Introduction to Nano science and Nanotechnology Part 4
BUIE21 Jan 15
1. Nanocrystals through De-
Wetting and De-mixing
Alokmay Datta
Surface Physics and Materials Science Division
Saha Institute of Nuclear Physics
2. 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
5. Fatty Acid
Head
Tail
Hydrophobic tail Hydrophilic head
Simpler Picture
Langmuir Trough Langmuir Monolayer
Dissolve in solvent
1.Lighter than water
2.Insoluble in water
3.Volatile
Spread on water
Wait for solvent to
Evaporate
Compress to required
Surface
Density
Amphiphiles and Monolayers
8. Found from
1.X-ray diffraction
2.X-ray and Neutron Reflectivity
using deuterated and normal
hydrocarbons in tails
Malik et al, Phys. Rev. B 52, R11654 (1995)
Phys. Rev. B 65, 033409 (2002)
What Happens with Two-tailed Amphiphiles?
9. 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 monolayer
partial coverage in ZnSt multilayers
XRR results
10. 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 templates
CdSt is `solid-like’ but CoSt is `liquid-like’
11. C O M
Cd-T
(unidentate co-ordination)
First Layer
(asymmetric monolayer)
Next Layer
(symmetric monolayer)
The Templates
Headgroup Bondings
and Co-ordinations (from FTIR
Spectroscopy)
Surface Morphology (from
AFM)
Co-T
(bidentate co-ordination)
12. 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/m
Temperature: 19°C
pH ~ 6 adjusted by NaHCO3
Nanodroplet by de-wetting
A. Checco et al Phys. Rev. Lett. 91, 186101, (2003)
13. 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
Intensity
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)
Intensity
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
14. Diffraction Results:
Molecule
Non Close
Packed
Structure
Unit Cell
Close
Packed
Structure
Head
Structure
Bidentate
Unidentate
Oxygen
Zinc
Carbon
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.
15. 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'
17. 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
18. 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
19. 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
20. 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
22. 2 0 n m
2 0 n m 2 0 n m
2 0 n m
2 0 n m
0˚ 10˚
20˚ 30˚
40˚
6.8 nm
Electron Tomography Pattern showing the 3-D
structure
23. Highly Symmetric Au Nano prism with each side 12 nm
5 n m
-111 -11-1
002
00-2
[110]
Fast Fourier Transform
24. 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
26. 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.
27. 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 oxidation
of methanol
29. c to Smectic Texture Transformation of MBBA during synthesis
30. Differential Scanning Calorimetry Study
The MBBA-AuNP conjugate system clearly indicates much higher phase transition
Temperature compared to pristine MBBA which indicates system trying to stabilize at
much higher TC due to induced smectic ordering
