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Liquid Metal Surfaces P. S. Pershan SEAS & Dept of Physics, Harvard Univ., Cambridge, MA, USA

Liquid Metal Surfaces P. S. Pershan SEAS & Dept of Physics, Harvard Univ., Cambridge, MA, USA. Colleagues. Harvard, Non-Harvard, Beam Line. z. Idea! Als-Nielsen, Christensen, Pershan,(1982). 1 st Synchrotron Studies: Liquid Crystal Surfaces .

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Liquid Metal Surfaces P. S. Pershan SEAS & Dept of Physics, Harvard Univ., Cambridge, MA, USA

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  1. Liquid Metal SurfacesP. S. PershanSEAS & Dept of Physics, Harvard Univ., Cambridge, MA, USA • Colleagues Harvard, Non-Harvard, Beam Line

  2. z Idea!Als-Nielsen, Christensen, Pershan,(1982) 1st Synchrotron Studies: Liquid Crystal Surfaces Tilt Monochromator to Steer beam downward by a Horizontal liquid surface. Liquid Crystal: Isotropic/Nematic/Smectic-A Surface Induced Smectic Reflectivity Reflectivity Normalized

  3. Kinematics & Reflectivity: Flat Surface Reflectivity:Flat Surface z x Fresnel Resolution: Not True for Liquids Reflectivity Electron Density (Liq. Xtal) Fresnel Structure Factor Temperature Dependence of Liq. Xtal Surface.

  4. No Layering for Water and Simple Liquids Liquid Crystal Simple Liquid du A. Braslau et al. PRL (1985). a l du<l Surface Defines a Layer du≥a Surface Does NotDefine a Layer Hard WallLayer Free Surface ✕ Layers Surface Roughness Molecular SimulationsChapela et al. (1977)

  5. Hg Ga In Free Surface of Liquid Metal: Hard Wall Metallic Liquids(D’Evelyn & Rice ‘83) Liquid: Positive Ions in Sea of Negative Fermi Liquid Interface Vapor: Neutral Atoms • Suppression of • Local Fluctuations • Local Hard Wall.  Layers Hg. Magnussen et al. (1995). Ga Regan et al.(1995). Goal: Measure Electron/Atom Density Profile!

  6. Capillary Waves & Thermal Roughness Flat surface: (Qzh<<1) Signal 2D Liquid Surface Sinha et al.’88 Rough Phase Shift

  7. Capillary Effects: H20 & Ga Water (Schwartz ’90): Slits 5.0 mm 2.0 mm 0.8 mm F(Qz) for Liquid Ga (Regan, ’96)

  8. Diffuse Scattering  Surface Tension(g) Compare Ga/In Diffuse Scattering for In b≠a g Compare r(z) In Ga Hg Ga In Solid Line No Adjustable Parameters

  9. Simplest Surface Structure Model DCM (Magnussen ’95)

  10. Elemental Liquid Metals Studied No Bump/Bump • Why are 1st Layers for Bi and Sn different from K, Ga and In? • Why is Hg different from all others? Measureable Difference in 1st Layer

  11. Eutectic Alloys J. W. Gibbs ~1920Surface Adsorption: A/B AlloyIf Surface Tension: A > B Surface is Rich in “B”. *(kJ/mol)Takeuchi and Inoue, Mater. Trans. 46 (2005)

  12. Alloy: Bi and Sn Bi=378, Sn=560, Energy Dispersion: f(E) Adsorption (Bi)≈ 398(Sn)≈567 dyne/cm Scat. Ampl. Gibbs Surface Adsorption(BiSn)

  13. Surface Freezing Au82Si18Eutectic R/RF × 20 DCM R/RF DCM 2D Surface Crystals:Grazing Incidence Diffraction 1st Order Transition There is no theoretical explanation!

  14. AuGe Eutectic(Should be Similar to Au-Si) Au-Si Au-Si Au-Ge Bumphigher density in 1st layer. No Energy effect  Ge in 1st layer ≤40atm%. f`(E) @AuL3-Edge ×0.82 11.05 kev 11.915 kev • Small Gibbs (Different from Au-Sn, etc)! • No Enhanced Layering or 2D order(Different from Au-Si)!

  15. AuSiGe-Ternary Eutectic Ge Time average 0.8atm%Ge Eutectic Line 18atm%Si Au Si 0% Si Surface Frozen Ge≤6.5 atm% What is the physics of the cross over from Si type to Ge type surface between 2.5 atm% and 6.5 atm%?

  16. Pd81Ge19(Dec.’08) Expected same 2D surface order for Pd81Ge19 as Au82Si18! Not found; however, something new! Metallic Clusters (Giant Unit Cells) Preliminary fit. Ref: Urban &Feuerbacher, J.Non-Crys.Sol.(04) Quenched Icosahedral Clusters Small angle oscillations! Mg32(Al,Zn)49 ~4% r/r∞ 14nm Others: NaCd2 30Å YbCu4.5 44-49Å Al3Mg2 28Å

  17. Summary • Metal/Vapor InterfaceAtomic Layering: • Surface Structure Factor - F(Qz):Measurement affected by thermal roughness. Requires knowledge of surface tension. • Surface tension: measured with diffuse scattering: • Surface tension effect demonstrated for Ga/In • Subtle differences in elemental surfaces (Ga, In, K vs. Sn, Bi vs Hg) • Alloys: Surface tension vs. Enthalpy of MixingGibbs absorption is not simple. No reliable theory. • Au82Si18 anomalously strong layering and 2D order.Why are Au82Si18, Au72Ge28 and Pd81Ge19 all different? • Need for THEORY! • New Result (Preliminary): Surfaces & Icosahedral Metallic Clusters

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