Auswahl der wissenschaftlichen Literatur zum Thema „Énergie des phonons“
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Zeitschriftenartikel zum Thema "Énergie des phonons"
Houver, Sarah, Sophie Eliet Barois, Pascale Roy und Romain Peretti. „La spectroscopie térahertz: électrons et vibrations“. Photoniques, Nr. 121 (2023): 36–41. http://dx.doi.org/10.1051/photon/202312136.
Der volle Inhalt der QuelleDissertationen zum Thema "Énergie des phonons"
Henriel-Ricordel, Catherine. „Nouveaux verres de fluorures et de fluorochlorures à basse énergie de phonons pour l'amplification optique à 1,3 micromètre“. Rennes 1, 1996. http://www.theses.fr/1996REN10122.
Der volle Inhalt der QuelleBerthou, 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.
Der volle Inhalt der QuelleIn 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
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.
Der volle Inhalt der QuelleBiological 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
Almeida, Silva Ribeiro Guilherme. „Strong anharmonicity in the phonon spectra of PbTe and SnTe evaluated via the stochastic self-consistent harmonic approximation“. Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066737.
Der volle Inhalt der QuelleAt room temperature, PbTe and SnTe are efficient thermoelectrics with a cubic structure. At low temperature, snte undergoes a ferroelectric transition with a critical temperature strongly dependent on the hole concentration, while PbTe is an incipient ferroelectric. In this thesis by using the stochastic self-consistent harmonic approximation, we investigate the anharmonic phonon spectra and the occurrence of a ferroelectric transition in both systems. We find that vibrational spectra strongly depends on the approximation used for the exchange-correlation kernel in density functional theory. If gradient corrections and the theoretical volume are employed, then the calculation of the free energy hessian leads to phonon spectra in good agreement with experimental data for both systems. In PbTe, we reproduce the transverse optical mode phonon satellite detected in inelastic neutron scattering and the crossing between the transverse optical and the longitudinal acoustic modes along the gamma-x direction. In the case of SnTe, we describe the occurrence of a ferroelectric transition from the high temperature fm3m Structure to the low temperature r3m one
Marronnier, Arthur. „Anharmonicity and Instabilities in Halide Perovskites for Last Generation Solar Cells“. Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX031/document.
Der volle Inhalt der QuelleHybrid halide perovskites (ABX3) have emerged over the past five years as absorber layers for novel high-efficiency low-cost solar cells combining the advantages of organic (molecule A) and inorganic (metal B, halogen X) materials. Very recently, fully inorganic perovskite quantum dots also shown promising efficiencies, making them a potentially stable and efficient alternative to their hybrid cousins.The aim of this PhD thesis is to study and better understand both the structural and thermodynamic instabilities of these halide perovskites, with a specific focus on purely inorganic CsPbI3 structures.We first use various ab-initio techniques, the majority of which are based on Density Functional Theory (DFT) and its linear-response approach (DFPT), to investigate the vibrational and electronic properties of the different phases of CsPbI3. While the black γ-phase, crucial for photovoltaic applications, is shown to behave harmonically around equilibrium, for the other three phases frozen phonon calculations reveal a Brillouin zone center double-well instability. We also show that avoiding the order-disorder entropy term arising from these double-well instabilities is key in order to prevent the formation of the yellow perovskitoid phase, and evidence a Rashba effect when using the symmetry breaking structures obtained through frozen phonon calculations. We then analyze the structural changes and the dynamical Rashba splitting along molecular dynamics trajectories in the light of our findings.In a second phase, we investigate the thermodynamical stability of hybrid perovskite MAPbI3. Our experimental ellipsometry-based study brings better understanding of the chemical decomposition of MAPbI3 into its two precursors, methylammonium and lead iodides, which we predicted using DFT stability diagram calculations and which we confirm by X-Ray diffraction. Last, we prove that hybrid perovskite structure MAPbI3 behaves more like inorganic compounds (high dielectric constant, low exciton binding energy) than like organic materials (low dielectric constant, high exciton binding energy)
Bah, Thierno Moussa. „Développement et caractérisation d’un démonstrateur de générateur thermoélectrique à base de membranes de silicium couplées à de l’ingénierie phononique“. Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1I036/document.
Der volle Inhalt der QuelleThe lack of reliable, safe and low-cost energy source seems to delay the blooming of the internet of things (IoT) and wireless sensors nodes. Thermoelectric harvesters feature those key advantages. Silicon presents the advantages to be most abundant, less environmental harmful and to benefit from facilities and technological processes for low cost thermoelectric harvesters mass production compared to the conventional materials (bismuth telluride alloys). However, silicon is a poor thermoelectric material due to its high thermal conductivity ( ). The possibility to reduce the thermal conductivity while preserving electrical conductivity and Seebeck coefficient is the key to upgrade silicon as an efficient thermoelectric material. To that end, efforts are oriented towards the phononic part of heat transport, which is the dominant contribution in semiconductors. The researches carried out during this thesis dealt with the integration of phonon engineered silicon membranes into thermoelectric harvester demonstrators and their characterizations with respect to the state of the art. The results demonstrated the feasibility of a silicon based thermoelectric harvester exhibiting performance (from few µW/cm2 for ΔT~5-10K to few mW/cm2 for ΔT>100K) sufficient for autonomous sensor nodes’ power supplying and comparable performance with the bismuth telluride state of the art harvester according to the harvesters’ cooling conditions. Moreover, this thesis demonstrated, in addition to the energy harvesting, the possibility of developing silicon based thermoelectric coolers, opening the way to possible integration of thermoelectric coolers in silicon based micro-electronic devices
Rault, Gabriel. „Verres à basse énergie de phonon pour l'amplification optique large bande“. Rennes 1, 2001. http://www.theses.fr/2001REN10056.
Der volle Inhalt der QuelleLafond, Fabien. „Hybrid functionals approach for the study of the properties of complex materials for photovoltaic applications“. Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0308.
Der volle Inhalt der QuelleElectrical properties of semiconductors are strongly influenced by the types of dopants and defects inserted or formed during the synthesis of materials. In the field of photovoltaics, these defects leads to various metastabilities and can degrade the efficiency and durability of solar cells. In this context, ab-initio simulation methods, such as Hartree-Fock (HF) or the one implemented in the framework of density functional theory (DFT), are relevant to understand these behaviours and thus optimise the photovoltaic materials. However, a good qualitative and quantitative description of properties requires sophisticated but time consuming method like GW. An interesting alternative can be provided by hybrid functionals, which combine HF and DFT. Firstly, hybrid functionals were optimised in order to accurately described the band gap for different compounds by varying the percentage of HF exact-exchange in the exchange term of the PBE and PBEsol functionals from the GGA approximation of DFT. The materials investigated were Si, Ge, SiGe, III-V and chalcopyrites. Results obtained by this approach were confronted to the one from the literature. The description of the electronic properties matched the one from GW. Temperature evolution of various thermodynamic properties was calculated via the quasi-harmonic approximation. In this approximation and for the range of studied materials, optimised hybrid functionals do not bring an enhancement compared to existing functionals. Nevertheless, they bring a coherent description of the materials. Secondly, these optimised hybrid functionals were used to systematically describe the impact of chemical composition on chalcopyrite’s properties for tandem solar cells. First, they enable the determination the compositions, structural and electrical properties of CuGaxIn1-x(SySe1-y)2 for band gap specific to this kind of application. As alkali metals leads to major enhancement of chalcopyrite efficiency, the effect of their incorporation in chalcopyrite bulk was address. Highlight was put on the substitution of copper by Li, Na, K, Rb and Cs. Their impact on the band gap was interpreted via the structural evolution and the thermodynamique stability of the different crystallines phases that can exists within the material. Finally, H, Fe and B point defects in silicon were simulated for a preliminary study on the light and elevated temperature induced degradation which is one of the ageing process of the silicon solar cells
Shpotyuk, Yaroslav. „Verres de chalcogénures : étude de leurs comportements métastables et développement de compositions à basses énergies de phonons“. Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S140/document.
Der volle Inhalt der QuelleChalcogenide glasses are developed because of their properties of transparency in the infrared. For example it is possible to manufacture optical fiber or planar wavguide for sensing in the mid-infrared. The purpose of this thesis is to study the metastable behavior of chalcogenide glasses when subjected to specific constraints: thermal behavior, γ ray irradiation, addition of destabilizing elements. Compositions doped with rare-earth have also been also studied in order to develop sources operating in the mid-infrared range
Duquesne, Jean-Yves. „Anélasticité des solides amorphes tétracoordonnés et polymériques : étude des excitations (tunnel et activées) de faibles énergies“. Paris 11, 1985. http://www.theses.fr/1985PA112098.
Der volle Inhalt der QuelleWe study the elastic and anelastic properties of amorphous germanium (tetra coordinated solid), or amorphous selenium (polymeric solid) and of selenium-germanium glasses. We use an ultrasonic wave propagation method at high frequency and a resonant method at low frequency. The investigated temperature and frequency ranges are typically: 0. 1 < T < 300 K; 10⁴ < F < 10⁸ Hz. We study then on one hand the existence of tunneling defects in tetra coordinated amorphous solids and, on the other hand, below the glass transition, the characteristics of the internal friction peak of the simplest existing polymer (selenium)(this peak is located well below the glass transition temperature). Selenium-Germanium glasses provide a way to follow the properties as the amorphous structure changes from a polymeric network to a tetra coordinated network