1. Introduction to Nanotechnology and Nanomaterials Chapter 2-3:
Basic Science for Nanotechnology
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Nanomaterials

2. 1. Crystal structure (General) 2. Surface Energy (Thermodynamics)
Contents
1. Crystal structure (General)
2. Surface Energy (Thermodynamics)
3. Kinetics (Nucleation and Growth, Phase Transformation)
4. Surface Passivation and Consolidation
5. Electronic and Optical Properties of Nanostructure 2
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3. Phase transformation deals with
Vapor phase to solid phase – film growth
Solution phase to solid phase – colloidal process
Solid phase transformation
Need thermodynamic driving force for phase transformation.

4. Derivation of Fick’s 1 st and 2nd equation:

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

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

8. q Nucleation Rate in Liquid
Basics- Kinetics
q Nucleation Rate in Liquid
The rate of nucleation per unit volume and per unit time, RN, is proportional to
N: number of growth species
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. Mono-dispersed Particle - Lamar diagram
Basics- Kinetics
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. Homogeneous Nucleation - subsequent growth (1) diffusion controlled
Basics- Kinetics
Homogeneous Nucleation
- subsequent growth
(1) diffusion controlled
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12. Homogeneous Nucleation
Basics- Kinetics
Homogeneous Nucleation
Flux by diffusion, d r x Jd
Since, 12
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13. Homogeneous Nucleation (2) interface controlled
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
Nanomaterials

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

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

17. - wetting - interparticle interaction
Basics- Kinetics
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
Nanomaterials
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
(1.6x10-19 joule/eV)(6x1023/mol) 19
Nanomaterials

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) 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
Nanomaterials
D.J.Shaw, Introduction to colloid and surface chemistry, 1992

23. 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 23
Nanomaterials
G. CaO, Nanostructures & Nanomaterials (2004)

24. Basics- Surface chemistry
Example- CdTe nanowire
dipole-dipole interaction between nano-particles produce nano-wires with self assembling modes
intermediate stage
nano-wire 24
Nanomaterials
Z. Tang, Science, 297 (2002)237

25. Basics- Surface chemistry
DLVO theory
(Derjaguin, Landau, Verwey, Overbeek)
primary
minima
secondary
kinetic barrier 25
Nanomaterials
P. C. Hiemenz, Principles of colloid and surface chemistry (1986)

26. 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)

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

28. Basics- Surface chemistry
The advantages of using surfactant in colloid chemistry:
Vacuum process
Wet-chemical process

29. Basics- Surface chemistry

30. 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 30
Nanomaterials
J. P. Schaffer et al, The Science and Design of Engineering Materials

31. Basics- Consolidation
Solid state sintering
final
intermediate
initial 31
Nanomaterials

32. Basics- Consolidation
Densification vs. Grain Growth
500mm
TiO2 & SiO2-doped Al2O3 32
Nanomaterials
O. S. Kwon, Acta Mater., 50 (2002)