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NANOPARTICLES: FUNCTIONALIZATION AND ELABORATION OFMATERIALS

THIERRY GACOIN

Groupe de Chimie du Solide,

Laboratoire de Physique de la Matière Condensée, Ecole Polytechnique - CNS !M "#$%,

&''() Palaiseau, *rance+

1. Introduction

Impressive progresses achieved in the last ten years for the synthesis of nanoparticles allows consideration of nmeros original applications in manydifferent fields sch as catalysis! optics! magnetic recording or "iology# Ascompared to "l$ materials! the originality of nanoparticles comes first fromtheir high srface area and their good optical transparency when they are welldispersed# %t it is also now well $nown that depending on the chemical natreof the particles! new physical properties arise from their small si&e in thenanometer range as compared to the "l$ materials' (antm confinement! plasmon e)citation! sperparamagnetism! the Colom" "loc$ing effect! etc#

Considering the case of colloidal nanoparticles! only a few applications can "e achieved directly from the as*synthesi&ed sspension! and frther wor$ hasto "e performed for the ela"oration of materials# +any different systems may "esynthesi&ed! "t the ma,ority of the stdies are performed on isolated particles!composite materials! or materials o"tained "y the direct assem"ly! organi&ed or

not! of the nanoparticles#

Substrate Hostmedia

Molecule,nanoparticle,

biological system

*iure '# -ifferentinteractionsthatmay

"econtroll

edthr oghsr face fnctional

i&ationof the

particles

./0

+ .aseashta etal+ /eds+0, Nanostructuredand d1anced Materials, ./01 ..0# 2 .334Spriner+ Printed in the Netherlands+



./5 THIERRY GACOIN

In all cases! the $ey isse for the synthesis of materials is the control of theinteractions "etween the particles and a host medim! a s"strate or other

individal species li$e molecles! other particles or "iological systems 6figre/7# This control is sally achieved throgh the so*called fnctionali&ation of the particles! which consists of the grafting onto their srfaces of molecleswith specific chemical fnctions# These fnctions may "e chosen either to ,stensre the sta"ili&ation of the particles "y playing on dispersion forces! or toallow their "inding to more or less specific sites of the target s"strate#

2. Functionai!ation o" Nano#artic$ Sur"ac$%

The main isse of nanoparticle fnctionali&ation is to cover its srface with amolecle that possesses the appropriate F fnctions depending on theinteractions that are re(ired for frther processing 6figre .7#

C F X

8igre .# 9chematic representation of the fnctionali&ation of a particle inorder to control its interactions with a s"strate

The srface chemistry of colloidal nanoparticles is already an importantaspect of their synthesis! since it allows control of the si&e and the colloidaldispersion of the particles dring their formation# This is sally achieved "y

sing comple)ing agents which "ind to the srfaces of the particles dring their formation# The comple)ing strength mst not "e so strong thatncleation:growth processes can occr# In some cases! fnctionali&ation of nanoparticles can "e achieved directly dring their synthesis! "y sing acomple)ing molecle which "ears the F fnction that will still "e present at theend of the synthesis# Nevertheless! a post*fnctionali&ation of the particles isgenerally preferred! mostly "ecase this strategy is more versatile and the natreof the fnctionali&ing fnction may not "e flly compati"le with good control of the si&e and dispersion state of the particles in the solvent sed for their synthesis#

;ost fnctionali&ation of the particles then re(ires the grafting! onto thesrfaces of the particles! of a molecle having a strctre which can "edescri"ed as C*R*F # The C grop ensres the "inding of the molecle at the



srface! mainly in two different ways#8<NCTIONA=I>ATION AN- E=A%ORATION O8 +ATERIA=9 ./?

F

F F F

F

F F F F

FF F F

FF

FF

Y@O'EF

F F F

F

F F

F F F F F F

F F

*iure %# 9chematic representation of two strategies for the fnctionali&ation of nanoparticles 'direct grafting 6left7 and encapslation with a silane 6right7

The first one is the direct grafting of the C*R*F molecles "y comple)ationof srface cations with the C grop 6figre B left7# 8or e)ample! thiol! phosphine

o)ide! phosphonates or car"o)ylates grops have commonly "een sed in thecase of chalcogenides! o)ide nanoparticles and no"le metal nanoparticles# Thecomple)ing strength of the C grop mst "e high enogh to ensre ma)immsrface coverage# This is of particlar importance! especially when the C*R*F molecle is grafted in s"stittion to the comple)ing agents that have previosly "een sed for the synthesis of the particles 6e#g# TO;O molecles for Cd9enanoparticles7# In that sense! it appears as very interesting to se polydentateligands! li$e dithiols or oligomeric phosphines which "ind mch more stronglyto the srfaces /D#

A second strategy consists of sing a silane as the C grop#Hydrolysis:condensation reactions lead to the formation of a silane coatingarond the particles with a fraction of 8 grops otside 6figre B right7# This process has "een sed in many systems! mostly o)ides .D! "t it has also "eeninvestigated in the case of chalcogenides BD# Its main advantage comes from thelarge nm"er of commercially availa"le silane copling agents! the chemistry of which is well docmented# +oreover! the core:shell strctre ensres a strong "inding of the fnctional grops with a high srface coverage# The main pro"lem is that there mst "e an affinity "etween the silane and the srface of the particle to ensre that the precipitation of the silane coating occrs on the

srfaces of the particles and not as isolated clsters# In all cases! special caremst "e ta$en for the elimination of sch navoida"le clsters#

Other fnctionali&ation processes have also "een sed! among which the



encapslation with a polymer which possesses "oth the C and the F fnction#Another interesting approach has "een developed recently in the case of TO;Ocapped Cd9e:>n9 particles# It consists of $eeping the TO;O molecles! andgrafting a fnctionali&ation molecle in which the C grop is a long al$yl chainwhich interacts with the octyl grops throgh hydropho"ic interactions !4D#



..3 THIERRY GACOIN

In all cases! it mst "e noted that fnctionali&ation of the particlesnecessarily yields a drastic change of their srfaces# The choice for the

fnctionali&ation fnction mst "e a compromise "etween having the ma)immnm"er of F grops and preserving the sta"ility of the particles in their dispersion media# In some cases! colloidal sta"ility may "e improved "y playingon the chemical natre of the lin$ing R radical of the C*R*F molecle# 8or e)ample! it has "een shown that the a(eos sta"ility of Cd9e nanoparticles can "e greatly improved "y sing ;EG fnctions D#

Another point is that it is (ite difficlt to o"tain a precise determination of the e)act nm"er of F grops that are effectively attached to the srfaces of the particles# A large part of the wor$ for the fnctionali&ation of nanoparticles issally devoted to this pro"lem# +any analytical techni(es may provide

complementary information 6N+R! infra*red spectroscopy! thermogravimetricanalysis7! "t non grafted molecles mst "e careflly removed#

3. Mat$ria% "ro& Nano#artic$%

B#/ 9ING=E NANO;ARTIC=E9

%ecase of the development of near field microscopy techni(es and confocalmicroscopies! more and more stdies are performed directly on singlenanoparticles# The prpose was initially to get information on the physical properties of single nanoparticles! avoiding the inhomogeneos "roadening of the signals coming from an assem"ly of particles# Recently! an originalapplication of single nanoparticle optical microscopy is their se as florescentla"els for the in*vitro or in*vivo trac$ing of the individal actions of "iomolecles 0D# Organic florescent componds have "een e)tensively sedfor this prpose! "t their application is severely limited "y their rapid photo* "leaching# ;romising reslts have "een o"tained sing semicondctor (antm

dots! despite the fact that their water sol"ili&ation is comple) and that their sefor long*term single*molecle trac$ing is hampered "y their florescenceintermittency 5D#

Other systems have also "een investigated more recently! among which arerare earth doped o)ide nanoparticles# As an e)ample! a recent stdy wasdevoted to the stdy of the locali&ation of Na

F channels in live cardiac

myocytes ?D# 9pecific interactions are e)pected throgh the fnctionali&ation of the particles with ganidinim grops! which are the active parts of comple)to)ins 6tetrodoto)in and sa)ito)in7 that are well $nown for specifically plggingthe Na

F channel moths# The lminescent o)ide particles sed in this wor$ are

Y@O'E nanocrystals prepared following a simple a(eos colloidal rote ?D#Their emission spectra consist of narrow lines with a main contri"tion at8<NCTIONA=I>ATION AN- E=A%ORATION O8 +ATERIA=9 ../



/0 nm# Their emission yield is a"ot .4 with an emission lifetime of 3#0ms#9rface fnctionali&ation of the particles was achieved throgh the covalentgrafting of ganidinim grops on a thin shell of polymeri&ed silane*"earingepo)y grops 6figre left7#

i

O OH OH NH2

SiSi

H F

OHO

R N

O NH2

SiY@O'E OH

SiO

Si O OH

Si O OH NH2

SiH F

OR N

O NH2

1'2 n& Si

OH

*iure $# 9chematic description of nanoparticles fnctionali&ed with ganidinim grops 6left7and an optical image of isolated nanoparticles deposited on a glass slide 6right7

The "iological activity of the ganidinim*fnctionali&ed nanoparticles was

compared to that of sa)ito)in# Action potentials were recorded "y means of intracelllar microelectrode techni(es# These e)periments showed thatfnctionali&ed nanoparticles do indeed "loc$ the Na

F channels similarly to

sa)ito)in! whereas no effect was measred sing nanoparticles withotganidinim grops or with free ganidinim grops alone#

Optical detection of particles deposited on glass slides can "e achieved (iteeasily "y sing wide field florescence microscopy 6figre right7# Individalimaging of the nanoparticles on cardiac cell mem"ranes confirmed the interactionsmeasred previosly "y electrophysiology e)periments# +oreover! the a"sence of

particles "ond to the mem"rane when the NaF channels are previosly "loc$ed "y

the sa)ito)in demonstrates the high specificity of the interactions "etween the particles and the channels# It may then "e conclded that fnctionali&ed Y@O'Enanoparticles mimic the "loc$ing effect of the sa)ito)in and "ehave as artificialto)ins# 9ch particles then provide a versatile tool for long*term single*molecletrac$ing! allowing frther wor$ on the dynamic and the aggregation "ehavior of

NaF channels on e)cita"le cell mem"ranes#

B#. CO+;O9ITE +ATERIA=9

+any applications of colloidal nanoparticles re(ire their incorporation within asolid polymer matri)# The main advantage is that it allows sta"ili&ation of the



... THIERRY GACOIN

particles in a solid material which can "e frther handled and sed for thefa"rication of devices# -epending on the volme fraction of particles! the host

matri) can "e seen either as a dispersing medim or simply as a "inder! which isonly devoted to ensring the mechanical resistance of the composite material#%l$ monoliths 6i#e# solids with dimensions of centimeters or more7 may "esynthesi&ed# However! an increasing nm"er of applications se thin filmsdeposited on varios s"strates "y spin! dip or plveri&ation coating# The mainadvantage of thin films 6compared to "l$ composite materials7 is that the properties of the coating come in addition to those of the s"strate 6which can "e not only mechanical! "t also optical! electrical! etc#7# +oreover! depositionof thin films can "e achieved on large comple) srfaces! sing relatively smallamonts of matter! which is of importance considering the high cost of colloidal

synthesis on an indstrial scale#

There are many e)amples of applications! sch as the ela"oration of magnetic recording media! optical filters! transparent lminescent materials!anti*reflective coatings! photocatalytic film! etc# Another important class of applications concerns the loading of polymers in order to improve their mechanical properties#

The main difficlty for the ela"oration of composite materials is of corsethe dispersion of the particles within the host medim with a high volmefraction# In general! incorporation of the nanoparticles is achieved from

colloidal sspension! and more rarely from dispersi"le powders# The hostmedim is an organic or inorganic polymer 6e#g# sol*gel silica7! and theincorporation of the particles is achieved into a li(id soltion of at least partially polymeri&ed precrsors# The final composite material is frther o"tained either "y letting the polymeri&ation process going on or throgh theevaporation of the solvent# In most cases! the sta"ility of the particles dring theformation of the solid is preserved if there is a specific interaction "etween the particles and the polymeric networ$ of the matri)# This interaction is controlled "y specific chemical fnctions following the strategy descri"ed for thefnctionali&ation of the particles# In some cases! the host polymer itself "earschemical fnctions that can react with the srface of the particles! "t moregenerally the particles have to "e fnctionali&ed# 8or e)ample! incorporation of chalcogenide nanoparticles in sol*gel silica matrices was sccessflly achievedsing a preliminary fnctionali&ation of the particles with a silane "earing athiol grop# The silane can polymeri&e with the other silane precrsors of thematri)! while the thiol grop comple)es the srface cations of the particles# Thereslting strong interaction "etween the particles and the growing silica clstersallows one to o"tain composite materials with high volme fractions of particles6p to B37 /3D# The general process is smmari&ed in figre 4#

8<NCTIONA=I>ATION AN- E=A%ORATION O8 +ATERIA=9 ..B



*iure 2# E)ample of a process sed for the incorporation of nanoparticles in a sol*gel silica matri)#

3.3 9O=*GE= +ATERIA=9 8RO+ CO==OI-9

The colloidal processing of ceramics is an emerging field of research inmaterials science //D# Controlled aggregation of highly concentrated colloids provides the opportnity to relia"ly prodce ceramic films and "l$ forms withoptimi&ed micro* or nano*strctres# In this field! the ela"oration of opticallytransparent materials represents the ltimate challenge! which has led to the

development of new chemical processes sch as sol*gel chemistry /.D# Thesynthesis of solid materials made from nanoparticles as "ilding "loc$s involvesthe aggregation of the particles to form a solid networ$# A transparent materialwill "e o"tained! rather than a diffsive powder! only if the aggregation issfficiently well controlled that the physical strctre of the aggregates preserves the homogeneity of the material in the visi"le wavelength range#

Theoretical aspects of colloid aggregation have "een the s",ect of a largenm"er of investigations "ased on e)perimental reslts gathered from modelsystems sch as gold /BD or silica /D colloids# +ost of these wor$s se theformalism of fractal geometry to give a mathematical description of the

morphology of the aggregates# Their main characteristics are then fond in their fractal dimension -f ! which determines the variation of their mass! m! as afnction of their radial dimension! r! throgh the relation mr

-f # A -f vale of B

corresponds to dense solids or solids with reglar porosities! whereas lower vales are fond for lacnar aggregates#

The sol*gel processing of transparent materials relies on the controlledformation of sch lacnar aggregates within the soltion which is called a sol#;ercolation of the aggregates reslts either from rapid solvent evaporation6deposition of thin films "y spin or dip*coating7 or simply "y their continos



.. THIERRY GACOIN

growth within the sol# This moment corresponds to the sol*gel transition! a gel "eing a rigid s$eleton of particles enclosing a continos li(id phase# The

carefl removal of the solvent from the li(id phase yields the final solidmaterial# This can "e an aerogel with a very low density if drying is achievednder spercritical conditions! or a dense )erogel if drying is made slowly at alow temperatre 6.3*/33JC7 to avoid fractres from capillary stresses /.D#

CO==OI-E 9O=

98

GE=

KEROGE=

*iure # # 9ol*gel aggregation of Cd9 nanoparticles throgh their controlled aggregationindced "y the progressive removal of srface thiol grops#

<ntil recently! sol*gel chemistry was restricted to a limited nm"er of

componds! mostly o)ides! and especially silica# The main "arrier for the e)tension

to other componds stems from the difficlty of the synthesis of highly concentrated

colloids with a controlla"le state of dispersion# Nmeros wor$s performed on the

colloidal synthesis of chalcogenides have nevertheless allowed the synthesis of

concentrated sspensions# 8or e)ample! it has "een shown that srface

comple)ation of Cd9 nanoparticles with *8lorophenylthiol allows one to sta"ili&e

highly concentrated sspensions in organic solvents sch as acetone /4D# It is well

$nown that thiol can "e easily o)idi&ed nder soft conditions into dislfides#

Controlled o)idation of the sta"ili&ation thiolates in concentrated Cd9 colloids leads

to the slow aggregation of the particles# 8ractal aggregates of particles are formed

and continosly grow ntil the sol trns into a gel /D 6figre 7# In the case of

concentrated sols! no visi"le light diffsion is o"served while the sol trns into agel! showing that the fractal aggregates do no have any characteristic strctral

dimensions of the order of the visi"le light wavelength#



Althogh large (antities of colloids wold "e re(ired for the developmentof sch synthetic processes! this stdy on chalcogenide nanoparticles cold

8<NCTIONA=I>ATION AN- E=A%ORATION O8 +ATERIA=9 ..4

open the way toward the development of sol*gel chemistry for the ela"oration of "l$ transparent chalcogenide materials#

B# ORGANI>E- NETLORM9 O8 NANO;ARTIC=E9

+any investigations have "een performed in the last .3 years to nderstandthe physical properties of nanoparticles considered as individal o",ects# Over the last few years! the (estion has "een raised of how to stdy effects resltingfrom physical interactions "etween the particles! i#e# effects which depend on thedistance "etween two particles when this distance is less than a few nanometers#It can "e! for e)ample! plasmon copling "etween metallic nanoparticles! chargetransport "etween semicondctor (antm dots! or magnetic interactions "etween magnetic particles#

As for the investigation of si&e effects! which was limited "y the si&edistri"tion of the particles! the stdy of physical effects reslting from particle* particle interactions re(ires either the se of near field microscopies or thedevelopment of materials in which the particle*particle distance is well $nownand with a narrow distri"tion# In this conte)t! there is an increased interest inthe ela"oration of periodic nanostrctres! in which the particles are organi&edinto .- or B- periodic networ$s with a lattice parameter that can "e varied in

the nanometer range#-ifferent strategies can "e sed for the realisation of sch nanostrctres# The

template approach consists of forming the particle within a medim whichalready has a periodic strctre# However! it is althogh $nown in somee)amples that colloidal nanoparticles can assem"le themselves directly into periodic arrays! thogh a process $nown as self*organi&ation which is similar tocrystalli&ation# Lell $nown e)amples of sch spontaneos arrangements arecolloidal crystals /0D! o"tained from highly charged late) particles in soltion!and artificial opals made throgh the slow decantation of silica particles /5D# In

"oth cases! the important factors allowing self*organi&ation of the particles istheir high monodispersity and their high sta"ility in the dispersion medim#Recent developments of colloid chemistry have allowed the synthesis of particles with a very good monodispersity! which are sally srfacefnctionali&ed with long al$yl chains so that they can "e sta"ili&ed in an organicsolvent with high concentration /?D# It has "een shown in many e)amples thatthe slow evaporation of the solvent leads to spontaneos formation of crystals of particles! either .- .3D or B- 6figre 07 ./*..D# The main pro"lem is that thedimensions of the organi&ed domains are sally small 6less than a few hndredsof nanometers7# As for classical crystal growth! improvement may "e o"tained

throgh the carefl control of the ncleation:growth of the strctre! which can "e optimi&ed to some e)tent "y playing on the e)perimental conditions! andespecially the evaporation rate of the solvent and the srface



.. THIERRY GACOIN

fnctionali&ation of the s"strate# As in the wor$ reported "y =in et al+ .3D ongold particles! it is then possi"le to o"tain .- strctres with an almost perfectorgani&ation over several microns#

*iure " # 6left7 .- sperlattice of gold nanoparticles 6after =in et al+ .3D7 6right7colloidal crystals of Co;tB nanoparticles 6after 9hevchen$o et al+ /?D7

(. Concu%ion%

+ost applications of colloidal nanoparticles re(ire the control of their interactions with a host medim! a s"strate or other individal species6molecle! particles! etc#7# This control is sally o"tained throgh the srfacefnctionali&ation of the particle! which consists of the grafting of a chemicalfnction F that will determine the natre and the strength of the interactions#Once fnctionali&ed! the particles may "e sed either directly 6for e)ample in "iological la"eling7! or for the development of different materials' compositesare o"tained throgh dispersion in the host medim transparent gels and)erogels are formed throgh controlled aggregation of the particles! andorgani&ed networ$s from their self assem"ly#

R$"$r$nc$%

/# Mim! 9# and %awendi! +#G# 6.33B7 Oligomeric ligands for lminescent and sta"le nanocrystals(antm dots! 3+ m+ Chem+ Soc+ 12)607 /4.*/4B#

. ;hilipse! A#;#! Nechifor! A#+# and ;atmamanoharan C 6/??7 Isotropic and "irefringent

dispersions of srface modified silica rods with a "ohemite needle core! Lanmuir 1*6/.74/*45#

B Gerion! -#! ;inad! 8#! Lilliams! 9#C#! ;ara$! L##! >anchet! -#! Leiss! 9# and Alivisatos! A#;#6.33/7 9ynthesis and properties of "iocompati"le water*sol"le silica*coated Cd9e:>n9semicondctor (antm dots! 3+ Phys+ Chem+ 4 1*)6B07' 55/*550/#



8<NCTIONA=I>ATION AN- E=A%ORATION O8 +ATERIA=9 ..0

14 -"ertret! %#! 9$orides! ;#! Norris! -##! Noirea)! @#! %rivanlo! A#H# and =i"cha"er! A#

6.33.7 In vivo imaging of (antm dots encapslated in phospholipid micelles Science2+,644??7 /04?*/0.#

5. ;ellegrino! T#! +anna! =#! Mdera! 9#! =iedl! T#! Mo$tysh! -#! Rogach! A#=#! Meller! 9#!

Radler! #! Natile! G# and ;ara$! L## 6.337 Hydropho"ic nanocrystals coated with anamphiphilic polymer shell' A general rote to water sol"le nanocrystals! nano Letters (6703B*030#

6. 9$aff! H# and Emric$! T# 6.33B7 The se of *s"stitted pyridines to afford amphiphilic! pegylated cadmim selenide nanoparticles! Chem+ Comm+ 1! 4.*4B#

7. Chan! L#C#L#! +a)well! -##! Gao! K#H#! %ailey! R#E#! Han! +#Y# and Nie! 9#+#! 6.33.7

=minescent (antm dots for mltiple)ed "iological detection and imaging! Curr+ 5pin+ 4iotechnol+ 1-! 3*#

8. -ahan! +#! =evi! 9#! =ccardini! C#! Rostaing! ;#! Rivea! %# and Triller! A# 6.33B7 -iffsion

dynamics of glycine receptors revealed "y single*(antm dot trac$ing! Science -*2 647'.*4#

9. %earepaire! E#! %issette! @#! 9aviat! +*;#! +ercril A#! +artin *=#! =ahlil M#! Gacoin T#!%oilot *;# and Ale)andro A# 6.337 8nctionali&ed florescent o)ide nanoparticles' artificialto)ins for sodim channel targeting and imaging at the single*molecle level! s"mitted tonanoLetters 6.337#

10. Gacoin! T#! Chapt! 8# and %oilot *;# 6/??7 +etal! semicondctor and magneticinclsions in gels! 3+ Sol-el Sc+ 6echn#! 2! 0?*5B#

11. =ewis! #A# 6.3337 Colloidal processing of ceramics! 3+ m+ Cer+ Soc# ,-6/37 .B/*.B4?#

12. %rin$er! C## and 9cherrer! G#L# 6/??37 in Sol-el science 7 the physics and chemistry o8 sol-el processin ! Academic ;ress =td! =ondon#

13.Leit&! -#A# and Hang! #9# 6/?57 in 8# 8amily and -#;# =anda 6eds#7! 9inetics o8 areation and elation! Elsevier 9cience ;"lishers %#@#

14. -ietler! G#! A"ert! C# and Cannel! -#9#! 6/?57 Gelation of colloidal silica! Phys+ e1+ Let+ )6.7 B//0*B/.3#

15. Gacoin! T#! +alier! =# and %oilot! *;# 6/??07 New transparent chalcogenide materialssing a sol*gel process! Chem+ Mat # + 607' /43.

16. Gacoin! T#! =ahlil! M#! =arregaray! ;# and %oilot! #;# 6.33/7 Transformation of Cd9colloids' 9ols! gels! and precipitates! 3+ Phys+ Chem+ 4 /34 6.7' /3..5*/3.B4

17. ;ierans$i! ;# 6/?57 Colloidal crystals! Contemporary Physics 2( 6/7' .4*0B

18.+ayoral! R#! Re(ena! #! +oya! #9#! =ope&! C#! Cintas! A#! +ige&! H#! +eseger! 8#!@a&(e&! =#! Holgado! +# and %lanco! A# 6/??07 B- long*range ordering in an 9iO.s"micrometer*sphere sintered sperstrctre! d1+ Mat+ +6B7' .40#

19. 9hevchen$o! E#@#! Talapin! -#@#! Rogach! A#=#! Mornows$i! A#! Haase! +# and Leller! H#6.33.7 Colloidal synthesis and self*assem"ly of CO;tB nanocrystals! 3+ m+ Chem+ Soc+ 12(6B57' //53*//54

20. =in! K#+#! aeger! H#+#! 9orensen! C#+# and Mla"nde! M##! 6.33/7 8ormation of long*range*ordered nanocrystal sperlattices on silicon nitride s"strates 3+ Phys+ Chem++ 4 1*)6/07' BB4B*BB40

21. +rray! C#%#! Magan! C#R# and %awendi! +#G#! 6.3337 9ynthesis and characteri&ation of monodisperse nanocrystals and close*pac$ed nanocrystal assem"lies! nn+ e1+ Mat+ Sc+ -*!44*/3#

22. Harfenist! 9#A#! Lang! >#=#! Lhetten! R#=#! @e&mar! I# and Alvare&! +#+# 6/??07 Three*dimensional he)agonal close*pac$ed sperlattice of passivated Ag nanocrystals! d1+ Mat+ +6/37' 5/0#

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