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 objective of this thesis is to explore the synthesis and characterization of high quality binary ZnTe nanowires with great potential for development of optoelectronic devices including high efficiency photovoltaic cells for energy conversion and high sensitivity photodetectors for green fluorescent protein bioimaging at single molecule level. To systematically explore the fabrication process for high quality nanowires, a chemical vapour deposition system was built for nanowire growth. Computational fluid dynamics simulations were used to optimize the reactor and growth parameters. The simulations were validated by experimental measurements. Room temperature photoluminescence measurements showed that high crystal quality with very low defects by single step growth was achieved. This single step growth technique makes a great improvement compared to the reported growth followed by annealing, which achieved equivalent crystal quality. This simplification could be of use in large scale synthesis of nanowires. The simulation results also showed that reactant species concentration is a key factor influencing the growth. A metal-organic chemical vapour deposition system was thus built to independently control reactant concentrations for ZnTe nanowire growth. Temperature-dependent photoluminescence measurements of as-grown ZnTe nanowires showed a strong near band-edge emission. In addition, a deep level oxygen-related band was observed for the first time. From the detailed analysis of thermal quenching of the photoluminescence, it was shown that the deep level emission was partially from the intermediate band of the material. This is of great importance due to the theoretical absorption efficiency that is as high as 63% for intermediate band materials, which is more than two times of that of current single junction concentrators, and few materials possessing this property. Individual ZnTe nanowires, grown after optimization, were patterned and contacted, and their conductivity and photoconductivity were measured at room temperature. A single ZnTe nanowire serving as a photodetector was shown to have the highest reported visible responsivity of 360 A/W (at 530 nm), and a gain of 8,640 (at 3 V bias). The responsivity is roughly 18 times higher than that of silicon avalanche photodiodes. This demonstrates that ZnTe nanowires are strong candidates for single photon detection.

Because of its potential application for flat panel displays, solid-state lighting and 1.5 µm emitter for fiber optical communications, organic light-emitting diodes (OLEDs) have been intensively researched. One of the major problems with current OLED technology relates to inefficient electron injection at the cathode interface, which causes high driving voltage and poor device stability. Making a low resistance cathode contact for electron injection is critical to device performance. This work mainly focuses on cathode interface design and engineering. The Ohmic contact using a structure of C60/LiF/Al has been developed in electron only devices. It is found that application of the C60/LiF/Al contact to Alq based OLEDs leads to a dramatic reduction in driving voltages, a significant improvement in power efficiency, and a much slower aging process. A new cathode structure based on metal-organic-metal (MOM) tri-layer films has been developed. It is found that MOM cathodes reduce reflection by deconstructive optical interference from two metal films. The absolute reflectance from the MOM tri-layer films can be reduced to as low as 7% in the visible light spectrum. In actual working devices, the reflectance can be reduced from ~80% to ~ 20%. MOM cathodes provide a potential low-cost solution for high contrast full-color OLED displays. Low voltage Erq based OLEDs at 1.5 µm emission have been developed. The Erq/Ag cathode interface has been found to be efficient for electron injection. Dramatic improvement in driving voltage and power efficiency has been realized by implementing Bphen and C60 into Erq devices as an electron transport layer. Integration of Erq devices on Si wafers has also been demonstrated.

This thesis explores a rigorous approach to model the behaviour of an electrochemical cell. A simple planar electrochemical cell consisting of stainless steel electrodes separated by a sulfuric acid electrolyte layer is modeled from first principles. The model is a dynamic model and is valid under constant temperature conditions. The dynamic model is based on the Poisson-Nernst-Planck electrodiffusion theory and physical attributes such as the impact of nonlinear polarization, the stoichiometric reactions of the electrolyte and changes to the transport coefficients are investigated in stages. The system of partial differential equations has been solved using a finite element software package. The simulation results are compared with experimental results and discrepancies are discussed. The results suggest that the existing theory is not adequate in explaining the physics in the immediate vicinity of the electrode/electrolyte interface even though the general experimental and simulation results are in qualitative agreement with each other.

Master of Science / Department of Physics / Robert Szoszkiewicz / Nanoscale modifications of polymer surfaces by scratching them with sharp tips with curvature radii of tens of nanometers and at variable temperatures are expected to provide wealth of information characterizing wear response of these polymers. Such studies are important in the light of understanding the nanoscale behavior of matter for future applications in advanced polymer coatings. This thesis describes how Atomic Force Microscopy (AFM) and hot-tip AFM (HT-AFM) methods were used to characterize thermal and mechanical properties of a 30 nm thick film of poly(styrene-block-ethylene oxide), PS-b-PEO, and modify its lamellar surface patterns. Additionally, it is revealed how contact AFM and HT-AFM methods can efficiently characterize the wear response of two popular polymer surfaces, poly(methyl methacrylate), PMMA, and polystyrene, PS. The AFM and HT-AFM studies on PS-b-PEO copolymer were aimed at producing spatial alignment of respective PS and PEO parts. Instead, however, surface ripples were obtained. These measurements are explained using mode I crack propagation model and stick-and-slip behavior of an AFM tip. In addition, HT-AFM studies allowed extraction of several thermo-physical properties of a PS-b-PEO film at local volumes containing about 30 attograms of a polymer. These thermo-physical quantities are: PEO melting enthalpy of, 111 ± 88 J g[superscript]-1, PS-b-PEO local specific heat of 3.6 ± 2.7 J g[superscript]-1K[superscript]-1, and molecular free energy of Helmholtz of 10[superscript]-20 J nm[superscript]-2 for the PEO within PS-b-PEO. Utilizing a spiral scan pattern at constant angular speed and at various temperatures at the AFM tip-polymer interfaces, the wear response of PS and PMMA polymers was characterized. Cross-sections along the obtained spiral wear patterns provided plots of polymer corrugation as a function of scanning speed. From these studies it was found that the corrugation of the modified polymer surface decays exponentially with linear velocity of the scanning tip.

Doctor of Philosophy / Department of Chemistry / Viktor Chikan / Doping quantum dots to increase conductivity is a crucial step towards being able to fabricate a new generation of electronic devices built on the “bottom-up” platform that are smaller and more efficient than currently available. Indium, tin, and gallium have been used to dope CdSe in both the bulk and thin film regimes and introduce n-type electron donation to the conduction band. CdSe quantum dots have been successfully doped with indium, tin, and gallium using the Li4[Cd10Se4(SPh16)] single source precursor combined with metal chloride compounds. Doping CdSe quantum dots is shown to effect particle growth dynamics in the “heterogeneous growth regime.” Doping with indium, tin, and gallium introduce donor levels 280, 100, and 50 meV below the conduction band minimum, respectively. Thin films of indium and tin doped quantum dots show improved conductivity over films of undoped quantum dots. Transient Absorption spectroscopy indicates that indium doping introduces a new electron energy level in the conduction band that results in a 70 meV blue shift in the 1Se absorption bleach position. Novel characterization methods such as in-situ fluorescence growth monitoring, single quantum dot EDS acquisition, static and time-resolved temperature dependant fluorescence spectroscopy were developed in the course of this work as well. These results show that doping CdSe quantum dots with indium, tin, and gallium has not only been successful but has introduced new electronic properties to the quantum dots that make them superior to traditional CdSe quantum dots.

Multijunction solar cells made from a combination of CQDs of differing sizes and thus bandgaps are a promising means by which to increase the energy harvested from the Sun’s broad spectrum. In this dissertation, we first report the systematic engineering of 1.6 eV PbS CQD solar cells, optimal as the front cell responsible for visible wavelength harvesting in tandem photovoltaics. We rationally optimize each of the device’s collecting electrodes—the heterointerface with electron accepting TiO2 and the deep-work-function hole-collecting MoO3 for ohmic contact—for maximum efficiency. Room-temperature processing enables flexible substrates, and permits tandem solar cells that integrate a small-bandgap back cell atop a low thermal-budget larger-bandgap front cell. We report an electrode strategy that enables a depleted heterojunction CQD PV device to be fabricated entirely at room temperature. We develop a two-layer donor-supply electrode (DSE) in which a highly doped, shallow work function layer supplies a high density of free electrons to an ultrathin TiO2 layer via charge-transfer doping. Using the DSE we build all-room-temperature-processed small-bandgap (1 eV) colloidal quantum dot solar cells suitable for use as the back junction in tandem solar cells. We further report in this work the first efficient CQD tandem solar cells. We use a graded recombination layer (GRL) to provide a progression of work functions from the hole-accepting electrode in the bottom cell to the electron-accepting electrode in the top cell. The recombination layers must allow the hole current from one cell to recombine, with high efficiency and low voltage loss, with the electron current from the next cell. We conclude our dissertation by presenting the generalized conditions for design of efficient graded recombination layer solar devices. We demonstrate a family of new GRL designs experimentally and highlight the benefits of the progression of dopings and work functions in the interlayers.

Organic semiconductors have the advantage over traditional inorganic semiconductors, such as Si or GaAs, in that they do not require perfect single crystal films to operate in real devices. Complicated multi-layer structures with nanometer scale thicknesses can thus be easily fabricated from organic materials using low-cost roll-to-roll manufacturing techniques. However, the discrete nature of organic semiconductors also implies that they typically contain almost no intrinsic charge carriers (i.e., electrons or holes), and thus act as insulators until electrical charges are injected into them. In electrical device applications this means that all of the holes and electrons within a device must be injected from the anode and cathode respectively. As a result, device stability, performance, and lifetime are greatly influenced by the interface between the organic materials and the electrode contacts. Despite the fundamental importance of the electrode/organic contacts, much of the basic physical understanding of these interfaces remains unclear. As a result, the current design of state-of-the-art organic optoelectronic devices tends to be based on trial and error experimentation, resulting in overly complicated structures that are less than optimal. In the present thesis, various electrode/organic interfaces relevant to device applications are studied using a variety of different techniques, including photoelectron spectroscopy and the iii temperature dependent current-voltage characteristics of single carrier devices. The fundamental understanding gleaned from these studies has been used to develop new strategies for controlling the energy-level alignment at electrode/organic interfaces. A universal method for tuning the work function of electrode materials using a halogenated organic solvent and UV light has been developed. Application of this technique in organic light emitting diodes enabled the first highly simplified two-layer device with a state-of-the-art record breaking efficiency.

Electroactive polymers (EAP) are an emerging branch of smart materials that possess the capability to change shape in the presence of an electric field. Opportunities for the advancement of knowledge were identified in the branch of EAP consisting of inherently electrically conductive polymers. This dissertation explores methods by which the unique properties of composite materials having conductive polymers as a constituent may be exploited. Chapter 3 describes the blending of polyaniline with conventional thermoplastics. Processing these polyblends into foams yielded a porous conductive material. The effect of blend composition and processing parameters on the resulting porous morphology and electrical conductivity was investigated. These findings represent the first systematic study of porous conductive polymer blends. In Chapter 4, multilayer electroactive polymer actuators consisting of polypyrrole films electropolymerized on a passive polymer membrane core were harnessed as actuators. The membrane is vital in the transport of ionic species and largely dictates the stiffness of the layered configuration. The impact of the mechanical properties of the membrane on the actuation response of polypyrrole-based trilayer bending actuators was investigated. Candidate materials with distinct morphologies were identified and their mechanical properties were evaluated. These results indicated that polyvinylidene difluoride membranes were superior to the other candidates. An electrochemical synthesis procedure was proposed, and the design of a novel polymerization vessel was reported. These facilities were utilized to prepare actuators under a variety of synthesis conditions to investigate the impact of conductive polymer morphology on the electromechanical response. Characterization techniques were implemented to quantitatively assess physical and electrochemical properties of the layered composite. Chapter 5 proposes a new unified multiphysics model that captures the electroactive actuation response inherent to conductive polymer trilayer actuators. The main contribution of this investigation was the proposal and development of a new hybrid model that unifies concepts from charge transport and electrochemomechanical models. The output of the proposed model was compared with published data and shown to be accurate to within 10%. Finally, Chapter 6 demonstrated the application of these materials for use as precision mirror positioners in adaptive optical systems.

Several nanomaterials systems, both inorganic and organic in nature, have been extensively investigated by a number of characterization techniques including atomic force microscopy (AFM), electron microscopy, Fourier transform infrared spectroscopy (FTIR), and energy dispersive x-ray spectroscopy (EDX). The first system consists of boron nitride nanotubes (BNNTs) synthesized via two different methods. The first method, silica-assisted catalytic chemical vapour deposition (SA-CVD), produced boron nitride nanotubes with different morphologies depending on the synthesis temperature. The second method, growth vapour trapping chemical vapour deposition (GVT-CVD), produced multiwall boron nitride nanotubes (MWBNNTs). The bending modulus of individual MWBNNTs was determined using an AFM three-point bending technique, and was found to be diameter-dependent due to the presence of shear effects. The second type of nanomaterial investigated is the biomineralized calcareous shell of the serpulid Hydroides dianthus. This material was found to be an inorganic-organic composite material composed of two different morphologies of CaCO3, collagen, and carboxylated and sulphated polysaccharides. The organic components were demonstrated to mediate the mineralization of CaCO3 in vitro. The final system studied is the proteinaceous cement of the barnacle Amphibalanus amphitrite. The secondary structure of the protein components was investigated via FTIR, revealing the presence of β-sheet conformation, and nanoscale rod-shaped structures within the cement were identified as β-sheet containing amyloid fibrils via chemical staining. These rod-shaped structures exhibited a stiffer nature compared with other structures in the adhesive, as measured by AFM nanoindentation.