Nano-Liquids, Nano-Particles, Nano-Wetting:
X-ray Scattering Studies
P.S. Pershan: Physics & DEAS, Harvard Univ.
Physics of Confined Liquids with/without Nanoparticles:





Confinement Phase transitions are suppressed and/or shifted.
When do Liquids fill nano-pores?
(i.e. wetting and capillary filling).
Contact Angles vary with surface structure. (i.e. roughness & wetting)
Attraction/repulsion between surfaces. (i.e. dispersions or aggregation)
Important for formation of Nanoparticle arrays:
(i.e. electronic/optical properties, potential use for sensors,
catalysis, nanowires)
How will these affect nano-scale liquid devices?
How will these affect processes that are essential for
nano-scale liquid technology?
Co Workers
Harvard Students and Post Docs
K Alvine
D. Pontoni
O. Gang
O. Shpykro
M. Fukuto
Y. Yano
Graduate Student PhD March 06,
Post Doc.
Former Post Doc.
Former Grad. Student & Post Doc.
Former Grad. Student & Post Doc.
Former Guest.
Current: NIST
Current: Brookhaven National Lab.
Current: Argonne National Lab
Current: Brookhaven National Lab
Current: Gakushuin Univ., Japan
Others
B. Ocko
D. Cookson
A. Checco
F. Stellacci
K. Shin
T. Russell
C. Black
Brookhaven National Lab.
Argonne National Lab.
Brookhaven National Lab.
MIT
U. Mass. Amherst
U. Mass. Amherst
I.B.M.
Experiments: Thin to Thick Liquids
Thin liquids adsorb on nano-structured surface
Liquids fill nano-pores
Thin liquids surround and solvate nano-particles
Control of Liquid Thickness
Outer cell: 0.03C
Inner cell: 0.001C
Wetting film on Si(100) at T
= Trsv + DTm.
Saturated
vapor
Nano Thin Films
Bulk liquid reservoir:
at T = Trsv.
Vapor Pressure Thickness
mP ~ DTm
Van der Waals
DTm ~ m ~ D 3
Van der Waals 1/3 Power Law
r r
r r 6
V ( r1  r2 ) ~ A r1  r2
Molecule-Molecule:
r1
z
r2
Molecule to Surface:
V (z) ~ 
3r 
d r2  A

r r 6
r1  r2  ~ A z 3

X-Ray Reflectivity: Film Thickness


Qz  4  sin 
2

2
R(Qz )  RF (Qz ) (Qz ) exp Qz2 eff
2
(Qz ) ~ A 2  B 2  2AB cosQz D

2
exp[Qz2 eff
]
Example of 1/3 Power Law
Methyl cyclohexane (MC) on Si at 46 °C
• Via temperature offset
DmComparisons
• Via gravity
Thickness L [Å]
For h < 100 mm,
Dm < 105 J/cm3
L  (2Weff /Dm)1/3  (DTm)1/3
L > ~500 Å
 small Dm, large L
• Via pressure
under-saturation
For DP/Psat > 1%,
DTm [K]
Dm > 0.2 J/cm3
L < 20 Å
 large Dm, small L
Dm [J/cm3]
Capillary Filling of Nano-Pores (Alumina)
Capillary Filling:
Dmor DT
Transition
Energy Cost of Liquid
Surface  2  R0  D 
Min: DR0
2
Volume  Dm  R02  R0  D 


Min: D0


Anodized Alumina (UMA)
Top
Fig. 1: AFM image (courtesy
UMA) of anodized alumina
sample. The ~15nm pores are
arranged in a hcp array with
inter-pore distance ~66nm
~90 microns thick
~ 15nm
Side
Fig 2: SEM (courtesy of UMA)
showing hcp ordering of pores
and cross-section showing large
aspect ratio and very parallel
pores.
SAXS Data
Pore fills with liquid Contrast Decreases
Short Range Hexagonal Packing
<10>
∆T decreasing
Thin films
<11>
<20>
Condensation
Capillary filling—film thickness
Wall film thickness [nm]
Transition
Liquid Layer ~ 1nm
Pore Diameter~15nm
What is the
filling process?
~ 2/D
Geometry: Theoretical Background
C. Rascon and A. O. Parry, "Geometry-dominated fluid adsorption on
sculpted solid substrates",Nature 407, 986 (2000).
Liquid Filling of
Troughs


y  L(x / x0 )

Parabolic Pits =2): Tom Russell (UMA)
Diblock Copolymer in
Solvent
Self Alignment on Si
PMMA removal by
UV degradation &
Chemical Rinse
Reactive Ion Etching
C. Black (IBM)
~40 nm Spacing
~20 nm Depth/Diameter
Height ~ r 2
 2
X-ray Grazing Incidence Diffraction (GID)
] In-plane surface structure
Diffraction Pattern of Dry Pits
Hexagonal Packing
Liquid Fills Pore:
Scattering Decreases:
Thickness D~Dm
Cross over to other filling!
X-ray Measurement of
Filling
GID
Reflectivity
Filling
Electron Density vs DT
Filling
Results for Sculpted
Surface
Sculpted is Thinner than Flat
 
 c ~ DT
 c
Flat Sample
R-P Prediction
c~3.4
c
Observed
c
Sculpted Crossover to
Flat
Gold Nanoparticles
& Controlled Solvation
Conventional Approach:
Dry Bulk Solution  Imaging of Dry Sample
Controlled Wetting:
Liftoff Area
Dry Monolayer  Adsorption (Wetting Liquid) Of Monolayer
Formation
Langmuir
Isotherms
Thiol Coated Au Particles
TEM
bi-modal distribution
Size Segregation
Stellacci et al OT: MPA (2:1)
OT=CH3(CH2)7SH
MPA=HOOC(CH2)2SH
GID: X-ray vs Liquid Adsorption
(small particles)
Adsorption
GID
Return to Dry
Qz
Qxy
Qxy
Qxy
Reversible Self Assembly: Annealing
Bimodal/polydisperse Au nanocrystals in equilibrium with undersaturated vapor
Poor vs Good Solvent
Good Solvent
(1) dry
Reversible
(2) ethanol DT ~ 1 K
Aggregation
in Poor
Solvent
(3) ethanol DT ~ 15 mK
(4)
QuickTime™ and a
TIFF (LZW) decompressor
dry are
again
(etOH
extracted)
needed
to see
this picture.
(5) toluene DT = 15 K
(6) toluene DT ~ 15 mK
Dissolution
in Good
Solvent
(7) toluene DT ~ 3 K
Self Assembly
NanoParticle SelfAssembly in Nanopores: Tubes
Empty
50 nm
SEM of empty pores, diameter~30nm
Fill with
Particles
~2nm dia.
Filled
TEM of nanoparticles in pores.
SAXS Experimental Setup
Brief experiment overview:
•Study in-situ SAXS/WAXS of particle self
assembly as function of added solvent.
•Solvent added/removed in controlled way
via thermal offset as in flat case.
Scattered
x-rays
Incident
x-ray's
Alumina membrane
With nano-particles
Top
z
DT
Qx
Toluene
Q
Small Qx: Pore-Pore Distances
Large Qx, Qy.Qz: Particle-Particle Distances
x
Qz
Small Q peaks pore filling hysteresis
Heating/Cooling, w/ nanoparticles
With nanoparticles
Thermal Cycling; Hysteresis
<01>
<11>
<02>
Volume (normalized)
Hex.
Packing
1.2
1
Heating
Cooling 2
Cooling 1
0.8
0.6
0.4
0.2
0
-0.2
0
Note: Shift in
Capillary Condensation
• Decrease/Increase in contrast indicates
pores filling/emptying.
•Capillary transition shifts from
for pores w/o nanoparticles
to about ~8K w/ nanoparticles
•Strong hysteresis
~2K
T~ /R
4
8
12
16
20
24
28
32
DT (K)
Below: w/o nanoparticles
Summary of Au-Au Scattering(Drying)
Images
Slices
Real space model
Intensity
Cylind.
Shell
q radial
Intensity
q radial
Intensity
Shell +
Isotropic
solution
q radial
Heating
Shell +
Isotropic
clusters
Summary
•
•
•
•
Control Thickness: DT~Dm
X-ray: Non-destructive probe
Capillary Filling: pores & structures
Thin Liquid Solvation