masse des porteurs peut atteindre 18 m0, favorise une accumulation des porteurs et conduit à une augmentation de leur fréquence plasma au cours du temps aprés photoexcitation, un effet qui n'a pas (encore) été observé dans d'autres matériaux. Enfin, j'ai développé une nouvelle méthode en théorie de perturbation de la fonctionnelle de la densité dépendante du temps (TDDFPT), qui permet de calculer la réponse électronique du matériau pour n'importe quelle valeur du moment transféré. Cette approche basée sur la méthode de récursion de Lanczos m'a permis de calculer les spectres de perte d'énergie électronique de Bi dans la gamme d'énergie 0-100 eV et de combler l'intervalle d'énergie entre les pertes des électrons de valence et celles des électrons de cœur. Cette méthode ouvre des perspectives considérables, comme le calcul des plasmons de surfaceThis work has been devoted to the theoretical study of bulk semimetallic bismuth with methods based on the density functional theory (DFT). Effects of spin-orbit coupling and of the exchange-and-correlation functionals in the local density (LDA) and generalized gradient approximation (GGA) have been systematically investigated. I have found that electron and hole pockets at the Fermi level are accurately reproduced, which has enabled me to successfully interpret the pump-probe experiments in the photoexcited bismuth performed in the Laboratoire des Solides Irradiés. The strong dependence on the electronic wave vector, of the calculated electronic coupling of the upper valence band with the zone-center A1g LO phonon, explains the observation of a strongly k-dependent oscillation amplitude of the upper valence band in time-resolved photoemission experiments upon activation of the coherent A1g phonon under photoexcitation. I have also shown that the presence of local extrema in the conduction and valence bands structure, where the carrier mass can be as large as 18 m0, favours an accumulation of photoexcited carriers in these extrema and contributes to the augmentation of the plasma frequency as a function of time after the photoexcitation, an effect which has no analogy in other materials (as yet). Finally, I have developed a new ab initio approach in the time-dependent density functional perturbation theory (TDDFPT), which allows us to calculate the electronic response of materials for any momentum transfer. This approach based on the Lanczos recursion method has enabled me to calculate for the first time the electron energy-loss spectrum of Bi in the 0-100 eV energy range, bridging the gap between valence and core losses. This method opens the way to the routine calculation of surface plasmons
27
Wong, Basil T. "THERMAL HEAT TRANSPORT AT THE NANO-SCALE LEVEL AND ITS APPLICATION TO NANO-MACHINING." UKnowledge, 2006. http://uknowledge.uky.edu/gradschool_diss/387.
Abstract:
Nano-manufacturing is receiving significant attention in industry due to the ever-growing interest in nanotechnology in research institutions. It is hypothesized that single-step or direct-write nano-scale machining might be achieved by coupling nano-probe field emission with radiation transfer. A laser may be used to heat a workpiece within a microscopic region that encloses an even smaller nanoscopic region subjected to a focused electron beam. The electron-beam supplies marginal heat sufficient to remove a minute volume of material by evaporation or sublimation. Experimentally investigating this hypothesis requires an estimate of the power needed in the electron-beam. To this end, a detailed numerical study is conducted to study the possibility of using the nano-probe field emission for nano-machining. The modeling effort in this case is divided into two parts. The first part deals with the electron-beam propagation inside a target workpiece. The second part considers the temperature increase due to the energy transfer between the electron-beam and the workpiece itself. A Monte Carlo/Ray Tracing technique is used in modeling the electron-beam propagation. This approach is identical to that of a typical Monte Carlo simulation in radiative transfer, except that proper electron scattering properties are employed. The temperature distribution inside a gold film is predicted using the heat conduction equations. Details of the various numerical models employed in the simulation and a series of representative results will be presented in this dissertation.
28
Hardikar, Rahul Padmakar. "Investigation of order parameters and critical coupling for the Peierls Extended Hubbard Model at one-quarter filling." Master's thesis, Mississippi State : Mississippi State University, 2004. http://library.msstate.edu/etd/show.asp?etd=etd-11112004-120413.
29
Hague, James P. "Band to Mott transition in the infinite dimensional Holstein model." Thesis, University of Warwick, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369426.
30
Li, Yuting. "Simulations and Electronic Structure of Disordered Silicon and Carbon Materials." Ohio University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1395410498.
31
Mai, Thuc T. "Optical spectroscopy of cooperative phenomena and their symmetries in solids." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555629359625425.
32
Berthou, Simon. "Etude opto-électronique des mécanismes de relaxation des électrons de haute énergie dans les hétérostructures en graphène." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC133/document.
Abstract:
Dans cette thèse, nous étudions le couplage électron-phonon dans le graphène, et en particulier l’influence du substrat. Il s’agit de quantifier par des mesures opto-électroniques le couplage des électrons avec les modes de phonons du substrat, que ce soit les modes de phonons polaritons de surface (SPP) pour les substrats isotropes comme le SiO2 ou les modes de phonons polaritons hyperboliques pour les substrats fortement anisotropes comme le h-BN. Pour ce faire, nous commençons par une revue générale du couplage électron-phonon dans le graphène avant de détailler les différentes méthodes expérimentales utilisées durant la thèse. Puis, nous détaillons les différents régimes de couplage pour un échantillon de graphène sur SiO2 et nous mettons en évidence la nécessité d’étudier des substrats ultra-propres. Nous présentons enfin les résultats obtenus pour un échantillon de graphène sur h-BN dans lequel nous mettons en évidence, en plus du couplage aux HPP,un régime de couplage nouveau qui consiste en l’émission de phonons-polaritons hyperboliques dans un régime d’effet tunnel Zener-KleinIn this thesis we study the electron-phonon coupling in graphene and in particular theinfluence of the substrate in the aforementioned coupling. We want to quantify by optoelectronicalmeasurements the coupling between the phonon modes of the substrate. It might be the couplingwith Surface Phonon Polaritons (SPPs) in case of isotropic substrates as SiO2 or Hyperbolic PhononPolaritons (HPPs) in case of highly anisotropic substrates. We start by a review about the state of theart on electron phonon coupling in graphene. Then we introduce the different experimental methodsused during this thesis. We present experimental results on an graphene on SiO2 sample. We identifythe different coupling regimes and point out the necessity of working on ultra clean samples toinvestigate the high energy regimes. Finally we prensent experimental results on a graphene on BNsample where we identify a new coupling regime consisting in HPP emission in a Zener-Klein transportregime
33
Wang, Yichun. "LEAKAGE CURRENT REDUCTION OF MOS CAPACITOR INDUCED BY RAPID THERMAL PROCESSING." UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_theses/640.
Abstract:
With the MOSFET scaling practice, the performance of IC devices is improved tremendously as we experienced in the last decades. However, the small semiconductor devices also bring some drawbacks among which the high gate leakage current is becoming increasingly serious.
This thesis work is focused on the of gate leakage current reduction in thin oxide semiconductor devices. The method being studied is the Phonon Energy Coupling Enhancement (PECE) effect induced by Rapid Thermal Processing (RTP). The basic MOS capacitors are used to check improvements of leakage current reduction after appropriate RTP process.
Through sets of experiments, it is found that after RTP in Helium environment could bring about four orders reduction in gate leakage current of MOS capacitors.
34
Almutairi, Alanoud. "Electronic band structure equations and Fermi surface evolution from 2D materials to 3D layered superconducting compounds." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/134414/1/Alanoud%20Mulfi%20Z_Almutairi_Thesis.pdf.
Abstract:
A simple approach for extracting the superconducting gap of materials from trendline fittings of key sections of their Electronic Band Structures (EBS), calculated using Density Functional Theory (DFT), is presented. The proposed approach works well for very different compositions, structure types and superconducting transition temperatures, indicating that it is robust, reliable and versatile. This approach provides many advantages in terms of required computational time and power, compared with similar information extracted from phonon dispersion calculations, making it accessible to wider DFT-computational chemistry and physics communities. The approach also identifies requirements for superconductivity and indirectly contributes towards understanding of superconductivity mechanisms.
35
Light, Brandon W. "Energy-efficient photon mapping." Link to electronic thesis, 2007. http://www.wpi.edu/Pubs/ETD/Available/etd-051007-092224/.
Abstract:
Thesis (M.S.) -- Worcester Polytechnic Institute.Keywords: mobile devices; photon mapping; global illumination; ray tracing; energy; mobile; computer graphics. Includes bibliographical references (leaves 66-68).
36
Jamison, John S. "Time and Space Resolved Spin-Heat Transport in the Magnetic Insulator Yttrium Iron Garnet." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586740671277489.
37
Hamyeh, Sobhi. "Étude de transfert d’énergie par des excitations de surface." Thesis, Troyes, 2020. http://www.theses.fr/2020TROY0013.
Abstract:
La taille des composants électroniques a récemment été réduite à quelques dizaines de nanomètres. Cette diminution perpétuelle de la taille des composants électroniques modernes et l’augmentation de leurs vitesses et fréquences de fonctionnement conduisent inévitablement à des points chauds, qui sont des dangers entrainant une défaillance du système s’ils sont laissés longtemps. Le premier objectif de cette thèse est d’optimiser des techniques efficaces et pratiques pour évacuer la chaleur des nano-composants électronique. Le deuxième objectif de cette thèse est de présenter des moyens pour contrôler le flux énergétique, afin de répondre à ces besoins scientifiques et industriels. Nous étudions le transport par les phonon-polariton de surface (PhPS), qui sont des ondes électromagnétiques résultant du couplage entre un champ électrique dans le moyen infrarouge et des phonons optiques. Nous étudions également les mécanismes de transport par un gaz d’électrons bidimensionnel (2DEG) confiné dans un puits quantique formé à des hétéro-interfaces. Nous démontrons que l’excitation des modes PhPS dans des couches polaires de quelques nanomètres d’épaisseur déposées sur des semi-conducteurs classiques peut améliorer le flux énergétique d’une manière considérable, et par la suite dissiper la chaleur accumulée dans des nano-composants. Nous démontrons aussi que la contrainte dans la couche d'AlN a un effet très important sur les propriétés de transport du gaz d'électrons bidimensionnel confiné dans le puits quantique AlN/ GaNThe size of electronic components has recently been reduced to a few tens of nanometers. This perpetual decrease in the size of modern electronic components and the increase in their operating speeds and frequencies inevitably leads to hot spots, which are hazards leading to system failure if left for long periods of time. The first objective of this thesis is to optimize efficient and practical techniques for heat dissipation from electronic nano-components. The second objective of this thesis is to provide ways to control the energy flow in order to meet these scientific and industrial needs.We study the transport by surface phonon-polariton (PhPS), which are electromagnetic surface waves resulting from the coupling between an electric field in the mid-infrared and optical phonons in a polar material. We also study the transport mechanisms by a two-dimensional electron gas (2DEG) confined in a quantum well formed at hetero-interfaces. We demonstrate that the excitation of PhPS modes in polar layers a few nanometers thick deposited on conventional semiconductors can improve the energy flow considerably, and consequently dissipate the heat accumulated in nano-components. We also demonstrate that the stain field in the AlN layer plays a critical role in governing the transport properties of the two-dimensional electron gas confined in the AlN/ GaN quantum well
38
Hendry, D. "Jet production in photon-photon interactions." Thesis, University of Glasgow, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375434.
39
Walker, Ian W. "Exclusive charged pion production in photon-photon interactions." Thesis, Lancaster University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305949.
40
Kang, Ji-Hwan. "Energy transfer enhancement of photon upconversion systems for solar energy harvesting." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45846.
Abstract:
Photon energy upconversion (UC), a process that can convert two or more photons with low energy to a single photon of higher energy, has the potential for overcoming the thermodynamic efficiency limits of sunlight-powered devices and processes. An attractive route to lowering the incident power density for UC lies in harnessing energy transfer through triplet-triplet annihilation (TTA). To maximize energy migration in multicomponent TTA-assisted UC systems, triplet exciton diffusivity of the chromophores within an inert medium is of paramount importance, especially in a solid-state matrix for practical device integration.
In this thesis, low-threshold sensitized UC systems were fabricated and demonstrated by a photo-induced interfacial polymerization within a coaxial-flow microfluidic channel and in combination with nanostructured optical semiconductors. Dual-phase structured uniform UC capsules allow for the highly efficient bimolecular interactions required for TTA-based upconversion, as well as mechanical strength for integrity and stability. Through controlled interfacial photopolymerization, diffusive energy transfer-driven photoluminescence in a bi-molecular UC system was explored with concomitant tuning of the capsule properties. We believe that this core-shell structure has significance not only for enabling promising applications in photovoltaic devices and photochromic displays, but also for providing a useful platform for photocatalytic and photosensor units.
Furthermore, for improving photon upconverted emission, a photonic crystal was integrated as an optical structure consisting of monodisperse inorganic colloidal nanoparticles and polymer resin. The constructively enhanced reflected light allows for the reuse of solar photons over a broad spectrum, resulting in an increase in the power conversion efficiency of a dye-sensitized solar cell as much as 15-20 %.
41
AYADI, MOHAMED. "Contribution a l'etude de la dynamique de reseau de quelques composes de la serie de la mathlockite (pbfcl)." Université Louis Pasteur (Strasbourg) (1971-2008), 1986. http://www.theses.fr/1986STR13183.
Abstract:
Etude de l'energie de cohesion de composes a structure de mathlockite; conditions de stabilite, expressions de la polarisation ionique, des constantes d'elasticite et des constantes dielectriques (modele de la coquille, presence de sites non centrosymetriques). Condition de synthese et de croissance cistalline de cahcl, bafcl, pbfcl et biocl; spectres raman et ir. Analyse des spectres de reflexion ir de bafcl (kramers-kronig et oscillateur classique). Determination de la densite d'etats et de la dispersion de phonons pour bafcl; calcul de certaines constantes d'elasticite
42
Selig, Marco. "Information theory based high energy photon imaging." Diss., Ludwig-Maximilians-Universität München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:19-178899.
43
Bertrand, Martine 1976. "Photon production in high energy heavy ion collisions." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=31196.
Abstract:
The production of photons in the energy range of 0 to 3 GeV is discussed as a signature of the creation of a quark-gluon plasma in ultrarelativistic nuclear collisions. However, they are also created in the hadronic phase. Therefore I investigate the role of the pirho → pigamma and pio → pigamma reactions in the photon emission from hot hadronic matter, and I compare their respective importance. These reactions are known to be the leading contributions. For this purpose I use diverse effective chiral Lagrangians that are in accord with known empirical properties of strong interaction. Then I discuss the relevance of my work to heavy ion collisions.
44
Muncey, Roderick John. "Polymers for photon-harvesting and solar energy conversion." Thesis, University of Sheffield, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434542.
45
Micklewright, Benjamin. "Gravitational radiation and photon rockets." Thesis, University of York, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245960.
46
Lindenberg, Kai. "Development and construction of the low-energy photon tagger NEPTUN." München Verl. Dr. Hut, 2007. http://d-nb.info/987775855/04.
47
Cornish, Carrie Sjaarda. "Highly efficient photon echo generation and a study of the energy source of photon echoes /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/6031.
48
Heaphy, Eileen Anne. "Jet photoproduction and photon structure." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252008.
49
Jerjen, Iwan. "Superconducting tunnel junctions as energy resolving single photon detectors /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17113.
50
Johnson, Erik D. Ph D. Massachusetts Institute of Technology. "High-energy photon transport modeling for oil-well logging." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53266.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 121-122).
Nuclear oil well logging tools utilizing radioisotope sources of photons are used ubiquitously in oilfields throughout the world. Because of safety and security concerns, there is renewed interest in shifting to electronically-switchable accelerator sources. Investigation of accelerator sources opens up the opportunity to study higher-energy sources. In this thesis, sources with a 10 MeV endpoint are examined, a several-fold increase over traditional techniques. The properties of high-energy photon transport are investigated for potential new or improved well logging measurements. Two obvious processes available with a high-energy photon source are pair production and photo neutron emission. A new measurement of formation density is proposed based on the annihilation radiation produced after the pair production of high-energy source photons in the rock formation. With a detector spacing of 55 cm, this measurement exhibits a sensitivity to density with a dynamic range of 10 across a typical range of formation density (2.0 - 3.0 g/cc), the same as traditional measurements. Increases in depth of investigation for these measurements can substantially improve the sampling of the formation and thus the quality and relevance of the measurement. Being distributed in angle and space throughout the formation, a measurement based on anni-hilation photons exhibits a greater depth of investigation than traditional methods. For a detector spacing of 39 cm (equivalent to a typical spacing for one detector in traditional approaches), this measurement has a depth of investigation of 8.0 cm while the traditional measurement has a depth of investigation of 3.6 cm.
(cont.) For the 55 cm spacing, this depth is increased to 9.4 cm. Concerns remain for how to implement an accelerator source in which energy spectroscopy, essential for identifying an annihilation peak, is possible. Because pair production also depends on formation lithology, the effects of chemical composition on annihilation photon flux are small (<20 %) for the studied geometry. Additionally, lithology measurements based on attenuation at high energies show too small an effect to be likely to produce a useful measurement. Photoneutron production cross sections at this energy are too small to obtain a measurement based on this process.
by Eric D. Johnson.
Ph.D.