2. Non-Harvard Collaborators: Ben Ocko, Elaine DiMasi, Olaf Magnussen Physics Dept. Brookhaven National Laboratory Moshe Deutsch: Bar Ilan University, Israel Binhua Lin, Mati Meron, Tim Graber, Jeff Gerbhardt, Advanced Photon Source Harvard Students/Postdocs Alexei Grigoriev, Patrick Huber, E.H. Kawamoto, Holger Tostmann, Mike Regan, Oleg Shpyrko. The Surface Structure of Liquid Metals and Alloys Support: DE-FG02-88-ER45379/NSF- DMR-0124936 * Current associates are underlined Oleg Shpyrko

3. Liquid Surfaces: Metals/Non-Metals Are Different For Metals Particle-Particle Interactions Change Across The Surface D'Evelyn &. Rice, J. Chem. Phys., 1983. 78: p. 5225. This influences the structure of 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

4. Non-Metal Liquids Predictions of Monte Carlo Calculations Average Density vs Distance From Surface(z) Chapela & Saville, 1978 Hard Wall = > Layers Free Surface No-Layer D'Evelyn & Rice, 1983 Metallic Liquids: Layers @Free Surface Liquid/Vapor Surface Structure Factor  (Q z )

5. X-ray Reflectivity: R(Q z ) &  (Q z ) Quantitative Measure of  (Q z )! Surface Structure Factor Prediction: Constructive Interference Q z =(4  )sin  =(2  /D) R(Q z )~|  (Q z )| 2 QzQz Surface Normal Wave vector Transfer Measured Hg (1995) Ga (1996) In (1999) Hg In Ga Note Difference

6. Thermal Effects on Reflectivity R(Q z ) = Ideal Flat Surface: Fresnel R F (Q z ) Structure Factor  (Q z ) Thermal Factor Differential Cross Section: Thermal Roughness  Phase Shifts QxQx Parallel Surface Wave Vector Transfer

7. Liquid vs Solid Surfaces Depends on Resolution Liquid Liquid Surface 2D SurfaceTension Gravity (|x-x’|~mm) Solid Independent of Resolution Resolution

8. Measure of Structure Factor Requires Thermal Effects be Removed R(Q z ) = Ideal Flat Surface: Fresnel R F (Q z ) Structure Factor  (Q z ) Thermal Factor  (Q z,T) R(Q z ) Large (T/  Q z 2 No specular peak if  ~2!  Surface Tension

9. To Understand Thermal Effects Diffuse Scattering From Liquid Surface Q x =(2  )[cos  -cos  ] Q z =(2  )[sin  +sin  ] Diffuse Scattering for Liquid Indium Solid Lines: Theory Known Surface Tension  is Only  Adjustable Parameter

10. Demonstration of Thermal Removed: Liquid Gallium Electron Density: Ga and In Average Electron Density Indium (with/without T effects). Electron Density Profile

11. Issue 1 What other metals can be studied? ElementTm (K)  Tm/  P_melt(mm) Ga302.937180.42 Hg234.284980.471.2E-06 Sn505.1185600.90 In429.325560.77 K336.83880.87~1.0E-6 Zn692.737820.892.2E-01 Al933.529141.02 Cu1356.613031.049.7E-04 Cd594.15701.041.1E-01 Bi544.53781.44 Li (Chemistry)453.693981.14 Au1337.5811691.141.6E-05 Tl576.74641.24 Pb600.644581.31  (i.e. T/  ) must be small P & T : low enough for UHV(Hg, K, Na are special)

12. Measurement of Potassium Good: Oxides Dissolve in Bulk Liquid  Clean Surface Bad: Low   at layering peak is large, R(Q z ) too small Ga In K Maximum Q z ~0.85Q Peak Data  Layering in K is same as Ga, In.  Debye-Waller X 10 -2

13. R(Q z ) Possible ModelSpacing of 1st Layer Reduced~10% Anomalous Layering of Liquid Sn Surface Bump Not seen in Ga,In Bump  Surface Density Is Higher Than Bulk!

14. Ga K H 2 O Is there experimental evidence that dielectric liquids are not layered? Water:  dynes/cmK:  dynes/cm R(Q z ) R(Q z )/R F (Q z ) Water does not show indication of surface layering!

15. If we can’t study other pure metals, what can we do? Alloys Surface Chemistry of Liquid Metals (oxidation) Surface: Heavier Bi rich liquid Bulk: lighter Ga rich liquid! GaBi: Binary Phase Diagram BiGa Thickness of heavier Bi rich layer. Short Range Wetting

16. Keep Looking: i.e. Alloys for Electronics Example: AuSi Low Temperature Eutectic AuSi Diffuse Scattering Alloy is Liquid  =780 dynes/cm

17. Summary 1- To Measure Liquid Surface Structure Factor |  (Q z )| Effects of Capillary Waves. 2- |  (Q z )| of Free Surface of Liquid Metals Exhibits Atomic Layering! 3- Water does Not! What about other non-metallic liquids. 4- Surfaces of Liquid Alloys: Interesting Physics Sn: Anomalous Surface GaBi: Short Range Wetting AuSi: Enormously Intense Future