2006 nano nanotechnology

8/14/2019 2006 Nano Nanotechnology

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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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2006 nano nanotechnology

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