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Introduction to nanotechnology:
Chapter 4 : Properties ofNanoparticles
Yang-Yuan ChenLow temperature and nanomaterial labatory
Institute of Physics, Academia Sinica
E-mail : [email protected]
http://www.phys.sinica.edu.tw/%7Elowtemp/
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Introduction:
1. Metal Nanoclusters
2. Semiconducting Nanoclusters
3. Rare Gas and Molecular
Clusters
4. Methods of Synthesis
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Nanoparticles
size? ~ 1-1000 nm
Criterion: Critical length or characteristic length 1. Thermal diffusion length
2. Scattering length ( mean free path)
3. Coherence length
4. Energy level spacing >> thermal energy KT
5. Surface effect
6. other
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Virus ~10 nm~100 nm
blood cell 200~300 nm
bacteria 200~600 nm
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Energy
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With FCC structure
Surface effect
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4.2.1 Magic numbers and structure
No. of electrons for an atom:electronic magic numbers example
He2: 1S2
Ne10: 1S2,2S2, 2P6
Ar 18: 1S2,2S2, 2P6 ,3S2, 3P6,Kr 36: 1S2,2S2, 2P6 ,3S2, 3P6,
2. No. of atoms for a nanoparticlesStructural magic number
The jellium model P75
3d10
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(Excimer Laser Ablation ELA )(2003/3)(1993/1)
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Electronic magic numbers: the total mumber of electrons on the superatom whenthe top level is filled
Structural magic number:Cluster has a size in which all the energy levels are filled
4.2.2 Theoretical Modeling of Nanoparticles
The jellium model P75
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Theoretical calculation:Cluster as molecular
Molecular orbital theory P78 Density functional theory P78
Find the structure and geometry with the lowest energy
4 2 3 G t i St t
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4.2.3 Geometric Structure
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Size dependent structure of Indiumnanoparticles
Face-centered tetragonal
Face-centered cubic
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Magic numberC20, C24, C28, C32, C36, C50, C60, C70
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3 0 4 0 5 0 6 0 7 0 8 0
(
720)*
(631)*
1 4 n m
1 6 n m
1 9 n m
(8
20)*
(413)*
(331)*(
411)*
(410)*
(
002)*
2 1 n m
b u l k
T a
c
oun
t(arb.
un
it)
(220)
(211)
(200)
(110)
2 ( d e g r e e )X ray spectra of Ta
000ulk33.36.7152.27.8955.34.7657.62.44
- Ta (%)Tetragonal-Ta (%)CubicSize(nm)
Size dependence of phase compositions
Tetragonal
Cubic
lattice constant of Ta
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10 15 20 25 30 35 403.300
3.305
3.310
3.315
bulk
cubic-Ta
0
Latticeconstant(A)
Size(nm)
lattice constant of Ta
10 15 20 25 30 35 40
0.5204
0.5208
0.5212
0.5216
bulk
Ta
c/a
Size(nm)
10 15 20 25
10.220
10.225
10.230
10.235
La
tticecons
tan
t(A)
c
a
Ta - Tetragonal
La
tticecons
tan
t(A
)
Size(nm)
o
5.320
5.325
5.330
5.335
o
4 2 4 Electronic Structure
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4.2.4 Electronic Structure
Quantum Size Effect :Energy level spacing >> KBT
Light-induced transitions between
these levels determines the color
Bulk 100 atoms 3 atoms
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Light-induced transition between these levels determines the color of the materials
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UV photo-electron spectroscopy
4 2 5 Reactivity
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4.2.5 Reactivity
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4.2.6 Fluctuations ?
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4.2.7 Magnetic cluster
Magnetized cluster
Nonmagnetic- magnetic transition
1. Orbital magnetic moment
2. Electron spin3. Levels filled with an even number of electrons net magnetic
moment=04. Transition ion atoms: Fe, Mn, Co with partially filled inner d-orbital levels-
net magnetic momentParrel align Ferromagnetic
5 Ferromagnetic cluster with DC field superparamagnetism
Superparamagnetism:
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Superparamagnetism
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Single domain
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FeSi2DC
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FC
ZFC
1. The temperature of peak value of in ZFC is defined as theBlocking temperature TB
2. of ZFC and of FC deviate at TB 3. Above TB, of ZFC and of FC are overlap.
1
2
Blocking Temperature
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Blocking Temperature
kB is the Boltzmann constant
K is the anisotropic constant
V is the volume of nanoparticle
-
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-500 0 500-5
0
5
50K
5K
M
(emu/g)
H/T (G/K)
FeSi2 40nm particles TB=20 K
1. T< TBHysteresis appearsin M-H. Due to thermal energy
is less than the interactionsamong particles
2. T> TBNo hysteresisappears in M-H. Since thermalenergy is larger than theinteractions among particles
N i i i i
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Nonmagnetic- magnetic transition
Rh
4 2 8 Bulk to Nanotransition
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4.2.8 Bulk to NanotransitionGold melting point
4 3 S i d ti N ti l
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4.3 Semiconducting Nanoparticles
4.3.1 Optical Properties
blue shift as size is reduced Due to band gap
Exciton: bound electron-holepair,produced by a photon having hv> gap
Hydrogen-like: energy level spacing Light-induced transition
Hydrogen-like: energy level spacing
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Hydrogen like: energy level spacing
Light-induced transition
Wh t h h th i f ti l
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What happens when the size of nanoparticles
becomes smaller than to the radius of the orbit ofexciton?
Weak-confinement size d> radius of electron-hole pair:
blue shift Strong-confinement
size d< radius of electron-hole pair:
Motion of the electron and the hole becomeindependent, the exciton does not exist
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Absorption edge, band gap
exciton
5. Size dependence properties of quantum dots CdSe surface
h d i
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charge density
300 350 400 450 500 550 600 650 700
~ 3 nm~ 4 nm
~ 5 nmA.U
Wavelength (nm)
20 25 30 35 40 45 50 55 60
Bulk
112
103110
102
101002
100
5 nm
4 nm
3 nm
Intensi
ty(arbun
its)
2 (degree)
absor
bance
4 3 2 Photofragmentation
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4.3.2 Photofragmentation Si or Ge can undergo fragmentation under laser light
Dissociate!
4 3 3 Coulombic Explosion
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4.3.3 Coulombic Explosion
F=e2/r2
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4 4 Rare Gas and Molecular Clusters
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4.4 Rare Gas and Molecular Clusters
4.4.1
Xenon clusters are formed by adiabaticexpansion of a supersonic jet of the gasthrough a small capillary into a vacuum.
Xenon
Repulsion of coulombic electronic coreDipole attractive potential
Lennard-Jones potential for
calculation structure
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superfluid
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superfluid
When T= 2.2 K lambda point
He4 becomes a superfluid, its viscositdrops to zero
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P. Sindzingre PRL
63,1061(1989)
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At ambient condition
80% of water molecularsAre bounded into clusters
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4 5 1 RF Plasma
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4.5.1 RF Plasma
4 5 2 Chemical Method
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4.5.2 Chemical Method
Reducing agents
Molybdenum
4.5.3. Thermolysis(Thermald iti )
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decomposition)LiN3
-> Li
Electron paramagnetic resorance(EPR)
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(EPR)
EPR measures the energy absorbed whenelectromagnetic radiation such as microwave
induces a transition between the spin states mssplit by a DC magnetic field.
ms
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4.5.4 Pulsed Laser Method
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5 u sed ase et od
Silver nitrate+ reducing agent -----> Silver nanoparticle
heating
Laser Ablation
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Laser Ablation
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1. Quantum size effects on the competition betweenKondo interaction and magnetic order in 0-D.
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0.1 1 100
2
4
6
8
TN
80 A
Bulk
80A & Bulk CeAl2
C/T
J/mol
-1
K-2)
T KConclusion:In 80A -CeAl2, magnetic ordering completely disappears and the reaches 9500mJ/mol Ce K2.
Unsolved problems:
In nanoparticle, only 0.7 Mole Ce 3+ left, Is the 0.3 mol non-magnetic Ce really on thesurface ? or it is just a coincidence.
5nm
(2 2 0) 4CePt
2 C (0 56 m l C T 4 6 K)
Size dependence of Kondo effects in CePt2 nanoparticles
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20 30 40 50 60 70 80 900
4000
8000
12000
16000
CePt2
3.8nm
22nm
33nm
bulk
5nm
(2,2,2)
(2,2,0)
(6
20)
(4
44)
(6
22)
(5
33)
(5
31)
(4
40)
(511)
(4
22)
(3
31)
(4
00)
(222)
(311)
(
220)
2(degree)
(2,2,2)
(2,2,0)
0
2
4
bulk
2 CKondo
(0.56 mol Ce, TK=4.6 K)
C(J/m
olK)
0
2
4
CKondo
(0.58 mol Ce, TK=4.4 K)
33nm
T K
0
2
4
CKondo(0.65 mol Ce, TK=3.4 K)22nm
0 5 10 150
2
4
3.8nm
CKondo
(0.71 mol Ce, TK=100 K)
X-ray spectra
TEM of nanoparticles
Specific heat of CePt2
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