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.

L’objectif de cette étude était de développer une nouvelle génération de catalyseurs, dits électrochimiques, capables d’abaisser la température de régénération des filtres à particules, et de diminuer les coûts du post-traitement des moteurs Diesel, en évitant notamment une surconsommation en carburant. Pour cela, un banc de mesure a été développé où de forts moyens analytiques pour les phases gazeuses (GC et analyseur de NOx), particulaires (spectromètre de masse à aérosols AMS) et de caractérisations physiques des aérosols (SMPS, Scanning Mobility Particle Sizer) ont été couplés. Le catalyseur électrochimique développé est composé d’un catalyseur oxyde de type pérovskite La0.5Sr0.23Ag0.27MnO3±δ (noté LSAM), en contact avec un électrolyte solide conducteur par les ions O2-, la zircone dopée à l’oxyde d’yttrium (YSZ). L’enduction de ce catalyseur électrochimique directement dans les canaux d’un filtre à particule (FAP) en céramique (SiC) a montré des performances permettant d’abaisser la température de régénération des FAP de 100°C voire de 260°C selon le flux de régénération. Ces performances sont le résultat d’un effet de synergie entre les phases de la pérovskite LSAM et du conducteur ionique YSZ / The aim of this study was to develop a new generation of catalysts, called electrochemical, which can lower the regeneration temperature of the particulate filter, and reduce post-treatment costs of Diesel engines, especially avoiding over-consumption of fuel. For this, a test bench has been developed where strong analytical analyzer for gas phases (GC and Nox analyzer), for particles (aerosol mass spectrometer AMS) and for physical characterization of aerosols (SMPS, Scanning Mobility Particle Sizer) have been coupled. The electrochemical catalyst developed is composed of a perovskite catalyst La0.5Sr0.23Ag0.27MnO3±δ (denoted LSAM), in contact with a solid electrolyte conductor by O2-ions, yttria stabilised zirconia (YSZ). The coating of the electrochemical catalyst directly into the channels of a particulate filter (DPF) showed performance to lower the DPF regeneration temperature of 100°C or even 260°C depending of the regeneration flow. These performances are the result of a synergistic effect between the phases of the perovskite LSAM and YSZ ionic conductor

This diploma thesis is focused on preparation of perovskite methylammonium lead bromide thin film layers and also thin film layers of its precursors, namely methylammonium bromide and lead(II) bromide, by spin-coating from the solution; and optical characterisation of the prepared thin film layers by UV-VIS spectroscopy and spectroscopical ellipsometry. Methylammonium bromide does not absorb in visible nor ultraviolet region, the maximum absorption of lead(II) bromide occurred in ultraviolet region, methylammonium lead bromide absorbs in visible region. Optical band gaps were determined by Tauc method to (3,5 ± 0,1) eV for lead(II) bromide and 2,15 eV, respectively 2,25 eV for perovskite. Refractive indices and extinction coefficients were determined by ellipsometry in range of wavelengths from 290 nm to 830 nm and their dependence with layer thickness was discussed. Ellipsometry model used in this thesis consist on Tauc-Lorentz oscillators for methylammonium bromide, methylammonium lead bromide and partially for lead(II) bromide, which another part is formed by New Amorphous oscillator.

This thesis is focused on the study of the detection of electromagnetic radiation using monocrystalline perovskites. Theoretical part deals with basic principles of detections and possible applications of hybrid perovskite crystals in the field of ultraviolet and visible spectrum detection. Parameters of the recently published perovskite photodetectors are also presented. Experimental part describes synthesis, structural and optical properties of MAPbBr3 single crystals and electrical characterization of the Au/MAPbBr3/Au photodetector. Photodetector parameters (responsivity, external quantum efficiency and specific detectivity) are calculated based on the spectral and switching (on/off) current responses.

Synthesis and bulk analysis of composite ceramic oxide materials and materials with perovskite-defect structure is presented within this work. Syntheses of these advanced ceramics materials were carroed out by using of nonconventional techniques (microwave-assisted hydrothermal synthesis and polycondensation techniques) and by conventional mechanochemical activation followed by high temperature solid state reaction. X-Ray difraction (XRD), Rietveld analysis, scaning microscopy (SEM), microalysis EDS-SEM, thermal analysis (TG), infrared spectroscopy (IR), determination of particles size and specific surface area were used for description of synthesized products. In case of perovskite system based on La-Sr-Fe-Ti-O electrochemical properties were studied. Part of work was focused on chemical analysis of synthesized composite oxide materials and decomposition hard structured products by using of nonconventional fields.

Indiana University-Purdue University Indianapolis (IUPUI) / The field of two-dimensional (2D) nanomaterials first began in earnest with the discovery of graphene in 2004 due to their unique shape-dependent optical, electronic, and mechanical properties. These properties arise due to their one-dimensional confinement and are further influenced by the elemental composition of the inorganic crystal lattice. There has been an intense focus on developing new compositions of 2D nanomaterials to take advantage of their intrinsic beneficial properties in a variety of applications including catalysis, energy storage and harvesting, sensing, and polymer nanocomposites. However, compared to the field of bulk materials, the influence of surface chemistry on 2D nanomaterials is still underdeveloped. 2D nanomaterials are considered an “all-surface” atomic structure with heights of a single to few layers of atoms. The synthetic methods used to produce 2D materials include bottom-up colloidal methods and top-down exfoliation related techniques. Both cases result in poorly controlled surface chemistry with many undercoordinated surface atoms and/or undesirable molecules bound to the surface. Considering the importance surfaces play in most applications (i.e., catalysis and polymer processing) it is imperative to better understand how to manipulate the surface of 2D nanomaterials to unlock their full technological potential. Through a focus of the ligand-surface atom bonding in addition to the overall ligand structure we highlight the ability to direct morphological outcomes in lead free halide perovskites, maximize optoelectronic responses in substoichiometric tungsten oxide, and alter physicochemical properties titanium carbide MXenes. The careful control of precursor materials including poly(ethylene glycol) (PEG) surface ligands during the synthesis of bismuth halide perovskites resulted in the formation of 2D quasi-Ruddlesden-Popper phase nanomaterials. Through small angle X-ray scattering (SAXS) and in conjunction with X-ray photoelectron spectroscopy (XPS) we were able to conclude that an in-situ formation of an amino functional group on our PEG-amine ligand was inserted into the perovskite crystal lattice enabling 2D morphology formation. Additionally, through UV-vis absorption and ultraviolet photoelectron spectroscopies we were able to develop a complete electronic band structure of materials containing varying halides (i.e., Cl, Br, and I). Furthermore, through the increased solubility profile of the PEG ligands we observed solvent controlled assemblies of varying mesostructures. We developed an ex-situ ligand treatment to manipulate the localized surface plasmon resonance (LSPR) response of anion vacancy doped tungsten oxide (WO3-x) nanoplatelets (NPLs). Upon ligand treatment to alter the surface passivating ligand from carboxylic acid containing myristic acid (MA) to tetradecylphosphonic acid (TDPA) we observed a >100 nm blue shift in the LSPR response. Using Fourier transform infrared (FTIR) and Raman spectroscopies in conjunction with DFT calculated Raman spectra we were able to conclude this shift was due to the formation of tridentate phosphonate bonds on the NPLs surface. Phosphonate bonding allows for an increase in surface passivation per ligand decreasing surface trapped electrons. These previously trapped electrons were then able to participate as free electrons in the LSPR response. Electron paramagnetic spectroscopy (EPR) further supported this decrease in surface traps through a decrease and shift of the EPR signal related to metal oxide surface trapped electrons. Lastly, using our knowledge of PEG ligands we were able to modify esterification chemistry to covalently attach PEG ligands to a MXene surface. The successful formation of an ester bond between a carboxylic acid containing PEG ligand and hydroxyl terminating group on the MXene surface was supported by FTIR spectroscopy and thermogravimetric analysis. The attachment of PEG resulted in a drastic change in the hydrophilicity of the MXene surface. Where MXenes were previously only processed in extremely polar solvents the PEG attachment allowed for high dispersibility in a wide range of polar and non-polar organic solvents, effectively increasing their processability. Further, this chemistry was modified to include an additional functional group on the PEG ligand to increase the valency of the post-modification MXene nanoflakes. Overall, work presented in this dissertation represents the development and application of surface chemistry to relatively new 2D nanomaterials. We believe our work significantly increases the knowledge of 2D halide perovskite formation, manipulation of LSPR active metal oxide materials, and the future processing of MXene materials.

In order to study the electronic and optical properties of complex materials an approach providing a reliable estimate of band gaps in combination with the reasonable description of the ground state is required. In the present study of pure and defective perovskite crystals, the fulfillment of such requirements is clearly demonstrated using a simple hybrid HF/DFT scheme containing an admixture of non-local Fock exchange. In present theoretical investigations, a wide class of perovskite oxides is represented by three, the most attractive (from a scientific point of view) crystals of SrTiO3, BaTiO3, and PbTiO3 in their high symmetry cubic phases. These perovskite crystals present a great technological and fundamental interest due to their numerous applications related to ferroelectricity, non-linear and electro-optics, superconductivity, and catalysis. Although the above-mentioned perovskite-type materials have been intensively investigated theoretically and experimentally at least in the last fifteen years, a proper description of their electronic properties is still an area of active research. In order to make a contribution to the explanation of various electro-optical effects observed in perovskite materials, their ground-state properties have been calculated from first principles and analyzed in the present study.

Les composés pérovskites halogénés AMX3 (A+ est un cation organique ou inorganique monovalent : Cs+, méthylammonium [CH3NH3]+ (MA) ; M2+ un cation métallique bivalent comme le Pb2+ et X un anion halogénure I-, Br- ou Cl-) possèdent des propriétés remarquables pour les absorbeurs des cellules photovoltaïques. La structure pérovskite offre la possibilité de moduler facilement les propriétés des matériaux en modifiant leur composition chimique : leur largeur de bande interdite peut être ajustée en variant la nature de l’halogène. Les travaux menés au sein de cette thèse portent sur l'élaboration et la caractérisation approfondie de matériaux pérovskites halogénés mixtes – c'est-à-dire avec un mélange d’ions sur les sites A, M ou X – de faibles dimensions tels que les couches minces et les nanocristaux.Un protocole de fabrication de cellules pérovskites de référence avec les absorbeurs CH3NH3PbI3 et CH3NH3PbI3-xClx et un rendement dépassant 10 % a été établi. Ceci a permis de fabriquer des couches minces pérovskites avec une épaisseur contrôlée et de manière reproductible sur différents substrats de TiO2 (compact, mésoporeux ou monocristallin). L’étude de ces couches par diffraction des rayons X au laboratoire et au synchrotron a mis en évidence une orientation préférentielle (001) des cristallites pour CH3NH3PbI3-xClx quel que soit le type de substrats de TiO2. En utilisant un substrat TiO2 monocristallin nous démontrons pour la première fois que le degré d’orientation et la taille des grains sont fortement augmentés (taux de couverture de surface 80%) par rapport aux substrats contenant du TiO2 mésoporeux ou une couche compacte polycristalline. La présence du chlore à l’interface TiO2–pérovskite et la faible rugosité du substrat sont des facteurs clés favorisant la croissance de cristallites orientés.Dans la deuxième partie de la thèse, l’influence de la substitution partielle du Pb2+ par des cations métalliques homovalents non toxiques (alcalino-terreux et métaux de transitions 3d) sur la structure et les propriétés optiques des nanocristaux pérovskite hybrides et inorganiques a été étudiées. La morphologie et la taille des nanocristaux hybrides MAPb1-xMxBr3 synthétisés par méthode de reprécipitation est largement impactée malgré une faible substitution (x : maximum 6% avec Mg2+). Au contraire dans les nanocristaux inorganiques CsPb1-xMxX3, synthétisés par injection à chaud, jusqu’à 16% du Pb2+ peut être remplacé par du Mg2+ ou du Sr2+ en conservant leur taille, forme, structure, propriétés d’absorption et de photoluminescence. Pour un taux de substitution plus élevé (une valeur maximale de 22% a été atteinte), la formation de la structure Cs4PbX6 est favorisée. / Metal halide perovskites AMX3 (A+ is an organic or inorganic cation: Cs+ methylammonium [CH3NH3]+ (MA); M2+ is a metallic cation such as Pb2+ and X a halide anion I-, Br- or Cl-) have remarkable properties as solar cell absorbers. In the perovskite structural framework the properties of the materials can be easily tailored by modifying their chemical composition. Changing for example the halide anion modulates their band gap. This thesis deals with the synthesis and the advanced characterisation of mixed halide perovskite materials – i.e. with mixed ions on the same site A, M or X – of low dimensions such as thin films and nanocrystals.A fabrication protocol was developed for reference solar cells with CH3NH3PbI3 and CH3NH3PbI3-xClx absorbers yielding a power conversion efficiency over 10%. The perovskite thin films could be fabricated with a controlled thickness and a high reproducibility on different TiO2 substrates (compact, mesoporous or monocrystalline). The study of these thin films by laboratory and synchrotron X-ray diffraction showed that the CH3NH3PbI3-xClx crystallites exhibit a preferential (001) orientation on any kind of TiO2 substrate. By using monocristalline TiO2 substrates we showed for the first time that the degree of orientation and the grain size increased considerably (the surface coverage was determined to be 80%) compared to mesoporous and compact polycrystalline TiO2 substrates. The presence of chlorine at the TiO2–perovskite interface and the low surface roughness of the substrate are key factors, which promote the growth of highly oriented crystallites.In the second part of the thesis, the influence of the partial substitution of lead with non-toxic homovalent metal cations (alcaline earth, 3d transition metals) on the structural and optical properties of hybrid and inorganic perovskite nanocrystals was studied. The morphology and the size of MAPb1-xMxBr3 hybrid nanocrystals synthesised by reprecipitation is clearly affected despite the low substitution (x: maximum 6% with Mg2+). Conversely, in CsPb1-xMxX3 inorganic nanocrystals synthesised by hot injection, up to 16% of Pb2+ could be replaced by Mg2+ or Sr2+, while keeping their size, shape, structure, absorption and photoluminescence properties. With a higher substitution ratio (up to 22% was achieved), the formation of the Cs4PbX6 structure is favoured.

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