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The Structure Liquid Surfaces P. S. Pershan DEAS & Dept. Of Physics, Harvard Univ. Cambridge, MA 02421 DMR-0124936; NSF 03-03916; DE-FG02-88-ER45379 O.

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Presentation on theme: "The Structure Liquid Surfaces P. S. Pershan DEAS & Dept. Of Physics, Harvard Univ. Cambridge, MA 02421 DMR-0124936; NSF 03-03916; DE-FG02-88-ER45379 O."— Presentation transcript:

1 The Structure Liquid Surfaces P. S. Pershan DEAS & Dept. Of Physics, Harvard Univ. Cambridge, MA 02421 DMR-0124936; NSF 03-03916; DE-FG02-88-ER45379 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). 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,

2 Pershan: BarIlan Jan 06 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 Franklin Surfactants (oil) calm water surface waves Footprint of whale (biomaterial on surface of sea). http://web.mit.edu/1.63/www/ (Chiang C, Mei and T. R Akylas http://web.mit.edu/1.63/www/

3 Pershan: BarIlan Jan 06 Modern Era of Surface Science Ref: A. Zangwill, Physics at Surfaces (Cambridge University Press,1988) 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) 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) Liquid Surfaces: Reflectivity: Als-Nielsen and Pershan ‘ 82 (Liquid Crystal) & ’ 85 (Water): GID: Dutta ‘ 88, Grayer-Wolf ‘ 88(Langmuir monolayer on water). THIS TALK: X-RAY AND LIQUID SURFACES

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

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

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

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

8 Pershan: BarIlan Jan 06 Fluctuations of Surface of Bulk Liquid q max ~1/Atom Not  (Q xy )

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

10 Pershan: BarIlan Jan 06 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

11 Pershan: BarIlan Jan 06 Data for Water with increasing  Q y (1/Å) Q z (or  i  Increasing 0.3 Å -1 to 1 Å -1  Increasing 0.08 to ~ 1 Shpyrko, Fukuto, Pershan, Ocko, Gog, I. Kuzmenko, Deutsch,,Phys. Rev. B (2004). CMC CAT Peak vanishes for slight increase in Q z

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

13 Pershan: BarIlan Jan 06 Nematic Phase: 1st Observed Surface Induced Layering First Data (Pershan, Als-Nielsen.PRL, ‘ 84) R F (Q z ) T-T NA 0.05 C 2.8 11.6 1/Width Surface vs. Bulk |  (Q z )| 2

14 Pershan: BarIlan Jan 06 Reflectivity & Surface Structure Factor (Layers) Structure Factor  (Q z )| 2 Thermal Factor R(Q z ) =R F (Q z ) Simple Surface Surface Structure Factor When do surface layers appear? Quantitative Measure of  (Q z )! Prediction: Constructive Interference Q z =(4  )sin  =(2  /D)

15 Pershan: BarIlan Jan 06 Density Profile vs Depth Solid-liquid interface Hard wall 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 Liquid Crystals are Different: Why? What else is different? Liquid vapor interface

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

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

18 Pershan: BarIlan Jan 06 Digest of Liquid Surface Order LayeringIn-Plane Surface Order Nematic/Isotropic Liquid XtalYesNo MicroemulsionsYesNo Long Chain Alkanes, Alcohols, etc NoYes H2OH2ONo Elemental Liquid MetalsYesNo Alloys of Liquid MetalsYes Langmuir MonolayersNoYes Experiments: Simulations: Atom & Small-Non-Metallic MoleculesNo

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

20 Pershan: BarIlan Jan 06 Typical Liquid Metal Measurements Hg In Ga Effect of T (Liquid Ga) Structure FactorThermal Factor Observe Apparent Difference 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).

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

22 Pershan: BarIlan Jan 06 Metallic Layering Is not Due to High Surface Tension R/(R F x Thermal) for Ga, In and K   In(~550mN/m) Ga(~750mN/m) K(~100mN/m) H 2 O(73mN/m) H 2 O vs Liquid Metals H2OH2O K

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

24 Pershan: BarIlan Jan 06 Liquid Metals of Electronic Interest (I): BiSn 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). Energy Dispersive Reflectivity 142 °C T m =138°C  (Bi) ≈ 398  (Sn)≈567 dyne/cm

25 Pershan: BarIlan Jan 06 Liquid Metals of Electronic Interest (II): Au 71 Sn 29  Sn =559 mN/m ;  Au =1258 Density vs z! Au Sn

26 Pershan: BarIlan Jan 06 Liquid Metals of Electronic Interest (III) Au 80.5 Si 19.5 eutectic alloy Detector (  S )-Scan Alloy is Liquid  =780 dynes/cm

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

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

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

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

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

32 Pershan: BarIlan Jan 06 Summary  Solid vs Liquid Surfaces  Reviewed X-ray Methods of Surfaces Special Requirements of Liquids CARS,  -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

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