none

The effect of pH and ionic strength on the equilibrium adsorptive behavior of β-lactoglobulin onto hydrophobic and hydrophilic silicon surfaces was studied using ellipsometry. Plots of amount adsorbed (μg protein/cm²) as a function of protein concentration (mg/ml) exhibited attainment of plateau values beyond a protein concentration of 0.250 mg/ml. At a given pH and ionic strength, plateau values associated with hydrophobic surfaces were observed to be greater than those associated with hydrophilic surfaces. The Langmuir adsorption isotherm was chosen as the most appropriate model to represent the data and was used to compare results obtained under different experimental conditions. Effects of pH and ionic strength on protein adsorption at hydrophilic surfaces indicate that electrostatics played a major role, while pH and ionic strength effects on adsorption to hydrophobic surfaces reflect a greater importance of nonelectrostatic interactions. / Graduation date: 1991

This research presents an analysis of low cost fabrication techniques for embedded thin film resistors suitable for large volume needs. High frequency applications are targeted from 2 to 40GHz. Two approaches are taken. The first utilizes commercially available foils to produce resistors using only thermocompression bonding and wet chemical etching. The second method utilizes electroless plating with a modified plasma treatment to promote adhesion to organic materials. This process uses only chemical baths to form the thin films. Several RF and millimeter wave applications using these processes have been explored including terminations and attenuators. Accurate simulations of resistor performance were obtained using impedance boundaries in conjunction with the finite element method. Resistors created using the foil transfer process are measured to be accurate within 5% of these simulated values. Electroless values are currently accurate to around 40%, with research underway expected to improve this to around 10%.

No description available.

The purposes of this thesis are to prepare ZnO and tin-doped In2O3 (ITO) films at low temperature and study their microstructure and optoelectronic properties. Low-temperature growth of undoped ZnO films with high transparency and low electrical resistance was prepared by ion beam sputtering. After systematic testing, a sheet resistivity as low as 2.95 x 10-3 £[-cm was obtained at a substrate temperature of 150 oC, ion source voltage of 850 V, and ion beam current of 30 mA. The transmittance of the ZnO films was in the range of 85-90%. Hall measurements showed that a high mobility of 21.41 cm2/Vs was obtained for films less than 200 nm thick. The related microstructures and physical properties were measured and discussed. ZnO nanofilm of (2-1-10) and (01-11) surfaces were prepared on NaCl (001) surface at 200 oC and 400 oC to produce nearly pure (2-1-10) and (01-11) textures respectively and the orientation relationships were determined and the interface discussed. By dissolving the NaCl substrate, the ZnO (2-1-10) and (01-11) surfaces several cm2 in area, which may have some useful applications, can be easily prepared. The photoluminescence spectrum from the (2-1-10) surface showed only a near-band-edge UV emission peak while the (01-11) surface showed a near band-edge UV emission and a broad green emission. Low-temperature preparation of transparent conducting electrode is essential for flexible optoelectronic devices. ITO films of high transparency and low electrical resistance were prepared at room temperature with a radio-frequency ion beam sputtering system. Specimens with a low sheet resistivity of 10-4 £[-cm and a high visible-light transmittance of 85-90% were obtained. Hall measurement was used to measure the mobility and carrier concentrations and the effects on resistivity were discussed. ITO films were deposited on glass substrates at 200 oC at various oxygen flow rates. At low oxygen flow rate the film surface has ITO whiskers with metallic In tips and a crystallographic relationship of (010)In//(110)ITO and (001)In//(001)ITO is present between them. The In tips act as the seeds for the growth of ITO whiskers by a vapor-liquid-solid growth mechanism. As the oxygen flow rate increases, the crystallinity of the ITO film decreases till an amorphous phase is formed. The microstructure, resistivity and transmittance of the films were studied as a function of oxygen flow rate. Thin films of high transmittance (~90%) and low resistivity (6 x 10-4 Ω-cm) were prepared at an intermediate oxygen flow rates.

Interactions between Mn12–acetate molecular magnets and thin gold films have been explored in light of the theory of weak localization. Low-temperature measurements of the magnetoresistance of gold films of varying thicknesses, with and without the presence of a surface layer of Mn12–acetate, have been performed using a dilution refrigerator. Quantitative fits to the data using the predictions of weak localization theory were performed using a least-squares fit method in order to determine characteristic times for elastic, inelastic, spin-orbit and spin scattering events within the gold. These data indicate that the presence of Mn12–acetate on the surface of the gold film leads to a significant enhancement of the spin scattering within the gold films.

The Mg-modified lead titanate [(Pb1-xMgx)TiO3,abbreviated to PMT] thin films were deposited on Pt/SiO2/Si substrates by spin coating with sol-gel processing in this thesis. 1,3 propanediol was used as solvent to minimize the number of cycles of spin coating and drying processes to obtain the desired thickness of thin film. By changing the Mg content (0~10 mol%) and the heating temperature (500~800¢J), the effects of various processing parameters on the thin films growth are studied. The effects of various Mg contents on the response of pyroelectric IR detector devices are studied also. Experimental results reveal that the Mg contents will influence strongly on grain size, dielectricity, ferroelectricity and pyroelectricity of PMT thin films. With the increase of Mg content, the grain size of PMT thin film decrease slightly, and the lattice structure of PMT thin film will change from tetragonal to cubic when the Mg content over 8 mole%. The relative dielectric constant of PMT thin film increases from 25 up to 91. The tan

Layer-by-layer (LbL) assembly was used to produce highly conductive thin films with carbon black (CB) and polyelectrolytes. The effects of sonication and pHadjustment of the deposition mixtures on the conductivity and transparency of deposited films were studied. Drying temperature was also evaluated with regard to thin film resistance. Sonication and oven drying at 70oC produced films with the lowest sheet resistance (~ 1500 Ω/sq), which corresponds to a bulk resistivity of 0.2 Ω⋠cm for a 14- bilayer film that is 1.3 μm thick. Increasing the pH of the PAA-stabilized mixture and decreasing the pH of the PEI-stabilized mixture resulted in films with 70% transparency due to thinner deposition from increased polymer charge density. Varying the number of bilayers allows both sheet resistance and optical transparency to be tailored over a broad range. Variation of deposition mixture composition led to further reduction of sheet resistance per bilayer. A 14 bilayer film, made from mixtures of 0.25wt% carbon black in 0.05wt% PAA and plain 0.1wt% PEI, was found to have a sheet resistance of approximately 325 Ω/sq. Bulk resistivity was not improved due to the film being 8 μm thick, but this combination of small thickness and low resistance is an order of magnitude better than carbon black filled composites made via traditional melt or solution processing. Applications for this technology lie in the areas of flexible electronics, electrostatic charge dissipation, and electromagnetic interference shielding.

The object of the present research is to design and fabricate metal-dielectric thin film multilayer structures that make use of the nonlinear optical (NLO) response of Ag for efficient nonlinear absorption for sensor protection. These structures employ structural resonances to overcome the challenges of reflection and absorption that limit access to this large NLO response. The research consists of three parts: first, we present a comprehensive analysis of the contributions to the nonlinear optical response of Ag. Second, we present a systematic investigation of the linear optical properties of Metal-Dielectric Photonic Band-Gap (MDPBG) structures, including optimization of the structure for a particular transmittance spectrum. Third, we study the linear and nonlinear optical properties of Induced Transmission Filters (ITFs). Each of these parts includes experimental results backed by modeling and simulation.

Metal oxides crystallized in perovskite structure are generally modified in two different ways. According to the general structural formula ABO3, the two ways are A-site modification and B-site modification. The primary significance of perovskite metal oxides rests on their importance in electronic devices. A particular class of perovskites, namely Lead Zirconate or modified Lead Zirconate has received a special attention because of their unique antiferroelectricity and various applications in devices. Among the other modifications, A-site modification of PbZrO3 by La is rare and not much explored. Chapter 1 describes various applications of antiferroelectric thin films along with the synthesis and characterization of pure and La modified PbZrO3, which are relevant to the work presented in this thesis. Sol-gel processing and spin coating technique to deposit solid oxide thin films are well known for their low cost of deposition as well as for their ability to achieve better stoichiometric chemical composition. Common crack formation problem of sol-gel grown films can be prevented by ‘drying control chemical adhesive’ like polyvinylpyrrolidone (PVP). Heat treatment of sol-gel derived thin films is generally determined by TGA and DTA. Crystalline phase of deposited solid thin films is determined by XRD whereas effect of modification can be ascertained by XRD peak assignment and relative crystalline peak shifting. Sol-gel grown film thickness is measured by common cross sectional SEM whereas AFM can detail the surface morphology. Chapter 2 summarizes the deposition and characterization of pure and La modified PbZrO3 thin films. Any nonmetal, which is insulator, is dielectric material and show dielectric dispersion in a frequency domain of low field alternative current. Among the most common feature of dielectric dispersion, Maxwell – Wagner type dispersion is well known. Similar kind of dielectric dispersion, named Maxwell – Wagner like dispersion, can be observed while the equivalent circuit consists of parallel G – C along with a series R. Universal power law of ac conductivity is the deciding factor to distinguish the nature of dispersion. Structural phase transition can be determined by dielectric response and it is widely known as dielectric phase transition. Effect of La modification on dielectric phase transition of PbZrO3 thin films depends on stabilization or destabilization of antiferroelectricity. Maximum dielectric constants of pure and modified PbZrO3 thin films depend on the crystallographic orientations of the growth. Chapter 3 presents dielectric properties of pure and La modified PbZrO3 thin films and these properties are correlated to the stabilization or destabilization of antiferroelectricity, relative integrated intensity of (202)O film orientation and trapped electron charge due to oxygen vacancies. Charge storage property of a capacitor is determined by the polarization of the capacitor on application of electric field whereas field dependent integrated area of polarization on withdrawal of electric field determines the recoverable capacitive energy storage. Among the three kinds of capacitors like linear or paraelectric, ferroelectric and antiferroelectric capacitors, antiferroelectric capacitor is known to be best for their ability to store huge amount of recoverable energy. The recoverable energy in antiferroelectrics can be increased by increasing squareness of the P – E hysteresis loop, applicable electric field, polarization or by the all possible combinations of them. Chapter 4 describes the correlation of relative integrated intensity of (202)O [RI(202)O] with critical applied electric field of P – E saturation to provide enhanced squareness of the hysteresis loops. This chapter also describes the variation of charge and recoverable energy storage properties with respect to RI(202)O. Like magnetocaloric effect, electrocaloric effect is capable to alter the temperature of a system by adiabatic polarization or depolarization. From the Maxwell’s relation of thermodynamics, assuming, (∂p ) = (∂s )electrocaloric effect can be calculated from temperature dependent polarization value of a paraelectric, ferroelectric or an antiferroelectric. Chapter 5 presents the electrocaloric effect of pure and La modified PbZrO3 thin films. Summary of present study and discussion have been delineated in Chapter 6 along with the future work which can give more insight into the understanding of antiferroelectric PbZrO3 thin films with respect to Pb and Zr site modification and with respect to different electrodes. (For formulas pl see the pdf file of the thesis)