Joanna McKittrick - US grants

Rapid solidification of oxide ceramics is a novel processing technique which can yield materials with microstructures and properties which cannot be obtained by other processing techniques. This proposal is for the purchase of an induction heating unit to heat oxides to their melting point and then rapidly solidify them. These materials have enormous potential for structural, magnetic, electrical, and superconducting applications as well as producing glasses of unique compositions. Two classes of oxide systems, ZrO2 containing ceramics and MBa2Cu3O7-x (M=Y,Dy,Gd) superconductors will be melted by induction heating and rapidly solidified by twin roller quenching. These materials will be examined by differential thermal analysis, scanning and transmission electron microscopy and x-ray diffraction.

9711044 McKittrick The development of high quality ferroelectric thin films is one of the main challenges to achieving giga-bit storage capacity on dynamic random access memory (DRAM) devices. Bulk ferroelectrics such as BaTiO3 are well characterized; however, the ferroelectric properties of thin films are not understood at a fundamental or even technical level. The microstructural features such as grain size, grain orientation (polycrystalline vs. epitaxial), stoichiometry, thickness of the film, residual stress, dopant concentrations and surface roughness have not been systematically studied or characterized. In order to use ferroelectric thin films, they must be sandwiched between conductive electrodes. These electrodes have been found to be the source of current leakage, increasing fatigue and aging damage. To fully exploit the optimized thin film structures, a basic understanding of the electrode is also necessary. This two year proposal seeks to systematically investigate the microstructure-electrical property dependence of paraelectric BaxS l-xTiO3, for megabyte DRAM applications. The objectives of this work are fourfold: (A) to optimize a conductive oxide electrode for the deposition of the ferroelectfic films, (B) to quantify the role of stoichiometry, grain size, thickness, and residual stress in thin film ferroelectrics and optimize the electrical properties, (C) investigate the effect of adding donor dopants to BaxSrl-xTiO3 with the goal of improving the electrical properties and (D) to fabricate superlattice structures of BaTiO3 and SrTiO3 and correlate the microstructural features with the electrical properties. This work will be performed at UC-San Diego and the Institute of Physics in Ensenada, Mexico which have different but complementary facilities. ***

9972509
McKittrick

Photoluminescence is the process by which photons (infrared , visible, ultraviolet [UV]) are emitted from a solid under excitation by higher energy photons. Rare earth activated oxides (e.g., europium-doped yttrium oxide are a class of solids that emit visible light when bombarded with UV photons. These materials have application in information displays, lighting, and scintillators. The luminescence emission intensity, spectral energy distribution (intensity as a function of wavelength), and luminescence decay rate are influenced by the application of temperature or stress. Previous work on quantifying these effects has been done almost exclusively on single crystals. Technologically important materials, such as polycrystalline thin-films, have not been examined. A better understanding of the effect of external influences on the luminescence properties of thin- films is necessary for these materials to have more wide-spread industrial use. The objective of this project is twofold: (1) determine the applicability of theoretically predicted luminescence behavior to experimental values obtained on rare earth doped yttrium oxide single crystals or polycrystalline compacts as a function of temperature and stress and to (2) identify and quantify the temperature, stress and microstructure dependent luminescence properties of thin-films and compare these values to what was obtained previously. In the research, luminescence property data on single crystals of rare earth activated yttrium oxide (and/or polycrystalline yttrium oxide as a function of temperature and stress wil be obtained and compared with the currently available fundamental equations predicting the behavior; thin-films will be fabricated and the luminescence properties examined as compared with the single crystal data as a function of temperature and stress; the effect of grain boundary density, dislocation density, segregation of activators and grain size on the thin-film luminescence properties will be quantified; and a model and predictive relationships will be provided that are based on the fundamental equations that include the effect of temperature, microstructural features and residual stress on the luminescence properties of thin-film rare earth activated yttrium oxide.
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Luminescent solids are used in many consumer applications, the most well known of these is as phosphors for computer display screens. This project will examine and try to understand the behavior of one class of these materials in order to increase the efficiently and thus decrease the cost of the materials. The project will be carried out by two researchers, one an expert in luminescent materials and one an expert in mechanical properties.
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This award from the Instrumentation for Materials Research program to the University of California San Diego is for the acquisition and installation of a cold cathode field emission gun scanning electron microscope(FEG-SEM) with analytical capabilities for the Electron Microscopy Facility of the Materials Science Program, part of the Jacobs School of Engineering at the University of California San Diego (UCSD). The new instrument will enhance existing and new research projects currently active at UCSD in the engineering, physics and chemistry departments, as well as at the Scripps Institute of Oceanography. The FEG-SEM will provide high beam stability, low energy fluctuation, low beam current and high brightness in a range of accelerating voltages, features that are required for imaging nanoscale features in electronic, magnetic, optical, structural, organic and biological materials. The instrument will enhance both graduate and undergraduate research and education. The graduate students will benefit from hands-on exposure to a state-of-the-art microscope that will aid significantly in their research projects. Undergraduates will particularly benefit from this class, as it will be offered to upper division students who have a materials emphasis in their major program (currently available in mechanical, electrical, physics and chemistry departments).

This award from the Instrumentation for Materials Research program to the University of California San Diego is for the acquisition and installation of a cold cathode field emission gun scanning electron microscope(FEG-SEM) with analytical capabilities for the Electron Microscopy Facility of the Materials Science Program, part of the Jacobs School of Engineering at the University of California San Diego (UCSD). The proposed equipment will replace the existing Cambridge 360 SEM, now 10 years old, and provide state-of-the-art capabilities. This system currently supports the research programs of faculty from departments and research units campus wide. The Materials Science Program will manage the new SEM and it will be available to all UCSD affiliated personnel and the outside community on an hourly fee basis.

The new instrument will enhance existing and new research projects currently active at UCSD in the engineering, physics and chemistry departments, as well as at the Scripps Institute of Oceanography (SIO). The FEG-SEM will provide imaging of detailed structures coupled with the elemental analysis capabilities; it is a crucial tool for modern materials research and for training the next generation of engineers and scientists.

The instrument will enhance both graduate and undergraduate research and education. The graduate and undergraduate students will benefit from hands-on exposure to a state-of-the-art microscope. A graduate level course in scanning electron microscopy will be introduced yearly into the Materials Science curriculum and will be available to all graduate students at UCSD and SIO. Undergraduates will particularly benefit from this class, as it will be offered to upper division students who have a materials emphasis in their major. In summary, the new instrument will provide a much-needed research and teaching tool by providing image and analytical capabilities not currently available to students on the UCSD campus.

NON-TECHNICAL DESCRIPTION: The synthetic materials (metals, polymers, ceramics, and composites) developed in research laboratories during the past century have revolutionized life. However, at present, the possibilities of designing and producing synthetic materials with improved performance are being exhausted. Therefore researchers are turning their attention to nature, trying to understand it better, with the goal of mimicking its designs. This emerging field of Biomimetics seeks to design properties into materials modeled after biological systems. The proposed study addresses the abalone shell that is highly prized as a source of nacre, or mother-of-pearl. Yet, is comprised of 95% chalk, which is weak and brittle. The complex nanostructure and microstructure of the shell are such that adding 5% of an organic glue leads to a toughness that is orders of magnitude higher than that of chalk. The goal of the proposed research is to understand, at the fundamental level, why the shell is so strong and to use this knowledge to develop a new generation of ceramic composites with superior properties.
TECHNICAL DETAILS: A four-year program with strong characterization and analysis components will be carried out: development of new micro- and nano-mechanical testing methods to establish viscoelastic mechanical response of the protein layer(s) that act as an adhesive between tiles. This approach requires the use of atomic force microscopy, nanoindentation and nanoscratch tests, a miniaturized shear test (analogous to the meso scale test used by the PI), modeling mechanical responses through novel mechanisms incorporating viscoelastic response of organic layer; identification and quantification of the changes in the organic layers that occur after deformation using micro-Raman spectroscopy and FTIR, and identification of mechanisms by which tiles grow in "Christmas tree" pattern and transmit their orientation from level to level. Based on these observations, a detailed growth model for aragonite (the orthorhombic phase of CaCO3) will be developed. The ultimate goal is the use of biologically-inspired techniques to synthesize new materials. Research will be carried out at University of California San Diego, Universidad Nacional Autonoma de Mexico, and the Lawrence Livermore National Laboratory. Graduate and undergraduate students from San Diego and Mexico will be involved in the learning process, as well as high school students. The Preuss School, a charter high school that is designed as in intensive college preparatory educational program for low-income students in the grades 6-12, will be involved. These students come from families whose parents have not received college training. Two senior high school students will work during the school year (4-6 hrs/week, as allowed by The Preuss School) and full time during their summer breaks (6 weeks). It is emphasized that no abalone are harmed or killed for these experiments.
This project is co-funded by the Office of International Science and Engineering and the Division of Materials Research.

TECHNICAL: Abalone shell is tough and fracture resistant. The structure has a brick-and-mortar organization with calcium carbonate (aragonite) bricks surrounded by the organic mortar. The toughness is attributed to the organized arrangement of the aragonite platelets and nanoscale features present at the mineral/organic interface. These nanoscale features include mineral bridges, nanoasperities on the surface of the aragonite tiles and the viscoelastic/adhesive properties of the organic. The main objectives of this work are to fabricate model ceramic/polymer laminates, identify and quantify the contributions of microstructural features that have been attributed to the toughening of the shell. This work is expected to lead to a new class of bioinspired composite materials that are strong, hard and fracture resistant. Students will be cross-trained in biology, materials science and nanoscience.

NON-TECHNICAL DESCRIPTION: Bioinspired materials are emerging as a new class of synthetic structures. The abalone shell is tough and fracture resistant, despite being built from weak constituents: organic matter and a soft mineral (ceramic). Under magnification, the shell has a "brick-and-mortar" structure of mineral bricks and organic mortar. Bioinspired synthetic layered materials based on this structure are expected to have exceptional toughness and fracture resistance. Fabrication and testing of layered organic (polymer) / ceramic structures that duplicate the structure of the abalone shell is the main focus of research. This work is expected to lead to a new class of composite materials that are strong, hard and fracture resistant. Graduate, undergraduate and high school students will be cross-trained in biology, materials science and nanoscience. New classes will be introduced into the curriculum and outreach to underrepresented student populations is a part of this project.

NON-TECHNICAL DESCRIPTION: Lighting accounts for 22% of the total US electrical energy use, which translates to $50 billion per year spent on lighting accompanied with 130 million tons of carbon emitted into the atmosphere from fossil fuel plants. Solid state lighting, based on blue-emitting light emitting diodes with a luminescent powder (phosphor), has emerged as highly efficient, long lasting light sources to replace incandescent and fluorescent lighting. The phosphor market in the US for white-emitting LEDs is currently $500M/year and is expected to reach $1B/year by 2015. Identifying new phosphors in a reliable and systematic way with high quantum efficiency and thermal stability is crucial for these new energy saving devices. Nanophosphors represent an exciting opportunity to reduce light scattering, thereby improving the extraction efficiency. This work is interdisciplinary and spans the fields of materials science, optical properties, chemistry, and atomic scale modeling that involves both experiments and modeling. Graduate students are trained in sophisticated electron microscopy techniques, theoretical and computational methods. Diversity efforts are continued and strengthened. The involvement of students from a Hispanic-serving Institution and a middle/high school that serves low-income students are included. New classes are developed for the graduate curriculum.

TECHNICAL DETAILS: Solid state lighting, based on blue-emitting (450 nm) light emitting diodes (LEDs) with a luminescent powder (phosphor), has emerged as highly efficient, long lasting light sources to replace incandescent and fluorescent lighting. New diodes that emit in the near UV (370-410 nm) have recently been recognized as chips that could improve the extraction efficiency of the light source. This new development requires the discovery of new phosphor systems in the nano-sized range to fully exploit this new technology. The phosphors used in this work are wide band gap materials (hosts) that contain a small amount of activator (rare-earth element). Depending on the host:activator combination, colors across the visible spectrum can be obtained. This project aims at validating the following three hypotheses: (1) using an empirical approach combined with first principles modeling, new high quantum efficiency, thermally stable phosphors can be identified for near UV LED white-emitting light sources, (2) the low quantum efficiency of nanosized phosphors can be determined and perhaps overcome and (3) modeling using a combination of semi-local and hybrid density functional theory will provide insight on the mechanisms for photon absorption and emission of new phosphor systems, the phase, chemical and thermal stability and on the quantum efficiency of nanosized phosphors. These hypotheses are tested by conducting by a variety of experimental and computational tasks: (1) the design of phosphors in which the excitation energy lies in the near UV spectral range of 370-410 nm, (2) the design of phosphors in which sensitization is via the excitation of complex functional groups, (3) using a combination of analytical tools, a systematic approach will be conducted to evaluate the factors behind the low quantum efficiency of nanosized phosphors (< 200 nm). Surface and bulk analyses will identify the local environment of the activator and the traps that quench the luminescence and (4) a hierarachy of first principles methods are used to investigate the phase stability, aqueous stability, thermal stability and electronic structure of the phosphor materials to be synthesized and tested experimentally. The theoretical calculations are used to guide and interpret experiments and also to guide which compositions and structures of the phosphor materials are most promising for UV LED applications.

Non-Technical Abstract: This collaborative project award by the Biomaterials program in the Division of Materials Research to University of Illinois Urbana-Champion and University of California San Diego is to investigate a new model of bone as a material that the two phases in bone, proteins and minerals, are interpenetrating (continuous), and to explore what implications this hypothesis has on bone's mechanical properties, including strength and resistance to fracture. Bone is made of collagen and other proteins, nano-sized minerals and water, all hierarchically self-assembled. Bone has excellent properties due to its complex hierarchical structure; it is strong, stiff, tough and light weight. However, factors contributing to these superior properties are still not well understood. This fundamental and interdisciplinary study will include state-of-the art experiments and multiscale modeling, and will focus on porcine developing bone (0-48 months) which exhibits significant changes in its structure and composition with age. Results from this research will lead to better predictions of bone quality in humans, which is still an outstanding clinical issue, and will guide in the design of novel synthetic composite materials with superior mechanical properties for applications in biomedical, transportation and energy fields. Students from diverse backgrounds will participate in this cutting-edge research. New courses will be developed and short courses and other presentations will be given to technical and lay audiences.


Technical Abstract: Bone is a biological nanocomposite material made of collagen and other proteins, hydroxyapatite minerals and water, all hierarchically assembled. This complex structure gives bone its superior properties (strong, stiff, tough and light weight). However, the contributing factors are still not well understood. In this collaborative project, researchers will test two hypotheses: 1) bone is a composite material made of interpenetrating organic and mineral phases; and 2) synthetic bioinspired composites with interpenetrating phases will have superior mechanical properties, compared to composites with a dispersed reinforcing phase. More specifically, these investigators will determine if the interpenetrating model is valid for bone with varying degrees of mineralization and different microstructures via multiscale experiments and modeling. Developing porcine bone (0-48 months old), which exhibits a range of microstructures and mineral contents will be studied as part of this project. Strains at the collagen/mineral level as a function of applied stress, using high energy x-rays diffracting at small- and wide-angles, will be compared with those obtained theoretically. In addition, synthetic bioinspired materials with interpenetrating phases will be designed and tested, and compared their properties to those of composites with a dispersed reinforcement. This project is expected to provide fundamental understanding of bone's hierarchical structure, which will lead to better predictions of bone quality and will guide the design of new bioinspired synthetic composites for different applications. Students from diverse backgrounds are expected to participate in this cutting-edge research, including the students from Title V Hispanic-serving high schools. New courses will be developed, and presentations will be given to technical and lay audiences.

NON-TECHNICAL DESCRIPTION: Lighting home and commercial buildings in the US account for 6% of the total US electrical energy use and 15% of the total electrical energy expenditure, which translates to $50 billion per year. There is an outstanding opportunity to reduce this cost by replacing current incandescent and fluorescent lighting with white light emitting diodes (LEDs). However, the color quality and efficiency must be improved further. These LED-based light bulbs produce white light by using a luminescent powder called a phosphor, coating on top of a near-ultraviolet (UV) or blue-emitting LED chip. The phosphor is a key component in these devices because it is critical for the overall efficiency and color of these bulbs; unfortunately, there are only a few viable phosphors available for this application today. Therefore, it is prudent to discover new phosphor systems to fully realize the conversion to new efficient lighting. The researchers are addressing this challenge by developing computational and data-driven methods to predict the properties of phosphors. This approach allows the directed discovery of new phosphors with enhanced optical response. This grant also supports extensive scientific education including sponsoring numerous research opportunities for high school and undergraduate students. These students, mostly from underrepresented groups, are learning how to synthesize and characterize phosphors as well as the importance of this energy-efficient technology. The graduate students supported by this work are trained to pursue opportunities in the optoelectronics industry and also across the technology sector where materials science play a crucial role. Finally, the computational products of this research are disseminated through open-source platforms, so all researchers benefit from the scientific developments.

TECHNICAL DETAILS: Replacing a traditional light bulb with an energy-efficient, phosphor converted-light emitting diode is one of the easiest ways to decrease electricity consumption. This goal requires the discovery of new phosphor systems, which convert the nearly monochromatic LED light into a broad spectrum white light, to fully make use of this technology. The phosphors investigated in this project are based on wide band gap materials (hosts) that contain a small amount of activator (rare-earth element). Depending on the host:activator combination, colors across the visible spectrum are obtained. The central hypothesis driving this research is that the quantum efficiency and thermal quenching resistance of a phosphor are related to the local coordination environment of the activator ion. This research employs advanced first-principles calculations, local structure analysis using X-ray and neutron scattering, and data science to establish a quantitative understanding of this relationship. Modeling these properties using computational tools and confirming the predictions through materials synthesis and characterization produces a feedback loop where our research results are improved with each discovery. The outcome is a series of design rules that will lead to the discovery of new phosphors with superior optical properties.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Keratin is a protein found on the outer covering of most animals, such as hair, nails, horns, hooves, beaks, and feathers. Keratinous materials are among the most robust biological materials, which have been optimized by nature for their functions. For example, horse hooves are impact resistant while being lightweight. The hooves can withstand powerful and dynamic forces, but the fundamental reasons that give rise to this property are not known. This research will significantly advance understanding of how hooves absorb energy and pave the way to build new impact-resistant, bioinspired materials. Designs by bioinspiration involve using ideas from nature and employing synthetic materials to create new engineering composite structures. Impact resistant materials are essential for a wide range of applications, which include body protection (body armor vests and helmets), defense (blast resistant structures), automotive industry (crash-resistant vehicles), aerospace (aircraft bird strikes), and space exploration (protection against space debris). This transdisciplinary research and educational program involving mechanical engineers, materials scientists, and biologists, includes the experimental and computational studies of keratin-based biological systems and designs and fabrication of new engineering materials with a superb energy absorption performance during high-speed impacts. The participating graduate students will be paired with undergraduate researchers during the academic year and high school students during the summer. Inclusion of underrepresented minority and women students is planned. The graduate students will have the unique experience of getting trained and using powerful instruments at national laboratories.

The objectives of this research project are to test the following hypotheses:
1. The hierarchical structure of hooves assists in energy absorption and resists high-speed impacts,
2. Multiscale modeling can predict the compression and impact behaviors of hooves,
3. Synthetic hoof-inspired materials will have outstanding impact resistant properties.
This research integrates concepts and methods from diverse fields (biomechanics, materials science and engineering, and biology). The methods and approaches include the state-of-the-art characterization of keratin-based materials (small and wide angle X-ray scattering, nano-and micro-computed tomography, small angle neutron scattering, electron microscopy, nano- to macroscale mechanical testing), development of new constitutive models, and designing, building and testing of impact resistant bioinspired materials based on the exceptional properties of hooves. This project's approach is transformative as it incorporates ideas from nature (accelerates discovery), utilizes a computational materials science approach (generates data) to screen parameter space and create a catalog of structure-property relations, and employs neural network approach to find optimal designs.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.