Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session W5: Functional Ceramics: the Nano/Microstructure-Property Relationship in Electronic, Optical, Biological and Structural Materials |
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Sponsoring Units: FIAP Chair: Robert Marzke, Arizona State University Room: LACC 502B |
Thursday, March 24, 2005 2:30PM - 3:06PM |
W5.00001: Bioinspired Self-Healing Materials Invited Speaker: Synthetic materials are designed to satisfy only one or two functions, but biologically produced ones are multifunctional and have properties (e.g., self-replicating, self-healing) that have yet to be introduced into man-made materials. The objective of this lecture will be to provide an understanding of the important processes for controlling materials properties through nano- and microstructural design and processing with the goal of attaining multifunctionality. A case study will be on the possibility of producing structural materials with self-healing characteristics. In an effort to mimic self-repair functions of living systems, we have been working with self-assembling complex fluids that respond to fields generated by the defects and deposit materials at the site of the defect. Presently, the techniques are limited to certain materials systems as coatings or thin films. We partially mimic the process of blood clotting as a process of colloidal aggregation at a defect site. We show that under the influence of an electrical field, colloidal particles detect a defect and aggregate at the defect site to form a protective layer. The basis of this process is the electrohdrodynamic flow generated by the inhomogeneities. We then make this a permanent protective layer through the electrodeposition of a metal binder in the interstitials of the colloidal aggregate. [Preview Abstract] |
Thursday, March 24, 2005 3:06PM - 3:42PM |
W5.00002: Metastable Phase Evolution in Oxide Systems Invited Speaker: Multi-component ceramics are often synthesized by routes that facilitate mixing at the molecular scale and subsequently generate a solid product at low homologous temperatures. Examples include chemical and physical vapor deposition, thermal spray, and pyrolytic decomposition of precursor solutions. In these processes the solid evolves rapidly from a highly energized state, typically in a temperature regime wherein long-range diffusion is largely constrained and the equilibrium configuration can be kinetically suppressed. The resulting product may exhibit various forms of metastability such as amorphization, nanocrystallinity, extended solid solubility and alternate crystalline forms. The approach allows access to novel combinations of structure and composition with unprecedented defect structures that, if reasonably durable, could have properties of potential technological interest. Understanding phase selection and evolution is facilitated by having a suitable reference framework depicting the thermodynamic hierarchy of the phases available to the system under the relevant processing conditions. When transformations are partitionless the phase menu and hierarchy can be readily derived from the relative position of the T0 curves/surfaces for the different pairs of phases. The result is a phase hierarchy map, which is an analog of the phase diagram for partitionless equilibrium. Such maps can then be used to assess the kinetic effects on the selection of metastable states and their subsequent evolution. This presentation will discuss the evolution of metastable phases in oxides, with emphasis on systems involving fluorite phases and their ordered or distorted derivatives. The concepts will be illustrated primarily with zirconia-based systems, notably those of interest in thermal barrier coatings, fuel cells and ferroelectrics (ZrO$_2$-MO$_{3/2}$, where M = Y, Sc, the lanthanides and combinations thereof, as well as ZrO$_2$-YO$_{3/2}$-TiO$_2$, ZrO$_2$-TiO$_2$-PbO, etc.). Of particular interest are the durabilities of metastable phases in systems that operate at high temperature, their decomposition paths and the implications to their functionality. [Preview Abstract] |
Thursday, March 24, 2005 3:42PM - 4:18PM |
W5.00003: Nanolayered EUV mirrors for the next generation lithography of integrated circuits Invited Speaker: High reflectivity multilayer mirrors are enabling extreme ultraviolet lithography (EUVL), a leading candidate for next generation semiconductor lithography, to print features smaller than 32 nm. However, the specifications for the lifetime and stability of these multilayer coatings are very stringent and current solutions are not satisfactory. The lifetime of EUV projection optics is limited by the oxidation of the capping layers while the lifetime of the condenser optics is limited by erosion, contamination, and thermal stability. Ceramic materials offer a new solution space, and in this talk I will present some preliminary studies that investigate their performance as protective, capping layers as well as materials to enhance multilayer thermal stability. I will also demonstrate how the microstructure of the capping layers affects the physical properties of the multilayers, such as reflectivity. Finally, the microstructural changes within the multilayers, designed for high thermal stability operation, will be discussed. For example, the microstructure of these multilayers changes as a function of the annealing temperature. With an appropriate multilayer design, all of the desired properties can be achieved and maintained stable for long periods of time. [Preview Abstract] |
Thursday, March 24, 2005 4:18PM - 4:54PM |
W5.00004: Nanoscale Structure and the Two-timescale Dynamics of Relaxor Ferroelectrics Invited Speaker: Jean Toulouse The structural basis for the original dynamics of relaxor ferroelectrics lies in the development of mesoscopic or intermediate range order, the polar nanoregions (PNR). The formation of these PNRs can itself be related to the atomic site disorder that is characteristic of ferroelectric relaxors. For example, in KTa$_{1-x}$Nb$_{x}$O$_{3}$ (KTN), the niobium ions are off-centered in a [111] direction, and in PbMg$_{1/3}$Nb$_{2/3}$O$_{3}$ (PMN) both Nb and Pb are off-centered, the latter in either a [110] or a [111] direction. These off-center ions can hop or tunnel between different symmetry-related positions and, with decreasing temperature, their motion can become correlated. In PMN, it is obvious that the hopping times of Pb and Nb will be very different because of the large difference in their masses as well as in their off-centering distances. It should therefore not be surprising to observe dynamics on two different timescales, and possibly also on two different length scales, simultaneously. This has a decisive influence on the physical properties of these systems, which are no longer simply a statistical average of the microscopic properties, but are determined at the mesoscopic level. A variety of experimental results suggest the existence of a two-timescale dynamics, which appears to be characteristic of the relaxor behavior. In this talk, we present a selection of the most meaningful results that support this assumption in several relaxor systems (KTN, PMN, PZN): these include Raman and neutron scattering, NMR, dielectric and ultrasonic results. We describe the evolution of the nanoscale structure with temperature and the corresponding evolution of the relaxor dynamics. We show that this evolution is characterized by four stages, a purely dynamic stage, a quasi-dynamic stage, a quasi-static stage and a static or frozen stage, which are also apparent in the macroscopic properties of relaxors. Finally, we point to intriguing similarities between the dynamics of relaxors and that of structural glasses. [Preview Abstract] |
Thursday, March 24, 2005 4:54PM - 5:30PM |
W5.00005: Proteins at the Biomaterial – Electrolyte Interface Invited Speaker: Proteins adsorb rapidly onto solid and polymeric surfaces because the association process is in the vast majority of cases energetically favourable, i.e. exothermic. The most common exceptions to this rule are hydrophilic interfaces with low net charge and high mobility, e.g. immobilized PEGs. Current research in the research area tries to understand and control unwanted and wanted adsorption by studying the adsorption kinetics, protein surface binding specificity, protein exchange at interfaces, and surface protein repulsion mechanisms. In blood plasma model systems humoral cascade reactions such as surface mediated coagulation and immune complement raise considerable interest due to the immediate association to blood compatibility, and in tissue applications the binding between surfaces and membrane receptors in cells and tissues. Thus, the understanding of interfacial events at the protein level is of large importance in applications such as blood and tissue contacting biomaterials, in vitro medical and biological diagnostics, food industry and in marine anti-fouling technology. Well described consequences of adsorption are a lowered system energy, increased system entropy, irreversible binding, conformational changes, specific surface/protein interactions, and in biomedical materials applications surface opsonization followed by cell-surface interactions and a host tissue response. This lecture will deal with some mechanisms known to be of importance for the adsorption processes, such as the influence of surface chemistry and surface energy, the composition of the protein solution, the Vroman effect, and residence time. Examples will be shown from ellipsometric experiments using different model surfaces in single/few protein solutions, and specific attention be given to blood serum and plasma experiments on coagulation and immune complement at interfaces. [Preview Abstract] |
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