NRC Postdoctoral AssociateshipThe National Research Council, through its Associateship Programs Office, conducts a national competition to recommend and make awards to outstanding scientists and engineers at the postdoctoral level for tenure as guest researchers at participating federal laboratories. In the program sponsored by the National Institute of Standards and Technology (NIST), a Research Associate is a resident researcher and a temporary employee of NIST. Associateships are analogous to fellowships at the postdoctoral level in universities, and are not intended to be permanent professional career positions. Opportunities at NIST are open only to citizens of the United States. Permanent residency status does not qualify as citizenship. Research Associateships at NIST are awarded only to persons who have held their doctorate less than five years at the time of application, and are offered on a two-year term basis. An evaluation is conducted after one year to ensure the Associate is making suitable progress.
Each applicant must submit a research proposal that relates to a specific opportunity for research at NIST. A proposal may be submitted at any time, but reviews are conducted twice each year in February and August. One or more Advisers are associated with each research opportunity. An Advisor is a person who conducts or directs research in that particular field, and who will act as a surrogate for the NRC in monitoring an Associate. All matters relating to an Associate's research program fall under the Adviser's purview. A proposal must first be approved by the Adviser and endorsed by the NIST Program Representative to be eligible for an award.
For more detailed information on eligibility requirements, salaries and benefits, and the proposal review process and schedule, go to the NIST-NRC web site.
Opportunities for Research
The following abstracts describe areas of research in the Metallurgy Division for which Associateships may be awarded. Before writing a proposal, applicants are advised to communicate directly with the Adviser, who can provide more specific information on current research and available facilities.
Microstructural Characterization and Structure-Property Relationships
Research Opportunity: 50.85.51.B1961
Adviser Information: Bonevich, John, Bendersky, Leonid A.
Keywords: Transmission electron microscopy; Alloys; Intermetallic materials; Metals and metallurgy; Structural biomaterial
Research emphasizes characterization of the microstructure of single- and multiphase materials to determine the relationship of structure with properties. Several characterization techniques are available, with special emphasis placed on the tools of optical and analytical and high-resolution transmission electron microscopy. Materials range from strength aluminum alloys and materials in electronic packaging to biomaterials.
Microstructure and Property Relationships in Materials
Research Opportunity: 50.85.51.B3830
Adviser Information: Bonevich, John
Keywords: Interface; Structure; Properties; HRTEM; AEM; Thin films; Nanostructure
Research focuses on the role of structure and chemistry of interfaces on the properties of metallurgical and ceramic systems. Characterization techniques include high resolution and analytical transmission electron microscopy coupled with compositional mapping on the atomic scale. Research programs include magnetic spin valve materials, thin-film ferroelectrics, multilayer nanostructured materials, as well as microstructure and properties of on-chip interconnects in ultralarge-scale integrated circuits.
Atomic Structure and Kinetics at Interfaces in Solids
Research Opportunity: 50.85.51.B5601
Adviser Information: Warren, James A.
Keywords: Electron microscopy; Simulation; Grain boundaries; Metal surfaces; Sintering; Grain growth
Much has been learned in recent years on the atomic scale from experiment and simulation about the structure and motion kinetics of interfaces which casts doubt on many long held principles about driving forces and interfaces' response to them. Research has focused and will continue to focus on individual puzzles, such as grain rotation during grain growth, diffusion induced grain boundary motion, curvature driven motion, effects of nonhydrostatic stress, massive and transformations; although a fundamental rethinking is always a possibility.
Mechanisms and Kinetics of Phase Transformations in Metals
Research Opportunity: 50.85.51.B1957
Adviser Information: Boettinger, William J., Warren, James A.
Keywords: Alloys; Fracture mechanics; Metal solidification; Phases and phase transitions; Vapor deposition
A broad investigation is continuing on all aspects of phase changes including nucleation, growth, spinodal decomposition, diffusion, strains, defects, interface structure and mobility, and for all phase changes including solidification, vapor deposition, electrodeposition, solid-state precipitation, order-disorder, and coarsening. The object is to understand the mechanism in order to influence kinetics and morphologies and thereby the properties of alloys.
Nonequilibrium Interfaces
Research Opportunity: 50.85.51.B1962
Adviser Information: Warren, James A., Boettinger, William J.
Keywords: Metals and metallurgy; Phase equilibria; Thermodynamics
During heat treatment of materials, there exist many situations in which interfaces can be modeled as being at equilibrium or near equilibrium. Nevertheless, it has been recognized that complex processes and structures at interfaces can occur during fabrication of multicomponent or multiphase materials when the system is not at equilibrium. For example, nonequilibrium interfaces develop during fabrication of composites, during solder wetting and spreading, liquid-phase sintering, and in other applications. Descriptions will be sought for the thermodynamics and kinetics of nonequilibrium interfaces. In addition to understanding interface processes, a further goal is the development of predictive models that could provide guidelines for engineering materials with specific physical, chemical, and mechanical properties.
Phase Field Modeling Tools and Bridging Length Scales
Research Opportunity: 50.85.51.B5602
Adviser Information: Warren, James A., Boettinger, William J.
Keywords: Phase field methods; Solidification; Theory and modeling
This project examines the use of order parameter techniques to model the evolution and characterization of microstructure in materials. Order parameter techniques, of which the phase field method has become a well-known example, have become the pre-eminent method for modeling the microstructural evolution that ultimately characterizes a vast array of materials. Efforts over the past few years have attempted to apply phase field models to solidification of alloys (including eutectics), grain growth and coalescence, electrodeposition, vacancy diffusion, and drug delivery. In addition, work has proceeded to identify the proper methods to couple stress and fluid flow to the phenomena listed above.
Solidification Processing of Alloys
Research Opportunity: 50.85.51.B1958
Adviser Information: Boettinger, William J., Warren, James A.
Keywords: Metal solidification; Alloys
To determine the optimum conditions for metals processing, this project is concerned with the effects of solidification conditions on the microstructure and properties of multicomponent alloys. Research involves both theoretical and experimental aspects of solidification, including rapid solidification, with emphasis on (1) evolution of microstructure by processes such as nucleation and growth of alloy phases from the melt and solid-state transformations during cooling; (2) convection in the melt, including its effect in micro- and macrosegregation; and (3) the effect of processing variables on microstructure-sensitive properties in metals.
The Center for Theoretical and Computational Materials Science
Research Opportunity: 50.85.51.B1819
Adviser Information: Warren, James A.
Keywords: Materials science; Models; Computer simulation
The Center for Theoretical and Computational Materials Science (CTCMS) was established in 1994 to accelerate the growth of the emerging field of computational materials science, and to promote its application to industrial problems in materials and material processing. The CTCMS investigates problems in materials theory and modeling with novel computational approaches, creates opportunities for collaboration, develops powerful new tools for materials theory and modeling, and accelerates their integration into industrial research. Current research areas include theory and simulation of phase transformation kinetics and morphology, micromagnetics, bridging length scales in composite materials, foams, dynamics of disordered and partially ordered materials, complex fluids, polymerization, biomaterials, materials reliability, reactive wetting, pattern formation, crystal growth, grain growth, sintering, thin-film growth, solidification, nanostructured materials, and first principles calculation of material properties.
Combinatorial Research of Functional Materials Research Opportunity: 50.85.51.B4819
Adviser Information: Bendersky, Leonid A.
Keywords: Combinatorial thin films; Hydrogen storage materials
Combinatorial research methods hold the promise of rapid identification of new materials with improved properties. The approach requires (1) fabrication of composition gradients or distinct cells in an array (combinatorial library), (2) library measurements with a small probe for important properties, and (3) library analysis for composition-processing-properties correlation. The objective of this project is to develop synthesis of combinatorial thin films, methods to measure properties of interest, and analyze composition-processing-properties correlations. We work with a variety of technologically important materials, including materials for hydrogen storage, for magnetic data storage, and oxide multiferroics.
Hydrogen Storage Materials
Research Opportunity: 50.85.51.B6789
Adviser Information: Bendersky, Leonid A., Kattner, Ursula R.
Keywords: Hydrogen storage materials; Calphad method
The current state-of-the-art of hydrogen storage materials falls far short of targets for vehicular applications; problems include inadequate gravimetric density, temperature and pressure regimes, and kinetics of absorption and desorption process. The objective of this project is to develop high-throughput measurement tools for determining in-situ hydrogen absorption and desorption characteristics. These measurement tools will be utilized in a combinatorial search of metallic materials suitable for storing hydrogen. Along with the experimental work, Calphad-type thermodynamic modeling will be used to understand the stability of the metal hydrides, to identify the correlation between composition and their thermophysical properties, and to analyze the reaction paths of the absorption and desorption process.
Transmission Electron Microscopy Study of Phase Transformations and Crystallography
Research Opportunity: 50.85.51.B1951
Adviser Information: Bendersky, Leonid A.
Keywords: Transmission electron microscopy; Phases and phase transitions
Different methods of analytical and high-resolution electron microscopy are used to characterize microstructures resulting from complex phase transformations. The broad range of studied transformations includes ordering/disordering, displacive (martensitic) reactions, phase separation (spinodal and precipitation) charge ordering, and incommensurate modulations. Research materials range from metallurgical alloys (Ti, Al), to intermetallics, to ceramics. Our recent emphasis is on studying materials for hydrogen storage, metallic glasses, and intermetallics. characterization, measurements, and modeling using the bi-directional reflectance distribution function. Opportunities are available at both Boulder and Gaithersburg campuses.
Copper Metallization
Research Opportunity: 50.85.51.B3962
Adviser Information: Moffat, Thomas P., Stafford, Gery R.
Keywords: Electronic interconnects; Electrodeposition
Industry is currently in the midst of changing from aluminum to copper for semiconductor interconnects. Several manufacturers have adopted electrodeposition technology as the processing method of choice. Research focuses on understanding the impact of various electrolyte additives on the morphological evolution, structure, and properties of the deposited materials. For the future, we are exploring novel schemes for depositing dilute copper alloys with enhanced resistance to electromigration.
Electrodeposition of Strained-Layer Superlattices and Nanowires
Research Opportunity: 50.85.51.B1974
Adviser Information: Moffat, Thomas P., McMichael, Robert D.
Keywords: Crystal superlattices; Electrodeposition; Nanowires; Magnetoresistance
A wide range of magnetic and opto-electronic superlattices and nanowires are being produced by electrodeposition. Emphasis is placed on understanding the relationship between the processing variables and the resulting structural, optical, and magnetic properties. The structure and morphology of these materials are characterized by scattering methods and scanning probe microscopy. Similarly, a wide range of techniques are available for characterizing the magnetic and opto-electronic properties.
Proximal Probe Studies of the Electrode-Electrolyte Interface
Research Opportunity: 50.85.51.B1981
Adviser Information: Moffat, Thomas P.
Keywords: Electrodes; Electrolysis and electrolytes; Electrodeposition; Metal films; Corrosion; Transition metals; Atomic force microscopy; Scanning tunneling microscopy
In situ scanning tunneling and atomic force microscopy are being used to investigate a variety of technologically relevant phenomena, which occur at electrode-electrolyte interfaces. Currently, we are investigating (1) metal on metal epitaxy by electrochemical processing; (2) the role of various organic and inorganic additives in the microstructural evolution of electrodeposited metal films; and (3) the structure and dynamics of corroding interfaces with emphasis on de-alloying phenomenon, and formation and breakdown of passivating oxide overlayers on transition metals.
Simulation of Electrocrystallization Processes
Research Opportunity: 50.85.51.B1982
Adviser Information: Moffat, Thomas P., Stafford, Gery R.
Keywords: Thin films; Metal films; Electrodeposition; Metal crystals
Growth of thin metal films may incorporate processing schemes ranging from electrocrystallization to physical vapor deposition and chemical vapor deposition. Our understanding of the scaling behavior associated with film growth is being revolutionized by recent developments in the characterization of physical vapor deposition by surface science methods coupled with the ability to perform realistic simulations. Placing the electrodeposition process on a foundation similar to that which exists for metal deposition by sputtering, evaporation, and molecular beam epitaxy will require a close coupling between experiment and simulation. Although experimental methods (e.g., scanning probe microscopy and surface x-ray scattering) are beginning to reveal some of the atomistic details associated with film growth, limited emphasis has been placed on exploring the opportunities provided by computer simulation. As long as appropriate consideration is given to the site bias dependence of the electrochemical reduction reaction, realistic simulation of the electrocrystallization process should be accessible.
Superconformal Deposition Processes for Integrated Circuits
Research Opportunity: 50.85.51.B5610
Adviser Information: Josell, Daniel, Moffat, Thomas P.
Keywords: Superconformal chemical vapor deposition; Superconformal electrodeposition; Metallizations; Microelectronics
Metallic structures in microelectronics transmit signals between active elements like transistors. For long-term stability and high-speed operation these conductors must be fabricated with neither seams nor voids. Superconformal deposition processes utilize surfactants to achieve bottom-up deposition in features that permits even high aspect ratio features to be filled flawlessly. The curvature enhanced accelerator coverage mechanism developed at NIST explained this effect. It permits accurate prediction of feature filling during superconformal deposition processes. In the past several years, this effort has achieved the first demonstration of superconformal silver and gold electrodeposition and the first quantitative predictions of superconformal copper electrodeposition and superconformal copper chemical vapor deposition. Future efforts will likely include alloy deposition to achieve controlled inhomogeneous depositions within patterned features, superconformal deposition of other elements, electrical measurements of sub-100 nm dimension structures, and extension of the CEAC mechanism to account for new effects and processes.
Electrodeposition of Alloys
Research Opportunity: 50.85.51.B1972
Adviser Information: Stafford, Gery R.
Keywords: Alloy deposition; Electrochemistry
Metallic alloys are commonly used in a wide range of technologies. The primary reason that alloys are favored over pure elements is that properties and structure can generally be fine-tuned simply by varying the composition. Alloys are generally finer grained, harder, stronger, and may have enhanced electrochemical behavior (corrosion resistance or electrocatalytic activity). In addition, they may possess special properties or unique crystallographic structures not shown by the parent metals. This makes them quite adaptable to new uses and environments. Electrodeposition is an attractive method for fabricating these alloys and intermetallic compounds since undesirable compositional inhomogeneities are very limited in scale and grain sizes are typically very small and uniform. Electrodeposition is also considered to be a nonequilibrium solidification process because the alloy structures considered to be in thermodynamic equilibrium at the deposition temperature are rarely produced. While exact correlations between electrodeposition and other nonequilibrium deposition schemes (rapid solidification, mechanical alloying, and physical vapor deposition) have not been developed, the excess free energy possible in alloys produced by these techniques is similar. Consequently, metallic glasses and unique crystalline and quasicrystalline materials are commonly electrodeposited. This research will examine the electrochemistry of alloy deposition as well as the structure and properties of electrodeposited alloys.
Residual Stress in Electrodeposited Thin Films
Research Opportunity: 50.85.51.B5609
Adviser Information: Stafford, Gery R., Guyer, Jonathan E.
Keywords: Electrodeposition; Residual stress; Wafer curvature
Metallic thin films formed by a number of deposition processes often develop sizable intrinsic stress. Residual elastic stress can drive post-deposition transformations such as whisker growth on the surface of thin films. Stress values that exceed the yield stress of the bulk deposit have also been implicated in the failure of thin films in microelectronic devices. Under some circumstances, complete delamination of the film from its substrate can result. Consequently, understanding the source of this stress is of some technological importance. Aside from any bulk lattice mismatch between the film and substrate, sources of stress in electrodeposited thin films include surface driven lattice parameter compression in individual nuclei, grain boundary formation when nuclei impinge, hydrogen evolution, precipitation of particles with molar volume different than the matrix, and incorporation of additives. Even when deposited on substrates of the same material, electrodeposits thicker than 100 nm typically have a residual compressive in-plane stress for reasons that are not entirely clear. This research will focus on in situ stress measurements, using wafer curvature techniques during the earliest stages of metal deposition from aqueous electrolytes.
Magnetic Imaging
Research Opportunity: 50.85.51.B1965
Adviser Information: Shapiro, Alexander J., Shull, Robert D., McMichael, Robert D.
Keywords: Magnetic fields; Magneto-optics; Images and image processing; Optical imaging; Microscopy; Scanning electron microscopy; Thin films
We use magnetic force microscopy (MFM), scanning electron microscopy (SEM), and magneto-optical indicator film (MOIF) imaging techniques as nondestructive methods to characterize magnetic domain structure in various technologically important magnetic materials such as spin valves, ultrathin multilayer, and granular systems. Well known capabilities of MFM and SEM are complemented by a new imaging method: MOIF. The domain structure is imaged with this technique through the interaction of polarized light with a transparent magneto-optical indicator film, which is placed on top of a magnetic sample. Since the polarization of light is affected by the magneto-static field of the sample (Faraday effect), we can identify the sample's magnetic domain structure through local changes in light polarization in the indicator film using a polarizing microscope. The MOIF method is expected to become a standard nondestructive quality control imaging technique for magnetic investigation of the next generation of magnetic sensors and storage devices. Using the above methods, we are studying static and dynamic magnetization and remagnetization processes and their relationships to thin-film characteristics and defects.
Magnetic Nanotechnology
Research Opportunity: 50.85.51.B5607
Adviser Information: Shull, Robert D., Shapiro, Alexander J.
Keywords: Nanomagnetism; Nanotechnology; Magnetic structure; Ferromagnetism; Superparamagnetism
The bulk magnetic character of materials with some nanometer scale critical material dimension (i.e., grain size, layer thickness, particle size. interparticle separation, rod diameter, nanocontact area) has been found to vary considerably from that found in the same materials lacking that nanoscale structure. Measurements focus on characterizing such novel magnetic behavior and understanding the origin of the new phenomena, so that the relationship between structure, processing, and properties can be established. Such a relationship is needed for industry to take advantage of these new materials. Novel phenomena being investigated include, but are not restricted to, enhanced magnetocaloric effects, unusual magnetic softness, improved magnetic hardness, giant magnetoresistance effects, spintronics, nanoparticles for medical imaging and disease treatment, ferromagnetism in semiconductors, optical transparency in ferromagnets, superparamagnetism, magnetorheology, and enhanced magneto-optic Kerr effects. In addition to a suite of magnetic measurements, numerous nonmagnetic measurement tools, including x-ray diffraction, electron and optical microscopy, and neutron reflectivity, are studied in this project. As a consequence of this work, very high sensitivity magnetic sensors, low energy loss transformers, room-temperature and low field magnetic refrigerators, higher energy product permanent magnets, transparent ferromagnets, and magnetically adjustable amplifiers may be possible in the future.
Magnetic Properties of High-Tc Superconducting Oxides
Research Opportunity: 50.85.51.B1967
Adviser Information: Shull, Robert D.
Keywords: High-temperature superconductors; Magnetic structure; Metal oxides; Mössbauer spectra
Research focuses on the magnetic state of bulk, thin-film, and single crystal high-transition-temperature superconducting oxides between room temperature and 2 K by means of alternating-current magnetic susceptometry, vibrating sample magnetometry, superconducting quantum interference device magnetometer, microwave absorption, and Mössbauer spectroscopy. Field- and time-dependence studies at various temperatures are performed to specify the magnetic flux-pinning characteristics of these new materials, and the effects of magnetic and nonmagnetic atomic substitutions are used to probe the origin of superconductivity in these oxides. In addition, the effect of new processing routes on the flux-pinning characteristics of these materials is being investigated.
Magnetic Structure of Alloys
Research Opportunity: 50.85.51.B1964
Adviser Information: Shull, Robert D., McMichael, Robert D.
Keywords: Alloys; Magneto-optics; Frequency measurement; Advanced materials; Magnetic structure; Mössbauer spectra; Nuclear magnetic resonance spectra
Research concerns the investigation of the magnetic properties of alloys and their relationship to metallurgical structures and processing variables. Computer-controlled equipment is available for alternating-current magnetic-susceptibility measurements as a function of frequency, temperature, and magnetic field. An automated vibrating sample magnetometer, a high-field (5-T) superconducting quantum interference device magnetometer, a magnetic force microscope, and a newly developed magneto-optical indicator film apparatus are available; as well as equipment for ferromagnetic resonance, Mössbauer effect, magnetocaloric effect, and magnetoresistance measurements. Interests include magnetic properties of advanced materials including thin magnetic films, compositionally modulated alloys, magnetic multilayers, magnetic nanocomposites, granular metals, high-temperature superconductors, metallic glasses, icosahedral crystals, and others. Time effects and relaxation phenomena are of particular interest. Applications to nondestructive-evaluation techniques, e.g., Barkhausen effect, are also pursued.
Mössbauer Effect Spectroscopy
Research Opportunity: 50.85.51.B1966
Adviser Information: Shull, Robert D., Shapiro, Alexander J.
Keywords: Metals and metallurgy; Mössbauer spectra; Superconductivity
Experiments focus on the magnetic, electronic, and metallurgical properties of materials. Computer-controlled equipment is available to determine and analyze Mössbauer-effect spectra including gamma-ray transmission and scattering modes and conversion electron detection. Iron, tin, and gadolinium sources are available. A superconducting magnet is available for high-field (5-T) work. Work includes the measurement of local environments in high-Tc superconductors, magnetic polarization in glassy metal alloys, and relaxation effects in nanocomposite granular metals.
Multicomponent Nanocrystalline Materials: Magnetic Engineering
Research Opportunity: 50.85.51.B1968
Adviser Information: Shull, Robert D.
Keywords: Magnetic structure; Metal crystals; Metal films; Metal matrix composites; Mössbauer effect; Sputtering; Vapor deposition; Nanotechnology
Atomic engineering attempts to tailor materials with specific magnetic properties focus on a new class of composite materials called nanocomposites. For these very-fine-particle (~ 2-20-nm) materials comprised of a metal and a nonmetal, one or both of which are magnetic, the magnetic properties vary considerably with the volume fractions and distribution of the constituents. Preparation of these materials by vapor-phase condensation techniques (vapor deposition, laser ablation, and sputtering) and by chemical methods (including sol-gel, metal-organo, and ionic substitution routes) is explored. Coupled with characterization by alternating-current susceptibility, bulk magnetization, magneto-optic Kerr-effect, magnetocaloric effect, and Mössbauer-effect observations, nanocomposites constitute an exciting self-contained laboratory for atomic-level fabrication of thin-film devices that possess novel and unique magnetic properties. Extensive efforts in both the experimental and theoretical (spin-glass behavior, micromagnetics, and percolation theory) aspects of these materials are pursued.
Manufacturing Problems in Magnetic Thin Films
Research Opportunity: 50.85.51.B1980
Adviser Information: Egelhoff, William F.
Keywords: Magnetic films; Thin films
We are studying the scientific principles that underlie manufacturing methods for magnetic thin-film products to determine when and why effects such as interdiffusion, surface segregation, and extrinsic contamination affect product quality. Films can be prepared by several different methods, and their composition, morphology, and structure can be correlated with their magnetic properties. Some of the techniques include magnetron sputtering, electron-beam evaporation, x-ray photoelectron and Auger-electron spectroscopy, ion-scattering spectroscopy, magnetoresistance measurements, the magneto-optical Kerr effect, scanning tunneling microscopy, and electron diffraction.
Spintronics
Research Opportunity: 50.85.51.B5606
Adviser Information: Egelhoff, William F.
Keywords: Spin-polarized electrons; Semiconductors; Microelectronics; Electron tunneling
The rapidly emerging field of "Spintronics" is based on the integration of magnetic materials with semiconductor devices. The term "spin" comes from the property of electron spin, which is the basis of ferromagnetism. If magnetic materials can be used to inject spin-polarized electron currents into semiconductors it may be possible to produce important new classes of microelectronic devices. Because these devices would operate on the electron spin, rather than the electron charge as in conventional electronics, they would be much faster, denser, and smaller. Potential devices based on spintronics could range from spin transistors for nonvolatile computer memory chips in the relatively near-term to entangled quantized electronic states for quantum computers of enormous power in the future. At this time, it is not certain if Spintronics will be a success. It certainly has great potential and many experts consider it a classic example of high-risk/high-payoff research. Thus, Spintronics represents an opportunity for NIST to assist US industry at a very early stage in the development of a high-risk field that could revolutionize microelectronics in the coming decades. In our initial work on Spintronics, we are fabricating and testing devices that inject and detect electrons using magnetic thin films separated from silicon by tunneling barriers consisting of ultrathin insulators such as Al2O3 and SiO2. Electrons cross the barrier by quantum mechanical tunneling. The current challenge is to find tunneling barriers that will maintain spin polarization during tunneling.
Ferromagnetic Resonance
Research Opportunity: 50.85.51.B1970
Adviser Information: McMichael, Robert D.
Keywords: Magnetic resonance; Ferromagnetism; Magnetic films; Anisotropy (physics)
Ferromagnetic resonance (FMR) techniques are used to measure various anisotropy energies used to control the magnetization direction and magnetization dynamics in thin films, including shape, magnetocrystalline, magnetostrictive, and surface-induced anisotropy energies in thin magnetic films and interactions between magnetic layers. Recent studies have included investigations of exchange bias effects in ferromagnetic/antiferromagnet bilayers, damping mechanisms, and thermal stability of multilayer spin valve films and strong magnetostatic anisotropies induced by nanotextured substrate materials. FMR measurements are complemented by vector vibrating sample magnetometry, SQUID magnetometry, magnetoresistance measurements, and magnetic force microscopy.
Magnetic Modeling and Measurement of Materials
Research Opportunity: 50.85.51.B1969
Adviser Information: McMichael, Robert D.
Keywords: Micromagnetism; Models; Magnetic structure
Research focuses on micromagnetic modeling and hysteresis modeling of magnetic materials, and on experimental verification of these models. Theoretical work includes micromagnetic modeling of moment and field distributions in magnetic materials including dynamic effects in devices. Specific interest areas include formulation and solution of standard problems and development and extension of the OOMMF micromagnetic computer code. Experimental verification of micromagnetic models is obtained from magnetic force microscopy imaging and through other experimental techniques including ac susceptibility measurements, SQUID magnetometry, magnetoresistance measurements, and ferromagnetic resonance.
Magnetic Imaging
Research Opportunity: 50.85.51.B1965
Adviser Information: Shapiro, Alexander J., Shull, Robert D., McMichael, Robert D.
Keywords: Magnetic fields; Magneto-optics; Images and image processing; Optical imaging; Microscopy; Scanning electron microscopy; Thin films
We use magnetic force microscopy (MFM), scanning electron microscopy (SEM), and magneto-optical indicator film (MOIF) imaging techniques as nondestructive methods to characterize magnetic domain structure in various technologically important magnetic materials such as spin valves, ultrathin multilayer, and granular systems. Well known capabilities of MFM and SEM are complemented by a new imaging method: MOIF. The domain structure is imaged with this technique through the interaction of polarized light with a transparent magneto-optical indicator film, which is placed on top of a magnetic sample. Since the polarization of light is affected by the magneto-static field of the sample (Faraday effect), we can identify the sample's magnetic domain structure through local changes in light polarization in the indicator film using a polarizing microscope. The MOIF method is expected to become a standard nondestructive quality control imaging technique for magnetic investigation of the next generation of magnetic sensors and storage devices. Using the above methods, we are studying static and dynamic magnetization and remagnetization processes and their relationships to thin-film characteristics and defects.
Test Methods for Evaluating Structure Steel Performance in Fire
Research Opportunity: 50.85.51.B6787
Adviser Information: Luecke, William E.
Keywords: Steel; Standard test method; Fire-resistive steel; Test methods
Fire-resistive (FR) steels are grades of structural steel that are designed to meet existing structural steel standards, but can offer improved high-temperature performance. Their increased resistance to deformation under fire conditions can enhance the safety of the occupants of buildings. Fire Resistive (FR) steels are used now in Europe and Japan, but United States building codes provide no incentive to use FR steel. In addition, no means exist to specify it in US codes. We are working through ASTM to develop performance standards that will allow users to specify grades of FR steel. As part of this standards activity, we are characterizing the performance of ordinary and FR steels, both to validate the test methods and to develop material models for use in finite element simulations of building performance in fire.
Measurements of Grain Orientation Effects and Strain-Induced Surface Structure
Research Opportunity: 50.85.51.B6784
Adviser Information: Stoudt, Mark R., Banovic, Stephen W.
Keywords: Microstructure; Surface characterization; Crystallographic texture; Electron backscatter diffraction; X-ray diffraction; Neutron diffraction
In polycrystals, the evolution of slip bands is usually accompanied by additional deformation in the grain boundary regions resulting from the variability in the orientation of individual grains with respect to the strain axis. The resulting anisotropy creates a macroscopic deformation that is a mixture of both primary slip and near grain boundary deformation. Since the morphology of the free surface is strongly dependent on the crystal orientation and the grain size distribution, careful analysis of the manner in which a deformation-induced surface morphology evolves can provide valuable information about the nature of the plastic flow within a particular grain. This research primarily focuses on in situ investigations of the uniaxial deformation behavior under controlled conditions. Studies of this type will reveal important details about the relationships between deformation mechanisms, grain orientations, and plastic strain needed for accurate models of the deformation behavior. High-resolution surface characterization analysis techniques include optical, scanning laser confocal, atomic force, and scanning electron microscopies. Electron backscattered, x-ray and neutron diffraction techniques are available for grain orientation analysis.
Microstructural Basis of Formability
Research Opportunity: 50.85.51.B1979
Adviser Information: Foecke, Timothy J., Banovic, Stephen W.
Keywords: Crack propagation; Creep mechanics; Electron microscopy; Plastic deformation; Scanning electron microscopy; Scanning transmission electron microscopy; Small-angle neutron scattering; Transmission electron microscopy
A material's formability arises from particular details of its microstructure. Research programs range from sheet metal forming to dislocation patterning studies of lightweight and commercially important materials. These investigations attempt to understand or rationalize the formability in terms of the underlying microstructural origins of deformation and plasticity. Both experimental and theoretical approaches are pursued. Mechanical testing equipment includes servohydraulic closed-loop machines, screw-driven universal testing machines (tension, compression, and torsion), and environmental chambers and ovens that are accessories for these machines. Microstructural characterization can be performed using available optical, scanning electron, transmission electron, and scanning transmission electron microscopes. Computers for data acquisition, machine control, and computation
Microstructural Origins of Surface Roughening and Strain Localizations
Research Opportunity: 50.85.51.B5611
Adviser Information: Banovic, Stephen W.
Keywords: Microstructure; Surface roughness; Crystallographic texture; Electron backscatter diffraction; X-ray diffraction; Neutron diffraction
Existing data, measurements methods, and the basic understanding of metallurgical factors that influence friction, tearing, and surface finish during sheet metal fabrication are insufficient to meet the finite element modeling requirements of industry. This project approaches the resultant need by exploring the microstructural origins of the distribution of slip, surface roughening, and strain localization during plastic straining. The primary focus of the investigations is the influence of initial material characteristics (grain size, shape, crystallographic texture) on the formability of commercially relevant Al and Fe base sheet metals as a function of multipass, biaxial deformation. Characterization techniques include optical and electron microscopy, profilometry (contact and laser), and diffraction techniques (electron backscattered, x ray, neutron) for texture evaluation.
Studies in Formability and Deformation
Research Opportunity: 50.85.51.B1978
Adviser Information: Foecke, Timothy J., Banovic, Stephen W.
Keywords: Plastic deformation; Constitutive laws; X-ray stress measurement; Texture analysis
Research centers on fundamental aspects of formability. Our goal is to refine the basic theories of deformation and formulate general concepts, emphasizing the role of plasticity and using concepts from dislocation theory. In addition, this theoretical research is correlated with experimental research in the Division. Studies focus on (1) the interpretation of formability testing results, (2) the reduction and analysis of formability testing data, and (3) the development of physical constitutive models to predict formability behavior. Use and extension of finite element analyses in these studies is anticipated.
Direct Measurement of Multiaxial Yield Surfaces
Research Opportunity: 50.85.51.B6276
Adviser Information: Foecke, Timothy J.
Keywords: Forming; Yield loci; X ray
A new capability has been developed where sheet metal can be multi-axially strained while stresses in various directions within the plane of the sheet are measured using x-ray diffraction. This system is being used to see how yield loci change with plastic strain level and with changes in multi-axial strain path. Opportunities exist to study structure-property relationships using electron microscopies and x-ray and neutron diffraction and theoretical work on modeling constitutive behavior. Numerous opportunities exist to interact with industrial partners through established, ongoing research collaborations.
Measurement of Ultrahigh Rate Tensile and Fracture Properties of Infrastructural Materials
Research Opportunity: 50.85.51.B6277
Adviser Information: Foecke, Timothy J.
Keywords: Kolsky; High-rate; Constitutive laws
Accurate prediction of the structural response of an infrastructural system (e.g., bridge, building) to extreme loadings depends on accurate high rate mechanical property data and detailed observations of dynamic crack growth. A new system based on the Split-Hopkinson Bar test is being developed to measure ultrahigh rate tensile and fracture behavior of infrastructural materials. Opportunities exist for experimental mechanicists and finite element modelers in helping develop, instrument, and use this system to measure ultrahigh rate constitutive behavior, and integrate this information into modeling schemes for use by the critical infrastructure protection community.
Measurements of the Underlying Processes of Metals Deformation
Research Opportunity: 50.85.51.B5612
Adviser Information: Levine, Lyle E.
Keywords: Dislocations; Transmission electron microscopy; Scanning electron microscopy; Atomic force microscopy; X-ray diffraction
The changes in mechanical properties that occur during the plastic deformation of metals result from the complex interaction of huge numbers of mobile and immobile (trapped) line defects called dislocations. The motion and trapping of these dislocations are extremely heterogeneous and produce revealing patterns of slip lines and bands on sample surfaces. We have conducted detailed transmission electron microscopy (TEM) and in situ atomic force microscopy (AFM) studies of how these slip structures evolve on pure Al single crystals. Such studies provide valuable qualitative and quantitative information that can be used to develop and validate fundamental deformation models. We have also used submicrometer X-ray beams at the Advanced Photon Source to directly measure the elastic strains (and the stresses) within individual dislocation cells in deformed Cu single crystals, a study that settles longstanding disagreements on the presence and distribution of such strains. Many other high-impact studies are possible using techniques (both in situ and ex situ) such as TEM, AFM, SEM, and X-ray diffraction on single crystals, polycrystals, pure metals, and alloys.
Quantitative Multiscale Modeling of Metals Deformation
Research Opportunity: 50.85.51.B5614
Adviser Information: Levine, Lyle E.
Keywords: Nanomechanics; Nanoindentation; Finite element modeling; Defect nucleation; Multiscale modeling; Molecular dynamics; Density functional theory
Nanomechanical properties are critical for the design of all nanodevices. For example, all nanodevices experience mechanical loads during processing and service, and quantitative predictions of failure strengths are needed to ensure reliability and maximize performance. Nanoindentation is a well-established experimental technique for exploring nanomechanical properties and provides valuable experimental data for comparison with our models. Quantitative simulation of nanoindentation requires spanning the full range of computational techniques (finite element approach, molecular dynamics using the embedded atom method and semi-empirical tight binding, and density functional theory) over six orders of magnitude from the continuum to the electronic structure of the constituent atoms. In addition to making valuable contributions to the art of designing nanodevices, these quantitative studies provide valuable opportunities for basic research into material behavior and energetics at the nanoscale.
Statistical Physics Applied to the Deformation of Metals
Research Opportunity: 50.85.51.B4440
Adviser Information: Levine, Lyle E.
Keywords: Dislocations; Statistical physics; Percolation theory; Complex systems; Chaos; Multiscale modeling
The changes in mechanical properties that occur during plastic deformation of metals result from the complex interaction of huge numbers of mobile and immobile (trapped) line defects called dislocations. In spite of this underlying complexity, mechanical property measurements exhibit a relatively simple and consistent behavior, requiring only a few empirically determined internal state variables for reasonably accurate simulation. We have shown that a deforming metal can be described as a self-organizing critical system and that the correct internal state variables are actually statistical parameters dealing with how mobile dislocations interact with cell walls. The controlling factor is the distribution of dislocation segment lengths in the walls. With only the Burgers vector and the elastic shear modulus as inputs, and with no adjustable parameters, this model correctly predicts the formation of slip lines and slip bands, the linear and nonlinear behavior of the stress-strain curve, and the magnitude of the flow stress. Many valuable extensions of this model are possible, including the behavior of alloys and polycrystals, the influence of temperature, and the role of large local stress fluctuations that we have recently measured experimentally. Both theory and modeling approaches are needed.
Synchrotron X-Ray Imaging Using USAXS
Research Opportunity: 50.85.51.B5615
Adviser Information: Levine, Lyle E.
Keywords: Synchrotron radiation; Small-angle scattering; X-ray imaging; X-ray microscopy
After nearly five years of development work, we have perfected an entirely new class of X-ray imaging techniques based on ultrasmall-angle X-ray scattering (USAXS). USAXS imaging is now operational at the Advanced Photon Source and provides high-contrast, high-resolution images of metal, ceramic, polymer, biological, and composite samples, with a USAXS-derived ability to extract quantitative structural data from selected sample volumes for length scales ranging from millimeters down to 1 nm. As an example, this advanced measurement technique has provided crucial quantitative structural data on the self-assembly of nanoscale three-dimensional conductive networks within a polymer matrix. Transmission USAXS images were used to show self-assembled conductive nanowires composed of interconnected nanoscale carbon black particles embedded within a polymer matrix. USAXS data from these structures give mean wire diameters as small as 24 nm ± 1 nm. USAXS imaging is the only existing measurement technique capable of imaging these self-assembled structures. Now that the USAXS imaging development work is essentially complete, our emphasis is shifting to microstructural studies of material systems of scientific or industrial interest.
Using Submicrometer Synchrotron X-Ray Beams for Spatially Resolved Measurements of Elastic Strains and Orientation
Research Opportunity: 50.85.51.B6786
Adviser Information: Levine, Lyle E.
Keywords: Dislocations; Dislocation substructure; X-ray diffraction; Synchrotron x-rays; X-ray microbeams
In a recent high-profile experiment, we used depth-resolved, submicrometer x-ray beams at the Advanced Photon Source (APS) to directly measure the elastic strains (and thus the stresses) within individual dislocation cells in heavily deformed Cu single crystals, a study that settles longstanding disagreements on the presence and distribution of such strains. The spatial resolution of these measurements was 0.5 um in all three dimensions. Although useful by itself, this set of measurements was just the first demonstration of an exciting new experimental capability for measuring elastic strains and crystallographic orientations with submicrometer resolution within complex microstructures. Current and planned research projects include (1) probing deformation microstructures with 0.5 um (and smaller) spatial resolution within extended three dimensional sample volumes, (2) probing the distributions of elastic strains within individual dislocation cell walls, (3) studying the evolution of dislocation cell and cell wall elastic strains as a function of applied plastic strain, and (4) repeating these various studies for different material systems. Even higher spatial resolution has been demonstrated and should become regularly available shortly. Work on this project would involve direct collaborations with researchers at Oak Ridge National Laboratory and the University of Southern California as well as with NIST staff. Associates would work at NIST but would be expected to travel to the APS several times a year to conduct experiments.
Dynamic Thermal Mechanical Analysis of Microstructures
Research Opportunity: 50.85.51.B5616
Adviser Information: Ricker, Richard E.
Keywords: Damping; Internal friction; Strain recovery; Stress relaxation; Nanostructured materials
Dynamic thermal mechanical analysis is a measurement technique where a sample is continuously loaded in a sinusoidal manner at fixed or varying temperatures with the magnitude and phase shift of the elastic response recorded as it changes with microstructure. Projects should explore the possibility of using this or similar measurement techniques to investigate technologically significant microstructures such as nanostructured materials, composites, intermetallics, or lead free solders; or to investigate microstructures with unique properties such as alloys with low coefficient of thermal expansion, shape memory alloys; or to investigate the influence of interstitial elements such as H, C, O, or N absorbed from the service or processing environment on the properties and performance of metals and alloys.
Hydrogen Effects on the Behavior of Materials for the Hydrogen Economy
Research Opportunity: 50.85.51.B5617
Adviser Information: Ricker, Richard E.
Keywords: Hydrogen; Fracture; Embrittlement; Hydrogen embrittlement
The use of hydrogen as a fuel will require the development of an infrastructure to produce, deliver, and utilize hydrogen safely. Hydrogen readily adsorbs onto the surface of most metals and alloys where it disassociates and diffuses into the solid as an interstitial solute. Once inside the matrix, hydrogen can dramatically alter the mechanical properties, but most notably, hydrogen can lower the fracture resistance of metals and alloys to the point where fracture occurs at a minor fraction of the yield stress. Projects should focus on understanding the influence of hydrogen on the fracture resistance of alloys that may be used for the production, containment, storage, distribution, or oxidation of hydrogen.
Dynamic Mechanical Property Measurements of Bulk Amorphous Metal Alloys and Other Novel Materials
Research Opportunity: 50.85.51.B6530
Adviser Information: Ridder, Stephen D.
Keywords: Metallic glass; Structural amorphous metal; Bulk amorphous metal; Strain rate; Kolsky bar
Amorphous metal alloys and other novel materials deform differently than more commonly used metals with simpler crystalline structures because of the lack of well-defined slip systems in these materials. The deformation behavior is studied at high strain rates using a Split-Hopkinson Bar, or Kolsky Bar. Electrical pulse heating is also employed to study how the dynamic material behavior is influenced at heating rates fast enough to achieve non-equilibrium structures at impact. Microstructural characterization using SEM, TEM, x-ray, and neutron scattering is used to identify and explore deformation mechanisms and establish structure-property relationships for these unique materials.
Relationships between Microstructure, Surface Roughness, and Friction during Deformation
Research Opportunity: 50.85.51.B6531
Adviser Information: Stoudt, Mark R.
Keywords: Surface characterization; Friction; Metal forming; Dislocation dynamics
The inhomogeneous evolution of surface asperities generated during metal forming promotes strain localization that results in tearing and increased friction between mating die surfaces. Much of the data in the literature do not adequately address the influence of variations in metallurgical condition on the friction behavior. The primary focus of this study is to evaluate the coefficients of static and sliding friction and the surface roughening behavior in commercially relevant Fe and Al-based sheet alloys with a prototype apparatus that has been developed to simulate the friction behavior under various metal forming conditions. The surfaces generated during these experiments are designed for additional analyses with various high-resolution surface characterization techniques including optical, scanning laser confocal, and scanning electron microscopy; surface profilometry; and crystallographic texture analysis.
The Relationships between Microstructure, Surface Topography, and Contact Behavior during Plastic Deformation
Research Opportunity: 50.85.51.B6785
Adviser Information: Stoudt, Mark R.
Keywords: Surface characterization; Friction ; Contact mechanics; Dislocation dynamics; Numerical modeling
Currently, the variability in friction behavior produced by inhomogeneous surface deformation is a significant obstacle impeding the widespread use of the many alloys intended to increase automobile fuel economy. It promotes strain localization resulting in component failure from tearing or wrinkling and accelerates die wear. Although many existing friction measurement systems are capable of providing relevant experimental data, these tests typically do not allow studies of the deformation mode (i.e., uniaxial, biaxial, or mixed) on the contact behavior. They are also not equipped to directly evaluate the influences of metallurgical variables, or the changes in the microstructural conditions (e.g., heat treatment, grain size, grain orientation) that are produced in the specimen during deformation. In addition to evaluating the relative influences of strain path and metallurgical condition on the evolution of the surface topography and on the coefficients of static and dynamic friction, this research also includes development of three-dimensional numeric analysis tools to accurately characterize the changes that occur on the surface. High-resolution surface characterization techniques including optical, scanning laser confocal, atomic force, and scanning electron microscopies, and surface profilometry are available as well as a friction testing apparatus that has been developed to simulate
Phase Equilibria in Multicomponent Alloys
Research Opportunity: 50.85.51.B4438
Adviser Information: Kattner, Ursula R., Boettinger, William J.
Keywords: Phase equilibria; Thermodynamics; Alloys
Knowledge of stable and metastable phase relations in multicomponent materials provides valuable information for the development of processing strategies for these materials. It is necessary to critically evaluate the data and perform critical experiments to derive the most accurate phase diagram. Thermodynamic calculation with the CALPHAD method provides a unique tool for testing the consistency of phase diagram and thermodynamic data, and the assessment of higher order systems through extrapolation of the subsystems. We are interested in research involving critical evaluation and experiments on phase diagrams of practical importance as well as the coupling of thermodynamic and kinetic analyses.
Diffusion in Advanced Materials
Research Opportunity: 50.85.51.B6790
Adviser Information: Campbell, Carelyn E.
Keywords: Diffusion mechanisms; Multicomponent diffusion; Calphad
Calphad-type models have been successfully employed to describe composition-dependent diffusion mobilities in a variety of disordered metallic systems and are currently being developed for a variety of ordered metallic systems. These composition dependent mobility descriptions can then be used in conjunction with multicomponent thermodynamic descriptions to model diffusion processes in a variety of disordered and ordered metallic systems. The next challenge is to model the diffusion mobilities in complex materials where a Calphad-type approach must be combined with mechanistic models that describe the specific microstructure elements. A variety of inputs from both experimental work and simulations (i.e., first principle, atomistic, and/or molecular dynamic calculations) will be needed to develop these types of models. Some of the complex material systems of interest are metallic glasses, nanocrystalline metals, hydrogen storage materials, and heavily deformed metals.
Diffusion Processes in Metals
Research Opportunity: 50.85.51.B1956
Adviser Information: Campbell, Carelyn E.
Keywords: Electron microscopy; Grain boundaries; Metals and metallurgy; Metal surfaces; Sintering
Diffusion-controlled phenomena and their influence on metallurgical processes such as alloy surface modification, precipitation, and sintering are of interest. Measurements and predictive modeling of grain-boundary diffusion, the diffusional degradation of protective coatings, and other interface-modification procedures are pursued theoretically and experimentally using electron microscopy and microanalytical techniques. Results are related to process variables encountered in metals pro
Modeling of Electrodeposited Solar Cell Device Fabrication and Operation
Research Opportunity: 50.85.51.B6788
Adviser Information: Guyer, Jonathan E., Josell, Daniel
Keywords: Semiconductor; Computer simulation; Theory and modeling; Superconformal electrodeposition
Vertical junction solar cell structures maximize the material available for light collection, while minimizing recombination losses. Newer solar cell materials, amenable to electrodeposition, open the possibility for superconformal filling of small vertical features (a technique widely applied in the "Damascene" process for making interconnects on computer chips). These fabrication techniques enable device structures and feature sizes not attainable with traditional fabrication methods. Research focuses on modeling device performance as a function of geometry and materials choices, as well as extending existing models of metal electrodeposition into the deposition of semiconductor materials.
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Last modified: Wednesday, 16 July, 2008 by Metallurgy Webmeister