Controlling Organic Phase Architecture via Templating with the Inorganic Phase and vice versa.

http://www.cem.msu.edu/~kanatzid/

Organic/Inorganic Nanocompositesfrom confined polymerization

Our work exploits confined polymerization and self-assembly, to organize inorganic and organic building-units into nanocomposite materials with targeted structural features spanning Å to µm length scales.

The techniques involve concepts in

supramolecular, host-guest inclusion templatingbiomimetic chemistry

our work has contributed to the idea that inorganic materialscan be synthesized by molecular design, self-assembly and crystal engineering.

NanocompositesNanocomposites of interestof interest

lamellar

delaminated

porous

Potential ApplicationsPotential Applications

Tough structural materialsTough structural materials

Smart membrane systemsSmart membrane systems

Battery cathode materialsBattery cathode materials

Sensor applicationsSensor applications

EMI shieldingEMI shielding

Electronic device components Electronic device components

Polymerization ofPolymerization of pyrrolepyrrole

NH NH

NHNH

NHH

H

NH

NH

NH

NH

NH NH

NH

NH

H NH NH NH

NHH

Ò

Ò

deprotonation

p-doped polypyrrole+ 2H +

.

+ 2H +

chain propagation primarily through 2,5 coupling

2,5 coupling

n

oxidation

+ .+'

at the 2,5 positions

+ 2H +

strongly acidic

+

+

dimerization

radical cation

oxidation+e-

+ '

+ '

disorderedbranched

Ordered parallel

N H

+ FeOCl

N H

+ FeOCln

INTERCALATIVE POLYMERIZATIONINTERCALATIVE POLYMERIZATION IN IN FeOCl FeOCl and Vand V22OO552H2H22OO

O2 H2O2

mw=5000~55 units

CH3CN

Kanatzidis, Marks et al JACS 109, 3797 (1987)

Also NH2

S

V2O5 Xerogel

0

10

20

30

40

50

60

0 1 2 3 4 5

Oxygen Depletion (%)

Aniline/V2O5 Xerogel Molar Ratio

2θ, degrees

PANI-V2O5

Inte

nsity

XX--ray Diffraction from PANIray Diffraction from PANI--FeOCl FeOCl ““single crystalsingle crystal””

a-axis

Ordering of polyaniline in FeOCl (Endotaxy)

c-axis

Cl

Fe

2x2 supercell

VV22OO55••nHnH22O O xerogelxerogelStructure of V2O5 xerogel

water

100-200 Å

1000-3000 Å

001

003004 005

2θ degrees (CuKα)

NaVO 3 to HVO 3Polymerization of HVO 3 Sol-Gel Transition

gel

wet gel

xerogel

V2O5.nH 2O

SALIENT FEATURES OF NANOCOMPOSITESSALIENT FEATURES OF NANOCOMPOSITES

Diverse Components Mixed at the Molecular Diverse Components Mixed at the Molecular ScaleScale

compoundcompound--likelikeclassical composite classical composite --likelike

Potential Polymer Chain Ordering in Potential Polymer Chain Ordering in IntralamellarIntralamellarSpaceSpace

polymer structure polymer structure enhanced propertiesenhanced properties

Maximization of Interface InteractionsMaximization of Interface Interactionsmodel systems for interface studiesmodel systems for interface studiesInteractions at interface responsible for advanced propertiesInteractions at interface responsible for advanced properties

Hybrid materials Hybrid materials …….. new properties.. new properties

Phyllosilicates, clays: montmorillonite, hectorite, fluorohectorite

Oxides: V2O5 xerogel, MoO3

Oxyhalides: FeOCl

Dichalcogenides: MoS2, TiS2, TaS2, NbSe2, WS2

MPS3: MnPS3, CdPS3, NiPS3

metal phosphates: α-Zr(HOPO3)2·H2O, α-Ti(HOPO3)2 ·H2O,

HUO2PO4·4H2O

Layered Double Hydroxides: [Ca2Al(OH)6]+[(OH).3H2O]-

Giannelis, Ruiz-Hitzky, Kanatzidis, Nazar, Lemmon, Jones, others...

Layered Inorganic Compounds as Host Materials

Methods for Polymer IntercalationMethods for Polymer Intercalation

inin--situsitu intercalativeintercalative redoxredox polymerizationpolymerizationpolypyrrolepolypyrrole//FeOClFeOCl, PANI/V, PANI/V22OO5 5 ((KanatzidisKanatzidis et al)et al)polypyrrolepolypyrrole//zeolitezeolite ((BeinBein et al)et al)polypyrrolepolypyrrole/clay (/clay (GiannelisGiannelis et al)et al)

monomer intercalation followed by induced monomer intercalation followed by induced topotactic polymerizationtopotactic polymerizationpostpost--intercalative intercalative nylon/clay (nylon/clay (KamigaitoKamigaito, , UsukiUsuki et al)et al)aniliniumanilinium/V/V22OO5 5 ((KanatzidisKanatzidis et al) et al)

direct polymer intercalationdirect polymer intercalation (solution/solid interface)(solution/solid interface)PPV/MoOPPV/MoO33 ((NazarNazar et al) (precursor polymer)et al) (precursor polymer)PEO/VPEO/V22OO5 5 ((KanatzidisKanatzidis et al) et al) PEO/clay (RuizPEO/clay (Ruiz HitzkyHitzky,, GiannelisGiannelis))PEO/CdPSPEO/CdPS33 (Clement et al)(Clement et al)PAN/PAN/zeolitezeolite ((BeinBein et al)et al)

……more methodsmore methods

direct polymer intercalation from the meltdirect polymer intercalation from the meltPEO/clay, polystyrene/clay (PEO/clay, polystyrene/clay (GiannelisGiannelis et al)et al)

polymer polymer encapsulationencapsulation by flocculation of a colloidal single layer by flocculation of a colloidal single layer suspension of the host suspension of the host

(nano(nano--composite self assembly) composite self assembly) PANI/MoSPANI/MoS22 ((KanatzidisKanatzidis et al)et al)

simultaneous polymerization/polymer simultaneous polymerization/polymer encapsulationencapsulation by flocculation of a by flocculation of a colloidal single layer suspension of the host colloidal single layer suspension of the host

(nano(nano--composite self assembly)composite self assembly)polypyrrolepolypyrrole/MoS/MoS22 ((KanatzidisKanatzidis et al)et al)

Alternating Alternating layer by layerlayer by layer deposition of one phase on top of anotherdeposition of one phase on top of anotherMalloukMallouk, , DecherDecher othersothers

Others...Others...

POLYMER ENCAPSULATIONPOLYMER ENCAPSULATION

waterLi

Li+

polymer solution

nanocomposite

dispersion

exfoliation

polymer

Host material

Exfoliated layers of MoSExfoliated layers of MoS22 , WS, WS22 , NbSe, NbSe22 and TaSand TaS22 have been have been used for the first time to produce plasticused for the first time to produce plastic--likelikenanocompositesnanocomposites

The exfoliation method applies to a large variety of soluble polThe exfoliation method applies to a large variety of soluble polymersymersEnables tuning of the mechanical properties in these materialsEnables tuning of the mechanical properties in these materials

PolyethylenePolyethylene

PolyethylenePolyethylene--oxide, PEOoxide, PEO

poly(propylene glycol) , poly(propylene glycol) ,

methyl cellulose, methyl cellulose,

poly(poly(ethylenimineethylenimine), PEI), PEI

Nylon Nylon

etc.etc.

PEOCH2CH2

On

NH

O nnylon

O

OO OMeO

OMe

O

MeOOMe

OMen

Some Encapsulated PolymersSome Encapsulated Polymers

PVP

PPG

PE

Methyl-cellulose

CHCH2

O

CH3

nCH2CH2

n

O

OOO

MeO

OMe

O

MeOOMe

OMe

n

PEOCH2

CH2

On

NO

CHCH2

n

CH2

CH2

NHn

PEINylon-6

NH

O nnylon

volts

mic

roam

ps

RectifyingRectifying polypyrrolepolypyrrole/ V/ V22OO55 xerogelxerogel junctionsjunctions

N H

H N

N H

H N

(polypyrrole)xV2O5

Conductivity type changes with xAt low x system is n-typeAt high x system is p-type

substrateV2O5 xerogel

drop of pyrrole

graded composition(ppy)xV2O5

rectifying junction

(ppy)xV2O5

(+) (-)

-6

-5

-4

-3

-2

-1

0

1

2

-300

-250

-200

-150

-100

-50

0

50

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

(polypyrrole)xV

2O

5

Log(cond), S/cm Thermopower, µV/K

Log(

cond

), S

/cm

Thermopow

er, µV/K

x value

I-V

(PEO)(PEO)xxVV22OO55 nanocompositesnanocomposites

-5 10 -5

0 10 0

5 10 -5

1 10 -4

1.5 10 -4

0 0.5 1 1.5 2 2.5 3 3.5

(PEO)xV

2O

5

Con

duct

ivity

(S/c

m)

x

2 6 10 14 18 22 26 30

Inte

nsity

V2O

5-nH

2O xerogel

2θ, degrees

(PEO)0.5

V2O

5-nH

2O

(PEO)1.5

V2O

5-nH

2O

0

1

2

3

4

5

0 500 1000 1500 2000 2500 3000

abso

rban

ce

λ, nanometers

Saturated with N2H4Optical Spectrum of PEO/V

2O

5

10

12.5

15

17.5

20

0 1 2 3 4 5 6

Interlayer Distance (Å)

Molar Ratio (x)

(PEO)xV

2O

5 -nH

2O

Response to NH3Response to N2H4

(PEO)xV2O5 as a sensitive N2H4 sensor

Time (sec)

Highly oriented filmsHighly oriented films

0 20 40 60 80 100 120 140

XRD Pattern of LixTaS

2•PEO Film

(M.W. = 100,000)

Inte

nsity

2-theta (deg)

001

002

003004005

006007008009

00100011

00120013001400150016 0017

0 0.2 0.4 0.6 0.8 1

One-Dimensional Electron-Density Maps of Li

xTaS

2¥PEO Nanocomposite

Ele

ctro

n de

nsity

z-axis

Experimental data

Type II PEO-HgCl2

complex comformation

Planar zigzag comformation,parallel arrangement

Planar zigzag comformation, perpendicular arrangement

Li -PEO-TaS2

-5

0

5

10

0 0.2 0.4 0.6 0.8 1

experimentmodel

elec

tron

dens

isty

c-axis

0

1000

2000

3000

4000

5000

6000

-100 -50 0 50 100

Line

wid

th (H

z)

Temperature (oC)

Li0.2TaS 2

Li-PEO-TaS 2

Type-II PEO-HgCl2 complex

PEO conformation in TaS2 and NbSe2 and Li-ion mobility

Li NMR static

Superconductivity in TaS2 and NbSe2

Free standing film of TaS2Meissner effect in NbSe2

Phyllo-morphous

EgEg?Eg

An array of nanocrystalsQuantum dotsAn array of

Quantum anti-dots

Bulk semiconductor

Porous Semiconductors (non-oxidic): A challenge

Inside-out version

MesoporousMesoporous Oxides via Liquid Crystal Oxides via Liquid Crystal Template RouteTemplate Route

Major Breakthrough ca 1989Major Breakthrough ca 1989: :

general synthetic strategy to general synthetic strategy to

orderedordered mesoporousmesoporous silicates by silicates by

MobilMobil1 1 (MCM(MCM--41, MCM41, MCM--48 etc), 48 etc),

opened the pathway for novel hybrid opened the pathway for novel hybrid

solids.solids.

ManyMany mesoporousmesoporous metal oxides metal oxides

have been synthesized based on have been synthesized based on

MCMMCM--X materialsX materials2,32,3..

ZrOZrO22, V, V22OO55, SnO, SnO22, TiO, TiO221. C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli,

J.S. Beck, Nature 1992, 359, 710.

G. D. Stucky et al, Chem. Mater. 1996, 8, 1147

AdamantaneAdamantane based frameworksbased frameworks

z

x y

S

Mn

Ge

Yaghi et alOzin et al

(Me4N)2MnGe4S10 microporous

MesostructuredMesostructured Wormholes ~35 Wormholes ~35 ÅÅ

surfactant filled pores

metal chalcogenide framework

Kanatzidis et al Advanced Mater. 2000, 12, 85-91

(R(R--NMeNMe33))22M(GeM(Ge44QQ1010) Q= S, Se) Q= S, Se

0 20 40 60 80 100

Inte

nsity

(arb

. uni

ts)

2θ (deg), CuKα

C14ZnGeS

30

35

40

45

12 13 14 15 16 17 18

CnCdGeSCnCdGeSe

d p (Å)

Surfactant Chain Length (n)

Diffuse scatteringAdjustable pore size

Non-periodic inorganic framework

Optical PropertiesOptical Properties

Diffuse scattering and Pair Distribution Diffuse scattering and Pair Distribution Functions Functions (with S. J . L.(with S. J . L. BillingeBillinge, M. F. Thorpe), M. F. Thorpe)

Influence of solventInfluence of solvent

In water: In water: (R(R--NMeNMe33))22MGeMGe44QQ1010

•• Disordered wormholeDisordered wormhole

InIn formamideformamide: : (R(R--NMENME33))22--xxMM1+x1+xGeGe44QQ10+10+δδ

•• Ordered hexagonal, cubicOrdered hexagonal, cubic

[Ge4Q10]4- [Ge4Q10-x]z- + xQ2-

2[SnSe4]4- [Sn2Se6]4- + 2Se2-

Biologically inspired nanocomposites (Fe4S4 ferredoxinoids)Fe4S4-MSU-1 and Fe4S4-M�SU-2 Angew Chemie 2000, 39, 4558

1

10

0 1 2 3 4 5

Cpy/Fe4S

4/Ge

4S

10

log(

a/s)

Energy, eV

Eg=1 eV

Fe

S

S

SFeFe

Fe

S

S

S

S

S

Q

GeQ

Ge

QGe

Q

GeQ Q

Q

Q Q

Q

Q=S, Se

Tra

nsm

ittan

ce

(i)

(ii)

(i)

(ii)

(iii)

423

(a) (b)

Wavenumber (cm-1)Velocity (mm/sec)

Rel

ativ

e T

rans

mis

sion

(%)

Characterization ofCharacterization of Fe4S4Fe4S4--MSUMSU--1 and Fe4S41 and Fe4S4--M�SUM�SU--22

Fe Mössbauer Infrared spectroscopy Fe4S4 cluster extractionUV/vis spectra

0

0.5

1

1.5

2

400 450 500 550 600 650 700 750 800

Fe4S4-MSU-1

Fe4S4-MSU-2

Abs

orba

nce

Wavelength (nm)

λmax

= 445 nm

MesostructuredMesostructured NonNon--OxidicOxidic Solids Based on the Solids Based on the Tetrahedral Clusters and Metal IonsTetrahedral Clusters and Metal Ions

1. M. Wachhold, K.K. Rangan, S.J.L. Billinge, V. Petkov, J. Heising, M.G. Kanatzidis, Adv. Mater. 2000, 12(2) 85-91.2. K. K. Rangan, S. J. L. Billinge, V. Petkov, J. Heising, M. G. Kanatzidis, Chem. Mater. 1999, 10, 2629.3. M.J. MacLachlan, N. Coombs, G.A. Ozin, Nature 1999, 397, 681.

Ge, Sn

Ge, Sn

S, Se, Te S, Se, Te

SiO4 analogstopologically similar structures?

SynthesisSynthesis+NR

R : CH3-(CH2)15-

Formamide : 20 ml

Surfactant : 10 mmol

K4SnSe4 : 1 mmol

Temperature : 75 oC

Supramolecular organization Slow addition of

M2+/FM solution

M2+ : Mn2+, Fe2+, Co2+, Zn2+, Cd2+, Hg2+

Immediate precipitation

aging for 24h

Mesostructured Chalcogenide Phases

wormhole

cubic

hexagonal

Surfactants set the stage for Surfactants set the stage for inorganic framework assemblyinorganic framework assembly

N+ N+N+ N+ N+

R-pyridinium R-quinolinium R-TMA- Gemini-Cn-s-n

R=CnH2n+1

Examples

CP/M/GeCP/M/Ge44SS1010 ((CPMGeSCPMGeS)) M=M=GaGa, In, In J. Am. Chem. Soc. 2000, 122, 10230

1.5 2 2.5 3 3.5 4 4.5 5

CPGaGeSCPInGeSCPBr

Inte

nsity

(arb

. uni

ts)

Energy (eV)

Excitation

Emission77 K

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

2 4 6 8 10 12 14

CPInGeS

CPGaGeS

Red

uced

PD

F G

(r)

r (�)

Ge-SM 3+ -S

Ge-Ge

S-S (2nd)Ge-S(2nd)

2 3 4 5 6 7 8 9 100

500

1000

1500

2000

Inte

nsity

(arb

. uni

ts)

2θ (deg), CuKα

100

110

200

Diffraction patternHexagonal 6mm

Walls are amorphous

Radial distribution function

TEM images

CPMGeSCPMGeS materials: CP/M/Gematerials: CP/M/Ge44SS1010

4 8 12 16 20 24

Inte

nsity

(arb

. uni

ts)

2θ (deg), CuKα

100

110

200

CPSbGeS

h k l d (�)1 0 0 35.521 1 0 20.012 0 0 17.33

M=Zn, Cd, Hg, Sb, In, Ga

(CP)2M1+x(Ge4S10)Sx

0 10 0

2 10 4

4 10 4

6 10 4

2 2.5 3 3.5 4

Cp_SbGe4S

10In

tens

ity

Energy, eV

2.88 ev

Hexagonal Hexagonal CPZnGeSCPZnGeS

1.2 1.6 2 2.4 2.8 3.2 3.6 4

CQZnGeSCPZnGeS

0

1 105

2 105

3 105

4 105

5 105

Inte

nsity

(arb

. uni

ts)

Energy (eV)

1.9 eV 2.4 eV

(CP)2Zn2(Ge4S10)S

Thermally stable up to 220 oC

Perhaps we donPerhaps we don’’t want to remove the t want to remove the surfactant!surfactant!

Add functionality to the surfactantAdd functionality to the surfactant•• Electronically active head groups or tailsElectronically active head groups or tails

S S

S S

S S

S S

S S

S S

S S

S S

electroluminescence

conduction band

valence band

š* band

radiative recombination

inorganic organic

PhotoluminescencePhotoluminescence

1.5 2 2.5 3 3.5

CPCdGeS4

CPCdSnS4

0

1 10 5

2 10 5

3 10 5

4 10 5

5 10 5

Inte

nsity

(arb

. uni

ts)

Energy (eV)

2.1 eV 2.4 eV

VB

CB

primarily S

primarily Ge

š*

š

hν

metal-sulfide network

organic head

1.2 1.6 2 2.4 2.8 3.2 3.6 4

CQZnGeSCPZnGeS

0

1 10 5

2 10 5

3 10 5

4 10 5

5 10 5

Inte

nsity

(arb

. uni

ts)

Energy (eV)

1.9 eV 2.4 eV

N

R

N

R

S

GeSGe

S Ge

S

GeS S

S

S

S

SS

SnSSn

S Sn

S

SnS S

S

S

S

S

Chemical Formula : (CP)Chemical Formula : (CP)44--2x2xMMxxSnSeSnSe44 (1.0<x<1.3)(1.0<x<1.3)

Sample Sn:Se4 M:Se4 % C, H, NM:Se4

Calc.Color

Mn 1.01 0.90 44.71, 7.10, 2.25 1.03 Orange

Fe 0.91 1.22 38.40, 6.23, 2.05 1.28Dark-

brown

Co 0.98 0.94 48.35, 6.64, 2.36 1.19Dark-

brown

Zn

(cubic)0.99 0.86 40.28, 6.17, 2.18 1.20

Yellow-

orange

Zn

(Hex)0.96 0.85 41.58, 6.44,2.29 1.15 Yellow

Cd 0.92 1.23 36.90, 6.01, 2.28 1.23 Yellow

Hg 1.03 1.09 34.65, 5.52, 1.92 1.20Dark

orange

Transmission Electron MicroscopyTransmission Electron MicroscopySurf / Zn2+ / SnSe4

Surf / Hg2+ / SnSe4

CubicCubic mesoporous chalcogenidemesoporous chalcogenide CPZnSnSeCPZnSnSe44

211

220

321420 332

h k l d (Å) 211 35.5 220 31.2 321 23.2 420 19.97 332 19.14

I a-3d a=87 Å

X-ray diffraction pattern

Ia-3d

P. N. Trikalitis, K. K. Rangan, T. Bakas and M. G. Kanatzidis, Nature 2001, 410, 671-675.

BandBand--gaps andgaps and Sn MSn Möössbauer ssbauer SpectroscopySpectroscopy

Rel

ativ

e Tr

ansm

issi

on, %

(A)

MnK4SnSe4

(B)

(C) (D)

(E) (F)

Velocity (mm/sec) Velocity (mm/sec)

Fe Zn

Cd Hg

Highly ordered CPHighly ordered CP--PtGePtGe44SeSe1010

4 8 12 16 20

Inte

nsity

(arb

. uni

ts)

2θ, Cu Kα

CP/Pt/Ge4Se

10

x 6

100

110

200

210

ao=39.98 �

hkl d(�)100 34.5110 20.0200 17.29210 13.0

The system PtThe system Pt2+2+ / [Sn/ [Sn22SeSe66]]44--

Se

Sn

[PtCl4]2- + [Sn2Se6]4-0

1000

2000

3000

4000

5000

6000

2 4 6 8 100

200

400

600

800

1000

1200

Inte

nsity

(arb

. uni

ts)

2θ (deg)

210

220

321 40

042

0 332

422

431

x 5

611

543

(C20Py)2PtSn2Se6

Single Crystals!Single Crystals!……??

TEM of a TEM of a CubosomeCubosome: [110] direction: [110] direction

Unit cell edge: 95ÅV=857,375 Å3

Density 1.8 g/cm3~34000 atoms per cell

ConclusionsConclusions

LamellarLamellar nanocompositesnanocomposites with electrically conductive and with electrically conductive and conventional polymers are large class of novel materialsconventional polymers are large class of novel materials

Conductive polymers can be encapsulated in porousConductive polymers can be encapsulated in porous solids directly by solids directly by inin situsitu intercalativeintercalative redoxredox polymerizationpolymerization

Exfoliated solids are superior for the synthesis of polymerExfoliated solids are superior for the synthesis of polymernanocompositesnanocomposites via via encapsulative precipitationencapsulative precipitation

The physical properties of lamellarThe physical properties of lamellar nanocompositesnanocomposites are affected by the are affected by the intercalated polymers.intercalated polymers.

ConclusionsConclusions

It is possible to construct organicallyIt is possible to construct organically templatedtemplated structures with heavier SiOstructures with heavier SiO44--analogs to produceanalogs to produce semiconductingsemiconducting solids with wellsolids with well--defineddefined mesoporesmesopores. .

The surfactantThe surfactant templated supramoleculartemplated supramolecular assembly of the assembly of the [SnSe[SnSe44]]44-- and and [Ge[Ge44QQ1010]]44-- anions with transition metals leads toanions with transition metals leads to mesostructuredmesostructured materials of materials of the general formulae the general formulae CPMGeQCPMGeQ and and (CP)(CP)44--2x2xMMxxSnSeSnSe44 (M=(M=MnMn, Fe, Co, Zn, , Fe, Co, Zn, CdCd, Hg)., Hg).

The The cc--(CP)(CP)44--2x2xZnZnxxSnSeSnSe44 represents the first example of cubic, nonrepresents the first example of cubic, non--oxidic oxidic mesophasemesophase..

NonNon--oxidicoxidic solids promise to produce solids promise to produce functionalfunctional mesostructuredmesostructured materials materials with novel electronic andwith novel electronic and photonicphotonic properties.properties.

Further work involving otherFurther work involving other chalcogenidechalcogenide building blocks e.g. building blocks e.g. [GeSe[GeSe44]]44--,,[GeTe[GeTe44]]44--, [SnTe, [SnTe44]]44-- and other metals ions e.g. Agand other metals ions e.g. Ag++, Pb, Pb2+2+, Bi, Bi3+3+, Sb, Sb3+3+ is needed.is needed.

Dr. Pantelis Trikalitis

Dr. Kasthuri K Rangan

Chung-Guey Wu

Yu-Ju Liu

Dr. Carl R. Kannewurf (NWU)Dr. Carl R. Kannewurf (NWU)Prof. Thomas Prof. Thomas BakasBakas,, IoanninaIoannina, Greece (, Greece (MMöössbauerssbauer))

Prof. VProf. V PapaefthymiouPapaefthymiou,, IoanninaIoannina, Greece (, Greece (MMöössbauerssbauer))

Students/Research AssociatesStudents/Research Associates

AcknowledgmentsAcknowledgments

National Science Foundation National Science Foundation

DMR-96-32472, CHE 99CHE 99--03706 (Chemistry Research Group).03706 (Chemistry Research Group).

Center for Advanced Microscopy, MSU for SEM and TEM facilities.Center for Advanced Microscopy, MSU for SEM and TEM facilities.