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Photo reflectance¡]PR¡^ and Contactless electroreflectance¡]CER¡^spectra of Zn and O-faces of a c-plane ZnO bulk have been measured at room temperature, respectively. It was found that the phase of PR is the same as that of CER for the Zn-face and they are inverted for the O-face. This indicates a polarization induced field existing in the c- plane ZnO bulk due to nonzero spontaneous polarization. In addition, a mercury lamp was focused on the ZnO sample in the CER measurements to provide a photovoltaic voltage to reduce electric field in the sample. The CER spectrum with Hg lamp is more blue-shifted and its amplitude is smaller than that without Hg lamp. Hence, the type of transitions was classified as excitonic transition. The A, B, and C excitonic transition energies were obtained by fitting experimental spectra.

In this study, a electrical pitting tester and SEM are employed to investigate the effects of supply voltage, supply current, and oil film thickness on the electrical behavior, the action forces, and the formation mechanism of electric pitting for the lubricated surface of steel pair at sliding speed of 1£gm/sec using an additive of MoS2 in paraffin base oil under DC electric field. According to the experimental results and the observations of the surface pitting, two electrical pitting regimes are found under the influences of shaft voltage, oil film thickness, and particle concentration of additive, namely, pitting and no- pitting regimes in static condition. The area of pitting regime increases with increasing additive concentration and supply current. Furthermore, The ratio of pitting area to the interface power increases rapidly with increasing additive concentration and oil film thickness. This results from the molten plateau that directly connects two specimens, and the interface power is mainly consumed at the heating of the plateau and the interfacial materials. However, the weld strength of the plateau isn¡¦t influenced with additive concentration. It is known from the observations of the surface pitting in dynamic pitting occurs that the pitting width increases with increasing oil film thickness and additive concentration. Finally, the formation processes of electric pitting on the lubricated surface for both static and sliding conditions are deduced from the results of the normal force, the friction force, the interface impedance and the observations of the surface pitting.

A flux declination predication model for nanoparticle-containing wastewaters treated by a simultaneous electrocoagulation/electro- filtration (EC/EF) process was investigated by perceiving blocked membrane pores, concentration polarization layer, cake layer, and applied electric field strength in this study. As nanotechnology develops, it has been used in many applications. However, its environmental impacts have not been extensively studied. Membrane technology is one of the direct and effective treatment methods for removing nanoparticles from wastewater. But nanoparticle-containing wastewater treated by membrane technology would face the problem of membrane fouling. In this study, oxide chemical mechanical polishing (CMP) wastewater, copper CMP wastewater, and nanosized TiO2-containing wastewater were treated by a EC/EF treatment module. In the EC/EF treatment module, iron, aluminum, and stainless steel were respectively selected as th anode and cathode. Polyvinylidene fluoride (PVDF) with a nominal pore size of 0.1 £gm and carbon/Al2O3 tubular inorganic composite membranes with a pore size ranging from 2 to 10 nm were used in this work. In this work, the changes of the relevant performance of membrane with changes of applied pressure (9.8-19.6 kPa), crossflow velocity (0.3-0.5 m/s) and applied electric filed strength (25-233 V/cm) were studied. The simulation results of a modified mathematic model showed that the flux declination would be fitted finely by an exponential function. Experimental results showed that a higher transmembrane pressure would yield a higher cake concentration and a higher crossflow velocity would yield the steady flux quickly. Overall speaking, the flux declination for nanoparticle-containing wastewaters treated by a simulataneous EC/EF process was described properly as a exponential form. The exponential function could simply show the flux declination of different samples treated by different modules in different situations.

ABSTRACT In this study, two chemical mechanical polishing (CMP) wastewaters were treated by crossflow electro-microfiltration. Also studied are the effects of operation parameters on their treatment efficiencies. In the semiconductor industry, presently, CMP has become the key technique to provide global planarization on interlevel dielectrics (ILD) and metal layers of wafers. In general, the post-CMP cleaning process will produce a great quantity of CMP wastewater. Normally, CMP wastewater consists of abrasives of high concentration and stability, chemicals (e.g., oxidant and surfactant), and a tremendous mass of de-ionized water. Because of the negatively charged suspended solids in CMP wastewater, crossflow electro-microfiltration was used to treat this type of wastewater. By applying an electric field to the system, the negatively charged suspended solids were expelled from the membrane surface moving toward the anode. Not only reducing the cake formation on the membrane, enhancement of the filtration rate and permeate flux have also been found when an external electric field is applied to the filtration system. In this investigation, CMP wastewaters obtained from wafer fabs A and B were first characterized by various standard methods. In CMP wastewater A, the suspended solids were found to have a high negative zeta potential, about ¡V78 mV. Its electrical conductivity was determined to be 127.2 £gS/cm. Before testing, each CMP wastewater was pre-filtered using a filter paper of 1.2 £gm in pore size. An experimental design based on the Taguchi method was employed. The L9 orthogonal arrays were utilized to investigate the effects of four experimental factors ( i.e., electric field strength, crossflow velocity, transmembrane pressure, and membrane pore size) on the filtration rate and permeate quality in the crossflow electro-microfiltration system. When the electric field strength applied was lower than the critical electric field strength, increases of the electric field strength, transmembrane pressure, and membrane pore size were found to be beneficial to the filtration rate. The experimental results were further subjected to the analysis of variance and regular analysis. For both CMP wastewaters A and B, the electric field strength and membrane pore size were determined to be very significant parameters. In this filtration system, the optimal treatment efficiency could be achieved by using a higher electric field strength, lower crossflow velocity, higher transmembrane pressure, and larger membrane pore size. The quality of permeate thus obtained was even better than the tap water quality standards. Therefore, the permeate might be worth recycling for various purposes.

This paper proposed a low-cost and high-throughput method to fabricate lensed optical fibers. SU-8 Photoresist is used as the material for fabricating the proposed lens structure and is directly applied on two kinds of optical fiber tip, single mode glass fibers (O.D.=125 £gm) and plastic graded-index plastic fiber (O.D.=500 £gm), utilizing surface tension force to form a hemi-circular shape lens structure. The hemi-circular shape SU-8 lens is then electrostatically pulled to form non-spherical shape in an uniform electric field at a temperature higher than the glass temperature (Tg) of SU-8. Microlens with various radius of curvature can be easily produced by tuning the applied electric fields during the electrostatic pulling process. In addition, this study also measures the UV-Vis-NIR spectrum SU-8 photoresist to confirm the optical property of SU-8. Results indicate the SU-8 has high optical transmittance from the wavelength range of 380-1600 nm. SEM observation also indicates the fabricated SU-8 microlens has excellent surface smoothness which is essential for optical applications. A commercial optical simulation software of ZEMAX® is used to predict the light path of the fabricated lensed fiber. The numerical results show good agreement with the experimental test obtained by projecting laser light into a diluted fluorescence solution. Furthermore, a Fabry-Perot laser chip with the wavelength of 1310 nm is used for light coupling test for the fabricated lensed fibers. Results show the coupling efficiency is up to 78% at working distance of 90 £gm while using the plastic lensed fiber (R =48 £gm), which is around 2 fold higher than that of a flat-end fiber. The coupling efficiency of glass lensed fiber (R =23 £gm) is up to 72% at working distance of 24 £gm, which is around 2.3 fold higher than that of a flat-end fiber. The proposed method is feasible of producing high-quality lensed optical fiber in a high throughput and low-cost way. The method proposed in the current study may give substantial impacts on fabricating lensed fiber in the future.

In this dissertation, charge transport through organic field effect transistors is explored. In particular, small molecule-based devices consisting of Pentacene semiconducting thin films are investigated. The relationship between electric field and carrier velocity is explored over a wide range of electric fields. These velocities are then compared to directly measured velocities measured from transient measurements. New device structures are fabricated in order to provide low voltage operation, along with a method to stabilize the output response and reduce bias stress effects. A novel method is proposed to investigate the dynamics of trap response rate in highly localized systems through the characterization of the large signal frequency response of a vii device. This method is then used to gain greater insight into bias stress effects and the ability of a transistor to respond to a rapidly changing input. A greater understanding of the transport of charge through a channel is obtained, leading to a more realistic picture in which a single mobility value is an insufficient description of carrier transport through a material. / text

This dissertation investigates the emulsification of aqueous liquid in immiscible organic liquid in various microfluidic environments, and addresses both experimental characterization and theoretical interpretation of the dynamics and design guidelines, as well as an application of microfluidic emulsification in fabrication of disk-like colloidal particle suspensions for studying its sedimentation behavior. In an attempt to understand the dynamics of drop formation in flow-focusing microfluidic channels, especially for an explanation of a transition from unique drop size to bimodal oscillating drop sizes as observed in the experiments, numerical simulation is developed to use the volume-of-fraction method to model the drop formation, and the simulation results help to interpret the transition in the theory of saddle-node transition in drop formation, as well as show the importance of selecting proper orifice length in flow-focusing microfluidic channel design. The electric technique for controlling of microfluidic emulsification is explored by a detailed study on low-frequency alternating-current electro-flow-focusing (EFF) emulsification in microfluidic channels. It is found that the droplet size variation is not a monotonic function of the electric field as in the case of direct-current EFF emulsification, which originates from the relaxation oscillation of the flow rate through the Taylor cone, and a power-law droplet size distribution was obtained at the voltage ramping-up stage. This emulsification process was modeled in analog to the charge accumulation and release in a resistor-capacitor electric circuit with an adjustable resistor, and the simulated data exhibit good agreement with the experiments. As an application of the microfluidic emulsification, a method of fabricating disk-like wax colloidal particle suspensions using electrospray is reported. Based on this technique, the first measurement of the hindrance function for sedimentation and creaming of disk-shaped colloids via the analytical centrifugation is reported. Disks align with the external flow right above the volume fraction of a few percent and this effect is extremely sensitive to the aspect ratio of disks. Due to this alignment effect, disk sedimentation/creaming demonstrate distinct trends in dilute and semi-dilute region.

Capacitive displacement sensors have many applications where non-contact, high precision measurement of a surface is required. Because of their non-contact nature they can easily measure conductive surfaces that are flexible or otherwise unable to be measured using a contact probe. Since the output of the capacitance gage is electrical, data points can be collected quickly and averaged to improve statistics. It is often necessary for capacitive displacement sensors to gage the distance from a curved (non-flat) surface. Although displacements can easily be detected, the calibration of this output can vary considerably from the flat case. Since a capacitance gage is typically factorycalibrated against a flat reference, the experimental output contains errors in both gain and linearity. A series of calibration corrections is calculated for rectifying this output. Capacitance gages are also limited in their overall displacement travel. A support stage is described that, along with control electronics, allow the properties of the capacitance gage to be combined with an interferometer to overcome this displacement limitation. Finally, an application is proposed that would make use of the capacitance sensor and support stage assembly.

Magnetic neural stimulation of straight neurons with bends (1) in a semi-infinite volume conductor with a planar interface and (2) in the model of the human head is analyzed. Two stimulating coils, namely the double-square and the double circular, producing the magnetic field for the neuron stimulation are considered. The results indicate that the stimulating coil characteristics (size, shape and location) and the neuron shape affect the magnitude and location of the stimulation. The activating function, defined as the electric field derivative along the neuron, has two components. One component depends on the derivative of the electric field along the straight section of the neuron, and the other on the field magnitude. For bent neurons in a semi-infinite volume conductor, an analytical expression of the activating function (the stimulus) of the neuron was derived. The maximal stimulation point is at the bend of the nerve and its position depends on the nerve shape and coil parameters. The analysis also shows a better performance (a stronger stimulus) for a double-circular (figure eight) coil than for a double-square coil of comparable size. Stimulating bent neurons in the human head is also analyzed. The head model consists of an outer sphere representing the skull and scalp and two inner spheres such that each represents one half of the brain. The 3D-impedance method was used to obtain the induced electric fields by the double-square and double-circular coils. Quasi-static conditions are assumed. The geometry of the neuron in this model approximates the normal configuration of motor neurons in the human head. The analysis shows that the stimulation occurs almost at the highest point on the nerve (the closest point to the coil) with the coil positioned in such a way that its center is directly over the highest point on the nerve. It is also shown that the double-square coil produces a stronger stimulus than the double-circular coil. This result is in contradiction with that for a bent neuron in a semi-infinite volume conductor, however, it agrees with the results obtained for a straight neuron [1]. The analysis of bent neurons represents a more realistic approximation of the actual anatomy. The results of this analyses confirms the conclusions and, therefore, usefulness of simplified analyses of straight neurons. The results are expected to be of some use in clinical applications where non-invasive neural stimulation is desired and location of stimulation needs to be known. / Graduate / 0544