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PolymerPolymer--metal nanocomposites for metal nanocomposites for functionalfunctionalapplications*applications*

F. Faupel, V. Zaporojtchenko, A. Biswas, R. Adelung, F. Faupel, V. Zaporojtchenko, A. Biswas, R. Adelung, H. Takele, U. SchH. Takele, U. Schüürmann, H. rmann, H. GreveGreve

Chair for MulticomponentChair for Multicomponent Materials Materials ChristianChristian--Albrechts University KielAlbrechts University Kiel

**supportedsupported by Technologyby Technology FoundationFoundation SchleswigSchleswig--Holstein (TSH)Holstein (TSH)

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OutlineOutline

• Properties of nanocomposites• Preparation

- Co-evaporation- Co-sputtering

• Examples:- Magnetic composites for > 1 GHz- Ultra-thin optical filters- Near percolation composites- Multifunctional composites

• Summary and outlook

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Nanocomposite - new class of materials

Metal cluster1 - 100 nm

Matrix material: Polymer

Magnetic Fe-Co-Ni clusters in Teflon-AF

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Some properties of nanocomposites

♦ Optical- d << λ ⇒ no light scattering ⇒ transparent magnets,

magneto-optical devices- Surface plasmon absorption ⇒ ultra thin filters- Tunable n ⇒ Bragg reflectors, sensors

♦ Electrical - R variation > 1010 ⇒ sensors

♦ Magnetic- Dielectric matrix ⇒ no eddy currents- Eddy current cut off frequency ∝ d -2 ⇒ inductors at f > 1 GHz- Spin-dependent tunneling ⇒ TMR devices- Nanorods by self organization ⇒ perpendicular recording > 1 Tb/cm2

♦ Catalytic- Very high surface area ⇒ reactive membranes

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Possible structures of nanocomposites :1D, 2D or 3D, multilayers, fragments

Cu on PMDA/ODA Ag/PMMAfragments

Ts = 400°C

Preparation:

mixing two or moreconstituents by VPD

-co-deposition-co-sputtering-plasma deposition-hybrid process-induced crystallization

AFM

TEM

20 nm

Teflon AF + Au clusters

Teflon AF + Ag clusters

14 nm MultilayerAu/Ag/ Teflon - host

Au nanowiresin Teflon AF

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Vapor phase deposition of composites - attractive optionfor implementation in microelectronic processing

Co-evaporation

Advantages• dry, solvent-free• thick films• low defect density• high purity• good process contro•deposition conformability

PolymersPolyimide, Polyamide, PU(polycondensation of monomers)Teflon AF, FEP, PMMA etc.(thermal decomposition and repolymerization on substrate)

quarz

microbalane

1

quarzmicrobalance2

metal evaporator polymer

evaporator

shuttersubstrate

UHV chamber

V. Zaporojtchenko et al., Microel. Eng. 50, 465 (2000)

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Co-evaporation of monomers +metal Polyimide with Cu

ONN

O

O

O

O

PMDA-ODA

Imidization of polyamic acid

Annealing imidization + metal aggregation

pyromellitic dianhydride

oxydianiline

Behnke, Zaporojtchenko, Strunskus, Faupel -Micromat, (2000), 1052.

200 °C 250 °C 300 °C

30 °C 100 °C 150 °C

60 nm

60 nm 60 nm 60 nm

60 nm60 nm

Effect of annealing temperature on cluster size for Cu in PMDA-ODA

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Tailoring of the size distribution

Effect of heating rate

2 °C/min 8 °C/min 12 °C/min

+ 30 min at 250 °C

Immobilization by imidization crucial!

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Also metal-polymer interaction is importantMetal mobility determined by chemical reactivity!

Ni

Same conditions:2 °C/min, 250 °C

Cu

Problem for reactive metals : cluster oxidation

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VPD of composites based on Teflon AF®

CC C C

O

F F

OF

F F

F

CCF3 CF3

m

n

Thermal decompositionand repolymerizationonon substrate

• Advantage: protection of clusters• Problem: low metal condensation coefficient

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Effect of low C in Teflon AF- Ni composite

280 nm

Filling Factor < 1 %

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Surface Processes

Monomers and metal atomsarriving on substrate

a) adsorption adsorptionb) diffusion repolymerizationc) agglomeration cross-linkingd) desorptione) diffusionf) coalescenceg) embedding

• substrate temperature• evaporation rates• condensation coefficient

Parameter

V. Zaporojtchenko et al. - Surface Sci. 532,300 (2003)

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Condensation coefficient

C very low for polymers with low surface energy!

Thran, Kiene, Zaporojtchenko, Faupel, Phys. Rev. Lett., Vol. 82, (1999), 1903 ff.

Teflon AF: C ~ 2 ·10-3

metalamountarrivingmetalamountadsorbedC =

C for Ag on some polymers

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Influence of atomic mobility and condensation coefficient on morphology of composites (TEM study)

50nm

Columnar growth aspect ratio 100:5

Spherical clusters

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Tandem + ion beam assisted depositionsubstrate

.

quarz

microbalance quarz microbalance

metal evaporator polymer

evaporatorion beam

Random nucleation

Preferred nucleation by IBAD

J. Zekonite,V. Zaporojtchenko,U.Schuermann, F.FaupelPolym. Surf. Modification V3, 243 (2004)

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Tandem evaporation + annealingHigh filling despite low C

Ni in Teflon AF

No cluster oxidation! A. Biswas et al., Nano Letters 3, (2003) 69.

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Nanocomposites by RF co-sputteringPTFE/Ag

T: target S: substrate Sh: shutter,W: window Ar-gas inletP: pump C: cooling q: quartz monitor

-Ag ; O -fluorine; •-carbon)

300 298 296 294 292 290 288 286 284

sputtered PTFE+Ag f=31,2%

CF3

CF2

CF

FxC - CFx

coun

ts/s

Binding energy [eV]

RF = 13.56 MHz

Schürman et al., Workshop Nanocomposite, Kiel 2003

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Transition 2D to 3Ddeposition + embedding metal particles

by thermal treatment or vapour induced crystallisation

Acetone

solvent provides chain mobility for polymer crystallisation

embedding of gold clusters has been observed after crystallisation

Macromolecule 2004

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XTEM after Crystallisation

50 nm

Clusters are narrowly dispersed in the Polymer but at different depths

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Transition 2D -1D Nanowires via cracks

Nucleation at cracksVery small C

R. Adelung et al., Nature Materials 3, 375 (2004)

Metal depositionStarting material Crack formation

Example: Au wires on Teflon

Optical nanocompositesApplications• Ultrathin optical filters• Bragg reflectors, sensors• Magnetooptical systems

ωplasmon tuned by:• nature of metal• cluster size, shape, distance • dielectric matrix

300 400 500 600 700 800

458 nm

norm

. Ext

inct

ion

[a.u

.]

Wavelength [nm]

60% 48% 37%_percolation 28% 20%

PTFE/Agfilling factor

Surface plasmon resonance: charge density oscillation ⇒ strong absorptionin visible range for nanoparticles of Au, Ag, Cu, ...

Strong field enhancement ⇒ surface enhanced Raman spectroscopy biosensors

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Nanocomposites with variable optical propertiesnear percolation

400 500 600 700 8000,0

0,2

0,4

0,6

0,8

1,0

1,2

546.5 568 nm532 nm

Abs

orba

nce

(-)

Wavelength (nm)

8.5% 14.7% 21.3% 33.2% 44.0%

Tailoring of refractive index n = 1.38 1.94 0.96f = 0 21% 50%

Percolation: f ~ 47%Au/Teflon

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Multilayer composites

20 nm

Teflon AF + Au clusters

Teflon AF + Ag clusters

Biswas, et al., Appl. Phys. Lett., Vol 84, (2004), 2655 ff

400 500 600 700 800 900

538 nm

437 nm

Abso

rptio

n (a

.u.)

Wavelength (nm)

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Multilayer periodic systemwith alternative high-and low-index layers

( Bragg Reflector )

Glass substrate Polymer n=1.38

Ag composite n= 2.2

400 600 8000

5

10

15

20

25

30

35

40 Reflexion

Ref

lect

ance

%

wavelength [nm]

100nm250nm

Spectral reflectance for 4x2 layersAg/ PTFE

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The working principle of the sensing based onTeflon composite layers: thickness, mass, density change

of polymer matrix ( Bragg Reflector or QCM)

400 600 8000

5

10

15

20

25

30

35

40 Reflexion

Ref

lect

ance

%

wavelength [nm]

Expose to organic vapor Wavelength shift after vapor exposure

alternative high-and low-index layers

TeflonTeflon composite

QCM-Sensor sensitivitydepend on composite selectivity

to organic vapors

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Magnetic nanocompositesInductive components in mobile communications

Hysteresis losses andlimit of the cut-off frequency

5-10 nm

Best solution- nanocompositehigh ρ ,Ms, FMR

moderate anisotropyEnergy to create Bloch wall >saved magnetostatic energy

Single DomainParticles

• Insulating matrix ⇒ no eddy currents

• Tuning of alloy without need of high ρ• Orientation of easy axis possible by field during

annealing or deposition

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Magnetic nanocomposites with single domain particles

-200 -150 -100 -50 0 50 100 150 200

-1,00

-0,75

-0,50

-0,25

0,00

0,25

0,50

0,75

1,00

in-plane 0° ("easy" axis) in-plane 90° ("hard" axis)

M /

MSbu

lk

magnetic field / [mT]

VSM - Vibrating Sample Magnetometry(Smart materials Group CAESAR Bonn)

0,01 0,1 1 10

0

100

200

300

400

Hc = 10 mT (100 Oe)Vibrating Sample Magnetometry

(110)

bcc

(211)(200)

frequency / [GHz]

real part µ' imaginary part µ''

ac p

erm

eabi

lity

High Frequency permeability measurementscut-off and FMR frequency > 2 GHz

FeNiCo Clusters in Teflon AF matrix

H.Greve et al. Keynote Lecture Nano 2004

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Tunneling magneto-resistance

Spin-dependent electron tunneling betweensuperparamagnetic clusters

Joint DFG/JSPS project with S. Deki, Kobe Univ.

Dispersion of Au-Co clusters by thermal decomposition of polyacrylonitrile matrix

∆ρ/ρ0 ∝ [L(mH/kT)/L(mHs/kT)]2

L: Langevin function

80 % at low H!

Nabika et el., J. Mater. Chem. 12, 2408 (2002)

f < fc: insulating

f > fc: metallic structure

2 3 4 5 6 7 810-4

10-3

10-2

10-1

100

101

102

103

104

105

106

107

Resi

stiv

ity (O

hm*c

m)

EDX Intensity Ag/F

Electrical properties near percolationResistivity variation 1010

PTFE /Ag on glass

fc ~ 32 -36 %

0,0027 0,0028 0,0029 0,0030 0,0031 0,0032 0,0033 0,0034 0,0035300G

400G

500G

600G

700G

Ea=0.24 eV

R heating (020704) Linear Fit of GlassHeat_F

Res

ista

nce

(log

Ω)

1/T (1/K)

Thermally activated tunneling

R~ exp (Ea/kT)

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Electrical properties of Ag/PTFE nanocompositesnear percolation

resistivity variation by substrate elongation

0,000 0,001 0,002 0,003 0,004 0,0050

2

4

6

8

10

0,20 0,25 0,30 0,35 0,40 0,45100µ

100m

100

100k

100M

SP

EZ. W

IDE

RST

AND

(Ohm

*cm

)

Ag-FÜLLFAKTOR

Substratausdehnung

Wid

erst

and

[Ω] x

109

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Summary and outlook

Nanocomposites: - novel magnetic, optical, electrical,chemical properties

Vapor phase deposition: - wide range of size and filling,narrow size distrib., alloys

Demonstr.applications: - softmagnetic ultra-high frequency materials

- ultra-thin multiwavelengths color filters and sensors

Outlook: - sensors based on near-percolation effect and piezoelectric substrates

- reactive membranes

- tunneling magnetoresistance materials- ultra-high density magnetic recording - transparent magnetic nanocompositesFurther information: http://www.tf.uni-kiel.de/matwis/matv/

e-mail ff@tf.uni-kiel.de

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Magnetic applicationInductive components in mobile communications

F - ( 0,8- 3GHz)Hysteresis losses and

limit of the cut-off frequencyBest solution- nanocomposite

high ρ ,Ms, fmoderate anisotropy

Ikeda et al - 2002 JAP(FeNiCo - J.o.M.a.M.M.)

~70 nm~6 nm

Single DomainParticles

Energy to create Bloch wall >saved magnetostatic energy

Eddy currents ~

ρ: resistivity d: particle diameter~10 nm

2w dρf ∝

S0kFMR MµHf ∝

Ferromagnetic resonance frequencyHk : anisotropy fieldMS : saturation magnetizationµ : permeability

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Tailoring the filling factor

• Substrate T• Deposition rates• Pinning

Metal volume fraction

1,5 2,0 2,5 3,0 3,5

0,05

0,10

0,15

0,20

0,25

fillin

g fa

ctor

, Con

dens

atio

n co

effic

ient

Ratio of deposition rates (M/P)

f c

polmet

polVm

fρρ

ρ−

−=

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Surface Processes

metal atoms arriving on substratea) adsorptionb) diffusionc) agglomerationd) desorptione) diffusion into bulkf) coalescence in bulkg) embedding of clusters

• substrate temperature• evaporation rates• condensation coefficient

Parameters

Nucleation also at defects and free radicals!V. Zaporojtchenko et al., Surface Sci. 532, 300 (2003)

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Teflon AF-Au composites

High filling even for extremely low sticking

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Polyimide-Cu composites

• Co-evaporation of monomers and Cu• Annealing ⇒ imidization + metal aggregation

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Alloy clusters

2,5 5,0 7,5 10,0 12,5 15,00

10

20

30

40

50

Volu

me

Frac

tion

(%)

Nanoparticle Size (nm)

(110)

bcc

(211)(200)

• No oxidation• narrow size distribution!

Patent pending

Fe-Ni-Co clusters in Teflon AF(elevated deposition T)

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Eddy current losses

Eddy currents limit cut-off frequency

2w dρf ∝ ρ: resistivity

d: feature size (particle diameter)

Nanoparticles for > 1GHz

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Magnetic poperties

Vibrating sample magnetometry and TEM

20 nm

200 nm Fe54Ni29Co17 / Teflon AF nanocomposite film

-200 -150 -100 -50 0 50 100 150 200

-2

-1

0

1

2 (b)

Mom

ent (

Tesl

a)

Field (mT)

No degradation effects after 3 months!

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High frequency permeability measurements

0,01 0,1 1 10

0

100

200

300

400

frequency / [GHz]

real part µ' imaginary part µ''

ac p

erm

eabi

lity

Cut-off frequency > 2 GHz

Preliminary results!

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Electrical properties near percolation

PTFE /Ag on glass

0,000 0,001 0,002 0,003 0,004 0,005

2,0G

4,0G

6,0G

8,0G

10,0GSilber-PTFE-Nanokomposit (Ag-Gehalt:33%) auf Polymersubstrat

Wid

erst

and

[Ω]

Substratausdehnung

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Multifunctional nanocomposites

Co-sputtering of Teflon and Ag

300 400 500 600 700 800

0,0

0,5

1,0

1,5

2,0

2,5

3,0sput. PTFE+Ag

407 nm

411 nm

Abs

orpt

ion

[a.u

.]Wavelength [nm]

filling factor 26% filling factor 21%

--- 20 nm

hydrophobic (Teflon) hard (crosslincing)antibacterial (Ag) colored (plasmons)

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Nanostructuring by selforganization

Self-cleaning by Lotus effect

Metal clusters as nanomaskson Teflon film + sputtering

hydrophobic nanoneedles

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Magnetic nanorods

50nm

Rods:a = 5 nmc = 100 nm

Application:Recording > 1 Tb/cm2

Fe-Ni-Co rods on Teflon-AFby co-evaporation

Patent pending

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Adelung, et al, Nature Materials, 3, 375 (2004)

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Summary and outlook

Nanocomposites: - novel properties: magnetic, optical, electrical, ....

Vapor phase deposition: - wide range of d and f, narrow size distrib., alloys

Demonstrated: - magnetic ultra-high frequency materials- ultra-thin multiwavelengths filters

Self-organization ⇒ : - Nanorods, wires, dotted wires, needles

Outlook: - orientation of easy axis and alloy tuning- ultra-high density magnetic recording- near-percolation sensors - reactive membranes- TMR materials- reactive membranes

Further information: http://www.tf.uni-kiel.de/matwis/matv/ff@tf.uni-kiel.de

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FMR - Ferromagnetic resonance frequency

magnetic moment will not follow an AC drive field > fFMR

S0kFMR MµHf ∝k

SH

Mµ =

MS

Hk

easy axis

hard axisHk : anisotropy fieldMS : saturation magnetizationµ : permeability

aim: MS high +Hk moderate

FMR in GHz range

tradeoff

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Electrical properties of nanocomposites near percolation

resistivity variation by plastic substrate elongationtemperature coefficient of resistance (TCR) ~ 0.1 !!!

20 30 40 50 60 70 80 90 100 110

10k

100k

Resistivity of Nanocomposite near Percolation on Polymer Substrate

Res

istiv

ity (Ω

cm)

Temperature (°C)

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Surface plasmon resonance (SPR) in nanocompositesSurface Plasmon Resonance

metal–dielectric nanocomposite is excited by light, photons are coupled at the metal–dielectric interface, causing an induced charged density oscillation and shows a strong absorption maximum at a particular wavelength, called the surface plasmon resonance (SPR) or plasmon polariton.

• amount of metal concentration• shape, size, and spatial distribution• distance between the clusters• incorporated metal particles• sorounding dielectric medium

300 400 500 600 700 800-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

Abso

rban

ce (-

)

Wavelength (nm)

4 % 8 % 16 % 29 % 40 %

Au-Teflon AF

Increasing metal volume concentration leads a plasmonband maximum shift to longer wavelengths.