Down-conversion (DC) and down-shifting (DS) layers are optical layers mounted on the top surface of a solar cell that can potentially increase the solar cell efficiency. The effect of DC and DS layers to enhance the performance of single-junction solar cells has been studied by means of simulation and experimental work. In this thesis a model is developed to study the effects of DC and DS layers by modifying the incident spectrum. The effect of the layers on ideal cells as well as commercial grade silicon and CIGS solar cells that are modeled in a device simulator is examined. Silicon nanocrystals (Si-nC) embedded in a silicon dioxide matrix to act as a DS layer were fabricated and characterized at McMaster University as part of this project. The measured optical properties as well as the photoluminescence measurements are used as input parameters to the optical model. The enhancement due to the Si-nC when coupled to silicon and CIGS solar cells is explored. Beside the DC and DS effects, there is also disturbance to the surface reflections due to the addition of a new layer to the top surface and is referred to as antireflection coating (ARC) effect. For the simulated silicon solar cell under the standard AM1.5G spectrum (1000W/m2), a maximum increase in Jsc of 8.4% is achieved for a perfect DS layer as compared to a reference cell, where 7.2% is due to ARC effect and only 1.2% is due to DS effect. On the other hand, there is an increase in Jsc of 19.5% for the CIGS solar cell when coupled to a perfect DS layer. The DS effect is dominant with 18%, while the ARC effect contributes only 1.5% to the total Jsc enhancement. Accurately characterizing DS layers coupled to solar cell requires knowledge of optical properties of the complete structure. Internal quantum efficiency is an important tool for characterizing DS systems, nevertheless, it is rarely reported. In addition, the ARC effect is not experimentally decoupled from the DS effect. In this work, a straightforward method for calculating the active layer contribution that minimizes error by subtracting optically-modeled electrode absorption from experimentally measured total absorption.

Pressure sensitive adhesives (PSAs) are polymeric materials with versatile applications in industrial and consumer products such as protective films, product labels, masking tape, and sticky notes, to name a few applications. World demand for emulsion–based products is on the rise due to worldwide legislation on solvent emissions. In order to completely replace emulsion-based PSAs with their solvent-based counterpart, the property modification of emulsion-based PSAs is required. The use of nanomaterials to modify polymer properties is well established. The aim of this thesis was to use cellulose nanocrystals (CNCs) as property modifiers for emulsion-based PSAs. CNCs are recognized as a highly efficient reinforcement nanofiller. Owing to their environmentally friendly characteristics, low density, high aspect ratio, non-toxicity, and abundant availability, the application of CNCs in composite materials is gaining increasing attention. In this thesis, the inclusion of CNCs in emulsion-based PSAs was carried out through in situ emulsion polymerization and blending technique. To the best of our knowledge, there is limited information about the synthesis of CNC/PSAs nanocomposites via in situ emulsion polymerization and the evaluation of their mechanical performance. The addition of CNCs to the polymerization formulation caused latex instability due to the negatively charged surfaces of the CNCs. After numerous attempts to overcome the stability issues, a stable polymerization formulation and protocol were developed. CNC/PSAs were synthesized via in situ seeded-semi batch emulsion polymerization, which is a common commercial production pathway for PSAs. The mechanical performance of the resulting PSA nanocomposite films, namely, shear strength, tack, and peel strength, was evaluated at several CNC loadings. All three PSA adhesive properties were simultaneously enhanced with increasing CNC loading. The inclusion of CNCs into the films increased their hydrophilicity. Consequently, the PSA films’ improved wettability on a stainless steel substrate imparted greater tack and peel strength. The blending of the CNCs with a base latex also led to improved adhesive properties. However, the property modification through blending was not as effective as that for the CNC/PSA films synthesized via in situ emulsion polymerization. Thus, CNCs are safe nanomaterials that have been shown to provide remarkable property enhancement of emulsion-based PSA films at low loadings (1wt%).

Thin film Nanocomposite (TFN) membranes are a relatively new class of high-performance semipermeable membranes for Reverse Osmosis (RO) applications. Large scale applications of TFN membranes have not been achieved yet due to the high production cost of the nanoparticles, agglomeration of the nanoparticles in the thin polyamide matrix of the membrane, and leaching out of typically toxic inorganic nanoparticles into the downstream. In this work, these challenges are addressed by incorporation of two different nanofillers: Cellulose NanoCrystals (CNC), and surface functionalized Halloysite NanoTubes (HNT). Amine groups, carboxylic acid groups, and the first generation of poly(amidoamine) (PAMAM) dendrimers were used for functionalization of the HNT. CNC and HNT are environmentally friendly, low/non-toxic, abundant, and inexpensive nanoparticles with a unique size, and chemical properties. TFN membranes were synthesized via in situ interfacial polymerization of m-phenylenediamine (MPD) with trimesoyl chloride (TMC) and the nanoparticles. The control Thin Film Composite (TFC) membranes, and CNC and HNT based TFN membranes were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-Ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared spectroscopy (FTIR) and contact angle measurements. The antifouling capacity of CNC based membranes was investigated with a solution of Bovine Serum Albumin (BSA) as the fouling agent. Also, the leachability of the HNT from the membranes was examined by shaking the membranes in a batch incubator for 48 h, and then tracing the leached out HNT using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Separation characteristics of the membranes were studied by desalination of synthetic brackish water with a cross flow RO filtration system. It was revealed that incorporation of functionalized HNT enhanced the permeate flux without sacrificing the salt rejection (99.1 % ± 0.1 %). Also, incorporation of 0.1% (w/v) CNC doubled the permeate flux (from 30 to 63 L/m2.h at 20 bar) without compromising the salt rejection (97.8%). At the same time, leaching out of HNT from the TFN membranes was decreased as a result of the HNT functionalization and formation of covalent bonds with the TMC. Also, antifouling properties of the CNC-TFN membranes were 11% improved in comparison with control TFC membrane.

Les nanocristaux colloïdaux synthétisés par voie chimique sont des sources prometteuses de lumière non-Classique à température ambiante. Ce travail est consacré à l'étude des propriétés optiques d'un type particulier de nanocristaux colloïdaux, appelé coeur-Bâtonnet, dans lequel un noyau de Seleniure de Cadmium (CdSe) sphérique est entouré d'une coquille de Sulfure de Cadmium (CdS) de forme cylindrique. En étudiant des particules de type coeur-Bâtonnet à température ambiante avec un microscope confocal, une caractérisation complète des propriétés optiques de ces émetteurs est réalisée. Nous étudions d'abord la statistique de clignotement de ces émetteurs. Nous montrons que les émetteurs coeur-Bâtonnet avec des coquilles épaisses se caractérisent par un clignotement réduit sur des échelles de temps courts, inférieurs à quelques millisecondes. Ensuite, une caractérisation détaillée de la statistique de photons des émetteurs coeur-Bâtonnet tenant compte du phénomène de clignotement est réalisée. La polarisation de l'émission est également étudié. Nous montrons que la polarisation d'émission peut être controlée en changeant la géométrie de la structure.Enfin, nous présentons également des expériences de couplage de ces émetteurs avec des dispositifs photoniques. Nous montrons la possibilité d'exciter un émetteur coeur-Bâtonnet en utilisant un nanofil d'oxyde de Zinc (ZnO). Nous montrons aussi que nous sommes en mesure d'orienter efficacement des nanoémetteurs uniques en utilisant la formation controlée de défauts dans des cristaux liquides. / Wet-Chemically synthesized colloidal nanocrystals are promising room temperature non-Classical light sources. This work is devoted to the study of the optical properties of a particular type of colloidal nanocrystals, called dot-In-Rods, in which a spherical Cadmium Selenide (CdSe) core is surrounded by a rod-Like Cadmium Sulfide (CdS) shell. By studying single dot-In-Rods at room-Temperature with a confocal microscope, a complete characterization of the optical, and especially quantum optical, properties of dot-In-Rods is provided for several geometrical parameters. We first study the blinking statistics of such emitters. We show that dot-In-Rods with thick shells are characterized by a reduced blinking that happens on fast timescales, typically on millisecond timescales. We then go on with a detailed characterization of the photon statistics of dot-In-Rods. A complete description of the photon statistics taking into account the blinking process is realized. The polarization of the emission is also investigated. We show that the emission polarization can be tuned by engineering the geometry. Finally, we also present experiments where we couple dot-In-Rods with various photonic devices. We demonstrate the possibility of excitation of a single emitter using a Zinc Oxyde (ZnO) nanowire. Using defects in liquid crystals, we also show that we are able to efficiently orientate single nanoemitters.

The original work presented in this thesis describes research into Si-based luminescent materials, prepared specifically by ion implantation and rapid thermal processing of thermal oxide films. An in-depth optical characterisation, employing photoluminescence (PL) and Raman spectroscopy was complimented with electron microscopy, revealing the source of efficient room temperature PL as nano-scale silicon inclusions (Si-NCs). The evolution of the Si-NC size and density with isothermal and isochronal annealing may be described using classical thermodynamics according to a diffusion limited, Ostwald ripening process. Values for the coarsening rate and activation energy, extracted from the evolution of the Si-NC size with annealing indicate that the transport of Si atoms and precipitate formation are enhanced in ion implanted films, attributable to the presence of vacancy and interstitial defects generated during ion irradiation. The PL and Raman spectra are well correlated with the evolving Si-NC size and density according to the quantum confinement (QC) model in which samples containing larger clusters emit at longer wavelengths. However, the formation of bound exciton states within the band gap of small clusters (< 2nm), as a result of specific surface chemistries, suppresses higher energy emissions. The increase in PL intensity with annealing was exactly correlated with the increase in PL lifetime, characteristic of the removal of non-radiative defects. A dependence of the PL dynamics on emission energy, with higher energies exhibiting shorter lifetimes, further evidences the QC effect. Blue shifted emission at high excitation flux and/or low temperature is correspondent with the slower PL dynamics and preferential saturation at longer wavelengths. Raman spectra were fit using a phonon confinement model, from which Si-NC size distributions were extracted and found to compare favourably with those obtained from TEM images. Stresses in the films, determined from the Raman peak position, were used as an independent method for calculating the Si surface energy, which is very close to the literature values. A single, high temperature anneal of Si and erbium (Er) co-doped films revealed a preferential aggregation of Er at the Si-NC formation site, which is of particular importance for the photo-sensitization of Er PL around 1.5μm. The Er PL was enhanced in the presence of Si-NCs by several orders of magnitude compared with a reference SiO2:Er. Whilst broadband pumping of the Er via Si-NCs evidences a non-resonant energy transfer mechanism with an efficiency which depends on the Si-NC size, the process is limited at high excitation flux by a combination of low sensitizer (Si-NC) density and non-radiative losses. Finally the Si-NC PL intensity in phosphorus (P) co-doped films was studied and found to depend strongly on the annealing conditions and P concentration. For lower temperature treatments, a factor 2 PL enhancement, relative to an un-doped reference was obtained, attributed to the passivation of Si-NC surface defects. Higher temperature treatments resulted in the monotonic quenching of the PL with increasing P concentration, attributed to the introduction of an efficient Augerre combination channel as a result of the ionization of P-donors inside large Si-NCs. A simple statistical model predicts this behaviour and provides an incidental estimate of the Si-NC size.

Orientador: Maria do Carmo Gonçalves / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-27T15:15:24Z (GMT). No. of bitstreams: 1 Leite_LilianeSamaraFerreira_M.pdf: 4562587 bytes, checksum: 0ee5828360fc15cbd08b98c4070e5bd3 (MD5) Previous issue date: 2015 / Resumo: Nesse trabalho, nanocristais de celulose (CNC) foram obtidos por hidrólise de fibras de algodão, utilizando-se três diferentes ácidos: ácido sulfúrico, clorídrico e fosfórico. Micrografias obtidas por microscopia eletrônica de varredura (SEM) e transmissão (TEM) confirmaram que as condições de hidrólise empregadas foram adequadas para isolar seus nanocristais. No entanto, foi também possível observar a presença de uma pequena fração de fibras não totalmente hidrolisadas em todas as amostras analisadas. Imagens de microscopia óptica por luz polarizada (PLM) revelaram que o processo de secagem por liofilização dos CNC conduz à formação de aglomerados com dimensões micrométricas. Modificações químicas nas superfícies dos CNC, empregando-se ácido acético e cloreto de hexanoíla, foram conduzidas com o objetivo de diminuir o seu caráter hidrofílico. As modificações foram confirmadas por espectroscopia na região do infravermelho e por imagens de PLM das suspensões dos CNC. Compósitos de acetato de celulose (CA), reforçados com CNC, foram preparados por extrusão, utilizando-se dois procedimentos para a incorporação da carga na matriz: mistura direta e masterbatch, sendo esse último conduzido na tentativa de evitar a etapa de liofilização, onde ocorre a formação de aglomerados de nanocristais. Ensaios mecânicos mostraram que não houve aumento significativo nas propriedades mecânicas para os compósitos preparados por mistura direta. Entretanto, compósitos preparados por masterbatch apresentaram aumento no módulo de Young em torno de 5% e 14%, para composições contendo 10 e 15 % nanocristais em massa, respectivamente. Esses resultados evidenciam a importância das condições de hidrólise para obtenção das nanopartículas, como também da escolha do método de preparação do compósito de forma a promover a menor formação de aglomerados e melhor dispersão da carga na matriz / Abstract: In this work, cotton fiber cellulose nanocrystals (CNC) were obtained by acid hydrolysis using three different acids: sulfuric acid, hydrochloric acid and phosphoric acid. Scanning (SEM) and transmission (TEM) electron micrographs confirmed that the acid hydrolysis conditions used were efficient to isolate their nanocrystals. However, in all samples analyzed, it was possible to observe the presence of some partially hydrolyzed fibers. Polarized Light Microscopy (PLM) showed that the freeze-drying process led to the formation of small CNC agglomerates with micron dimensions. CNC surface functionalization was carried out with the purpose of reducing the hydrophilic character, by using acetic acid and hexanoyl chloride. Chemical modifications at the surface were confirmed by infrared spectroscopy and the hydrophilic character decrease was confirmed by PLM images of the functionalized CNC. Cellulose acetate composites, reinforced with CNC, were obtained by melt extrusion using two techniques for the introduction of reinforcing agent: direct mixing and masterbatch. The latter were carried out prevent CNC agglomeration formation due to the freeze-drying process. Mechanical tests showed that there was no significant increase in of the composites prepared by direct mixing mechanical properties. However, composites prepared from masterbatch showed a 5% and 14% increase in Young's modulus for 10 and 15 wt% CNC content, respectively. These results show the importance of the hydrolysis conditions on the nanoparticle synthesis, as well as the choice of an appropriate reinforcing agent load method so as to avoid agglomeration and increase load dispersion in the matrix / Mestrado / Mestra em Química

Quantum materials have strong electron correlation effects. According to the “structure-property” relationship, it is crucial to study the structure of quantum materials to better understand and manipulate the physical properties. The quantum effects are significant at the atomic microscopic length scale, which is not feasible to be studied by the average long-range structure measurement from conventional diffraction methods. Instead the local structure probe, pair distribution function (PDF) analysis, can effectively reveal the mystery of local structure, which is sensitive to the local behavior rather than the bulk average properties. In this thesis, the joint neutron and x-ray PDF (NXPDF) method is implemented. Because of their different interactions with matters, a combination of neutron and x-ray scattering can help comprehensively understand the atomic structures of some strongly correlated d- and f-electron systems that are difficult to be studied alone. Though powerful for understanding the structure of complex materials, performing the PDF modeling and structure refinement usually requires a lot of work on model selection for candidate structures. To address this problem, a new approach is developed to obtain candidate atomic structures from NXPDF, called structure-mining, in a highly automated way. It fetches, from open structural databases, all the structures meeting the experimenter's search criteria and performs structure refinements on them without human intervention. Tests on various material systems show the effectiveness and robustness of the algorithm in finding the correct atomic crystal structure. It works on crystalline and nanocrystalline materials including complex oxide nanoparticles and nanowires, low-symmetry and locally distorted structures, and complicated doped and magnetic materials. The examples of applying structure-mining method to identify the local structures of Pr₆O₁₁, BaFeₓTi₁−ₓO₃, and MgTi₂O₄ materials, which have strongly correlated 𝓭- and 𝑓-orbital electronic states under study in the thesis, are shown as well. This approach could greatly reduce the traditional structure searching work for quantum materials as well as other systems. The NXPDF method is first applied to the praseodymium oxide semiconductor nanoparticles to investigate the local structure behavior accompanied by the loss of electrical conductivity when temperature changes. The Pr and O sublattices can be determined precisely by x-ray and neutron PDF, respectively, because of their distinct x-ray atomic form factors and neutron scattering lengths. A combination of a highly ordered structure motif and a locally distorted oxygen deficient structure environment can describe the measured NXPDFs reasonably well. The iron doped barium titanate BaFeₓTi₁−ₓO₃ system is also investigated using PDF methods for studying the multiferroic behavior in the nanocrystals, which are synthesized near room temperature. The perovskite structure is established to be non-centrosymmetric, consistent with predictions of the pseudo-Jahn-Teller effect being the underlying cause of off-center displacements of B-site (Ti and doped Fe) atom, lowering the symmetry in order to make additional overlap between the 3d orbital of Ti and neighboring O atoms to create π molecular orbitals. This triggers the spontaneous polarization of the crystal. The PDF results establish that Fe is successfully doped into the ferroelectric BaTiO₃ phase, and the measured dielectric and magnetic properties also validate the multiferroic behavior of the synthesized BaFeₓTi₁−ₓO₃ nanocrystals. In addition, the NXPDF analysis is also conducted on the MgTi₂O₄ system to track the evolution of the local atomic structure across the temperature-dependent metal-insulator transition, and the results reveal that local tetragonality is persistent, preformed with reduced magnitude, deep in the metallic and on average cubic regime. Significantly, the high temperature local state revealed by PDF is not continuously connected to the orbitally ordered band insulator ground state and the transition cannot be characterized as a trivial order-disorder type. The shortest Ti-Ti bond lengths corresponding to spin singlet dimers shift to longer distances on warming but are still shorter than those seen in the cubic average structure. These seemingly conflicting observations could be reconciled within the model of a local fluctuating t₂g orbital-degeneracy-lifted (ODL) precursor state. These results undoubtedly establish the effectiveness of the joint neutron and x-ray PDF analysis to investigate the structure-property relationship on the sub-nanometer length scale of strongly correlated electron materials, utilizing the complementary structure information obtained from neutron and x-ray scattering.

abstract: Satisfying the ever-increasing demand for electricity while maintaining sustainability and eco-friendliness has become a key challenge for humanity. Around 70% of energy is rejected as heat from different sectors. Thermoelectric energy harvesting has immense potential to convert this heat into electricity in an environmentally friendly manner. However, low efficiency and high manufacturing costs inhibit the widespread application of thermoelectric devices. In this work, an inexpensive solution processing technique and a nanostructuring approach are utilized to create thermoelectric materials. Specifically, the solution-state and solid-state structure of a lead selenide (PbSe) precursor is characterized by different spectroscopic techniques. This precursor has shown promise for preparing thermoelectric lead selenide telluride (PbSexTe1-x) thin films. The precursor was prepared by reacting lead and diphenyl diselenide in different solvents. The characterization reveals the formation of a solvated lead(II) phenylselenolate complex which deepens the understanding of the formation of these precursors. Further, using slightly different chemistry, a low-temperature tin(II) selenide (SnSe) precursor was synthesized and identified as tin(IV) methylselenolate. The low transformation temperature makes it compatible with colloidal PbSe nanocrystals. The colloidal PbSe nanocrystals were chemically treated with a SnSe precursor and subjected to mild annealing to form conductive nanocomposites. Finally, the room temperature thermoelectric characterization of solution-processed PbSexTe1-x thin films is presented. This is followed by a setup development for temperature-dependent measurements and preliminary temperature-dependent measurements on PbSexTe1-x thin films. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020

Conventional liquid lubricants are faced with limitations under extreme cyclic operating conditions, such as in applications that require lubrication when changing from atmospheric pressure to ultrahigh vacuum and ambient air to dry nitrogen (e.g., satellite components), and room to elevated (>500°C) temperatures (e.g., aerospace bearings). Alternatively, solid lubricant coatings can be used in conditions where synthetic liquid lubricants and greases are not applicable; however, individual solid lubricant phases usually perform best only for a limited range of operating conditions. Therefore, solid lubricants that can adequately perform over a wider range of environmental conditions are needed, especially during thermal cycling with temperatures exceeding 500°C. One potential material class investigated in this dissertation is lubricious oxides, because unlike other solid lubricant coatings they are typically thermodynamically stable in air and at elevated temperatures. While past studies have been focused on binary metal oxide coatings, such as ZnO, there have been very few ternary oxide and no reported quaternary oxide investigations. The premise behind the addition of the third and fourth refractory metals Ti and Zr is to increase the number of hard and wear resistant phases while maintaining solid lubrication with ZnO. Therefore, the major focus of this dissertation is to investigate the processing-structure-tribological property relations of composite ZnO, TiO2 and ZrO2 phases that form ternary (ZnTi)xOy and quaternary (ZnTiZr)xOy nanocrystalline coatings. The coatings were processed by atomic layer deposition (ALD) using a selective variation of ALD parameters. The growth structure and chemical composition of as-deposited and ex situ annealed ternary and quaternary oxide coatings were studied by combined x-ray diffraction/focused ion beam microscopy/cross-sectional transmission electron microscopy, and x-ray photoelectron spectroscopy/Auger electron spectroscopy, respectively. It was determined that the structure varied from purely nanocrystalline (ternary oxides) to composite amorphous/nanocrystalline (quaternary oxides) depending on ALD parameters and annealing temperatures. In particular, the ZnTiO3 ilmenite phase with (104) textured nanocolumnar grains, exhibiting high stacking fault/partial dislocation densities >1012/cm2, was responsible for the excellent tribological behavior. Steady-state sliding friction coefficients down to 0.12 in humid air and 0.2 in dry nitrogen were measured along with sliding and fretting wear factors in the range of 10-6 to 10-7 mm3/N·m, even after ex situ annealing to 550°C. Additionally, the quaternary oxide phase Zn(Ti,Zr)O3 in solid solution exhibited a low fretting wear rate of 1x10-6 mm3/N·m. In contrast, certain phases, such as Zn2TiO4 cubic spinel, that form at annealing temperatures >550°C were responsible for high friction and wear. Mechanistic studies using the above techniques revealed low friction and wear-reducing surfaces and subsurfaces were due to different velocity accommodation modes (VAM). In the case of the ternary system, sliding-induced plastic deformation was possible when ZnTiO3 (104) stacking faults, bordered by partial dislocations, serve as a pathway for the dislocations to glide parallel to the sliding direction and hence achieve low friction and wear via an intrafilm shear VAM. It was evident that the individual nanocolumnar ZnTiO3 grains were plastically sheared as opposed to being fractured during wear. Conversely for the quaternary system, an interfacial sliding VAM between the counterface and a mechanically mixed layer (tribofilm) composed of the refined coating and counterface material, that also served as a source for the formation of cylindrical rolls, was responsible for wear reduction. Therefore, these lubricious oxides are a potential candidate for solid lubrication at high temperatures (up to 550 °C) and in space environments.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第22081号 / 農博第2373号 / 新制||農||1073(附属図書館) / 学位論文||R1||N5235(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 矢野 浩之, 教授 和田 昌久, 教授 辻井 敬亘 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM