The Structure Liquid Surfaces

1
The Structure Liquid Surfaces

• P. S. Pershan
• DEAS Dept . Of Physics, Harvard Univ.
• Cambridge, MA 02421

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).
DMR-0124936 NSF 03-03916 DE-FG02-88-ER45379
2
Condensed Matter 20th Century
SolidsBulk (3d) Structure ? Band Gaps,
exotic Fermi Surfaces, etcSurfaces (2d) ?
Localized Electron States, physisorption,
metal/semiconductor interface (rectification),
etc.
Liquids Absence of Structure ? Less
PhenomenaBulk (3d) Liquid Structure
FactorSurfaces (2d) Surface tension, Langmuir
monolayers, wetting.
Ancient History of Liquid SurfacesPliny the
Elder (50 AD) Ben Franklin Surfactants (oil)
calm water surface waves
3
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)
THIS TALK X-RAY AND LIQUID SURFACES
Liquid Surfaces Reflectivity Als-Nielsen and
Pershan 82 (Liquid Crystal)85 (Water)GID
Dutta 88 , Grayer-Wolf 88(Langmuir monolayer on
water).
4
X-ray Reflectivity Flat Surfaces
X-ray Energy Typical Binding Energy
Index of Refraction
Critical Wavevector Qc(4p/?)sin(?) 2p/???/c
5
X-Rays and Crystal Surfaces
Surface Information Intensity along truncation
rods Extra Peaks due to Surface Phases
(reconstruction)
6
Liquid vs Solid Surfaces
Surfaces ARE NOT FLAT!
Liquid Surface Information Surface Structure
Factor ?(Qz) Extra peaks due to Langmuir
monolayer or Surface Frozen phases.
7
Surface Roughness
Reflectivity ?Structure Factor Debye -Waller
8
Fluctuations of Surface of Bulk Liquid
qmax1/Atom
Not ?(Qxy)
9
Effect of Resolution
Scan Detector ?s
Small angles liquids are like solids / large
angles they are not!
10
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
Data for Water with increasing ?
CMC CAT
Shpyrko, Fukuto, Pershan, Ocko, Gog, I. Kuzmenko,
Deutsch,,Phys. Rev. B (2004).
12
Surface Induced Layering ?(Qz)Nematic Surface
?Smectic-A Order
13
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
14
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)!
15
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?
16
Simple Thoughts on Surface Layering
Order Parameter ?(r) Electron, Mass, or
Particle Density
Bulk Susceptibility Zsurf(Q0?)
17
In Plane Surface Order
18
Digest of Liquid Surface Order
Experiments
Simulations
19
Why are Liquid Metals Different?
This influences the structure of the surface!
Goal Measure Intrinsic Surface Structure Factor
?(Qz)
20
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
21
Removal of Thermal Factor
Indium T- effects removed not removed
Ga In with T-effects removed
22
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
H2O
23
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
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
Tm138C
25
Liquid Metals of Electronic Interest (II) Au71
Sn29
?Sn559 mN/m ?Au1258
26
Liquid Metals of Electronic Interest (III)
Au80.5Si19.5 eutectic alloy
Detector (?S)-ScanAlloy is Liquid g780 dynes/cm
27
Surface Phase Transition vs T
Reflectivity/(RF)?2 Phases
Not Divided by Thermal
28
Model Density Profiles AuSi(Preliminary)
29
In-plane structure model AuSi2 Low Temperature
Phase
2D Order of Surface Phases (GID)
Electron Density 1/2 to 1/3 bulk
Silicide on Au(111)Green Bauer, JAP, 81 (7.35
Åx 9.22 Å)
Truncation Rod ?Monolayer
30
AuSi, AuGe vs Elements
31
The Future The Buried Liquid/Solid Interface
Problems with conventional approach
Absorption in Liquid Bulk Diffuse Scattering
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 Liquids CARS, ?-CAT, CMC
• Surface Roughness Capillary Waves
• Examples of Liquid Surface Order
• Liquid Metals vs Non-Metals
• Alloys AuSi gt10 x Others Surface Freezing
• Future Buried Interfaces