0-D, 1-D, 2-D Structures
(not a chapter in our book!)
NANO 101
Introduction to Nanotechnology
1
Overview
Bottom Up
Top Down
Chemistry!
Milling
Large size distribution
• No control of shape
• Impurities
•
Crystal Growth
• 0-D particles
• 1-D particles
• 2-D films
Lithography
2
Top-Down Approaches
• Milling
– Broad size distribution (tens to hundreds of nm)
– Varied shape and geometry
– Impurities and defects from milling
• Lithography
– Also includes bottom up method
https://sites.northwestern.edu/vanduyne/files/2012/10/2001_Haynes_4.pdf
3
Particle Requirements
• Uniform size
• Uniform morphology
• Uniform chemical composition and crystal structure
• Monodispersed
4
Homogeneous Nucleation/
Supersaturated solution
kT C 

G   ln
  Co 
G = Gibbs free energy
K = Boltzmann constant
Co = equilibrium concentration
T = temperature
Ω = atomic volume
Two competing forces
• Surface energy
• Volume energy
N&N Fig. 3.2
5
Nucleation and Growth Rates
N&N Fig. 3.4
6
Hot Injection
• A way to separate nucleation and growth:
– One ionic precursor is heated to ~ 300 C
– Other precursor is a room temp and injected
– Rapid nucleation occurs followed by temperature
drop and growth phase
7
Hot Injection
8
Growth of Nanoparticles
9
Chem. Rev., 2014, 114 (15), pp 7610–7630
Making Nanoparticles
D
i
f
f
u
s
i
o
n
Growth
1. Nucleation
2. Diffusion from bulk to surface
3. Adsorption to surface
4. Irreversible incorporation onto surface
If the slowest step is diffusion  uniform particles
If the slowest step is layer by layer growth  nonuniform particles
10
Favoring Diffusion-limited Growth
• Low concentrations
– Large diffusion distance
• High solution viscosity
• Introduce diffusion barrier
• Change rate of chemical reactions
– Reactants used
– Catalysts
11
Other Strategies:
• Heat up method – in situ formation of reactive
precursors
• Slow addition of precursors – for RT growth
12
0-D Nanostructures: Surface Area and Energy
Surface energy increases
with surface area
•
•
C. Nutzenadel et al., Eur. Phys. J. D. 8, 245 (2000).
Large surface energy = instability
Driven to grow to reduce surface energy
13
Electrostatic Stabilization
Establish Surface Charge Density
Adsorption of ions/charged species
+
-
+
-
+
-
+
+
+
-
-
+
+
+
+
+
+
+
+
-
+
+
+
+
+
-
+
-
+
+
+
+
•
14
Steric Stabilization
“Capping”
Anchored
• Irreversible binding
Adsorbed
• Random, weak
15
What is on the surface?
• Current area of research:
Probing the surface of platinum nanoparticles with 13CO by solid-state NMR and IR spectroscopies
Nanoscale, 2014,6, 539-546
16
Example: Colloidal Gold
• Comprehensive study on synthesis and properties
of colloidal gold published by Faraday (1857)
• Classic method
– Precursor: dilute chlorauric acid (HAuCl4)
– Reducing agent: sodium citrate (NaC6H5O7)
– Reaction temperature: 100 °C
– Product: stable, uniform, ~20 nm particles
17
Colloidal Gold Particle Size
18
N&N Fig. 3.9
Colloidal Gold Particle Size
19
N&N Fig. 3.9
Synthesis of Metallic Nanoparticles
• Reduction of metal complexes in dilute solutions
• Precursors
– Elemental metals, inorganic salts, metal complexes
• Reduction agents
• Stabilizers
– PVA
– Sodium polyacrylate
20
Other Methods
• Brust Synthesis
•Reverse Micelle
21
Influence of “Capping”
•
•
•
•
•
Addition of polymer stabilizer
Used on surface to prevent agglomeration
Affects growth by limiting growth site
May interact with solute, catalyst, solvent
Can affect morphology
N&N Fig. 3.13
22
Growth of Pt Nanoparticles
• Found that ligands can terminate growth instead
of change growth rate.
23
Influence of Temperature
N&N Fig. 3.14
24
Influence of Concentration
J. Phys. Chem. B, Vol. 108, No. 40, 2004
25
Influence of Time
Rhodium nanocrystals
J. Phys. Chem. C, Vol. 111, No. 16, 2007
26
Influence of pH
Initial pH of reaction can affect size
SnO2 J. Phys. Chem. B, Vol. 108, No. 40, 2004
27
Formation of Nanoparticles in Solution
Advantages:
1. Stabilization from agglomeration
2. Extraction of nanoparticles from solvent
3. Surface modification and application
4. Mass production
28
MBE Quantum Dots
http://www.nanowerk.
com/nanotechnologynews/newsid=37518.p
hp
http://www.mbe.ethz.
ch/index.php?id=mbe
• Self-assemble due to lattice mismatch
29
How are these 0D?
GaAs
GaAs
In As
E
30
Formation of Nanoparticles on
Substrates
• Advantages:
– No ligands needed
– Very stable
– Ready for electronic application
– Access different materials easily
31