Parallel-plate electrostatic actuators driven by a voltage difference between two electrodes suffer from an operation range limited to 30% of the gap that has significantly restrained their applications in Microelectromechanical systems (MEMS). In this thesis, the travel range of an electrostatic actuator made of a micro-cantilever beam electrode above a fixed electrode is extended quasi-statically to 90% of the capacitor gap by introducing a voltage regulator (controller) circuit designed for low frequency actuation. The developed large-stroke actuator is valuable contribution to applications in optical filters, optical modulators, digital micro-mirrors and micro-probe based memory disk drives. To implement the low-frequency large-stroke actuator, the beam tip velocity is measured by a vibrometer, the corresponding signal is integrated in the regulator circuit to obtain the displacement feedback, which is used to modify the input voltage of the actuator to reach a target location. The voltage regulator reduces the total voltage, and therefore the electrostatic force, once the beam approaches the fixed electrode so that the balance is maintained between the mechanical restoring force and the electrostatic force that enables the actuator to achieve the desired large stroke. A mathematical model is developed for the actuator based on the mode shapes of the cantilever beam using experimentally identified parameters that yields good accuracy in predicting both the open loop and the closed loop responses. The low-frequency actuator also yields superharmonic resonances that are observed here for the first time in electrostatic actuators. The actuator can also be configured either as a bi-stable actuator using a low-frequency controller or as a chaotic resonator using a high-frequency controller. The high-frequency controller yields large and bounded chaotic attractors for a wide range of excitation magnitudes and frequencies making it suitable for sensor applications. Bifurcation diagrams reveal periodic motions, softening behavior, period doubling cascades, one-well and two-well chaos, superharmonic resonances and a reverse period doubling cascade. To verify the observed chaotic oscillations, Lyapunov exponents are calculated and found to be positive. Furthermore, a chaotic resonator with a quadratic controller is designed that not only requires less voltage, but also produces more robust and larger motions. Another metric of chaos, information entropy, is used to verify the chaotic attractors in this case. It is found that the attractors have a common information entropy of 0.732 independent of the excitation amplitude and frequency.

This thesis develops methods to exploit static and dynamic instabilities in electrostatic MEMS to develop new MEMS devices, namely dynamically actuated micro switches and binary micro gas sensors. Models are developed for the devices under consideration where the structures are treated as elastic continua. The electrostatic force is treated as a nonlinear function of displacement derived under the assumption of parallel-plate theorem. The Galerkin method is used to discretize the distributed-parameter models, thus reducing the governing partial differential equations into sets of nonlinear ordinary-differential equations. The shooting method is used to numerically solve those equations to obtain the frequency-response curves of those devices and the Floquet theory is used to investigate their stability. To develop the dynamically actuated micro switches, we investigate the response of microswitches to a combination of DC and AC excitations. We find that dynamically actuated micro switches can realize significant energy savings, up to 60 %, over comparable switches traditionally actuated by pure DC voltage. We devise two dynamic actuation methods: a fixed-frequency method and a shifted-frequency method. While the fixed-frequency method is simpler to implement, the shifted-frequency method can minimize the switching time to the same order as that realized using traditional DC actuation. We also introduce a parameter identification technique to estimate the switch geometrical and material properties, namely thickness, modulus of elasticity, and residual stress. We also develop a new detection technique for micro mass sensors that does not require any readout electronics. We use this method to develop static and dynamic binary mass sensors. The sensors are composed of a cantilever beam connected to a rigid plate at its free end and electrostatically coupled to an electrode underneath it. Two versions of micro mass sensors are presented: static binary mass sensor and dynamic binary mass sensor. Sensitivity analysis shows that the sensitivity of our static mass sensor represents an upper bound for the sensitivity of comparable statically detected inertial mass sensors. It also shows that the dynamic binary mass sensors is three orders of magnitude more sensitive than the static binary mass sensor. We equip our mass sensor with a polymer detector, doped Polyaniline, to realize a formaldehyde vapor sensor and demonstrate its functionality experimentally. We find that while the static binary gas sensor is simpler to realize than the dynamic binary gas sensor, it is more susceptible to external disturbances.

Plasmonic nanoparticles support surface plasmon resonances that are sensitive to the environment. Factors contributing to the refractive index sensitivity are explored systematically through simulation, theory, and experiment. Particles small with respect to the wavelength of light and with size parameters much less than 1 have optical properties accurately predicted by quasi-electrostatic theory while particles with larger size parameters necessitate electrodynamics. A theory is developed that captures the effects of geometry on the refractive index sensitivity with a single factor, plasmon band location, and, although based on electrostatic theory, well predicts the sensitivity of particles whose properties are beyond the electrostatic limit. This theory is validated by high quality simulations for compact particles with shape parameters approaching 1 and, therefore, electrodynamic in nature, as well as higher aspect ratio particles that are electrostatic. Experimentally observed optical spectra for nanorods immobilized on glass and subjected to changes in n of the medium are used to calculate the sensitivity of the particles, found to be well matched by a variation on the homogeneous plasmon band theory. The separate electrostatic and electrodynamic components of plasmon band width, are explored and the overall width is found to affect the observability of the aforementioned sensitivity similarly within each particle class. The extent of the sensing volume around a spherical particle is explored and found to vary with particle size for small particles. Through simulation of oriented dielectric layers, it is shown particles are most sensitive to material located in regions of highest field enhancement. Variations on seed-mediated growth of gold nanorods results in spectra exhibiting a middle peak, intermediate to the generally accepted longitudinal and transverse modes. Simulated optical properties and calculated field enhancement illustrates the correlation between geometry and optical properties and allows for identification of the middle peak. / Dissertation

Computational methods are a convenient resource to solve drawbacks of drug research such as high cost, time-consumption, and high risk of failure. In order to get an optimum search of new drugs we need to design a rational approach to analyze the molecular forces that govern the interactions between the drugs and their target molecules. The objective of this project is to get an understanding of the interactions between drugs and proteins at the molecular level. The interaction energy, when protein and drugs react, has two components: non-covalent and covalent. The former accounts for the ionic interactions, the later accounts for electron transfer between the reactants. We study each energy component using the most popular analysis tools in computational chemistry such as docking scoring, molecular dynamics fluctuations, electron density change, molecular electrostatic potential (MEP), density of states projections, and the transmission function. We propose the probability of transfer of electrons (transmission function) between reactants in protein-drug complexes as an alternative tool for molecular recognition and as a direct correlator to the binding affinity. The quadratic correlation that exists between the electron transfer rate and the electronic coupling strength of the reactants allow a clear distinguishability between ligands. Thus, in order to analyze the binding affinity between the reactants, a calculation of the electronic coupling between them is more suitable than an overall energetic analysis such as free reaction energy.

For the past few decades, Ni-YSZ (yttria-stabilized zirconia) has been the dominate anode material of high temperature (>1000¢J) solid oxide fuel cells (SOFCs). However, the conductivity of Ni/YSZ is not enough when the operation temperature is in the intermediate rage of 500~700¢J. Instead, Ni/CGO is a good candidate as the anode material of intermediate temperature SOFCs (IT-SOFC), due to its enhanced conductivity. This work was aimed at the preparation of Ni/CGO composite anodes using the electrostatic assisted ultrasonic spray pyrolysis (EAUSP) method. By properly adjusting the deposition parameters, highly porous composite films with desired phases and microstructure rendering low electrode impedances were obtained. The results indicated that deposition temperature and the applied voltage dictated the evolution of film morphology and hence the interface impedance between the electrode and the electrolyte. Therefore, the optimum deposition parameters for the best microstructure and hence minimum interface impedance were 12 kV for the applied voltage, 6 : 4 for the Ni-CGO mole ratio, 450¢J for the deposition temperature. The microstructure thus obtained possessed a cauliflower-like structure with high porosity. The resultant interface impedance at 550¢J was 0.09 Ωcm2, lower than that obtained from the conventional anode preparation routes of dip-casting (0.14 Ωcm2) or mechanical mixing (0.12 Ωcm2).

A reflective type Fresnel lens using an array of micromirrors is designed and fabricated using the MUMPs?? surface micromachining process. The focal length of the lens can be rapidly changed by controlling both the rotation and translation of electrostatically actuated micromirrors. The suspension spring, pedestal and electrodes are located under the mirror to maximize the optical efficiency. The micromirror translation and rotation are plotted versus the applied voltage. Relations are provided for the fill-factor and the numerical aperture as functions of the lens diameter, the mirror size, and the tolerances specified by the MUMPs?? design rules. Linnik interferometry is used to measure the translation, rotation, and flatness of a fabricated micromirror. The reflective type Fresnel lens is controlled by independent DC voltages of 16 channels with a 0 to 50V range, and translational and torsional stiffness are calibrated with measured data. The spot diameter of the point source by the fabricated and electrostatically controlled reflective type Fresnel lens is measured to test focusing quality of the lens.

Interparticle interactions determine the microstructure, stability, rheology, and optical properties of concentrated colloidal suspensions involved in paint, paper, cosmetic, and pharmaceutical industries, etc. Frequency domain photon migration (FDPM) involves modeling the photon transport in a multiple scattering medium as a diffusion process in order to simultaneously determine isotropic scattering and absorption coefficients from measured amplitude attenuation and phase shift of the propagating photon density wave. Using FDPM, we investigated the impact of electrostatic interaction upon the optical properties and structure of dense charged suspensions. We demonstrated that electrostatic interactions among charged polystyrene latex may significantly affect the light scattering properties and structure of dense suspensions at low ionic strength (<0.06 mM NaCl equivalent) by actual FDPM measurement. We showed that the structure factor models addressing electrostatic interaction can be used to describe the microstructure of charged suspensions and quenched scattering due to electrostatics, and demonstrated that FDPM has the potential to be a novel structure and surface charge probe for dense suspensions. We also showed that the FDPM measured isotropic scattering coefficients may respond to the change in effective particle surface charge, and displayed the potential of using FDPM for probing particle surface charge in concentrated suspensions. We presented that the interference approximation implies a linear relationship between the absorption coefficient and volume fraction of suspension. We illustrated that FDPM measured absorption coefficient varies linearly with suspension volume fraction and affirmed the interference approximation from a perspective of light absorption. The validation of the interference approximation enables us to develop the methodology for estimating absorption efficiencies and imaginary refractive indices for both particles and suspending fluid simultaneously using FDPM. We further demonstrated a novel application of FDPM measured absorption coefficients in determining pigment absorption spectra, and displayed the potential of using FDPM as a novel analytical tool in pigment and paint industry.

Pyrolysis has been a useful procedure to treat waste-tire, which decomposes waste-tire at high temperature in the absence of oxygen. This thermal decomposition process generates pyrolysis oil, combustible gas, and char, which distribute in liquid phase, gas phase, and solid phase, respectively. Pyrolysis oil and combustible gas are fuels, while char is composed of carbon black and ash. Thus, char would be economically worth while to be treated before reuse. In this study, based on the resistivity difference between carbon black and ash, ash can be removed from char in the principle of electrostatic separation and thus increase the value of char. In this study, the objective was to separate ash from char by electrostatic separation process, different char including waste-tire pyrolytic char (raw char), low pressure re-pyrolytic char, ZnO-added char (12% ZnO mixed with 600 oC re-pyrolytic cahr) and man-made char (N600 carbon black mixed with 14.5% metallic oxide) were tested. The Electro-Static Separator (ESS) was designed and constructed with two types of discharge electrodes including a needle-plate electrode (NPE) and a needle-bar electrode (NBE) and two kinds of dust feeders to generate either fine or coarse particles. The results indicated that raw char had higher collection efficiency using the NBE system than the NPE system in the operating voltages of -7 kV to -15 kV because the surface area of the NBE system was less than the NPE system, thus led higher surface charge density for the NBE system than the NPE system, resulting in higher discharge current of the NBE system. In order to lower resistivity and reduce deposited pyrolysis oil on char, low pressure repyrolysis process was used. Because the removal efficiency of pyrolysis oil is proportional to repyrolysis temperature, more pyrolysis oil can be removed from the surface of char, resulting in more carbon blacks exposed on the char surface as conductive material. Thus, the collection efficiency of 600 oC repyrolytic char was less than that of 400 oC repyrolytic char. Furthermore, because particle charging quantity was proportional to particle size, fine char particles had less collection efficiency than coarse char particles. However, both raw char and repyrolytic char, the collection efficiency of carbon and ash had similar trends, suggesting that similar percentage of carbon and ash were collected on the plate and penetrated the ESS system. Therefore, the separation efficiency of carbon and ash were similar, same situation was observed for the ZnO-added char. In order to verify the feasibility of carbon and ash separation by electrostatic separation process, N660 carbon black mixing with 14.5% man-made ash (Al2O3, ZnO and CaO composed) to simulate man-made char, which was further used to proceed the electrostatic separation experiments in this study. The results indicated that the collection efficiency of man-made char increased with operating voltage, and the ash content seems to increase with voltage. Carbon black is a low resistivity material, which causing sparkover during the experiments, thus operating voltage cannot be regulated more than -8.25 kV. In order to verify the feasibility of carbon black and ash separation by the principle of electrostatic separation, this study applied non-linear regression to model the collection efficiency of man-made char, carbon black and ash, and further simulate the collection efficiency at higher electrical field strength. The simulated results indicated that the maximum collection efficiency of carbon and ash was approached around -10 kV/cm of carbon black and ash and their collection efficiencies were similar. The collection efficiency of ash was close to the ash content of man-made char (the collection efficiency of ash equal to the collected ash per mass of injected char), suggesting that most injected ash was collected by the ESS system. In addition, the ash content of penetration char was also simulated, the modeling results showed that the ash content of penetrated char were lower than 2%, while was relatively lower than the raw man-made char, and more than 75% injected char could penetrate the ESS system during the operation procedure. According to the modeling results, solid-solid separation technology could be more efficient if carbon and ash are independently separate particles, and lower resistivity materials would penetrate the ESS system and higher resistivity materials would be collected by the electrostatic separation process.

Optical beam induced current (OBIC) mapping has found wide-spread applications in characterizing semiconductor devices and integrated circuitry. In this study, we have used a two-photon scanning microscope to investigate InGaN light emitting diodes (LED). The defects induced by electrostatic discharge (ESD) can be clearly identified by DC-OBIC images. Additionally, we have combined an E-O modulator and a high frequency phase sensitive lock-in amplifier to conduct time-resolved study on the dynamical properties of the LEDs. The defects also exhibit different delay time when compared with the normal parts.

Single molecule force spectroscopy is an important technique to determine the interaction forces between biomolecules. Atomic force microscopy (AFM) is one of the tools used for this purpose. So far, AFMs usually use cantilevers as the force sensors and piezoelectrics as the actuators which may have some drawbacks in terms of speed and noise. In this research, a micromachined membrane actuator was used in two important types of experiments, namely the single molecule pulling and force-clamp based force spectroscopy. These two methods permit a more direct way of probing the forces of biomolecules, giving a detailed insight into binding potentials, and allowing the detection of discrete unbinding forces. To improve the quality of the experiments there is a need for high force resolution, high time resolution and increase in the throughput. This research focuses on using the combination of AFM and membrane based probe structures that have electrostatic actuation capability. The membrane actuators are characterized for range, dynamics, and noise to illustrate their adequacy for these experiments and to show that the complexity they introduce does not affect the noise level in the system. The control system described in this thesis utilizes the novel membrane actuator structures and integrates it into the current AFM setup. This is a very useful tool which can be implemented on any AFM without changing its mechanical architecture. To perform an experiment, all that is needed is to place the membrane actuator on the AFM stage, under the imagining head, and run the control system, which was implemented using LabVIEW. The system allows the user to maintain a precise and continuous control of the force. This was demonstrated by performing a life time experiment using biomolecules. Moreover, by slightly modifying the control scheme, the system allows us to linearize the membrane motion, which is inherently non-linear. The feasibility of using this control system for a variety of loading rate experiments are also demonstrated.