This study presents results on the use of ellipsometry as a novel probe for thin films of a diblock copolymer. Ellipsometry makes use of the change in polarisation induced upon reflection of light from a film covered substrate to enable calculation of the refractive index and thickness of the film. The infom1ation obtained in these measurements can be compared to differential scanning calorimetry, with the additional advantages that small sample volumes and slow cooling rates can be employed, and expansion coefficients can be determined. The work is presented in two parts; first crystallisation within the phase-separated domains is studied, then a morphological transition in the diblock ordering is characterised. By studying the temperature dependence of the film thickness and refractive index, crystallisation kinetics within very small volumes( 10^-10 L) of a poly (butadiene-b-ethylene oxide) diblock copolymer are measured. Through a comparison of two different PEO block lengths, a reduction in both the crystallisation and melting temperatures is demonstrated as the domain volume is decreased. Upon cooling, an additional transition is observed. We ascribe this to a morphological transition from a layer of ordered spheres to a lamellar layer at the substrate, which is consistent with a comparison between the data and simulated ellipsometry data. The sensitivity of ellipsometry makes it a well suited and versatile technique for probing thin film kinetics in diblock copolymers. / Thesis / Bachelor of Science (BSc)

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In recent years, the ferroelectric oxides belonging to the family of layered perovskite, e.g., SrBi₂(Ta₁₋_xNb_x)₂O₉ (or SBTN), were identified as promising candidates for nonvolatile memory applications. SrBi₂Ta₂O₉ (or SBT) thin films were found to exhibit no fatigue up to 10¹² switching cycles, very good retention properties and low leakage current densities on Pt electrodes. However, high temperature processing, ie. 750 - 800°C, is needed for SBT to exhibit ferroelectric properties. Moreover, the fundamental properties of SBTN have not been fully characterized. In this research, SBTN solid solutions were studied from two aspects: the technical aspect and scientific aspect. From the technical point of view, low temperature processing of SBTN ferroelectric thin films was developed. In this part of study, SBTN thin films were made by metalorganic decomposition method (MOD) and were deposited on Pt-electrodes. The structure development study by a non-destructive optical method, spectroscopic ellipsometry, was proposed to determine nucleation and grain growth temperatures. The information on structure development can be obtained by observing how the refractive indices and film thicknesses change as functions of annealing temperature. The results of structure development study for SBT thin films suggest that the ferroelectric properties are controlled by grain growth process rather than nucleation process. The critical factor for ferroelectric properties was to have grain size exceeding a critical value, i.e., 0.1 µm. Applying this concept, low temperature processing can be achieved by growing larger grains at lower temperature. The processing temperature of SBTN thin films was reduced by 50 - 100°C by adding excess Bi or increasing Nb/Ta ratio. The optimum excess Bi content in SBT was 30 - 50%; within this range, limited solid solution of Bi₂O₃ and SBT was formed. From the scientific aspect of view, optical properties and ionic transport phenomena of SBTN bulk ceramics were investigated for the first time. The reason of using bulk ceramics is to exclude the difficulties associated with thin film technology, e.g., grain size effect and electrode-ferroelectric interface effect. These bulk property studies provide fundamental understanding of SBTN materials and provide a guideline for process development in device applications. The optical dispersion functions of bulk SBTN were obtained by using various angle spectroscopic ellipsometry with a surface layer correction. The values of refractive indices were found to vary with composition, which are possibly associated with crystallographic orientation. Using the Lorentz Oscillator model, the approximate energy band gaps of SBTN solid solutions were estimated to be about 5 eV. The ionic transport phenomena of SBT and SrBi₂Nb₂O₉ (or SBN) were investigated by using impedance spectroscopy. This technique allows to separate the effect of ion transport in grain, grain boundary and electrode-ferroelectric interface. In this study, the fatigue model of bismuth layered oxides was discussed through ionic conductivity and interface absorption effect. One conducting species, oxygen vacancies with positive charges, was assumed in the model. High ionic conductivities of SBT and SBN (~ 10¯⁷ S/cm) comparing to Pb(Zr₁₋_xTi_x)O₃ (~ 10¯¹¹-10¯¹⁰ S/cm) suggests high defect concentration and high charge mobility in bismuth layered oxide materials. As a result, the most possible model to explain high resistance to fatigue of SBT/SBN was the easy recovery of oxygen vacancies from the entrapment at electrode-ferroelectric interfaces. / Ph. D.

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The advancement of photonics technologies depends on synthesis of novel materials and processes for device fabrication. The characterization techniques of the optical, electrical and magnetic properties of the synthesized materials and devices, by non-contact, non-invasive and nondestructive methods plays a significant role in development of new photonics technologies. The research reported in this thesis focuses on two such aspects of photonic materials characterization: Magneto-Optic characterization and Spectroscopic Ellipsometry. The theoretical and experimental basis of these two techniques, and experimental data analysis are presented in two parts. In Part 1, the changes in magneto-optic parameters of FePT PS-P2VP block copolymer nanocomposites with increasing concentrations of FePt nanoparticles in the block copolymer are analyzed. We present the results of change in MO anisotropy factor with the wt% of FePt and try to analyze these changes with further experimentation. Part 2 presents the results of spectroscopic ellipsometry of group III-IV multilayered thin film materials to give their precise thicknesses and optical constants. Both these techniques are unique ways to understand novel material characteristics for future use in device development.

L’objectif de ce travail est l’étude et la modélisation d’un capteur de gaz à base d’oxyde métallique semiconducteur de type p (cas de CuO). Pour cela, des couches minces de CuO ont été élaborées dans l‘équipe microcapteurs de IM2NP à partir de deux techniques différentes : la pulvérisation cathodique réactive magnétron radio-fréquence et l’oxydation thermique des couches minces de cuivre déposées par évaporation thermique sous vide. Différentes techniques de caractérisation ont été mises en oeuvre pour évaluer les propriétés des couches minces obtenues en vue de les optimiser pour l’application capteur. La microscopie à force atomique (AFM) et la microscopie électronique à balayage (MEB) ont révélé une nanostructure homogène dont la morphologie présente la porosité désirée. Les analyses par diffraction de rayons X (DRX) ont montré que ces couches minces présentent une monophase de CuO avec une orientation préférentielle (111), les études optiques par ellipsométrie dans le domaine visible ont permis d’estimer les pourcentages de porosité dans chaque couche. Ces couches possèdent la cristallinité et la pureté requises pour l'utilisation en capteurs de gaz. Les performances de ces couches minces de CuO ont été évaluées pour la détection de l’ozone et de l’éthanol. Sur la base de ces résultats, un modèle dynamique a été développé simulant la réaction entre les espèces oxygénées ionisées adsorbées à la surface d'un semiconducteur de type p avec un gaz, qui permet d’évaluer l’influence des paramètres de fonctionnement (Température de fonctionnement, pression d’oxygène et concentration de gaz). / The objective of this work is to study and model a gas sensor based on a p-type metal oxide semiconductor (case of CuO). For this, thin layers of CuO have been developed in the microsensor team at the IM2NP laboratory from two different techniques: radio frequency reactive magnetron sputtering and thermal oxidation of thin copper films deposited by thermal evaporation under vacuum. Different characterization techniques have been implemented to evaluate the properties of the thin films obtained in order to optimize them for sensor applications. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed a homogeneous nanostructured morphology which has the desired porosity. Diffraction analysis (XRD) showed that these thin films have a single phase of CuO with a preferred orientation (111). Optical studies by ellipsometry in the visible spectral region were used to estimate the percentage of porosity in each layer. These layers have the crystallinity and purity required for use in gas sensors. The performances of these thin layers of CuO were evaluated for the detection of ozone and ethanol. Based on these results, a dynamic model was developed to simulate the reaction between the ionized oxygen species adsorbed on the surface of a p-type semiconductor with a gas, which is used to evaluate the influence of operating parameters (working temperature, oxygen concentration and gas pressure).