published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / abstract / toc / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2017 / This research has considered an idealistic non-interleaved planar transformer wherein only the electromagnetic parasitic capacitive and inductive elements arising out of the transformer geometry are taken into account, without considering material limitations. A suitable model for the planar transformer is used to analyse its frequency and power transfer characteristics; this model was validated by three dimensional electromagnetic simulations of various planar transformer structures in FEKO simulation software. The capacitive and inductive parasitics in this model have been found to be functions of the dielectric thickness. The theoretical bandwidth for the planar transformer is defined in this research as a function of dielectric thickness. The effect of dielectric thickness of the transformer windings on the bandwidth of the transformer is analysed, based on the premise that the inherent parasitic capacitive and inductive elements would affect the transfer characteristics of the transformer. Upon conclusion of this analysis, it is found that the dielectric thickness of a planar transformer can be optimised such as to present an optimised bandwidth. A closed form analytic expression for the optimum dielectric thickness value is derived and presented in this research. In a design example of a 4:1 50W transformer presented in this research, it has been shown that the bandwidth can be improved by 384%, along with a power density improvement of 45%, upon choosing of an optimum dielectric thickness of 0.156mm to replace a standard 0.4mm thick dielectric. It should be noted that the results derived in this research are purely theoretical, justified by many idealisations and assumptions that are argued throughout the research. It is thus expected that practical results should at best approach the theoretical results, due to the known non-ideal nature of reality. / CK2018

Xu Yan = 納米銅(銅的氧化物)與三氧化二鋁復合物薄膜的製備和特性研究 / 許燕. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 50-51). / Text in English; abstracts in English and Chinese. / Xu Yan = Na mi tong (tong de yang hua wu) yu san yang hua er lv fu he wu bo mo de zhi bei he te xing yan jiu / Xu Yan. / Abstract --- p.i / 摘要 --- p.ii / Acknowledgements --- p.iii / Table of Contents --- p.iv / List of Figures --- p.viii / List of Tables --- p.xi / Chapter CHAPTER 1 --- Introduction / Chapter 1.1 --- Nanostructured Materials --- p.1 / Chapter 1.2 --- Objective of this Work --- p.1 / Chapter CHAPTER 2 --- Background / Chapter 2.1 --- Correlation of AES-CuLMM spectrum and Cu nanocluster size --- p.3 / Chapter 2.1.1 --- Typical AES-CuLMM spectra --- p.3 / Chapter 2.1.2 --- A simplified model --- p.4 / Chapter 2.1.3 --- correlation of AES-CuLMM spectra and the simplified model --- p.4 / Chapter 2.2 --- Previous works --- p.5 / Chapter CHAPTER 3 --- Instrumentation / Chapter 3.1 --- Sputtering --- p.6 / Chapter 3.1.1 --- Principles of sputtering --- p.6 / Chapter 3.1.1.1 --- Concepts of sputtering --- p.6 / Chapter 3.1.1.2 --- Initiating the plasma --- p.8 / Chapter 3.1.1.3 --- Depositing a film onto the substrate --- p.8 / Chapter 3.1.2 --- Radio-frequency (RF) magnetron sputtering --- p.9 / Chapter 3.1.2.1 --- RF sputtering --- p.9 / Chapter 3.1.2.2 --- Magnetron Sputtering --- p.10 / Chapter 3.2 --- Deposition system --- p.10 / Chapter 3.2.1 --- Instrumentation --- p.11 / Chapter 3.2.1.1 --- Vacuum system --- p.11 / Chapter 3.2.1.2 --- Sputter target and power supplies --- p.12 / Chapter 3.2.1.3 --- Substrate mounting --- p.13 / Chapter 3.2.2 --- Experimental --- p.13 / Chapter 3.3 --- X-ray Photoelectron Spectroscopy (XPS) --- p.14 / Chapter 3.3.1 --- Basic Principles --- p.14 / Chapter 3.3.2 --- Instrumentation --- p.17 / Chapter 3.3.3 --- Qualitative and quantitative analysis --- p.17 / Chapter 3.3.3.1 --- Spectra interpretations --- p.17 / Chapter 3.3.3.2 --- X-ray emission line width --- p.18 / Chapter 3.3.3.3 --- Qualification --- p.18 / Chapter 3.3.3.3.1 --- Chemical composition --- p.18 / Chapter 3.3.3.3.2 --- Sputter depth profiling --- p.18 / Chapter 3.3.3.3.3 --- Auger parameter --- p.19 / Chapter 3.4 --- Transmission Electron Microscopy (TEM) --- p.19 / Chapter 3.4.1 --- An overview of TEM --- p.19 / Chapter 3.4.2 --- Imaging mode and diffraction mode --- p.21 / Chapter 3.4.3 --- Electron-Specimen interactions --- p.21 / Chapter 3.4.3.1 --- Elastic scattering --- p.22 / Chapter 3.4.3.2 --- Inelastic scattering --- p.22 / Chapter 3.4.4 --- Imaging mechanisms for TEM --- p.23 / Chapter 3.4.4.1 --- Mass-thickness contrast --- p.23 / Chapter 3.4.4.2 --- Diffraction contrast --- p.23 / Chapter 3.4.5 --- TEM sample preparation --- p.25 / Chapter CHAPTER 4 --- Chemical and Structure Characterization of Cu(CuOx)/Al2O3 Composite Thin Films / Chapter 4.1 --- Overview --- p.26 / Chapter 4.2 --- Results and discussions --- p.26 / Chapter 4.2.1 --- Set I: Achieving the stoichiometry of A1203 matrix --- p.26 / Chapter 4.2.2 --- Set II: keeping A1203 stoichiometry and studying on the correlation of CuLMM spectra and average Cu cluster size --- p.32 / Chapter 4.2.2.1 --- Chemical information obtained by XPS --- p.32 / Chapter 4.2.2.2 --- Nanostructure studied by TEM --- p.38 / Chapter 4.2.2.3 --- Mechanical properties inspected by nano-indentation --- p.43 / Chapter 4.2.2.4 --- Optical properties --- p.43 / Chapter 4.2.3 --- Set III: Duration of deposition --- p.44 / Chapter 4.2.4 --- Set VI: Pressure effect on the average size of Cu nanoclusters --- p.45 / Chapter CHAPTER 5 --- Conclusions --- p.48 / References --- p.50

Lau Wing Fai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 101-105). / Abstracts in English and Chinese. / Abstract --- p.i / Abstract (Chinese version) --- p.iii / Acknowledgement --- p.iv / Content --- p.v / List of figure caption --- p.vii / List of table caption --- p.xi / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Nomenclature --- p.1 / Chapter 1.2 --- Comparison of diamond and DLC --- p.2 / Chapter 1.3 --- Comparison of the amorphous hydrogenated and hydrogen free amorphous carbon --- p.4 / Chapter 1.4 --- Application of DLC --- p.7 / Chapter 1.5 --- ta-C growth mechanism --- p.9 / Chapter 1.6 --- Recent activities on ta-C films --- p.11 / Chapter 1.7 --- Goal of this project and organization of this thesis --- p.11 / Chapter Chapter 2 --- Deposition of ta-C films / Chapter 2.1 --- Ta-C film deposition systems --- p.12 / Chapter 2.1.1 --- Direct ion beam deposition --- p.13 / Chapter 2.1.2 --- Laser ablation --- p.14 / Chapter 2.1.3 --- Mass selected ion beam deposition (MSIBD) --- p.15 / Chapter 2.1.4 --- Arc discharge and filtered arc discharge (FAD) methods --- p.16 / Chapter 2.2 --- The pulsed filtered vacuum arc deposition system --- p.18 / Chapter 2.2.1 --- Working principle --- p.18 / Chapter 2.2.2 --- Film thickness control --- p.20 / Chapter 2.3 --- System modification --- p.22 / Chapter 2.3.1 --- Cathode erosion improvement --- p.22 / Chapter 2.3.2 --- Enhancement of stabilization of the cathodic arc --- p.23 / Chapter 2.4 --- Sample preparation --- p.24 / Chapter 2.4.1 --- Film deposition --- p.24 / Chapter 2.4.2 --- Thermal treatments --- p.24 / Chapter Chapter 3 --- Characterization methods / Chapter 3.1 --- Raman spectroscopy --- p.25 / Chapter 3.2 --- IR Photoelasticity (PE) --- p.27 / Chapter 3.2.1 --- Basic principle --- p.27 / Chapter 3.2.2 --- Senarmont method --- p.30 / Chapter 3.3 --- Ellipsometry --- p.33 / Chapter 3.3.1 --- Principle of ellipsometry --- p.33 / Chapter 3.3.2 --- Mathematical representation --- p.37 / Chapter 3.3.2a --- Bulk layer --- p.37 / Chapter 3.3.2b --- Single layer structure --- p.38 / Chapter 3.3.3 --- Spetroscopioc rotating analyzer ellipsometer --- p.39 / Chapter 3.3.4 --- Analysis method --- p.42 / Chapter 3.3.5 --- Forouhi and Bloomer (F.B.) model --- p.43 / Chapter 3.4 --- Tribology --- p.44 / Chapter 3.4.1 --- The definition of friction --- p.44 / Chapter 3.4.2 --- Tribometer --- p.46 / Chapter Chapter 4 --- Results / Chapter 4.1 --- As-deposited samples --- p.47 / Chapter 4.1.1 --- Sp3 fraction --- p.47 / Chapter 4.1.2 --- Stress --- p.52 / Chapter 4.1.3 --- Optical properties --- p.57 / Chapter 4.1.3.1 --- Optical model for ta-C film --- p.57 / Chapter 4.1.3.2 --- Figure of merit --- p.59 / Chapter 4.1.3.3 --- Result and discussion --- p.59 / Chapter 4.1.4 --- Mechanical properties --- p.70 / Chapter 4.1.4.1 --- Hardness --- p.70 / Chapter 4.1.4.2 --- Friction --- p.76 / Chapter 4.2 --- Annealed samples --- p.81 / Chapter 4.2.1 --- Thermal stability of the ta-C film --- p.81 / Chapter 4.2.2 --- Stress relaxation --- p.85 / Chapter 4.2.3 --- Stress and G peak shift --- p.92 / Chapter Chapter 5 --- Future work / Chapter 5.1 --- Film roughness and thickness profile improvement --- p.95 / Chapter 5.2 --- Pulsed substrate bias --- p.97 / Chapter 5.3 --- Field emission and doping possibility --- p.97 / Chapter Chapter 6 --- Conclusion --- p.98 / Reference --- p.101 / Conference / publications --- p.105

Two technologies, immersion and imprint lithography, represent important stepping stones for the development of the next generation of lithography tools. However, although the two approaches offer important advantages, both pose many significant technological challenges that must be overcome before they can be successfully implemented. For imprint lithography, special care must be taken when choosing an etch barrier because studies have indicated that some physical material properties may be size dependent. Additionally, regarding immersion lithography, proper image focus requires that the optical path length between the lens and substrate be maintained during the entire writing process. The work described in this document was undertaken to address the two challenges described above. A new mathematical model was developed and used in conjunction with AFM nano-indentation techniques to measure the elastic modulus of adhesive, thin polymer films as a function of the film thickness. It was found that the elastic modulus of the polymer tested did not change appreciably from the value determined using bulk measurement techniques in the thickness range probed. Additionally, a method for monitoring and controlling the optical path length within the gap of a nearly index-matching cavity based on coherent broadband interference was developed. In this method, the spectrum reflected for a cavity illuminated with a modelocked Ti:Sapphire laser was collected and analyzed using Fourier techniques. It was found that this method could determine the optical path length of the cavity, quickly and accurately enough to control a servo-based feedback system to correct deviations in the optical path length in real time when coupled with special computation techniques that minimized unnecessary operations. / text

We investigate some of the mechanical design factors of wafers and the effect on strength. Thin, solid, pre-stressed films are proposed as a means to improve the bulk mechanical properties of a wafer. Three-point bending was used to evaluate the laser scribe density and chemical processing effect on wafer strength. Drop and strike tests were employed to investigate the edge bevel profile effect on the mechanical properties of the wafer. To characterize the effect of thin films on strength, one-micron ceramic films were deposited on wafers using PECVD. Coated samples were prepared by cleaving and were tested using four-point bending. Film adhesion was characterized by notched four-point bending. RBS and FTIR were used to obtain film chemistry, and nanoindentation was used to investigate thin film mechanical properties. A stress measurement gauge characterized residual film stress. Mechanical properties of the wafers correlated to the residual stress in the film.

Study of Ordered Macroporous Polymer Films by Templating Breath Figures Lulu Song 193 pages Directed by Dr. Mohan Srinivasarao Macroporous films with highly ordered pore patterns have many potential applications. Some examples include microstructured electrode surfaces, photonic band gap materials and filters for cell sorting and bio-interfaces. In this dissertation we discuss a moist-casting method to prepare hexagonally-ordered macroporous films with pore sizes in the range of sub-micron to several microns, where condensed water droplets (breath figures) work as templates. Compared with other templating methods, this one is fast and simple. Well-ordered porous films can be obtained in tens of seconds and the pore size can be easily tailored and dynamically controlled by adjusting the casting conditions. More importantly, there is no need to remove the templates; water droplets just evaporate when the casting processes are finished. This study was carried out with the intention of characterizing the structures, understanding film-formation processes and exploring special properties and possible applications. For the structural characterization, film morphology was studied in detail by normal optical microscopy and laser scanning confocal microscopy (LSCM). Several interesting features have been revealed. Meanwhile, the degree of the order of the porous structures were characterized both in real space via Voronoi diagram and bond-orientational correlation function, and in reciprocal space via Fraunhofer diffraction pattern. To further understand the mechanism, the evaporation of the polymer solutions during the film formation was studied by monitoring their mass over time. Besides, the evolution of breath figures formed on the evaporating polymer solutions was in-situ recorded via a high-speed camera coupled to an optical microscope. Combined with the information on the film structures obtained via LSCM, explanations for some detailed features have been attempted. Wetting property of these films was studied in some detail. The films exhibited lotus effect, mimicking natural non-wetting surfaces. To improve the solvent stability and mechanical properties of the macroporous films for possible applications, crosslinking of the polymer matrix was tried by heating. Crosslinked structures with hexagonal arrays of cone-like air holes were obtained, which might find use as micron-sized beakers for small-quantity analysis.