Mémoire par articles. / Ce mémoire contient trois articles reliés par l'idée sous-jacente d'une généralisation de la dualité de Schur-Weyl. L'objectif principal est d'obtenir une description algébrique du centralisateur de l'image de l'action diagonale de U_q(sl_2) dans le produit tensoriel de trois représentations irréductibles, lorsque q n'est pas une racine de l'unité. La relation entre une algèbre de Askey-Wilson étendue AW(3) et ce centralisateur est examinée à cet effet. Dans le premier article, les éléments du centralisateur de l'action de U_q(sl_2) dans son produit tensoriel triple sont définis à l'aide de la matrice R universelle de U_q(sl_2). Il est montré que ces éléments respectent les relations définissantes de AW(3). Dans le deuxième article, la matrice R universelle de la superalgèbre de Lie osp(1|2) est utilisée de manière similaire avec l'algèbre de Bannai-Ito BI(3). Dans ce cas, le formalisme de la matrice R permet de définir l'algèbre de Bannai-Ito de rang supérieur BI(n) comme le centralisateur de l'action de osp(1|2) dans son produit tensoriel n-fois. Le troisième article propose une conjecture qui établit un isomorphisme entre un quotient de AW(3) et le centralisateur de l'image de l'action diagonale de U_q(sl_2) dans le produit tensoriel de trois représentations irréductibles quelconques. La conjecture est prouvée pour plusieurs cas, et les algèbres de Temperley-Lieb, Birman-Murakami-Wenzl et Temperley-Lieb à une frontière sont retrouvées comme quotients de l'algèbre de Askey-Wilson. / This master thesis contains three articles related by the underlying idea of a generalization of the Schur-Weyl duality. The main objective is to obtain an algebraic description of the centralizer of the image of the diagonal action of U_q(sl_2) in the tensor product of three irreducible representations, when q is not a root of unity. The connection between a centrally extended Askey-Wilson algebra AW(3) and this centralizer is examined for this purpose. In the first article, the elements of the centralizer of the action of U_q(sl_2) in its threefold tensor product are defined with the help of the universal R-matrix of U_q(sl_2). These elements are shown to satisfy the defining relations of AW(3). In the second article, the universal R-matrix of the Lie superalgebra osp(1|2) is used in a similar fashion with the Bannai-Ito algebra BI(3). In this case, the formalism of the R-matrix allows to define the higher rank Bannai-Ito algebra BI(n) as the centralizer of the action of osp(1|2) in its n-fold tensor product. The third article proposes a conjecture that establishes an isomorphism between a quotient of AW(3) and the centralizer of the image of the diagonal action of U_q(sl_2) in the tensor product of any three irreducible representations. The conjecture is proved for several cases, and the Temperley-Lieb, Birman-Murakami-Wenzl and one-boundary Temperley-Lieb algebras are recovered as quotients of the Askey-Wilson algebra.

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Recently, there has been a growing interest in semiconductor and semiconducting oxide nanowires for applications in electronics, energy conversion, energy storage and optoelectronic devices such as field effect transistors, solar cells, Li- ion batteries, gas sensors, light emitting diodes, field emission displays etc. Semiconductor and semiconducting oxide nanowires have been synthesized widely by different vapor transport methods. However, conditions like high growth temperature, low vacuum, carrier gases for the growth of nanowires, limit the applicability of the processes for the growth of nanowires on a large scale for different applications. In this thesis work, studies have been made on the growth of semiconductor and semiconducting oxide nanowires at a relatively lower substrate temperature (< 500 °C), in a high vacuum (1× 10-5 mbar), without employing any carrier gas, by electron beam and resistive thermal evaporation processes. The morphology, microstructure, and composition of the nanowires have been investigated using analytical techniques such as SEM, EDX, XRD, XPS, and TEM. The optical properties of the films such as reflectance, transmittance in the UV-visible and near IR region were studied using a spectrophotometer. Germanium nanowires were grown at a relatively lower substrate temperature of 380-450 °C on Si substrates by electron beam evaporation (EBE) process using a Au-assisted Vapor-Liquid-Solid mechanism. High purity Ge was evaporated in a high vacuum of 1× 10-5 mbar, and gold catalyst coated substrates maintained at a temperature of 380-450 °C resulted in the growth of germanium nanowires via Au-catalyzed VLS growth. The influence of deposition parameters such as the growth temperature, Ge evaporation rate, growth duration, and gold catalyst layer thickness has been investigated. The structural, morphological and compositional studies have shown that the grown nanowires were single-crystalline in nature and free from impurities. The growth mechanism of Germanium nanowires by EBE has been discussed. Studies were also made on Silicon nanowire growth with Indium and Bismuth as catalysts by electron beam evaporation. For the first time, silicon nanowires were grown with alternative catalysts by the e-beam evaporation method. The use of alternative catalysts such as Indium and Bismuth results in the decrease of nanowire growth temperature compared to Au catalyzed Si nanowire growth. The doping of the silicon nanowires is possible with an alternative catalyst. The second part of the thesis concerns the growth of oxide semiconductors such as SnO2, Sn doped Indium oxide (ITO) nanowires by the electron beam evaporation method. For the first time, SnO2 nanowires were grown with a Au-assisted VLS mechanism by the electron beam evaporation method at a low substrate temperature of 450 °C. SEM, XRD, XPS, TEM, EDS studies on the grown nanowires showed that they were single crystalline in nature and free of impurities. The influence of deposition parameters such as the growth temperature, oxygen partial pressure, evaporation rate of Sn, and the growth duration has been investigated. Studies were also done on the application of SnO2 nanowire films for UV light detection. ITO nanowires were grown via a self-catalytic VLS growth mechanism by electron beam evaporation without the use of any catalyst at a low substrate temperature of 250-400 °C. The influence of deposition parameters such as the growth temperature, oxygen partial pressure, evaporation rate of ITO, and growth duration has been investigated. Preliminary studies have been done on the application of ITO nanowire films for transparent conducting coatings as well as for antireflection coatings. The final part of the work is on the Au-assisted and self catalytic growth of SnO2 and In2O3 nanowires on Si substrates by resistive thermal evaporation. For the first time, SnO2 nanowires were grown with a Au-assisted VLS mechanism by the resistive thermal evaporation method at a low substrate temperature of 450 °C. SEM, XRD, XPS, TEM, and EDS studies on the grown nanowires showed that they were single crystalline in nature and free of impurities. Studies were also made on the application of SnO2 nanowire films for methanol sensing. The self-catalytic growth of SnO2 and In2O3 nanowires were deposited in high vacuum (5×10-5 mbar) by thermal evaporation using a modified evaporation source and a substrate arrangement. With this arrangement, branched SnO2 and In2O3 nanowires were grown on a Si substrate. The influence of deposition parameters such as the applied current to the evaporation boat, and oxygen partial pressure has been investigated. The growth mechanism behind the formation of the branched nanowires as well as nanowires has been explained on the basis of a self-catalytic vapor-liquid-solid growth mechanism. The highlight of this thesis work is employing e-beam evaporation and resistive thermal evaporation methods for nanowire growth at low substrate temperatures of ~ 300-500 °C. The grown nanowires were tested for applications such as gas sensing, transparent conducting coatings, UV light detection and antireflection coating etc. The thesis is divided into nine chapters and each of its content is briefly described below. Chapter 1 In this chapter, a brief introduction is given on nanomaterials and their applications. This chapter also gives an overview of the different techniques and different growth mechanisms used for nanowires growth. A brief overview of the applications of semiconductors and semiconductor oxide nanowires synthesized is also presented. Chapter 2 Different experimental techniques employed for the growth of Si, Ge, SnO2, In2O3, ITO nanowires have been described in detail in this chapter. Further, the details of the different techniques employed for the characterization of the grown nanowires were also presented. Chapter 3 In this chapter, studies on the growth of Germanium nanowires by electron beam evaporation (EBE) are given. The influence of deposition parameters such as growth temperature, evaporation rate of germanium, growth duration, and catalyst layer thickness was investigated. The morphology, structure, and composition of the nanowires were investigated by XRD, SEM, and TEM. The VLS growth mechanism has been discussed for the formation of the germanium nanowires by EBE using Au as a catalyst. Chapter 4 This chapter discusses the growth of Si nanowires with Indium and Bismuth as an alternate to Au-catalyst by electron beam evaporation. The influence of deposition parameters such as growth temperature, Si evaporation rate, growth duration, and catalyst layer thickness has been investigated. The grown nanowires were characterized using XRD, SEM, TEM and HRTEM. The Silicon nanowires growth mechanism has been discussed. Chapter 5 This chapter discusses the Au-catalyzed VLS growth of SnO2 nanowires by the electron beam evaporation method as well as Antimony doped SnO2 nanowires by co-evaporation method at a low substrate temperature of 450 °C. The grown nanowires were characterized using XRD, SEM, TEM, STEM, Elemental mapping, HRTEM, and XPS. The effect of deposition parameters such as oxygen partial pressure, growth temperature, catalyst layer thickness, evaporation rate of Sn, and the growth duration of nanowires were investigated. The SnO2 nanowires growth mechanism has been explained. Preliminary studies were made on the possible use of pure SnO2 and doped SnO2 nanowire films for UV light detection. SnO2 nanowire growth on different substrates such as stainless steel foil (SS), carbon nanosheets films, and graphene oxide films were studied. SnO2 nanowire growth on different substrates, especially SS foil will be useful for Li-ion battery applications. Chapter 6 This chapter discusses the self catalyzed VLS growth of Sn doped Indium oxide (ITO) nanowires by the electron beam evaporation method at a low temperature of 250-400 °C. The grown nanowires were characterized using XRD, SEM, TEM, STEM, HRTEM, and XPS. The effect of deposition parameters such as oxygen partial pressure, growth temperature, evaporation rate of ITO, and the growth duration of the nanowires were investigated. Preliminary studies were also made on the possible use of self-catalyzed ITO nanowire films for transparent conducting oxides and antireflection coatings. ITO nanowire growth on different and large area substrates such as stainless steel foil (SS), and Glass was done successfully. ITO nanowire growth on different substrates, especially large area glass substrates will be useful for optoelectronic devices. Chapter 7 In this chapter, studies on the growth of SnO2 nanowires by a cost-effective resistive thermal evaporation method at a relatively lower substrate temperature of 450 °C are presented. The grown nanowires were characterized using XRD, SEM, TEM, HRTEM, and XPS. Preliminary studies were done on the possible use of SnO2 nanowire films for methanol sensing. Chapter 8 This chapter discusses the self-catalytic growth of SnO2 and In2O3 nanowires by resistive thermal evaporation. The nanowires of SnO2 and In2O3 were grown at low temperatures by resistive thermal evaporation using a modified source and substrate arrangement. In this arrangement, branched SnO2 nanowires, and In2O3 nanowires growth was observed. The grown nanowires were characterized using XRD, SEM, TEM, HRTEM, and XPS. The possible growth mechanism for branched nanowires growth has been explained. Chapter 9 The significant results obtained in the present thesis work have been summarized in this chapter.

Vanadium oxides are being used as the thermal sensing layer because of their applications in infrared detectors. They have high temperature coefficient of resistance, favorable electrical resistance and compatibility with the MEMS technology. Of all oxides of vanadium, only vanadium dioxide (VO2)has been highly investigated as it shows first order transition (semiconducting to metal transition-SMT)at 68 oC. First order transition is understood as the sharp change in the electrical resistance. The change in resistivity in this case is of the order of 105 over a temperature change of 0.1 oC at 68 oC in a single crystal. Doping vanadium oxides with elements like Mo and W reduce the transition temperature. This is very important for room temperature electrical and optical detection. Though most of the research groups subscribe to PLD, cost-effective methods with large area deposition are major focus of this research. Hence for synthesizing VO2 in bulk and thin films, Solution Combustion Synthesis (SCS), Ultrasonic Nebulized Spray Pyrolysis of Aqueous Combustion Mixture (UNSPACM) Chemical vapour deposition (CVD)and microwave are explored. Synthesis of doped VO2 films in CVD has not been done extensively to yield optical quality thin films. Chapter I surveys the use of phase transition in oxides system for a variety of practical applications. In particular, Vanadium dioxide (VO2) is chosen as it is found to be very useful for infrared and metamaterials based applications. VO2 is known for its first-order semiconducting to metallic transition (SMT). This chapter attempts to explain the influence of processing, doping, annealing, etc on the SMT characteristics. Important aspects such as the idea of hysteresis in VO2 and similarity to martensitic transformation are discussed. The scope and objectives of the thesis are discussed here. Chapter II explains in detail the materials and methods used to synthesize VO2 both in bulk and in thin lm form and methods used to study their characteristics. Brief description on the principle and the working of the home-built experimental set up needed for this study is elicited. In chapter III, attempts were made to understand the phase stability of VO2 and the evolution of crystal structures during the phase transition. VO2 crystallizes in P21/c space group at room temperatures with lattice parameters a=5.752 Ab=4.526 Ac=5.382 Aα=90 β=122.60 γ=90 . Precise control of synthesis parameters is required in stabilizing pure phase in bulk as well as thin lm form. This study focuses on the novel large scale two step synthesis of VO2 using Solution Combustion Synthesis. This involves synthesis of product utilizing redox reaction between metal nitrate and suitable fuel. Generally the products are nanocrystalline in nature due to self-propagation of the exothermic combustion reaction. First step involved the synthesis of V2O5 by combustion reaction between Vanadyl nitrate and urea. In the second step, the as-synthesized V2O5 has been reduced by a novel reduction technique to form monophasic VO2. The presence of competing phases like M1, M2, M3 and R are investigated by XRD, Raman spectroscopy, DSC, Optical and high temperature X-ray diffraction. Chapter IV deals with the reduction in phase transition temperature by doping the SCS synthesized VO2 with W and Mo. Effect of doping on the transition temperature was studied using differential scanning calorimetry (DSC) in both W and Mo. Electrical characteristics of Mo doped VO2 and Optical characteristics of the W-doped VO2 were also studied using four probe resistivity measurements and UV-VIS Spectroscopy respectively. W addition was found to be more effective in reducing the phase transition temperature. To understand further more on the W addition, X-ray photo-electron spectroscopy measurements were performed. W-addition alters the V4+-V4+ bonding and with W addition it is observed that V was present in V3+state. W was present in W6+ state. The addition of W to VO2 introduces more electrons to the systems and disturbs the V4+-V4+ thus reducing the phase transition temperature of VO2. Chapter V describes the large scale, large area deposition of thin films of VO2 by a cost effective method. A novel technique to deposit vanadium dioxide thin films namely, UNSPACM is developed. This simple two-step process involves synthesis of a V2O5 lm on an LaAlO3(LAO) substrate followed by a controlled reduction to form single phase VO2. The formation of M1 phase (P21/c) is confirmed by Raman spectroscopic studies. A thermally activated metal{insulator transition (MIT) was observed at 61 oC, where the resistivity changes by four orders of magnitude. The infrared spectra also show a dramatic change in reflectance from 13% to over 90% in the wavelength range of 7-15 m. This indicates the suitability of the films for optical switching applications at infrared frequencies. A trilayer metamaterial absorber, composed of a metal structure/dielectric spacer/vanadium dioxide (VO2) ground plane, is shown to switch reversibly between reflective and absorptive states as a function of temperature. The VO2 lm, which changes its conductivity by four orders of magnitude across an insulator{metal transition, enables the switching by forming a resonant absorptive structure at high temperatures while being inactive at low temperatures. The fabricated metamaterial shows a modulation of the reflectivity levels of 58% at a frequency of 22.5 THz and 57% at a frequency of 34.5 THz. Chapter VI explains the W doped VO2 thin films synthesized by UN-SPACM. Morphology of the thin films was found to be consisting of globular and porous nanoparticles having size 20 nm. Transition temperature decreased with the addition of W. 1.8 at. %W doping in VO2 transition temperature has reduced upto 25 oC. It is noted that W-doping in the pro-cess of reducing the transition temperature, alters the local structure and also increases room temperature carrier concentration. The presence of W, as was seen in Chapter IV, altered V4+-V4+ bonds and introduced V3+. W was found to be in W6+ state suggesting W addition increased the carrier concentration. Hall Effect measurements suggested the increased carrier con-centration. The roughness of the synthesized films were very high for them to be of de-vice quality, despite encouraging results obtained by electrical measurements. Hence in order to further improve the smoothness and thereby the optical quality of thin films, Chemical Vapour Deposition (CVD) is employed. Chapter VII outlines the effect of processing parameters and post pro-cessing annealing on the semiconductor-metallic transition of VO2. Here in this chapter, the influence of substrate temperature on the SMT properties of VO2 is explored. At different substrate temperatures, the percentage of phase fraction of V in V3+, 4+ and V5+ differed. Besides, the morphology also varied with substrate temperatures. Similarly it is observed that with annealing the VO2 film deposited on glass substrates, SMT properties enhanced which was attributed to filling out of oxygen vacancies. Si based substrates and non-Si based substrates were used for depositing VO2 thin films by CVD. Their temperature coefficient of resistance and SMT properties were studied in order to understand their potential in bolometer and thermal to optical valve based applications. Chapter VIII involves the study of VO2 thin films for thermal to optical valves. ITO coated glass substrates were used for the purpose. Thin films were deposited by both UNSPACM and CVD. It was observed that the reflectivity pro les of the films synthesized by the above said methods were very different. Hence in the process of understanding the huge difference in the reflectivity pro les, classical harmonic oscillator, Lorentzian model was employed to t the experimental data at room temperature whereas Drude-Lorentzian model was used to t the data at higher temperature (at 100 oC- after transition). With this fitting plasma frequencies of the CVD films were calculated. It was observed that defect chemistry of films synthesized by these methods were different. In order to further improve the smoothness of the films, microwave method was proposed in Chapter IX. The preliminary results showed the presence of uniform spheres and 3 D hierarchical structures of VO2 consisting of nanorods. This was extended to deposit VO2 thin films on ITO. DSC and Infrared reflectance pro le of VO2 nanopowder suggested the phase transition. Chapter X summarizes the work done for the thesis and provides insights to the applications and to the future work. The work reported in this thesis has been carried out by the candidate as part of the Ph.D.program. She hopes that this would constitute a worth-while contribution towards development of VO2 thin film technology and its challenges for reliable infrared device applications.

Active layer morphology of polymer-based solar cells plays an important role in improving power conversion efficiency (PCE). In this thesis, the focus is to improve the device efficiency of polymer-based solar cells. In the first objective, active layer morphology of polymer-solar cells was optimized though a novel solvent annealing technique. The second objective was to explore the possibility of replacing the highly sensitive aluminum cathode layer with a low-cost and stable alternative, copper metal. Large scale manufacturing of these solar cells is also explored using roll-to-roll printing techniques. Poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl (PCBM) were used as the active layer blend for fabricating the solar cell devices using bulk heterojunction (BHJ), which is a blend of a donor polymer and an acceptor material. Blends of the donor polymer, P3HT and acceptor, PCBM were cast using spin coating and the resulting active layers were solvent annealed with dichlorobenzene in an inert atmosphere. Solvent annealed devices showed improved morphology with nano-phase segregation revealed by atomic force microscopy (AFM) analysis. The roughness of the active layer was found to be 6.5 nm. The nano-phase segregation was attributed to PCBM clusters and P3HT domains being arranged under the solvent annealing conditions. These test devices showed PCE up to 9.2 % with current density of 32.32 mA/cm2, which is the highest PCE reported to date for a P3HT-PCBM based system. Copper was deposited instead of the traditional aluminum for device fabrication. We were able to achieve similar PCEs with copper-based devices. Conductivity measurements were done on thermally deposited copper films using the two-probe method. Further, for these two configurations, PCE and other photovoltaic parameters were compared. Finally, we studied new techniques of large scale fabrication such as ultrasonic spray coating, screen-printing, and intense pulse light sintering, using the facilities at the Conn Center for Renewable Energy Research at the University of Louisville. In this study, prototype devices were fabricated on flexible ITO coated plastics. Sintering greatly improved the conductivity of the copper nano-ink cathode layer. We will explore this technique’s application to large-scale fabrication of solar cell devices in the future work.

Contemporary Canadian prairie women poets write about the mother figure to counter maternal suppression and the homogenization of maternal representations in literature. Critics, like Marianne Hirsch and Andrea O’Reilly, insist that mothers tell their own stories, yet many mothers are unable to. Daughter and mother stories, Jo Malin argues, overlap. The mother “becomes a subject, or rather an ‘intersubject’” in the text (2). Literary depictions of daughter-mother or mother-child intersubjectivities, however, are not confined to auto/biographical or fictional narratives. As a genre and potential site for representing maternal subjectivities, poetry continues to reside on the margins of motherhood studies and literary criticism. In the following chapters, I examine the writing strategies of selected poets and their representations of mothers specific to three transformative occasions: mourning mother-loss, becoming a mother, and reclaiming a maternal lineage. Several daughter-poets adapt the elegy to remember their deceased mothers and to maintain a connection with them. In accord with Tanis MacDonald and Priscila Uppal, these poets resist closure and interrogate the past. Moreover, they counter maternal absence and preserve her subjectivity in their texts. Similarly, a number of mother-poets begin constructing their mother-child (self-other) relationship prior to childbirth. Drawing on Lisa Guenther’s notions of “birth as a gift of the feminine other” and welcoming the stranger (49), as well as Emily Jeremiah’s link between “‘maternal’ mutuality” and writing and reading practices (“Trouble” 13), I investigate poetic strategies for negotiating and engaging with the “other,” the unborn/newborn and the reader. Other poets explore and interweave bits of stories, memories, dreams and inklings into their own motherlines, an identification with their matrilineage. Poetic discourse(s) reveal the limits of language, but also attest to the benefits of extra-linguistic qualities that poetry provides. The poets I study here make room for the interplay of language and what lies beyond language, engaging the reader and augmenting perceptions of the maternal subject. They offer new ways of signifying maternal subjectivities and relationships, and therefore contribute to the ongoing research into the ever-changing relations among maternal and cultural ideologies, mothering and feminisms, and regional women’s literatures. / May 2016