A utilização de aditivos incorporadores de ar em concretos é uma prática comum na construção civil e sua aplicação influencia significativamente diversas propriedades do concreto no estado fresco e endurecido. O objetivo deste estudo foi avaliar a influência do teor de ar incorporado, por meio de aditivo, no desempenho de concretos com diferentes teores de agregados. O programa experimental incluiu avaliação da eficiência de aditivos na incorporação de ar em pastas de cimento, análise microestrutural e ensaios para determinação de propriedades físicas, mecânicas e de durabilidade de concretos com diferentes teores de ar e agregados. No estado fresco, foram realizados ensaios para determinação do teor de ar, massa específica e abatimento. No estado endurecido foram realizados ensaios de massa específica, absorção, resistência à compressão, módulo de elasticidade, velocidade de propagação da onda ultrassônica, carbonatação acelerada e condutividade térmica. Utilizando Microtomografia Computadorizada de Raios-X (Micro-CT) foram dimensionados e quantificados os poros presentes nas amostras dos concretos, bem como determinadas suas porosidades. Os concretos com ar incorporado apresentaram redução na resistência mecânica. Os concretos com menores teores de agregados apresentaram menor resistência mecânica, menor velocidade da frente de carbonatação e menor condutividade térmica. De acordo com os resultados obtidos, pode-se concluir que o aditivo a base de resinas sintéticas foi mais eficiente na incorporação de ar; maiores teores de ar implicam em variabilidade nos resultados de ensaios de resistência à compressão e módulo de elasticidade; os concretos com maiores teores de agregados apresentaram maior velocidade da frente de carbonatação, para mesmos teores de ar incorporado; a condutividade térmica é inversamente proporcional ao teor de ar incorporado no concreto, e quanto menor o teor de agregados, menor a condutividade térmica; o aumento do teor de ar no concreto promove aumento no diâmetro equivalente dos poros e redução da incidência de poros esféricos. / The use of entraining air additives in concrete is a common practice in construction and its application influences several concrete properties in the fresh and hardened state. The aim of this study was evaluate the influence of air entrained content, by additive, in concrete performance with different aggregate contents. The experimental program included the evaluation of additives effectiveness of air entrainment in cement pastes, microstructural analysis and the concretes physical and mechanical properties and durability, with different levels of entrained air and aggregates. Tests were performed in fresh to determine the air content, density and slump. In hardened concrete, density, absorption, compressive strength, elastic modulus, ultrasonic pulse velocity, accelerated carbonation and thermal conductivity tests were performed. By computed X-ray microtomography, the pores present in the concrete samples were sized and quantified and determined the concretes porosities. The air entrained concrete presented decrease in mechanical strength. Concretes with lower aggregate levels presented lower mechanical strength, carbonation speed and thermal conductivity. According to the results, it can be concluded that the synthetic resins base additive was more efficient in air entrainment; larger air content implies variability in the results of the compressive strength and elastic modulus tests; concrete with higher aggregate levels presented higher carbonation speed, for the same entrained air content; thermal conductivity is inversely proportional to the air entrained content in concrete, and as lower was the aggregate content, lower was the thermal conductivity; the increase of air content in concrete promotes increase in the pores diameter and reduction of the incidence of spherical pores.

Les matériaux nanostructurés suscitent un intérêt qui va croissant en raison de leurs propriétés chimiques et physiquesexceptionnelles. A cause de la complexité et du coût des développements expérimentaux à l’échelle nano, la simulationnumérique devient une alternative de plus en plus populaire aux études expérimentales. Dans ce travail de thèse, nous avons essayé de combiner des simulations à l’échelle atomique avec de la modélisation en milieu continu pour évaluer la conductivité thermique et la réponse élastique de matériaux nanostructurés. Nous avons utilisé des simulations de dynamique moléculaire pour calculer la réponse mécanique et thermique des matériaux sur des volumes à l’échelle nano. Des méthodes de micromécanique et la méthode des éléments finis, qui utilisent la mécanique des milieux continus, ont permis d’évaluer les propriétés mécaniques des matériaux à l'échelle macroscopique. Les résultats obtenus par ces simulations numériques ont été ensuite comparés avec ceux issus de l’expérience. / Nanostructured materials are gaining an ongoing demand because of their exceptional chemical and physical properties. Due to complexities and costs of experimental studies at nanoscale, computer simulations are getting more attractive asexperimental alternatives. In this PhD work, we tried to use combination of atomistic simulations and continuum modeling for the evaluation of thermal conductivity and elastic stiffness of nanostructured materials. We used molecular dynamics simulations to probe and investigate the thermal and mechanical response of materials at nanoscale. The finite element and micromechanics methods that are on the basis of continuum mechanics theories were used to evaluate the bulk properties of materials. The predicted properties are then compared with existing experimental results.

O presente trabalho, realizado junto ao Grupo de Novos Materiais e Dispositivos (GNMD), no Laboratório de Microeletrônica do Departamento de Sistemas Eletrônicos da Escola Politécnica da USP, visou determinar algumas das propriedades termo-mecânicas de materiais depositados pela técnica de plasma enhanced chemical vapor deposition (PECVD) que são importantes para o desenvolvimento de sistemas microeletromecânicos (MEMS). O módulo de elasticidade, a tensão mecânica residual, o coeficiente de expansão térmica e a condutividade térmica de filmes finos de carbeto de silício amorfo hidrogenado (a-SiC:H) e de oxinitreto de silício (SiOxNy) foram estudados. Medidas de nanoindentação e ressonância de cantilevers foram utilizadas para a obtenção do módulo de elasticidade e os resultados obtidos foram similares (75 e 91 GPa) pelos dois métodos e compatíveis com valores encontrados na literatura. Além disso, obteve-se o módulo de elasticidade de filmes de cromo (285 GPa). A tensão mecânica residual dos filmes utilizados neste trabalho foi medida através da curvatura do substrato induzida pela deposição dos filmes e pela deformação de cantilevers. O valor médio da tensão mecânica, obtido pela curvatura do substrato, variou de -69 MPa até -1750 MPa, mostrando grande dependência das condições de deposição dos filmes. O método que utiliza a deformação de cantilevers possibilitou a obtenção do gradiente de tensão mecânica, que também mostrou uma dependência das condições de deposição, sendo sempre o a-SiC:H quase estequiométrico o menos tensionado. O coeficiente de expansão térmica foi medido utilizando a técnica do gradiente de temperatura e o valor obtido foi similar a valores reportados na literatura para o carbeto de silício cristalino. Para um a-SiC:H quase estequiométrico foi obtido um coeficiente de expansão térmica de 3,41 m/oC, enquanto para um a-SiC:H rico em carbono o valor foi de 4,36 m/oC. Também foi verificado que a variação da resistência do cromo em função da temperatura é pequena, não permitindo sua utilização como sensor de temperatura e inviabilizando a obtenção da condutividade térmica dos filmes estudados. Além disso, foram apresentados trabalhos promissores, mostrando o potencial dos materiais estudados para o desenvolvimento de MEMS. Nesses trabalhos, demonstrou-se a viabilidade de integrar microestruturas atuadas termicamente e guias de onda ópticos, utilizando os materiais estudados neste trabalho. Foram fabricados chaves ópticas, portas lógicas ópticas, fontes de luz integradas e acoplamento das fontes de luz com guias de onda. / This work, realized at the New Materials and Devices Group (GNMD) at the Microelectronics Laboratory of the Department of Electronic Systems of the Polytechnic School of the University of São Paulo, focused at the determination of thermo-mechanical properties of materials deposited by plasma enhanced chemical vapor deposition (PECVD) that are important for the development of microelectromechanical systems (MEMS). The Youngs modulus, the residual stress, the coefficient of thermal expansion and the thermal conductivity of amorphous hydrogenated silicon carbide (a-SiC:H) and silicon oxynitride (SiOxNy) thin films were studied. Nanoindentation and the resonance of cantilevers were used to obtain the Youngs modulus. The results were similar (75 and 91 GPa) with both methods and compatible with literature values. Further, the Youngs modulus of chromium films was also obtained (285 GPa). The residual stress of thin films was obtained through the substrate curvature induced by the film deposition and through the deformation of cantilever beams. The residual stress, obtained through the substrate curvature, varied between -69 MPa and -1750 MPa, showing great dependence on the deposition conditions of these materials. The deformation of cantilevers allowed the determination of the stress gradient and it was also affected by the deposition conditions. In all stress measurements the near stoichiometry a-SiC:H film was less stressed. The coefficient of thermal expansion was measured using the temperature gradient technique and the obtain values were similar to those reported in the literature for crystalline silicon carbide. For a near stoichiometry a-SiC:H film, a value of 3.41 m/oC was obtained, while a carbon rich film showed a thermal expansion coefficient of 4.36 m/oC. It was also verified that the variation of the chromium resistance as a function of temperature is small. This did not allow the utilization of chromium as a temperature sensor, which prevented the obtention of the thermal conductivity of the studied films. Also, some promising works were presented, showing potential applications of the studied materials for the development of MEMS. In these works, the viability of integration of thermal actuated microstructures and optical waveguides was demonstrated. In these works, optical switches, optical logic gates, integrated light sources and coupling of integrated light sources with optical waveguides were presented.

Le transport thermique dû à des excitations magnétiques dans les composés 1D contenant des chaines et échelles de spins fait actuellement l’objet d’une collaboration fructueuse entre chimistes et physiciens du solide. Le composé à chaines de spins Sr₂CuO₃, qui est un excellent exemple de chaine de type Heisenberg antiferromagnétique de spins S = ½, présente une conductivité thermique anisotrope due à des excitations magnétiques le long des chaines, appelées spinons. Afin de comprendre les mécanismes de diffusion responsables de la conduction thermique magnétique observée, nous avons introduit du désordre dans les chaines en effectuant des substitutions chimiques sur les ions qui composent celles-ci. En appliquant la méthode de croissance dite de “zone solvante” (traveling solvent floating zone method) nous avons élaboré des monocristaux de grande pureté de Sr₂CuO₃ substitués, d’une part par des ions Ca²⁺ (S = 0) qui viennent remplacer des ions Sr²⁺ (S = 0) e, situés en dehors des chaines, créant ainsi un désordre dans les liaisons ; et d’ autre part, des cristaux du même composé, substitué par des ions nickel Ni²⁺ (S = 1) qui prennent cette fois la place des ions Cu²⁺ (S = ½) dans les chaines, introduisant du désordre dans la distribution des sites. Après caractérisation des cristaux par les techniques traditionnelles de diffraction X et chimiques, nous avons fait une étude systématique de leurs propriétés magnétiques et thermiques. Des mesures Raman, de susceptibilité magnétique et de chaleur spécifique ont confirmé l’existence du désordre attendu, et ont suggéré que la substitution par le nickel amenait une rupture des chaines alors que celle par le calcium introduisait des défauts dans les chaines. Par ailleurs, à l’aide de mesures de RMN du ⁶³Cu, nous avons pu observer l’ouverture d’un gap de spins dans le spectre d’excitation des spinons, lié au désordre crée. L’analyse des courbes de conductivité thermique semble indiquer la présence d’une forte interaction spinon-phonon qui limite la conduction thermique à basse température. On notera, en particulier, que pour de forts taux de substitution en calcium, la conductivité thermique croit avec la température, mettant ainsi en évidence l’origine magnétique, associée aux spinons, de la conduction thermique. / Heat transport due to magnetic excitations in strongly correlated electronic materials containing low dimensional spin structures such as chains and ladders is an emerging field of research due to a fruitful collaboration between condensed matter physicists and solid state chemists. The spin chain compound Sr₂CuO₃, which is known to be the best realization of the S = ½ Heisenberg antiferromagnetic model, exhibits anisotropic thermal conductivity due to magnetic excitations, called spinons, of the spin chains. In order to understand its magnetic thermal conduction and the nature of scattering mechanisms involved, we have induced disorder into the chain structure by carrying out chemical substitution. Employing the sophisticated traveling solvent floating zone method we have grown high purity single crystals of Ca-substituted Sr₂CuO₃, in which Ca²⁺ (S = 0) ions substitute Sr²⁺ (S = 0) ions situated off the spin chains in the lattice creating a bond disorder, and Ni-substituted Sr₂CuO₃ in which Ni²⁺ (S = 1) ions substitute Cu²⁺ (S = ½) ions in the spin chains creating a site disorder. After characterizing the crystals using standard techniques, we have performed a systematic study of their magnetic and thermal properties. Raman spectra, magnetic susceptibility and specific heat measurements performed on these crystals confirmed the introduction of the anticipated disorder, suggesting that the substituted Ni atoms lead to breaking of the spin chains, and the Ca atoms act as effective in-chain defects. We observed the phenomenon of opening of a spingap in the otherwise gapless spinon excitation spectrum due to the induced disorder using ⁶³Cu NMR measurements. Our analysis of the thermal conductivity measurements points towards the presence of a strong spinon-phonon scattering that limits heat conduction at low temperatures. Remarkably, substituting high concentrations of Ca, we observed that thermal conductivity increases linearly with temperature, revealing the intrinsic magnetic thermal conduction due to spinons.

Les propriétés électro-thermo-mécaniques remarquables qui peuvent apparaître dans les nanofils de silicium font l'objet d'un nombre croissant de travaux de recherche. Ces travaux de thèse de nature fortement expérimentale, visent à donner une meilleure connaissance de ces propriétés dans le cas de nanofils, en silicium monocristallin, fabriqués par approche descendante. Pour caractériser la piézorésistivité, deux méthodes de chargement mécaniques ont été développées : la flexion 4 points de puce et la traction/compression in situ avec un actionneur MEMS. La méthode 3ω a été choisie pour des mesures de conductivité thermiques. Ces propriétés ont été étudiées en fonction de la température et la contrainte dans une station sous pointes cryogénique.Les résultats montrent que les nanofils fabriqués à partir de substrats SOI amincis peuvent, de manière inattendue, être fortement contraints en compression après fabrication. Les nanofils de type p présentent, même en régime de mesure dynamique, des coefficients piézorésistifs élevés qui décroissent fortement avec la température et permettent une détection intégrée de mouvement de MEMS avec une limite de détection inférieure à l'Angström. Les mesures thermiques confirment l’effet d’échelle attendu de la conductivité thermique, la décroissance avec la température est compatible avec les résultats théoriques et expérimentaux précédemment publiés. / Remarkable nanoscale electro-thermo-mechanical properties of silicon nanowires are increasingly studies. This experimental thesis investigates such properties for top-down fabricated monocrystal silicon nanowires.A four points bending set-up and a MEMS actuator are developed to apply ex situ and in situ mechanical stress on nanowires. Those devices are characterised in a cryogenic environment within a microprobe station. Electrical properties and piezoresistivity are studied using those systems. Moreover, the 3ω method measures the thermal conductivity of these nanowires.From buckling of silicon nanowires, unexpected high compressive stress (>100 MPa) was identified in top silicon layers of SOI substrates. Drift-compensated measurements show that p type silicon nanowires present large piezoresistive coefficients which decrease with temperature. Additionally, the MEMS device demonstrates the possibility to detect ample MEMS movements with sub-ångström resolution using the nanowires as piezoresistive nanogauges. The thermal conductivity was found consistent with previously reported values for silicon nanowires, and expectedly decreases with temperature.

Orientadores: Edson Correa da Silva e Antonio Manoel Mansanares / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin. / Made available in DSpace on 2018-09-26T17:40:21Z (GMT). No. of bitstreams: 1 Albuquerque_MarcosLazarodeSouza_D.pdf: 2664850 bytes, checksum: 47305c651cc9350b772372c3f4181f3e (MD5) Previous issue date: 2008 / Resumo: Neste trabalho desenvolveu-se um experimento de detecção fototémica com dois sensores piroelétricos em uma célula capacitiva que permite a realização de medidas térmicas e elétricas em materiais pastosos em função da temperatura.A célula idealizada para medidas elétricas e térmicas é um capacitor plano de placas paralelas capaz de obter das amostras investigadas os parâmetros de efusividade térmica, difusividade térmica,condutividade térmica e constante dielétrica relativa,simultaneamente,além de detectar transições,em especial fusão.A célula capacitiva fotopiroelétrica é composta por dois sensores piroelétricos entre os quais a amostra é posicionada.Um elemento Peltier associado a um termistor é utilizado para o controle de temperatura.Incide sobre a célula um feixe de radiação eletromagnética oriunda de uma fonte Laser Ar + (514,5 nm ).A radiação modulada atinge diretamente um dos sensores que é opaco e que está em contato térmico com a amostra.O calor gerado no primeiro sensor se propaga, então,pelo sistema amostra-segundo sensor gerando sinais nos dois sensores que são amplificados em amplitude e fase por dois amplificadores seletivos.Ao mesmo tempo,os sinais elétricos da célula capacitiva são registrados por uma ponte RCL operando em 2 kHz.A aquisição de dados dos sinais térmicos é procedida em programa escrito em ambiente LabView para varredura de freqüência de 0 a 100 Hz.Preliminarmente,medidas foram realizadas com margarina e mostraram o potencial da metodologia na verificação do comportamento térmico e elétrico de materiais pastosos.Foi investigado um conjunto de oito amostras constituídas por pares de componentes em proporções e métodos de sínteses diferentes de três tipos de óleos vegetais:algodão,palma e soja.Para a obtenção da constante dielétrica relativa da amostra,o valor da capacitância da mesma foi normalizado pelo valor de capacitância da célula vazia (dielétrico o ar).Modelos para a interpretação dos dados experimentais das medidas térmicas e elétricas foram desenvolvidos.Os gráficos dos sinais de amplitude e fase térmicas detectados pelos sensores foram plotados em função da freqüência de modulação e ajustados pelas equações teóricas dos sensores para a obtenção dos parâmetros térmicos.Foram obtidos valores dos parâmetros efusividade térmica, difusividade térmica,condutividade térmica e constante dielétrica relativa das oito amostras investigadas, além da identificação da região do ponto de fusão das mesmas.Os resultados mostraram que a célula desenvolvida neste trabalho para a aplicação em materiais pastosos pode identificar a região do ponto de fusão,obter os parâmetros térmicos e a constante dielétrica relativa das amostras investigadas / Abstract: This work consists in the development of an experimental apparatus of photopyroelectric detection using two pyroelectric sensors in a capacitive cell which allows the accomplishment of electrical and thermal measurements of pasty materials as a function of the temperature.The idealized cell for electrical and thermal measurements is based in a parallel plane-plate capacitor whose metallic plates are the internal surfaces of the pyroelectric sensors.The system is capable to obtain thermal parameters like effusivity, diffusivity and conductivity,and electric parameters like the dielectric constant for the investigated samples.The identification of the melt point region from either the thermal measurements of the photopyroelectric signal amplitude and phase or the electrical measurements is possible as well.The capacitive photopyroelectric cell is composed by two pyroelectric sensors.An insulator support is used to accommodate the samples which are placed between the sensors.An aluminum piece hold all parts of the cell;one Peltier element is associated with a termistor to control the temperature.An eletromagnetic radiation beam from a Ar + laser incides on the cell and is modulated by an acoustic-optic modulator.The modulated radiation reaches one of the sensors which is opaque and in contact with the sample.Two L ck-in amplifiers amplify the signals originated in each sensor due to the propagation of heat while the electrical signals are registered by an automatic RCL bridge operating at 2 kHz.For data acquisition a Labview language computer software was used allowing to frequency scanning from 0 to 100 Hz. Preliminary experiments were carried out with margarine and showed the methodology pontential in the verification of the thermal and electrical behavior of pasty materials.It was investigated a set of eight samples formed by different compositions of three vegetable oils:cotton,palm and soy in different proportions and within two synthesis methods (basic mixture of intersterification).The sample capacitance was normalized by the empty cell to obtain the relative dielectric constant of the sample.The models for the thermal and electrical data interpretation were developed.For the thermal case simulations were proceeded for a basic oil in order to verify the model.The graphs for thermal amplitude and phase from both sensors were plotted as a function of modulation frequency from which the thermal properties were obtained by fitting the model equations.The values of thermal effusivity,thermal diffusivity, thermal conductivity and relative dielectric constant were obtained for the samples and the transition melting region as well.The results have shown that the cell here developed is very suitable for the determination of thermal and electrical properties of pasty samples and the determination of transition as well. / Doutorado / Física Geral / Doutor em Ciências

Este trabalho apresenta o estudo, a implementação e a caracterização de transdutores compostos por uma estrutura formada por grades de Bragg (FBG, Fiber Bragg Gratings) e grades de período longo (LPG, Long Period Gratings) em fibra óptica com cobertura metálica autoaquecida para medição da condutividade térmica e da difusividade térmica de materiais baseado no método do fio quente (HWM, Hot-Wire Method) convencional. O autoaquecimento da fibra óptica do dispositivo desenvolvido neste trabalho é provocado pela luz de espectro infravermelho injetada por um laser de bombeamento, que é espalhada por uma LPG e absorvida por um filme fino metálico depositado na superfície da fibra. Os transdutores apresentados são compactos, simples, robustos e imunes a interferências eletromagnéticas. O arranjo experimental utilizando o dispositivo híbrido LPG-FBG foi capaz de medir as condutividades térmicas do ar atmosférico e da água comum com precisões de 27% e 14%, respectivamente. Foram identificados vários fatores que afetam a precisão e a exatidão das medidas realizadas, sendo propostas diversas formas de correções de modo a melhorar o desempenho do arranjo. Foi demonstrada com sucesso a viabilidade da aplicação original do arranjo experimental utilizando o dispositivo híbrido LPG-FBG em fibra óptica autoaquecida para a medição de propriedades térmicas de fluidos (ar e água). / This work presents the study, implementation, and characterization of transducers composed of a structure formed by Fiber Bragg Gratings (FBG) and Long Period Gratings (LPG) in optical fiber with self-heating coverage for measurement of thermal conductivity and thermal diffusivity of materials based on the Hot-Wire Method (HWM). The self-heating fiber optic device developed in this work is caused by the light of infrared spectrum injected by a pumping laser, which is spread by an LPG and absorbed by a thin metallic film deposited on the surface of the fiber. The transducers are compact, simple, robust and immune to electromagnetic interference. The experimental arrangement using the optical fiber sensor based on LPG-FBG hybrid structure was able to measure the thermal conductivity of atmospheric air and water with accuracies of 27% and 14%, respectively. Several factors were identified that affect the precision and the accuracy of the measures carried out, whereby various forms of corrections are being proposed to improve overall performance. The viability of the original application of the experimental arrangement using the LPG-FBG hybrid device in self-heating optical fiber for the measurement of thermal properties of fluids (air and water) has been successfully demonstrated.

Material thermal properties are highly sought after to better understand the performance of a material under particular conditions. As new materials are created, their physical properties will determine their performance for various applications. These properties have been estimated using many techniques including experimental testing, numerical modeling, and a combination of both. Existing methods can be time consuming, thus, a time-efficient and precise method to estimate these thermal properties was desired. A one-dimensional finite difference numerical model was developed to replicate the heat transfer through an experimental apparatus. A combination of this numerical model and the Continuous Genetic Algorithm optimization technique was used to estimate material thermal properties of fibrous insulation from test data. The focus of this work was to predict these material thermal properties for an Alumina Paper that is commonly used in aerospace applications. The background, methodology, and results are discussed.

Les matériaux à changement de phase (PCM) sont utilisés pour la réalisation de mémoire non volatile. Ces matériaux possèdent la particularité de passer d’un état cristallin à un état amorphe à l’aide d’une impulsion de chaleur, créant ainsi un processus propre au stockage de l’information. Les PCMs sont généralement basés sur des composés ternaires de type Ge-Sb-Te (GST) avec une température de transition de l’ordre de 125°C, rendent ces matériaux inutilisable dans le domaine de l’automobile et pour des applications militaires. Pour contourner cette limitation, le GST est remplacé par le composé In-Sb-Te (IST) possèdent une température de transition plus élevé et un temps de transition beaucoup plus rapide (nanoseconde). Les propriétés thermiques de l’IST et de ses interfaces au sein de la cellule PCM peuvent influencer la température de transition. C’est pourquoi la mesure de la conductivité thermique nous donnera une estimation de la valeur de cette transition.Différentes techniques ont été misent en oeuvre pour mesurer la conductivité thermique des couches minces d’IST en fonction de la concentration en Te, à savoir ; la radiométrie photo-thermique modulée (MPTR) et la méthode 3ω dans une gamme de température allant de l’ambiant jusqu'à 550°C.Les résultats obtenus par les deux techniques de caractérisation thermiques démontrent que la conductivité thermique de l'IST diminue lorsque l'on augmente la teneur en Te. L'augmentation de la teneur en Te pourrait donc conduire à un alliage thermiquement plus résistif, qui est censé apporter l'avantage d'un flux de chaleur plus confiné et limiter la cross-talk thermique dans le dispositif de mémoire à changement de phase. / Phase change memories (PCM) are typically based on compounds of the Ge-Sb-Te (GST) ternary system. Nevertheless, a major drawback of PCM devices is the failure to fulfill automotive-level or military-grade requirements (125°C continuous operation), due to the low crystallization temperature of GST. To overcome this limitation, alloys belonging to the In-Sb-Te (IST) system have been proposed, which have demonstrated high crystallization temperature, and fast switching. Thermal properties of the chalcogenide alloy and of its interfaces within the PCM cell can influence the programming current, reliability and optimized scaling of PCM devices. The two methods, namely: 3ω and Modulated Photothermal Radiometry (MPTR) technique was implemented to measure the thermal conductivity of IST thin films as well as the thermal boundary resistance at the interface with other surrounding materials (a metal and a dielectric). The experiment was carried outin situ from room temperature up to 550oC in order to investigate the intrinsic thermal properties at different temperatures and the significant structural rearrangement upon the phase transition.The results obtained from the two thermal characterization techniques demonstrate that the thermal conductivity of IST decreases when increasing the Te content. Increasing the Te content could thus lead to a more thermally resistive alloy, which is expected to bring the advantage of a more confined heat flow and limiting the thermal cross-talk in the phase change memory device.

Avec la miniaturisation croissante des systèmes micro et nanoélectroniques, les problématiques thermiques revêtent un enjeu croissant. En effet, la faible taille des composants rend problématique l'évacuation de chaleur. Selon la NASA, 90% des défaillances sont imputables à des défauts d'interconnections thermiques et d'après l'US Air Force, 55% des défaillances électroniques sont attribuables à des effets thermiques. Devenues très courantes dans les domaines des nanotechnologies et des énergies renouvelables, les couches minces présentent des caractéristiques thermiques propres (confinement) et des défis métrologiques particuliers (taille des échantillons, influence du substrat sur la mesure). Le transfert de chaleur à l'échelle submicrométrique diffère du transfert de chaleur dans les matériaux massifs à cause de l'effet de confinement spatial propre aux nanostructures. Ainsi, la diffusivité thermique α et la conductivité thermique κ de ces couches minces sont des paramètres qui affectent la performance et la durée de vie de ces couches dans une application donnée. Ce mémoire de thèse porte sur le développement d'un banc de mesure, basé sur les variations de réflectivité d'un matériau en fonction de la température ou thermoréflectance, pour la caractérisation thermique à l'échelle submicrométrique. Dans ce travail, nous avons développé des modèles thermiques tridimensionnels dans des systèmes à deux et trois couches ainsi que les expressions théoriques du signal de thermoréflectance mesuré suite à une excitation thermique de la surface de l'échantillon. Ces expressions ont été développées en tenant compte de l'effet des résistances thermiques aux interfaces. Les modèles ont été validés expérimentalement par des mesures sur des couches minces d'or déposées sur un substrat de silice. Les mesures de thermoréflectance ont été ensuite appliquées à des couches minces d'acide polylactique. Finalement, des couches minces d'oxyde de zinc dopées par différentes concentrations d'aluminium ont été élaborées par voie électrochimique et leurs propriétés thermiques étudiées à l'aide du banc de mesure de thermoréflectance. / With the increasing miniaturization of micro and nanoelectronic systems, the thermal behavior of these systems has become more and more important. The small size of the components makes the heat emitted more troublesome. According to NASA, 90% of failures are due to thermal interconnection faults and according to the US Air Force, 55% of electronic failures are attribuable to thermal effects. Most electronic chips are manufactured using thin films technologies ; therefore, the characteristics of thin metal films have been the bottom line in the ongoing research in nanotechnology and renewable energy domain. Nanoscale heat transfer is different from the heat transfer in bulk materials due to the spatial confinement effect specific to nanostructures. Furthermore, the thermal diffusivity α and thermal conductivity κ of these films are critical parameters affecting their performance and lifetime in a given application. This thesis is devoted to setting up a measurement bench, based on the reflectivity variations of a material as a function of temperature (thermoreflectance), in order to thermally characterize thin films. In this work, a three-dimensional theoretical model is developed in order to describe the temperature distribution in two and three layers systems and obtain the expression of the measured thermoreflectance signal when the surface of the sample is heated by an intensity-modulated Gaussian laser beam. These expressions are obtained by taking into consideration the effect of thermal boundary resistances. These models have been validated experimentally on thin films of gold deposited on fused silica substrate. The thermoreflectance measurements have been then performed on thin films of polylactic acid. Finally, thin films of zinc oxide doped with different concentrations of aluminum have been elaborated during this thesis. The thermal characterization of these films is carried out with the thermoreflectance bench.