The Neutron Scattering Facilities at the NIST Research Reactor offer a unique opportunity in the US for studying the structure and dynamics of biological macromolecules and biomimetic systems as a function of chemical or biological environment. Two 30m small-angle neutron scattering (SANS) instruments and reflectometers provide the country's best combined capabilities for surface and structural studies. Both SANS and reflectometry are well-suited for in situ structural studies of macromolecules in solution ranging in size from 1 nm to 100 nm. In addition, a wide range of dynamic processes encompassing the 10-7 to 10-12 s time scales will soon be accessible with the completion of three state-of-the-art neutron spin-echo, high-resolution time-of-flight and back scattering spectrometers. These techniques provide information on macromolecular dynamics which is complementary to, and in many cases more direct than, that obtained from NMR and electron spin resonance and which can be directly compared with molecular dynamics computer simulations. In this program, both structure and dynamics studies are being pursued, using this unique variety of measurement capabilities, to probe structure-function relationships in macromolecules and other biologically and technologically important systems. The program is being carried out with close collaboration and support from NIST's Biotechnology Division.
ELECTRONIC PACKAGING AND INTERCONNECTION
The U.S. microelectronics industry, valued at over $300 billion in 1995, is confronted with technological changes at an unprecedented pace and urgency. This is partially due to increased consumer expectations, rapid product evolutions, and heightened international competition. In response to these pressures, the U.S. semiconductor and module interconnection industries, representing combined sales of over $54 billion in 1995, have taken the landmark steps of developing technology roadmaps. These two roadmaps, entitled The National Technology Roadmap for Semiconductors and The National Technology Roadmap for Electronic Interconnects, produced by the Semiconductor Industry Association and the Institute for Interconnecting and Packaging Electronic Circuits, respectively, identify roadblocks and performance characteristics for the manufacture of globally competitive products. Significant portions of these roadmaps address the packaging and interconnection of semiconductor devices, a technology which now amounts to over one-third the delivered cost of integrated circuits.
To assist this strategic and rapidly growing U.S. industry, the NIST Materials Science and Engineering Laboratory has embarked on a new program in electronics packaging and interconnection that addresses industry's most pressing challenges surrounding the utilization of advanced materials and material processes. With a specific mission to develop and deliver to U.S. electronics and electronic materials industries measurement tools and data for materials and processes used in semiconductor packaging, module interconnection and component assembly, the strategy used to implement this program is based upon three primary needs.
This strategy is the outgrowth of two industry-led workshops conducted at NIST. The first, conducted in 1990, set the course for the Laboratory's emerging plans in packaging, interconnection and assembly. The second, conducted in early 1994, identified a series of cross-cutting barriers, critical technical challenges and opportunities for NIST in materials science and engineering deemed most needed by the U.S. microelectronics industry. The results of this workshop are contained in NISTIR 5520, Metrology and Data for Microelectronics Packaging and Interconnection.
Now in its second full year of funding, the program has in place a portfolio of projects involving the talents and operations of metallurgists, polymer scientists, and materials reliability specialists. During this period, the MSEL program has developed numerous single- company and consortia-based collaborations that involve over twenty-three U.S. companies; fifteen universities; four other government agencies or laboratories; and eight consortia, standards bodies and associations. These collaborations have resulted in forty-six technical publications, sixteen of which were published in 1995, and numerous individual accomplishments that directly impact industry's research and development needs.
EVALUATED MATERIALS DATA
The objective of the Data Technologies program is to develop and facilitate the use of evaluated databases for the materials science and engineering communities. Both research- and application-directed organizations require readily available evaluated data to take advantage of the large volume of materials information developed on public and private sponsored programs. This information, particularly numeric data, is available in an ever increasing number of publications published worldwide. The necessity to consolidate and allow rapid comparison of properties for product design and process development underlies the database projects.
Evaluated Data projects are conducted in cooperation with the NIST Standard Reference Data Program Office and include compilation and evaluation of numeric data as well as recently initiated efforts directed at more effective distribution and use of data.
Database projects in MSEL include:
These projects are developed with the cooperation of the materials community and complement various research programs.
HIGH TEMPERATURE SUPERCONDUCTIVITY
A significant program in high-Tc (critical transition temperature) superconductivity is being conducted in MSEL and other Laboratories at NIST. The primary focus of the MSEL Program is on bulk superconducting materials for wire and magnet applications. In carrying out this program, researchers in MSEL work closely with their counterparts in other NIST Laboratories, and collaborators in U.S. industry and other National Laboratories.
The primary thrusts of the program are as follows:
METALS DATA AND CHARACTERIZATION
Basic data describing the properties of metals and advanced materials based on metals form an important component of the technological infrastructure which NIST supports. Information of this kind is essential to the understanding of the behavior of metals in different conditions and to the effective design of structures and devices containing metals. The measurement base is an MSEL mission strategic thrust.
This program is focussed on the development of techniques to measure various properties of metallic materials and the acquisition of data of technological significance. It includes activities involving measurements of mechanical, magnetic, and optical properties which impact a number of different technology sectors. For instance, in collaboration with the Copper Development Association, the mechanical behavior of lead-free plumbing solders is being investigated to provide the comprehensive and reliable database needed to establish internal working pressure standards for drinking water pipe joints. In contrast with these traditional measurements involving a widely used material, high speed optical techniques are being developed in another project to measure selected thermophysical properties of solid and liquid materials at high temperatures. The goals of this work are to generate accurate bench-mark data on selected key materials and to develop new high-temperature thermophysical standards. In other work involving a collaboration with ALCOA and USCAR, models are being developed and verified for the press-and-sinter and powder forge processes for metal matrix composites. The goal of this work is to develop lightweight materials for automotive applications. In the area of characterization, a technique is being developed which visualizes stress fields in opaque materials using the acoustic microscope. Work in the past year has included collaborations with DuPont, Libby Owens Ford, and Sonix.
NANOSTRUCTURED MATERIALS
Nanostructured Materials are a new class of materials which provide one of the greatest potentials for improving performance and extended capabilities of products in a number of industrial sectors, including the aerospace, tooling, automotive, recording, cosmetics, electric motor, duplication, and refrigeration industries. Encompassed by this class of materials are multilayers, nanocrystalline materials and nanocomposites. Their uniqueness is partially due to the very large percentage of atoms at interfaces and partially to quantum confinement effects.
One critical need for their implementation is their characterization and measurement science which is the focus of the NIST program. For many properties, it is not known whether the exciting novel behavior found in these new materials is due to new physics or to a logical extension of large-size behavior to small dimensions. Examples include the deformation and fracture behavior (wherein it is not known whether dislocations even exist in these materials), optical characteristics (wherein uncertainties exist in whether the properties are due to interface or quantum mechanical effects), magnetic properties (wherein it is not known what magnetic domains even look like in nanostructured materials or how they move in response to a magnetic field), and thermal properties (wherein the propagation of phonons through interfaces is poorly understood). Consequently, implementation of this new type of material into marketable products is significantly delayed. NIST is providing the measurement science to answer these critical unknowns. Important needs also include the identification of preparation methods for industrial-size quantities of material, extension of the capabilities of conventional measurement tools to the nanometer-size scale, and the development of consolidation methods which still retain the nanometer grain size of the initial nanocrystalline powders. For multilayers, understanding the development of epitaxy and control of both composition and interdiffusion at the interface are of critical importance.
By experimentally addressing these issues, by bringing together the industrial and scientific communities through the organization of workshops and conferences in the area, and by the development and preparation of appropriate standards, NIST acts to accelerate the utilization of these materials by the industrial sector. In addition, collaborations established in the area with Xerox, General Motors, Nanophase Technologies, Pratt and Whitney, Caterpillar, Lockheed-Martin, Hewlett Packard, IBM, Seagate, and Motorola Corporations, for example, enable NIST to leverage its activities with the much larger, but complementary, capabilities of other organizations.
NEUTRON CHARACTERIZATION
This program encompasses the basic and applied research efforts and neutron scattering method development centered on the Neutron Condensed Matter Science Group in the Reactor Radiation division. Group scientists and visiting researchers lead broad-based mission research in chemistry, solid state physics, materials science and biology, often in collaboration with other divisions in MSEL and the Biotechnology, Surface and Microanalysis, Thermophysics, and Analytical Chemistry divisions in CSTL), and with over 100 universities and industries from all over the U.S. (and the world). Group scientists also develop and maintain state of the art capabilities and instruments as a national resource for cold and thermal neutron scattering research, including scientific leadership and oversight in the development and use of 10 experimental stations in the Cold Neutron Research Facility.
Current areas of emphasis in the multidisciplinary research program include: studies of the structure and excitations of high technology magnetic and superconducting materials, thin films and multilayers; crystallographic analysis of the atomic and molecular arrangements in catalysts, ceramics, superconductors, ionic conductors, and fullerites; sophisticated neutron diffraction analysis of residual stress and texture which affect properties and performance of technologically important alloy, ceramic and composite structures and components; studies by neutron reflectometry and small angle scattering (SANS) of macromolecular and microstructures in materials and of molecular and magnetic surfaces and interfaces; inelastic neutron scattering studies of molecular bonding states and dynamic processes in chemical catalysts, sieves, polymers and battery materials, and molecular scale curing processes in cements; and studies of biomolecular structure and dynamics in proteins, lipid bilayers and membranes.
NONDESTRUCTIVE EVALUATION
Nondestructive evaluation (NDE) is the determination of product quality using test methods which do not damage the product. At MSEL, the NDE Program is directed to the development of model-based methods of physical measurement which characterize the internal geometries of materials, such as defects, microstructures, and lattice distortions. The goal of NDE is to convert these measurement methods into sensors suited for production line and in- service measurements of materials quality and serviceability. The NDE program makes important contributions to two MSEL strategic thrusts: advanced materials and measurement technology.
A primary focus of the NDE Program is microstructural characterization of metals and alloys, composite materials, and engineered surfaces. The idea is that models relate microstructure and physical properties. Thus, by measuring quantities related to physical properties, the salient microstructural features can be ascertained. For example, sound velocity is related to elastic properties, and thus, ultrasonic measurements can be used to characterize fiber- orientation distributions in composites or texture in metals. These model-based measurements enable industry to replace microscopy with nondestructive methods for the microstructural characterization needed to assure the quality of advanced materials.
The NDE Program is making significant contributions to measurement technology and materials modeling. Our primary emphasis has been on acoustic methods. We have worked with industry to commercialize advances in noncontact ultrasonics, wave-form based acoustic emission, composites NDE and nonlinear ultrasonics. Research is also underway in magnetic, thermal and radiographic techniques. Modeling advances include Green's function methods for wave propagation in anisotropic materials, obtaining elastic constants from resonance spectra, and determining texture based on ultrasonic measurements.
POLYMER CHARACTERIZATION
The Polymer Characterization program provides measurement methods, data, and standard reference materials needed by U.S. industry, research laboratories, and other federal agencies to characterize polymers for processibility, properties, and performance. Molecular weight and molecular weight distribution are the molecular characteristics of polymers that most affect their processing, properties and performance. Properties and performance may also vary widely depending on the solid state structure formed during processing. Therefore, the focus of the program is on techniques that measure molecular weight, its distribution and the solid state structure of polymers. Primary methods employed for molecular weight are dilute solution light scattering and osmometry; chromatographic techniques, which require calibration by standards of known molecular mass, provide information on molecular weight distribution. Recent activities seek to exploit recent advancements in mass spectrometry using mass assisted laser desorption ionization (MALDI) to determine molecular weights of synthetic polymers. Other spectroscopic methods, solid state nuclear magnetic resonance (NMR) and infrared, as well as x-ray diffraction are developed and applied to elucidate the solid state structure of polymers.
The polymer industry and standards organizations assist in the identification of current needs for standard reference materials. Based on these needs, research on characterization methods and measurements are conducted leading to the certification of standard reference materials. Standards are produced for calibration of gel permeation chromatographs, the principal method used by industry for assessing molecular weight and molecular weight distributions, and melt flow standards that are used in the calibration of instruments used to determine processing conditions for thermoplastics.
STANDARD REFERENCE MATERIALS
The NIST Standard Reference Materials Program serves as the nation's primary source of reference standards used to develop accurate methods of analysis, calibrate measurement systems and assure the long-term adequacy of measurement assurance programs. The aim is to assist industry, science, and academia to achieve the level of product conformance and measurement quality that meet national and international commerce and trade.
As the world commerce and trade markets have become more global, customers are using SRMs more and more. All data derived from measurements in which SRMs are part of the measurement system have the capability of being traceable to a common and recognized set of standards and, consequently, the compatibility of data can be realized.
The technical staff of the Materials Science and Engineering Laboratory produces a series of standards for materials suppliers and users that are key elements in assisting this industry to develop and/or improve its competitive edge in the global arena. MSEL designs, develops and produces many SRMs related to ceramics, polymers, metals and related materials. These SRMs are routinely employed in the production and processing of materials. Many projects are conducted in cooperation with applicable industries and are an integral part of the Laboratory's research efforts.
SYNCHROTRON RADIATION
The Materials Microstructural Characterization Group in the Ceramics Division operates two x-ray experimental stations at the National Synchrotron Light Source (NSLS), where researchers from NIST, industry, universities and other government laboratories carry out state-of-the-art measurements on ceramic, semiconductor, photonic, metallurgical, biological, and other materials of high scientific or technological interest. X-ray measurement capabilities include ultra-small-angle scattering (USAXS), topography, diffraction-imaging microscopy, x-ray absorption fine structure spectroscopy (XAFS), standing-wave x-ray scattering (SWXR), and reaction-kinetic surface science measurements.
The range of studies performed over the past year include processing-microstructure relationships in plasma-sprayed ceramic deposits, sintering of nanostructured ceramics, strain- induced microcracking in high-Tc superconducting composite tapes, grain-size/pore-size trajectories within ceramic microstructures during processing, diffraction imaging of ZnSe, strain and bond distortion in ultra-thin semiconductor films, and the determination of atomic- scale and molecular-scale structures at technologically important surfaces and interfaces.
In addition, as part of a national facility, time on the NIST instruments at the NSLS is made available to qualified researchers based on peer-reviewed proposals. In the past year, researchers from chemical, aerospace, energy and materials production industries as well as from NIST laboratories, other government laboratories and universities have completed experiments that could not have been performed elsewhere in the United States. The long- term goal of research at these facilities is to enable researchers to address basic issues so that U.S. manufacturers can provide superior materials based on structural information not available elsewhere.
Looking toward the future, the NIST Materials Science and Engineering Laboratory (MSEL) has entered a Collaborative Access Team (CAT) agreement with the University of Illinois, Oak Ridge National Laboratory, and U.O.P. Corporation, the purpose of which is to build and operate x-ray instruments on sector 6 at the Advanced Photon Source (APS) now under construction at the Argonne National Laboratory. The CAT is called UNI-CAT in recognition of the University, National Laboratory, and Industrial components of this team. This partnership is particularly attractive to us at NIST because there is significant overlap with current and future NIST interests.
The APS will offer a 102-104 increase in brilliance compared to the best synchrotron x-ray sources of today. In the years to come, the APS will supplant the NSLS as this nation's premier x-ray source. The APS beam lines now being built by UNI-CAT incorporate the newest technology which will not only enable NIST scientists to improve significantly our real-time x-ray microscopy, ultra-small-angle x-ray scattering, in-situ x-ray topography and EXAMS capabilities, but will also offer opportunities for cutting-edge experiments in structural crystallography (and time-resolved structural scattering), surface/interface scattering, diffuse scattering, and magnetic scattering. NIST scientists will extend our present portfolio of characterization capabilities to include an even wider range of materials measurement of importance to materials scientists and to U.S. industry.
VISCOELASTICITY OF POLYMERS
The goals of the Viscoelasticity of Polymers Program are motivated by the rapid growth in polymers in engineering applications, including wholly new uses. The efficient development of new applications for polymers requires improved design methods for estimating dimensional stability and long term performance. Technical factors include dimensional tolerances, process-induced residual stresses and fatigue behavior in complex thermal, stress and humid environments during use.
The goals of the Viscoelasticity of Polymers Program are to develop measurement strategies that produce mechanical properties data in efficient ways and concurrently to build methodologies that can be applied in the design and development of finished polymers. The approach uses the theoretical frameworks of continuum constitutive equations and micro- to meso-scale physical models to interrelate the mechanical responses under different loading conditions and to test model predictions using available measurement methods. The work involves the first major effort to measure the mechanical and rheological responses of a single class of solid polymer in multiple geometries of deformation and modes of loading as well as in different temperature histories. The combination of experiment and modeling results in both improved models and the development of new experimental methods for measuring material property parameters. Furthermore, the measurement and modeling requirements are renewed continuously by coordinating the efforts through collaborations with and support activities for other Programs in the Polymers Division including the Polymer Characterization Program, the Polymer Theory and Modeling Program, the Electronic Packaging and Interconnects Program, as well as other agency and miscellaneous projects that result from the Program's activities.
In addition, the Program seeks actively to work with Industrial research programs. Activities such as workshops and special symposia that improve the interaction of the Program with outside industry and the general technical and scientific communities are also fostered.