by Gao Yun. / "November 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (p. 165-171). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

by Chiah Man Fat. / "March 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Studying quasi-one-dimensional (1D) semiconductor nanostructures is an attractive and active research field in nanoscience and nanotechnology. Their controllable growth is the foundation for observing novel properties and fabricating useful nano-devices and is also a challenge. / We believe that our work in perfecting the fabrication of aligned 1D semiconductor nanostructures and control of their morphology, crystal structure and orientation will shed more light on the understanding on 1D physics and advancement in nanotechnology. / We have studied the control of the structure, morphology and alignment of Zn-Cd-Se 1D nanostructures by fine tuning their growth conditions and judiciously choosing substrates in a metalorganic chemical vapor deposition (MOCVD) reactor. We found that the products are zincblende structured nanoneedles at relatively low temperatures and pressures, and wurtzite structured nanowires at high temperatures and pressures. We have fabricated aligned 1D nanostructures of different chemical compositions by exploiting the epitaxial relationship between the lattices of Zn-Cd-Se system and GaAs substrate. From the systematic studies of the orientations of the aligned samples, we demonstrated that they can be controlled by the crystallographic surface of the substrate. We also found that the orientation can be affected by the growth temperature. Three growth models are suggested to explain the aligned growth for zincblende and wurtzite 1D nanostructures and complex shaped three-bladed nanoswords. Observations and angular measurements of the orientations and growth directions by electron microscopy and analyses by pole stereographs offer supporting evidences for the models. Polarized photoluminescence studies of individual CdSe nanowires obtained under controlled growth have been achieved. / Liu, Zhuang = 通過金屬有機物化學氣相沉積法合成晶體結構, 形貌及生長取向性可控的硒鋅鎘族准一維納米結構 / 劉壯. / "July 2007." / Adviser: Sui Kong Hark. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1062. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307. / Liu, Zhuang = Tong guo jin shu you ji wu hua xue qi xiang chen ji fa he cheng jing ti jie gou, xing mao ji sheng chang qu xiang xing ke kong de xi xin ge zu zhun yi wei na mi jie gou / Liu Zhuang.

When porous silicon is plated with a catalytic metal, the two materials can act together as a single entity whose electrical properties are sensitive to its environment – the sensing component of an electrochemical gas sensor. Etching pores into silicon is an electrochemical process; and which type of doped silicon used is one of its key parameters. For nearly all reported porous silicon gas sensors, the silicon has been of the p-doped variety – because p-doped porous etching is better understood and the layers that result from it are more predictable – despite n-doped silicon having potentially significant benefits in ease of fabrication and being more conducive to plating by a catalyst. This experiment is an attempt at creating a palladium plated n-doped porous silicon layer, and an examination into what differentiates this fabrication process and the layers that result from the traditional p-doped type. The porous layers to be plated are to be the same and would ideally have properties that are a close approximation to what a functional gas sensor would require. This experiment defined a process that fabricated this “ideal” layer out of N-type, , double polished silicon wafers with a resistance of 20 Ω cm. The wafers were subjected to the anodic etching method with an HF/ethanol mixture as the electrolyte; and only two (of among many) fabrication parameters were varied: HF concentration of the electrolyte and total etching time. We find that a concentration of 12% HF (by volume) and an etching time of 6 hours result in layers most appropriate to carry into plating. The anodization current density is 15 mA cm-2. Deposition of the catalyst, palladium, is done using the electroless method by immersing the porous layer in a .001M PdCl2 aqueous bath. Characterization of this Pd/Porous Silicon layer was done by measuring resistivity by four point probe and imaging through Scanning Electron Microscopy. It was found that layers of a maximum average of 63 ± 6% porosity were created using our fabrication method. There is evidence of palladium deposition, but it is spotty and irregular and is of no improvement despite the n-doping wafer makeup. Resistivity in well-plated regions was measured to be 7-10 Ωcm, while resistivity in regions not well-plated was measured to be 70-140 Ω cm. This is comparable to previous literature values, indicating n-silicon porous silicon can be fabricated and still have potential as a catalytic layer, should metal deposition methods improve.

No description available.

Pressure measurement using a strain gauge bonded with epoxy adhesive to a metallic mechanical support has been, and still is, extensively employed, however, for some applications the use of an epoxy is inadequate, especially when temperatures exceed 120C. There is therefore particular interest in the use of thin film techniques to vacuum deposit strain gauges directly on metallic substrates. Such devices are highly cost effective when produced in large quantities due to the manufacturing techniques involved. This makes them ideally suited for use in large-volume products such as electronic weighing scales and pressure transducers. In this thesis, new techniques for fabricating thin film vapour deposited strain gauge transducers on metal substrates for application as novel pressure sensors in the fastener industry are developed. Clearly, for a vapour deposited strain gauge to function correctly, it is essential that it be deposited on a defect free, high quality electrically insulating film. This was a significant challenge in the present study since all available physical vapour deposition (PVD) equipment was direct current (DC) and insulators of around 4 um thick were needed to electrically isolate the strain gauges from metal. As a result, several methods of depositing insulators using DC were developed. The first involved the use of DC magnetron sputtering from an aluminium target to reactively deposit up to 4 um thick AlN. DC magnetron discharges suffer arc instability as the AlN forms on the target and this limits the maximum thickness that can be deposited. Consequently, the arc instability was suppressed manually by increasing argon gas flow at the onset of arcing. Although the deposited AlN showed a high insulating resistance, it was found that the breakdown voltage could significantly increase by (a) utilising a metallic interlayer between the thin film insulator and the metallic substrate and (b) annealing in air at 300C. A second deposition method involved the use of DC magnetron sputtering to deposit modulated thin film insulators in which an aluminium target was used to reactively deposit alternating layers of aluminium nitride and aluminium oxide. These films showed significant increases in average breakdown voltage when the number of layers within the composite film was increased. The third method involved the deposition of AlN thin film insulators using partially filtered cathodic arc evaporation with shielding. Initially, AlN was deposited under partially filtered conditions to obtain a relatively thick (~ 4 um) coating then, while still depositing under partially filtered conditions, a smooth top coating was deposited by using a shielding technique. The deposition of metal macroparticles is an inherent problem with cathodic arc deposition and shielding is one form of macroparticle filtering. Such particles are highly undesirable in this study as they are electrically conductive. A fourth coating technique for depositing insulators on steel was based on thermal spray technology. Insulating films of Al2O3 were plasma sprayed and then polished to thereby fabricate viable electrical insulators for vapour deposited strain gauges. With respect to depositing strain gauges two methods were employed. The first involved the sputter deposition of chromium through a shadow mask to form a strain gauge with gauge factor sensitivity of around 2. The second used cathodic arc evaporation to fabricate a multi-layered strain gauge composed of alternating CrN and TiAlN layers that yielded a gauge factor of around 3.5. The technique achieves better compatibility between gauge and insulator by allowing a wider selection of materials to form the gauge composition. Finally, a novel pressure sensor in the form of a load cell was developed that consisted of a chromium strain gauge on a steel washer electrically insulated with AlN thin film. The load cell showed good performance when tested under compressive load.

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Babatunde Ogunnaike, Dept. of Chemical Engineering, and Robert W. Birkmire, Dept. of Materials Science & Engineering. Includes bibliographical references.

<p>Patterning of multi crystalline silicon Solar cell is prepared with photolithography etching. Electroless plating is used to get metallization of Nickel contacts. SEM analysis of Nickel deposition and measurement of contact resistance for series and shunt resistance is done. To increase the fill factor, the screen printed electrodes are subjected to different firing temperatures there by increasing the efficiency of solar cell. Nickel-silicide formation at the interface between the Silicon and Nickel enhances stability and reduces the contact resistance, resulting in higher energy conversion efficiency.</p><p> </p>

Patterning of multi crystalline silicon Solar cell is prepared with photolithography etching. Electroless plating is used to get metallization of Nickel contacts. SEM analysis of Nickel deposition and measurement of contact resistance for series and shunt resistance is done. To increase the fill factor, the screen printed electrodes are subjected to different firing temperatures there by increasing the efficiency of solar cell. Nickel-silicide formation at the interface between the Silicon and Nickel enhances stability and reduces the contact resistance, resulting in higher energy conversion efficiency.

I have explored the use of the matrix assisted pulsed laser evaporation (MAPLE) and MAPLE direct write (MDW) to create thin films of biological materials. MAPLE is a novel physical vapor deposition technique used to deposit thin films of organic materials. The MAPLE process involves the laser desorption of a frozen dilute solution (1-5%) containing the material to be deposited. A focused laser pulse (~200 mJ/cm2) impacts the frozen target, which causes the solvent to preferentially absorb the laser energy and evaporate. The collective action of the evaporated solvent desorbs the polymeric solute material towards the receiving substrate placed parallel and opposite to the target. The bioresorbable polymer PDLLA and the anti-inflammatory pharmaceutical dexamethasone were processed using MAPLE, and characterized using Fourier transform infrared spectroscopy, atomic force microscopy and x-ray photoelectron spectroscopy. MDW is a CAD/CAM controlled direct writing process. The material to be transferred is immersed in a laser-absorbing matrix or solution and coated onto a target or support positioned microns to millimeters away from a receiving substrate. Using a UV microscope objective, a focused laser pulse is directed at the backside of the ribbon, so that the laser energy first interacts with the matrix at the ribbon/matrix interface. This energy is used to gently desorb the depositing material and matrix onto the receiving substrate. I have deposited neuroblasts within a three-dimensional extracellular matrix. These two laser processing techniques have enormous potential for functional medical device and tissue engineering applications.