1 NANOPARTICLES: Definition and Significance Synthesis and Characterization Stabilization Ordering...

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NANOPARTICLES:

•Definition and Significance

•Synthesis and Characterization

•Stabilization

•Ordering

•Optical Properties

•Magnetic Properties

•Catalysis

•Other Applications

Acknowledgements: M. D. Porter

2

Definitions*Nanoparticle- Particle with 1 dimension in the 10-100 nm size range.

Colloid- Particle with dimensions in the 1 nm – 1 mm (?) size range.

Quantum Dot- Particle with all 3 dimensions in the 1-10 nm size range.

Latex- Aqueous suspension of polymer particles.

Natural- Contains Protein Impurities; May Cause Allergies

Synthetic- Made via Emulsion Polymerization

SignificanceThe size of Nanoparticles leads to unique characteristics.

*These definitions are constructed from a compilation of literature, and represent the most commonly used verbiage over a span of years

3

Metallic Nanoparticle Synthesis

M++ Reductant Nanoparticle

M+

M+

M+

M+

M+

M++ ne-

M

M = Au, Pt, Ag, Pd, Co, Fe, etc.

Reductant = Citrate, Borohydride, Alcohols

Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, 18-52.

4

Control FactorsAverage Size

Reductant Concentration

Stirring Rate

Temperature

Size Distribution

Rate of Reductant Addition

Stirring Rate

Fresh Filtered Solutions

Stabilization

Solution CompositionHayat, M. A. , Ed., Colloidal Gold: Principles, Methods, and Applications; Academic Press: San Diego, 1989; Vol 1.

5

Functionalized Reductions

M+

+ ReductantFunctionalizedNanoparticleSurfactant

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

Y

X

YX

YX

Y

Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, 18-52.

6

Bimetallic Nanoparticle

Core-Shell

Mixed Alloy

M1 M1 M2

+ M2+ + Reductant

M1M1+ + Reductant

M1+ + M2

+ + Reductant

Toshima, N.; Yonezawa, T. New Journal of Chemistry 1998, 1179-1201.

7

Semiconductor Nanoparticles(Q-dots)

R

RNC

Se

SeCd

Se

SeCN

R

R

TOP/TOPO200ºC

PO CdSe OP

POO

P

Pickett et al. The Chemical Record 2001, 1, 467-479

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Semiconductor Nanoparticles

Mix Intermicelle exchange

Cd 2+

S2-

Cd 2+

S2-

CdS

CdS

Thiol capping

Micelle disruption

CdSCdS

Functionalized particles can be isolated by centrifugation or by precipitation Shipway et al.

Chemphyschem 2000, 1, 18-52

CdCl2

Na2S

9

10

CharacterizationTechnique Information

TEM/SEM Size/Shape/Size Distribution

UV/vis absorbance Size/Size Distribution

AFM Size/Shape/Size Distribution

X-ray Composition

IR Functionality

11

Stabilization of Polymer Nanoparticles•Stable Dispersion- All particles exist as single entities; order or disorder

•Aggregation- General term for unstable states

•Flocculation- Disorder, with weak attraction

•Coagulation- Disorder, with strong attraction

Figure adapted from: Ottewill, R. H. In Emulsion Polymerization; Piirma, I., Ed.; Academic Press: New York, 1982, pp 1-49.

Low [electrolyte]

Strong repulsion

Order

Intermediate [electrolyte]

Repulsive contacts

Disorder High [electrolyte]

Stable

Aggregated

Coagulated

Flocculated

12

Forces

1. Electrostatic- Charged surfaces and stabilizers

2. Steric- Geometric effects/solvation effects

3. van der Waals- Attraction of hydrocarbon chains towards each other

X

XXXX

X

XXXX

X

X

XXXX

X

X XX X

X

X

XXXX

X

X

X

X

X

X

X

XXXX

X

X

X

X

X

X

Y

YYY

Y

Y

YY

Y

Y

X, Y = Cationic, Anionic, or Nonionic Functional Groups

Ottewill, R. H. In Emulsion Polymerization; Piirma, I., Ed.; Academic Press: New York, 1982, pp 1-49.

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Ionic Groups

-

--

-

- ---

--

-

-Stabilizer

-

--

-

- ---

--

-

-

+

+

+

+

++

+

Neutralization of surface charge causes aggregation -

-

--

-

- ---

--

-

-

--

-

--

-- -

Tails bind via hydrophobic attraction- enhanced stability

OR

Hydrophobic attraction binds tails, leading to an excess of positive charge

Stabilization

-

--

-

- ---

--

-

-

++

+

+

+

+

+More Stabilizer

+

+

+

14

Nonionic Groups

-

-

-

-

- --

---

-

-

Hydrophobic interactions bind the tail group to the NP, while the polar head groups extend into solution

Polar head groups are hydrated, providing a steric barrier to prevent aggregation

15

Surface Charges

arsr e

r

a

Where:

IkT

Ne A

1000

8 2

2

Verwey, E. J. W.; Overbeek, J. T. G. Theory and Stability of Lyophobic Colloids: The Interaction of Sol Particles Having an Electrical Double Layer; Elsevier, Inc.: New York, New York, 1948.

r = Potential at distance r from NP surface

s = Potential at NP surface

a = radius of NP

r = distance from NP surface

e = elementary charge

NA = Avogadro’s number

= Permittivity of free space

k = Boltzmann’s constant

T = Temperature

I = Ionic Strength

-

--

-

- ---

--

-

-+

+

+

+

+

+

+

+

+

--

-+

++

+

+

+

+

16

Effect of Electrolyte Concentration on Potential Profiles

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4 5 6 7 8 9 10

Distance

C1 > C2

C1

C2

Low C

High C

17

Interaction Energy

Vt = Vr + Va

Where

Vr = Potential energy of electrostatic interactions (may include contribution from steric interactions)

Va = Potential energy of van der Waals interactions

Vr Double layer term (DLVO theory) surface charge & environment (electrolyte & solvent); thickness and density of adsorbed layer and interaction with solvent

Va Material nature (dispersion frequency, static polarizability, density)- Hamaker constants*

•Derjaguin, B. V., Landau, L., Acta Physicochim. USSR, 1941, 14, 633

•Verwey, E. J. W.; Overbeek, J. T. G. Theory and Stability of Lyophobic Colloids: The Interaction of Sol Particles Having an Electrical Double Layer; Elsevier, Inc.: New York, New York, 1948.

•Hamaker, H. C., Physica, 1937, 4, 1058.

*An estimate of the Hamaker constant may be determined from AFM measurements: Argento, C.; French, R. H. Journal of Applied Physics 1996, 80, 6081-6090.

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19

Nanoparticle Films

20

Ligand Directed Assembly

Bifunctional ligand

nanoparticle

substrate+

+

Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, 18-52.

21Natan, M. J.; et. al. Chem. Materials 2000, 12, 2869-2881

Tapping mode AFM (1m x 1m) of HSCH2CH2OH linked Au colloid multilayers: (A) monolayer; (B) 3 Au treatments; (C) 5 Au treatments; (D) 7 Au treatments; (E) 11 Au treatments.

• Monolayer formed by adsorption of Au particles on 3-mercaptopropyltrimethoxysilane derivatized SiO2 surface

• Multilayers constructed by immersion in a 5 mM solution of 2-mercaptoethanol for 10 min. followed by immersion in Au particle solution for 40 – 60 min.

22

Electrostatic Assembly

• Polycationic polymer

• Very stable in most solvents

• Control inter-layer spacing

• Conductive, semiconductive, or insulating

- --- -

--- --

+ ++

+- -- - --

Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, 18-52.

23

Convective Self Assembly

• Definition: Particles are allowed to freely diffuse. As the solvent evaporates, particles crystallize in a hexagonally close-packed array.

• Optimize: Particle concentration Particle/substrate charge Evaporation

Top View

Colvin, V.L.; et al. J. Am. Chem. Soc. 1999, 121, 11630-11637.

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Microcontact Printing

• PDMS stamp to “ink” a capture monolayer on a substrate followed by nanoparticle adsorption

• PDMS stamp to “ink” the nanoparticles directly onto the substrate

Side View

Top View

Shipway, A.N.; Katz, E.; Willner, I. CHEMPHYSCHM. 2000, 1, 18-52.

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AFM of Microcontact Patterned Nanoparticle Array

Natan, M. J.; et al. Chem. Mater. 2000, 12, 2869-2881

AFM scan (10 m x 10 m) of microcontact printed Au surfaces. HOOC(CH2)15SH is initially stamped on substrate. The surface is then exposed to 1.0 mM 2-mercaptoethylamine followed by exposure to a 17 nM solution of 12 nm Au nanoparticles.

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27

Optical Properties and Applications of Nanoparticles

Plasmon Absorbance

Surface-Enhanced Raman Spectroscopy (SERS)

Fluorescence Spectroscopy

28

Plasmon Absorbance - Background

• Surface Plasmon (SP): Coherent oscillation in e-density at the metal and dielectric interface when e-field (of incident light) forces loosely held conduction electrons to move with the field

• Plasmon Absorbance: absorption of EM radiation of SP at a particular energy

29

Plasmon Absorbance - Factors

• Surface functionality, temperature, and the solvent

• Particle concentration and particle size

S. Link et al. J. Phys. Chem. B 1999, 103, 4212-4217

30

GOLD QUANTUM DOTSVARIOUS DIAMETERS

31

Plasmon Absorbance - Applications• Coupled – Plasmon

Absorbances

Storhoff et al. J. Am. Chem. Soc., 120 (9), 1959 -1964, 1998.

1

2

32

Plasmon Absorbance – Applications (continued)

Storhoff et al. J. Am. Chem. Soc., 120 (9), 1959 -1964, 1998.

AB

S of

D

NA

33

Surface Enhanced Raman Spectroscopy

SERS • Enhanced e-magnetic field as a consequence of SP and

the appearance of new electronic states in the absorbate as a consequence of absorption

• Enhancement occurs when the exciting radiation is coincident with the plasmon absorbance of the nanoparticles

Creighton et al. J. Chem. Soc. Faraday Trans. 2 1979, 75, 790-798

• Aggregated nanoparticles have additional plasmon resonances associated with interparticle plasmon coupling

34

SERS - Factors• Particle size

Nie et al. J. Am. Chem. Soc. 1998, 120, 8009-8010

35

SERS - Applications

Au nanoparticle with Raman label and antibody

Antibody

Antigen (analyte)

Linker molecule

Raman signal to detector

Laser

Raman Reporter molecule

0.8 cm

Porter group

36

Application - Analysis of Prostate Specific Antigen (PSA)

1000 ng/mL

100 ng/mL

10 ng/mL

0 ng/mL

Antibody Anti-PSA (prostate specific antigen)

Antigen PSA

Raman label

DSNB

Integration time

60 seconds

PSA-Prostate cancer marker-Different forms-Analysis of composition change gives information of the malignancy

37

38

Binds w/o Mg2+

Binds & cuts w Mg2+

39

Fluorescence – Applications

Nie et al. Anal. Chem., 72 (9), 1979 -1986, 2000.

40

Dye addedto DNA

Nanoparticle fluor.Random binding via histones

41

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POTENTIAL APPLICATIONS

RAPID GENE MAPPING

FUND. STUDY OF PROTEIN – DNA INTERACTIONS

-HOW DOES PROTEIN FIND SPECIFIC BINDING SITEAMONG MANY NONSPECIFIC SITES?

-HOW DOES RNA POLYMERASE MOVE DURING TRANSCRIPTION?

ALL ON SINGLE-MOLECULE BASISINTEGRATE AVG. PROPS. OF ENSEMBLE OF MOLECULES

43

44

45

46

47

48

49

PARTIAL FILLING

TIC

RIC for nortriptylineAnalytes 10 ppm

1 = nortriptyline 2 = salbutamol 3 = diphenhydramine

50

?

51

52

AC 2004, 362A

53

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MICROPARTICLES HOST CODING ELEMENTS -ORG. SOLVENT, POLYMER PARTICLES SWELL OPEN CODING ELEMENTS ENTER IN WATER, PARTICLES CLOSE, TRAPPED

-CODING ELEMENTS BOUND TO PARTICLE SURFACE ALSO CONTAIN CAPTURE REAGENTS

CODING ELEMENTS (COLORED)

-FLUORESCENT ORGANIC DYES (Δλ = 50 to 200 nm)

-FLOUR. SEMICON NANOCRYSTALS (Δλ = 10 to 20 nm)

-IR, RAMAN REPORTERS

55

Au

Ag

GaAs

GaP

Al stripeson Si

Photolith.& etching

56

Particles coated with antihuman IgG+ flourescein tagged human IgG

Particles coated with anti-rabbit IgG+ Texas red tagged rabbit IgG

IMMUNOASSAY

Was istlos?

57

Magnetic Nanoparticles

• Small size implies superparamagnetism

• Ferrofluids: a colloidal mixture of magnetic nanoparticles

• Generally made through a reduction reaction, however, other methods have been used– Hydrothermal Synthesis– Laser Ablation

58

Magnetic Cell Sorting

MP MP

Modify MP by attaching an effector

Roger, Pons, Massart, et al. Eur. Phys. J. AP 5, 321-325 (1999)

59

Bind to Specific Cells

MP

MP

MP

MPMP

+

Cell

MP

MP

MP

MPCell

MP

Cell Cell

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Uses for magnetically labeled cells

A: Cell sorting B: Magnetic Fluid Hyperthermia

Jordan, A. et al. J Magn Mater, 201 (1999) 413-419

Roger, J.; et. al. Eur Phys. J. AP 5, 321-325 (1999)

61

Drug TargetingGene Transfection

Both are methods of delivery using magnetic fields.

Magnetic particles with the appropriate ligands attached are injected into the body and manipulated to the positions where they will be activated using magnetic fields.

At this point, the gene/drug will be taken up by the cell and act as it is supposed to (depending on the application)

Often used in conjunction with MFH (mag. fluid hyperthermia)

Scherer, F; et al. Gene Therapy, 9 p. 102-109 (2002)

62

Other Possible Uses for Magnetic Nanoparticles

• MRI Contrast Enhancementa

• GMR Detection Methodsb

• Magnetocaloric Refrigerationc

a: Ahrens, E. T; et al. Proc. Natl. Acad. Sci. USA: 95 p. 8443-8448 (1998)

b: Tondra, M; Porter, M; Lipert R; J. Vac. Sci. Tech. A: 18 p. 1125-1129 (2000)

c: McMichael, R. D.; et al. J. Magn. Magn. Mater. 111 p. 29-33 (1992)

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Magnetic Fluid Hyperthermia (MFH)

• Also known as magnetocytolysis• Inject fluid containing MP’s into patient • Use constant magnetic field to maneuver

particles to desired location (tumor, for example)

• Expose area to oscillating magnetic field to cause extremely localized heating

• Prototype unit being built in Germany

Jordan, A. et al. J Magn Magn Mater, 201 (1999) 413-419

64

Animal Test Results

Jordan, A. et. al. J. Magn Magn Mater, 201 (1999) 413-419

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Magnetic Recording MediaCan be manufactured through a 6 step process

Todorovic, M. Schultz, S. Wong, J. Scherer, A. App. Phys. Lett. 1999 (74) 2516-2518

Left: synthesis scheme.

Right: SEM image of substrate. a)before step (f). b)same array filled with nickel c) MFM (12m x 12 m) image of array.

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Magnetic Recording MediaEach nickel “column” has dimensions on the order of 170 nmdiameter, 200 nm high and 2 m apart. This leads to a particledensity below that of today’s hard drives (by approximatelya factor of 10), however, it demonstrates that other methods for data storage are feasible.

This method can be used with current read/write heads

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Magnetic Recording Media

• Current methods of recording are proprietary (i.e. very little information about how they work is available)

• Theoretical density limit for data storage is on the order of 100 Gbits/in2

• Theoretical density limit for reliable data storage is only on the order of 40 Gbits/in2

68

Nanomotors/Generators using Ferrofluids

Zahn, M. J. Nano. Rsrch, 3: 73-78, 2001

69

Nanomotors/Generators using Ferrofluids

• Currently, few applications explored (mostly theoretical)

• Paradoxical results– below a critical magnetic field strength,

ferrofluids move opposite an AC field.– Fluid viscosity is dependent on the field

strength (zero viscosity fluid reported)

Ref’s in review: Zahn, M. J. Nano. Rsrch. 3: 73-78, 2001

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CatalysisAu nanoparticles supported on TiO2 substrates show high activity for oxidation of CO at room temperature and below.

TiO2 Support

Oxygen Adsorption (on TiO2)

CO adsorption (on Au)

Haruta, M.; Date, M. Applied Catalysis A: General 2001, 222, 427-437.

Reaction proceeds at corner, step, and edge sites of Au

2-3 Atoms high

12 Atoms in length

3.5 nm Au nanoparticle

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Bimetallic Catalysis

Figure taken from: Toshima, N.; Yonezawa, T. New Journal of Chemistry 1998, 1179-1201 and references therein.

Geometric effects lead to higher activity and selectivity for certain reactions.

CH2=CH-CN + H2O CH2=CH-CONH2

Reaction proceeds most favorably with Pd-Cu particles, and is 100% selective when using a 3:1 Cu:Pd ratio.

CH3-CH-CN

OH

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Effect of Composition

Catalytic activity as a function of nanoparticle composition for the hydrogenation of 1,3-Cyclooctadiene

Figure taken from: Toshima, N.; Yonezawa, T. New Journal of Chemistry 1998, 1179-1201.

Interaction of the two metals:

Pd Pt

e- density

C=C bond prefers e- deficient sites (donor acceptor interactions); leads to selective hydrogenation

74

Electrochemical Reactions•Electrochemistry using a roughened silver electrode has been compared to that using an array of silver nanoparticles on a support.

•Different molecules adsorb differently on the two surfaces; i.e. there are different types of active sites.

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CVs of methylviologen in 0.1 M Na2SO4 at (a) EC roughened electrode, and (b) NP array electrode

Surface Properties

Couple 1: -0.66 V & 0.72 V; Ep = 60 mV

pi

Couple 2: -0.53 V & -0.55 V; Ep = 60 mV

pi

(a)

(b)No adsorption of MV!

No active sites for adsorption of MV on nanoparticle array

Zheng, J.; Li, X.; Gu, R.; Lu, T. Journal of Physical Chemistry B 2002, 106, 1019-1023.

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Surface ComparisonSEM images of (A) EC roughened electrode and (B) NP array electrode

Ag Electrode polished, then roughened by potential steps in 0.1 M KCl

NP array made by dipping an Indium-Tin Oxide (ITO) electrode in poly-L-lysine for two hours, then into a colloidal silver solution overnight

Defect sites on the EC roughened electrode must be active for MV adsorption.

Zheng, J.; Li, X.; Gu, R.; Lu, T. Journal of Physical Chemistry B 2002, 106, 1019-1023.

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Applications of Latex Particles•Butadiene

•Tires, Belts, Cables, Shoes, etc.

•Oil-resistant Products

•Styrene

•Linoleum, Plastics, Coatings

•Vinyl Acetate

•Adhesives and Paints

•Acrylate

•Adhesives, Paints, Primers, and Leather Finishing

•Chloroprene

•Belts, Hoses, Cables, etc.

•Natural Rubber Latex

•Gloves

•Condoms

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Drying of Paint

http://www.pcimag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,1846,268,00.html

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Rings…

Stone, H. A.; Shmuylovich, L.; Shen, A. Q. Langmuir 2002, 18, 3441-3445.

Rings form as the contact line between the liquid and dry substrate undergoes pinning and de-pinning cycles, while mass transport occurs toward the boundary (rate of evaporation highest at edge). Particles build-up at the interface during each pinning cycle so that rings are left when the liquid dries.

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Pinning and De-pinning

Stone, H. A.; Shmuylovich, L.; Shen, A. Q. Langmuir 2002, 18, 3441-3445.

Where a particle adheres to the surface a pinning event takes place. Mass transfer builds-up particles at this pinning site until there are no more particles in the vicinity of the edge. At this point, the contact line becomes de-pinned, and will move back until there is another adhered particle. This mechanism leads to the formation of rings when a polymer nanoparticle is left to dry on a glass slide.

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Ordering in Rings

Stone, H. A.; Shmuylovich, L.; Shen, A. Q. Langmuir 2002, 18, 3441-3445.

Mass transfer during a pinning event drives ordering in ring-forming systems such that a closest-packed layer of particles forms.

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83

84

85

Periodic Table of the Elements

103Lr

(260)

102No

(259)

101Md

(258)

100Fm

(257)

99Es

(252)

98Cf

(251)

97Bk

(247)

96Cm

(247)

95Am

(243)

94Pu

(244)

93Np

(237)

92U

238

91Pa

231

90Th

232

71Lu

175

70Yb

173

69Tm169

68Er

167

67Ho

165

66Dy

162

65Tb

159

64Gd

157

63Eu

152

62Sm150

61Pm

(145)

60Nd

144

59Pr

141

58Ce

140

8A18

7A17

6A16

5A15

4A14

3A13

Lanthanides

Actinides

109Une

(266)

108Uno

(265)

107Uns

(262)

106Unh

(263)

105Ha

(262)

104Rf

(261)

89Ac

227

88Ra

226

87Fr

(223)

83Bi

209

82Pb

207

81Tl

204

80Hg

201

79Au

197

78Pt

195

77Ir

192

76Os

190

75Re

186

74W

184

73Ta

181

72Hf

178

57La

139

56Ba

137

55Cs

133

51Sb

122

50Sn

119

49In

115

48Cd

112

47Ag

108

46Pd

106

45Rh

103

44Ru

101

43Tc

(98)

42Mo

95.9

41Nb

92.9

40Zr

91.2

39Y

88.9

38Sr

87.6

37Rb

85.5

86Rn

(222)

85At

(210)

84Po

(209)

52Te

128

53I

127

54Xe

131

36Kr

83.8

35Br

79.9

34Se

79.0

33As

74.9

32Ge

72.6

31Ga

69.7

30Zn

65.4

29Cu

63.5

28Ni

58.7

27Co

58.9

26Fe

55.8

25Mn

54.9

24Cr

52.0

23V

50.9

22Ti

47.9

21Sc

45.0

20Ca

40.1

19K

39.1

18Ar

39.9

17Cl

35.4

16S

32.1

15P

31.0

14Si

28.1

13Al

27.0

2He

4.00

10Ne

20.2

9F

19.0

8O

16.0

7N

14.0

6C

12.0

5B

10.88B

2B12

1B111098

7B7

6B6

5B5

4B4

3B3

12Mg

24.3

11Na

23.0

4Be

9.01

3Li

6.94

2A2

1A1

1H

1.01

86

Organic Nanoparticles

Organic compound

+ Lipophilic solvent

Water +

Stabilizer

Emulsification

Separation of solvent

Hydrosol of organic compound

Horn et al.

Angew. Chem. Int. Ed

2001, 40, 4330-4361

Polymer Nanoparticle Synthesis

Initiator

X

XXXX

X

XXXX

X

X

XXXX

X

X XX X

X

X

XXXX

X

X

X

X

X

X

X

XXXX

X

X

X

X

X

X

Monomer

Micelle formed from emulsifier

Polymer

Stability Sphere

•Colloid Science, Kruyt, H. R., Ed.; Elsevier: New York, New York, 1952; Vol. 1

•Mysels, K. J. Introduction to Colloid Chemistry; Interscience: New York, 1959

•Irja Piirma, Ed., Emulsion Polymerization; Academic Press: New York, 1982

•Eliseeva, V. I.; Ivanchev, S. S.; Kuckanov, S. I.; Lebedev, A. V. Emulsion Polymerization and its Applications in Industry; Plenum: New York, 1981

•Bovey, F. A.; Kolthoff, I. M.; Medalia, A. I.; Meehan, E. J. In High Polymers; Mark, H., Melville, H. W., Marvel, C. S., Whitby, G. S., Eds.; Interscience: New York, 1955; Vol. IX

88

Other Techniques

Laser Ablationa

Electrochemistryb

Hydrothermal Synthesisc

(Supercritical water)

Sol-Geld

a: Neddersen, J; et al. Appl. Spec. 47 p. 1959-1964 (1993)b: Lu, D; Tanaka, K. J. Phys. Chem. 100 p. 1833-1837 (1996)c: Cabanas, A; Poliakoff, M. J. Mater. Chem. 11 p. 1408-1416 (2001)d: Moreno, E; et al. Langmuir 18 p. 4972-4978 (2002)

89

DLVO Theory

•Ottewill, R. H. In Emulsion Polymerization; Piirma, I., Ed.; Academic Press: New York, 1982, pp 1-49.

•See also DLVO theory : Derjaguin, B. V., Landau, L., Acta Physicochim. URSS, 1941, 14, 633, and Verwey, E. J. W.; Overbeek, J. T. G. Theory and Stability of Lyophobic Colloids: The Interaction of Sol Particles Having an Electrical Double Layer; Elsevier, Inc.: New York, New York, 1948.

Vr + Va

0

Separation Distance (nm)0 200

Repulsion

Attraction

90

Photolithography Patterning

• Typically pattern the capture monolayer followed by particle adsorption

• Few examples of patterning

after nanoparticle deposition

91

Photolithography Patterned Nanoparticles

SEM image of Au nanoparticles adsorbed onto a patterned (3-mercaptopropyl)-trimethoxysilane monolayer on SiO2 coated silicon wafer.

AFM image (80 m x 80 m) of a three-layer coating of nanoparticles followed by photopatterning.

Chen, D.; et al. Thin Solid Films, 1998, 327-329, 176-179.

Pris, A.D.; Porter, M. D. Nano Lett. 2002, 2(10), 1087-1091.

92

Electron Beam Lithography

• Coat substrate with polymer film

Write pattern with e- beam

Dissolve exposed polymer

Evaporate metal into “holes”

Somorjai, G. A.; et al. J. Chem. Phys. 2000, 113(13), 5432-5438.

93

Images of Nanoparticle Arrays Formed by Electron Beam Lithography

AFM and SEM of Pt nanoparticle array. Particles are 40 nm in diameter and spaced 150 nm apart.

Somorjai, G. A.; et al. J. Chem. Phys. 2000, 113(13), 5432-5438.

Spin-coat PMMA on Si (100) wafer with 5 nm thick SiO2 on surface.

Beam current: 600 pA

Accelerating Voltage: 100 dV (100 kV?)

Beam diameter: 8 nm

Exposure time: 0.6 s at each site

Pt deposition: 15 nm by e- beam evaporation

94

Nanosphere Lithography

Hulteen, J.C.; Van Duyne, R.P. J. Vac. Sci. Technol. A 1995, 13(3), 1553-1558.

(A) Representation of a single-layer nanosphere mask formed by convective self assembly.

(B) Illustration of the exposed sites on the substrate with single-layer mask

(C) AFM image (1.7 m x 1.7 m) of Ag deposited on mica with a mask of 264 nm diameter nanoparticles.

Mask preparation: Spin coat 267 nm polystyrene nanoparticles at 3600 rpm.

Deposition: Ag vapor deposition

Mask removal: sonicate 1-4 min. in CH2Cl2