Abstract A thin film deposition system using ultrasonic atomization is designed and constructed. Solution containing precursors is transported by carrying gas to the heated substrate where deposition is accomplished by pyrolysis. Tests including series of varying flow rate of carrying gas and varying substrate temperature were carried out with solutions of SnCl4 precursor in C2H5OH solvent and N2 as carrying gas. Also, TaCl5 was used as dopant to improved the electrical conductivity. The effects of doping in crystallinity, surface morphology, optical transmittance and electrical conductivity of the deposited thin films were examined and the optimal percentage of doping for electrical conductivity and optical transmittance was found. XRD reveals that the thin film was amorphous when the deposition temperature was below 350¢J. Polycrystalline thin films with grains size of 30~50nm were obtained with deposition temperature of 400~500¢J and N2 flow rate of 2.5 ~10 l/min. SEM examination reveals that porosity increases with increasing deposition temperature and N2 flow rate, which consequently reduces the electron mobility, as seen in Hall measurement. No discernible difference was observed between the morphology of the doped and undoped thin films. As shown in the UV-Visible spectra representative transmittance of all films at 550nm radiation ranges between 70% and 82%. No discernible effect was observed for Ta-doping. Hall measurement reveals that Ta-doping increases the electron mobility and carrier concentration by several times and one order of magnitude, respectively. The minimum resistivity is 1.2*10-1 £[- cm occurring at 4 at% Ta doping.

Nowadays, the need for three-dimensional miniaturized components is increasing in many areas, such as electronics, biomedics, aerospace and defence, etc. To support the demands, various micro-scale fabrication techniques have been further introduced and developed over the last decades, including micro-electric-mechanical technologies (MEMS and LIGA), laser ablation, and miniature machine tools (mMTs). Each of these techniques has its own benefits, however miniature machine tools are superior to any others in enabling three-dimensional complex geometry with high relative accuracy, and the capability of dealing with a wide range of mechanical materials. Thus, mMTs are emerging as a promising fabrication process. In this work, various researches have been carried out based on the mMTs. The thesis presents micro-machining, in particular, micro-milling force model and three relevant subsystems for miniature machine tools (mMTs), to enhance machining productivity/efficiency and dimensional accuracy of machined parts. The comprehensive force model that predicts micro-endmilling dynamics has been developed. Unlike conventional macro-machining, the cutting mechanism in micro-machining is complex with high level of non-linearity due to the combined effects of edge radius, size, and minimum chip thickness effect, etc., resulting in no chip formation when the chip thickness is below the minimum chip forming thickness. Instead, part of the work material deforms plastically under the edge of a tool and the rest of the material recovers elastically. The developed force model for micro-endmilling is effective to understand the micro-machining process. As a result, the micro-endmilling force model is helpful to improve the quality of machined parts. In addition, three relevant subsystems which deliver maximum machining productivity and efficiency are also introduced. Firstly, ultrasonic atomization-based cutting fluid application system is introduced. During machining, cutting fluid is required at the cutting zone for cooling and lubricating the cutting tool against the workpiece. Improper cutting fluid application leads to significantly increased tool wear, and which results in overall poor machined parts quality. For the micro-machining, conventional cooling methods using high pressure cutting fluid is not viable due to the potential damage and deflection of weak micro-cutting tools. The new atomization-based cutting fluids application technique has been proven to be quite effective in machinability due to its high level of cooling and lubricating. Secondly, an acoustic emission (AE)-based tool tip positioning method is introduced. Tool tip setting is one of the most important factors to be considered in the CNC machine tool. Since several tools with different geometries are employed during machining, overall dimensional accuracy of the machined parts are determined by accurate coordinates of each tool tip. In particular, tool setting is more important due to micro-scale involved in micro-machining. The newly developed system for tool tip positioning determines the accurate coordinates of the tool tip through simple and easy manipulation. At last, with the advance of the 3D micro-fabrication technologies, the machinable miniaturized components are getting complex in geometry, leading to increased demand on dimensional quality control. However, the system development for micro-scale parts is slow and difficult due to complicated detection devices, algorithm, and fabrication of a micro-probe. Consequently, the entire dimensional probing system tends to become bulky and expensive. A new AE-based probing system with a wire-based probe was developed to address this issue with reduced cost and size, and ease of application. / Graduate