<p> III-nitride based photocathodes have been the subject of much research in photoemissive devices for ultraviolet (UV) detection in astronomy and defense applications. In order to achieve high quantum efficiency (QE), negative electron affinity (NEA) is necessary to allow for carriers that have relaxed to the conduction band minimum to escape. NEA in III-nitride UV photocathodes is conventionally reached via cesium-based surface treatment of p-type GaN. However, this treatment is highly reactive in air and photocathodes using this technology have been reported to suffer from chemical instability and QE degradation over time. </p><p> Recent work has shown the potential to take advantage of the spontaneous and piezoelectric polarization exhibited by III-nitride materials in order to achieve permanent NEA in AlGaN-based photocathode structures without the need for cesiation. The N-polar orientation has potential for improved and expanded device design space due to the reversal of the built-in and stress-induced polarization fields. However, achieving smooth high-quality N-polar material has traditionally been a challenge due to the formation of large hexagonal hillock structures on a typical N-polar surface. Furthermore, achieving high-conductivity p-type material is crucial for high efficiency photocathodes (among other devices), but has been a long-standing challenge in III-nitrides due to the high ionization energy of the Mg dopant and tendancy for self-compensation. </p><p> Rapid development and optimization of device design requires accurate modeling of the photoemission process to shorten the feedback loop, but the complexity of the photoemission process makes development of accurate models difficult. Traditionally, it has been assumed that photo-excited hot-carriers are thermalized to the conduction band minimum during transport, which allows for simplified modeling. This assumption breaks down for high-energy excitation or reflection-mode photocathodes, and more accurate treatments are needed. The development in recent years of accurate Monte Carlo modeling of III-nitrides enables simulation of hot-carrier transport. Application of Monte Carlo transport for photoemission modeling has recently been studied in Cs-treated NEA GaAs photocathodes with close agreement to experimental results. </p><p> This work outlines development of Cs-free III-nitride photocathodes via use of surface treatments and materials optimization resulting in peak quantum efficiencies of 23\% for N-polar devices. This high QE is comparable to results from cesiated devices. Physics-based device simulations show the promise of N-polar orientation, with the ability to obtain a similar band profile as Ga-polar with 2 orders of magnitude lower p-doping in addition to the potential for substantial narrowing of surface band bending region. Materials development and optimization focused on two aspects: surface morphology and doping efficiency. These optimizations have resulted in a decrease in undesirable surface features by over 3 orders of magnitude via the use of indium surfactant and buffer optimization. For Ga-polar photocathode structures, free hole concentrations in excess of 1 x 10¹⁸ cm^&ndash;3 was achieved in AlGaN absorber of 28% Al composition, via the use of a pulsed deposition technique, representing over a 3 times increase from traditional epitaxy method. Application of the same technique to N-polar films showed reduced doping effectiveness as compared to Ga-polar films due to differences in surface configuration. As part of this study, Monte Carlo simulator based on the open-sourced GNU Archimedes was developed. The Monte Carlo simulation was developed to support III-nitrides and photoexcitation and emission processes in devices based on this material system. Simulated results showed close agreement with experimentally measured values, validating the technique. Results point towards several important factors affecting emission behavior and suggest future research focus. Additionally, photoemission simulation gives evidence towards proper satellite valley band parameters which are subject to much uncertainty.</p><p>

<p>Chemotherapy combinations for cancer treatments harbor immense therapeutic potentials which have largely been untapped. Of all diseases, clinical studies of drug combinations are the most prevalent in oncology, yet their effectiveness is disputable, as complete tumor regressions are rare. Our research has been devoted towards developing delivery vehicles for combinations of chemotherapy drugs which elicit significant tumor reduction yet limit toxicity in healthy tissue. Current administration methods assume that chemotherapy combinations at maximum tolerable doses will provide the greatest therapeutic effect ? a presumption which often leads to unprecedented side effects. Contrary to traditional administration, we have found that drug ratios rather than total cumulative doses govern combination therapeutic efficacy. In this thesis, we have developed nanoparticles to incorporate synergistic ratios of chemotherapy combinations which significantly inhibit cancer cell growth at lower doses than would be required for their single drug counterparts. The advantages of multi-drug incorporation in nano-vehicles are many: improved accumulation in tumor tissue via the enhanced permeation and retention effect, limited uptake in healthy tissue, and controlled exposure of tumor tissue to optimal synergistic drug ratios. To exploit these advantages for polychemotherapy delivery, two prominent nanoparticles were investigated: liposomes and polymer-drug conjugates. Liposomes represent the oldest class of nanoparticles, with high drug loading capacities and excellent biocompatibility. Polymer-drug conjugates offer controlled drug incorporations through reaction stoichiometry, and potentially allow for delivery of precise ratios. Here, we show that both vehicles, when armed with synergistic ratios of chemotherapy drugs, significantly inhibit tumor growth in an aggressive mouse breast carcinoma model. Furthermore, versatile drug incorporation methods investigated here can be broadly applied to various agents. Findings from our research can potentially widen the therapeutic window of chemotherapy combinations by emphasizing investigations of optimal drug ratios rather than maximum drug doses and by identifying appropriate nanoparticles for their delivery. Application of these concepts can ultimately help capture the full therapeutic potential of combination regimens.

<p> Manipulation of single cells and particles is important to biology and nanotechnology. Our electrokinetic (EK) tweezers manipulate objects in simple microfluidic devices using gentle fluid and electric forces under vision-based feedback control. In this dissertation, I detail a user-friendly implementation of EK tweezers that allows users to select, position, and assemble cells and nanoparticles. This EK system was used to measure attachment forces between living breast cancer cells, trap single quantum dots with 45 nm accuracy, build nanophotonic circuits, and scan optical properties of nanowires. With a novel multi-layer microfluidic device, EK was also used to guide single microspheres along complex 3D trajectories. The schemes, software, and methods developed here can be used in many settings to precisely manipulate most visible objects, assemble objects into useful structures, and improve the function of lab-on-a-chip microfluidic systems.</p>

<p> On-chip Interconnection Networks are shifting from multicore to manycore systems and are tending to be heterogeneous with the integrated modules from different vendors of various sizes and shapes. Each module has different properties such as routers, link-width. From a system designer's perspective, making layouts of metal-wired links among interconnection modules for communication will be impractical as it increases the design cost in terms of the communication complexity and power leakage on these links. We can replace all links with wireless or optical links for high-performance, reducing latency. However, it comes with a high-cost. Therefore, we formulate the optimization model to minimize the cost (communication links between subnets) and maximize their data flows in the network-on-chip. </p><p> Since the optimization model using the optimizers such as CPLEX and Gurobi to achieve the best possible solutions, the solution time to a large set of given problems is not acceptable. Hence, we present a mincostflow-based heuristic algorithm (LINCA) that minimizes the quantification of hybrid routers corresponding to the application-specific traffic for manycore systems. LINCA guarantees the performance of hybrid networks on chip. Its results are validated against the manycore system architecture. Our evaluation shows that LINCA can significantly reduce the cost of using hybrid routers (communication links) in the manycore systems. It reduces cost by 84 percent on average across a variety of applications, compared with all of hybrid routers being deployed in the network without using the optimization model. However, we observed that the solution time of LINCA is increased exponentially for large scale networks. We then proposed an efficient predictive framework for optimized reconfiguring on-chip interconnection network. </p><p> The predictive model is built based on the optimization model and learning-based algorithms. As we wish to reduce the communication complexity of the interconnection links in the entire on-chip network, our objective is to minimize those links corresponding to the application-specific traffic demands. Thereby, the overall power dissipation can be mitigated. We believe that our approach will be an essential step when scaling out.</p><p>

Interactions between surfactants and polymeric nanostructures have gained increasing attention due to their potential application in many disciplines. In this study, a well-defined random copolymer containing 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA2080) (poly(MEO2MA-co-PEGMA2080)) was synthesized using the atom transfer radical polymerization (ATRP) process, and its thermo-responsive behaviors in aqueous solution were investigated. In comparison to other thermo-sensitive random copolymers based on oligo(ethylene glycol) methacrylates (OEGMA), this copolymer exhibited an unusual thermal induced two-stage aggregation process. The copolymer chains associated at the first thermal transition followed by a rearrangement process at the second thermal transition to produce a stable core-shell micellar structure. Furthermore, the binding interactions between cationic surfactants and this copolymer were examined below and above its cloud point. In general, the binding interactions between cationic surfactants and neutral polymers are weak and cationic surfactants are very selective and only bind to those polymers with specific hydrophobic groups. Significant hydrophobic interactions were observed between surfactant monomers and the polymer backbone. The binding occurred uncooperatively at low surfactant concentration, which was confirmed by electromotive force (EMF) measurements. Moreover, the binding affinity of three cationic surfactants follows the sequence: CTAB > TTAB > DoTAB. Cellulose Nanocrystals (CNC) with diameter of 10-20 nm and length of 200-400 nm, derived from native cellulose, is a promising new class of nanomaterials due to its high specific strength, high surface area, and unique optical properties. Currently, most of researches focused on the improvement of its steric stability, dispersability and compatibility in different solvents or matrices. A thermo-responsive polymer, namely Jeffamine M600 (a 600 Da polypropylene glycol) was grafted on the surface of cellulose nanocrystals (CNC) via a peptide coupling reaction. The better dispersion of the modified CNC in water was demonstrated, and the interactions between surfactants and M600-grafted CNC were investigated via isothermal titration calorimetry (ITC). Three types of surfactants with dodecyl alkyl chain and different head groups, namely cationic dodecyltrimethylammonium bromine (DoTAB), anionic sodium dodecyl sulfate (SDS), and nonionic poly(ethylene glycol) dodecyl ether (Brij 30) were studied. Physical mechanisms describing the interactions of cationic, anionic and nonionic surfactants and M600-grafted CNC were proposed. Chitosan molecules are water-soluble in acidic media due to the protonation of amino groups. However, some applications of chitosan are restricted by its poor solubility in basic media. A biocompatible derivative of chitosan, N-carboxyethylchitosan (CECh) was synthesized by Michael addition reactions, which possessed high solubility in both acidic and basic media due to the modification by carboxyl groups. The aggregation behavior of CECh in aqueous solution under the effects of pH, polymer concentration, as well as a gemini surfactant, was investigated by turbidity, zeta potential, fluorescence spectroscopy, viscosity, and surface tension measurements. This research demonstrates that nanostructures comprising of thermo-responsive copolymers can be controlled and manipulated by temperature and surfactants, and they play an important role in the physical properties of surfactants-polymeric complexes. The results from this research provide the fundamental knowledge on the self-assembly behavior and the binding mechanism of various novel polymeric systems and surfactants, which can be utilized to design and develop systems for personal care formulations and drug delivery systems.

Interactions between surfactants and polymeric nanostructures have gained increasing attention due to their potential application in many disciplines. In this study, a well-defined random copolymer containing 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA2080) (poly(MEO2MA-co-PEGMA2080)) was synthesized using the atom transfer radical polymerization (ATRP) process, and its thermo-responsive behaviors in aqueous solution were investigated. In comparison to other thermo-sensitive random copolymers based on oligo(ethylene glycol) methacrylates (OEGMA), this copolymer exhibited an unusual thermal induced two-stage aggregation process. The copolymer chains associated at the first thermal transition followed by a rearrangement process at the second thermal transition to produce a stable core-shell micellar structure. Furthermore, the binding interactions between cationic surfactants and this copolymer were examined below and above its cloud point. In general, the binding interactions between cationic surfactants and neutral polymers are weak and cationic surfactants are very selective and only bind to those polymers with specific hydrophobic groups. Significant hydrophobic interactions were observed between surfactant monomers and the polymer backbone. The binding occurred uncooperatively at low surfactant concentration, which was confirmed by electromotive force (EMF) measurements. Moreover, the binding affinity of three cationic surfactants follows the sequence: CTAB > TTAB > DoTAB. Cellulose Nanocrystals (CNC) with diameter of 10-20 nm and length of 200-400 nm, derived from native cellulose, is a promising new class of nanomaterials due to its high specific strength, high surface area, and unique optical properties. Currently, most of researches focused on the improvement of its steric stability, dispersability and compatibility in different solvents or matrices. A thermo-responsive polymer, namely Jeffamine M600 (a 600 Da polypropylene glycol) was grafted on the surface of cellulose nanocrystals (CNC) via a peptide coupling reaction. The better dispersion of the modified CNC in water was demonstrated, and the interactions between surfactants and M600-grafted CNC were investigated via isothermal titration calorimetry (ITC). Three types of surfactants with dodecyl alkyl chain and different head groups, namely cationic dodecyltrimethylammonium bromine (DoTAB), anionic sodium dodecyl sulfate (SDS), and nonionic poly(ethylene glycol) dodecyl ether (Brij 30) were studied. Physical mechanisms describing the interactions of cationic, anionic and nonionic surfactants and M600-grafted CNC were proposed. Chitosan molecules are water-soluble in acidic media due to the protonation of amino groups. However, some applications of chitosan are restricted by its poor solubility in basic media. A biocompatible derivative of chitosan, N-carboxyethylchitosan (CECh) was synthesized by Michael addition reactions, which possessed high solubility in both acidic and basic media due to the modification by carboxyl groups. The aggregation behavior of CECh in aqueous solution under the effects of pH, polymer concentration, as well as a gemini surfactant, was investigated by turbidity, zeta potential, fluorescence spectroscopy, viscosity, and surface tension measurements. This research demonstrates that nanostructures comprising of thermo-responsive copolymers can be controlled and manipulated by temperature and surfactants, and they play an important role in the physical properties of surfactants-polymeric complexes. The results from this research provide the fundamental knowledge on the self-assembly behavior and the binding mechanism of various novel polymeric systems and surfactants, which can be utilized to design and develop systems for personal care formulations and drug delivery systems.

Doping in bulk semiconductors (e.g., n- or p-type doping in silicon) allows for precise control of their properties and forms the basis for the development of electronic and photovoltaic devices. Recently, there have been reports on the successful synthesis of doped semiconductor nanocrystals (or quantum dots) for potential applications in solar cells and spintronics. For example, nanocrystals of ZnSe (with zinc-blende lattice structure) and CdSe and ZnO (with wurtzite lattice structure) have been doped successfully with transition-metal (TM) elements (Mn, Co, or Ni). Despite the recent progress, however, the underlying mechanisms of doping in colloidal nanocrystals are not well understood. This thesis reports a comprehensive theoretical analysis toward a fundamental kinetic and thermodynamic understanding of doping in ZnO, CdSe, and ZnSe quantum dots based on first-principles density-functional theory (DFT) calculations. The theoretical predictions of this thesis are consistent with experimental measurements and provide fundamental interpretations for the experimental observations. The mechanisms of doping of colloidal ZnO nanocrystals with the TM elements Mn, Co, and Ni is investigated. The dopant atoms are found to have high binding energies for adsorption onto the Zn-vacancy site of the (0001) basal surface and the O-vacancy site of the (0001) basal surface of ZnO nanocrystals; therefore, these surface vacancies provide viable sites for substitutional doping, which is consistent with experimental measurements. However, the doping efficiencies are affected by the strong tendencies of the TM dopants to segregate at the nanocrystal surface facets, as indicated by the corresponding computed dopant surface segregation energy profiles. Furthermore, using the Mn doping of CdSe as a case study, the effect of nanocrystal size on doping efficiency is explored. It is shown that Mn adsorption onto small clusters of CdSe is characterized by high binding energies, which, in conjunction with the Mn surface segregation characteristics on CdSe nanocrystals, explains experimental reports of high doping efficiency for small-size CdSe clusters. In addition, this thesis presents a systematic analysis of TM doping in ZnSe nanocrystals. The analysis focuses on the adsorption and surface segregation of Mn dopants on ZnSe nanocrystal surface facets, as well as dopant-induced nanocrystal morphological transitions, and leads to a fundamental understanding of the underlying mechanisms of dopant incorporation into growing nanocrystals. Both surface kinetics (dopant adsorption onto the nanocrystal surface facets) and thermodynamics (dopant surface segregation) are found to have a significant effect on the doping efficiencies in ZnSe nanocrystals. The analysis also elucidates the important role in determining the doping efficiency of ZnSe nanocrystals played by the chemical potentials of the growth precursor species, which determine the surface structure and morphology of the nanocrystals.

<p> Organic chemistry used to augment nanoparticles and nanotubes, as well as more traditional materials, is a subject of great interest across multiple fields of applied chemistry. Herein we present an example of both nanoparticle and nanotube augmentation with organic small molecules to achieve an enhanced or otherwise infeasible application. The first chapter discusses the modification of two different types of Microbial Fuel Cell (MFC) anode brush bristle fibers with positive surface charge increasing moieties to increase quantitative bacterial adhesion to these bristle fibers, and therefore overall MFC electrogenicity. Type-1 brush bristles, comprised of polyacrylonitrile, were modified via the electrostatic attachment of 1-pyrenemethylamine hydrochloride. Type-2 brush bristles, comprised of nylon, were modified via the covalent attachment of ethylenediamine. Both modified brush types were immersed in an <i>E. Coli</i> broth for 1 hour, stained with SYTO^&reg; 9 Green Fluorescent Nucleic Acid Stain from ThermoFisher Scientific (SYTO-9), and examined under a Biotek Citation 3 fluorescent microscope to visually assess differences in bacterial adherence. In both trials, a clear increase in amount of bacterial adhesion to the modified bristles was observed over that of the control. The second chapter demonstrates a potential biomedical technology application wherein a polymerizable carbocyanine-type dye was synthesized and bound to a chitosan backbone to produce a water-soluble photothermal nanoparticle. Laser stimulation of both free and NP-conjugated aqueous solutions of the carbocyanine dye with Near-Infrared (NIR) Spectrum Radiation showed an increase in temperature directly correlated with the concentration of the dye which was more pronounced in the free particle solutions.</p>

<p> The 21st century is witnessing a tremendous demand for transistors. Life amenities have incorporated the transistor in every aspect of daily life, ranging from toys to rocket science. Day by day, scaling down the transistor is becoming an imperious necessity. However, it is not a straightforward process; instead, it faces overwhelming challenges. Due to these scaling changes, new technologies, such as FinFETs for example, have emerged as alternatives to the conventional bulk-CMOS technology. FinFET has more control over the channel, therefore, leakage current is reduced. FinFET could bridge the gap between silicon devices and non-silicon devices. The semiconductor industry is now incorporating FinFETs in systems and subsystems. For example, Intel has been using them in their newest processors, delivering potential saving powers and increased speeds to memory circuits. Memory sub-systems are considered a vital component in the digital era. In memory, few rows are read or written at a time, while the most rows are static; hence, reducing leakage current increases the performance. However, as a transistor shrinks, it becomes more vulnerable to the effects from radioactive particle strikes. If a particle hits a node in a memory cell, the content might flip; consequently, leading to corrupting stored data. Critical fields, such as medical and aerospace, where there are no second chances and cannot even afford to operate at 99.99% accuracy, has induced me to find a rigid circuit in a radiated working environment. This research focuses on a wide spectrum of memories such as 6T SRAM, 8T SRAM, and DICE memory cells using FinFET technology and finding the best platform in terms of Read and Write delay, susceptibility level of SNM, RSNM, leakage current, energy consumption, and Single Event Upsets (SEUs). This research has shown that the SEU tolerance that 6T and 8T FinFET SRAMs provide may not be acceptable in medical and aerospace applications where there is a very high likelihood of SEUs. Consequently, FinFET DICE memory can be a good candidate due to its high ability to tolerate SEUs of different amplitudes and long periods for both read and hold operations.</p>

<p> An increasing demand exists for the treatment of hypersaline industrial wastewaters such as those from the shale gas industry, seawater desalination plants, and thermoelectric power-generating facilities. Membrane distillation (MD) is an emerging thermal-based desalination process, which can potentially treat hypersaline industrial wastewaters by exploiting low-grade or waste heat. High performance MD membranes are the key to the advancement and further commercialization of this emerging desalination technology. This research aims at (i) developing novel MD membranes with special surface wettability using advanced materials and surface engineering techniques and (ii) gaining fundamental understanding of the scaling and fouling mechanisms of the newly developed MD membranes.</p><p> Engineering the wettability of materials and interfaces can effectively be leveraged to membrane fabrication. Omniphobic membranes that resist wetting from both water and oil can extend MD applications for desalination of emerging high-salinity wastewaters containing diverse low surface tension contaminants. Fundamental understanding of interfacial phenomena and relating such knowledge to membrane surface wettability are crucial to improving omniphobic MD membrane design and performance. This work elucidates the factors that determine surface omniphobicity of microporous membranes and evaluates the potential application of these membranes in desalination of low surface tension wastewaters by membrane distillation. Specifically, the effects of surface morphology and surface energy on membrane surface omniphobicity were systematically investigated by modifying a prototype glass fiber substrate with silica nanoparticles and fluoroalkylsilane. A re-entrant structure, defined as a nanoscale architecture with increased air to solid ratio, developed by the spherical silica nanoparticles was found to play a critical role in rendering the membrane surface omniphobic, </p><p> Electrospinning is a promising and versatile technique to fabricate omniphobic membranes, because electrospun nanofibers with cylindrical shape feature a re-entrant structure and could be further engineered for additional levels of re-entrant structures. This work presents a facile approach to fabricate a robust omniphobic membrane by exploiting the versatility of electrospinning, which allows the preparation of a nanofiber scaffold with targeted physical and chemical properties. The fabricated electrospun omniphobic MD membranes were evaluated in terms of wetting resistance to various low surface tension liquids and desalination performance with feed solutions of varying surface tensions. </p><p> Microporous polyvinylidene fluoride (PVDF) membranes have been widely used for MD applications because of their hydrophobic nature, excellent chemical compatibility, and facile processability. However, application of conventional hydrophobic PVDF membranes in MD is limited due to their susceptibility to wetting and fouling by low surface tension contaminants. This study presents scalable surface engineering of a conventional hydrophobic PVDF microporous substrate to produce an omniphobic membrane. Desalination performance of the fabricated omniphobic membrane was evaluated in direct contact membrane distillation with synthetic wastewaters containing low surface tension contaminants, including surfactants and mineral oil. The performance of the fabricated omniphobic membrane with produced water from the shale gas industry was further examined to highlight its potential application in desalinating complex, high salinity industrial wastewaters.</p><p> The performance of MD systems is hampered by fouling and inorganic scaling, particularly when a system treats hypersaline industrial wastewaters with high levels of total dissolved solids and organic matter. This dissertation research investigated fouling and scaling mechanisms of omniphobic membranes, focusing on the impact of surface chemistry. The omniphobic membranes were fouled by hydrophobic, low surface tension contaminants via attractive interactions, but further adsorption into the pores was prevented by a thermodynamic barrier created by a re-entrant structure, which sustains a metastable non-wetting condition. Also, the non-adhesive and slippery surface nature of the omniphobic membrane was shown to delay both homogeneous and heterogeneous nucleation, demonstrating its potential for a high recovery MD system to treat hypersaline industrial wastewaters.</p><p> This work presents pioneering advances in the development of novel MD membranes with special wettability for extended MD applications. The fundamental understanding of the interfacial phenomena, advanced materials, and surface engineering techniques as well as fouling and scaling mechanisms will shed light on the design parameters for high membrane performance and efficient process operation. These important insights can inform the realization of emerging membrane-based technologies for sustainable treatment of challenging industrial wastewaters. The implications of the results in this dissertation are potentially far-reaching; we anticipate that they will shape the discussion of next generation desalination technologies.</p><p>