Nano-Liquids, Nano-Particles, Nano-Wetting: X-ray Scattering Studies Physics of Confined Liquids with/without Nanoparticles: Confinement Phase transitions.

Nano-Liquids, Nano-Particles, Nano-Wetting: X-ray Scattering Studies

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?

P.S. Pershan: Physics & DEAS, Harvard Univ.

Co Workers

Harvard Students and Post DocsK Alvine Graduate Student PhD March 06, Current: NIST D. Pontoni Post Doc.O. Gang Former Post Doc. Current: Brookhaven National Lab.O. Shpykro Former Grad. Student & Post Doc. Current: Argonne National LabM. Fukuto Former Grad. Student & Post Doc. Current: Brookhaven National LabY. Yano Former Guest. Current: Gakushuin Univ., Japan

OthersB. Ocko Brookhaven National Lab.D. Cookson Argonne National Lab.A. Checco Brookhaven National Lab.F. Stellacci MITK. Shin U. Mass. AmherstT. Russell U. Mass. AmherstC. Black I.B.M.

Experiments: Thin to Thick LiquidsThin liquids adsorb on nano-structured surface

Thin liquids surround and solvate nano-particles

Liquids fill nano-pores

Control of Liquid Thickness

Saturated vapor Bulk liquid reservoir:

at T = Trsv.

Wetting film on Si(100) at T = Trsv + T.

Outer cell: 0.03CInner cell: 0.001C

T ~δ ~D−3

Vapor Pressure Thickness

δδP ~ T

Van der Waals

Nano Thin Films

Van der Waals 1/3 Power Law

Molecule to Surface: V (z) ~ d3r

r2 Arr1 −

rr2

6⎡⎣⎢

⎤⎦⎥~A z3∫

Molecule-Molecule: V (

rr1 −

rr2 ) ~A

rr−

rr2

6

r1

r2

z

X-Ray Reflectivity: Film Thickness

Qz = 4π λ( )sinα

€

Φ(Qz )2

~ A2 + B2 + 2AB cos QzD[ ]

R(Qz ) =RF (Qz) Φ(Qz)

2exp −Qz

2σeff2

( )

exp[−Qz

2σeff2 ]

Example of 1/3 Power Law

Methyl cyclohexane (MC) on Si at 46 °C

T [K]

Thi

ckne

ss L

[Å

]

L (2Weff /)1/3 (T)1/3

[J/cm3]

• Via temperature offset

Comparisons

• Via gravity

For h < 100 mm,

< 105 J/cm3

L > ~500 Å

small , large L

• Via pressure under-saturation

For P/Psat > 1%,

> 0.2

J/cm3

L < 20 Å

large , small L

Capillary Filling of Nano-Pores (Alumina)

or TCapillary Filling:

Transition

Energy Cost of Liquid

2πγ R0 −D⎡⎣ ⎤⎦Surface

Min: DR0

π R0

2 − R0 −D( )2⎡

⎣⎢⎤⎦⎥

Volume

Min: D0

Anodized Alumina (UMA)

Fig. 1: AFM image (courtesy UMA) of anodized alumina sample. The ~15nm pores are arranged in a hcp array with inter-pore distance ~66nm

Fig 2: SEM (courtesy of UMA) showing hcp ordering of pores and cross-section showing large aspect ratio and very parallel pores.

~90 microns thick

Top

Side~ 15nm

SAXS Data

Pore fills with liquid Contrast Decreases

<10>

<11> <20>

Short Range Hexagonal Packing

∆T decreasing

Thin films

Condensation

Capillary filling—film thickness

Wal

l film

thi

ckne

ss [

nm]

~ 2γ/D

TransitionLiquid Layer ~ 1nm

Pore Diameter~15nm

What is the filling process?

Geometry: Theoretical BackgroundC. Rascon and A. O. Parry, "Geometry-dominated fluid adsorption on

sculpted solid substrates",Nature 407, 986 (2000).

y =L(x / x0 )

γ

γ 2 γ 2

Liquid Filling of Troughs

Parabolic Pits γ=2) Tom Russell (UMA)

Diblock Copolymer in Solvent

Self Alignment on Si

PMMA removal by UV degradation &

Chemical Rinse

Reactive Ion EtchingC. Black (IBM)

~40 nm Spacing

~20 nm Depth/Diameter

Height ~ r2

γ ≈2

X-ray Grazing Incidence Diffraction (GID) In-plane surface structure

Diffraction Pattern of Dry PitsHexagonal Packing

Thickness D~3 Cross over to other filling!

Liquid Fills Pore: Scattering Decreases:

X-ray Measurement of Filling

Electron Density vs T

GID

Filling

Reflectivity

Filling

Results for Sculpted Surface

Γc ~ T( )

−βc

R-P Predictionβc~3.4

βc 3

Observedβc 06

Sculpted Crossover to

Flat

Flat Sample

Sculpted is Thinner than Flat

Gold Nanoparticles & Controlled Solvation

Conventional Approach:Dry Bulk Solution Imaging of Dry Sample

Controlled Wetting:Dry Monolayer Adsorption (Wetting Liquid)

LangmuirIsotherms

Formation

Liftoff AreaOf Monolayer

Thiol Coated Au Particles Stellacci et al OT: MPA (2:1)OT=CH3(CH2)7SHMPA=HOOC(CH2)2SH

TEMbi-modal distribution

Size Segregation

GID: X-ray vs Liquid Adsorption(small particles)

GIDA

dsorption

Return to Dry

Qz

QxyQxy Qxy

Bimodal/polydisperse Au nanocrystals in equilibrium with undersaturated vapor

Good SolventPoor vs Good Solvent

Rev

ersi

ble

Aggregation in Poor Solvent

Dissolution in GoodSolvent

Self Assembly

(1) dry

(2) ethanol T ~ K

3 ethαnoλ T ~ 5 K

4 δy αγαin etOH extαcteδ

5 toλuene T 5 K

6 toλuene T ~ 5 K

toλuene T ~ 3 K

Reversible Self Assembly: Annealing

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

NanoParticle SelfAssembly in Nanopores: Tubes

Empty

SEM of empty pores, diameter~30nm

50 nm

Fill with Particles ~2nm dia.

FilledTEM 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

T

Incident x-ray's

Toluene

Alumina membraneWith nano-particles

Small Qx: Pore-Pore Distances

Large Qx, Qy.Qz: Particle-Particle Distances

z

x

Q

Qz

Qx

Top

Heating/Cooling, w/ nanoparticles

Hex. Packing

Small Q peaks pore filling hysteresis

<01>

<11>

<02>

With nanoparticles

• Decrease/Increase in contrast indicates pores filling/emptying.

Below: w/o nanoparticles

•Capillary transition shifts from ~2K for pores w/o nanoparticles to about ~8K w/ nanoparticles

•Strong hysteresis T~ /R

Note: Shift in Capillary Condensation

Summary of Au-Au Scattering(Drying)Real space modelSlices

q radial

Inte

ns

ity

q radial

Inte

ns

ity

q radial

Images

Inte

ns

ity

Cylind.Shell

Shell + Isotropicclusters

Shell + Isotropicsolution

Heatin

g

Summary

• Control Thickness: T~• X-ray: Non-destructive probe

• Capillary Filling: pores & structures

• Thin Liquid Solvation