buie21 jan 15
TRANSCRIPT
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Nanocrystals through De-Wetting and De-mixingAlokmay DattaSurface Physics and Materials Science DivisionSaha Institute of Nuclear Physics
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Self-organization and Nanocrystals
• Self-organization is essentially a non-equilibrium phenomenon
• It requires two or more competing forces that are close in strength
• Two common areas where such forces are present are • De-wetting and• De-mixing
• These maybe utilized to build spontaneously ordered supramolecular patterns and structures such as Nanocrystals
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De-Wetting
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Wetting & dewetting
Substrate
LiquidLiquid
Substrate
SG = SL + LG cosc
Substrate
Wetting S 0
DewettingS 0
Hydrophobic surface
Liquid
Spreading coefficient,S = SG – (SL + LG )
S = LG (cosc – 1)
Young’s equation
Young-Dupre equation
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Fatty Acid
Head
Tail
Hydrophobic tail Hydrophilic head
Simpler Picture
Langmuir Trough Langmuir Monolayer
Dissolve in solvent 1.Lighter than water2.Insoluble in water3.VolatileSpread on waterWait for solvent to
EvaporateCompress to required
Surface Density
Amphiphiles and Monolayers
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Water
Tail
Hydrogen
Oxygen Carbon
Metal2+ 2+
2++ + +
Head
-
Langmuir Monolayer
Langmuir monolayers with divalent Metal ions in water
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Langmuir-Blodgett film deposition with one-tailed amphiphiles
Langmuir-Blodgett Films
a)Front view
(b) Closer view of the dipper
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Found from 1.X-ray diffraction2.X-ray and Neutron Reflectivity using deuterated and normal hydrocarbons in tailsMalik et al, Phys. Rev. B 52, R11654 (1995)Phys. Rev. B 65, 033409 (2002)
What Happens with Two-tailed Amphiphiles?
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200nm
1.0µm
3.0µm
1 ML
3 ML
9 ML
Wetting on High Energy Surface: ZnSt LB Films on Si
Complete wetting
Partial Wetting
EDP shows full coverage in ZnSt monolayerpartial coverage in ZnSt multilayers
XRR results
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400nm
400nm
Cd-T
Co-T
Defect-free morphology
`Pinhole’ defects present
AFM image of LB Templates
Template Formation: CdSt and CoSt trilayers (AML + SML) deposited on hydrophilic silicon (100) substrate by three subsequent vertical passages of substrate through air/water interface with Stearic acid Langmuir Monolayer (LM), containing Cd2+ and Co2+ in subphase, starting from water.
AML
SML
De-wetting on Low Energy Surface: ZnSt LB Films on Organic Films
CdSt and CoSt LB films are used as organic templatesCdSt is `solid-like’ but CoSt is `liquid-like’
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C O M
Cd-T (unidentate co-ordination)
First Layer(asymmetric monolayer)
Next Layer(symmetric monolayer)
The Templates
Headgroup Bondingsand Co-ordinations (from FTIR Spectroscopy)
Surface Morphology (from AFM)
Co-T (bidentate co-ordination)
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Nanocrystal Formation: The Cd-Stearate (Cd-T) and Co-Stearate (Co-T) Langmuir-Blodgett templates were vertically passed through the air/water interface with Stearic acid LM containing Zn2+ in subphase , from air to water and back to air.
Sample 1: ZnSt nanocrystal on Cadmium bearing template (Cd-T)Sample 2: ZnSt nanocrystal on Cobalt bearing template (Co-T)
AML
SML
Zinc Stearate (ZnSt) nanocrystals
Sample 1 Sample 2
Growth of ZnSt Nanocrystals
LB Deposition Conditions
Surface pressure: 30mN/mTemperature: 19°CpH ~ 6 adjusted by NaHCO3
Nanodroplet by de-wetting A. Checco et al Phys. Rev. Lett. 91, 186101,
(2003)
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1.6µm 1.6µm
Self-assembled ZnSt nanocrystals show difference in structure on Cd-T and Co-T templates
ZnSt on Cd-T ZnSt on Co-T
(Height of nanocrystal ~ 25 nm)0.12 0.18 0.24
0.0
1.0x10-9
2.0x10-9
3.0x10-9
4.0x10-9
Inte
nsity
qz ()
Zinc Stearate on Cadmium Stearate template (E=260 eV)
0.14 0.21
0.0
7.0x10-10
1.4x10-9
Zinc Stearate on Cobalt Stearate template (E=260 eV)
Inte
nsity
qz ()
Diffraction measurements in the vicinity of C K-edge (BEAR beamline, Elettra Synchrotron, Italy)
Peak Zn on Cd-T Zn on Co-T Reflection Plane
1 51.93 (M) x (1/2,1/2,1/2)
2 43.33 (S) 43.94 (S) (001)
3 30.50 (S) X (101)+(011)
4 25.65 (W) 25.96 (S) (111)
Assigned diffraction peaks
1
2 3
4
2 4
1. Peak 2 (d ~ 43 Å) correspond to headgroup separation in multilayers of untilted ZnSt molecules.
2. Peak 2 correspond to reflection from (001) planes (assuming d to be lattice spacing c).
3. Peak 3 (Cd-T only) correspond to doubly degenerate (101) + (011) reflection.
4. Peak 4 correspond to reflection from (111) plane.
Structure of ZnSt nanocrystals
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Diffraction Results:
Molecule
Non Close Packed
Structure
Unit Cell
Close Packed
Structure
Head
Structure
Bidentate Unidentate
OxygenZincCarbon
Tail Structure
Carbon
Hydrogen
Molecule
Molecular Structure
• Intensity of (111) peak is considerable for ZnSt on Co-T but very weak in case of Cd-T, consistent with a close packed structure for nanocrystals on Co-T and a non-close packed structure of the same on Cd-T.
• These structures for the nanocrystals are not observed in bulk ZnSt crystals.• Peak 1 (CdSt) corresponds to reflection from a (½½½) plane, i.e., some superlattice.• Exact nature of this superlattice has not been ascertained but most probably it is coming from the
fact that Zn-bearing carboxylate group has two structures – unidentate and bidentate bridged. Absence of this superlattice in Co-T suggests a mixture of the two structures in each unit cell, as seen in ZnSt LB multilayers.
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Dipole moment mismatch at interface
ZnSt on Co-T
CdSt on Co-T
CoSt on Cd-T
ZnSt on Cd-T
Mater. Res. Express 1 (2014) 025006
The De-wetting 'Force'
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De-Mixing
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Our Main Actor – The Liquid Crystal MBBA(N-(4-Methoxybenzylidene)-4-butylaniline)
•The Imine (-C=N) has an electron lone-pair located on nitrogen.
•MBBA has a well-defined Nematic-Isotropic (N-I) Phase Transition and no well-defined Nematic-Smectic Transition
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The Nematic-Isotropic Transition
• The Nematic phase is unique since it requires no extra interaction over a fluid phase, it is a ‘higher density liquid phase’ just as a simple liquid is a ‘high density gas phase’
• However, unlike the simple liquid, it breaks the rotational symmetry simply due to the anisotropy in the molecular shape, which is decided by the molecular conformation. This has made the categorization of N-I transition ambiguous.
• We shall see in our results the strong role played by this idea
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Growth of Au Nano-prisms
Basic Ideas: 1.The electron lone-pair on the imine group may be used to reduce HAuCl4 to Au in a slow and regulated way 2.The Liquid Crystal, in this reactive and charged environment, may develop positional order, i.e. go over to a ‘Smectic-like’ phase, and this phase, in turn would provide an ordered matrix for nanoparticle growth
The growth technique consisted of prolonged slow heating of a solution of HAuCl4 and MBBA in alcohol. It was seen that alcohol was necessary but other than a slowing down of the reaction rate with hydrocarbon chain length no change was observed from methanol to propanol
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Characterization of Gold Nano Particle
Transmission Electron Microscopy (TEM)
Existence of Highly Faceted Nano Particle
SAED Pattern showing different crystal planes of Au that matched well with grazing incidence x-ray diffraction
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EDAX Spectrum
Faceted crystals
Spheres
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20 nm
20 nm 20 nm
20 nm
20 nm
0˚ 10˚
20˚ 30˚
40˚6.8 nm
Electron Tomography Pattern showing the 3-Dstructure
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Highly Symmetric Au Nano prism with each side 12 nm
5 nm
-111 -11-1
002
00-2
[110]
{111}
Fast Fourier Transform
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Grazing Incidence X-Ray Diffraction (GIXRD)
Interplanar spacing ≈ 0.207 nm Lattice Spacing ≈ 0.413 nm
Good Agreement with TEM and standard literature
Average Crystallite Size ≈ 30 nm
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UV-Visible Absorption Spectroscopy
Characteristic Plasmon resonance bandClearly visible at 513 nm
Size of the Au Nano particle increases with Increasing Nano particle precursor
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Effect of Solvent in Nano Particle Production
Role of Methanol is very important in nano particle production. Methanol itself cannot reduce HAuCl4 to produce nano particle in the matrix.
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Fourier Transform Infrared Spectroscopy
Red Shift in imine stretch by 26 cm-1 signifies co-ordination between MBBA–AuNP System.
A new peak is appearing at 1655 cm-1 due to oxidationof methanol
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Probable Reaction Mechanism
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Nematic to Smectic Texture Transformation of MBBA during synthesis
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Differential Scanning Calorimetry Study
The MBBA-AuNP conjugate system clearly indicates much higher phase transitionTemperature compared to pristine MBBA which indicates system trying to stabilize atmuch higher TC due to induced smectic ordering
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Ag-60-Au-40AgNO3 + HAuCl4
High ResolutionTransmissionElectronMicroscopy
The Star Structure
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Au Ag
Au AgAu Core Ag Shell (Star)
Total Core-Shell Composite
The Star Core-Shell Structure from Element Mapping
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People Involved
1. Smita Mukherjee, UPMC, Paris
2. Nupur Biswas, IISc, Bangalore
3. Kaustabh Dan, SINP
4. Biswarup Satpathi, SINP
5. Madhusudan Roy, SINP
6. Stefano Nannarone, Elettra Sincotrone, Trieste
7. Angelo Giglia, Elettra Sincotrone, Trieste
8. Sarah Hidki, UPMC, Paris
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Thank You!