The Structure Of The Liquid Vapor Interface

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Download or read book Experimental and Theoretical Studies of Liquid-Solid and Liquid-Vapor Interfaces of Metals and Alloys, Grant DE-FG02-06ER46321 written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The research supported by ER46321 was designed to understand in microscopic detail the structures of the interfaces between liquid metals and alloys and solid media. The system chosen for study, because of detailed knowledge of the structure of the corresponding liquid alloy-vapor interface, was the interface between a Si crystal and a dilute alloy of Pb in Ga. Experimental study of the Si:PbGa interface was anticipated to be very difficult; it requires preparation of an interface between a liquid metal and a solid surface that is flat to better than a nanometer on the scale length of the x-ray coherence, alignment of the x-ray beam and the surface in the sub-micro radian regime, and the use of high energy x-rays to penetrate the window and reach the interface without disastrous loss of intensity. The experimental design was subject to compromises forced by the limit to the highest x-ray energy available at the ChemMatCARS beam-line, namely 30 keV, which reduced the scattered signal relative to what can be obtained with higher x-ray energy. Although considerable progress was achieved during the support period and its no-cost extension, the difficulties encountered prevented completion of the studies and the data collected are incomplete. These data hint at the existence of unexpected structural features of the interface, in particular that Pb dimers play an important role in the interfacial structure. These data provide a different picture of the interface from the pentagonal structure inferred to be present in the interface between pure Pb and Si 001 (Nature 408, 839 (2000)), but much like the Ga dimers in the interface between liquid Ga and the 100 face of diamond (Nature 390, 379 (1997), J. Chem. Phys. 123, 104703 (2005)). However, during the latter part of the support period significant progress was made in the theoretical description of the liquid metal-crystal interface. In particular, stimulated by the results of an experimental study of the interface between liquid Hg and the reconstructed (0001) face of sapphire, we developed an extension of the self-consistent quantum Monte Carlo scheme previously used to study the structure of the liquid metal-vapor interface. The calculated density distribution is in very good agreement with that inferred from the experimental data. We conclude, contrary to the original interpretation offered by Tamam et al (J. Phys. Chem. Lett. 2010, I, 1041-1045), thast to account for the difference in structure between the liquid Hg-vapor and liquid Hg-reconstructed (0001) Al2O3 interfaces it is not necessary to assume there is charge transfer from the Hg to the Al2O3. Rather, the available experimental data are adequately reproduced when the van der Waals interaction of the Al and O atoms with Hg atoms and the exclusion of the electron density from the Al2O3 via repulsion of the electrons from the closed shells of the ions in the solid are accounted for. We believe this interpretation will be applicable to a wide range of liquid metal-crystal interfaces.