Ce travail porte sur le fractionnement des produits de fission et les actinides mineurs (simulées par des terres rares) dans une vitrocéramique borosilicate riche en molybdène contenant des cristallites de powellite (CaMoO4) étudié par techniques d'analyse élémentaire (LIBS, LA-ICP-MS, et l'EMPA). Il a été montré que des terres rares et Sr (émetteur bêta) sont incorporés préférentiellement dans la phase powellite, tandis que Al, Fe, Zr, Zn et Cs (sources bêta-decay) restent dans le verre. Le comportement de monocristaux orientés de powellite dopé en terres rares (simulants des actinides mineurs) sous irradiations est décrit et commenté afin de comprendre son comportement à long terme dans des conditions de stockage, en utilisant l'interférométrie optique, la spectroscopie Raman, TEM, et la spectroscopie de photoluminescence. On observe que l'irradiation induit un gonflement dans powellite augmentant avec la dose d'irradiation (de 0,012 à 1,2 dpa). La saturation est atteinte à 1,2 dpa. Une contrainte anisotrope associée à un changement du volume de la maille dans le monocristal de powellite a été mis en évidence et analysée par suivi de la position des raies v1 (Ag) et v3 (Eg) des modes Raman. Le désordre induit dans la structure de powellite irradiée est signé par l'augmentation de la largeur des raies Raman. La caractérisation fine par TEM indique que les dommages structuraux induits dans la powellite irradiée suivent l'évolution suivante de la structure cristalline : défauts ponctuels, dislocations, mosaïcité. Il a été confirmé à la fois par Raman et par TEM que la structure powellite résiste fortement à l'irradiation et n'atteint jamais l'état d'amorphisation dans la gamme dpa étudiée (0,012 à 5,0) / The fractionation of fission products and minor actinides (simulated by rare-earth elements) is studied in a Morich borosilicate glass-ceramic containing powellite (CaMoO4) crystallites, using elemental analysis techniques (LIBS, LA-ICPMS, and EMPA). For Mo-rich borosilicate glass-ceramic containing powellite crystallites, it was suggested that rare earth elements and Sr (beta-decay source) are prone to incorporate into the powellite phase, while Al, Fe, Zr et Cs (beta-decay source) and Zn remain in the glass matrix. The behavior of rare-earth (surrogates of radioactive minor actinides) doped powellite single crystal under irradiations figure out its longterm behavior in storage conditions, using optical interferometry, Raman spectroscopy, TEM, and luminescent spectroscopy. It is observed that the irradiation-induced swelling in powellite first increased with irradiation dose (0.012 to 1.2 dpa), then reached saturation after 1.2 dpa Anisotropic stress and lattice volume change induced by irradiation in powellite single crystal were found and analyzed by determining the peak position of V1 (Ag) et V3 (Eg) Raman modes. Structure disorder of irradiated powellite in medium-range order was represented by the Raman linewidth broadening. According to the TEM characterization, the structural damages of irradiated powellite followed an evolution of crystalline structure, point defects, dislocations, mosaicity. It was confirmed by both Raman and TEM that powellite resisted strongly and never reached amorphization within the studied dpa range (0.012 to 5.0)

La technique de spectroscopie basée sur la diffusion Raman Stokes spontanée est un procédé standard employé dans de nombreux domaines allant de la thermodynamique à la médecine, en passant par la science des matériaux. À la faveur d'un échange d'énergie inélastique, elle permet de déterminer les fréquences des vibrations moléculaires présentes dans un objet. On peut ainsi remonter à l'identification des molécules et ainsi caractériser l'objet d'étude sans utiliser de marqueur spécifique. Cette méthode est néanmoins affligée de défauts. Outre la présence d'un signal de fluorescence qui peut submerger la réponse Raman, le désavantage majeur est le long temps d'exposition que requière cette technique. Dans le cas d'étude d'échantillon biologique, cela proscris son usage pour des mesures de microspectroscopie : la cartographie spectrale d'objet microscopique. Afin de pallier ce problème, de nouvelles techniques ont été développées. C'est le cas de la spectroscopie employant la diffusion Raman anti-Stokes Cohérente (ou CARS pour Coherent Anti-Stokes Raman Scattering). Du fait de sa cohérence et de sa directivité le signal anti-Stokes affiche une intensité 10^5 to 10^6 fois plus importante que dans le cas de la diffusion Raman spontanée, ce qui permet alors d'abaisser le temps d'exposition à un niveau tolérable pour les objets biologiques lors d'une mesure de microspectroscopie. De plus, le caractère anti-Stokes du signal l'épargne de la contribution de la fluorescence. Pourtant, un défaut majeur limite encore l'utilisation de cette technique : le bruit de fond non résonant. Ce phénomène peut diminuer, voir noyer la contribution résonante qui porte l'information. Cette thèse a permis le développement de techniques CARS autorisant une réduction du bruit de fond non résonant. Pour ce faire un dispositif de spectroscopie CARS multiplex (M-CARS) en configuration copropagative a été construit. Ses capacités sont illustrées par des mesures spectrales d'échantillons minéral, végétal et biologique. À partir de ce système, il a été établi une méthode innovante permettant de discriminer le signal résonant du bruit non résonant en utilisant un champ électrique continu. Il est aussi démontré la mise en place d'un procédé qui a permis de mener la première mesure de microspectroscopie M-CARS en configuration contrapropagative sur un échantillon biologique. Cette configuration limite la collecte du signal à l'objet d'étude, empêchant ainsi l'acquisition du signal résonant et non résonant issu du solvant, principal responsable du bruit de fond non résonant lors d'une mesure CARS en configuration copropagative. / The spectroscopy technique based on spontanée Raman Stokes scattering is a standard process used in many fields spanning from thermodynamic and medicine, to materials sciences. An inelastic energy exchange permits to determinate the frequency of the molecular vibrations in an object. One can identify the molecules and thus, can characterize the object of study in a label-free way. Nevertheless, this method is afflicted with faults. Beside the presence of fluorecence that can drown the Raman answer, the main drawback is the long exposition time required. In the case of biological sample, this can prohibit the use of spontaneous Raman scattering for microspectroscopy measures: the spectral mapping of microscopic objects. To avoid this problem, new techniques have been developed. It is the case of Coherent anti-Stokes Raman scattering (CARS) spectroscopy. Due to its coherence and its directivity, the anti-Stokes signal has an intensity 105 to 106 times greater than the spontaneous Raman scattering one. The exposition time is then reduced to a tolerable level for biological objects during microspectroscopy measures. Moreover, the anti-Stokes characteristic of the signal prevents the fluorescence contribution. However, a major fault still limits the use of this technique: the nonresonant background. This phenomenon can diminish, even overwhelm the resonant contribution carrying the information. This thesis permitted the development of CARS approaches that allow the reduction of the nonresonant background. To do so, a multiplex CARS (M-CARS) spectroscopy apparatus in a forward configuration has been built. Its abilities are illustrated with spectral measures of mineral, vegetal and biological samples. Based on this system, it has been established an innovative method that can discriminate the resonant signal from the nonresonant one thanks to a static electric field. It has been also been demonstrated the development of a process that has allowed the first M-CARS microspectroscopy measure of a biological sample in a contrapropagative configuration. This setup limits the collect of the signal to the object of study, avoiding the acquisition of the resonant and resonant signals coming from the solvent, responsible for the major part of non resonant background during a CARS measure in a forward configuration.

Dans ce travail, le composé de structure apatite La9,33(SiO4)6O2+3x/2 (-0,2<x<0,27) a été synthétisé et caractérisé en vue d’applications comme matériau d’électrolyte dans les piles à combustible à conduction anionique (IT-SOFC) et potentiellement protonique (PC-SOFC).Des pastilles et membranes denses d’oxyapatite pure ont été élaborées à partir de poudres synthétisées par voie solide, mises en forme par pressage isostatique ou coulage en bande et thermocompression, et frittées à 1550°C. Les échantillons ont été caractérisés électrochimiquement par spectroscopie d’impédance complexe et semi-perméation à l’oxygène et à l’hydrogène. Les phases La2SiO5 et La2Si2O7, qui peuvent apparaître lors de la synthèse de l’oxyapatite, ont été élaborées selon un protocole similaire, afin de caractériser leurs propriétés de conduction anionique. Ces phases ont d’autre part été utilisées lors d’essais d’élaboration d’oxyapatite à microstructure orientée le long de l’axe c, par frittage réactif d’échantillons d’architecture multicouche composés initialement d’une alternance de bandes La2SiO5 et La2Si2O7.Des tests de protonation en autoclave, à 550°C et 50 bars de pression de vapeur d’eau, ont été réalisés afin d’étudier le mécanisme d’insertion des protons dans la structure de l’oxyapatite. Des analyses thermogravimétriques, effectuées sur les échantillons protonés, ont permis de localiser les espèces protoniques insérées (surface/cœur) et de faire une analyse semi-quantitative de ces dernières. Les pertes de masses observées sont d’autant plus importantes que le temps de protonation et la stœchiométrie en oxygène des échantillons sont élevés. Des caractérisations structurales par diffraction des rayons X et spectroscopie Raman ont mis en évidence une augmentation conséquente du volume de la maille et un élargissement des grands canaux de la structure, ainsi qu’un changement de symétrie et une augmentation du désordre au sein de ces derniers. Ainsi, il semble que l’insertion des protons dans l’oxyapatite se fasse de manière préférentielle à l’intérieur des grands canaux de la structure. / This work is devoted to the synthesis and characterization of apatite-type La9,33(SiO4)6O2+3x/2 (-0,2<x<0,27), as electrolyte material for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC) and potentially Proton Conducting SOFC (PC-SOFC).Pure and dense oxyapatite pellets and membranes were prepared from powders synthetized by solid-state reaction and shaped by isostatic pressing or tape-casting process and thermocompression, then sintered at 1550�C. The electrochemical properties of the samples were characterized by complex impedance spectroscopy and O2 and H2 semi-permeation. La2SiO5 et La2Si2O7 phases, which may appear during the oxyapatite synthesis, were prepared following a similar process, in order to study their electrochemical properties. Theses phases were also used in an experiment whose purpose was to elaborate highly c-axis-oriented apatite-type lanthanum silicate polycrystals by combined use of tape casting and reactive diffusion between La2SiO5 and La2Si2O7.In order to study the protonation process of oxyapatite, tests were performed in autoclave with water at 550�C and 50 bars. Thermogravimetric analyses enabled to locate (surface/bulk) and to make a semi-quantitative analysis of inserted protonic species. The longer the protonation time and the higher the oxygen stoichiometry are, the greater the mass loss is. Moreover, structural studies by X ray diffraction and Raman spectroscopy revealed that the cell volume was increased and the channels of the structure enlarged, while the symmetry was modified and the disorder increased inside them. Thus, it appears that the protonic species insertion in oxyapatite takes place preferentially inside the channels of the structure.

Ce travail de thèse est porté sur l’étude des interactions protéines-protéines, protéines-peptides ainsi que la stabilité des protéines en faisant appel à la spectroscopie Raman et infrarouge. Dans la première partie, nous nous sommes focalisés sur l’étude de l’interaction entre les différentes protéines d’adrénodoxine et d’adrénodoxine réductase afin d’apporter de nouvelles données pour compléter la compréhension du mécanisme d’échange électronique. Le deuxième objectif à atteindre dans le cadre de ce travail est de suivre les changements conformationnels au niveau de la structure secondaire et tertiaire qui se produisent en présence et en absence des peptides lors de la formation des complexes. Enfin, la dernière partie est dédiée dans un premier temps à une étude comparative de la stabilité des hémocyanines de Limulus polyphemus et Eurypelma californicum issue de deux organismes ayant des conditions de vie différentes en suivant l’effet de la température (294-20 K) et du pH sur la structure secondaire des protéines. Dans un deuxième temps l’étude porte sur l’influence de la teneur en oxygène sur la structure secondaire et sur le site actif des hemocyanines de Limulus polyphemus, Eurypelma californicum et Astacus leptodactylus. / This thesis is focused on the study of protein-protein and protein-peptide interactions as well as the study of proteins stability by means of Raman and infrared spectroscopies. In the first part, we focused on the interactions between different adrenodoxin and adrenodoxin reductase proteins in order to get a better understanding of the electron transfer mechanism. The second part of the thesis concerns the changes in the secondary and tertiary structure of PDZ domains in the presence and absence of peptides during complex formation. The last part is dedicated to a comparative study of hemocyanins originated from organisms living in vastly different conditions such as Limulus polyphemus and Eurypelma californicum. This part of the project concerns the effect of temperature (294-20 K) and pH on the secondary structure of proteins. Finally the influence of oxygen binding on the secondary structure and the active site of Limulus polyphemus, Eurypelma californicum and Astacus leptodactylus was investigated.

Le développement des nano et biotechnologies pousse à la recherche de techniques de caractérisation adaptées à l’étude des systèmes nanostructurés. La spectrométrie Raman exaltée de surface (SERS) est une technique d’analyse en plein essor dans ce domaine.Dans ce travail de thèse nous nous sommes attachés à étudier, par cette technique, différents types de systèmes nanostructurés : des biomolécules et des films minces inorganiques. Le but était d’accéder à des informations sur la structure et les liaisons chimiques présentes dans ces systèmes. L’étude a été complétée par des observations par microscopie électronique en transmission notamment.Dans un premier temps, a été réalisée l’étude de molécules d’intérêt biologique. L’objectif était la compréhension des modes d’interaction nanoparticules métalliques/protéines menée sur des nanoparticules d’argent bio-conjuguées avec des protéines depuis leur synthèse jusqu’à leur caractérisation. Les résultats ont montré la chimisorption des protéines à la surface de nanoparticules d'argent possiblement par leurs terminaisons azotées. La technique SERS a également été expérimentée dans le domaine des basses fréquences pour caractériser la structure de dépôts minces de caféine, molécule d’intérêt pharmaceutique.Dans un second temps, l’étude de couches minces nanostructurées par spectrométrie Raman et SERS a été réalisée. Des couches minces nanocomposites TiO2:Au, ont été étudiées pour décrire les premières étapes de croissance des nanoparticules sous l’effet de la température dans ces matériaux. Des films ultraminces de TiO2 d’épaisseur contrôlée ont été déposés sur substrats fonctionnalisés avec des nanoparticules d’or pour étudier leur exaltation par effet SERS. / This work addressed the study of several kinds of nanostructured systems, biomolecules and inorganic thin films, mainly by Surface Enhanced Raman Spectroscopy (SERS). The aim was to investigate the structure and the chemical bonds. Transmission electron microscopy (TEM) was also used to complete the structural characterization of the different samples.Firstly, the study was conducted on molecules of biological interest. The aim was to study the interaction between silver nanoparticles and proteins. With this aim, silver nanoparticles bioconjugated with different proteins (hemoglobin, cytochrome C, BSA and lysozim) were synthesized. SERS results allowed concluding that proteins are chemisorbed on the silver nanoparticules surface. SERS was also used in the low frequency range to characterize the structure of thin deposits of caffeine, a molecule of pharmaceutical interest.Raman spectroscopy and SERS were also used to study nanostructured TiO2:Au thin films. The first stages of the growth of gold nanoparticles in Au doped TiO2 thin films under annealing treatments were studied by low frequency Raman spectroscopy and TEM. Finally, it was shown that SERS effect can be used for the characterization of ultra-thin TiO2 films. With this aim, ultra-thin TiO2 films were deposited by Atomic Layer Deposition on Si substrates functionalized with gold nanoparticles and studied by SERS.

[pt] Nesta tese descrevemos a preparação de grafeno, puro e dopado com boro, de camadas simples como também a produção de duas ou mais camadas de grafeno. O processo de transferência para outros substratos é discutido objetivando aplicações futuras. Descrevemos também a caracterização morfológica utilizando a microscopia eletrônica de varredura por emissão de campo (FESEM). Espectroscopia Raman e por fotoelétrons induzidas por raios x (XPS) foram utilizadas para detectar e quantificar a dopagem com boro em amostras crescidas sobre substratos de cobre e transferidas para substratos de quartzo. Os resultados indicaram que a temperatura, pressão e tempo de crescimento são de fundamental importância para a síntese de grafeno, tendo sido realizado um estudo para formação a diferentes temperaturas, pressões e tempos de crescimento. Análises por XPS e por Raman indicaram que a maioria das amostras foram dopadas com boro de forma substitucional, apresentando também outros tipos de ambientes químicos na amostra, além das bandas G e 2D terem se deslocado para vermelho, que é um indicativo de dopagem. / [en] This thesis describes the preparation of pure and boron doped single layer graphene but, also graphene of two or more layers. The process of transfer to other substrates is discussed aiming future applications. We also describe the morphological characterization using field emission scanning electron microscopy (FESEM). Raman spectroscopy and x-ray induced photoelectron spectroscopy (XPS) were used to detect and quantify the doping with boron in the samples grown on copper substrate and transferred onto quartz substrates. The results indicated that the temperature, pressure and time of growth are crucial for graphene synthesis and we conducted a study in order to test different synthesis conditions: temperatures, pressures and times of growth. Analysis by XPS and Raman spectroscopy indicated that the majority of the samples were doped with boron in a substitution manner, also presenting other types of chemical environments in the sample in addition to the G and 2D bands had shifted to red, which is indicative of doping.

Extensive research has been performed on the interaction of dithiocarbonates (xanthate) with a wide variety of substrates. This study the focuses on the interaction of trithiocarbonates (TTC) with pyrite and copper. The mechanism of adsorption of the xanthate is compared to that of the TTC. For the xanthate to adsorb it is necessary for an oxidant to be present, since xanthate adsorbs via charge transfer processes (electrochemical processes). It was found by the use of cyclic voltammetry and contact angle measurements that collector adsorption of the TTC can occur in both oxidising and reducing (thus the absence of an oxidant) conditions. Neither the TTC monomer nor the dimer could be detected on the surface by the use of Raman spectroscopy. The collector species on the surface was the TTC decomposition products namely the thiol or thiolate. Electrochemical impedance spectroscopy (EIS) confirmed that the TTC can interact under oxidising and reducing conditions. EIS showed that the rate of adsorption of the collector species for anodic currents increases relatively to the rate of adsorption for cathodic currents. Different adsorption mechanisms are realised for the different polarisation conditions. It is postulated that the TTC species serves as an intermediate for the adsorption of the thiol or thiolate on the surface, ultimately rendering the surface hydrophobic. Decomposition tests, performed by employing UV/Vis spectroscopy, indicated that the TTC is very unstable between a pH of 4 and 11. The thiol or thiolate however does not readily adsorb onto the substrates (indicated by the EIS measurements). Microflotation tests confirmed the thiolate’s inability to render pyrite hydrophobic. The microflotation tests also indicated that the TTC became less effective in recovering pyrite after it was left to decompose for a couple of hours. / Dissertation (MSc (Metallurgy))--University of Pretoria, 2008. / Materials Science and Metallurgical Engineering / unrestricted

Landlebende Pflanzen weisen differenzierte Gewebetypen auf, die neben der Aufrechterhaltung physiologischer Stoffwechselvorgänge äußeren mechanischen Belastungen standhalten müssen. Durch zweckmäßige Verteilung von Festigkeitsgeweben über den Sprossquerschnitt erlangen Pflanzen die notwendigen Versteifungen und Stabilitäten. Zur ortsaufgelösten Darstellung der unterschiedlichen Pflanzengewebe wird auf die Methode der Ramanspektroskopie zurückgegriffen. Dazu werden valide ramanspektroskopische Methoden entwickelt, die die Bestimmung der Cellulosekristallinität sowie die Quantifizierung des Lignins und der Hemicellulosen zum Ziel haben. Am Beispiel eines Pflanzenquerschnittes des Gemeinen Flachs Linum usitassimum werden die spektroskopischen Methoden angewandt und die Verteilung der unterschiedlichen Gewebetypen aufgezeigt und diskutiert.

Les travaux ont pour objectif de trouver des catalyseurs capables de remplacer les organo-étains pour la réticulation de matériaux adhésifs. La stratégie employée au laboratoire exploite des outils de la chimie en parallèle afin d’en tester un grand nombre pour accéder plus rapidement à la découverte de systèmes catalytiques performants. / The aim of this work is to discover new catalytic systems to replace organotin compounds. The strategy used on our laboratory exploits tools of high throughput experiments to test a large number of catalysts in the same time in order to discover new catalytic systems more quickly.

This thesis is divided into two parts; the first part presents results on the effect of the flow of fluids and electrochemical bias on single walled carbon nanotubes (SWNT). Issues pertaining to the entry of water into the cylindrical pores of the SWNT and its freezing dynamics have also been addressed in the first part of the thesis. The second part of the thesis deals with Raman scattering studies of iron perovskite namely CaFeO3 and La0.33Sr0.67FeO3 across their charge-disproportionation transition temperatures. PART 1 Chapter 1: Introduction This chapter presents an overview of the systems studied in this thesis, i.e., (i) SWNT and (ii) iron perovskite’s containing iron in Fe4+(d4) state, namely CaFeO3 and La0.33Sr0.67FeO3. It also contains an introduction to the two spectroscopic techniques used in the present thesis, namely Raman scattering and Nuclear Magnetic Resonance. A quantum mechanical picture of Raman scattering, in general, and resonance Raman scattering in particular along with a brief introduction to the apparatus used both for the micro Raman and the low temperature experiments is presented in this chapter. A general introduction to Nuclear Magnetic Resonance (NMR) is also given with an emphasis on various interactions leading to the broadening of the NMR absorption linewidths. Chapter 2: Carbon nanotube liquid flow sensors This chapter presents experimental results and theoretical understandings of the generation of electrical signals by flowing polar/ionic liquids over a mat of SWNT. We first present experimental findings that the flow of a variety of liquids on SWNT bundles induces an electrical signal (voltage/current) in the sample along the direction of the flow. The electrical response is found to be a logarithmic function of the flow speed over a wide range. The magnitude of the signal generated depends sensitively on the ionic conductivity and the polar nature of the liquid and weakly on the viscosity of the liquid. Furthermore its direction can be controlled by electrochemical biasing of the nanotubes. The ratio of the open circuit voltage to the short circuit current is found to be governed by the nanotube resistance. These experimental findings are inconsistent with the conventional idea of a streaming potential as the possible cause. Our measurements suggest that the dominant mechanism responsible for this highly sub-linear response should involve a direct forcing of the free charge carriers in the nanotubes by the fluctuating Coulombic field of the liquid flowing past it. Two alternative understandings of the experimental findings are also presented in this chapter. The first mechanism invokes the idea of a “pulsating ratchet” whereby the charge carriers in the nanotubes experience an asymmetric spatial bias because of the shear-induced deformation of the ion-plus-polar atmosphere at the liquid-solid interface temporally modulated by the liquid flow. In addition, we also propose that experimental findings can be understood qualitatively in terms of three interrelated ideas: (a) Induced friction: The fluctuating charge density of the ions close to the nanotube couples coulombically to the charge carriers in the nanotube and, therefore, offers a friction to the motion of these charge carriers (in addition to the Ohmic friction intrinsic to the carbon nanotubes); (b) Flow-induced drag: In virtue of the above frictional coupling, an imposed liquid flow drags the charge carriers along through the nanotube; (c) Reduction of induced friction at high flow speeds: The space-time correlated Coulombic fluctuations, inherent to the liquid electrolyte, are advected by the liquid flow, and thus get Galilean boosted (Doppler shifted) as seen in the mean rest frame of the drifting carriers in the nanotube. This would cause a reduction of the frictional grip to the motion of the charge carriers in the nanotube with increasing flow speed resulting in a sublinear dependence of the charge drift-velocity (electrical response) on the liquid flow speed. With the above in mind, a quantitative derivation of these frictional effects, first from a heuristic argument, and then analytically from a Langevin-equation treatment have been presented. Chapter 3: Direct generation of voltage and current by gas flow over carbon nanotubes and semiconductors Having obtained experimental evidence of the generation of liquid flow induced electrical signals over single-walled carbon nanotubes, it was only natural to look for the same effect by flowing gases over nanotubes. We show here a direct generation of measurable voltages and currents when gas flows at modest speeds of a few meters per second over single-walled carbon nanotubes . Interestingly, unlike the previous effect (generation of voltages by flow of liquids over single-walled carbon nanotubes), this effect is not specific to single-walled carbon nanotubes and occurs for a wide variety of solids, including single and multi-walled carbon nanotubes, doped semiconductors and metals. Moreover, the gas flow induced signals depend quadratically on the gas flow velocities. This is in sharp contrast to the results obtained by flowing liquids over single-walled carbon nanotubes where the liquid flow generated signal was found to be logarithmically dependent on the flow velocities. In this chapter we provide evidence that the underlying mechanism for the gas flow generated electrical signal is an interplay of Bernoulli’s principle and the Seebeck effect: Pressure difference along streamlines gives rise to temperature difference across the sample which, in turn, produces the measured voltage. Chapter 4: Water at nanoscale confined in single-walled carbon nanotubes studied by NMR In this chapter, we seek experimental evidence of the occupancy of water in the cylindrical pores of the nanotubes. Proton NMR studies have been carried out as a function of temperature from 210 K to 300 K of water confined within SWNT. The NMR lineshape at and below the freezing point of bulk water is asymmetric which can be decomposed into a sum of two Lorentzians. The intensities of both the components decrease with lowering of temperature below 273 K, one component L1 vanishing below 242 K and the other component L2 below 217 K. Following the simulations of Koga et al. (Nature, 412, 802, 2001) showing that the radial density profile of confined water in SWNT has a distribution peak at the center which disappears below the freezing temperature, the L1 component is associated with the protons of the water molecules at the center and the L2 component is associated with protons of water molecules associated at a distance ~ 3Å away from the walls of the nanotubes. In this scenario the complete freezing of the water at ~ 212 K is preceded by the withdrawal of the water molecules from the center of the nanotubes. Chapter 5: Electrochemical tuning of band structure of single walled carbon nanotubes probed by in-situ resonance Raman scattering The work presented in this chapter is motivated by the experimental observation that SWNT have excellent actuating properties, i.e, porous sheets of carbon nanotubes were shown to suffer length changes when subjected to electrochemical bias, with action observed up to 1 KHz. The fast response of the nanotube actuator rules out any mechanism related to the intercalation of ions as is applicable to the case of the polymer actuators. This chapter presents results of in-situ resonance Raman scattering of SWNT investigated under electrochemical biasing. The experimental results show that the intensity of the radial breathing mode varies significantly in a non-monotonic manner as a function of the cathodic bias voltage, but does not change appreciably under anodic bias. The tangential mode is, however, not affected. These results can be quantitatively understood in terms of the changes in the energy gaps between the one-dimensional van Hove singularities in the electron density of states arising possibly due to the alterations in the overlap integral of π-bonds between the p-orbitals of adjacent carbon atoms. This chapter also contains results from ab-initio restricted Hartree Fock calculations in a simplistic geometry where a nanotube is surrounded by two concentric rings of ions. The ab-initio calculation results suggest that the dominant contribution to the strain developed in the nanotubes originates from the electrostatic interactions between the ions and the delocalized π electrons as compared to the doping effects. PART 2 Chapter 6: Raman scattering in CaFeO3 and La0.33Sr0.67FeO3 across the charge disproportionation phase transition Temperature dependent micro-Raman studies of orthorhombic CaFeO3 and rhombohedral La0.33Sr0.67FeO3 were carried out with an aim to study the role of phonons in the formation of the charge disproportioned state (Fe4+ → Fe5++Fe3+) below the transition temperature (Tco) of 290 K and 200 K, respectively. Shell model lattice dynamics calculations were performed for CaFeO3 to assign the Raman modes and determine their vibrational pattern. Temperature dependence of the peak positions and peak widths of various modes for both the systems show distinct changes across their respective transition temperatures. In CaFeO3 the symmetric stretching mode at 707 cm−1 splits into two modes, 707 cm−1 and 684 cm−1 . Interestingly, the 707 (684) cm−1 mode appears only in HH(HV) polarization. In comparison, the Raman band at 704 cm−1 in La0.33Sr0.67FeO3 which has been assigned to the Raman forbidden symmetric stretching mode, disappears below Tco. In addition, two modes at 307 cm−1 and 380 cm−1 of La0.33Sr0.67FeO3 approach each other at Tco. Our experiments show that for both the systems, CaFeO3 and La0.33Sr0.67FeO3, the lattice distortion changes across Tco. Chapter 7: Summary and future outlook The last chapter summarizes our main findings reported in the thesis. It also contains possible future studies which are worth pursuing to add further insights in the issues addressed.