The production of sub-micron structures has created a need for techniques to characterize these structures. This is especially true since many of the materials composing these structures do not behave as would be predicted by traditional meso-scale equations. This paper considers both experimental and theoretical aspects of the three-point bending method for measuring the elastic modulus of 1-D nanostructures such as wires, tubes, and belts. Three-point bending tests were performed using an atomic force microscope (AFM) on silica nanowires suspended over micro-channels. Detailed consideration was given to AFM calibration, measurement uncertainty, and the importance of the boundary conditions existing where the wires are anchored to the test structure. Correct representation of the boundary conditions is critical for the use of models with the observed data to estimate the elastic modulus. The standard fixed and simple beam models have been used exclusively for estimating the elastic modulus, despite their unrealistic representation of boundary conditions. The Winkler model is applied here to represent an elastic bond between the nanowires and the polymer film anchoring them to the test structure. The application of this model requires measurement of the elastic modulus of the polymer, which was accomplished in this study via indentation testing with an AFM probe. The results clearly indicate that the silica nanowires in this study, with diameters between 50 and 130 nm, have an apparent elastic modulus greater than bulk. The results suggest that the apparent elastic modulus increases with smaller diameters in a way consistent with predictions made through the consideration of energy stored in the nanowires in the form of surface tension.

Remarkable advances have been made since rapid solidification was first introduced to the field of materials science and technology. New types of materials such as amorphous alloys and nanostructure materials have been developed as a result of rapid solidification techniques. While these advances are, in many respects, ground breaking, much remains to be discerned concerning the fundamental relationships that exist between a liquid and a rapidly solidified solid. The scope of the current dissertation involves an extensive set of experimental, analytical, and computational studies designed to increase the overall understanding of morphological selection, phase competition, and structural hierarchy that occurs under far-from equilibrium conditions. High pressure gas atomization and Cu-block melt-spinning are the two different rapid solidification techniques applied in this study. The research is mainly focused on Al-Si and Al-Sm alloy systems. Silicon and samarium produce different, yet favorable, systems for exploration when alloyed with aluminum under far-from equilibrium conditions. One of the main differences comes from the positions of their respective T0 curves, which makes Al-Si a good candidate for solubility extension while the plunging T0 line in Al-Sm promotes glass formation. The rapidly solidified gas-atomized Al-Si powders within a composition range of 15 to 50 wt% Si are examined using scanning and transmission electron microscopy. The non-equilibrium partitioning and morphological selection observed by examining powders at different size classes are described via a microstructure map. The interface velocities and the amount of undercooling present in the powders are estimated from measured eutectic spacings based on Jackson-Hunt JH) and Trivedi-Magnin-Kurz TMK) models, which permit a direct comparison of theoretical predictions. For an average particle size of 10 microm with a Peclet number of ~0.2, JH and TMK deviate from each other. This deviation indicates an adiabatic type solidification path where heat of fusion is reabsorbed. It is interesting that this particle size range is also consistent with the appearance of a microcellular growth. While no glass formation is observed within this system, the smallest size powders appear to consist of a mixture of nanocrystalline Si and Al. Al-Sm alloys have been investigated within a composition range of 34 to 42 wt% Sm. Gas atomized powders of Al-Sm are investigated to explore the morphological and structural hierarchy that correlates with different degrees of departure from full equilibrium conditions. The resultant powders show a variety of structural selection with respect to amount of undercooling, with an amorphous structure appearing at the highest cooling rates. Because of the chaotic nature of gas atomization, Cu-block melt-spinning is used to produce a homogeneous amorphous structure. The as-quenched structure within Al-34 to 42 wt% Sm consists of nanocrystalline fcc-Al on the order of 5 nm) embedded in an amorphous matrix. The nucleation density of fcc-Al after initial crystallization is on the order of 1022-1023 m-3, which is 105-106 orders of magnitude higher than what classical nucleation theory predicts. Detailed analysis of liquid and as-quenched structures using high energy synchrotron X-ray diffraction, high energy transmission electron microscopy, and atom probe tomography techniques revealed an Al-Sm network similar in appearance to a medium range order MRO) structure. A model whereby these MRO clusters promote the observed high nucleation density of fcc-Al nanocrystals is proposed. The devitrification path was identified using high temperature, in-situ, high energy synchrotron X-ray diffraction techniques and the crystallization kinetics were described using an analytical Johnson-Mehl-Avrami JMA) approach.

The emphasis of this research is to study and elucidate the underlying mechanisms of reversible hydrogen storage in pristine and Ti-doped sodium aluminum hydrides using molecular modeling techniques. An early breakthrough in using complex metal hydrides as hydrogen storage materials is from the research on sodium alanates by Bogdanovic et al., in 1997 reporting reversible hydrogen storage is possible at moderate temperatures and pressures in transition metal doped sodium alanates. Anton reported titanium salts as the best catalysts compared to all other transition metal salts from his further research on transition metal doped sodium alanates. However, a few questions remained unanswered regarding the role of Ti in reversible hydrogen storage of sodium alanates with improved thermodynamics and kinetics of hydrogen desorption. The first question is about the position of transition metal dopants in the sodium aluminum hydride lattice. The position is investigated by identifying the possible sites for titanium dopants in NaAlH4 lattice and studying the structure and dynamics of possible compounds resulting from titanium doping in sodium alanates. The second question is the role of titanium dopants in improved thermodynamics of hydrogen desorption in Ti-doped NaAlH4. Though it is accepted in the literature that formation of TiAl alloys Ti-Al and TiAl3) is favorable, reaction pathways are not clearly established. Furthermore, the source of aluminum for Ti-Al alloy formation is not clearly understood. The third question in this area is the role of titanium dopants in improved kinetics of hydrogen absorption and desorption in Ti-doped sodium alanates. This study is directed towards addressing the three longstanding questions in this area. Thermodynamic and kinetic pathways for hydrogen desorption in pristine NaAlH4 and formation of Ti-Al alloys in Ti-doped NaAlH 4, are elucidated to understand the underlying mechanisms of hydrogen desorption. Density functional theory formalism as implemented in CASTEP Cambridge Serial Total Energy Package) is used to study the structure and energetics of pristine and Ti-doped sodium alanates. From investigations of various models of sodium alanates with Ti dopants, it is shown that the difference between the energy required for Ti&rarr；SNa Ti-substituted Na at the lattice site on the surface) and Ti&rarr；TI Ti placed on top of the surface interstitial SI site) is 0.003 eV atom-1, and is minimal compared to other models. Since less energy is required for Ti&rarr；S Na and Ti&rarr；TI, these two sites SNa and T I) would be preferred by the Ti dopants. In Ti&rarr；SNa model, Ti is coordinated to two aluminum and seven hydrogen atoms resulting in the possible formation of a TiAl2H7 complex. At elevated temperatures 423 and 448 K), the number of aluminum atoms coordinating with titanium in the complex increase from two at distances in the 2.6-2.7 A range) to five at distances in the 2.6-2.7 A range). Besides the formation of a Ti-Al-H complex, Al-Al association with a 2.97 A bond length) is also seen from the DFT-MD results. In the case of Ti&rarr；TI, Ti is coordinated to two aluminum and two hydrogen atoms resulting in the possible formation of a TiAl2H2 complex. TiAl2 H2 complex becomes TiAl3H6 and TiAl 3H7 at elevated temperatures of 423 and 448 K, respectively. The investigation of thermodynamics pathways in Ti-doped sodium alanates illustrates a three step reaction pathway to the formation of TiAl3 Ti and AlH3 after the first reaction, TiAl after the second and finally TiAl3). This investigation also suggests aluminum in its ＋3 oxidation state present in aluminum hydride species is responsible in the formation of Ti-Al alloys. From kinetics studies, the proposed mechanism is related to transition from AlH4- to AlH6 3-. The rate limiting step is determined to be associated with hydrogen evolution from association of AlH3 species nucleating aluminum phase. This step is 15 kJ/mol higher than the nearest highest barrier in the reaction path related to transition from AlH52- to AlH63-. From the DFT-MD simulations, it is observed that the titanium dopants are present on the surface during the entire simulation time and exhibit the role in catalytic splitting of hydrogen from surrounding AlH4 groups. Besides the catalytic role, Ti dopants also form bonds with Al, and we also see that the AlH4 groups on the surface and that are present in the sub-surface layers are drawn towards the Ti dopants. This association of Al around titanium indicates the initiation of Al nucleation site facilitated by Ti dopants residing on the surface.

The ternary Mg-Mn-Ce phase diagram was experimentally studied and thermodynamically calculated at the Mg-rich corner. More than twenty binary and ternary alloys were synthesized and heat-treated at both ambient and elevated temperatures. The microstructures and lattice parameters of the samples were studied via XRD, SEM/EDS and EPMA to determine phase equilibria. The ternary phase diagram was also calculated via thermodynamic calculation software FactSage. The results from both experiment and the assessment were compared and discussed. The binary phase diagrams were re-examined, especially the Mg-Ce system. In order to investigate the composition range of the intermetallic compounds Mg12Ce and Mg41Ce5, and to clarify data in the existing phase diagram, both the solid-liquid diffusion couple method and alloys synthesized with target phases were analyzed. Pure Mg – Ce contact was vacuum-encapsulated in quartz tube and the Mg and Ce inter-diffused at 400&deg；C. Alloys prepared were cast and annealed at a temperature range of 300-550&deg；C. All the four single-phase zones corresponding to the Mg-Ce phase diagram were observed via the diffusion couple technique. However, the stoichiometry of Mg12Ce studied on the synthesized and annealed alloys showed that on the Mg rich side of the present phase diagram, the compositional range of Mg12Ce should be redesignated as Mg11.17-10.81) Ce at ambient temperature, and Mg11.31-10.75)Ce at 530&deg；C. Mg41Ce5, on the other hand, has been confirmed as a line compound, but with composition 11.3at% Ce, rather than 10.9at% Ce. The binary phase diagram study was also extended to the Ce-rich side of Mg-Ce system. A new phase, Mg4Ce, was found in the study of phase Mg3Ce. Based on the investigation of the intermetallics in the Mg-Ce binary system, a modified phase diagram was suggested to accommodate the stoichiometry of Mg11Ce, Mg39Ce5, and Mg3Ce. The experimental study on the ternary phase diagram was conducted on three isopleths: 0.6, 1.8 and 2.5wt% Mn, respectively, and Ce varied between 0 and 25wt%. All alloys were synthesized from high purity starting materials. Two types of thermal analyses, namely, cooling curve analysis CCA) and differential scanning calorimetry DSC), were used to determine the liquidus and solid phase transformation temperatures. The heating/quenching tests on selected samples were conducted for phase analysis. The results showed that only one invariant point for ternary eutectic reaction was observed in the three isopleths, and the composition is 1wt% Mn and 22wt% Ce at 592&deg；C. Furthermore, a solid-solution type of ternary intermetallic compound Mg, Mn)11Ce is formed, holding the same tetragonal structure as Mg12Ce. The solid solution of Mn in Mg12Ce varies between 0.3&sim；0.6 at%, depending on alloy composition and quenching temperature. Finally, the phase diagram calculation with FactSage program was conducted and the small disagreement between the modeling results and present experimental data were found, especially for the eutectic temperature for L &rarr； Mghcp) ＋ Mg12Ce. This is mainly because the present experimental data were not available when the thermodynamic modeling had been performed. The Gibbs energy of Mg12Ce phase was re-optimized and the revised data can accurately reproduce the experimental results within experimental error limits.

New derivatives of carbon nanostructures: nanotubes, nano-onions and nanocrystalline diamonds were obtained through fluorination and subsequent functionalization with sucrose. Chemically modified nanocarbons show high solubility in water, ethanol, DMF and can be used as biomaterials for medical applications. It was demonstrated that sucrose functionalized nanostructures can find applications in nanocomposites due to improved dispersion enabled by polyol functional groups. Additionally, pristine and chemically derivatized carbon nanotubes were studied as nanofillers in epoxy composites. Carbon nanotubes tailored with amino functionalities demonstrated better dispersion and crosslinking with epoxy polymer yielding improved tensile strength and elastic properties of nanocomposites.

Ga, W, Mo and other nonmagnetic atom additions lead to large enhancements in the magnetostriction of the alpha-Fe phase. However, the magnetostrictive behavior of Fe, as well as how the solute additions modify the magnetostrictive behavior of Fe are not fully understood. The magnetostrictive strain arises from the magnetoelastic coupling of the atoms. The nature of magnetoelastic coupling is thought to depend on the interatomic spacing of magnetic ion cores, though the exact nature of this dependence is not fully understood. This work examined the local atomic structure through extended x-ray absorption fine structure EXAFS) measurements that allow an estimation of near-neighbor interatomic distances and near neighbor solute distribution. EXAFS measurements were made on as-grown, long-term annealed, and ordered Fe-27.5 at.% Ga alloy single crystals at the Fe and Ga Kalpha-edges. The EXAFS data were processed using AthenaRTM software and analyzed using Artemis RTM software. The results suggest that a lower level of Ga-Ga covalent bonding in the long-term annealed alloy and its larger magnetostriction value 32 lambda100 of 340 x 10-6) are attributed to the decrease in covalently bonded Ga-Ga dimers in the alloy. A detailed study of magnetostriction in Fe-W alloy single crystals was also made extending previous work that showed a large increase in the magnetostriction of Fe with W additions of 4.4 and 10 at.%. Single crystals of Fe-3 at.% W, Fe-6 at.% W, Fe-7.5 at.% W were obtained using vertical Bridgman technique. Magnetostriction measurements made on as-grown and annealed [001]-oriented single crystal samples showed that annealing enhanced the magnetostriction levels and the magnetostriction constant lambda100 increases rapidly up to 4.4 wt.% W and then decreases at a much lower rate at higher W contents due to increasing propensity to form second phases. The addition of W to Fe decreases the saturation magnetization much more rapidly than that in Fe-Ga alloys. Magnetostriction and magnetization in Fe-10 at.% Mo-10 at.% Ga, and Fe-15 at.% Mo-5 at.% Ga and Fe-20 at.% Ga single crystals were also examined. The results showed that the substitution of Ga with Mo in Fe-20 at.% Ga alloys drastically decreases the magnetostriction and that magnetization rapidly decreased with the substitution of Ga with Mo.

Electromigration EM) and thermomigration TM) reliability of Pb-free solder joints are emerging as critical concerns in advanced packages. In this study, EM and TM phenomena in Sn-2.5Ag solder joints with thick Cu or thin Ni under-bump metallurgy UBM) were investigated. A series of EM tests were performed to obtain activation energy Q) and current density exponent n), and to understand failure mechanisms. Joule heating was also taken into account. Q and n values were determined as follows: for Cu UBM solders, Q ＝ 1.0 eV and n ＝ 1.5； for Ni UBM solders, Q ＝ 0.9 and n ＝ 2.2. Important factors limiting EM reliability of Pb-free solder joints were found to be UBM dissolution with extensive intermetallic compound IMC) growth and current crowding. IMC growth without current stressing was found to follow the parabolic growth law whereas linear growth law was observed for Cu6Sn 5 and Ni3Sn4 under high current stressing. For Cu UBM solders, the apparent activation energy for IMC growth was consistent with the activation energy for EM, which supports that EM failure was closely related to IMC growth. In contrast, for Ni UBM solders the apparent activation energy was higher than the EM activation energy. It was suggested that the EM failure in the Ni UBM solders could be associated with more than one mass transport mechanism. The current crowding effect was analyzed with different thicknesses of Ni UBM. It was found that the maximum current density in solder could represent the current density term in Blacks equation better than the average current density. FEM studies demonstrated that current crowding was mainly controlled by UBM thickness, metal trace design, and passivation opening diameter. A large temperature gradient of the order of 103 &deg；C/cm was generated across the sample to induce noticeable TM and to compare its effect against that of EM. TM-induced voiding was observed in Ni UBM solders while UBM dissolution with IMC formation occurred in Cu UBM solders. However, the relative effect of TM was found to be several times smaller than that of EM even at this large temperature gradient.

My research involves both fundamental studies and applications of the electrodes whose surfaces are chemically modified. Conductive polymers are one of the major materials that are used to modify electrode surfaces. The thorough understanding of the behavior of conductive polymers in ionic liquids is interesting and important as the ionic liquids are becoming promising solvents. With polyvinyl ferrocene) as the model conductive polymer, electrochemical studies were performed in various ionic liquid electrolytes. A theoretical square model and dynamic equilibrium were proposed to describe the interaction between conductive polymers and ionic liquids when the electrons transferred between the electrode and electrolyte. These findings were applied to enable and accelerate the structure relaxation of conductive polymers so that the conductive polymers were capable of delivering peptides efficiently. Incorporation of metallic nanoparticles to the conductive polymer matrix entitled new properties to the conductive polymer, increasing conductivity and providing catalytic abilities. This modification on electrode surface might bring potential uses in gas sensing, energy storage, energy conversion, etc. Conductive polymer coated electrodes produced unique double layer in ionic liquids and a fundamental study of quantum charging help to understand the double layer properties. I also studied the application of surface modified electrodes in chemo- and biosensing. A nonregeneration protocol was created to save the cost and the time in analyzing interfacial binding activities and to prevent the potential of deterioration caused to biological ligands by the conventional regeneration. In the study of carbohydrate/protein interactions, a “click” chemical reaction was first used in constructing a carbohydrate-based biosensor, which was capable of detecting and analyzing proteins specifically and accurately. In another biosensor design, the hydrogen bonding between the template and the ligand was used and enhanced the ability, sensitivity and accuracy of the studies of antibody-antigen binding. We successfully developed a lab course with a homemade SPR device at a very affordable price. The characterization showed the homemade SPR device is accurate and it is a good tool for preliminary studies and for the college education.

Through light absorption and emission as well as charge carrier generation, transport and recombination, pi-conjugated molecules are central to electronic devices including organic field-effect transistors, organic light-emitting diodes, and organic solar cells. This thesis reports on materials development via molecular design, material synthesis and processing, device fabrication and characterization. Major accomplishments are summarized as follows. A series of oligofluorene-co-bithiophene)s, OF2Ts, have been synthesized and characterized for an investigation of the effects of oligomer length and pendant aliphatic structure on thermotropic properties, light absorption and emission, and anisotropic field-effect mobilities. Solvent-vapor annealing at room temperature was shown to be capable of orienting OF2Ts into monodomain glassy-nematic films with an orientational order parameter emulating that achieved with conventional thermal annealing on a rubbed polyimide alignment layer. Comprising hole- and electron-transporting moieties with flexible linkages, non-conjugated bipolar compounds have been developed for use as hosts for electrophosphorescence. These materials are characterized by an elevated glass transition temperature, morphological stability against crystallization, LUMO and HOMO levels unaffected by chemical bonding, and triplet energy unconstrained by the electrochemical energy gap. Phosphorescent OLEDs containing solution-processed emitting layers were fabricated with TRZ-3CzMP)2, TRZ-1CzMP)2 and CzMP)2 hosting Irmppy)3 for an illustration of how chemical composition and hence charge transport properties affect device performance. Bulk heterojunction organic solar cells comprising an active layer of P3HT:PCBM blend at a 1:1 mass ratio with thickness from 130 to 1200 mn have been fabricated and characterized before and after thermal annealing. Before thermal annealing, both short circuit current density and power conversion efficiency decrease with an increasing film thickness, resulting in an inverse spectral response for thick-film devices. Thermal annealing decreases the thin-film device efficiency but substantially increases that of the thick-film devices while eliminating the inverse character of spectral response therefrom. A conjugated oligomer-C60 Dyad has been synthesized to demonstrate its ability to modulate the extent of phase separation between rod-like OFTB and spherical PCBM. While thermal annealing of the OFTB:PCBM at a 1:1 mass ratio results in a eutectic mixture, OFTB:Dyad:PCBM film at a 9:2:9 mass ratio undergoes phase separation into interspersed 30-nm amorphous domains at approximately equal fractions upon thermal annealing. Geometric surfactancy is inferred by analogy to the widely reported formation of microemulsions in traditional oil-surfactant-water systems and ternary polymer blends.

This thesis is divided into two research initiatives: The fabrication and study of bulk, co-continuous, cellulosic-polymer composites with the aid of supercritical CO2 SC CO2)； and the study of polyvinyl alcohol) PVOH) modification and surface activity in ionic liquids. The first part of this thesis utilizes the tunable solubility, gas-like diffusivity, and omniphilic wettability of SC CO2 to incorporate and subsequently polymerize silicone and polyenemer) prepolymer mixtures throughout various cellulosic substrates. Chapters two and three investigate the mechanical properties of these composites and demonstrate that nearly every resulting composite demonstrates an improved flexural modulus and energy release rate upon splitting. Fire resistance of these composites was also investigated and indicates that the heat release rate, total heat released, and char yield were significantly improved upon for all silicone composites compared to the untreated cellulosic material. Chapter four looks specifically at aspen-silicone composites for thermo-oxidative studies under applied loads in order to study the effect of silicone incorporation on the failure kinetics of aspen. The aspen-silicone composites tested under these conditions demonstrated significantly longer lifetimes under the same loading and heating conditions compared with untreated aspen. The second part of this thesis focuses on studying ionic liquids as potentially useful solvents and reaction media for polyvinyl alcohol). Two ionic liquids 1-Butyl-3-methylimidizolium chloride and tributylethylphosphonium diethylphosphate) were found to readily dissolve PVOH. More importantly, we have demonstrated that these solvents can be used as inert reaction media for PVOH modification. Both ionic liquids were found to facilitate the quantitative esterification of PVOH, while only the phosphonium ionic liquid supports the quantitative urethanation of the polymer. In an attempt to tune the surface properties of ionic liquid/polymer solutions, PVOH was also partially esterified with low surface energy substituents. Both surface tension and surface composition of the ionic liquid/polymer solutions can be manipulated by the stoichiometric addition of low surface energy acid chlorides. This work on the modification of PVOH can be directly applied to the modification of polysaccharides such as cellulose which could have important implications from a sustainability and energy standpoint.