Over the past few years, energy storage devices have received tremendous interest due to the increasing demand for sustainable and renewable energy in modern society. Supercapacitors are considered as one of the most promising energy storage devices because of their high power density and long cycle life. However, low energy density remains as the main shortcoming for supercapacitors. The overall performance of supercapacitors is predominantly determined by the characteristics of the electrodes. Specifically, constructing nanostructured electrode material has been proven as an efficient way to improve the performance by providing large surface area and short ionic and electronic diffusion paths. Another approach to improve the performance of supercapacitors is the rational design of the asymmetric supercapacitor (ASC), which can extend the operation voltage. In this regard, we have focused on the synthesis and utilization of several nanomaterials, in particular, pseudocapacitance materials such as metal oxides and metal phosphides, on both positive and negative electrodes, as well as the ASC design and fabrication. First, three-dimensional TiO2 nanorod arrays have been synthesized on Ti substrate by a facile one-step hydrothermal method and demonstrated as an ideal supercapacitor positive electrode, which exhibited good areal capacitance and excellent cycling stability. Owing to the novel “dissolve and grow” mechanism, this method provides a simple and low-cost technique for flexible supercapacitor application. Second, using cobalt phosphide and iron phosphide as examples, we have demonstrated metal phosphides as high-performance supercapacitor negative electrodes for the first time. Cobalt phosphide nanowire arrays have been synthesized and presented a high capacitance of 571.3 mF/cm2. To improve the cycling stability, gel electrolyte was used to suppress the irreversible electrochemical reaction. The flexible solid-state asymmetric MnO2//CoP supercapacitor exhibited good electrochemical performance, such as a high energy density of 0.69 mWh/cm3 and a high power density of 114.2 mW/cm3. Furthermore, a PEDOT coating has been adapted to further enhance the cycling stability as well as capacitance performance of FeP nanorod arrays. The FeP/PEDOT electrode represents an outstanding capacitance of 790.59 mF/cm2 and a good stability of 82.12% retention after 5000 cycles. In addition, a MnO2//FeP/PEDOT ASC was fabricated with an excellent volumetric capacitance of 4.53 F/cm3 and an energy density of 1.61 mWh/cm3.

Recently, there has been growing interest in using transition metals (TM) for catalytic and electromagnetic applications, due to the ability of TMs to form stable compounds in multiple oxidation states. In this research, the focus has been on the synthesis and characterization of carbon-supported TM nanoparticles (NPs), specifically palladium (Pd) and gold (Au) NPs, for catalytic applications, and transition metal oxides (TMO) NPs, specifically Fe3O4 NPs for electromagnetic applications. Carbon supports have several advantages, such as enabling even distribution of particles, offering large specific surface area with excellent electron conductivity, and relative chemical inertness. In this dissertation, for catalytic applications, emphasis was on removal of trichloroethylene (TCE) from groundwater. For this application, carbon-supported Pd/Au NP catalysts were developed. Pd was chosen because it is more active, stable and selective for desired end-products, and Au has shown to be a good promotor of Pd's catalytic activity. Often, commercially available Pd-based catalysts are made using harsh chemicals, which can be harmful to the environment. Here, an environmentally friendly process with aspects of green chemistry was developed to produce carbon-supported Pd/Au NP catalysts. This process uses a combination of sonochemistry and solvothermal syntheses. The carefully designed carbon-supported Pd/Au NP catalyst material was systematically characterized, tested against TCE, and optimized for increased rate of removal of TCE. Electron microscopy and spectroscopy techniques were used to study the material including structure, configuration and oxidative state. The Pd/Au NPs were found mainly to form clusters with an aggregate-PdShellAuCore structure. Using state-of-the-art direct detection with electron energy loss spectroscopy, the Pd NPs were found to have an oxidative state of zero (0). The formation of the catalyst material was studied in detail by varying several synthesis parameters including type of solvent, sonication time, synthesis temperature etc. The most optimized catalyst was found remove TCE at double the rate of corresponding commercial Pd-based catalysts in a hydrogen headspace. This material was found to catalyze the removal of TCE via traditional hydrodehalogenation and shows promise for the removal of other contaminants such as trichloropropane (TCP), carbon tetrachloride (CT). This green approach to make and optimize TM materials for specific applications was extended to TMOs, specifically magnetite (Fe3O4) and further developed for the application of electromagnetism. As catalysts, Fe3O4 is used for removal of p-nitrophenol from water. However, since the carbon-supported Pd/Au material system was developed and optimized for catalysis, here, carbon-supported Fe3O4 NPs were developed for electromagnetic applications. There has been growing interest in tuning the magnetic properties of materials at room temperature with the use of external electric fields, for long-term applications in data storage and spintronic devices. While a complete reversible change of material properties has not yet been achieved, some success in partial switching has been achieved using multiferroic spinel structures such as Fe3O4. These materials experience a change in magnetic moment at room temperature when exposed to the electric fields generated by electrochemical cells such as lithium ion batteries (LIBs) and supercapacitors (SC). In the past, a 1% reversible change was observed in Fe3O4 using LIBs. Here, building on the developments from previous material system, Fe3O4 NPs were directly hybridized onto the graphene support in order to increase the observable change in magnetic moment. The material was systematically designed and tested for this application, including a study of the material formation. A simple, environmentally friendly synthesis using the solvothermal process was implemented to make the graphene-supported Fe3O4 NPs. This new material was found to produce a reversible change of up to 18% in a LIB. In order to overcome some of the difficulties of testing with a LIB, a corresponding hybrid SC was designed, built and calibrated. The graphene-supported Fe3O4 NPs were found to produce a net 2% reversibility in the SC, which has not been reported before. The results from both the LIB and SC were analyzed to better understand the mechanism of switching in a spinel ferrite such as Fe3O4, which can help optimize the material for future applications. The focus of this dissertation was on the development of a methodology for carbon-supported TM and TMO NPs for specific applications. It is envisioned that this approach and strategy will contribute towards the future optimization of similar material systems for a multitude of applications.

Radiosensitization is a novel targeted therapy strategy where chemical compounds are being explored to enhance the sensitivity of the tissue to the effects of ionizing radiation. Among the different radiosensitizers alternatives, nanomaterials have shown promising results by enhancing tumor injury through the production of free radicals and reactive oxygen species (ROS). In this work, Gold-supported titania (Au@TiO2) nanocomposites were synthesized through an innovative strategy using X-ray irradiation, and their potential as radiosensitizers was investigated. Radiosensitization of Au@TiO2 nanocomposites was assessed by monitoring the decomposition of Methylene Blue (MB) under X-ray irradiation in the presence of the nanomaterial. Radiosensitization of Au@TiO2 was thoroughly investigated as a function of parameters such as Au loading, TiO2 particle size, nanomaterial concentration, different irradiation voltages, and dose rates. Results showed that the presence of Au@TiO2 increases significantly the absorbed dose, thus enhancing MB decomposition. The mechanism behind Au@TiO2 radiosensitization relies on their interaction with X-rays. TiO2 produces reactive ROS whereas Au leads to the generation of photoelectrons and Auger electrons upon exposure to X-rays. These species lead to an enhanced degradation rate of the dye, a feature that could translate to cancerous cells damage with minimal side effects. The radiosensitization effect of Au@TiO2 nanocomposites was also tested in biological settings using Microcystis Aeruginosa cells. The results showed an increase in cell damage when irradiated in the presence of Au@TiO2 nanocomposites. Au@TiO2 nanocomposites were fabricated using X-ray radiolytic synthesis, a method that diverges from conventional fabrication processes and leads to negligible by-product formation, an important feature for medical and catalytic applications. In this work, Au nanoparticles are supported on TiO2 with a mean particle size of either 6.5 nm or 21.6 nm, using different ligands such as NaOH or urea, and under different absorbed doses to determine the effects of these parameters on the nanomaterials’ characteristics. Overall, Au@TiO2 synthesized by X-rays showed remarkable promise as radiosensitizers, a concept relevant to a number of medical, biological and environmental applications.

Nanostructured metallic multilayers (NMMs) are well-known for their high strength in smaller bilayer thicknesses. Six Al/Ti (NMM) with different individual layer thickness were tested for their mechanical hardness using a nanoindentation tool. Individual layer thicknesses were chosen carefully to cover the whole confined layer slip (CLS) model. Nano-hardness had a reverse relation with the square root of individual layer thickness and reached a steady state at ~ 5 nm bilayer thickness. Decreasing the layer bilayer thickness from ~ 104 nm to ~ 5 nm, improved the mechanical hardness up to ~ 101%. Residual stresses were measured using grazing incident X-ray diffraction (GIXRD). Effect of residual stress on atomic structure and dislocation propagation was then investigated by comparing the amount and type of stresses in both aluminum and titanium phases. Based on the gathered data from GIXRD scans tensile stress in Ti phases, and compressive stress in Al would increase the overall coherency of structure. Wear rate in coatings is highly dependent on design and architect of the structure. NMM coatings are known to have much better wear resistance compare to their monolithic constituent phases by introducing a reciprocal architect. In current study wear rate of two Al/Ti NMMs with individual layer thicknesses of ~ 2.5 nm and ~ 30 nm were examined under normal loads of 30 µN, 60 µN, and 93 µN. Wears strokes were performed in various cycles of 1, 2, 3, 4 5 and 10. Wear rates were then calculated by comparing the 3D imaging of sample topology before and after tests. Nano-hardness of samples was measured pre and post each cycle of wear using a nanoindentation tool. The microstructure of samples below the worn surface was then characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), focus ion beam (FIB) and an optical profilometer. Orientation mapping was performed to analyze the microstructure of layers beneath the nano indents. TEM imaging from the cross section of worn samples indicated severely plastically deformed layer (SPDL) below the worn surface. Shear bands and twins are visible after wear and below the worn surface. Decreasing the layer thickness from 30 nm to 2.5 nm resulted in ~ 5 time’s better wear resistance. Nanowear caused surface hardening which consequently increased nano hardness up to ~ 30% in the sample with 2.5 nm individual layer thickness. Increasing the interfaces density of NMMs will significantly improve the corrosion resistance of coating. Reciprocal layers and consequently interfaces will block the path of aggressive content toward the substrate. Corrosion rate evolution of Al/Ti multilayers was investigated through DC corrosion potentiodynamic test. Results seem to be very promising and demonstrate up to 30 times better corrosion resistance compared to conventional sputtered monolithic aluminum. Corrosion started in the form of pitting and then transformed to the localized galvanic corrosion. Decreasing the bilayer thickness from ~ 10.4 nm to ~ 5 nm will decrease the corrosion current density (icorr) of ~ 5.42 × 10-7 (A/cm2) to ~ 6.11 × 10-10 (A/cm2). No sign of corrosion has been seen in the sample with ~ 2.5 nm individual layer thickness. Further AFM and TEM analysis from surface and cross section of NMMs indicate that a more coherent layer by layer structure improves the corrosion rate. Interfaces have a significant role in blocking the pores and imperfections inside coating.

This dissertation involves the study of epitaxial behavior of one-dimensional nanomaterials like single-walled carbon nanotubes and Indium Arsenide nanowires grown on metallic catalyst surfaces. It has been previously observed in our novel microplasma based CVD growth of SWCNTs on Ni-Fe bimetallic nanoparticles that changes in the metal catalyst composition was accompanied by variations in the average metal-metal bond lengths of the nanoparticle and that in turn, affected nanotube chirality distributions. In this dissertation, we have developed a very simplistic model of the metal catalyst in order to explain the nanotube growth of specific nanotube chiralities on various Ni-Fe catalyst surfaces. The metal catalyst model is a two-dimensional flat surface with varying metal-metal bond lengths and comprising of constituent metal atoms. The effect of the composition change was modeled as a change in the bond length of the model catalyst surface and density functional theory based calculations were used to study specific nanotube caps. Our results indicated that nanotube caps like (8,4) and (6,5) show enhanced binding with increased metal-metal bond lengths in the nanoparticle in excellent agreement with the experimental observations. Later, we used this epitaxial nucleation model and combined with a previously proposed chirality-dependent growth rate model to explore better catalysts that will preferentially grow an enhanced chirality distribution of metallic nanotubes. From our DFT calculations and other geometrical considerations for nanotube growth, we demonstrated that the pure Ni0.5Cu0.5 metal nanoparticles and its lattice-strained surfaces can serve as a promising catalyst for enhanced growth of metallic nanotubes. Finally, we extended this model of epitaxial growth to study the growth of,andoriented nanowires on gold metal nanoparticles where a faster growth rate ofnanowires was previously observed in experiments on shaped nanoparticles than that on spherical nanoparticles. The DFT calculations indicated an enhanced growth selectivity of theoriented nanowires on the Au(111) surfaces. However, the DFT results also show that theandNWs will preferentially grow on the Au(100) surface than on the Au(100) surface. The epitaxial model based DFT calculations of nanotube and nanowire growth on metal catalyst surfaces presented in this dissertation, provide a deep insight into their epitaxial growth mechansims and, can be easily exploited to layout better design principles of synthesizing catalysts that helps in growing these one-dimensional nanomaterials with desired material properties.

Metal-Insulator-Metal (MIM), Metal-Insulator-Insulator-Metal (MIIM), and Metal-Insulator-Insulator-Insulator-Metal (MIIIM) quantum tunneling diodes have been designed, fabricated, and characterized. The key interest of this work was to develop tunneling diodes capable of operating and detecting THz radiation up to 30THz, which is well beyond the operation ranges of other semiconductor-based diodes. Al2O3, HfO2 and TiO2 metal oxides were employed for studying the behavior of metal-insulator-metal (MIM) and metal-insulator-insulator-metal (MIIM) quantum tunneling diodes. Specifically, ultra-thin films of these oxides with varied thicknesses were deposited by atomic layer deposition (ALD) as the tunneling junction material that is sandwiched between platinum (Pt) and titanium (Ti) electrodes, with dissimilar work functions of 5.3 eV and 4.1 eV, respectively. Due to the unique and well-controlled tunneling characteristic of the ALD ultra-thin films, reproducible MIM and MIIM diode devices have been developed. The DC characteristics of MIM and MIIM tunneling junctions with different junction areas and materials were investigated in this work. The effects of the different compositions and thicknesses of the tunneling layer on the diodes were studied systematically. Through the introduction of stacked dual tunneling layers, it is demonstrated that the MIIM and MIIIM diodes exhibited a high degree of asymmetry (large ratio between forward and reverse currents) and a strong nonlinearity in their I-V characteristics. The characterization was performed on diodes with micro and nano-scale junction areas. The MIM diodes reported herein exhibited lower junction resistances than those reported by prior works. Moreover, a study was conducted to numerically extract the average barrier heights by fitting the analytical model of the tunneling current to the measured I-V responses, which were evaluated with respect to the thickness of the constituent tunneling layer. RF characterization was performed on the MIM diodes up to 65GHz, and its junction impedance was extracted. A rigorous procedure was followed to extract the diode equivalent circuit model to obtain the intrinsic lumped element model parameters of the MIM diodes.

Nanoporous carbons are among the widely studied and promising materials on hydrogen storage for on-board vehicles. However, the nature of nanoporous carbon structures, as well as the relationship between local structure and hydrogen adsorption are still unclear, and hinder the design of carbon materials for optimum hydrogen storage. This dissertation presents a systematic modeling effort of hydrogen storage in nanoporous carbon materials. Tight binding molecular dynamics simulations are utilized to simulate the amorphous carbons over a wide range of density. The resulting structures are in good agreement with experimental data of ultra-microporous carbon (UMC), a wood-based activated carbon, as indicated by a comparison of the microstructure at atomic level, pair distribution function, and pore size distribution. To estimate gas adsorption in complex geometries, an efficient numerical algorithm (based on a continuum gas adsorption model) is developed for calculating the gas uptake at room temperature and moderate pressures. This algorithm is a classical approximation of the quantum mechanical model by Patchkovskii et al.1 and proven to be much faster than other commonly used methods. The gas adsorption calculations in carbon structures from tight-binding simulations demonstrate both a promising hydrogen storage capacity (1.33 wt% at 298K and 5 MPa) and a reasonable heat of adsorption (12-21 kJ/mol). To our knowledge, this is the first work to directly calculate hydrogen adsorption capacity in amorphous carbon. This work demonstrates that increasing the heat of adsorption does not necessarily increase the hydrogen uptake. In fact, the available adsorption volume is as important as the isosteric heat of adsorption for hydrogen storage in nanoporous carbons.

Using equilibrium molecular dynamics simulations, an analysis of the key thermophysical properties critical to heat transfer processes is performed. Replication of thermal conductivity and shear viscosity observations found in experimental investigations were performed using a theoretical nanopthesis-fluid system and a novel colloid-fluid interaction potential to investigate the key nanofluid parameters. Analysis of both the heat current (thermal conductivity) and stress (shear viscosity) autocorrelation functions have suggested that the dominant physical mechanisms for thermal and momentum transport arises from enhancements to the longitudinal and transverse acoustic modes energy transfer brought about by the increased mass ratio of the nanopthesis to the fluid. This conclusion was further supported by analysis of the local density fluctuations surrounding increasing nanopthesis diameters where the longitudinal acoustic mode characteristics for density fluxes were seen to be enhanced by the presence of the heavier platinum nanopthesiss. It is then concluded that the key macroscopic characteristic in obtaining the largest thermal energy transfer enhancement is through the mass of the nanopthesis relative to the base fluid. Also, the small local density effects in the nanofluid are greatly affects the viscosity calculations. These conclusions provide the theoretical framework for many of the experimental results obtained.

Presently there are deep concerns over the environmental consequences and the consumption of non-renewable energy sources, with the accelerated greenhouse effect, triggered enormous interest in the use of renewable energy sources e.g., solar, hydropower, wind and geothermal. However the intermittent nature of harvesting renewable energy sources has recently gained considerable attention in the alternative reliable, cost effective, and environmentally friendly energy storage devices. The supercapacitor and lithium ion batteries are considered more efficient electrical energy storage devices than conventional energy storage systems. Both devices have many useful and important applications; they could be an excellent source for high power and high energy density, especially in portable electronic devices and Electrical Vehicles (EVs) or Hybrid Electrical Vehicles (HEVs). In order to make the efficient usage of these stationary energy storage devices, state of the art research on new and advanced electrode materials is highly needed. The aim of this dissertation is to investigate the scope of graphene/metal oxide-conducting polymer nanocomposites electrodes for light weight, high power density and wider voltage window supercapacitor devices. The facile chemical polymerization approach was used to synthesize the aromatic and heterocyclic conducting polymer nanocomposites. For aromatic nanocomposites, several materials were synthesized includes ZnO-PANI, ZnO/G-PANI,RuO2-PANI and G-PANI. Subsequently these materials have been characterized by physical, structural techniques e.g Raman Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Xray-Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). In addition to material characterization the prepared material was also characterized by electrochemical measurements using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chrono potentiometry for supercapacitor electrodes. Since graphene is a two-dimensional single-atom-thick sp2 hybridized carbon structure due to its extraordinary characteristic, high electrical conductivity, chemical stability and large theoretical surface area (over 2600 m2 g−1) has gained immense interest in the future generation of renewable energy devices. Therefore, among all aromatic based nanocomposites, the Graphene-Polyaniline (G-PANI) rendered promisingly high specific capacitance around 440 F/g with the excellent cyclic stability. The higher specific capacitance of G-PANI might be due to the high conductivity and superior electrochemical properties of graphene in G-PANI nanocomposites. However, besides the G-PANI, other aromatic nanocomposites e.g., RuO2-PANI, ZnO-PANI and G/ZnO-PANI also showed the potential of low cost and flexible supercapacitor electrodes with the reasonably good specific capacitance as 360 F/g, 300 F/g, and 275 F/g. We have further investigated the role of conductivity by adding different amount of graphene in G-PANI nanocomposites to optimize device performance with the specific capacitance and columbic efficiency of 440 F/g and 90% respectively.Further the other important parameters, relate with the electrode thickness, type of electrolytes, concentration of electrolytes and the effect of the solvent has also been studied to achieve the overall performance and reliability of the device. Moreover, in order to have the comprehensive study of conducting polymer besides the aromatic conducting polymer the heterocyclic polymers e.g., polythiophene and poly (3, 4-ethylenedioxythiophenes) (PEDOT) nanocomposites were studied at length to evaluate their role for the cost effective, large surface area and flexible green energy storage devices and has shown great prospects for commercial application. Therefore, G-Cps nanocomposites have proved to be a promising electrode material choice to facilitate the ionic diffusion and contact of the electrolytes to improve the specific capacitance and performance of the device.

Nanoparticle and nanoparticulate films have been grown by a unique approach combining a microwave and nebulized droplets where the concentration and thus the resulting particle size can be controlled. The goal of such a scalable approach was to achieve it with the least number of steps, and without using expensive high purity chemicals or the precautions necessary to work with such chemicals. This approach was developed as a result of first using a laser unsuccessfully to achieve the desired films and particles. Some problems with the laser approach for growing desired films were solved by substituting the higher energy microwave for the laser. Additionally, several materials were first attempted to be grown with the laser and the microwave, and what was learned as result of failures was implemented to successfully demonstrate the technique. The microwave system was characterized by using direct temperature measurements and models. Where possible, the temperature of deposition was determined using thermocouples. In the region of the waveguide, the elemental spectral lines were measured, and the temperature was calculated from measured spectral peaks. From the determined temperature, a diffusion calculation modeled the rate of heat transfer to the nebulized droplets. The result of the diffusion calculations explained the reason for the failure of the laser technique, and success for the microwave technique for simple chemistries. The microwave assisted spray pyrolysis (MPAS) technique was used to grow ZnO nanoparticles of varying size. The properties of the different size particles was measured by optical spectroscopy and magnetic measurements and was correlated to the defects created. The MPAS technique was used to grow films of Ca3Co4O9 containing varying sizes of nanoparticulates. The resistivity, Seebeck coefficient, and the power factor (PF) measured in the temperature range of 300-700 K for films grown by MPAS process with varying concentrations of calcium and cobalt chlorides are presented. Films with larger nanoparticles showed a trend toward higher PFs than those with smaller nanoparticles. Films with PFs as high as 220 μW/mK 2 were observed in films containing larger nanoparticles.