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The goals of this project were to synthesize voltage-gated ion channels based upon previously studied pore-formers and to further explore the mechanism of ion transport with this type of pore-former. The syntheses of bis-macrocyclic bola-amphiphiles started with two different macrocycles prepared via a two-step cyclization from maleic anhydride by reaction with 1,8-octanediol alone or with triethyleneglycol. The macrocycles were then modified to a set of mono-adducts and bis-adducts by Michael addition of thiols (3-mercaptopropanol, 2-mercaptoacetic acid, or 3-mercaptopropionic acid). The mercaptopropanol adduct was converted to a mesylate and coupled with a carboxylate derivative to form a bis-macrocycle. Repetitious gel permeation chromatography gave a bis-macrocycle bearing only one head group, a carboxylate. The second head group was added via Michael addition to give a bis-macrocyclic bola-amphiphile which could have either the same head groups or different head groups. Two symmetrical transporters were synthesized via another route: two macrocycles reacted with 2-mercaptoethyl sulfide to generate a bis-macrocycle, and the same head group was then simultaneously added to both ends to give a symmetrical bola-amphiphile. Transporters with different combinations of head groups were synthesized to compare head group effects on cation transport properties, while different macrocycles were used in the backbone of transporter candidates to give two series of compounds for comparison of their behaviors. The second phase of this project investigated the transport properties of candidates using pH-stat titration. The pH-stat titration of bilayer vesicles allowed determination of dynamic transport properties: transport rate, apparent kinetic order and cation selectivity. Combined with information from planar bilayer experiments (done by D. Loock), it was found that an asymmetrical bis-macrocyclic bola-amphiphile with an acetate and a succinate head group behaves as voltage-gated ion channel in planar bilayers. An ion transport mechanism of the present system was proposed which involves the formation of active aggregates (probably dimers or oligomers). / Graduate

White organic light-emitting diodes (WOLEDs) resemble light more naturally, with emission spectrum that is comfortable to the human eye. A lot of effort has been devoted to improve the performance of WOLEDs. This research work was aimed at studying the emission behavior of WOLEDs, improving the device performance, and thereby developing several novel device concepts for application in high performing transparent WOLEDs and organic proximity sensors. Emission behavior, in terms of color stability and injection characteristics of phosphorescent organic light-emitting diodes (OLEDs), was investigated systematically and optimized via the experimental optimization and optical simulation. The transparent WOLEDs can be almost invisible at daytime and can emit a pleasant diffused light at night, allowing the surface light source to shine in both directions. It is an exciting new lighting technology that could bring new device concepts. However, undesirable angular-dependent emission and asymmetrical emission characteristics are often observed in transparent WOLEDs. In this work, a pair of optically and electrically comparable transparent anode and cathode was introduced to form weak microcavity transparent WOLEDs, e.g., employing a pair of Ag (10 nm)/MoO3 (2.5 nm)-modified indium tin oxide anode and Al (1.5 nm)/Ag (15 nm)/NPB (50 nm) cathode. It is found that the avoidance of the spectral overlap between the peak wavelengths of the emitters and the resonant wavelength of the organic microcavity moderates the angular-dependent electroluminescence emission behavior, thereby improving the color stability of the transparent white WOLEDs over a broad range of the viewing angles. As a result, the transparent WOLEDs developed possess a visible-light transparency of >50%, a symmetrical bi-directional illumination with an almost identical power efficiency of 11 lm/W (measured at 100 cd/m2) and the similar CIE coordinates of (0.36, 0.43) and (0.38, 0.46) measured from both sides of the devices. Efficient charge injection is a prerequisite for achieving low turn-on voltage and improved hole-electron current balance in OLEDs. Metal oxide (e.g. MoO3) is a commonly used hole-injection layer (HIL) for reducing the energy barrier at the anode/organic interface for efficient charge injection. However, fluctuation in the quality of the metal oxide-based HIL, e.g., changes due to the MoO3 formulation, film fabrication and post-treatment conditions, often places a practical challenge limiting reproducibility of the device performance. In this work, an effective solution-processed HIL that consists of a mixture of PEDOT:PSS and MoO3 was developed for application in OLEDs. It is found that the presence of the solution-processed HIL at the interface between the anode and the organic improves the hole injection and the performance reproducibility of the phosphorescent OLEDs. The effect of the presence of the MoO3 in the solution-processed HIL on charge injection in phosphorescent OLEDs, with a configuration of glass/ITO/CBP/ CBP:Ir(ppy)2acac/TmPyPB/LiF(1.0 nm)/Al(70 nm), was examined. It is shown that solution-processed HIL has a superior hole injection characteristic at the HIL/hole transporting layer (HTL) interface compared to that in the devices fabricated with a pristine PEDOT:PSS or a pure MoO3 HIL, yielded phosphorescent OLEDs with an external quantum efficiency of ~25% and a power efficiency of ~75 lm/W @ 1000 cd/m2. The morphological and surface electronic properties of the hybrid HIL were also investigated by AFM, XPS and UPS measurements, revealing the formation of a good contact at the HIL/HTL interface in the phosphorescent OLEDs. Apart from improving the device performance, a new organic proximity sensor based on the monolithic integration of organic photo-detectors (OPDs) and OLEDs was also developed. A MoO3-modified thin silver interlayer, serving simultaneously as a transparent cathode for the OPDs and an anode for the OLEDs, is used to link the functional organic electronic components. In the integrated OLED/OPD-based proximity sensors, the OLED components function as an illumination source while the coupled OPD units enable a high absorption when light is reflected from objects to create an optical signal. The photosensitivity is enhanced using organic photosensitive bulk heterojunction in the OPDs, thereby realizing a high photosensitivity and the high external quantum yield at a low reverse bias. The signal to noise ratio, optical and frequency responses of the integrated organic proximity sensors were optimized and examined. The design and fabrication flexibility of the integrated OLED/OPD-based organic proximity sensors also have cost benefits, making it possible for application in wearable units and compact information systems.

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Measurement of the differential capacitance (C) of a Schottky diode as a function of voltage (V) is widely used to probe dopant profiles in semiconductors. However, the theory of the dopant profiling method is based on an approximation, and does not work well when the dopant concentration changes rapidly with distance. The region beyond the maximum of an implanted Gaussian profile is of particular interest in connection with ingot qualification tests for GaAs, and it is just there that the problem is the most serious. In this thesis, an investigation was made by numerical simulation on problems associated with the profiling method. Programs were written to calculate the differential capacitance-voltage relation for GaAs Schottky diodes with and without deep energy levels, and with a specified dopant distribution. The programs predict what the approximation method would indicate for the dopant profiles according to a set of canonical equations used in the profiling method. The predicted and the specified dopant profiles were then compared. Mainly ion-implanted dopant profiles in semiconductors were studied although doped epitaxial layers were also considered. For ion-implanted GaAs, the predicted dopant profiles were found to be about 10% lower near the peak region than the true dopant profiles, and the predicted profiles were confirmed to be too high in the tail region. For doped epitaxial layers, the predicted profile was found, in some cases, to give good estimates for the dopant concentrations on the high and low sides of the true step profile, but in some others, the predicted profiles were found to be totally misleading. For GaAs with deep levels, a method of calculating the differential capacitance was developed to take into account the fact that the deep levels do not respond to the 1 MHz a.c. signal normally used in the C(V) measurements. It is believed to simulate the experimental C(V) measurements more realistically. The tail sections of the predicted profiles were found to increase with the concentration of background shallow donor atoms in the deep-level-free semiconductor before ion-implantation, and with the number of impurity atoms which are channelled or diffused to the region during or after ion-implantation. This implies that although the profiling method is erroneous in the tail section, it can nevertheless be used on a comparative basis to indicate the level of background shallow dopant concentration, and the degree of channelling or diffusion. The effects of the substrate parameters in liquid encapsulated Czochralski (LEC) GaAs, which include the concentrations of EL2, net shallow acceptors, and sometimes Cr, have been investigated on the predicted dopant profiles for ion-implanted samples. Increases in Cr and net shallow acceptor concentrations were found to increase the steepness of the predicted dopant profile, while an increase in EL2 concentration has little effect. A method of estimating dopant activation efficiency in GaAs has been proposed. This method uses the author's second program to avoid underestimations of the activation efficiency in GaAs caused by the peak lowering in the predicted dopant profiles. The concept of Debye length in semi-insulating LEC GaAs was also discussed. The Debye length given by the standard formula for semiconductors with shallow donors and acceptors can become inapplicable when deep levels are present. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

This thesis describes a mathematical-graphical analysis and some analog computer simulation studies that were carried out to determine the feasibility of a proposed circuit to be used for analog-to-digital conversion. The circuit analysed and simulated contains a stack of tunnel diodes which are constructed from the same type of semiconductor material. The switching characteristics of this circuit are controlled primarily by the ratios and the values of the capacitances which shunt the individual tunnel diodes and to a lesser extent by the interdiode capacitances. This is revealed in a study of the effects of different circuit parameter variation A two tunnel diode stack circuit (two bits of information capacity) is analysed by studying the nature of the switching trajectories in the proximity of the singular points of the equations describing -the circuit operation. Three different modes of operation, each of which differs in the manner in which the 11 state is reached, are revealed for this circuit. The analysis indicates a feature of the circuit which can be used to determine the final state of the circuit before steady state conditions have been reached. An extension of the two tunnel diode stack circuit to one containing three tunnel diodes yielded eight stable and accessible states. This indicates that the circuit proposed will be able to realize 2[superscript n] states with n tunnel diodes. It is shown that different interdiode capacitance connections will facilitate the achievement of this result. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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