<p> Resonators are a major component in RF electronic products. They are used in a host of ways to filter radio signals. Modern and Future RF communications have placed high demands on the industry; requiring low power usage, wide array of applications and resistance to noise. </p><p> In this thesis, a discussion of the motivation for RF MEMS filters and basic theory is given with an explanation of the concepts of Q factor, piezoelectricity, acoustics theory, the major types of resonators (SAW, BAW, CMR or LAMB), apodization theory and techniques as well as design, simulation of CMR and BAW devices, testing and process development of aluminum nitride by RF reactive sputtering at RIT. </p><p> Finite element analysis was performed on a number of factors of aluminum nitride contour mode resonators (CMR) from piezoelectric film thickness, to electrode pitch, electrode thickness and electrode configuration; to understand the effects. First order and second order vibration modes were seen including symmetric <i>S</i>₀, <i>S</i>₁ and antisymmetric <i>A</i>₀, <i>A</i>₁ resonant modes in the pizeoacoustic devices and higher. A series of time dependent video simulations of SAW, BAW and LAMB wave resonators were also performed, perhaps the first of their kind. </p><p> The RF reactive sputtering deposition for aluminum nitride was developed at RIT by a fractional factorial experiment with the factors being RF power, nitrogen to argon flow rate ratios, changing the distance of the wafer to the platen from 5 to 4 cm, use of a aluminum, molybdenum or virgin silicon seed layer and chamber pressure. In nearly all cases it was found that an RF power of 1000W is the most important factor contributing to the &lang;002&rang; orientation. The decreasing of the target distance may inhibit a reaction mechanisms in the plasma resulting in a more amorphous deposition. It may be due to the increase in temperature resulting from the higher RF power that promotes the growth of &lang;002&rang; oriented aluminum nitride. A molybdenum seed layer tends to have a stronger &lang;002&rang; peak relative to aluminum and a chamber pressure of 3mT was found to exhibit a deposition that most favors the &lang;002&rang; oriented aluminum nitride. </p><p> It was found that molybdenum is not consumed in a wet etch of KOH. Molybdenum is oxidized during photo resist ashing. The Contact Vias were necessarily over retched in order to ensure complete removal of Al-N over the Bottom Electrode. </p><p> C-V measurements were done on the aluminum nitride to determine its quality, the measured extensional piezoelectric coefficient <i>d</i>₃₃ is -0.000108716 <i>nm/V</i>, which is -0.108716 <i> pm/V</i> lower than 8pm/V typically reported. The lower piezo electric coefficient measured as compared with typical values, may be due to low film density a result of the high power used in the RF reactive sputtering that was used to heat the platen to a high enough temperature to promote the?002?oriented growth of AlN. </p><p> A series of iterations were designed and S11 frequency response measured. The electrode overlap from 25 to 50 to 75&mu;m, it does not appear to have an effect on the resonant frequency, but does increase the amplitude of the response at that die's given frequency. Increasing the anchor width from 5&mu;m to 10&mu;m to 20&mu;m lowers the relative amplitude of the response therefore lowering the Q of the resonator. It may be that the increasingly wide anchor, increases the mechanical resistances within the device and thereby lowers the Q factor of the resonator. Increasing the number of electrodes increases the relative amplitude of the response. Increasing pitch from 5&mu;m to 6&mu;m seems to have a small effect on the resonant frequency of the devices, shifting them from 4.57 to 4.59 GHz. A quality factor was measured, with an anchor width of 5&mu;m, pitch of 5&mu;m, 24 electrodes and an electrode overlap of 75&mu;m had a measured Q value of 98.8.</p>

<p> The objective of this research effort focused on the evaluation of asphalt mixtures with respect to thermal cracking. Preliminary investigations soon indicated that a fundamental evaluation of thermal cracking was highly dependent upon the more complicated understanding of asphalt binder oxidation. The oxidation of asphalt binders within an asphalt mixture were understood to potentially be influenced by the mixture characteristics (i.e. air void levels, binder content, etc.) and aggregate properties (i.e. aggregate absorption, gradation, etc.). Therefore, this study was conducted in order to investigate and quantify the effects different aggregate sources and mixture properties may have on the oxidation and thermal cracking performance of asphalt mixtures. </p><p> The investigation specifically focused on quantifying the oxidation of the asphalt binder alone and as part of the asphalt mixture when subjected to isothermal oven aging. The oxidation parameters of pan-aged asphalt binders were quantified, according to the standard of practice in the industry. These parameters were then compared to extracted and recovered mixture-aged asphalt binders to examine the influence of the main aggregate and mixture factors on the binder oxidation. The study observed differences between the pan-aged and mixture-aged asphalt binders in terms of oxidation kinetics, rheological measures, and the combined effect represented as the hardening susceptibility. </p><p> Further evaluation of the binder oxidation based upon the dynamic modulus measures indicated marked influences of the mixture characteristics, the individual component materials, and the interactions between the investigated factors. </p><p> Differentiation of the experimental factors was further identified by the newly developed low-temperature evaluation method, Uniaxial Thermal Stress and Strain Test (UTSST). The UTSST provides a fundamental approach to characterize the thermo-viscoelastic properties of asphalt mixtures permitting the pragmatic evaluation of changes in the stiffness and overall behavior of mixtures as a function of oxidative aging. Five distinct stages in the UTSST modulus were identified as thermo-viscoelastic properties, which are identified as a function of temperature: viscous softening, viscous-glassy transition, glassy hardening, crack initiation, and fracture stages. </p><p> Through consideration of the thermo-viscoelastic properties, marked differences in the binder oxidation were noted between the experimental factors. Typically, decreases in the viscous response of the mixtures as well as increases in both the stiffness and brittle behavior were observed with aging. The evaluation method provides definitive measures to monitor multiple aspects of the performance of asphalt mixtures subjected to thermal loading.</p>

<p> Solid lubrication of space-borne mechanical components is essential to their survival and the continued human exploration of space. Recent discoveries have shown that PTFE when blended with alumina nanofillers exhibits greatly improved physical performance properties, with wear rates being reduced by several orders of magnitude. The bulk processes used to produce the PTFE-alumina blends are limiting. Co-sputter deposition of PTFE and a filler material overcomes several of these limitations by enabling the reduction of particle size to the atomic level and also by allowing for the even coating of the solid lubricant on relatively large areas and components. The goal of this study was to establish a baseline performance of the sputtered PTFE films as compared to the bulk material, and to establish deposition conditions that would result in the most bulk-like film possible. In order to coax change in the structure of the sputtered films, sputtering power and deposition temperature were increased independently. Further, post-deposition annealing was applied to half of the deposited film in an attempt to affect change in the film structure. Complications in the characterization process due to increasing film thickness were also examined. Bulk-like metrics for characterization processes the included Fourier transform infrared spectroscopy (FTIR), X-ray spectroscopy (XPS), nanoindentation via atomic force microscopy, and contact angle of water on surface measurements were established. The results of the study revealed that increasing sputtering power and deposition temperature resulted in an increase in the similarity between the fluorocarbon films and the bulk PTFE, at a cost of affecting the potential of the film thicknesses, either by affecting the deposition process directly, or by decreasing the longevity of the sputtering targets.</p>

<p> Bi₂Sr₂CaCu₂Ox (Bi2212) superconducting round wires are a well-known high temperature superconductor due to their isotropic properties, high fill factor, and ease of winding. There have been extensive experiments to improve the wires&rsquo; performance, yet there is little understanding of how the internal microstructure of the wires influences the mechanical behavior. This is due to the multiple phases and their complex arrangements inside the wires, making it challenging for traditional approaches to investigate and simulate the wires&rsquo; behavior. The peridynamic theory, using non-local interactions and integral constitutive equations, can provide a solution to these challenges from the Bi2212 wires microstructure. To reduce computation cost, in this study the peridynamic formulas are developed for 2D simulations. Dynamic relaxation and energy minimization methods to find the steady-state solution are used and compared. The model shows m-convergence and &delta;-convergence behaviors when m increases and &auml; decreases. Model verification shows close quantitative matching to finite element analysis results. The 2D peridynamic model is then used to simulate mechanical behavior of Bi2212 wires. Various types of natural and artificial defects are simulated and compared quantitatively. Both defect geometry and physical characteristics are investigated to study their influence on the stress concentration in the material. The results show significant stress concentration around defects and protruding growths of the Bi2212 phase.</p>

<p> Polymeric membrane based separation technologies are crucial for addressing the global issues such as water purification. However, continuous operations of these processes are often hindered by fouling which increases mass transport resistance of the membrane to permeation and thus the energy cost, and eventually replacement of the membrane in the system. In comparison to other anti-fouling strategies, the use of controlled surface topography to mitigate fouling has not been realized mainly due to the lack of methods to create targeted topography on the porous membrane surface. </p><p> This thesis aims to develop a new methodology to create surface-patterned polymeric separation membrane to improve their anti-fouling characteristics during filtration. First, successful fabrication of sub-micron surface patterns directly on a commercial ultrafiltration (UF) membrane surface using nanoimprint lithographic (NIL) technique was demonstrated. Comprehensive filtration studies revealed that the presence of these sub-micron surface patterns mitigates not only the onset of colloidal particle deposition, but also lowers the rate of growth of cake layer after initial deposition, in comparison with un-patterned membranes. The anti-fouling effects were also observed for model protein solutions. Staged filtration experiments, with backwash cleaning, revealed that the permeate flux of the patterned membrane after protein fouling was considerably higher than that of the pristine or un-patterned membrane. </p><p> In addition to the surface-patterning of UF membranes, successful fabrication of a surface-patterned thin film composite (TFC) membrane was shown for the first time. A two-step fabrication process was carried out by (1) nanoimprinting a polyethersulfone (PES) support using NIL, and (2) forming a thin dense film atop the PES support via interfacial polymerization (IP). Fouling experiments suggest that the surface patterns alter the hydrodynamics at the membrane-feed interface, which is effective in decreasing fouling in dead end filtration system. </p><p> In summary, this thesis represents the first ever fabrication of functional patterned polymeric separation membrane and systematic investigation of the influence of submicron surface patterns on pressure-driven liquid membrane separations. The results presented here will enable an effective non-chemical surface modification anti-fouling strategy, which can be directly added onto current commercial separation membrane manufacturing route.</p>

<p> Given a rapidly developing world, the need exists for inexpensive renewable energy alternatives to help avoid drastic climate change. Photovoltaics have the potential to fill the energy needs of the future, but significant cost decreases are necessary for widespread adoption. Semiconductor nanocrystals, also known as quantum dots, are a nascent technology with long term potential to enable inexpensive and high efficiency photovoltaics. When deposited as a film, quantum dots form unique nanocomposites whose electronic and optical properties can be broadly tuned through manipulation of their individual constituents. </p><p> The contents of this thesis explore methods to understand and optimize the optoelectronic properties of PbSe quantum dot films for use in photovoltaic applications. Systematic optimization of photovoltaic performance is demonstrated as a function of nanocrystal size, establishing the potential for utilizing extreme quantum confinement to improve device energetics and alignment. Detailed investigations of the mechanisms of electrical transport are performed, revealing that electronic coupling in quantum dot films is significantly less than often assumed based on optical shifts. A method is proposed to employ extended regions of built-in electrical field, through controlled doping, to sidestep issues of poor transport. To this end, treatments with chemical redox agents are found to effect profound and reversible doping within nanocrystal films, sufficient to enable their use as chemical sensors, but lacking the precision required for optoelectronic applications. Finally, a novel doping method employing "redox buffers" is presented to enact precise, stable, and reversible charge-transfer doping in porous semiconductor films. An example of oxidatively doping PbSe quantum dot thin films is presented, and the future potential for redox buffers in photovoltaic applications is examined.</p>

<p>Continuous-fiber ceramic matrix composites (CMCs) are of interest as hot-section components in gas turbine engines due to their refractoriness and low density relative to metallic alloys. In service, CMCs will be subjected to spatially inhomogeneous temperature and stress fields. Robust tools that enable prediction of deformation and fracture under these conditions are therefore required for component design and analysis. Such tools are presently lacking. The present work helps to address this deficiency by developing models for CMC mechanical behavior at two length scales: that of the constituents and that of the components. Problems of interest are further divided into two categories: &lsquo;1-D loadings,&rsquo; in which the stresses are aligned with the fiber axes, and &lsquo;2-D loadings,&rsquo; in which the stress state is more general. </p><p> For the former class of problems, the major outstanding issue is material fracture, not deformation. A fracture criterion based on the attainment of a global load maximum is developed, which yields results for pure bending of CMCs in reasonable agreement with available experimental data. For the latter class of problems, the understanding of both the micro-scale and macro-scale behavior is relatively immature. An approach based upon analysis of a unit cell (a single fiber surrounded by a matrix jacket) is pursued. Stress fields in the constituents of the composite are estimated using analytical models, the accuracy of which is confirmed using finite element analysis. As part of a fracture mechanics analysis, these fields enable estimation of the steady-state matrix cracking stress for arbitrary in-plane loading of a unidirectional ply. While insightful at the micro-scale, unit cell models are difficult to extend to coarser scales. Instead, material deformation is typically predicted using phenomenological constitutive models. One such model for CMC laminates is investigated and found to predict material instability where none should exist. Remedies to the model to correct this deficiency are proposed; the remediated model is subsequently utilized in conjunction with an analytical model to probe stress fields adjacent to holes and notches in CMC panels. However, even the revised model is incapable of capturing the range of experimental behavior reported for CMCs with both stiff and compliant matrices. To ameliorate this deficiency, a new elastic-plastic constitutive model is developed. It extends the deformation theory of plasticity from metals to CMCs, and its predictions of near-notch strain fields in an open-hole tension test compare favorably to strains measured using digital image correlation. Based on these developments, future experimental and modeling work is proposed. With respect to the latter, cohesive interface simulations seem particularly suited for capturing multiple interacting damage mechanisms at multiple length scales in a physically sensible manner. In principle, they can function as virtual tests, guiding both engineering design and materials development. </p>

By means of torsion testing, the microstructures and mechanical properties produced in a 0.14%C-1.18%Mn steel were investigated over a wide range of hot rolling conditions, cooling rates and coiling temperatures. The reheating temperature was varied between 800$ sp circ$C and 1050$ sp circ$C, and strains between 0 and 0.8 were applied. This led to austenite grain sizes ranging from 10 to 150$ mu$m. Two cooling rates, 55$ sp circ$C/s and 90$ sp circ$C/s, were applied and cooling was interrupted at coiling temperatures ranging from 550$ sp circ$C to 300$ sp circ$C. / Optical microscopy and TEM were used to study the microstructures. The mechanical properties were studied by means of tensile testing. A method developed by IRSID for deducing the transformation kinetics from the cooling data was adapted to the present context and used successfully to interpret the observed influence of the process parameters. (Abstract shortened by UMI.)

Low hot ductility at the straightening stage of the steel continuous casting process, where the surface temperature ranges from 600 to 1200°C, is associated with transverse cracking on the billet surface. This is attributed to various microalloying elements, which are essential for the mechanical characteristics of the final products. Thermomechanical processing is a new approach to alleviate this problem. In this work, two grades of Nb-containing steel, one modified with B, were examined. In order to simulate the key parameters of continuous casting, specimens were melted in situ and subjected to thermal conditions similar to that occurring in a continuous casting mill. They were also deformed at different stages of the thermal schedule. Finally, the hot ductility was evaluated at the end of the thermal schedule, corresponding to the straightening stage in continuous casting at which the hot ductility problem occurs in the continuous casting process. / The results showed that the presence of B is noticeably beneficial to the hot ductility. Failure mode analysis was performed and the mechanism of fracture was elaborated. As well, the potential mechanisms under which B can improve the hot ductility were proposed. / Deformation during solidification (i.e. in the liquid + solid two phase region) led to a significant loss of hot ductility in both steels. By contrast, deformation in the delta-ferrite region, after solidification, was either detrimental or beneficial depending on the deformation start temperature. / The hot ductility was considerably improved in the steel without B when deformation was applied during the delta → gamma transformation. The effect of such deformation on the other steel grade was not significant. Examination of the microstructure revealed that such improvement is related to a grain refinement in austenite. Therefore, the effect of deformation parameters was studied in detail and the optimum condition leading to the greatest improvement in the hot ductility was determined. / Finally, some solutions to the industrial problem in the continuous casting process were proposed.

Damping of steel beams with constrained viscoelastic layers is studied in both the frequency and time domains. Cantilevered steel beam specimens with various configurations of constrained viscoelastic layers are experimentally and analytical subjected to random frequency vibrations, spike inputs, and large finite rotations A frequency dependent shear modulus is used to express the viscoelastic material behavior in the frequency domain, and a Prony series representation of the shear relaxation modulus is used for time domain simulations. The simulated response converges using approximately five Prony terms in the series. Increase in damping from one to two layers of constrained viscoelastic treatment and the detrimental effect of a discontinuous constrained viscoelastic treatment is observed experimentally. Predicted responses obtained using the proposed finite element model exhibit similar trends. Natural frequencies and damping factors obtained from linear and nonlinear time domain finite element analyses are found to be in good agreement with experimental results.