Aim of this work was, to investigate the preparation of Si NC memories by sputter deposition. The milestones are as follows: - Review of relevant literature. - Development of processes for an ultrathin tunnel-oxide and high quality sputtered SiO2 for use as control-oxide. - Evaluation of methods for the preparation of an oxygen-deficient silicon oxide inter-layer (the precursor of the Si NC layer). - Characterization of deposited films. - Establishment of techniques capable of probing the phase separation of SiOx and the formation of Si NC. - Establishment of annealing conditions compatible with the requirements of current CMOS technology based on experimental results and simulations of Si NC formation. - Preparation Si NC memory capacitors using the developed processes. - Characterization of these devices by suitable techniques. Demonstration of their memory functionality.

Cellulose nanocrystals (CNCs) are attractive nanomaterials due to their superior mechanical properties, renewability, and natural abundance. Their surface hydroxyl groups, along with surface charges induced during their production, allow CNCs to be easily dispersed in an aqueous medium, especially with sustainable water-based production methods such as emulsion polymerization. Moreover, their surface functionality makes them highly suitable for modification, thereby making them even more versatile. Emulsion polymer latexes are heterogeneous mixtures, having a continuous aqueous phase along with a dispersed organic phase. Latex polymers are used in a wide range of applications such as in coating and adhesive films. Because of the bi-phasic nature of emulsion polymerizations, the surface properties of CNCs play a crucial role in their location relative to the organic phase, and how well-dispersed they are in the cast films. In this thesis, three grades of CNCs (Celluforce Inc.) with either hydrophilic, partially-hydrophobic, or hydrophobic surface properties, were combined with conventional emulsion and miniemulsion polymer formulations to investigate their effect on the properties of pressure sensitive adhesive (PSA) films. In the first instance, hydrophilic CNCs were tested in a seeded semi-batch emulsion polymerization. Using a sequential experimental design, the effects of polar comonomer, surfactant, chain transfer agent, and CNC loading on latex stability and PSA properties were studied. By increasing polymer chain entanglements and the work of adhesion, the hydrophilic CNCs were observed to simultaneously improve the three key properties of acrylic-based PSA films, i.e., tack, peel strength and shear strength. In the second part of this project, we compared the role of hydrophilic and partially-hydrophobic CNCs in PSA property modification. Viscosity measurements and atomic force microscopy revealed differences in the degree of association between the two types of CNCs and the latex particles. Dynamic strain-sweep tests showed that hydrophilic CNC nanocomposites softened at lower strains than their partially-hydrophobic counterparts. This behaviour was confirmed via dynamic frequency tests and modelling of the nanocomposites’ storage moduli, which suggested the formation of CNC aggregates of, on average, 3.8 and 1.3 times the length of CNCs. These results confirmed that the partially-hydrophobic CNCs led to improved CNC dispersion in the PSA films and ultimately, enhanced PSA properties. In the third part of the project, mini-emulsion polymerization (MEP) was used to embed the hydrophobic CNCs within the polymer particles in contrast to the hydrophilic and partially-hydrophobic CNCs which resided mainly in the aqueous phase or near the water-particle interface. Higher CNC loadings led to increased particle size, decreased polymerization rate and number of particles, while only slightly increased the viscosity and the work of adhesion. PSA film properties decreased upon the incorporation of hydrophobic CNCs. Transmission electron microscopy showed that CNCs were expelled from the latex particles at higher loadings, suggesting the incompatibility of the acrylic polymer and the CNCs’ modifying agents. The ability to modify CNCs enables one to achieve a range of hydrophilicity/hydrophobicity. This makes them extremely versatile in a heterogeneous mixture such as in an emulsion polymerization. Because emulsion polymers are used in a wide range of applications with a broad spectrum of properties (i.e., not only as adhesives but as non-tacky coatings), our ability to control CNC location relative to the polymer particles in the latex opens the door to a world of high value-added sustainable polymer products.

Access to clean water is one of the world's greatest concerns. Because 97% of global water resources are seawater, desalination via reverse osmosis (RO) membrane process has become a vital technology to obtain drinkable water. At the same time, the discharge of industrial waste effluents containing heavy metal ions to the available water resources (seawater and brackish water) without adequate pre-treatment is a major cause of water pollution. Heavy metal rejection using nanofiltration (NF) membrane process is a recognized water treatment methodology. Thin-film nanocomposite (TFN) membranes have shown vast performance enhancement using both RO and NF processes. However, TFN membrane fabrication has been limited due to poor dispersion of the nanoparticles in the polyamide (PA) layer of the membrane, and the leaching of the often-hazardous nanoparticles from the TFN membranes. For various reasons such as their dispersibility in aqueous media, safety, high aspect ratio, and functionality, cellulose nanocrystals (CNCs) are an ideal nanoparticle for inclusion in TFN membranes. Because of their hydrophilicity, CNCs have more commonly been dispersed in the aqueous monomer solution during PA interfacial polymerization. In this thesis, we investigated two different CNC modification routes to improve CNC dispersion within the trimesoyl chloride (TMC)/n-hexane (non-aqueous) monomer solution. In one case, we acetylated the CNCs (ACNCs) using a straightforward, efficient, solvent-free method to achieve a more uniform CNC dispersion in the PA layer. The resulting ACNCs were less hydrophilic, which allowed increased nanoparticle loading and improved dispersion in the PA layer. In an RO desalination process, compared to unmodified CNC-TFN membranes, the NaCl rejection of the ACNC-TFN membranes remained stable (at 98-99%) up to a 0.4 wt% loading, while water permeability increased by up to 40%. For the second case, we synthesized L-cysteine functionalized CNCs (CysCNCs) and incorporated them into the PA layer for testing in an NF wastewater treatment process. The amine functional groups of L-cysteine covalently bonded with the acyl chloride groups of the TMC monomer. This resulted in improved nanoparticle dispersion but could also have prevented nanoparticle leaching. Moreover, because L-cysteine contains strong chelating groups, their inclusion in the PA layer led to improved heavy metal rejection. A loading of 0.1 wt% CysCNCs in the TFN membranes provided high rejection of both copper and lead ions, 98.1 and 95.2%, respectively. The CysCNCs were also evaluated in an NF desalination process resulting in a 40% increase in water permeability with almost no decline in Na₂SO₄ (97-98%), MgCl₂ and NaCl rejection. The modified CNCs enabled us to overcome the water permeability/selectivity trade-off in CNC-TFN membranes for both RO and NF membrane desalination. Finally, we developed an experimental protocol to investigate the effect of the adsorption of heavy metal ions (if any) on the performance of thin film composite (TFC) and TFN membranes in NF. We confirmed that adsorption occurred, and the equilibrium capacity of the membranes was reached after 8 - 12 h of the experiment. Despite reaching the equilibrium capacity, the water permeability and heavy metal rejection remained at their highest values. This led to the conclusion that the adsorbed heavy metals altered the membrane surface, thereby improving the performance of both TFC and TFN membranes. The ability to modify CNCs enables one to achieve a controlled range of hydrophilicity/ hydrophobicity. This allows one to fine-tune CNC compatibility with the TMC/n-hexane non-aqueous monomer solution and enable improved dispersion in the PA layer, eventually leading to improved TFN membrane performance for both RO and NF processes.

No description available.

Cellulose nanocrystals (CNCs) are nanomaterials that have shown promise as reinforcement filler materials. Their small size, high modulus, and high aspect ratio makes CNCs good reinforcing materials. CNCs are typically introduced into softer polymer materials, which can have incompatible surface chemistry such as aliphatic chains, leading to aggregation and poor reinforcement of the material. The intrinsic hydrophobicity of the CNC surfaces suggests that dispersal into hydrophobic polymer matrices, which the CNCs could potentially reinforce, represent a significant challenge. Therefore, new non-traditional strategies are needed to introduce CNCs into polymer materials. The hydroxyl groups on the surfaces of CNCs can be functionalized using a variety of chemical techniques to yield materials that can interact better with solvents or polymers. Additionally, surface groups can allow the CNCs to react with environmental stimuli (smart materials). The primary focus of this work is the incorporation of CNCs in hydrophobic matrices. Herein we introduce a new method of dispersing CNCs in polyethylene (PE), a substance of legendary hydrophobicity that is also the most common synthetic polymer used in consumer packaging. The prospect of increasing the mechanical strength of PE by incorporating CNC materials as fillers may lead to the possibility of using less polymer to obtain the same strength. This thesis approaches the problem of dispersing CNCs within PE by first functionalizing the CNCs with a catalyst capable of polymerizing ethylene and other α-olefins. The catalyst 1,1'-bis(bromodimethylsilyl)zirconocene dibromide (catalyst 1) is equipped with anchoring groups that are capable of attachment to the surface hydroxyl groups of CNC particles. After immobilizing catalyst 1 onto various CNC samples, introduction of solvent, organoaluminum cocatalyst, and monomer (ethylene alone or ethylene plus 1-hexene) afforded high density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) samples, respectively, containing well-dispersed CNCs as filler materials. Chapter 2 provided important information on the attachment of catalyst 1 to cellulose nanocrystals and the successful polymerization of ethylene from the cellulose nanocrystals. The resulting composite materials showed a in Young's modulus that was three-fold that of PE samples we tested (1600 ± 100 vs 500 ± 30) and about 10% greater relative to a commercial high modulus PE sample (1450 MPa). The increase in Young's modulus along with the lack of macroscopic aggregates led to the conclusion that we have developed a viable method to disperse CNCs in polyolefin matrices. Chapter 3 focused on the dispersal of CNCs in a softer, more pliable polyethylene grade known as linear low-density polyethylene (LLDPE). LLDPE incorporates a small fraction of 1-hexene into polyethylene as a randomly inserted comonomer, giving rise to properties suitable for applications in plastic films and bags among other end uses. Catalyst 1 functionalized CNCs were added to a reaction vessel with both ethylene and 1-hexene to afford LLDPE CNC composites. Different loading of catalyst 1 on CNC aerogels afforded the same amount of catalyst in each reaction but allowed for different CNC loadings in each reaction. The composite materials showed increasing Young's modulus with increasing cellulose nanocrystal content. Chapter 4 describes how CNCs were functionalized with the intention of filling reverse osmosis membrane materials to have surface chemistry that could be impart antibacterial properties and increase flux. CNCs were functionalized with carboxylic acid by 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-mediated oxidation, then amine functionalization by carbodiimide coupling chemistry, and finally functionalized with a zwitterionic group by β-propiolactone ring opening. Amine coupling was confirmed with X-ray photoelectron spectroscopic analysis, and a second carboxylic acid peak was confirmed using infrared spectroscopy. These results were further verified with conductometric titration showing that after each respective reaction there were 1060 mmol kg-1 of carboxylic acid groups, 520 mmol kg-1 of amine groups, and 240 mmol kg-1 of zwitterionic groups. This CNC material was left to undergo future testing for desirable membrane properties. Chapter 5 assesses the possible value in creating a new composite material using a functionalized polynorbornene, poly(5-triethoxysilyl-2-norbornene) (PTESN). The composites were fabricated by using the solvent casting method, dispersing the CNCs in a toluene solution of polymer and drying. The composite materials showed an increase in Young's modulus with increased loading. The 20 wt% CNC in PTESN had a Young's modulus of 970 MPa, a significant increase over the Young's modulus of the polymer lacking the filler (540 MPa). In summary, this dissertation advances new techniques for the incorporation of CNCs as fillers in polymer-based nanocomposites. We are confident that further refinement and development of our results will find wide-ranging application. / Doctor of Philosophy / Cellulose nanocrystals (CNCs) are materials that can be added to polymers to form composite materials having increased stiffness. CNCs have the primary advantages over other filler materials of providing significant reinforcement without changing the color or increasing the density of the overall composite. CNCs are therefore good for designing polymer composites that need to be lightweight and aesthetically pleasing. Packaging materials (especially plastic bags and plastic films) are dominated by polyolefin materials such as polyethylene, which is already lightweight and colorless. The challenge of mixing polyethylene and CNCs is that their surface chemistry is incompatible, "like oil and water." To overcome the natural tendency for the CNC filler material to separate from the surrounding polyethylene matrix, a catalyst was attached to the surface of the CNCs and polymerization ensued from that catalyst leading to a composite material in which tiny CNC particles were trapped in the matrix Good dispersal of the component substances in the composite and of excellent overall reinforcement were proven by physical analysis.

Cellulose nanomaterials (CNMs) have been widely studied for their potential as sustainable fillers in polymer nanocomposites, optical responsiveness in suspensions and thin films, and their orientation-dependent liquid crystalline behavior in suspensions. Cellulose nanocrystals (CNCs) have seen a particular prominence due to their versatility across a breadth of applications. The unique structure of CNCs, represented as nanoscale rods with a slight twist, provides for their self-assembly into liquid crystalline phases when their concentration is increased and can be used to generate iridescent materials with tunable wavelengths. Further, CNCs are often used as fillers in nanocomposites, due to their high single crystal Young's modulus, achieving vast enhancements in stiffness when incorporated above a critical concentration where a percolating network is formed. The breadth of applications for CNCs strongly depend not only on their crystalline structure, but crucially on the interactions between particles. These interactions are well-known, yet a complete understanding to enable the full exploitation of the properties attainable in CNC-based materials is lacking. The principal emphasis of this dissertation lies in further improving our comprehension of the interactions between CNCs across a variety of applications such that their full potential can be achieved. A review of the current research of CNC-based materials is provided to guide the discussion herein. Interparticle interactions are studied in aqueous suspensions of CNCs in evaporating sessile droplets. This system provides a complex interrelationship between mass, heat, and momentum transport which collectively provide a change in the local CNC concentration as a function of time. CNC interactions can be controlled throughout the evaporation process as a result of these local concentration variations. We implement a novel approach using time-resolved polarized light microscopy to characterize the evolution of these particle interactions via the orientation of CNCs as a function of CNC concentration and droplet volume. Ultimately, boundary interactions at the leading edge of the contact line during evaporation was found to drive a cascade of local CNC interactions resulting in alignment post-deposition. Computational analysis evaluated the influence of evaporation-induced shear flow during evaporation. Orientation was found to be independent of the bulk fluid flow, corroborating the importance of interparticle interactions on the ensuing alignment of CNCs. Characterization of an evaporating droplet of initially liquid crystalline suspension of CNCs verified the simulations which predicted that orientation was not coupled with entrainment. Finally, the multiple modes of orientation showed that local control over CNC properties can be realized through governance of the interactions between CNCs. The interactions of CNCs in polymer nanocomposites were also studied for the development of smart materials which can adapt their properties in response to external stimuli. A well-known example of this phenomena is found when CNCs are introduced as fillers in thermoplastic polyurethanes (TPUs) above a critical concentration required to achieve percolation. The interactions between CNCs in the percolating network provide a strong enhancement to the modulus of these materials. However, these materials soften upon exposure to water following the disruption of inter-CNC hydrogen bonding by the diffusing water molecules, as prevailing theories suggest. CNCs simultaneously enhance water transport into hydrophobic matrices. Thus, a complete understanding of the interrelationship between the mass transport and mechanical performance can facilitate the development of humidity sensing or shape memory materials which operate as a result of the interactions between CNCs inside of a polymer matrix. Despite an increase in the equilibrium water uptake with increasing CNC concentration, a decrease in the apparent diffusivity of water within the nanocomposites was observed as a result of swelling of the bulk polymer. Additionally, we developed a modification to the commonly used percolation model to predict the time-dependent evolution of storage modulus during water-induced softening. We found that the solvent mass transport can be directly coupled to the mechanical integrity of the percolating network of CNCs by evaluating the hydrogen bonding state of the network as a function of time. Finally, a novel nanocomposite filler comprised of CNCs and 2,2,6,6- tetramethylpiperidine 1-oxyl (TEMPO) oxidized cellulose nanofibrils (TOCNFs) was prepared through solution casting to improve the mechanical performance of the individual reinforcements alone. The physical interaction length is increased by incorporating CNMs of different length scales resulting in increased tensile strength and elongation. Further, the morphology, evaluated with polarized light microscopy, atomic force microscopy, and simulated with dissipative particle dynamics, revealed the combined fillers exhibit a cooperative enhancement between CNMs. Characterization of the crystallinity through x-ray diffraction confirmed the interactions occur primarily between the crystalline domains of each material. Accordingly, the combination of CNMs resulted in nanocomposite fillers which can be implemented such that the weak interfaces with polymer matrices can be bridged with fillers providing reinforcement over a broader length scale. / Doctor of Philosophy / Cellulose nanocrystals (CNCs) are sustainable and biorenewable nanoparticles derived from cellulose. These materials have been widely studied and are commonly used among a plethora of applications such as in reinforcing fillers in polymer nanocomposites, optically responsive materials that can be used in packaging or anti-counterfeiting technologies, as well as in suspension modifiers for skin care products. These techniques tune the interactions between individual CNCs to modify the behavior of the bulk material. The specific interactions are well-known, yet a complete understanding of the influence of these interactions resulting in the utility of CNC-based materials in various applications is lacking. The principal emphasis of this dissertation lies in further improving our comprehension of the interactions between CNCs across a variety of applications such that their full potential can be achieved. Interactions between CNCs were investigated in three systems comprising of a range of typical use cases for CNC-based materials. The behavior of CNCs was examined in evaporating droplets of aqueous suspensions. These materials exhibited a change in orientation in the final deposit which is dependent on variations in local CNC concentration during drying. These concentration changes describe the relative strength of interactions between CNCs which ultimately influences the final alignment of these materials. Further, these interactions provide a pathway to deposit a controlled orientation of CNCs on a substrate which can be utilized for optically responsive materials or serve as templates for other orientation-dependent materials. CNCs were also incorporated into a thermoplastic polyurethane (TPU) matrix to provide increased stiffness. In these composites, water preferentially interacts with CNCs preventing the nanoparticles from interacting with one another. As water is absorbed, these materials soften as a result of the reduced interactions between CNCs. We investigated the influence of dynamically changing CNC interactions on the mechanical performance of these materials during water absorption and developed an analytical model to describe the observed softening behavior. Finally, CNCs were combined with 2,2,6,6- tetramethylpiperidine 1-oxyl oxidized cellulose nanofibers (TOCNFs) and cast into thin films. The mechanical properties of these differently sized, yet chemically similar, nanoparticles were compared as a function of CNC composition. A cooperative enhancement of the ultimate tensile strength and elongation was observed at low CNC loadings where CNCs and TOCNFs were found to self-organize during casting in a mutually beneficial manner.

Yes / Purpose: Dexibuprofen is an enantiomer of ibuprofen with low bioavailability which results from its hydrophobic nature. Nanosuspensions have developed a podium to solve the in vitro dissolution problem that frequently occurs in current research. Materials and methods: The drug and polymer solutions were mixed in a microchannel fluid reactor and the successive embryonic nanosuspension was decanted into a vial having the polymer solution. The impact of different process and formulation parameters including inlet angle, antisolvent and solvent flow rate(s), mixing time, drug concentration, polymer type and concentration was evaluated. Results and discussion: Stable dexibuprofen nanocrystals with a particle size of 45±3.0 nm and polydispersity index of 0.19±0.06 were obtained. Differential scanning calorimetry and powder X-ray diffraction confirmed the crystallinity. The key parameters observed were inlet angle 10°, antisolvent to solvent volume of 2.0/0.5 mL/min, 60 minutes mixing with 5 minutes sonication, Poloxamer-407 with a concentration of 0.5% w/v and drug concentration (5 mg/mm). The 60-day stability studies revealed that the nanocrystals were stable at 4°C and 25°C. The scanning electron microscopy and transmission electron microscopy images showed crystalline morphology with a homogeneous distribution. Conclusion: Stable dexibuprofen nanocrystals with retentive distinctive characteristics and having marked dissolution rate compared to raw and marketed formulations were efficiently fabricated. In future perspectives, these nanocrystals could be converted to solid dosage form and the process can be industrialized by chemical engineering approach

Ce travail de thèse concerne la réalisation et l'analyse des propriétés optiques de nanocristaux de silicium. Ces objets de taille nanométrique possèdent des propriétés optiques remarquables, en particulier de photoluminescence. Les propriétés de confinement quantique qui les caractérisent permettent d'obtenir un signal de luminescence intense dans le domaine du visible. Des composants optoélectroniques et photoniques ont été envisagés à base de nanocristaux de silicium. Les raisons physiques du fort signal de luminescence en revanche sont encore mal comprises. Les nanocristaux de silicium sont élaborés par évaporation. L'élaboration et le recuit thermique de multicouches SiO/SiO2 permet d'obtenir des nanocristaux de silicium de diamètre moyen bien contrôlé. Ceux-ci sont issus de la démixtion de la couche de SiO selon la réaction SiOx --> Si + SiO2. Le contrôle du diamètre des nanocristaux de silicium permet de maîtriser la région spectrale de luminescence dans la région du visible.La première partie de ce travail de thèse vise à isoler un ou quelques nanocristaux de silicium. L'objectif est de remonter à la largeur homogène de ces nano-objets. Dans un premier temps, une étude centrée sur le matériau SiOx est réalisée afin de réduire la densité surfacique de nanocristaux de silicium. Dans un deuxième temps, des moyens de lithographie ultime sont mis en oeuvre afin de réaliser des masques percés de trous de diamètres de l'ordre de la centaine de nanomètre. Des expériences de spectroscopie optique sont réalisées sur ces systèmes.La deuxième partie de ce travail vise à contrôler l'émission spontanée de lumière issue des nanocristaux de silicium. Ceci se fait en couplant les modes électroniques aux modes optiques confinés d'une microcavité optique. Le manuscrit détaille les moyens développés afin d'obtenir une microcavité optique dont les modes optiques puissent se coupler efficacement aux nanocristaux de silicium. Les propriétés optiques de ces systèmes sont finalement analysées. / This work concerns the implementation and analysis of optical properties of silicon nanocrystals. These nanoscaled objects have remarkable optical properties, especially in photoluminescence. The properties of quantum confinement that characterize them allow obtaining an intense luminescence signal in the visible range. Optoelectronic and photonic devices have been proposed based on silicon nanocrystals. The physical reasons of the strong luminescence signal, however, are still poorly understood. The silicon nanocrystals are prepared by evaporation. The preparation and thermal annealing of multilayers SiO/SiO2 leads to silicon nanocrystals with a well controlled average diameter. They are created during the demixing of the SiO layer by the reaction SiO ? Si + SiO2. The control the diameter of the silicon nanocrystals influences directly the spectral region of luminescence in the visible region.The aim of first part of this work is to isolate one or a few silicon nanocrystals. The intent is to trace the homogeneous width of these nano-objects. Initially, a study focusing on the SiOx material is conducted to reduce the surface density of silicon nanocrystals. In a second step, lithography is implemented to make masks with holes with diameters of about one hundred nanometers. Optical spectroscopy experiments were performed on these systems.The second part of this work aims controlling the spontaneous emission of light from silicon nanocrystals. This is done by coupling the electronic transmission to optical modes confined in an optical microcavity. The manuscript describes the methods developed to obtain an optical microcavity whose optical modes can be coupled effectively to the silicon nanocrystals. The optical properties of these systems are finally analyzed

<p>The discovery, formulation, and characterization of novel compositions of matter for aid in the diagnosis and treatment of disease has ever been a compelling force behind nanomaterials development. In instances of disease originating from oncogenic mutation, proliferation, and metathesis; cancer has long been a most difficult dysfunction to diagnosis and treat in virtue of its innate alteration and disregulation of otherwise well-managed and healthful cellular processes. To date, cancer therapies have relied largely on highly toxic chemotherapy or radiation treatments, addressing the overarching problem of individual cellular mutations in a global sense, often deleterious to the overall health of the patient. Ever-progressing work on nanomaterial-based applications to either promote cancer diagnosis or implement novel therapeutic means of drug delivery, activation, or the precisely-targeted destruction of cancer cell lines has been afforded much attention in the integrated biological and materials science fields. Recent developments in nanosized laser materials incorporating lanthanide-doped sensitizer and activator pairs and the development of numerous crystallographic, co-dopant, morphological, and/or surface-appended optimizations to these materials have given rise to a novel class of nanomaterials, with unique photophysical properties that have direct import into light-based activation of chemical processes, triggered non-invasively through biological tissues, and merging intra-cellularly targetable nanocrystalline compositions and ex vivo light activation. Upconverting nanocrystals (UCNCs) are one such class of nanomaterial wherein near-infrared (NIR) light, at the nadir of tissue absorption, can serve to sequentially or cooperatively excite long-lived lanthanide (Ln3+) 4f excited states and, through various energy transfer processes coupled between both the UCNC material composition and its integral Ln3+ dopants, are capable of building an excited state population capable of emitting in higher frequencies than its incident NIR excitation.</p><p>In the study of these UCNCs, the prospect of activating intra-cellular photodynamic processes or drugs of low cellular toxicity, until light activated in a precisely localized regime (e.g. the nucleus of a cell), has motivated extensive research into the generation of novel UCNC materials, in multiple compositions and on multiple size scales to direct the mechanisms of upconversion (UC) to produce high fluence ultraviolet (UV) photons upon NIR (972 nm) excitation. Continuing optimizations have yielded a high ytterbium (Yb) sensitizer, cubic &#945;-NaYbF4 UCNC composition, codoped with a thulium activator, to generate excited state saturated UV transitions, 1I6 &#8594; 3F4 (349 nm) and 1D2 &#8594; 3H6 (362 nm), and their refinement to afford dominant UV emissive spectral signatures at low NIR laser excitation. Their photophysical dynamics are sparsely described in the literature, breaking from both fields of laser photonics and conventional inorganic nanoscience, and require renewed emphasis to be afforded in exacting crystallographic, photophysical, and size dependent effect characterization, heavily directing the structure-function relationships of luminescent Ln3+ dopants and their host crystal matrices. Requisite in this study is a call for the optimization of uniform, monodisperse, and reproducible preparations of unique UCNCs and precise characterization of the properties they display and the origins thereof.</p><p>Offered herein are the enveloping efforts to more fully understand the mechanistic processes of UC of both poorly characterized, literature standard materials, novel UCNCs tuned for enhancement of UC emission in the UV, and the adaptations to each that ultimately affect their photophysical dynamics. A tandem course of this research follows from inorganic shelling, passivation methodologies to ameliorate crystallographic surface defects and UC luminescence quenching sites to overall enhance the dominant UV emissivity of novel co-doped UCNC. These state-of-the-art UC materials are: 1) &#945;-NaYbF4: Tm3+, interlaced with gallium, chromium, yttrium, and other trivalent metal ions, serving to finely modulate UC mechanistic processes and enhance luminescent properties and 2) sodium co-doped LaF3 and BaLaF4 (0.5%Tm, 20%Yb), displaying 3 and 2 orders of magnitude enhancement of UV emissions due to controlled perturbation of the local crystal field environment. The Core @ Shell architectural derivatives of these materials exhibit an eminent departure from classical luminescent fluorophores, phosphors, or quantum confined luminescent nanomaterials, in both degree of luminescent flux generation and the complicated mechanistic processes they are derived from.</p><p>To a great extent, this work attempts to establish testable grounds for comparison of UCNCs; extending from interrogation of photophysical lifetime measurements, excitation versus emissive flux power dependence studies, high resolution X-ray photoelectron spectroscopy (HR-XPS) and power diffraction (HR-XRD) assessments of crystallographic defects and perturbations on the atomic scale, and the establishment of new metrics of radiant flux versus absolute quantum yield for use in comparison of UCNCs towards their applicability in areas of variable or limited excitation flux and the ultimate utility of discerning hit-to-lead UCNC materials for medical nanodevice compositions. A salient component affecting these metrics is the direct surface interactions with respect to solvents, coordinating ligands, and appended functional moieties for enhancement of UCNCs towards specific applications; largely directed towards cancer biology and medical study. In a confluence of inquisition of UCNCs and their high energy, UV luminescent properties, interfacing with the surface presenting effects of solublization and bio-targeting molecular functionalization; literature standard, &#946;-NaYF4 (2%Er, 20%Yb) UCNCs have been generated in highly uniform compositions to assess the size-dependent effects with respect to luminescent quenching surrounding a UCNC surface and functionalization methodologies have been offered as a proof of concept towards the construction of an optimized biomolecular targeting nanodevice, with known limits and predictable interactions, both to NIR excitation light and potential intra-cellular biological environments.</p><p>The ultimate goal of these explorations is the innovative fusion of the above concepts into a nanotherapeutic device involving: 1) the generation of a well-studied and predictable NIR-absorbing and dominant UV-emissive UCNC, with defined co-dopant optimizations and employing an optimal Core @ Shell architecture, 2) the requisite surface functionalization needed to afford aqueous solubility and a means of covalently conjugating targeting molecules of interest, and 3) the ultimate and equal assessment of such a composite system with respect to possible alternate materials in the literature and novel UCNCs currently under development. To date, no such convergent study has been conducted to any degree of reproducibility or certainty of desired and defined functionality. In this work is described in detail each optimized component for such a device or potentially one marked by differing, but assessable conditions for alternate applications. The optimization of a sub-10 nm, dominant UV-emissive UCNC, the crystallographic and photophysical origins of its UC mechanism under varied conditions, and the optimal means of their employment (both in terms of establishing equivalent metrics and utility in cancer nanotherapeutics), assessment, and readdressing of, as yet undiscovered limits to these materials are presented.</p> / Dissertation

Nanomaterials such as carbon nanotubes, gold nanorods, magnetic nanocrystals, and binary nanocrystal superlattices have exciting potential applications. However, before these ideas can be applied, it is imperative to fully understand the materials synthesis. Multiwall carbon nanotubes were synthesized in supercritical toluene using cobaltocene, nickelocene, ferrocene, or metal nanocrystals as catalysts. Toluene served as both the solvent and carbon source for nanotube growth. The reaction was optimized by introducing supplemental carbon sources; either hexane or ethanol increased the yield relative to pure toluene and catalytic amounts of water minimized carbon filament and amorphous carbon formation. Gold nanorods were synthesized by the colloidal seed-mediated, surfactantassisted approach using cetyltrimethylammonium bromide (CTAB) obtained from ten different suppliers. The gold nanorod yield depended strongly on the CTAB used: with the same recipe, three of the CTABs produced only spherical particles, whereas the other CTABs produced nanorods with nearly 100% yield. Inductively coupled plasma mass spectrometry revealed a trace iodide impurity in the CTABs that did not yield nanorods. Further experiments introducing potassium iodide to the nanorod synthesis verified the detrimental effect of iodide on nanorod formation. Multifunctional colloidal core-shell nanoparticles of magnetic nanocrystals or gold nanorods coated with a fluorescent dye (Tris(2,2 -bipyridyl)dichlororuthenium(II) hexahydrate) doped silica shells were also synthesized. The as-prepared magnetic nanocrystals were initially hydrophobic and silica coated using a microemulsion approach, while the gold nanorods were hydrophilic and silica coated using a Stöber process. These colloidal heterostructures have the potential to be used as dual-purpose tags, exhibiting a fluorescent signal that could be combined with either dark-field optical contrast or enhanced contrast in magnetic resonance imaging. Binary superlattices (BSLs) of large iron oxide and small gold nanocrystals were assembled by slow evaporation of colloidal dispersions on tilted substrates. SEM and grazing incidence small angle X-ray scattering (GISAXS) confirmed the BSLs were simple hexagonal AB2 superlattices with long range order. GISAXS also revealed that the superlattice was slightly contracted perpendicular to the substrate as a result of solvent drying during the deposition process. Additionally, in some BSLs nearly periodic superlattice dislocations consisting of inserted half-planes of gold nanocrystals were observed. / text