Orientador: Hugo Enrique Hernandez Figueroa / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-19T08:38:08Z (GMT). No. of bitstreams: 1 Silva_AlexandreManoelPereiraAlvesda_D.pdf: 7013947 bytes, checksum: c23d3c786fbf204c86a3e94bd5da9bd2 (MD5) Previous issue date: 2011 / Resumo: O projeto e o estudo de lentes plasmônicas operando nos comprimentos de onda de 650nm e 1550nm são, aqui, apresentados. Uma lente desse tipo permite que a luz proveniente de um guia de ondas micrométrico, por exemplo, uma fibra óptica, seja acoplada em estruturas como guias de ondas nanométricos ou nanocavidades ressonantes, a distâncias curtas, reduzindo, sobremaneira, a área necessária somente para acoplamento. São analisadas, também, as condições do foco para que haja um acoplamento eficiente de luz aos guias de ondas nanométricos. O foco conformado por essa lente localiza-se a distâncias da ordem de um comprimento de onda. A lente plasmônica recebe essa denominação por utilizar os polaritons de plasmons de superfície como meio de transportar a luz pela lente. Os polaritons de plasmons de superfície são ondas eletromagnéticas superficiais que se propagam na interface entre um meio dielétrico e um meio condutor. Eles permitem que haja modos propagantes em guias de ondas com dimensões muito inferiores ao limite da difração, como em fendas nanométricas recortadas em um filme metálico. é possível controlar a constante de propagação e, por conseguinte, a variação de fase dentro de uma fenda desse tipo, controlando a espessura da mesma. Dispondo várias fendas ao longo de um filme metálico, é possível projetar uma lente plana pelo controle da modulação da fase de saída dessas diversas fendas. Esse comportamento é semelhante ao de um arranjo de antenas, porém, o foco é formado na região de campo próximo. Após uma varredura dos parâmetros construtivos da lente, foi possível obter uma lente de perfil plano que permita o acoplamento eficiente entre guias de ondas com diferenças de dimensão de mais de uma ordem de grandeza dentro de distâncias da ordem de um comprimento de onda. Uma proposta de lente posicionada na ponta de uma fibra óptica é sugerida, a qual permite o acoplamento ou excitação de uma ou mais estruturas ópticas ao mesmo tempo / Abstract: The project and the study of plasmonic lenses operating in the wavelengths of 650nm and 1550nm are presented. Such a lens allows the light coupling from a microsized waveguide, for instance, an optical fiber, to nanosized structures such as nano-waveguides or nano-cavities, within short distances, reducing the amount of area used just for coupling. It is also analyzed the focus conditions for efficient coupling to dielectric nano-waveguides. The lens focus is placed at distances about one wavelength apart. This lens is called plasmonic lens because the excitation of surface plasmon polaritons allows the propagation of light through it. Surface plasmon polaritons are electromagnetic surface waves that propagate along the interface of a dielectric media and a conductor. They allow the formation of propagating modes within waveguides bellow the diffraction limit, such as nano-slits cut into a metallic film. The propagation constant therefore, the phase variation inside such a slit, is controlled by its width. Then, placing several slits along the metallic film, it is possible to design a plane lens by designing the phase modulation of several slits cut into a metallic film. This behavior is similar to an antenna array, however, the focus is formed within the nearfield zone. After some variations on the design parameters, it is obtained a plane lens showing an efficient coupling between different dimensions dielectric waveguides within one wavelength distance from the lens. A lens configuration positioned on a optical fiber is proposed. This configuration allows coupling or excitation of one or more optical structures at the same time / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

Abstract This work presents a method for the fabrication of Li₂MoO₄ ceramics at room-temperature based on utilizing a small amount of water with Li₂MoO₄ powder. The densification of the ceramic takes place during pressing. Thus the shape and size of the final ceramic compact can easily be managed by controlling the mould dimensions and the amount of material. Post-processing at 120 °C is applied to remove residual water from the compact. This post-processing temperature can be chosen to be suitable to the other materials integrated, such as the substrate or electrodes, as long as the post-processing time is adequate to remove the residual water. The dielectric properties (relative permittivity of 5.1 and a loss tangent value of 0.00035 at 9.6 GHz) after optimization of the powder particle size, sample pressing pressure, and post-processing time were similar to those achieved for Li₂MoO₄ ceramics fabricated by sintering at 540 °C. The dielectric properties of Li₂MoO₄ ceramics were also modified using composite methods. For example, an addition of 10 volume-% of BaTiO₃ increased the relative permittivity from 6.4 to 9.7 and the loss tangent value from 0.0006 to 0.011 at 1 GHz. To investigate the thermal dependence of the permittivity, different amounts of rutile TiO₂ were incorporated into a Li₂MoO₄ ceramic matrix fabricated with the method described in this work. As the amount of TiO₂ increased from 10 to 30 volume-%, the thermal coefficient of permittivity decreased from 180 ppm/°C to -170 ppm/°C. The low processing temperature made the fabrication approach introduced here feasible for silver electrode integration without the formation of extra phases, which were observed in sintered samples with similar compositions in another study. A patch antenna was realized utilizing a Li₂MoO₄ ceramic disk fabricated by the room-temperature method. The antenna operating at ~4 GHz showed reasonably good performance. A relative humidity of 80% lowered the resonant frequency by 3.25% from the initial value, and reduced the total and radiation efficiencies of the antenna by ~2 dB. The changes were slowly reversible. Use of a silicone conformal coating reduced the shift of the resonant frequency to 1.26% from the initial value and also reduced the effect on efficiencies to ~1 dB. The use of the coating also speeded up the reversibility of the changes when the humidity was decreased. / Tiivistelmä Tässä työssä esitellään menetelmä, jolla Li₂MoO₄-keraameja voidaan valmistaa huoneenlämpötilassa. Menetelmä hyödyntää pientä määrää Li₂MoO₄-vesiliuosta ja sen kiteytymistä. Keraami tiivistyy kappaletta puristettaessa, joten sen koko ja muoto ovat sama kuin muotilla riippuen vain keraamin määrästä. Kappaleeseen jäänyt vesi poistetaan lämpökäsittelyllä yleensä 120 celsiusasteessa. Jälkikäsittelylämpötila voidaan valita muiden integroitavien materiaalien mukaan, kuten alusta- tai elektrodimateriaalin, kunhan jälkikäsittelyaikaa muokataan vastaavasti, jotta kaikki vesi poistuu. Optimoimalla Li₂MoO₄-jauheen partikkelikokoa, puristuspainetta ja jälkikäsittelyaikaa saavutettiin samankaltaiset dielektriset ominaisuudet taajuudella 9,6 GHz (suhteellinen permittiivisyys 5,1 ja häviötangentti 0,00035) kuin Li₂MoO₄-keraameilla, jotka on sintrattu 540 celsiusasteessa. Li₂MoO₄-keraamien dielektrisiä ominaisuuksia muokattiin myös lisäaineilla. Esimerkiksi 10 tilavuus-% BaTiO₃-jauhetta kasvatti suhteellista permittiivisyyttä taajuudella 1 GHz arvosta 6,4 arvoon 9,7 ja häviötangenttia arvosta 0,0006 arvoon 0,011. Myös eri määriä TiO₂-jauhetta (rutiili) lisättiin Li₂MoO₄-matriisiin permittiivisyyden lämpötilariippuvuuden tutkimiseksi. TiO₂-jauheen määrän kasvaessa 10 tilavuusprosentista 30 tilavuusprosenttiin laski permittiivisyyden lämpötilariippuvuus arvosta 180 ppm/°C arvoon -170 ppm/°C. Matalan käsittelylämpötilan ansiosta työssä esitelty valmistusmenetelmä soveltui käytettäväksi hopeaelektrodien kanssa. Aiemman tutkimuksen mukaan nämä komposiittimateriaalit muodostivat ei-toivottuja faaseja sintrattaessa hopean kanssa. Menetelmällä valmistettua Li₂MoO₄-keraamikiekkoa käytettiin mikroliuska-antennin valmistuksessa. Taajuudella 4 GHz toimivan antennin suorituskyky oli suunnitellun kaltainen. 80 prosentin suhteellinen ilmankosteus laski resonanssitaajuutta 3,25 % alkuperäisestä arvosta ja vähensi antennin kokonais- ja säteilytehokkuutta noin 2 dB. Muutokset palautuivat hitaasti. Silikonisuojalakan käyttö vähensi taajuuden laskua 1,26 prosenttiin alkuperäisestä arvosta ja tehokkuudet laskivat vain noin 1 dB. Suojalakan käyttö nopeutti muutosten palautuvuutta ilmankosteuden laskiessa.

Cette thèse s’intéresse à l’endommagement laser d’optiques réflectives en régime sub-picoseconde. Ces composants optiques, réalisés à partir d’empilements sub-micrométriques de matériaux diélectriques, sont couramment utilisés dans les installations laser de puissance telles que le laser PETAL. Ce dernier, construit sur le centre du CEA-CESTA en France, a été conçu pour délivrer des impulsions de 500 fs et de quelques kJ à une longueur d’onde de 1053 nm, dans le but d’atteindre des puissances supérieures à 6PW. Dans ce type d’installations de puissance, afin de limiter l’accumulation d’effets non-linéaires liés à la propagation d’impulsions intenses, des optiques réflectives en fin de chaîne se substituent aux optiques en transmission. Les composants optiques illuminés par les plus fortes densités de puissance sont des réseaux de compression, des miroirs et une parabole qui servent respectivement à la compression temporelle des impulsions, au transport du faisceau ainsi qu’à sa focalisation. Le phénomène d'endommagement laser est le paramètre principal qui limite la puissance accessible par ces lasers. Il est nécessaire de comprendre et de maîtriser ce phénomène afin de fiabiliser une installation laser et également d’améliorer ses performances. Trois axes d’études ont donc été explorés. Le premier concerne la conception d’optiques réflectives. Des définitions de structures sont recherchées afin d’obtenir de hautes efficacités de diffraction dans le cas des réseaux et des forts coefficients de réflexion dans le cas des miroirs, tout en diminuant le renforcement du champ électrique dans les structures, l’une des causes de l’endommagement laser. Le second axe d’étude porte sur la mise en place d’une métrologie fine de l’endommagement laser avec le développement de nouvelles procédures de test. Elles amènent de nouveaux points de vue pour la qualification de la résistance au flux laser des optiques. En dernier lieu, nous étudions le phénomène de croissance des dommages lorsqu’ils sont soumis à plusieurs irradiations laser. L’évolution de la surface des dommages lors de séquences de croissance est observée, quantifiée et comparée à un modèle numérique. Cela nous permet de mieux comprendre la phénoménologie de la croissance des dommages en régime sub-picoseconde. A terme, elles permettront de développer des modèles de prédiction de l’endommagement et des outils pour l’amélioration des optiques utilisées sur chaîne laser. / In this thesis, laser-induced damage phenomenon of reflective components is investigated in the sub-picosecond regime. These components, made of stacks of dielectric materials, are widely used in powerful laser facilities such as PETAL laser. PETAL laser has been built at the CEA-CESTA in France to deliver multi-kJ/500fs pulses at 1053nm and reach a power higher than 6PW. For this kind of laser systems, reflective components are commonly used instead of optics operating in transmission to limit the accumulation of non-linear phase along the beam propagation due to the high intensities. Optical components irradiated by the highest power densities are the pulse compression gratings, transport mirrors and the focusing parabola, located at the end of the laser chain. Nowadays, laser-induced damage is the main factor that limits the overall performances of powerful laser systems. This manuscript presents three study axes to better understand and control damage phenomenon. The first one concerns the conception of reflective optics for the petawatt applications. The design of new structures has been investigated to reach high diffraction efficiencies in the case of pulse compression gratings and a high reflectivity in the case of mirrors, while reducing the Electric-field enhancement which is one of the causes of the laser-induced damage. The second axis deals with the development of a precise damage metrology with new testing tools which brings new perspectives and a new viewpoint for the assessment of the laser resistance of optical components. Finally, the third axis concerns the study the damage growth after several irradiations in the sub-picosecond regime. The evolution of the damage area during growth sequences is observed and compared to numerical simulations. It enables to improve the understanding in the growth phenomenon. In the end, these studies will allow to develop predictive models of the laser-induced damage and new tools for the conception of reflective optics for petawatt applications.

Le dioxyde de carbone, principal gaz à effet de serre lié aux activités humaines, est considéré comme l’un des gaz les plus problématiques pour notre environnement ces dernières années, principalement à cause du réchauffement climatique qu’il engendre. C’est pour cette raison que l’augmentation de sa teneur dans l’atmosphère nous concerne tous quant aux conséquences futures pour notre planète. Afin de limiter l’émission de CO2, sa conversion en composés à valeur ajoutée présente un grand intérêt et est possible notamment via des procédés plasmas. Plus particulièrement, les décharges à barrière diélectrique (DBD) sont utilisées depuis quelques années pour générer des plasmas froids opérant à pression atmosphérique, principalement pour des applications en traitement de surface, mais également pour le traitement d’effluents gazeux.Lors de cette thèse, nous nous sommes focalisés sur le processus de dissociation du CO2 en CO et O2 via un réacteur DBD à flux continu et avons analysé sa conversion et son efficacité énergétique via différentes études. Celles-ci ont été réalisées grâce à plusieurs méthodes de diagnostic, comme par exemple la spectrométrie de masse utilisée pour déterminer la conversion et l’efficacité du processus, la spectroscopie d’émission optique, l’oscilloscope pour une caractérisation électrique, etc. afin d’avoir une meilleure compréhension du comportement des décharges CO2.Dans un premier temps, nous avons réalisé une étude détaillée d’un plasma CO2 pur où nous avons fait varier différents paramètres, tels que le temps de résidence, la fréquence, la puissance, la pulsation de la haute tension et l’épaisseur et la nature du diélectrique. Le CO2 donne lieu généralement à une décharge filamentaire, consistant en de nombreuses microdécharges réparties au niveau de la zone du plasma. Celles-ci constituent la principale source de réactivité dans une DBD. Un aperçu détaillé de l’aspect physique de ces microdécharges a été réalisé grâce à la caractérisation électrique, permettant de mieux comprendre les propriétés électriques de la décharge et des microdécharges. En effet, nous avons pu déterminer l’importance de la tension présente au niveau du plasma, de l’intensité du courant plasma, du nombre de microdécharges et de leur temps de vie sur l’efficacité du processus de dissociation de CO2.Ensuite, nous avons conclu ce travail avec des études combinant le CO2 en phase plasma avec de l’eau ou du méthane afin de produire des molécules à valeur ajoutée telles que les syngas (CO et H2), mais aussi des hydrocarbures (C2H6, C2H4, C2H2 et CH2O) dans le cas de l’ajout du méthane. A travers ces études, nous avons obtenu une meilleure connaissance de la chimie et de la physique qui ont lieu dans ce type de plasma. / Carbon dioxide appears as one of the most problematic gases for the environment, mostly because it is responsible for global warming. This is why its increasing concentration into the atmosphere, mainly due to anthropogenic activities, is a real concern for planet Earth. In order to prevent the release of large amounts of CO2, its conversion into value-added products is of great interest. In this context, plasma-based treatments using dielectric barrier discharges (DBDs) are nowadays more and more used for the conversion of this gas. In this thesis, we investigated the CO2 splitting process into CO and O2 via a flowing cylindrical DBD and we studied its conversion and energy efficiency by means of several diagnostic methods, such as mass spectrometry to determine the conversion and energy efficiency of the process, optical emission spectroscopy for gas temperature measurements, and an oscilloscope for electrical characterization, in order to obtain a better understanding of the CO2 discharge itself.First, we focused on an extensive experimental study of a pure CO2 plasma where different parameters were varied, such as the gas residence time, the operating frequency, the applied power, the pulsation of the AC signal, the thickness and the nature of the dielectric. CO2 discharges typically exhibit a filamentary behavior, consisting of many microdischarges, which act as the main source of reactivity in a DBD. A detailed insight in the physical aspects was achieved by means of an in-depth electrical characterization, allowing more insight in the electrical properties of the discharge and more specifically in the microdischarges, which are spread out throughout the active zone of the plasma. It was found throughout this work that the plasma voltage, which reflects the electric field and thus determines how the charged particles are accelerated, the plasma current, which reflects the electron density, but also the number of microdischarges and their average lifetime, play an important role in the efficiency of the CO2 dissociation process. It was revealed that the microdischarge number is important as it represents the repartition of the locations of reactivity. Indeed, as the microfilaments are more spread out in the same discharge volume, the probability for the CO2 molecules to pass through the reactor and interact with at least one microdischarge filament becomes more important at a larger number of microfilaments.The second part of the thesis was dedicated to discharges combining CO2 and H2O or CH4, both being hydrogen source molecules. The combined CO2/H2O or CO2/CH4 conversion allows forming value-added products like syngas (CO and H2), but also hydrocarbons (C2H6, C2H4, C2H2 and CH2O), at least in the presence of methane. Throughout this study, we tried to obtain a better knowledge of the chemistry and physic behind these conversion processes. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Progress in the fields of wearable computing, soft robotics and bio hybrid engineering depend on new classes of soft multifunctional materials that match the mechanical properties of soft biological tissue and possess high toughness, while having metal-like electrical and thermal properties.

L’identification par radio fréquence (RFID) connectée à des capteurs est une technologie grandissante pour les emballages intelligents. Ces travaux de thèse ont porté sur l’étude des propriétés électriques (impédance et capacité) et diélectriques (permittivité diélectrique et pertes) des protéines notamment le gluten de blé, en fonction des molécules environnementales connues comme des marqueurs de dégradation des denrées alimentaires. Les effets de ces molécules (eau, dioxyde de carbone et éthanol) sur les propriétés électriques et diélectriques du gluten de blé ont été analysés. Dans le but d’effectuer des mesures dans des conditions optimales, plusieurs étapes ont été mises en place:Le développement d’une méthode, permettant une haute exposition du gluten de blé à l’atmosphère environnant, afin d’acquérir des mesures électriques et diélectriques du gluten de blé dans des conditions contrôlées de température, vapeurs et de gaz ;L’analyse des effets des vapeurs et gaz sur les propriétés diélectriques du gluten de blé, ainsi que la détermination de différents paramètres tels que la sensibilité et l’hystérésis, propres aux capteurs ;L’enduction du gluten de blé sur une étiquette RFID, testée en fonction de l’humidité et dans des conditions réelles d’utilisation. Les effets sur la distance de lecture de l’étiquette RFID ont été analysés.Les résultats obtenus sont prometteurs au vu des modifications de la permittivité diélectrique et des pertes, indiquant une modification structurelle de la protéine, qui aurait un impact sur la réponse RFID. La permittivité diélectrique a été augmenté de 5.01±0.06 à 9.22±0.06, de 7.81±0.07 à 12.02±0.03 et de 6.66±0.01 à 11.77±0.01, pour une croissance de 20% à 95% de l’humidité relative, de 0% à 40% de dioxyde de carbone et de 0% à 0.1% d’éthanol respectivement, aboutissant à une sensibilité de 26.70±0.13fF/%RH,31.38±0.06fF/%CO2 et 25.50±0.05pF/%éthanol pour les 3 vapeurs et gaz. Les propriétés diélectriques du gluten et sa sensibilité aux vapeurs et aux gaz offrent de nouvelles perspectives sur la conception de capteurs à bas coûts et écologiques, connectés à des étiquettes RFID passives pour les emballages intelligents et pour le contrôle de la chaîne alimentaire. / Radio frequency identification (RFID) interfaced to sensors is a growing technology for intelligent packaging. The present thesis work is based on the study of the electrical (impedance and capacitance) and dielectric properties (dielectric permittivity and loss) of proteins principally wheat gluten, as a function of environmental molecules known as markers of food degradation. The impacts of those molecules (water, carbon dioxide and ethanol), usually found in food packages, on the electrical and dielectric properties of wheat glutenhave been investigated. In order to perform measurements in the optimum conditions, several steps have been set up:The development of a methodology, allowing a high exposure of wheat gluten to the surrounding atmosphere, offering the possibility to perform electrical measurements and identify dielectric properties of wheat gluten in controlled conditions of vapors and gases ;Analyzing the impact of vapors and gases on the dielectric properties of wheat gluten, and the determination of several parameters such as sensitivity and hysteresis, specific to sensors ;The coating of wheat gluten on a RFID tag, tested as a function relative humidity and in real conditions of use. The subsequent impacts on the reading range of the RFID tag have been analyzed.The results obtained are promising according to modifications of the dielectricpermittivity and loss, indicating a structural modification of the protein, sought to have an impact on the RFID response. The dielectric permittivity was increased from 5.01±0.06 to 9.22±0.06, from 7.81±0.07 to 12.02±0.03 and from 6.66±0.01 to 11.77±0.01, for an increase in relative humidity from 20% to 95%, in carbon dioxide from 0% to 40% and in ethanol from 0% to 0.1%, respectively, resulting in a sensitivity of 26.70±0.13fF/%RH, 31.38±0.06fF/%CO2 and 25.50±0.05pF/%ethanol for the 3 vapors and gases. The dielectric properties of wheat gluten and its sensitivity to vapors and gases offer new insights on theconception of low cost, eco-friendly sensors sought to be interfaced to passive RFID tags for intelligent packaging for food and supply chain monitoring.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15371号 / 工博第3250号 / 新制||工||1489(附属図書館) / 27849 / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 中部 主敬, 教授 小寺 秀俊, 教授 田畑 修 / 学位規則第4条第1項該当

Les transistors organiques sont la base de nombreuses applications de l'électronique organique mais leur rendement électrique ainsi que leur stabilité dans le temps sont encore des verrous technologiques devant être levés. De plus, le phénomène de transport de charges dans ces dispositifs reste une notion encore à l'étude même si différents modèles sont utilisés afin d'expliquer l'effet de champ des transistors organiques. C'est dans ce cadre que s'inscrit cette étude portant sur la caractérisation par spectroscopie d'admittance de jonctions Métal/oxyde/semi conducteur organique/métal. Elle a pour but d'analyser le comportement électrostatique du semi conducteur organique. Les mesures de spectroscopie d'admittance ont été réalisées sur une large bande de fréquence (0.1Hz à 1Mhz) dans laquelle les pertes diélectriques mesurées peuvent être associées à des phénomènes d'orientation (oscillation) de dipôles présents dans la structure. Les réponses en fréquences montrent trois types de comportements dynamiques. A basses fréquences, nous avons observé une diffusion ionique, liée au déplacement d'ions H+ à travers la structure. A hautes fréquences, la réponse est due aux imperfections de l'oxyde. Enfin, aux fréquences intermédiaires, la réponse du semi-conducteur organique est identifiée et attribuée à des dipôles permanents. A partir de ces différentes réponses, un modèle analytique est établi et permet de décrire l'ensemble des réponses dynamiques. Le comportement du semi-conducteur est décrit par la somme d'une fonction de type Debye et de type Cole-Cole. L'analyse des paramètres de ce modèle a permis de mettre en évidence l'influence des dipôles permanents sur la permittivité du film de semi-conducteur organique. Enfin, ce modèle a été validé sur différents échantillons à base de pentacène et a été ensuite appliqué au Poly-3-hexylthiophène. / Organic transistors are vital in many applications of organic electronics but the electrical performance and time stability are technological limitation in order to make this technology reliable. Moreover, in these devices, the charge transport phenomenon has not to be clearly understood even if different models are commonly used to explain the field effect in organic transistors. In this context, this thesis talks about the admittance spectroscopy characterization of metal / oxide / organic semiconductor / metal junctions and analysis the organic semiconductor electrostatic behavior.The admittance spectroscopy measurements were performed on a wide frequency range (0.1Hz to 1MHz) in which the measured dielectric loss may be associated with the orientation phenomenon (as oscillation) of dipoles present in the structure.The frequency responses show three dynamic behaviors. At low frequencies (<10Hz), we observed an ionic diffusion, which is related to the ions movement of H+ through the structure. At high frequencies, (>10kHz) the response is due to defects into the oxide. Finally, at intermediate frequencies, the organic semiconductor response is identified and assigned to the permanent dipoles into the bulk. From these responses, an analytical model is developed and used to describe the dynamic responses. The semi-conductor behavior is described by the sum of a Debye and Cole-Cole function type. The analysis of the model parameters has highlighted the influence of permanent dipoles on the organic semiconductor permittivity. Finally, this model has been agreed on different samples based on pentacene and was applied to the Poly-3-hexylthiophene.

No description available.

Disorder in materials often brings in new and exotic physical properties along with it. It is thus very important to study different kinds of disorder and their implications on various material properties. In this thesis, we study selected transition metal oxide families of compounds, each being associated with a specific kind of disorder and investigate effects of that disorder on their dielectric and magnetic properties. In Chapter1, we have given brief introductions on the origin of magnetic and dielectric properties in materials and have also discussed various mechanism which give rise to multiferroism in materials which exhibit both spontaneous magnetic ordering and spontaneous electric ordering in the same phase of the material. In Chapter2,we describe the various methodologies adopted in this thesis. In Chapter3,we mainly study the effect of cationic size-disorder in deciding un-usually robust dielectric properties of Ln2CuTiO6(Ln=Y,Dy,Ho,Er,Yb) family of compounds. We discover that these materials, in addition to possessing large dielectric constant values, also exhibit exceptional stabilities of their dielectric constants with respect to large changes in temperature and frequency. We further find that this class of materials are non-ferroelectrics though its hares the same non-centrosymmetric space group, P63cm,with the well-known multiferroic YMnO3 that undergoes a ferroelectric transition at 940K. Using first principles calculations, we establish that exceptional dielectric properties result from a combination of two separate effects. Extensive size disorders at the Cu/Ti B-site suppress the expected ferroelectric transition, leading to relatively large values of the dielectric constant for every compound investigated in this series. Additionally, it is shown that the majority contribution to the dielectric constant arises from intermediate-frequency polar vibrational modes, making it relatively stable against temperature variations. In Chapter4, we study the effect of cation anti-site disorder on the magnetic, electric and dielectric properties of the solid solution series of (x)Fe2O3-(1-x)FeTiO3 for several values of x. For intermediate values of x, these solid solution members are found to be strong ferrimagnets. Anti-site cation disorder, between Fe and Ti, however strongly reduces the magnetic moment values. By tuning the degree of cation anti-site disorder, we attain multi-functionality in these samples. We have performed detailed characterizations of valence states of Fe and Ti across the solid solution series using x-ray photoelectron spectroscopy and x-ray absorption spectroscopy. Using x-ray magnetic circular dichroism, we validate the microscopic model of magnetism and suggest a microscopic picture of the anti-site cation disorder for these samples. In Chapter5,we study the effects of controlled chemical disorder in SrTiO3 lattice, by performing site-specific doping of Mn in SrTiO3. We find that site specific Mn doping has decisive influence on their dielectric properties with qualitatively and quantitatively different behaviors between these doped samples .Using electron paramagnetic resonance experiments, we establish the site specific doping of Mn in SrTiO3 lattice. We find that while Mn doping at Ti site continues to remain paraelectric, Mn doping at the Sr site becomes a relaxor ferroelectric. We find samples having Mn substituted at both Sr and Ti sites simultaneously to be also relaxor ferroelectrics. Combining experiments with first principles calculations, we understand the origin for the high temperature dielectric properties of various Mn doped SrTiO3 samples. We show that Mn ions doped at the Sr sites off-centers and gives a significant dipolar contribution to their dielectric constants. While demonstrating the superior dielectric properties of Mn doped SrTiO3 ceramics ,we also elucidate their magnetic properties in details. In Chapter6,we study the effect of cation anti-site disorder on the magnetic and dielectric properties of undoped and Lu doped La2NiMnO6 samples. Using detailed spectroscopic characterizations of these samples with x-ray absorption experiments, coupled with d.c.magnetization and a.c.susceptibility measurements, we demonstrate that while the doped samples are ferromagnetic, the undoped samples exhibit re-entrant spin-glass magnetism. We also show that the dielectric properties of undoped La2NiMnO6,crys-tallizing in monoclinic and rhombohedral phases are distinctly different and we study their dielectric relaxations in details. We also demonstrate multiferroism in Lu doped La2NiMnO6 samples. In Appendix A, we study the electronic origin of ferroelectric polarization in the spin spiral compound ,MnWO4. Using x-ray absorption spectroscopy on synthesized MnWO4 samples, coupled with configuration interaction calculations, we establish quantitatively a significant population of Mn 3d states beyond the expected half filling and provide a critical insight into the significant presence of spin-orbit coupling and consequent finite polarization in this system. In Appendix B, we study charge-transfer doping in few-layer grapheme covered with electron acceptor (Tetracyanoethylene) and donor (Tetrathiafulvalene) molecules using x-ray photoelectron spectroscopy. We give quantitative estimates of the extent of doping in these samples and thereby elucidate the origin of unusual shifts of their Raman G bands in contrast to electrochemically doping schemes. In conclusion, we investigate, in this thesis, properties of different classes of compounds in presence of distinctly different kinds of disorder and establish the critical role of disorder in each case in tuning their desirable physical properties.