Jerome B. Cohen - US grants

The purpose of this research is to examine local atomic order in several metallic alloy systems that display a metastable transitional state. Early stages of homogeneous precipitation is examined in aluminum-copper-magnesium, iron-beryllium and nickel-beryllium alloys. Precipitation from nickel-aluminum alloys is studied to better understand formation of ordered precipitates. The structure of ferrous martensites immediately following the quench is being determined; structural changes from tempering is also pursued. Local atomic order in mercury- cadmium-telluride is being determined using synchrotron anomalous dispersion techniques. Advanced X-ray diffraction methods are the primary experimental tool used to characterize the alloy systems. Advanced diffuse X-ray scattering techniques from atomic displacements and the associated analysis are part of the research.

Long & Medium-Term Research: Development of Stable Si and Ge Single Crystal Monochromators Under High Heat Loads This award recommendation is made under the Program for Long & Medium-Term Research at Foreign Centers of Excellence. The program seeks to enable U.S. scientists and engineers to conduct long-term research abroad at research institutions of proven excellence. Awards provide opportunities for the conduct of joint research, and the use of unique or comple- mentary facilities, expertise and experimental conditions in foreign countries. This award for a proposal sponsored by Dr. Jerome B. Cohen will support a twelve month visit to the United Kingdom by Dr. John P. Quintana to work with Prof. Michael Hart of the University of Manchester on "Development of Stable Si and Ge Single Crystal Monochromators Under High Heat Loads." Synchrotron radiation has become an extremely important tool in material studies. Insertion devices greatly increase the flux to the point where heat load induced physical distortions of the optical elements limit the flux and resolution of the final beam. The heat load problem will be more severe on the next generation synchrotrons such as the Advanced Photon Source (APS) and the European Synchrotron Radiation Facility (ESRF). Consequently, new optics, including monochromator designs are necessary to fully exploit the capabilities of these high brightness sources. The proposed study will develop stable monochromators for current high brightness synchrotron radiation sources as well as very high power sources (APS and ESRF). The basic method will be to improve on the basic thin wall adding the capability to elastically distort the crystal to counter deformations at high heat loads. The award recommendation provides funds to cover, as appropriate, international travel, local travel abroad, stipend, dependents' allowance if applicable, and a flat administrative allowance of $250 for the U.S. home institution.

Long & Medium-Term Research: X-ray Analysis of Thin Film Materials Including Wear Resistant Coatings and Superlattice Structure. This award recommendation is made under the Program for Long & Medium-Term Research at Foreign Centers of Excellence. The program seeks to enable U.S. scientists and engineers to conduct long-term research abroad at research institutions of proven excellence. Awards provide opportunities for the conduct of joint research, and the use of unique or compli- mentary facilities, expertise and experimental conditions in foreign countries. This award for a proposal sponsored by Dr. Jerome Cohen is to support a 15 month visit by Dr. Carla J. Shute to Sweden to work with Professor Torsten Ericsson of the Institute of Technology in Link ping on "X-Ray Analysis of Thin Film Materials Including Wear Resistant Coatings and Superlattice Structure." The properties of thin film materials are of considerable interest due to their enhanced mechanical behavior over bulk specimens of the same material. The researchers will examine two types of thin film structures: TiN wear resistant coatings and Mo/V superlattice structures. They will examine the residual stresses in both of these materials by the sin.theta polycrystalline x-ray diffraction technique. For the TiN films, the researchers will study the mechanism of compressive stress generation during growth under low energy ion bombardment. For the Mo/V superlattices, they will examine the tetragonal strain distortion theories for the supermodulus effect. The supermodulus effect is a two-three fold increase in the elastic modulus of thin film modulated structures observed for a small range of wavelengths of the composition modulation. They will also make measure- ments of the tetragonal strain, gradient in strain near the interface, and strength and coherency of the interface as a function of the wavelength of the modulation to determine if coherency strains can explain this enhanced mechanical behavior. The award recommendation provides funds to cover, as appropriate, international travel, local travel abroad, stipend, dependents' allowance if applicable, and a flat administrative allowance of $250 for the U.S. home institution.

This x-ray diffraction system is suitable for powder diffraction experiments, single crystal and thin film work, and is equipped with a full Eulerian specimen carrier for texture measurements. Access to this fully automatic, user-friendly system will be made to faculty and students throughout the University, in need of rapid specimen characterization, and will be incorporated in a teaching laboratory for training of students. Materials research efforts currently underway include: the local arrangement of point defects in non-stoichiometric oxides; studies of mercury-cadmium-telluride II-IV semiconductors to determine the state of local chemical order and atomic displacements; studies in iron-nickel-carbon steels to elucidate the effects of carbon ordering on matensite formation and determination of phase fractions and lattice paramaters of steels; determination of periodicities in two dimensions in metal-metal, metal-ceramic, and metal-semiconductor interfaces; residual stress measurements in microcracking ceramics, and phase characterization of zirconia oxide thermal barrier coatings.

Cohen 9304725 Northwestern University, E.I. Du Pont de Nemours and Dow Chemical have formed a Collaborative Access Team, known as DUNU, and are proposing to instrument and operate a sector at the Advanced Photon Source. A funding schedule, with costs to be shared equally by both parties has been agreed upon, covering both a five year construction phase, as well as a ten year minimum operations phase. Currently DUNU employs three full-time senior scientists and engineers headquartered at Northwestern (a nationwide search is on for a fourth senior scientist), with extensive experience in beam line construction and operations both at the Cornell High Energy Synchrotron Source (CHESS) and the National Synchrotron Light Source (NSLS Brookhaven), plus management of one of the largest x-ray diffraction laboratories in the country. The purpose of this Collaborative Access Team is to carry out research on the structure of advanced materials. Our understanding of the structure (atomic to micron level) is a crucial prerequisite to the development of new materials with enhanced properties. Synchrotron radiation has become an essential tool in every aspect of structural analysis and has revolutionized many subfields of science and engineering. Many members of our CAT have been very active users of our national facilities. The vastly increased capabilities of "third generation" machines, such as the APS and similar storage rings in Europe and Japan, promise a second revolution. A broad research program has been formulated, involving currently more than 30 principal investigators from Du Pont and Northwestern. At least fifty other scientists and engineers, students and post-doctoral fellows will ultimately be involved. Although many fields of materials science and engineering are represented in this research program, the research to be supported by the instrumentation in this project has a particular focus: It deals with materials, whose intermediate scale structure (nanometer to micrometer) has a profound influence on their properties. Such materials are of immense technological importance and include precipitation-hardening alloys, ceramics, polymers, cement and composite materials. Many elements of this research program are totally beyond current capabilities at available x-ray sources (conventional and synchrotron). The instrumentation that we will develop depends heavily (or crucially) on the characteristics of the APS. It is grouped in two experimental stations, both utilizing undulator radiation: 1. General purpose scattering instrument, suitable for all types of diffraction experiments (amorphous, powder and single crystal work, surface and interface diffraction, standing waves etc.). Collimated beams (0.1-1 mm) and microbeams will be available for diffraction and microprobe work. The microbeam capability is of particular interest in the context of this proposal. 2. Small Angle X-ray Scattering microtomography instrument equipped with 2-D position sensitive detector and environmental chamber with multiple attachments (low and high temperature, UHV, sample changer). This may be the first x-ray instrument with sufficient imaging and scattering resolution to allow the two techniques to overlap in studying micron- sized structural features. We believe that DUNU possesses all the key ingredients of a productive and strong Collaborative Access Team. Northwestern University anchors an interactive research community through its interdisciplinary research centers (many of which, such as the Materials Research Center and the Center for Advanced CementBased Materials are supported by the National Science Foundation) and individual faculty research. E.I. Du Pont de Nemours & Co. brings its immense capabilities in scientific research and development. It is a world leader in process chemistry and engineering and t he manufacturing of high technology products. It is the intent of this collaboration not only to share a station at this major facility, but to develop interactive, collaborative research between the two institutions (we have installed a videoconferencing link to aid this interaction).

9700674 Cohen The local atomic arrangements at surfaces of alloys is the major theme of this research. Of particular interest is how changes in the environment, such as reconstruction or interplanar spacing normal to the surface or segregation ,affect phase transitions such as ordering and clustering. Strain plays an important role in such reactions, and a beam line at Argonne Laboratory's new Synchrotron (the Advanced Photon Source, or APS) is used employing an X-ray glancing incidence technique. The X-rays sample a shallow range of depths producing diffuse scattering that is analyzed in a position-sensitive detector. From these data short range order parameters and distortions are obtained. Samples include single crystals of aluminum alloys that are prepared featuring a few facets with different possible relaxations. After heat treatment to produce zones, concentration profiles vs. depth are determined and Auger electron spectroscopy and low energy electron diffraction are used to look for evidence of surface reconstruction or relaxation. Diffuse scattering is measured vs. depth, and the surface structures and displacements modeled and compared to the bulk structure. %%% An understanding of surface structure aids in analysis of related phenomena, such as corrosion of metal alloys and crack initiation. ***