Nanomaterial toxicity is a major concern and could potentially hamper the progress of biomedical nanotechnology development. Dispelling these concerns requires that the consequences of nanomaterial exposure are evaluated, and the findings will determine whether developmental hurdles can be overcome. This thesis evaluates the both in vivo and in vitro impact of quantum dots (QD , zinc sulphide capped cadmium selenide semiconductor nanocrystals) a fluorescent nanoparticle label with potential as an optical in vivo imaging agent. This work reviews nanoparticle characterization techniques and their importance to biological responses, and surveys QD interactions both in vivo and in vitro. We collected pharmacokinetic and toxicity data by a) quantitatively surveying the in vivo absorption, distribution , metabolism and excretion of QDs, and b) measuring the impacts of QDs on relevant organs (in vivo) and cells (in vitro). Neither of these areas had been explored when this thesis was started. In vivo, intravenous QD dosing in Sprague-Dawley rats showed uptake into reticuloendothelial cells with surface coating dependent kinetics, slow degradation, no excretion detected in feces or urine, and no indications of toxicity. The liver took up the majority of dose after 90 minutes and small amounts of QDs appeared in the spleen, kidney, and bone marrow. After 30 days, the cadmium concentration in the kidneys increased to 3µg/g without a proportional amount of zinc, indicating QD breakdown. In vitro we noted phagocytic capacity comparable to in vivo results, QD breakdown, and a retention of normal macrophage function thereby demonstrating that primary rat liver macrophages (Kupffer cells) are an appropriate in vitro system with which to investigate the cellular responses to quantum dots. Such an in vitro model will facilitate faster evaluation of individual nanotechnologies intended for in vivo use. This dissertation addresses a lack of in vivo background information needed to understand the consequences of QD exposure; though QD fail to demonstrate pharmacokinetics desirable for in vivo imaging agents, they are not toxic. Importantly, we provide in vitro data that will lead to the development of accurate and efficient in vitro primary screening methods that will be central to the further development of biomedical nanotechnologies.

With growing global energy demand there will be an increased need for sources of renewable energy such as solar cells. To make these photovoltaic technologies more competitive with conventional energy sources such as coal and natural gas requires further reduction in manufacturing costs that can be realized by solution processing and roll-to-roll printing. Colloidal quantum dots are a bandgap tunable, solution processible, semiconductor material which may offer a path forward to efficient, inexpensive photovoltaics. Despite impressive progress in performance with these materials, there remain limitations in photocarrier collection that must be overcome. This dissertation focuses on the characterization of charge recombination and transport in colloidal quantum dot photovoltaics, and the application of this knowledge to the development of new and better materials. Core-shell, PbS-CdS, quantum dots were investigated in an attempt to achieve better surface passivation and reduce electronic defects which can limit performance. Optimization of this material led to improved open circuit voltage, exceeding 0.6 V for the first time, and record published performance of 6% efficiency. Using temperature-dependent and transient photovoltage measurements we explored the significance of interface recombination on the operation of these devices. Careful engineering of the electrode using atomic layer deposition of ZnO helped lead to better TiO2 substrate materials and allowed us to realize a nearly two-fold reduction in recombination rate and an enhancement upwards of 50 mV in open circuit voltage. Carrier extraction efficiency was studied in these devices using intensity dependent current-voltage data of an operational solar cell. By developing an analytical model to describe recombination loss within the active layer of the device we were able to accurately determine transport lengths ranging up to 90 nm. Transient absorption and photoconductivity techniques were used to study charge dynamics by identifying states in these quantum dot materials which facilitate carrier transport. Thermal activation energies for transport of 60 meV or lower were measured for different PbS quantum dot bandgaps, representing a relatively small barrier for carrier transport. From these measurements a dark, quantum confined energy level was attributed to the electronic bandedge of these materials which serves to govern their optoelectronic behavior.

Transition metal oxide thin films are commonly used in organic electronics devices to improve charge-injection between electrodes and organic semiconductors. Some oxides are good hole-injectors, while others are good electron-injectors. Transition metal oxides are materials with many diverse properties. Many transition metals have more than one stable oxidation state and can form more than one oxide. Each oxide possesses its own unique properties. For example, transition metal oxide electronic band structures can range from insulating to conducting. They can exhibit a wide range of work functions. Some oxides are inert, while others are catalytically active. Such properties are affected by numerous factors, including cation oxidation state and multiple types of defects. Currently it is not fully understood which oxide properties are the most important to their performance in organic electronics. In the present thesis, photoemission spectroscopy is used to examine how changes in certain oxide properties–such as cation oxidation states and defects—are linked to the oxide properties that are relevant to organic electronics devices—such as an oxide’s work function and electron band structure. In order to unravel correlations between these properties, we controllably change one property and measure how it changes affects another property. By performing such tests on a wide range of diverse transition metal oxides, we can discern broadly-applicable relationships. We establish a relationship between cation oxidation state, work functions and valence band structures. We determine that an oxide’s electron chemical potential relative to an organic’s donor and acceptor levels governs energy-level alignment at oxide organic interfaces. We establish how interfacial reactivity at electrode/oxide interfaces dictates an oxide’s work function and electronic structure near the interface. iii These findings demonstrate some of the very interesting fundamental relationships that exist between chemical and electronic properties at interfaces. These findings should assist in the future development and understanding of the functional interfaces of organic semiconductors and transition-metal oxides.

There are several factors which conspire to limit the efficiency of solar cells. One of these is the fact that a solar cell is unable to absorb photons of energy less than the band gap of the semiconductor from which it is made; in the case of some high-band gap materials such as amorphous silicon – the model system used in this study – this can mean that as much as 50% of the solar spectrum is unusable. Upconversion phosphors – materials which can, by way of two or more successive photon absorptions, convert low energy (typically near infrared) light into high energy (typically visible) light – offer a potential solution to this problem as they can be used to convert light, which would otherwise be useless to the cell, into light which can be used for power generation. In this thesis we work towards the application of NaYF4-based upconverters to enhanced efficiency amorphous silicon (a-Si) photovoltaic power generation. We begin by synthesizing these upconverters at a range of temperatures and studying the crystallographic and spectroscopic properties of the resulting materials, elucidating heretofore undocumented trends in their luminescence and crystallography, including the effect of synthesis temperature on upconversion intensity, crystallite size, and lattice parameter. We also investigate the emission quantum yield of these materials, beginning with an in depth discussion and investigation of two methods for recording absolute quantum yields. We demonstrate that the quantum yields of the materials may vary by a factor of over 100, depending on the synthesis conditions. After we have fully characterized these properties we turn our attention to the application of these materials to amorphous silicon solar cells, for which we provide a proof of concept by demonstrating the effect of upconversion luminescence on the photoconductance of an a-Si film. We conclude by developing a roadmap for future improvements in the field.

A new approach is discussed for the generation of high purity silicon from silica fume (SF), which is a waste by-product from the manufacture of metallurgical grade silicon. Process steps were developed and optimized including purification of SF, reduction by magnesium, and post-reduction leaching. Reduction was carried out successfully with initial HCl leached SF in a sealed chamber with varying Mg/SF ratios, temperature and time. These variables affected the production of silicon from SF. Suitable reduction conditions were found to be within the temperature range 750-850C and at approximately 2:1 ratio of Mg/SF. Reduction products were treated using a three-stage acid leaching. XRD, QXRD and ICP analyses of the final silicon powder product indicated that silicon with low impurity levels (low boron content) can be produced. Therefore, silicon produced by magnesiothermic reduction can be an attractive source for the production of solar grade silicon.

Electrochemical capacitors (ECs) have drawn much attention owing to their fast charging/discharging rate, and long lifetime up to millions of cycles. Applications of EC range from large scale transportation to miniaturized electronics. The research reported herein explores the development of an economical process for the synthesis of high performance electrode material for high power ECs. A two stage synthesis process which consists of electroplating of molybdenum oxide followed by thermal nitridation was developed. X-ray diffraction and X-ray photoelectron spectroscopy revealed the material to be Mo oxide with nitrogen substitution, Moz(O,N). In a three electrode system, the Moz(O,N) electrodes showed capacitance as high as 16 mF/cm2. Symmetric EC cells achieved state of the art time constant of 100 ms. Ultrahigh power ECs were demonstrated for the first time using Moδ(O,N) electrodes and SiWA-H3PO4-PVA electrolyte, achieving with 10 ms time constant one of the lowest time constants reported for EC.

The mechanisms underlying the effect of alterations in Type I collagen on bone mechanical properties are not well defined. Clinical tools for evaluating fracture risk, such as dual energy x-ray absorptiometry (DXA) and quantitative ultrasound (QUS) focus on bone mineral and cannot detect changes in the collagen matrix. The mechanical response tissue analyzer (MRTA) is a potential tool for evaluating fracture risk. Thus, the focus of this work was to investigate the effects of collagen degradation on bone mechanical properties and examine whether clinical tools can detect these changes. Female and male emu tibiae were endocortically treated with 1 M potassium hydroxide (KOH) solution for 1-14 days and then either mechanically tested in three-point bending, fatigued to failure or fatigued to induce stiffness loss. Computed Tomography scans, DXA, QUS, MRTA and three-point bend testing in the elastic region were performed on emu tibiae before and after either KOH treatment or fatigue to induce stiffness loss. Fracture surfaces were examined to determine failure mechanisms. Bone mineral and bone collagen were characterized using appropriate techniques. Bone mineral-collagen interface was investigated using Raman spectroscopy and atomic force microscopy (AFM). Endocortical KOH treatment does not affect bone mineral however, it causes in situ collagen degradation, rather than removal and may be weakening the mineral-collagen interface. These changes result in significantly compromised mechanical properties. Emu tibiae show significant decreases in failure stress and increased failure strain and toughness, with increasing KOH treatment time. The significant increase in toughness of KOH treated bones is due to structural alterations that enhance the ability of the microstructure to dissipate energy during the failure process, thereby slowing crack propagation, as shown by fracture surface analysis. KOH treated samples exhibit a lower fatigue resistance compared to untreated samples at high stresses only for both sexes. Partial fatigue testing results in similar decreases in modulus for all groups and sexes. The MRTA detected these changes whereas DXA and QUS did not. MRTA detects changes in bone mechanical properties induced by changes in collagen quality and fatigue and could be a more effective tool for predicting fracture risk.

Organic light emitting diodes (OLEDs) are being commercialized in display applications, and will be potentially in lighting applications in the near future. This thesis is about the design of high performance OLEDs, which includes both the electrical and optical design of OLEDs. In particular, the following work is included in this thesis: i) Energy level alignment and charge injection at metal/organic interfaces have been systematically studied. ii) Transition metal oxide anodes have been developed to inject sufficient holes into the OLEDs due to their high work function. The oxide anodes have also been used to systematically study the transport properties in organic semiconductors. iii) Highly simplified OLED devices with unprecedentedly high efficiency have been realized using both fluorescent and phosphorescent emitters. The high performance was enabled by using a high work function metal oxide anode and a hole transport material with very a deep highest occupied molecular orbital (HOMO). iv) An optical model has been developed to describe the optical electric field across the OLED device. By using the model, a high performance flexible OLED using metal anode was designed and realized.

There are several factors which conspire to limit the efficiency of solar cells. One of these is the fact that a solar cell is unable to absorb photons of energy less than the band gap of the semiconductor from which it is made; in the case of some high-band gap materials such as amorphous silicon – the model system used in this study – this can mean that as much as 50% of the solar spectrum is unusable. Upconversion phosphors – materials which can, by way of two or more successive photon absorptions, convert low energy (typically near infrared) light into high energy (typically visible) light – offer a potential solution to this problem as they can be used to convert light, which would otherwise be useless to the cell, into light which can be used for power generation. In this thesis we work towards the application of NaYF4-based upconverters to enhanced efficiency amorphous silicon (a-Si) photovoltaic power generation. We begin by synthesizing these upconverters at a range of temperatures and studying the crystallographic and spectroscopic properties of the resulting materials, elucidating heretofore undocumented trends in their luminescence and crystallography, including the effect of synthesis temperature on upconversion intensity, crystallite size, and lattice parameter. We also investigate the emission quantum yield of these materials, beginning with an in depth discussion and investigation of two methods for recording absolute quantum yields. We demonstrate that the quantum yields of the materials may vary by a factor of over 100, depending on the synthesis conditions. After we have fully characterized these properties we turn our attention to the application of these materials to amorphous silicon solar cells, for which we provide a proof of concept by demonstrating the effect of upconversion luminescence on the photoconductance of an a-Si film. We conclude by developing a roadmap for future improvements in the field.

A new approach is discussed for the generation of high purity silicon from silica fume (SF), which is a waste by-product from the manufacture of metallurgical grade silicon. Process steps were developed and optimized including purification of SF, reduction by magnesium, and post-reduction leaching. Reduction was carried out successfully with initial HCl leached SF in a sealed chamber with varying Mg/SF ratios, temperature and time. These variables affected the production of silicon from SF. Suitable reduction conditions were found to be within the temperature range 750-850C and at approximately 2:1 ratio of Mg/SF. Reduction products were treated using a three-stage acid leaching. XRD, QXRD and ICP analyses of the final silicon powder product indicated that silicon with low impurity levels (low boron content) can be produced. Therefore, silicon produced by magnesiothermic reduction can be an attractive source for the production of solar grade silicon.