High-power diode lasers (HPDL) are being increasingly used in industrial applications. Deposition of nickel from nickel carbonyl (Ni(CO)4) precursor by laser-induced chemical vapor deposition (CVD) was studied with emphasis on achieving high deposition rates. An HPDL system was used to provide a novel energy source facilitating a simple and compact design of the energy delivery system. Nickel deposits on complex, 3-dimensional polyurethane foam substrates were prepared and characterized. The resulting “nickel foam” represents a novel material of high porosity (>95% by volume) finding uses, among others, in the production of rechargeable battery and fuel cell electrodes and as a specialty high-temperature filtration medium. Deposition rates up to ~19 µm/min were achieved by optimizing the gas precursor flow pattern and energy delivery to the substrate surface using a 480W diode laser. Factors affecting the transition from purely heterogeneous decomposition to a combined hetero- and homogeneous decomposition of nickel carbonyl were studied. High quality, uniform 3-D deposits produced at a rate more than ten times higher than in commercial processes were obtained by careful balance of mass transport (gas flow) and energy delivery (laser power). Cross-flow of the gases through the porous substrate was found to be essential in facilitating mass transport and for obtaining uniform deposits at high rates. When controlling the process in a transient regime (near the onset of homogenous decomposition), unique morphology features formed as part of the deposits, including textured surface with pyramid-shape crystallites, spherical and non-spherical particles and filaments. Operating the laser in a pulsed mode produced smooth, nano-crystalline deposits with sub-100 nm grains. The effect of H2S, a commonly used additive in nickel carbonyl CVD, was studied using both polyurethane and nickel foam substrates. H2S was shown to improve the substrate coverage and deposit uniformity in tests with polyurethane substrate, however, it was found to have no effect in improving the overall deposition rate compared to H2S-free deposition process. Deposition on other selected substrates, such as ultra-fine polymer foam, carbon nanofoam and multi-wall carbon nanotubes, was demonstrated. The HPDL system shows good promise for large-scale industrial application as the cost of HPDL energy continues to decrease.

High-power diode lasers (HPDL) are being increasingly used in industrial applications. Deposition of nickel from nickel carbonyl (Ni(CO)4) precursor by laser-induced chemical vapor deposition (CVD) was studied with emphasis on achieving high deposition rates. An HPDL system was used to provide a novel energy source facilitating a simple and compact design of the energy delivery system. Nickel deposits on complex, 3-dimensional polyurethane foam substrates were prepared and characterized. The resulting “nickel foam” represents a novel material of high porosity (>95% by volume) finding uses, among others, in the production of rechargeable battery and fuel cell electrodes and as a specialty high-temperature filtration medium. Deposition rates up to ~19 µm/min were achieved by optimizing the gas precursor flow pattern and energy delivery to the substrate surface using a 480W diode laser. Factors affecting the transition from purely heterogeneous decomposition to a combined hetero- and homogeneous decomposition of nickel carbonyl were studied. High quality, uniform 3-D deposits produced at a rate more than ten times higher than in commercial processes were obtained by careful balance of mass transport (gas flow) and energy delivery (laser power). Cross-flow of the gases through the porous substrate was found to be essential in facilitating mass transport and for obtaining uniform deposits at high rates. When controlling the process in a transient regime (near the onset of homogenous decomposition), unique morphology features formed as part of the deposits, including textured surface with pyramid-shape crystallites, spherical and non-spherical particles and filaments. Operating the laser in a pulsed mode produced smooth, nano-crystalline deposits with sub-100 nm grains. The effect of H2S, a commonly used additive in nickel carbonyl CVD, was studied using both polyurethane and nickel foam substrates. H2S was shown to improve the substrate coverage and deposit uniformity in tests with polyurethane substrate, however, it was found to have no effect in improving the overall deposition rate compared to H2S-free deposition process. Deposition on other selected substrates, such as ultra-fine polymer foam, carbon nanofoam and multi-wall carbon nanotubes, was demonstrated. The HPDL system shows good promise for large-scale industrial application as the cost of HPDL energy continues to decrease.

Piezoelectric actuators (PEA) hold the most promise for precision positioning applications due to their capability of producing extremely small displacements down to 10 pm (1 pm = 10-12 m) as well as their high stiffness and force output. The piezoelectric-driven stick-slip (PDSS) actuator, working on the friction-inertia concept, has the capacity of accomplishing an unlimited range of motion. It also holds the promises of simple configuration and low cost. On the other hand, the PDSS actuator has a relatively low efficiency and low loading capability, which greatly limits its applications. The purpose of this research is to improve the performance of the PDSS actuators by employing specially-designed working surfaces.<p> The working surfaces, referred as anisotropic friction (AF) surfaces in this study, can provide different friction forces depending on the direction of relative motion of the two surfaces, and are used in this research to accomplish the aforementioned purpose. To fabricate such surfaces, two nanostructure technologies are employed: hot filament chemical vapour deposition (HFCVD) and ion beam etching (IBE). The HFCVD is used to deposit diamond on silicon substrates; and the IBE is used to etch the diamond crystalloid with a certain angle with respect to the coating surface to obtain an unsymmetrical-triangle microstructure. <p> A PDSS actuator prototype containing the AF surfaces was developed in this study to verify the function of the AF surfaces and characterize the performance of PDSS actuators. The designed surfaces were mounted on the prototype; and the improvement in performance was characterized by conducting a set of experiments with both the normal isotropic friction (IF) surfaces and the AF surfaces, respectively. The results illustrate that the PDSS actuator with the AF surface has a higher efficiency and improved loading capability compared to the one with the IF surfaces.<p> A model was also developed to represent the displacement of the novel PDSS actuator. The dynamics of the PEA and the platform were approximated by using a second order dynamic system. The pre-sliding friction behaviour involved was investigated by modifying the LuGre friction model, in which six parameters (Note that three parameters are used in the LuGre model) were employed to represent the anisotropic friction. By combining the PEA mechanism model, the modified friction model, and the dynamics of end-effector, a model for the PDSS actuator with the AF surface was developed. The model with the identified parameters was simulated in MATLAB Simulink and the simulation results obtained were compared to the experimental results to verify the model. The comparison suggests that the model developed in this study is promising to represent the displacement of the novel PDSS actuators with AF surfaces.

Chemical vapor deposition (CVD) has been the main method for synthesizing diamond thin films on hetero substrate materials since 1980s. It has been well acknowledged that both nucleation and growth of diamond on non-diamond surfaces without pre-treatment are very difficult and slow. Furthermore, the weak adhesion between the diamond thin films and substrates has been a major problem for widespread application of diamond thin films. Up to now, Si has been the most frequently used substrate for the study of diamond thin films and various methods, including bias and diamond powder scratching, have been applied to enhance diamond nucleation density. In the present study, nucleation and growth of diamond thin films on Ti3SiC2, a newly developed ceramic-metallic material, using Microwave Plasma Enhanced (MPE) and Hot-Filament (HF) CVD reactors were carried out. In addition, synchrotron-based Near Edge Extended X-Ray Absorption Fine Structure Spectroscopy (NEXAFS) was used to identify the electronic and chemical structures of various NCD films. The results from MPECVD showed that a much higher diamond nucleation density and a much higher film growth rate can be obtained on Ti3SiC2 compared with on Si. Consequently, nanocrystalline diamond (NCD) thin films were feasibly synthesized on Ti3SiC2 under the typical conditions for microcrystalline diamond film synthesis. Furthermore, the diamond films on Ti3SiC2 exhibited better adhesion than on Si. The early stage growth of diamond thin films on Ti3SiC2 by HFCVD indicated that a nanowhisker-like diamond-graphite composite layer, different from diamond nucleation on Si, initially formed on the surface of Ti3SiC2, which resulted in high diamond nucleation density. These results indicate that Ti3SiC2 has great potentials to be used both as substrates and interlayers on metals for diamond thin film deposition and application. This research may greatly expand the tribological application of both Ti3SiC2 and diamond thin films. The results demonstrated that NEXAFS is a reliable and powerful tool to identify NCD films.

<p>Controlling the properties of single walled carbon nanotubes (SWNTs) is the major challenge toward their future applications. This dissertation describes several contributions to this chanllenge. </p><p>This dissertation begins with the brief review on carbon nanotubes (CNTs), including discovery, structure, properties, challenges, synthesis and applications. The remaining parts can be divided into three sections. They demonstrate the control of SWNT properties as well as their devices by direct synthesis and metal decoration. </p><p>Two studies are described on the control of SWNT properties by direct synthesis. The first demonstrates the controlled synthesis of SWNTs in terms of their diameter, uniformity, and density by the chemical vapor deposition (CVD) method. The approaches employed include using uniform nanoparticles with specific sizes as catalysts to grow different diameter SWNTs, specially small diameter tubes less than 1 nm; using laser irradiation to grow uniform and high quality SWNTs; and changing the gas flow pattern to obtain different density. The second study demonstrates the growth of aligned SWNTs by flow and substrate guidance. Horizontally aligned ultralong nanotubes are synthesized on Si substrate by both high flow and low flow. The guided growth by the quartz substrate is shown by a large variety of metal catalysts to further the understanding of the growth mechanism. Moreover, top gated FETs have been explored for the selective growth of purely semiconducting, horizontally aligned SWNTs grown on quartz by a ethanol/methanol mixture. </p><p>The control of SWNT device performance is also described, in particular, the correlation between the SWNT field effect transistor (FET) configuration and its gate dependence response. The effects of FET channel length, nanotube density and diameter on the device performance are demonstrated. A model has been constructed in order to simulate the electronic behavior. An interesting metallic behavior has been observed. </p><p>Finally, control of SWNT properties by Palladium decoration after growth is used to manipulate their properties. Moreover, two novel applications including improvement of carbon nanotube film conductivity and catalysis of nanostructure growth are developed.</p> / Dissertation

The primary goal of this research was to develop the laser chemical vapor deposition (LCVD) process to be able to directly deposit carbon nanotubes onto substrates selectively. LCVD has traditionally been used to directly deposit complex geometries of other materials, including many metals and ceramics. Carbon nanotube deposits were formed using codeposition and other techniques. Multiwall carbon nanotubes as small as 7 nm were synthesized. Utilizing electron microscopy, deposits were characterized to determine the effects of laser power, catalyst and hydrocarbon concentration, time, pressure, and other variables on the number of nanotubes formed, their size, and their spatial location. The most important variables were shown to be hydrocarbon and catalyst concentration and laser power. These results were analyzed and statistics based models were developed to express these trends. Additionally, the process was also used successfully to deposit linear patterns of carbon nanotubes. Carbon nanotube deposits were also carried out in the presence of an electric field. It was demonstrated that a field of sufficient strength could be used to orient tube growth. LCVD is a thermally driven process and a thermal feedback and control system is typically employed to allow for real time control of the reaction zone temperatures. The current thermal imaging system installed on the LCVD reactor is limited to operation at temperatures above which nanotube deposition occurs. A heat and mass transport model was therefore developed to simulate deposition temperatures and provide an estimate of the desired laser power needed to achieve a desired reaction temperature. This model included all significant modes of heat transport including conduction, natural convection and radiation. Temperature dependant material properties were also employed to help achieve greater accuracy. Additionally, the model was designed to be able to simulate a scanning laser beam which was used to deposit linear patterns of carbon nanotubes. Modeling calculations of laser heating compared favorably with experimental data. The results of this work show that LCVD has potential for use in the commercial market for selective direct deposition of patterns of aligned carbon nanotubes on multiple substrate materials.

Electron Beam Chemical Vapor Deposition (EBCVD) is a process by which an electron beam is used to decompose adsorbed reagent molecules to produce a deposit. The primary electrons from the beam, and especially the secondary electrons emitted from the substrate, dissociate the adsorbed molecules. Important factors for the deposition process include the beam parameters and reagent gas composition. Simple structures are fabricated through utilization of the various scanning modes of an SEM. Fibers (pillar-like structures) can be deposited, and lines (wall-like structures) can be deposited easily. This investigation focuses on the process parameters controlling deposition rate and geometry for platinum and carbon fibers and lines in a modified SEM. Platinum deposition was performed using a system with a small diameter needle that supplied a localized flow of gas from an organometallic platinum compound. Carbon deposition was performed in the Environmental mode, in which the microscope chamber is filled with a specified pressure of reagent gas. Statistically designed experiments were performed for platinum fiber and line deposition. Analysis indicated that the beam current and deposition time were dominant factors in determining the deposition rate. The voltage also had a significant effect on fiber deposition. For platinum line deposition, the effects of the dwell time and line time were also studied. The line time had a significant effect on line height deposited per scan. Optimization analysis was performed, and results indicated that high voltage and high beam current led to higher aspect ratios. Medium voltage and low beam current were preferable for depositing minimal width lines (less than 200 nm). Low voltage and high beam current were preferable for maximum deposition rates. EDS and EELS performed for platinum deposits in a TEM indicated amorphous structure with no carbon detected. This differs significantly from previously reported results. Statistically designed experiments were performed for carbon line deposition. The voltage, beam current, and dwell/line time were studied. Increasing line time led to a significant increase in line height/scan and appeared to be a dominant factor. Lower beam currents appeared to favor higher deposition rates. TEM analysis indicated that carbon deposits were mostly amorphous.

The goal of this research is to investigate how to deposit SiC material from methyltrichlorosilane (MTS) and H2 using the LCVD technique. Two geometries were targeted, fiber and line. In order to eliminate the volcano effect for LCVD-SiC deposition, a thermodynamics model was developed to check the feasibility and determine the deposition temperature ranges that will not cause the volcano effect, theoretically. With the aid of the thermodynamic calculations and further experimental explorations, the processing conditions for SiC fibers and lines without volcano effect were determined. The experimental relationships between the volcano effect and the deposition temperatures were achieved. As for the SiC lines, the deposition conditions for eliminating volcano effect were determined with the help of surface response experiment and the experience of SiC fiber depositions. The LCVD process of SiC deposition was characterized by performing a kinetic study of SiC deposition. The deposits were characterized by the means of polishing, chemical etching, and SEM technique. A coupled thermal and structural model was created to calculate the thermal residual stress present in the deposits during the deposition process and during the cooling process. Laser heating of LCVD system was studied by developing another model. The transient temperature distribution within the fiber and substrate was obtained. The theoretical relationships between the laser power and the fiber heights for maintaining constant deposition temperatures were achieved.

This thesis is devoted to the fabrication of carbon nanotube structures for microelectronics packaging applications with an emphasis on fundamental studies of nanotube growth and assembly, wetting of nanotube structures, and nanotube-based composites. A CVD process is developed that allows controlled growth of a variety of CNT structures, such as CNT films, bundles, and stacks. Use of an Al2O3 support enhances the Fe catalyst activity by increasing the CNT growth rate by nearly two orders of magnitude under the same growth conditions. By introducing a trace amount of weak oxidants into the CVD chamber during CNT growth, aligned CNT ends can be opened and/or functionalized, depending on the selection of oxidants. By varying the growth temperature, CNT growth can be performed in a gas diffusion- or kinetics-controlled regime. To overcome the challenges that impede implementation of CNTs in circuitry, a CNT transfer process was proposed to assemble aligned CNT structures (films, stacks &bundles) at low temperature which ensures compatibility with current microelectronics fabrication sequences and technology. Field emission and electrical testing of the as-assembled CNT devices indicate good electrical contact between CNTs and solder and a very low contact resistance across CNT/solder interfaces. For attachment of CNTs and other applications (e.g. composites), wetting of nanotube structures was studied. Two model surfaces with two-tier scale roughness were fabricated by controlled growth of CNT arrays followed by coating with fluorocarbon layers formed by plasma polymerization to study roughness geometric effects on superhydrophobicity. Due to the hydrophobicity of nanotube structures, electrowetting was investigated to reduce the hydrophobicity of aligned CNTs by controllably reducing the interfacial tension between carbon nanotubes (CNTs) and liquids. Electrowetting can greatly reduce the contact angle of liquids on the surfaces of aligned CNT films. However, contact angle saturation still occurs. Variable frequency microwave (VFM) radiation can greatly improve the CNT/epoxy interfacial bonding strength. Compared to composites cured by thermal heating, VFM-cured composites demonstrate higher CNT/matrix interfacial bonding strength, which is reflected in composite negative thermal expansion. The improved CNT/epoxy interface enhances the thermal conductivity of the composites by 26-30%.

In this paper, polar free-standing (0002)GaN wafer were fabricated by using the hydride vapor phase epitaxy(HVPE) technique on (002) LiGaO2 substrates. Polar of The (0002) GaN affects its luminous efficiency, but compared to other surface between the substrate, it has the smallest lattice mismatch. With the high growth rate of HVPE, hoping to grow high quality GaN thick layer. In the self-designed reactor, Metallic gallium and NH3 were the source of Ga and N. Nitrogen and hydrogen were used as the carrier gases HCl and nitrogen was designed to pass through liquid Ga to form GaCl fully. GaN deposition was realized Efficaciously by conducted steady NH3 and GaCl flows to the substrate suface, accommodated with additional hydrogen and nitrogen atmosphere flows.The parameters set of research mainly focus on reaction pressure, temperature, and growth time. In order to obtain better crystal quality, more attempts were made to grow buffer layer by chemical vapor deposition first, then a thick GaN layer by HVPE. The next step is to do the experiment and analyze with various instruments. Scanning Electron Microscope and atomic force microscopy Atomic Force Microscpoic are used to observe the surface morphology. X-ray Diffracion and transmission electron microscopy are used to know the lattice structure, and to understand the interface between the substrate and the GaN film crystal structure and epitaxial relationship. Finally, Photoluminescence spectroscopy is used to measure its optical properties and compare its defects and epitaxial quality.