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The Structure Liquid Surfaces

Other Current and Principal Collaborators: J. Als-Nielsen, V. Balagurusamy , E. DiMasi, E. Kawamoto, O. Gang, P. Huber, O. Magnussen, K. Penanen, M. Regan, ,M.Schlossman, D.Schwartz, H. Tostmann, . The Structure Liquid Surfaces.

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The Structure Liquid Surfaces

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  1. Other Current and Principal Collaborators: J. Als-Nielsen, V. Balagurusamy, E. DiMasi, E. Kawamoto, O. Gang, P. Huber, O. Magnussen, K. Penanen, M. Regan, ,M.Schlossman, D.Schwartz, H. Tostmann, The Structure Liquid Surfaces • O. G. Shpyrko, A. Y. Grigoriev, R. Streitel,D. Pontoni, P. S. Pershan, M. Deutsch, and B. M. Ocko, "Atomic-scale surface demixing in a eutectic liquid BiSn alloy."Phys. Rev. Lett. 95, 106103 (2005). • O. G. Shpyrko, A. Y. Grigoriev, R. Streitel, V. Balagurusamy, P. S. Pershan, M. Deutsch, B. M. Ocko, M. Meron, and B. Lin, "Surface freezing and surface layering in AuSi Liquid Alloy",In Preparation (2005). P. S. Pershan DEAS & Dept . Of Physics, Harvard Univ. Cambridge, MA 02421 DMR-0124936; NSF 03-03916; DE-FG02-88-ER45379

  2. Footprint of whale (biomaterial on surface of sea).http://web.mit.edu/1.63/www/ (Chiang C, Mei and T. R Akylas Condensed Matter: 20th Century Solids:•Bulk (3d) Structure  Band Gaps, exotic Fermi Surfaces, etc•Surfaces (2d)  Localized Electron States, physisorption, metal/semiconductor interface (rectification), etc. Liquids: Absence of Structure  Less Phenomena•Bulk (3d): Liquid Structure Factor•Surfaces (2d): Surface tension, Langmuir monolayers, wetting. Ancient History of Liquid Surfaces:Pliny the Elder (~50 AD) & Ben FranklinSurfactants (oil) calm water surface waves Pershan: BarIlan Jan 06

  3. Modern Era of Surface Science True emergence of solid state surface physics:  Electron Spectroscopy (Brundle, 1974) & Auger Spectroscopy (Harris, 1974) followed by STM, AFM, etc ••••Synchrotron: SSRL(1973), NSLS (1984), APS (1998) •••• Ref: A. Zangwill, Physics at Surfaces (Cambridge University Press,1988) X-rays & Surfaces (Solid): •Reflectivity (Parratt ’54)•Grazing Incidence Diffraction(GID) (Marra, Eisenberger, Cho ’79) New tool: probe buried interfaces and structure far below the surface (i.e. GaAs-Al interface) THIS TALK: X-RAY AND LIQUID SURFACES Pershan: BarIlan Jan 06 Liquid Surfaces: Reflectivity: Als-Nielsen and Pershan ‘82 (Liquid Crystal)&’85 (Water):GID: Dutta ‘88 , Grayer-Wolf ‘88(Langmuir monolayer on water).

  4. Critical Angle (c) Classical Optics: Fresnel Reflectivity from Flat SurfaceA. H. Compton and S. K. Allison ‘35: X-ray Reflectivity: Flat Surfaces X-ray Energy: Typical Binding Energy: Index of Refraction Critical Wavevector Qc=(4π/)sin() 2π//c Pershan: BarIlan Jan 06

  5. Bragg Scattering From Crystal ks Reflection ~ ki Truncation Rods from Crystal Surface X-Rays and Crystal Surfaces Pershan: BarIlan Jan 06 Surface Information: Intensity along truncation rods Extra Peaks due to Surface Phases (reconstruction)

  6. Surface Structure Factor If Liquid Surface was FLAT Specular would be the Only Truncation Rod Bulk Liquid Diffuse Scattering: Separated via (Qx,Qy) Liquid vs Solid Surfaces Surfaces ARE NOT FLAT! Pershan: BarIlan Jan 06 Liquid Surface Information: Surface Structure Factor (Qz) Extra peaks due to Langmuir monolayer or Surface Frozen phases.

  7. For a solid: Fourier Transform  Surface Roughness Pershan: BarIlan Jan 06 Reflectivity Structure Factor + Debye -Waller

  8. Fluctuations of Surface of Bulk Liquid qmax~1/Atom Pershan: BarIlan Jan 06 Not (Qxy)

  9. Solid: Effect of Resolution on R(Qz)is Minor Liquid: Small i~Nearly Solid Like Liquid: Large i~Capillary Effects Dominate Increasing Qz or Effect of Resolution Scan Detector s Pershan: BarIlan Jan 06 Small angles liquids are like solids / large angles they are not!

  10. Simulated Detector Scan The Liquid Surface Reflectometer HasyLab: Als-Nielsen, Christensen, Pershan, PRL (`82). NSLS: X22B, X19C APS: CHEMMATCARS, CMC, CAT ESRF: ID15A (Alternate Design) H. Reichert ‘03 Pershan: BarIlan Jan 06

  11. Peak vanishes for slight increase in Qz Qz (or iIncreasing 0.3 Å-1 to 1 Å-1 Increasing0.08 to ~ 1 Qy(1/Å) Data for Water with increasing  CMC CAT Shpyrko, Fukuto, Pershan, Ocko, Gog, I. Kuzmenko, Deutsch,,Phys. Rev. B (2004). Pershan: BarIlan Jan 06

  12. Isotropic/Nematic/Smectic-A Surface Induced Smectic z Surface Induced Layering: (Qz)Nematic Surface Smectic-A Order Pershan: BarIlan Jan 06

  13. 1/WidthSurface vs. Bulk |(Qz)|2 Nematic Phase: 1st Observed Surface Induced Layering First Data (Pershan, Als-Nielsen.PRL, ‘84) RF(Qz) T-TNA 0.05 C 2.8 11.6 Pershan: BarIlan Jan 06

  14. Surface Structure Factor Simple Surface Structure Factor F(Qz)|2 Thermal Factor R(Qz) = RF(Qz) Reflectivity & Surface Structure Factor (Layers) Prediction: Constructive Interference Qz=(4p/l)sin a =(2p/D) •When do surface layers appear? •Quantitative Measure of F(Qz)! Pershan: BarIlan Jan 06

  15. Solid-liquid interfaceHard wall Density Profile vs Depth Liquid vapor interface Molecular Simulations G. A. Chapela, G. Saville, S. M. Thompson, and J. S. Rowlinson, "Computer simulation of a gas-liquid interace",J. C. S. Faraday Trans II 73, 1133 (1977).Lennard-Jones (12,6) molecules Accepted Lore: Density Profile at Free Surface is Monotonic Pershan: BarIlan Jan 06 Liquid Crystals are Different:• Why?• What else is different?

  16. Bulk (3d)Correlation Function: Characteristic Wavevector: Q0 & Correlation Length:  Surface Induced Layering: Surface Field: h(z=0) Translation Energy vs Entropy Simple Thoughts on Surface Layering Order Parameter (r): Electron, Mass, or Particle Density Bulk Susceptibility: Zsurf(Q0) Pershan: BarIlan Jan 06

  17. 2D Crystal 2D Liquid Langmuir Monolayeron H2O or Hg 2D Surface Crystal Surface Freezing Long Chain Alkanes Metallic Alloys SubSurface 3D Liquid Solid/Liquid Interface •Commensurate/Incommensurate 2d •Layering In Plane Surface Order Pershan: BarIlan Jan 06

  18. Digest of Liquid Surface Order Experiments: Simulations: Pershan: BarIlan Jan 06

  19. D'Evelyn & . Rice, J. Chem. Phys., 1983. Simuation (Lennard-Jones Liquids) For Metals Particle-Particle InteractionsChange Across The Surface Metallic Liquids Dielectric Liquids Vapor: Neutral Atoms Interactions are Same in Vapor and Liquid Different Interactions Liquid: Positive Ions in Sea of Negative Fermi Liquid Why are Liquid Metals Different? Pershan: BarIlan Jan 06 This influences the structure of the surface! Goal: Measure Intrinsic Surface Structure Factor (Qz)

  20. Hg Ga In Observe Apparent Difference Typical Liquid Metal Measurements • Magnussen, Ocko, Regan, Penanen, PershanM. Deutsch ,PRL (1995). • Regan, Kawamoto, Pershan, Maskil, Deutsch, Magnussen, Ocko, L. E. Berman, PRL (1995). • Tostmann,DiMasi, Pershan, Ocko, Shpyrko, M. Deutsch, PRB (1999). Effect of T (Liquid Ga) Structure Factor Thermal Factor Pershan: BarIlan Jan 06

  21. Liquid Ga Electron Density Profile Removal of Thermal Factor Indium T- effects removed& not removed Ga & In with T-effects removed Pershan: BarIlan Jan 06

  22. R/(RF x Thermal) for Ga, Inand K Metallic Layering Is not Due to High Surface Tension H2O vs Liquid Metals  In(~550mN/m)Ga(~750mN/m)K(~100mN/m)H2O(73mN/m) K Pershan: BarIlan Jan 06 H2O

  23. Gibbs Absorption: GaBi Alloy (Bi)= 398 mN/m (Ga)=750 mN/m Pershan: BarIlan Jan 06 Monolayer of Bi Coats Liquid Surface Thick Wetting Layer of Bi-Rich Liquid vs Temperature

  24. (Bi)≈ 398(Sn)≈567 dyne/cm Liquid Metals of Electronic Interest (I): BiSnO. G. Shpyrko, A. Y. Grigoriev, R. Streitel, D. Pontoni, P. S. Pershan, M. Deutsch, and B. M. Ocko, "Atomic-scale surface demixing in a eutectic liquid BiSn alloy."Phys. Rev. Lett. 95, 106103 (2005). Energy Dispersive Reflectivity 142 °C Tm=138°C Pershan: BarIlan Jan 06

  25. Density vs z! Au Sn Liquid Metals of Electronic Interest (II): Au71 Sn29 Sn=559 mN/m ; Au=1258 Pershan: BarIlan Jan 06

  26. Liquid Metals of Electronic Interest (III) Au80.5Si19.5 eutectic alloy Pershan: BarIlan Jan 06 Detector (S)-ScanAlloy is Liquid g=780 dynes/cm

  27. Simple Layering Model (i.e. Ga or In)1200 dyne/cm 718 dyne/cm Surface Phase Transition vs T Reflectivity/(RF)2 Phases Not Divided by Thermal Pershan: BarIlan Jan 06

  28. Typical ProfilesGa & In Low T Phase High T Phase Model Density Profiles AuSi(Preliminary) Pershan: BarIlan Jan 06

  29. 2D Order of Surface Phases (GID) Au (4) Si(8) In-plane structure model: AuSi2 Low Temperature Phase Electron Density~ 1/2 to 1/3 bulk Silicide on Au(111)Green & Bauer, JAP, ‘81 (7.35 Åx 9.22 Å) Pershan: BarIlan Jan 06 Truncation Rod Monolayer

  30. AuSi ~ 10 x AuGe & elements AuSi, AuGe vs Elements Pershan: BarIlan Jan 06

  31. Effects: •Layering induced by hard wall!•Surface induced in-plane order! Path > 20 mm Ga Abs. Length 0.05mm(10 KeV) 0.13mm(30KeV) H. Reichert, et a;/ Physica B-Condensed Matter (03). van der Veen and Reichert, MRS Bulletin (04). The FutureThe Buried Liquid/Solid Interface Problems with conventional approach: •Absorption in Liquid•Bulk Diffuse Scattering Pershan: BarIlan Jan 06 Si Abs. Length ~17 mm(70 Kev) Beam Height ~10 m Path ~ 5 mm

  32. Summary • Solid vs Liquid Surfaces • Reviewed X-ray Methods of Surfaces Special Requirements of LiquidsCARS, -CAT, CMC • Surface Roughness: Capillary Waves • Examples of Liquid Surface Order • Liquid Metals vs Non-Metals • Alloys: AuSi >10 x Others: Surface Freezing • Future: Buried Interfaces Pershan: BarIlan Jan 06

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