US-France Cooperative Research: Studies of Surface Melting in Crystalline Systems

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This award will support collaborative research in low temperature physics between Drs. Jay Dash and Oscar Vilches and their students, University of Washington, and Professors Michel Bienfait and Jean Suzanne, University of Aix-Marseille, France. The objective of the proposed project is to carry out studies of surface melting in crystalline systems. Two systems of particular interest are hydrogen dioxide-ice and thick physisorbed films of solid hydrogen isotopes. The surface melting of ice is of both fundamental interest and environmental importance. Ice undergoes melting or disordering transitions at its surfaces with many types of solids. The fundamental mechanisms which cause these changes, the characteristics of the transition layers and their dependence on the chemistry and morphology of the substrate are in dispute. The proposed research will seek to determine these characteristics by a combination of techniques, especially neutron diffraction and quasi-electric neutron scattering. The melting temperature of molecular hydrogen can be depressed to below 7.2 K by a combination of surface and quantum effects. The study of this effect is of major importance to the understanding of quantum fluids and solid- liquid interfaces of dissimilar materials. The proposed research focuses on characterization of the surface melted liquid by quasi elastic neutron scattering, complementary to thermodynamic measurements currrently underway at the University of Washington. The research will benefit from the complementary expertise of the two groups of investigators. Drs. Dash, Vilches and thier students have had a leading role in the study of adsorbed films and thier surfaces, particularly by thermoidynamic techniques. Drs. Bienfait and Suzanne have ha a comparably prominent role in the study of these same systems, but primarily by scattering techniques.