Thesis (MSc)--Stellenbosch University, 2012. / Please refer to full text for abstract.

Polymer and organic electronic memory devices offer the potential for cheap, simple memories that could compete across the whole spectrum of digital memories, from low cost, low performance applications, up to universal memories capable of replacing all current market leading technologies, such as hard disc drives, random access memories and Flash memories. Polymer memory devices (PMDs) are simple, two terminal metal-insulator-metal (MIM) bistable devices that can exist in two distinct conductivity states, with each state being induced by applying different voltages across the device terminals. Currently there are many unknowns and much ambiguity concerning the working mechanisms behind many of these PMDs, which is impeding their development. This research explores some of these many unanswered questions and presents new experimental data concerning their operation. One prevalent theory for the conductivity change is based on charging and charge trapping of nanoparticles and other species contained in the PMD. The work in this research experimentally shows that gold nanoparticle charging is possible in these devices and in certain cases offers an explanation of the working mechanism. However, experimental evidence presented in this research, shows that in many reported devices the switching mechanism is more likely to be related to electrode effects, or a breakdown mechanism in the polymer layer. Gold nanoparticle charging via electrostatic force microscopy (EFM) was demonstrated, using a novel device structure involving depositing gold nanoparticles between lateral electrodes. This allowed the gold nanoparticles themselves to be imaged, rather than the nanoparticle loaded insulating films, which have previously been investigated. This method offers the advantages of being able to see the charging effects of nanoparticles without any influence from the insulating matrix and also allows charging voltages to be applied via the electrodes, permitting EFM images to capture the charging information in near real-time. Device characteristics of gold nanoparticle based PMDs are presented, and assessed for use under different scenarios. Configurations of memory devices based on metal-insulator-semiconductor (MIS) structures have also been demonstrated. Simple interface circuitry is presented which is capable of performing read, write and erase functions to multiple memory cells on a substrate. Electrical properties of polystyrene thin films in the nanometre thickness range are reported for the first time, with insulator trapped charges found to be present in comparable levels to those in silicon dioxide insulating films. The dielectric breakdown strength of the films was found to be significantly higher than bulk material testing would suggest, with a maximum dielectric strength of 4.7 MV•cm-1 found, compared with the manufacturers bulk value of 0.2 – 0.8 MV•cm-1. Conduction mechanisms in polystyrene were investigated with the dominant conduction mechanism found to be Schottky emission.

There is a need for wind sensors with high accuracy and measurement frequency for deployment on the surface of Mars. The wind data obtained to date have been adversely affected by thermal contamination and calibration issues. Improved data would not only help to constrain and validate theoretical models, but also increase safety and longevity of lander operations. The mechanical and thermal wind sensing techniques used on previous missions, whilst sufficient for basic meteorology, are wholly inadequate for measuring fundamental phenomena such as dust and volatile transport. Two promising technologies, optical and acoustic anemometry, could permit precise and high-frequency measurement of three-dimensional wind speeds on the Martian surface. Ultrasonic acoustic anemometry, which relies on time-of-flight measurements, was ultimately chosen for its lower processing requirements and ability to measure the speed of sound; and therefore temperature. Capacitive transducers were selected for their low impedance and high sensitivity, to maximise signal transmission through the rarefied Martian atmosphere. These transducers, which consist of a metallised polymer film oscillating on top of a contoured metal backplane, were evaluated for their suitability as anemometers on the Martian surface. A theoretical framework was assembled to model transducer performance and determine which factors are the most important in determining received signal amplitude. A pair of transducers were designed and manufactured to allow for testing of a wide range of parameters including thickness of the oscillating membrane and diameter. Tests were carried out on the assembled transducers to investigate the dependence on these parameters, and their behaviour was generally found to fit the assembled theoretical framework well. Transducer performance was highly dependent on roughness depth of the backplanes, as expected. The frequency response of the transducers was dominated by the backplane roughness at atmospheric pressure but by film thickness at low pressures. Cross-correlation of the sent and received signals was confirmed as the most reliable signal detection method at low signal amplitudes. The transducers were tested under simulated Martian conditions (a low-pressure carbon dioxide atmosphere with airborne dust), and found to be capable of accurately and reliably measuring the incident wind speed. The cumulative deposition of airborne dust noticeably reduced received signal amplitude, but further testing is required to determine the effect of significant amounts of dust on transducer performance. The impact of the transducer heads impeding the incident fluid flow was found to be very significant in wind tunnel testing. Preliminary computational models were found to accurately predict these effects, but a more comprehensive modelling campaign and experimental validation would be required to ensure accurate instrument calibration.

The conception of electrospinning can trace its roots back more than 400 years, when it was observed that rubbed amber can deform a droplet of water on a smooth surface, and is based upon simple concepts of charge separation and surface tension. Since that time, considerable effort has been directed at both the cause and utility of this phenomenon. The specific aim of this dissertation project was to develop an automated electrostatic processing apparatus that was capable of controlling the three-dimensional architecture of an electrospun scaffold to further improve its utility in tissue engineering. The efficacy of using this technique has been well documented and can be adapted to produce tissue engineering scaffolds for a variety of tissues and organs. This apparatus incorporates precise mandrel motion. The system is capable of 0 - 5000 revolution per minute rotation, 0 - 25 inch per second translation and ± 40° rotation about the electrospinning jet axis for repeatable scaffold production. Fiber alignment and scaffold density are precisely controlled by rotating a mandrel along one axis, translation along that same axis, and rotation around the second axis perpendicular to the electrospun fiber stream. The control is accomplished with a PC based "supervisory" control program written partially in the LabVIEW® programming language and partially in SI Programmer supplied by Applied Motion Products. Scaffold thickness and fiber diameters are determined by the syringe metering pump flow rate, material being electrospun and solution concentrations. Through extensive laboratory analysis (mechanical testing and both optical and electron microscopy), parameters such as fiber orientation, diameter and mechanics can be predictive from specific polymer setups. Our laboratory has demonstrated the ability to electrospin natural and synthetic polymers and this apparatus will be utilized to tailor scaffolds to meet specific tissue engineering needs by creating a truly biomimicking scaffold / extracellular matrix.

Ces travaux s'inscrivent dans un contexte où les contraintes vis-à-vis des décharges électrostatiques sont de plus en plus fortes, les circuits de protection sont un problème récurrent pour les circuits fonctionnant à hautes fréquences. La capacité parasite des composants de protection limite fortement la transmission du signal et peut perturber fortement le fonctionnement normal d'un circuit. Les travaux présentés dans ce mémoire font suite à une volonté de fournir aux concepteurs de circuits fonctionnant aux fréquences millimétriques un circuit de protection robuste présentant de faibles pertes en transmission, avec des dimensions très petites et fonctionnant sur une très large bande de fréquences, allant du courant continu à 100 GHz. Pour cela, une étude approfondie des lignes de transmission et des composants de protection a été réalisée à l'aide de simulations électromagnétiques et de circuits. Placés et fragmentées le long de ces lignes de transmission, les composants de protection ont été optimisés afin de perturber le moins possible la transmission du signal, tout en gardant une forte robustesse face aux décharges électrostatiques. Cette stratégie de protection a été réalisée et validée en technologies CMOS avancées par des mesures fréquentielles, électriques et de courant de fuite. / Advanced CMOS technologies provide an easier way to realize radio-frequency integrated circuits (RFICs). However, the lithography dimension shrink make electrostatic discharges (ESD) issues become more significant. Specific ESD protection devices are embedded in RFICs to avoid any damage. Unfortunately, ESD protections parasitic capacitance limits the operating bandwidth of RFICs. ESD protection size dimensions are also an issue for the protection of RFICs, in order to avoid a significant increase in production costs. This work focuses on a broadband ESD solution (DC-100 GHz) able to be implemented in an I/O pad to protect RFICs in advanced CMOS technologies. Thanks to the signal transmission properties of coplanar / microstrip lines, a broadband ESD solution is achieved by implementing ESD components under a transmission line. The silicon proved structure is broadband; it can be used in any RF circuits and fulfill ESD target. The physical dimensions also enable easy on-chip integration.

Une solution pertinente afin d'alimenter des capteurs isolés consiste à récupérer l'énergie disponible dans leur environnement immédiat. Parmi les sources d'énergie envisageables, notre choix s'est porté sur les vibrations mécaniques ambiantes. Notre contribution porte sur l'étude et la réalisation, par un procédé de fabrication collective, d'un transducteur électrostatique sans électrets en technologie MEMS Silicium. Nous proposons une étude analytique permettant d'optimiser l'efficacité du générateur électrostatique, tout en considérant une limite sur la tension maximale aux bornes du transducteur afin de ne pas endommager le circuit de conditionnement. Le design proposé prend également en compte d'éventuelles variations de l'amplitude des vibrations externes. Le dispositif a été fabriqué au sein de ESIEE Paris et présente un volume total de moins de 100 mm3.Les tests expérimentaux ont montré un comportement fortement non-linéaire de la structure. Nous avons obtenu une conversion d'énergie mécanique en énergie électrique correspondant à une puissance maximale de 2.3 μW à 260 Hz, pour une accélération de 1 g et à une pression de 0.15 Torr, lorsque le système est pré-chargé avec une tension de 10 V. Une fois implémenté dans un circuit de pompe de charge et pour les mêmes conditions d'accélération et de pression, le système peut fonctionner en complète autonomie pendant plus de 500 secondes pendant lesquelles la puissance délivrée varie de 1.4 μW à 940 nW avec une tension de pré-charge de 10.6 V / A relevant solution to power isolated sensors is to harvest the energy available in their immediate environment. Among the possible sources of energy, our choice was made on ambient mechanical vibrations. We have designed and fabricated a silicon-based and batch-processed MEMS electrostatic transducer which does not use an electret. We present an analytical method to optimize the efficiency of the electrostatic generator, while a voltage limitation on the transducer's terminal is set to prevent any damage in the conditioning electronics. The proposed design also takes into account some possible variations in the amplitude of external vibration. The device was fabricated in ESIEE Paris and its volume is less than 100 mm3. The device was tested experimentally and exhibits a strong non-linear behavior. We obtained a conversion of mechanical energy into electrical energy corresponding to a power of 2.3 μW at 260 Hz, with an acceleration of 1 g and a pressure of 0.15 Torr, when the system is pre-charged with a voltage of10 V. When the device is implemented in a charge pump circuit and under the same parameters of acceleration and pressure, the system can operate in autonomous mode for more than 500 seconds during which the output power varies from 1.4 μW to 940 nW when the pre-charge voltage is 10.6 V

Abstract Charge density studies have been conducted on ten CB1 cannabinoid receptor antagonists via high resolution x-ray crystallography. Bond critical point values and various other properties derived from these studies including the electrostatic potential were analyzed in correlation to the affinity of each compound with the CB1 receptor. Correlation/anti-correlation was found between several properties and Ki. The data was also interpreted by principal component analysis with three principal components accounting for 85% of the data variation. Data mining was limit due to the low sample count and the requirements set for the inclusion of correlated/anti-correlated variables left fewer variables to analyze. The model presented is left for future interpretation.

Neste trabalho foi realizado um estudo experimental da turbulência e do transporte de partículas e energia induzido por flutuações na borda do plasma do tokamak TBR-1. Para isto, foi utilizado um conjunto de sondas eletrostáticas (incluindo uma sonda tripla de resposta rápida) e magnéticas, especialmente construído para este fim. Técnicas de análise espectral foram aplicadas aos dados e permitiram verificar a influência das flutuações da temperatura nos parâmetros de transporte. Os resultados mostram que o nível relativo das flutuações da temperatura é da ordem de 10% e os da densidade e do potencial variam de ~10 a ~ 30 %. As flutuações eletrostáticas possuem faixas largas de freqüência e números de onda, o que caracteriza a borda do plasma como um meio turbulento. Estas flutuações se propagam no sentido da deriva diamagnética dos íons. A correção das flutuações das grandezas do plasma utilizando as flutuações da temperatura causou mudanças significativas nos transportes de partículas e energia induzidos por flutuações, nas posições mais internas da borda do plasma. O tempo de confinamento de partículas, calculado a partir deste transporte, está na faixa de ~1 a ~ 1,5 ms, que é da mesma ordem do tempo de confinamento obtido por outros métodos, indicando assim que o transporte induzido por flutuações pode ser considerado como o principal processo de perda de partículas na borda do plasma. Utilizando perturbações magnéticas externas, verificamos que a temperatura e a densidade diminuem e há alterações significativas nas características das flutuações eletrostáticas e magnéticas. Os transportes de partículas e de energia também são afetados, diminuindo nas posições mais internas da borda do plasma. Estes efeitos mostram que a borda do plasma torna-se um meio menos turbulento e que estas perturbações são um meio efetivo de controle do transporte nesta região. / In this work we report an experimental study of the turbulence and the particle and energy transport due to fluctuations in the plasma edge of the TBR-1 tokamak. For this study a special set of electrostatic probes (including one fast response triple probe) and magnetic probes have been constructed. The triple probe permitted measurements of temperature fluctuations. Spectral analysis techniques were applied to the data and permitted to verify the influence of temperature fluctuations on the transport parameters. Our results indicate that the relative level of temperature fluctuations is ~ 10 % and the relative levels of density and potential fluctuations are in the range from ~ 10 to ~ 30 %. The electrostatic fluctuations are broadband in frequencies and wave numbers indicating that plasma edge is a turbulent medium. These fluctuations propagate in the ion diamagnetic drift direction. If temperature fluctuations are taken into account, significant modifications in the calculated transport parameters are obtained mainly in the inner positions of plasma edge. The particle confinement time, calculated from the transport corrected by the temperature fluctuations, is in the range from ~ 1 to ~ 1.5 ms. These values are comparable with those calculated by using other methods, indicating that transport induced by fluctuations is the main process of particle loss in the TBR-1 plasma edge. Controlled electrical currents circulating in helical windings were used to produce magnetic perturbations. These perturbations produce a decrease in the plasma mean density and temperature, and a significant alteration in the electrostatic and magnetic fluctuations. The transport parameters are also affected, decreasing at the inner positions of the plasma edge. The effect of these magnetic fields shows that these perturbations are an effective mean to control the transport in this region.

Kin-Fai Ho. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves [61-66]). / Abstracts in English and Chinese. / Contents / ACKNOWLEDGMENT / ABSTRACT / Chapter CHAPTER 1 --- INTRODUCTION / Chapter 1.1 --- Air Pollution in Hong Kong / Chapter 1.2 --- Brief introduction of Particulate Matter / Chapter 1.2.1 --- Total suspended particulates / Chapter 1.2.2 --- Respirable suspended particulates / Chapter 1.2.3 --- PM2.5 / Chapter 1.3 --- Lead in Air Particulate and its Harmful Effects on Human / Chapter 1.4 --- Air Sampling / Chapter 1.5 --- Sample Treatment / Chapter 1.5.1 --- Acid digestion method / Chapter 1.5.2 --- Slurry sampling method / Chapter 1.5.3 --- Comparison between acid digestion and slurry sampling method / Chapter 1.5.4 --- Chemical modification / Chapter CHAPTER 2 --- EXPERIMENTAL / Chapter 2.1 --- Apparatus / Chapter 2.2 --- Instrumental analysis / Chapter 2.2.1 --- Electrothermal atomic absorption spectrometry / Chapter 2.2.2 --- Background correction by the Zeeman effect / Chapter 2.3 --- Reagents / Chapter 2.4 --- Procedure / Chapter 2.4.1 --- Collection of air sample / Chapter 2.4.2 --- Treatment of sample collected on filter / Chapter 2.4.2.1 --- Digestion Procedure / Chapter 2.4.2.2 --- Procedure for Slurry Preparation / Chapter 2.4.3 --- Temperature program employed / Chapter 2.4.4 --- Sample introduction / Chapter 2.4.5 --- Determination of Lead in PM 2.5 by Acid Digestion Method / Chapter 2.4.6 --- Determination of Lead in PM 2.5 by Developed Method / Chapter 2.4.7 --- Study of particle size and suspension behavior of PM 2.5 in solvent / Chapter CHAPTER 3 --- RESULTS AND DISCUSSION / Chapter 3.1 --- Choice of filter for air sampling / Chapter 3.2 --- Choice of Solvents for Suspension of Air Particulates / Chapter 3.3 --- Ultrasonic agitation / Chapter 3.4 --- Effect of the sonication time / Chapter 3.5 --- Particle size and Effect of stabilization agents / Chapter 3.6 --- Effect of acid predigestion of the slurry sample / Chapter 3.7 --- Chemical Modification / Chapter 3.7.1 --- Use palladium as chemical modifier / Chapter 3.7.2 --- Amount of chemical modifier / Chapter 3.7.3 --- Effect of nitric acid / Chapter 3.8 --- Optimization of the graphite furnace temperature / Chapter 3.9 --- Effect of using platform / Chapter 3.10 --- Sample injection volume / Chapter 3.11 --- Recovery study of Lead in PM2.5 / Chapter 3.12 --- The limit of detection and precision of the developed method / Chapter CHAPTER 4 --- CONCLUSION / APPENDIX / REFERENCES

Nanoscale lithography is the key component of the semiconductor device fabrication process. For the sub-10 nm node device, the conventional deep ultraviolet (DUV) photolithography approach is limited by the diffraction nature of light even with the help of double or multiple patterning. The upcoming extreme ultraviolet (EUV) photolithography can overcome this resolution limit by using very short wavelength (13.5nm) light. Because of the prohibitive cost of the tool and the photomask, the EUV lithography is only suitable for high volume manufacturing of high value. Several alternative lithography technologies are proposed to address the cost issue of EUV such as directed self-assembly (DSA), nanoimprint lithography (NIL), scanning probe lithography, maskless plasmonic photolithography, optical maskless lithography, multiple electron-beam lithography, etc.<div><br></div><div>Electron-beam lithography (EBL) utilizes a focused electron beam to write patterns dot by dot on the silicon wafer. The beam size can be sub-nanometers and the resolution is limited by the resist not the beam size. However, the major drawback of EBL is its low throughput. The throughput can be increased by using large current but at the cost of large beam size. This is because the interaction between electrons in the pathway of the electron beam. To address the trade-off between resolution and throughput of EBL, the multiple electron-beam lithography was proposed to use an array of electron-beams. Each beam has a not very large beam current to maintain good resolution but the total current can be very high to improve the throughput. One of the major challenges is how to create a uniform array of electron beamlets with large brightness.<br></div><div><br></div><div>This dissertation shows a novel low-cost high-throughput multiple electron-beam lithography approach that uses plasmonic enhanced photoemission beamlets as the electron beam source. This technology uses a novel device to excite and focus surface electromagnetic and electron waves to generate millions of parallel electron beamlets from photoemission. The device consists of an array of plasmonic lenses which generate electrons and electrostatic micro-lenses which guide the electrons and focus them into beams. Each of the electron beamlets can be independently controlled. During lithography, a fast spatial optical modulator will dynamically project light onto the plasmonic lenses individually to control the switching and brightness of electron beamlets without the need of a complicated beamlet-blanking array and addressable circuits. The incident photons are first converted into surface electromagnetic and electron waves by plasmonic lens and then concentrated into a diffraction-unlimited spot to excite the local electrons above their vacuum levels. Meanwhile, the electrostatic micro-lens will extract the excited electrons to form a finely focused beamlet, which can be rastered across a wafer to perform lithography. The scalable plasmonic enhanced photoemission electron-beam sources are designed and fabricated. An array of micro-scale electrostatic electron lenses are designed and fabricated using typical micro-electro-mechanical system (MEMS) fabrication method. The working distance (WD) defined as the gap from the electron lens to the underneath silicon wafer is regulated using a gap control system. A vacuum system is designed and constructed to host the multiple electron-beam system. Using this demo system, the resolution of the electron beams is confirmed to be better than 30 nm from the lithography results done on poly methyl methacrylate (PMMA) and hydrogen silsesquioxane (HSQ) resists. According to simulation results, the electron beam spot size can be further optimized to be better than 10 nm.<br></div><div><br></div><div>This scheme of high-throughput electron-beam lithography with multiple plasmonic enhanced photoemission beamlets has the potential to be an alternative approach for the sub-10 nm node lithography. Because of its maskless nature, it is cost effective and especially suitable for low volume manufacturing and prototype demonstration.<br></div><div><br></div><div><br></div>