Magneto-optical materials such as permalloy can be used to create artificial spin- ice (ASI) lattices with antiferromagnetic ordering. Magneto-optical materials used to create diffraction lattices are known to exhibit magnetic scattering at the half- order Bragg peak while in the ground state. The significant drawbacks of studying the magneto-optical generation of OAM using x-rays are cost, time, and access to proper equipment. In this work, it is shown that the possibility of studying OAM and magneto-optical materials in the spectrum of visible light at or around 2 eV is viable. Using spectroscopic ellipsometry it is possible to detect a change in the magnetization of thin permalloy films with thicknesses between 5 and 20 nm. Patterns consistent with OAM were found at 1.95 eV using a square lattice with a 4𝜋 radial phase shift in the antiferromagnetic ground state. Evidence of magnetic scattering at the half-order Bragg peak using 1.95 eV was also found.

Currently organic-inorganic hybrid perovskite solar cells (PSCs) is one kind of promising photovoltaic technology due to low production cost, easy fabrication method and high power conversion efficiency. Charge transport layers are found to be critical for device performance and stability. A traditional electron transport layer (ETL), such as TiO2 (Titanium dioxide), is not very efficient for charge extraction at the interface. Compared with TiO2, SnO2 (Tin (IV) Oxide) possesses several advantages such as higher mobility and better energy level alignment. In addition, PSCs with planar structure can be processed at lower temperature compared to PSCs with other structures. In this thesis, planar-structure perovskite solar cells with SnO2 as the electron transport layer are fabricated. The one-step spin-coating method is employed for the fabrication. Several issues are studied such as annealing the samples in ambient air or glovebox, different concentration of solution used for the samples, the impact of using filter for solutions on samples. Finally, a reproducible fabrication procedure for planer-structure perovskite solar cells with an average power conversion efficiency of 16.8%, and a maximum power conversion efficiency of 18.1% is provided.

Efficient and robust blue InGaN multiple quantum well (MQW) light emitters have become ubiquitous; however, they still have unattained theoretical potential. It is widely accepted that “localization” of carriers due to indium fluctuations theoretically enhance their efficiency by moderating defect-associated nonradiative recombination. To help develop a complete understanding of localization effects on carrier dynamics, this thesis explores degree of localization in InGaN MQWs and its dependence on well thickness and number of wells, through temperature and power dependent photoluminescence measurements. Additionally, silicon-compatible, nontoxic, colloidally synthesizable 2-5 nm Ge1-xSnx alloy quantum-dots (QDs) are explored for potential visible to near-IR optoelectronic applications. While bulk Ge is an indirect gap material, QD confinement allows enhanced direct transitions, and alloying with Sn improves transition oscillator strengths. Temperature dependent steady-state and time-resolved photoluminescence reveal relaxation pathways involving bright/dark excitons and surface states in Ge1-xSnx QDs, showing their great potential for future use.

Nanomagnetic devices have been projected as an alternative to transistor-based switching devices due to their non-volatility and potentially superior energy-efficiency. The energy efficiency is enhanced by the use of straintronics which involves the application of a voltage to a piezoelectric layer to generate a strain which is ultimately transferred to an elastically coupled magnetostrictive nanomaget, causing magnetization rotation. The low energy dissipation and non-volatility characteristics make straintronic nanomagnets very attractive for both Boolean and non-Boolean computing applications. There was relatively little research on straintronic switching in devices built with real nanomagnets that invariably have defects and imperfections, or their adaptation to non-Boolean computing, both of which have been studied in this work. Detailed studies of the effects of nanomagnet material fabrication defects and surface roughness variation (found in real nanomagnets) on the switching process and ultimately device performance of those switches have been performed theoretically. The results of these studies place the viability of straintronics logic (Boolean) and/or memory in question. With a view to analog computing and signal processing, analog spin wave based device operation has been evaluated in the presence of defects and it was found that defects impact their performance, which can be a major concern for the spin wave based device community. Additionally, the design challenge for low barrier nanomagnet which is the building block of binary stochastic neurons based probabilistic computing device in case of real nanomagnets has also been investigated. This study also cast some doubt on the efficacy of probabilistic computing devices. Fortunately, there are some non-Boolean applications based on the collective action of array of nanomagnets which are very forgiving of material defects. One example is image processing using dipole coupled nanomagnets which is studied here and it showed promising result for noise correction and edge enhancement of corrupted pixels in an image. Moreover, a single magneto tunnel junction based microwave oscillator was proposed for the first time and theoretical simulations showed that it is capable of better performance compared to traditional microwave oscillators. The experimental part of this work dealt with spin wave modes excited by surface acoustic waves, studied with time resolved magneto optic Kerr effect (TR-MOKE). New hybrid spin wave modes were observed for the first time. An experiment was carried out to emulate simulated annealing in a system of dipole coupled magnetostrictive nanomagnets where strain served as the simulated annealing agent. This was a promising outcome and it is the first demonstration of the hardware variant of simulated annealing of a many body system based on magnetostrictive nanomagnets. Finally, a giant spin Hall effect actuated surface acoustic wave antenna was demonstrated experimentally. This is the first observation of photon to phonon conversion using spin-orbit torque and although the observed conversion efficiency was poor (1%), it opened the pathway for a new acoustic radiator. These studies complement past work done in the area of straintronics.

This dissertation explores the different ways to create thin film-based biosensors that are capable of rapid and label-free detection of cortisol, a non-specific biomarker closely linked to stress, within the physiological range of 10pM to 10 uM. Increased cortisol levels have been linked to stress-related diseases, such as chronic fatigue syndrome, irritable bowel syndrome, and post-traumatic stress disorder. It also plays a role in the suppression of the immune system as well. Therefore, accurate measurement of cortisol in saliva, serum, plasma, urine, sweat, and hair, is clinically significance to predict physical and mental diseases. In this dissertation, thin film-based electrochemical immunosensors were fabricated using a self-assembled monolayer (SAM) functionalized by cortisol specific antibodies to detect cortisol at 10 pM level sensitivities in the presence of a redox probe. The fabricated electrochemical cortisol immunosensors were able to detect cortisol in human saliva samples and the outcomes were validated using the standard Enzyme Linked Immuno Sorbent Assay (ELISA) technique. With the aim of improving signal amplification and label-free cortisol detection, copper nanoparticles were incorporated on screen-printed carbon electrodes (SPCE) for the fabrication of electrochemical cortisol immunosensor. This SPCE-based sensor showed a sensitivity of 4.21µA/M and the limit of detection 6.6nM. Both the SAM and SPCE-based immunosensors were not thermally stable due to the instability of antibodies at room temperature. To address this issue, an antibody-free immunosensor was fabricated. Molecular Imprinted Polymer (MIP) was used to template the target cortisol molecule. The MIP-based sensing platform was prepared using polypyrrole, a thermally stable conducting polymer. The conductivity of the polymer ensured good electrical performance. The polypyrrole-based MIP was synthesized by means of electrochemical polymerization and was used to detect cortisol within the physiological range at room temperature. MIP-based sensors exhibited the detection limit of 1 pM, and were cost-effective, easy to fabricate, temperature stable, and reusable. The sensing performance of the resulting sensors was comparable to those of commercially available technologies, such as ELISA. Aiming to perform cortisol sensing at point-of-care (POC), an Extended Gate Field Effect Transistor (EGFET) was integrated with a developed MIP cortisol sensor. The as developed MIP-EGFET sensor was used to detect the cortisol concentration in the range of 1 pM to 100 nM. A few of the major advantages of the developed sensor are its ability to provide a direct readout and simpler electronic systems, which are necessary for miniaturized Point of Care devices.

L‐glutamate is associated with several neurological disorders; thus, monitoring fast dynamics of L‐glutamate is of great importance in the field of neuroscience. Electrode miniaturization demanded by many applications leads to reduced surface area and decreased amounts of immobilized enzymes on coated electrodes. As a result, lower signal‐to‐noise ratios are observed for oxidase‐enzyme based sensors. To increase the signal‐to‐noise ratio we have developed a process to fabricate micro‐ and nano‐ structures on the microelectrode surface. Localized surface‐plasmon resonances (SPR) has been extensively used to design label‐free biosensors that can monitor receptor‐ligand interactions. A major challenge with localized SPR sensors is that they remain highly susceptible to interference because they respond to both solution refractive index changes and surface binding of the target analyte. The key concept introduced in the present work is the exploitation of transverse and longitudinal resonance modes of nanorod arrays to differentiate between bulk refractive index changes and surface interactions. The transverse bulk sensitivity of the localized SPR sensor (107 nm/RIU) remains competitive with typical single mode gold nanosphere SPR sensors. The figure of merit for the device’s cross‐sensitivity (1.99) is comparable to that of typical wavelength‐interrogated propagating SPR sensors with self referencing.

Cadmium sulfide (CdS) and cadmium telluride (CdTe) are two leading semiconductor materials used in the fabrication of thin film solar cells of relatively high power conversion efficiency and low manufacturing cost. In this work, CdS/CdTe solar cells with a varying set of processing parameters and device designs were fabricated and characterized for comparative evaluation. Studies were undertaken to elucidate the effects of (i) each step in fabrication and (ii) parameters like thickness, sheet resistance, light absorptivity solution concentration, inert gas pressure etc. Best results were obtained when the thickness of CdS planar film for the window layer was in the range of 150 nm to 200 nm. Also, CdS nanowires were fabricated for use as the window layer in CdS-CdTe solar cells. Their materials characteristics were studied with scanning electron microscopy (SEM) and X-ray Diffraction (XRD). Spectral absorption measurements on the planar CdS films and nanowire CdS layers were performed and results compared. It was established that the nanowire CdS design was superior because its absorption of sunlight was far less than that of planar CdS film, which would lead to enhanced performance in the CdS-CdTe solar cell through higher short circuit current density and higher open circuit voltage. Diode behavior of CdS-CdTe devices on planar CdS and nanowire CdS was analyzed and compared. KEYWORDS: Thin Film Solar Cell, Nanowire, UV Absorption, Open-circuit Voltage, Close Space Sublimation

Semiconductor nanostructures have attracted considerable research interest due to their unique physical and chemical properties at nanoscale which open new frontiers for applications in electronics and sensing. Zinc oxide nanostructures with a wide range of applications, especially in optoelectronic devices and bio sensing, have been the focus of research over the past few decades. However ZnO nanostructures have failed to penetrate the market as they were expected to, a few years ago. The two main reasons widely recognized as bottleneck for ZnO nanostructures are (1) Synthesis technique which is fast, economical, and environmentally benign which would allow the growth on arbitrary substrates and (2) Difficulty in producing stable p-type doping. The main objective of this research work is to address these two bottlenecks and find a solution that is inexpensive, environmentally benign and CMOS compatible. To achieve this, we developed a Sonochemical method to synthesize 1D ZnO Nanorods, core-shell nanorods, 2D nanowalls and nanoflakes on arbitrary substrates which is a rapid, inexpensive, CMOS compatible and environmentally benign method and allows us to grow ZnO nanostructures on any arbitrary substrate at ambient conditions while most other popular methods used are either very slow or involve extreme conditions such as high temperatures and low pressure. A stable, reproducible p-type doping in ZnO is one of the most sought out application in the field of optoelectronics. Here in this project, we doped ZnO nanostructures using sonochemical method to achieve a stable and reproducible doping in ZnO. We have fabricated a homogeneous ZnO radial p-n junction by growing a p-type shell around an n-type core in a controlled way using the sonochemical synthesis method to realize ZnO homogeneous core-shell radial p-n junction for UV detection. ZnO has a wide range of applications from sensing to energy harvesting. In this work, we demonstrate the successful fabrication of an electrochemical immunosensor using ZnO nanoflakes to detect Cortisol and compare their performance with that of ZnO nanorods. We have explored the use of ZnO nanorods in energy harvesting in the form of Dye Sensitized Solar Cells (DSSC) and Perovskite Solar Cells.

Reliability and sensitive information protection are critical aspects of integrated circuits. A novel technique using near-field evanescent wave coupling from two subwavelength gratings (SWGs), with the input laser source delivered through an optical fiber is presented for tamper evidence of electronic components. The first grating of the pair of coupled subwavelength gratings (CSWGs) was milled directly on the output facet of the silica fiber using focused ion beam (FIB) etching. The second grating was patterned using e-beam lithography and etched into a glass substrate using reactive ion etching (RIE). The slightest intrusion attempt would separate the CSWGs and eliminate near-field coupling between the gratings. Tampering, therefore, would become evident. Computer simulations guided the design for optimal operation of the security solution. The physical dimensions of the SWGs, i.e. period and thickness, were optimized, for a 650 nm illuminating wavelength. The optimal dimensions resulted in a 560 nm grating period for the first grating etched in the silica optical fiber and 420 nm for the second grating etched in borosilicate glass. The incident light beam had a half-width at half-maximum (HWHM) of at least 7 µm to allow discernible higher transmission orders, and a HWHM of 28 µm for minimum noise. The minimum number of individual grating lines present on the optical fiber facet was identified as 15 lines. Grating rotation due to the cylindrical geometry of the fiber resulted in a rotation of the far-field pattern, corresponding to the rotation angle of moiré fringes. With the goal of later adding authentication to tamper evidence, the concept of CSWGs signature was also modeled by introducing random and planned variations in the glass grating. The fiber was placed on a stage supported by a nanomanipulator, which permitted three-dimensional displacement while maintaining the fiber tip normal to the surface of the glass substrate. A 650 nm diode laser was fixed to a translation mount that transmitted the light source through the optical fiber, and the output intensity was measured using a silicon photodiode. The evanescent wave coupling output results for the CSWGs were measured and compared to the simulation results.

Cobalt Ferrite has important, size-dependent magnetic properties. Consequently, an overview of particle size is important. Co-precipitation in air was the fabrication method used because it is comparatively simple and safe. The effects of three different reaction times including 1, 2, 3 hour(s) on particle size were compared. Also, the effectiveness of three different capping agents (Oleic Acid, Polyvinylpyrollidone (PVP), and Trisodium Citrate) in reducing aggregation and correspondingly particle size were examined. Using Welch’s analysis of variance (ANOVA) and the relevant post hoc tests, there was no significant difference (p=0.05) between reaction times of 1 hour and 2 hours, but there was a significant difference between reaction times of 2 hours and 3 hours. Potentially, because of increased coarsening for the 3 hour reaction time. PVP and Oleic Acid were shown to be effective in reducing aggregation; however, Citrate was not effective. Possibly, the synthesis procedure was inadequate.