Four denture base materials of poly(methyl methacrylate) (QC-20, Pladent-20, Hygenic, and Optilon-399) were prepared by convention water bath and microwave-energy cured methods. While the resin was in the dough stage, it was packed into two molds (65 mm ¡¦15 mm ¡¦10 mm) in the fiber reinforced plastic flask. The variation of temperature with time was recorded by two thermocouples during the microwave heating at 80, 160, and 240 watts, respectively. Microwave polymerization was carried out in the same equipment. The microwave flask containing the same size of resin blocks were processed at 80, 160, 240, and 560 watts for 15, 10, 7, and 2 min, separately. Then each flask was turned over, and cured an additional 2 min at 560 watts. In the case of water-bath method, the resin in the dough stage was packed in the Brass flask, and then cured at 70¢J for 9 hours. Ten specimens were prepared for each condition studied. The surface hardness, porosity, flexural properties and solubility of both process conditions were evaluated. The samples were sectioned by microtome and stained 2 % Osmiun tetroxide, then the morphology of Optilon-399 was observed by using TEM (Transmission electron microscopy) at 160 KV. The result indicate that the flexural strength for Optilon-399 specimens prepared by water-bath method was 20 MPa higher than that prepared in microwave oven, however, there were no obvious difference between the samples cured at different power. Phase separation in two different sizes was observed in all of the Optilon-399 specimens. The larger domain was with 0.18 mm~0.67 mm diameter has dispersed rubber phase surrounded by a rubber periphery. The smaller domain with 0.1 mm diameter is rich with rubber phase. The size and distribution of the larger domain were correlated with the microwave power and curing time. The sample cured by water-bath has the largest average domain diameter (0.395¡Ó0.068 mm). In the specimens prepared by microwave method, the domain size decreased with increasing power. In additions, the domain size varied across the specimen. The size difference between the largest and the smallest domain for specimens cured at 80W was 0.03 mm, and that for specimens cured at 560W was 0.05 mm. This indicated that the larger the power watt was, the higher the morphology difference was.

Advancements in the semiconductor industry require new materials with improved performance. With the introduction of copper as the interconnect material for integrated circuits, efficient diffusion barriers are required to prevent the diffusion of copper into silicon, which is primarily through grain boundaries. This dissertation reports the processing of high quality stoichiometric thin films of TiN, TaN and HfN, and studies their Cu diffusion barrier properties. Epitaxial metastable cubic TaN (B1-NaCl) thin films were grown on Si(001) using an ultra-thin TiN (B1-NaCl) seed layer which was as thin as 1 nm. The TiN/TaN stacks were deposited by Pulsed Laser Deposition (PLD), with the TiN thickness systematically reduced from 15 to 1 nm. Microstructural studies included X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Preliminary Cu diffusion experiments showed that the TiN seed layer thickness had little or no obvious effect on the overall microstructure and the diffusion barrier properties of the TaN/TiN stacks. Epitaxial and highly textured cubic HfN (B1-NaCl) thin films (~100 nm) were deposited on MgO(001) and Si(001) using PLD. Low resistivities (~40 mu omega-cm) were measured with a four point probe (FPP). Microstructural characterizations included XRD, TEM, and HRTEM. Preliminary Cu diffusion tests demonstrated good diffusion barrier properties, suggesting that HfN is a promising candidate for Cu diffusion barriers. Cubic HfN (B1-NaCl) thin films were grown epitaxially on Si(001) substrates by using a TiN (B1-NaCl) buffer layer as thin as ~10 nm. The HfN/TiN stacks were deposited by PLD with an overall thickness less than 60 nm. Detailed microstructural characterizations included XRD, TEM, and HRTEM. The electrical resistivity measured by FPP was as low as 70 mu omega-cm. Preliminary copper diffusion tests showed good diffusion barrier properties with a diffusion depth of 2~3 nm after vacuum annealing at 500 degrees C for 30 minutes. Additional samples with Cu deposited on top of the cubic HfN/TiN/Si(001) were vacuum annealed at 500 degrees C, 600 degrees C and 650 degrees C for 30 minutes. The diffusivity of copper in the epitaxial stack was investigated using HRTEM. The measured diffusion depths, 2 Dt , were 3, 4 and 5 nm at 500 degrees C, 600 degrees C and 650 degrees C respectively. Finally, the diffusivity of Cu into epitaxial HfN was determined to be D=D0 exp(-Q/kT)cm2s-1 with D0=2.3x10-14cm2s-1 and Q=0.52eV.

As silicon-based transistor technology continues to scale ever downward, anticipation of the fundamental limitations of ultimately-scaled devices has driven research into alternative device technologies as well as new materials for interconnects and packaging. Additionally, as power dissipation becomes an increasingly important challenge in highly miniaturized devices, both the implementation and verification of high mobility, high thermal conductivity materials, such as low dimensional carbon nanomaterials, and the experimental investigation of heat transfer in the nanoscale regime are requisite to continued progress. This work furthers the current understanding of structure-property relationships in low dimensional carbon nanomaterials, specifically carbon nanotubes (CNTs) and graphene, through use of combined thermal conductance and transmission electron microscopy (TEM) measurements on the same individual nanomaterials suspended between two micro-resistance thermometers. Through the development of a method to measure thermal contact resistance, the intrinsic thermal conductivity, [kappa], of multi-walled (MW) CNTs is found to correlate with TEM observed defect density, linking phonon-defect scattering to the low [kappa] in these chemical vapor deposition (CVD) synthesized nanomaterials. For single- (S) and double- (D) walled (W) CNTs, the [kappa] is found to be limited by thermal contact resistance for the as-grown samples but still four times higher than that for bulk Si. Additionally, through the use of a combined thermal transport-TEM study, the [kappa] of bi-layer graphene is correlated with both crystal structure and surface conditions. Theoretical modeling of the [kappa] temperature dependence allows for the determination that phonon scattering mechanisms in suspended bi-layer graphene with a thin polymeric coating are similar to those for the case of graphene supported on SiO₂. Furthermore, a method is developed to investigate heat transfer through a nanoscale point contact formed between a sharp silicon tip and a silicon substrate in an ultra high vacuum (UHV) atomic force microscope (AFM). A contact mechanics model of the interface, combined with a heat transport model considering solid-solid conduction and near-field thermal radiation leads to the conclusion that the thermal resistance of the nanoscale point contact is dominated by solid-solid conduction. / text

No description available.

The main purpose of this thesis is to improve the fundamental knowledge of non-isothermal tempering of martensite phase and its effects on the reduction in hardness (softening) with respect the base metal occurring at the heat affected zone (HAZ) of resistance spot welded dual-phase (DP) steels. This thesis also aims at understanding the influence of HAZ-softening on the joint performance of various DP steel grades. The tempering of martensite occurring at the sub-critical HAZ (SC-HAZ) of resistance spot welded DP600, DP780 and DP980 steels has been systematically evaluated by microhardness testing through Vickers indentation and the degree of tempering has been correlated to the HAZ-softening. From the joint performance analysis of similar and dissimilar steel grade combinations assessed through standardized testing methods, three important issues have been targeted: a) the joint strength (maximum load to failure), b) the location of failure (failure mode), and c) the physical characteristic of the weld that determines certain type of failure (weld nugget size). In addition, a partial tensile test has been conducted in order to evaluate the initiation of failure in dissimilar steel grade combinations. It has been shown that HAZ-softening lowered the weld size at which transition from interfacial to pullout failure mode takes place along with increased load-bearing capacity and higher energy absorption. Thus, it is concluded from mechanical testing that HAZ-softening benefits the lap-shear tensile joint performance of resistance spot welded DP steels by facilitating pullout failures through failure initiation at the SC-HAZ (tempered region). Instrumented nanoindentation testing was employed to further investigate HAZ-softening along the SC-HAZ by evaluating individual phases of ferrite matrix and tempered martensite islands. Although the ferrite matrix presented a slight reduction in hardness at nanoscale, higher reduction in hardness (softening) resulted for tempered martensite; thus confirming that tempered martensite is the major contributor to softening at micro-scale. A comparison between nanohardness and microhardness testing made at different distances from the line of lower critical temperature of transformation (Ac1) allowed revealing the actual extension of the SC-HAZ. In this regard, good correlation was obtained between nanohardness results along the SC-HAZ and the microstructural changes analyzed by electron microscopy (i.e., the tempering of martensite occurring at various distances far from Ac1 was correlated to low temperature tempering of dual phase steels). An in-depth analysis of the tempering of martensite phase at high temperature in DP steel subjected non-isothermal conditions i.e., rapid heating, extremely short time at peak temperature and rapid cooling (resistance spot welding), has been carried out mainly through analytical transmission electron microscopy (TEM). In addition, an isothermal tempering condition (i.e., slow heating and long time at peak temperature) in DP steel has been evaluated for complementing the analysis. Both non-isothermal and isothermal conditions have been correlated to the softening behaviour. TEM analysis of the base metal in the DP steel indicated that the morphology of the martensite phase is dependent on its carbon content, and its tempering characteristics are similar to that of equal carbon containing martensitic steel. The isothermally tempered structure is characterized by coarsening and spheroidization of cementite (θ) and complete recovery of the martensite laths; whereas precipitation of fine quasi-spherical intralath θ-carbides, coarser plate-like interlath θ-carbides, decomposition of retained austenite into elongated θ-carbides, and partial recovery of the lath structure were observed after non-isothermal tempering of DP steel. This difference in tempering behaviour is attributed to synergistic effect of delay in cementite precipitation due to higher heating rate, and insufficient time for diffusion of carbon that delays the third stage of tempering process (cementite coarsening and recrystalization) during non-isothermal. The finer size and the plate-like morphology of the precipitated carbides along with the partial recovery of the lath structure observed after non-isothermal tempering strongly influenced the softening behaviour of DP steel. The chemical analysis of θ-carbides through extraction replicas for three different DP steels revealed that the chemistry of the carbides is inherited from the parent DP steel during non-isothermal tempering at high temperature confirming that non-isothermal tempering DP steel is predominantly controlled by carbon diffusion.

Recent studies of fcc metals with dense twins (~10 nm spacing) have revealed impressive mechanical properties, along with improved ductility and electrical conductivity in comparison to nanocrystalline metals with similar feature sizes. Many important fcc metals could benefit from these “nanotwinned” microstructures, however, not all fcc metals readily form such twins. The tendency of fcc metals to form twin boundaries is related to the twin boundary energy; those with low twin boundary energy, such as silver (Ag), easily form twins. Increasing twin boundary energy interferes with twin formation, to the point that in metals with high twin boundary energy, like aluminum (Al), twins are quite rare. This thesis focuses on the synthesis of nanotwinned Ag and Al via physical vapor deposition. Nanotwinned Ag is readily fabricated, however, a template approach had to be developed to induce twins in Al. The microstructures and their relationships to observed mechanical properties are also discussed. Grain boundaries interfere with dislocation transmission by posing a slip system discontinuity between grains. Twin boundaries are a special class of grain boundaries in which the grains on either side of the boundary are related by mirror symmetry. Twin boundaries inhibit dislocation transmission, providing strength in the same manner as grain boundaries. However, their symmetrical structure reduces the free volume and grain boundary energy. Accordingly, coherent twin boundaries are often more energetically stable than grain boundaries, and their coherency allows plasticity mechanisms to remain active under conditions where such mechanisms may be inhibited at grain boundaries. Hence, twin boundaries may provide a metal with unique combinations of high strength and good ductility, conductivity, and thermal stability.

No description available.

This thesis describes the examination of novel block copolymers that contain Ru(bpy)32+ complexes incorporated into one block of diblock copolymers made by ROMP. With the intent of exploring the potential usefulness of these interesting materials in applications such as light-harvesting and sensing, a systematic study of the solution self-assembly, luminescence properties, and the ability of the metal complex to engage in electron and energy transfer reactions has been conducted. / The solution self-assembly of block copolymers that contain Ru(bpy) 32+ complexes was examined first. Using a series of these block copolymers, a detailed study of the effects of block length, block ratio, polymer concentration and solution conditions on the copolymer self-assembly is presented. Using TEM, a number of morphologies were reproducibly observed including star micelles, large compound micelles, tubules, and interestingly, vesicles. These structures all contain the metal complex Ru(bpy)3 2+ within their core domains. / The luminescence properties of two block copolymers containing Ru(bpy) 32+ were examined: one polymer self-assembled into star micelles, the other into vesicles. Comparison of the unassembled polymer chains and the self-assembled polymers indicated that self-assembly, and confinement of the Ru(bpy)32+ complexes into the core domains of the aggregates, did not seriously adversely affect the luminescence properties of the metal complex. Measurement of the luminescence lifetime decay of the polymers suggested that energy migration occurred among the metal complexes along the polymer chain. The ability of the metal complexes within self-assembled structures to participate in electron transfer reactions with small molecules was also explored. It was found that from within the core domains of self-assembled structures, the Ru(bpy)32+ complexes could still engage in electron transfer reactions with molecules on the outsides or the insides of the aggregates, likely a result of energy migration. / The ability of Ru(bpy)32+ complexes within the cores of micelles to participate in energy transfer was explored. Micelles were formed in aqueous solutions using polymers that possessed both the metal complex and a water-soluble block. Several methods were attempted to encapsulate two molecules, a derivative of coumarin 2 and an Os(bpy)3 2+-based molecule, inside these micelles. It was observed that Ru(bpy) 32+ could act as an energy acceptor from the coumarin derivative, and could act as an energy donor to the osmium-based complex. Encapsulation of the small molecules greatly enhanced the efficiency of energy transfer, by non-covalently bringing the small molecules in close proximity to the Ru(bpy)32+ complexes. / Polymers were synthesized that contained a Ru(bpy)3 2+-based block and were terminated with the molecular recognition unit biotin. These polymers, upon self-assembly, formed micelles with biotin groups on their periphery. The addition of the protein streptavidin, which has a strong binding affinity for biotin, resulted in the aggregation of the self-assembled structures. This established the potential for self-assembled metal-containing aggregates to form higher-order structures. / Early work is presented in Appendix A involving block copolymers that contain hydrogen-bonding groups. Several methods were attempted to elucidate the solution morphologies of these polymers, namely IR, 1H NMR, DLS, and pyrene fluorescence. The transition of this initial work to polymers that contain the Ru(bpy)32+ complex is also described.

The oligomerisation of protein subunits is an area of much research interest, in particular the relationship to protein function. In the last decade, the potential to control the interactions involved in order to design constructs with tuneable oligomeric properties in vitro has been pursued. The subject of this thesis is the quaternary structure of members of the peroxiredoxin family, which have been seen to assume an intriguing array of organisations. Human Peroxiredoxin 3 (HsPrx3) and Mycobacterium tuberculosis alkyl hydroperoxide reductase (MtAhpE) catalyse the detoxification of reactive species, preferentially hydrogen peroxide and peroxynitrite respectively, and form an essential part of the antioxidant defence system. As well as their biomedical interest, the ability of these proteins to form organised supramolecular assemblies makes them of interest in protein nanotechnology. The work described focusses on the elucidation of the quaternary structure of both proteins, resolving previous debates about their oligomeric state. The factors influencing oligomerisation were examined through biophysical characterisation in different conditions, using solution techniques including chromatography, light and X-ray scattering, and electron microscopy. The insight gained, along with analysis of the protein-protein interfaces, was used to alter the quaternary structure through site-directed mutagenesis. This resulted in a level of control over the protein’s oligomeric state to be achieved, and novel structures with potential applications in nanotechnology to be generated. The activity of the non-native structures was also assessed, to begin to unravel the relationship between peroxiredoxin quaternary structure to enzyme activity. The formation and structure of very high molecular weight complexes of HsPrx3 were explored using electron microscopy. The first high resolution structural data for such a complex is presented, analysis of which allowed the theory of an assembly mechanism to be proposed.

No description available.