1. Introduction to Nanotechnology and Nanomaterials
Chapter 2: Basics
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2. Contents q Introduction q Basics q Synthesis of Nano Materials
Fabrication of Nano Structure
Nano Characterization
Properties and Applications 2
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3. Basics q Crystal structure q Surface q Kinetics Surface chemistry
Consolidation
Quantum confinement 3
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4. Thin film agglomeration:
Paper to read:
“Comparison of the agglomeration behavior of Au and Cu films sputter deposited on silicon dioxide, J.-Y. Kwon, T.-S. Yoon and K.-B. Kim, J. Appl. Phys. 93(6), 3270 (2003)
Can find out the paper in

5. Basics- Kinetics Homogeneous Nucleation - supersaturation (DGv)
- surface
spherical nuclei 5
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W. D. Callister, Materials Science and Engineering

6. Basics- Kinetics Homogeneous Nucleation ex) supersaturated solution
For nanoparticles 6
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7. Basics- Kinetics q Nucleation Rate Nanomaterials7
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W. D. Callister, Materials Science and Engineering

8. Basics- Kinetics q Nucleation Rate in Liquid a 1 2 y
The rate of nucleation per unit volume and per unit time, RN, is proportional to
n: #of atoms/unit area
c: #of atoms/unit volume 1 2 a y 8
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9. Basics- Kinetics Phase Transformation in Liquid: Stokes law:
From the Stokes-Einstein Relation,
Stokes law:
Einstein relation:
Now, if we assume that a=r=l,
the diameter of the growth species

10. Basics- Kinetics Mono-dispersed Particle - Lamar diagram
How to achieve the uniformity in size?
High rate of nucleation
Quick down to the minimum concentration.
 prevent further nucleation
Mono-dispersed Particle
- Lamar diagram 10
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T. Sugimoto, Adv. Colloid Interface Sci., 28 (1987) 65

11. Basics- Kinetics Homogeneous Nucleation - subsequent growth
(1) diffusion controlled
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12. Basics- Kinetics Homogeneous Nucleation Flux by diffusion, d r x Jd
Since, 12
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13. Basics- Kinetics Homogeneous Nucleation (2) interface controlled
The growth proceeds layer by layer; the growth species are incorporated into one layer and proceeds to another layer
The surface process is so fast that second layer growth proceeds before the first layer growth is complete 13
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14. Basics- Kinetics Homogeneous Nucleation - for the uniformity in size
 diffusion controlled process is desired
- how to achieve it
 extremely low concentration of growth species
high viscosity, diffusion barrier, controlled supply of growth species
(2-1)
(2-2)
(1) 14
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Nanomaterials

15. Basics- Kinetics Homogeneous Nucleation ex) ZnS
diffusion of the HS- ion to the growing
particle is the rate-limiting process 15
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R.Williams et al., J. Colloid Interface Sci. 106, 388 (1985).

16. Basics- Kinetics q Heterogeneous Nucleation Nanomaterials16
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W. D. Callister, Materials Science and Engineering

17. Basics- Surface chemistry
q Dispersion
- a highly homogeneous suspension of solids with a well-defined rheological behavior
q Dispersion in liquid
- wetting - interparticle interaction 17
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R. J. Pugh, Surface and Colloid Chemistry in Advanced Ceramic Processing

18. Basics- Surface chemistry
q Stabilization 18
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R. J. Pugh, Surface and Colloid Chemistry in Advanced Ceramic Processing

19. Basics- Surface chemistry
Electrostatic Stabilization
Surface charge density:
Preferential adsorption of ions
Dissociation of surface charged species
Isomorphic substitution of ions
Accumulation and depletion of electrons
Physical adsorption of charged species onto the surface 19
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20. Basics- Surface chemistry
The concentration of charge determining ions corresponding to a neutral or zero charged surface is defined as a point-of-zero charge (p.z.c).
At pH>p.z.c – the oxide surface is negatively charged due to the hydroxyl groups, OH-
At pH<p.z.c – the oxide surface is positively charged due to hydrogen ions, H+
The surface charge density or surface potential, E in volt, is now simply related to the pH and the Nernst equation. 20
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21. Basics- Surface chemistry
Electric Potential at the Proximity of Solid Surface
The distributions of both ions are mainly controlled by a combination of
(a) Coulombic force or electrostatic force
(b) entropic force or dispersion
(c) Brownian motion
Formation of double layer:
(a) Stern layer: electric potential drops linearly through the tightly bound layer of solvent and counter ions
(b) Gouy layer (diffuse double layer): beyond the Helmholtz plane until the counter ions reach the average concentration in the solution
(c) z(zeta) potential: potential at plane of shear (slipping plane, Helmholtz plane) 21
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22. Basics- Surface chemistry
In the Gouy layer, the counter ions diffuse freely and the electric potential does not reduce linearly.
Double layer thickness is typically of about 10 nm.
An electrostatic repulsion between two equally sized spherical particles of radius r, and separated by s 22
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D.J.Shaw, Introduction to colloid and surface chemistry, 1992

23. Chapter 1: Water
Dielectric constant: 78
Viscosity: 1 cp

24. Chapter 1: Water For hydrogen model
The potential ,V, is taken as the Coulombic potential , and solve Schrodinger equation by setting the polar coordinates.
Wave function is designated by four quantum numbers.

25. (1) (2) Models for Double-Layer Structure
(from Electrochemical Methods; Fundamentals and Applications)
Since the metallic electode is a good conductor, it supports no electric field within itself at equilibrium.
Any excess charge on a metallic phase resides strictly at the surface.
Helmholtz proposed that the counter-charge in solution also resides at the surface – two sheets of charge, having opposite polarity, separated by a distance of molecular order.
Such a structure is equivalent to a parallel capacitor,
(1)
(2)

26. The Gouy-Chapman Theory
Even though the charge on the electrode is confined to the surface, the same is not necessarily true of the solution.
A finite thickness would arise due to an interplay between the tendency of the charge on the metallic phase to attract or repel the carriers according to polarity
And the tendency of thermal process to randomize them.
(3)
The total charge per unit volume in nay lamellar is then,
(4)
From Poisson equation,
(5)
Poisson-Boltzmann equation
(6)

27. Since,
(7)
(8)
(9)
(10)

28. For symmetrical electrolyte z:z solution (electrolyte having only one cationic species and one anionic species, both with charge z,
(11)

29. The potential Profile in the Diffuse Layer:
Equation (11) can be rearranged and integrated in the following manner,

30. Thus,
(13)
(14)
The reciprocal of k has units of distance and characterizes the spatial decay of potential: Electric double layer thickness

31. The Relation between sM and f0:
Since,
(19)
(20)
Differential Capacitance:
(21)

32. Stern’s Modification:
In the Gouy-Chapman Model,
The ions are not restricted with respect to location in the solution phase
They are considered as point charges that can approach the surface arbitrary closely
Therefore, at high polarization, the effective separation distance between the metallic and solution phase charge zones decreases continuously toward zero.
This is not realistic. The ions have a finite size and cannot approach the surface any closer than the ionic radius.
If they remain solvated, the thickness of the primary solution sheath would have to be added to that radius.
In other word, we can envision a “plane of closest approach” for the centers of the ions at some distance x2

33. The interfacial model, first suggested by Stern, can be treated by extending the considerations of the last section,
(22)
(23)
(24)
Since the charge density at any point from the electrode surface to the OHP is zero (?), the potential profile in the compact layer is linear,
(25)

34. Note also that all of the charges on the solution side resides in the diffuse layer, and its magnitude can be related to f2,
(26)
(27)
(28)
(29)
(30)

35. Basics- Surface chemistry
Van der Waals attraction
induced dipole- induced dipole (London) ~ x-6
permanent dipole- induced dipole (Debye) ~ x-6
permanent dipole- permanent dipole (Keesom) ~ x-6
Attraction between two spheres 35
Nanomaterials
G. CaO, Nanostructures & Nanomaterials (2004)

36. Basics- Surface chemistry
Example- CdTe nanowire
dipole-dipole interaction between nano-particles produce nano-wires with self assembling modes
intermediate stage
nano-wire 36
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Z. Tang, Science, 297 (2002)237

37. Basics- Surface chemistry
DLVO theory
primary
minima
secondary
kinetic barrier 37
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P. C. Hiemenz, Principles of colloid and surface chemistry (1986)

38. Basics- Surface chemistry
DLVO theory
- effect of
Hamaker constant surface potential electrolyte conc.
10-2 M
10-3 M
Larger – smaller thickness of double layer- more attraction
Larger – more attraction
Larger – more repulsion
P. C. Hiemenz, Principles of colloid and surface chemistry (1986)

39. Basics- Surface chemistry
Steric Stabilization
Steric stabilizer : amphipathic block
or graft copolymer
D. H. Napper, Polymeric Stabilization of Colloidal Dispersions (1983)

40. Basics- Stability of Nanoparticle
Metal oxide nanoparticles in aqueous suspensions
- kinetic stability- energy barrier (DLVO theory)
- dispersion, aggregation, flocculation
- thermodyamic stability- surface energy minimization
- Ostwald ripening (dissolution-reprecipitation)
* Is it possible to avoid the ripening of nanoparticles in suspension and to control their dimension by monitoring the precipitation conditions?
ex) thermodynamically stable dispersed system- microemulsion
answer) possible
When the pH of precipitation is sufficiently far from the point of zero charge and the ionic strength sufficiently high, the ripening of nanoparticles is avoided. The stability condition, defined by a 'zero' interfacial tension, corresponds to the chemical and electrostatic saturation of the water-oxide interface. In such a condition, the density of charged surface groups reaches its maximum, the interfacial tension its minimum and further adsorption forces the surface area to expand and consequently, the size of nanoparticles to decrease.
L. Vayssieres, Int. J. Nanotech. 2, 411 (2005)

41. Basics- Stability of Nanoparticle
q Microemulsion
- clear, stable, isotropic liquid mixtures of oil, water, and surfactant, frequently in combination with a co-surfactant.
- aqueous phase may contain salt(s) and/or other ingredients, and the “oil” may actually be a complex mixture of different hydrocarbons and olefins.
- thermodynamically stable
- interfacial tension is very low (10-2~10-3 mN/m)
E. Ruckenstein, Chem. Phys. Lett. 57, 517 (1978)
B.K. Paul, Current Science 80, 990 (2001)

42. Basics- Stability of Nanoparticle
Metal oxide nanoparticles in aqueous suspensions
point of zero
interfacial tension
stable
- no growth
g decreases
as pH increases
unstable
-ripening
S.M.Ahmed, J. Phys. Chem. 73, 3546 (1969)
L. Vayssieres, Int. J. Nanotech. 2, 411 (2005)

43. Basics- Consolidation
Consolidation (sintering)
processes involved in the heat treatment of powder compacts at elevated temperatures, usually at T > 0.5Tm [K], in the temperature range where diffusional mass transport is appreciable resulting in a dense polycrystalline solid.
- pore removal
densification
MgO-doped Al2O3 43
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J. P. Schaffer et al, The Science and Design of Engineering Materials

44. Basics- Consolidation
Solid state sintering
final
intermediate
initial 44
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45. Basics- Consolidation
Densification vs. Grain Growth
500mm
TiO2 & SiO2-doped Al2O3 45
Nanomaterials
O. S. Kwon, Acta Mater., 50 (2002)