Fung Yun Ming. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references (leaves 134-140). / Abstracts in English and Chinese. / Abstract --- p.I / Acknowledgement --- p.III / Contents --- p.IV / List of Figure captions --- p.VIII / List of Table captions --- p.XIII / Chapter Chapter 1 --- Introduction --- p.1 / Chapter Chapter 2 --- Theory and Applications / Chapter 2.1 --- Principle of field emission / Chapter 2.1.1 --- The Fowler-Nordheim Theory --- p.3 / Chapter 2.1.2 --- Field emission from metals --- p.6 / Chapter 2.1.3 --- Field emission from semiconductors --- p.8 / Chapter 2.1.3.1 --- Advantages and limitations of silicon --- p.9 / Chapter 2.1.4 --- Application of the Fowler-Nordheim theory --- p.10 / Chapter 2.1.5 --- Factors influencing field emission efficiency --- p.11 / Chapter 2.2 --- Applications --- p.11 / Chapter 2.2.1 --- Operation of a Field Emission Displays --- p.11 / Chapter 2.2.2 --- Basic structure of a Field Emission Displays --- p.13 / Chapter 2.2.3 --- Parameters relevant to applications --- p.15 / Chapter 2.3 --- The fabrication processes --- p.17 / Chapter 2.3.1 --- The anisotropic wet etching method --- p.18 / Chapter 2.3.2 --- The isotropic wet etching method --- p.19 / Chapter 2.3.3 --- Field emission from coating materials --- p.20 / Chapter 2.3.3.1 --- Coating enhancement --- p.20 / Chapter 2.3.3.2 --- Diamond and diamond-like films --- p.21 / Chapter 2.3.3.3 --- Metallic coatings --- p.22 / Chapter 2.3.3.4 --- Porous silicon coatings --- p.22 / Chapter 2.3.3.5 --- Silicon carbide coatings --- p.22 / Chapter 2.3.4 --- Fabrication of field emitters with gate --- p.23 / Chapter Chapter 3 --- Sample Preparation and Characterization Methods / Chapter 3.1 --- Sample preparation --- p.25 / Chapter 3.2 --- The fabrication process / Chapter 3.2.1 --- Isotropic etching of silicon / Chapter 3.2.1.1 --- The anodization process --- p.25 / Chapter 3.2.1.2 --- Porous silicon formation --- p.26 / Chapter 3.2.2 --- Anistropic etching of silicon --- p.27 / Chapter 3.2.3 --- The sputtering system --- p.28 / Chapter 3.2.4 --- The MEVVA Ion Source Implanter --- p.30 / Chapter 3.3 --- Characterization Methods / Chapter 3.3.1 --- Atomic Force Microscopy (AFM) --- p.32 / Chapter 3.3.2 --- Scanning Electron Microscopy (SEM) --- p.34 / Chapter 3.3.3 --- Field emission measurement / Chapter 3.3.3.1 --- Vacuum requirements --- p.35 / Chapter 3.3.3.2 --- Testing system / Chapter 3.3.3.3 --- Fluctuation of field emission --- p.38 / Chapter Chapter 4 --- Fabrication of Silicon Tips and their field emission charateristics / Chapter 4.1 --- The anodization etching process / Chapter 4.1.1 --- Introduction --- p.40 / Chapter 4.1.2 --- Experimental details --- p.42 / Chapter 4.1.3 --- Results and Discussions / Chapter 4.1.3.1 --- N type (100) sample --- p.45 / Chapter 4.1.3.2 --- Ntype(lll) sample --- p.60 / Chapter 4.1.3.3 --- Fluctuations of the emission current --- p.64 / Chapter 4.1.3.4 --- The effect of Concentration of HF solution on First Step Anodization --- p.68 / Chapter 4.1.3.5 --- The effect of the Concentration of HF solution on Second Step Anodization --- p.70 / Chapter 4.1.3.6 --- Gated silicon field emitter --- p.70 / Chapter 4.1.4 --- Conclusions --- p.73 / Chapter 4.2 --- Anisotropic texturing process / Chapter 4.2.1 --- Introduction --- p.74 / Chapter 4.2.2 --- Experimental details --- p.76 / Chapter 4.2.3 --- Results and Discussions --- p.78 / Chapter 4.2.4 --- Conclusion --- p.92 / Chapter 4.3 --- Formation of Porous Silicon Layer on silicon / Chapter 4.3.1 --- Introduction --- p.93 / Chapter 4.3.2 --- Experimental details --- p.94 / Chapter 4.3.3 --- Results and Discussions --- p.95 / Chapter 4.3.4 --- Conclusion --- p.100 / Chapter 4.4 --- Chapter Summary --- p.101 / Chapter Chapter 5 --- Improvement in the field emission characteristics of the silicon tips upon coating with low work function materials / Chapter 5.1 --- Amorphous carbon coating / Chapter 5.1.1 --- Introduction --- p.102 / Chapter 5.1.2 --- Experimental details --- p.103 / Chapter 5.1.3 --- Results and Discussions --- p.104 / Chapter 5.1.4 --- Conclusion --- p.118 / Chapter 5.2 --- Silicon carbide coated Silicon emitter by MEWA / Chapter 5.2.1 --- Introduction --- p.119 / Chapter 5.2.2 --- Experimental details --- p.120 / Chapter 5.2.3 --- Results and Discussions --- p.121 / Chapter 5.2.4 --- Conclusion --- p.125 / Chapter 5.3 --- Chapter Summary --- p.126 / Chapter Chapter 6 --- Conclusions --- p.127 / Reference --- p.134 / List of publications --- p.140

by Zhu, Ming. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 73). / Abstracts in English and Chinese. / ABSTRATE (ENGLISH) --- p.I / ABSTRATE (CHINESE) --- p.III / ACKNOWLEDGEMENTS --- p.V / TABLE OF CONTENTS --- p.VI / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Introduction to organic semiconductors --- p.1 / Chapter 1.2 --- Charge transport in organic semiconductors --- p.1 / Chapter 1.2.1 --- Polaron models --- p.2 / Chapter 1.2.2 --- Scher-Montroll model --- p.2 / Chapter 1.2.3 --- Gaussian disorder model --- p.3 / Chapter 1.3 --- Organic semiconductors in this thesis --- p.5 / Chapter 1.4 --- Several key issues --- p.6 / References --- p.7 / Chapter 2. --- Experimental Techniques --- p.9 / Chapter 2.1 --- Materials Purification --- p.9 / Chapter 2.1.1 --- Motivation --- p.9 / Chapter 2.1.2 --- Basic principle --- p.9 / Chapter 2.1.3 --- Purification setup --- p.10 / Chapter 2.1.4 --- Parameters optimization --- p.11 / Chapter 2.2 --- Sample Fabrication --- p.11 / Chapter 2.2.1 --- Substrate treatment --- p.12 / Chapter 2.2.2 --- Thermal vacuum evaporation --- p.12 / Chapter 2.2.3 --- Spin coating --- p.12 / Chapter 2.3 --- Electrical measurement techniques --- p.13 / Chapter 2.3.1 --- J-V characteristics --- p.13 / Chapter 2.3.1.1 --- Injection versus bulk limited current --- p.13 / Chapter 2.3.1.2 --- Space Charge Limited Current --- p.15 / Chapter 2.3.1.3 --- Trap controlled Space Charge Limited Current --- p.15 / Chapter 2.3.2 --- Admittance spectroscopy --- p.17 / References --- p.20 / Chapter 3. --- Steady state J-V characteristics of organic thin films in sandwiched structures --- p.22 / Chapter 3.1 --- Experimental --- p.22 / Chapter 3.2 --- Results and discussions --- p.23 / Chapter 3.2.1 --- J-V characteristics of CuPc and TPD-PS thin films --- p.23 / Chapter 3.2.2 --- J-V characteristics of CuPc thin films with different cathodes --- p.26 / Chapter 3.2.3 --- Variable temperature J-V characteristics of CuPc thin films --- p.28 / References --- p.31 / Chapter 4. --- Dynamic Properties of Organic Semiconductors Performed by Admittance Spectroscopy --- p.32 / Chapter 4.1 --- Introduction to admittance spectroscopy --- p.32 / Chapter 4.2 --- Theoretical models --- p.32 / Chapter 4.3 --- Experimental --- p.36 / Chapter 4.3.1 --- Experimental scheme --- p.36 / Chapter 4.3.2 --- Sample preparation --- p.36 / Chapter 4.4 --- Results and discussion --- p.37 / Chapter 4.4.1 --- Unpurified CuPc --- p.37 / Chapter 4.4.2 --- Purified CuPc --- p.40 / Chapter 4.5 --- Conclusion --- p.43 / References --- p.44 / Chapter 5. --- Air-induced Trap Effect in Organic Semiconductors --- p.45 / Chapter 5.1 --- Introduction to negative capacitance phenomenon --- p.45 / Chapter 5.2 --- Experimental --- p.46 / Chapter 5.3 --- Results and discussion --- p.46 / Chapter 5.3.1 --- Admittance spectroscopy with different electrodes --- p.46 / Chapter 5.3.2 --- Admittance spectroscopy with different concentrations of oxygen --- p.48 / Chapter 5.3.3 --- Admittance spectroscopy with different humidities --- p.50 / Chapter 5.4 --- Conclusion --- p.53 / References --- p.56 / Chapter 6. --- N-type Doping of Magnesium to Zinc-Phthalocyanine (ZnPc) --- p.58 / Chapter 6.1 --- Introduction --- p.58 / Chapter 6.2 --- Experimental --- p.60 / Chapter 6.3 --- Results and discussion --- p.61 / Chapter 6.4 --- Conclusion --- p.66 / References: --- p.67 / Chapter 7. --- Summary and future work --- p.68 / Summary --- p.68 / Future work --- p.69 / References: --- p.72 / Appendix --- p.73

Neurons are characterized by an electric potential which is established between their inside and outside media. They exhibit specific voltage fluctuations, in response to strong enough current impulses, called action potentials. In this work, a bang-bang controlled bilinear system (BLS) is derived to approximate the generation of a simple neuron's action potential. The shape of the response, as well as the timing seem to be useful for experimental planning and interpretation to neural physiologists. The BLS-model has the potential to aid the design and fabrication of commercial neural networks for communication, control and computing. In this manner, a variable-structure membrane impedance, such as exhibited by a stable focus and a saddle point in state space, and/or other modes, arises naturally. Added positive and negative stimuli, such as from other neurons, have the capability to alter the voltage across the inside and the outside media of the neuron and elicit an advanced or delayed response in the action potential. Such latency is significant as noted above, and is an active area of experimental research. The response shape and the timing with respect to some other event(latency} are related to experimental data. This simple model is compared to the complex and highly celebrated Hodgkin-Huxley model for the squid giant axon. The bang-bang feedback control is given a biological interpretation of sodium and potassium ion channels in this axon, that yields a variable-structure membrane impedance. / Graduation date: 2000

DNA molecules possess high density genetic information in living beings, as well as selfassembly and self-recognition properties that make them excellent candidates for many scientific areas, from medicine to nanotechnology. The process of electron transport through DNA is important because DNA repair occurs spontaneously via the process that restores mismatches and lesions, and furthermore, DNA-based molecular electronics in nano-bioelectronics can be possible through the process. In this thesis, we study theoretically the transport properties through a one-dimensional one-channel DNA model, a quasi-one-dimensional one-channel DNA model, and a two-dimensional four-channel DNA model by using the Tight-Binding Hamiltonian method. We show graphical outputs of the transmission, overall contour plots of transmission, localization lengths, the Lyapunov exponent, and current-voltage characteristics as a function of incoming electron energy and magnetic flux which are obtained using Mathematica run on the CSH Beowulf Cluster. Our results show that the semiconductor behavior can be observed in the I-V characteristics. The current through a quasi-one-dimensional one-channel DNA model starts to flow after the breakdown voltage and remains constant after threshold voltage. The variations of the temperature make the fluctuations of the system. As the temperature increases, the sharp transmission resonances are smeared out and the localization lengths are also decreased. Due to a magnetic field penetrating at the center of the two-dimensional DNA model, the Aharonov- Bohm (AB) oscillations can be observed. / Sequence dependent electron transport through a one-dimensional, one-channel DNA model -- Backbone-induced effects on charge transport through a quasi one-dimensional DNA molecule -- Temperature and magnetic fields effects on the electron transport through two-dimensional and four-channel DNA model.

published_or_final_version / Pharmacology and Pharmacy / Master / Master of Medical Sciences

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The application of spectral induced polarization (SIP) to geohydrologic and geotechnical problems is considered. Some fundamental electrochemical characteristics of sulfides are reviewed. An alternate theory of the underlying cause of IP is presented. A modified field method is proposed. Two field sites are studied. Prevailing electrochemical thought is that most sulfides, especially pyrite and chalcopyrite, have passivating surface coatings. With this thought in mind, existing geophysically-oriented electrochemical measurements may be reinterpreted quite differently than has previously been done. Large impedances at low frequencies have traditionally been attributed by geophysicists to diffusional phenomena related to rapid reactions occurring at the sulfide surface. Large impedances at low frequencies with clays have traditionally been attributed to restrained ionic diffusion between zones of clay particles. Although they appear to be due to quite different mechanisms, both of these low frequency dispersions may be explained by a single rate limiting mechanism. Using fractal geometry, the large low frequency dispersions observed on sulfides may be explained by distributed high charge-transfer resistances on rough surfaces. With high surface resistances sulfides may behave like insulating clay particles and allow charge separation to occur in surface conduction current flow. Although displacement currents may flow in sulfides they are considered to be minimal in comparison to the surface conduction currents. The concept of a common polarization phenomenon allows the previous studies on rock samples containing clay particles and/or sulfides to be equated on the basis of particle size. With clay-coated sand grains it may be possible to estimate intrinsic hydraulic conductivity based on the interpreted polarizable grain size. Aquifers, and partially water saturated zones, may be IP targets if they have small amounts of polarizable clay minerals. Aquifer detection and grain size estimation are demonstrated. Theoretical work and field studies show the advantages of using a modified dipole-dipole array and data presentation methods. The large amounts of data gathered during broad-band SIP surveys are demonstrated to be very useful in layered-earth geohydrologic problems. The higher frequency data contain much earth-structure information, are easily gathered, and allow immediate qualitative structural interpretation. Lower frequency data contain information useful in aquifer characterization.

No description available.

No description available.