Evidences for liquid encapsulation in PMMA ultra-thin film grown by liquid injection Photo-CVD

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Evidences for liquid encapsulation in PMMA ultra-thin

film grown by liquid injection Photo-CVD

Claudiu Constantin Manole, Olivier Marsan, Cedric Charvillat, Ioana

Demetrescu, Francis Maury

To cite this version:

Claudiu Constantin Manole, Olivier Marsan, Cedric Charvillat, Ioana Demetrescu, Francis

Maury.

Evidences for liquid encapsulation in PMMA ultra-thin film grown by liquid injection

Photo-CVD. Progress in Organic Coatings, Elsevier, 2013, vol.

76 (n° 12), pp.

1846-1850.

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To link to this article : DOI:10.1016/j.porgcoat.2013.05.027

URL :

http://dx.doi.org/10.1016/j.porgcoat.2013.05.027

This is an author-deposited version published in:

http://oatao.univ-toulouse.fr/

Eprints ID: 14102

To cite this version:

Manole, Claudiu Constantin and Marsan, Olivier and Charvillat, Cedric and

Demetrescu, Ioana and Maury, Francis Evidences for liquid encapsulation in

PMMA ultra-thin film grown by liquid injection Photo-CVD. (2013) Progress in

Organic Coatings, vol. 76 (n° 12). pp. 1846-1850. ISSN 0300-9440

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Evidences

for

liquid

encapsulation

in

PMMA

ultra-thin

ﬁlm

grown

by

liquid

injection

Photo-CVD

Claudiu

Constantin

Manole

a,b,∗

_,

_Olivier

_Marsan

a

_,

_Cedric

_Charvillat

a

_,

_Ioana

_Demetrescu

b

_,

Francis

Maury

a

a_CIRIMAT,_{CNRS/INPT/UPS,}₄_allée_E._Monso,_BP_44362,₃₁₀₃₀_Toulouse_cedex_4,_France b_UPB,_Faculty_of_Applied_Chemistry_and_Materials_Science,_1-7_Polizu_011061,_Bucharest,_Romania

Keywords:

Poly(methylmethacrylate) Photo-CVD

DirectLiquidInjection RamanConfocalSpectroscopy AtomicForceSpectroscopy

a

b

s

t

r

a

c

t

Thispaperdealswiththecharacterizationofultra-thinfilmsofPMMAgrownbyanoriginal photo-assistedChemicalVaporDepositionprocessequippedwithapulsedliquidinjectionsystemtodeliver themonomer.Thenanometricthickfilmsshowedagoodabilitytoencapsulatealiquidphaseas micro-dropletsprotectedbyathinpolymerictightmembraneintheformofblisters.Techniquesthatarecapable toanalyzetheseheterogeneousstructuresatmicro-andnanoscopicscalesuchasRamanConfocal Spec-troscopyandAtomicForceMicroscopywereusedtocharacterizethesepolymerfilms.Theliquiddroplets werefoundtobemonomerencapsulatedbyaPMMAfilm.Thespecificpropertiesoftheseultra-thin filmsexhibitself-healingcapabilitiesatmicroscopicscalemakingthemattractiveforfunctionalization ofsurfacesandinterfaces.

1. Introduction

TheChemicalVaporDeposition(CVD)isavaluableand

versa-tiletechniquetogrowmicro-andnanostructuredmaterials.Itﬁnds

applicationsinmanynanofabricationareasforinstancetoproduce

carbonnanotubes[1],lowdielectrics[2],core–shell

nanostruc-tures[3]andnanocompositecoatings[4].TodevelopindustrialCVD

processesseveraltechnologiescompetetodeliverthehighﬂow

ratesofreactivegasrequiredforhighgrowthratesandlargescale

reactors.Startingfromliquidmolecularcompoundsasprecursors,

thisincludesforinstanceAerosolAssistedCVD[5]andpulsedDirect

LiquidInjectionCVDcoupledtoaﬂashvaporizationoftheliquid

monomertoformthevaporphase(DLI-CVD)[6].Forthislast

tech-niqueawideareaofapplicationsistargetedbyintensiveresearch

oninorganicmaterials,eitheroxides[7–9]orcarbides[6,10,11].

OrganicmaterialsarealsodepositedbyCVDprocessesusing

vari-ousactivationtechniquesofthereactivegasphasetocompensate

theverylowdepositiontemperatureimposedbythesethermally

fragilematerials.Thuspolymericthinﬁlmsweregrownbyinitiated

CVD(iCVD),e.g.hot-ﬁlamentactivation[12,13],PlasmaEnhanced

CVD(PECVD)[14]andtheGrahamprocess[15]usingrespectively

chemical,plasmaandthermalactivationmethods.

∗ Correspondingauthorat:FacultyofAppliedChemistryandMaterialsScience, UniversityPolitehnicaBucharest,Str.Polizu1-7,011061,sector6,Bucharest, Roma-nia.Tel.:+40214023930;fax:+40213111796.

E-mailaddress:claudiu.manole@ymail.com(C.C.Manole).

The ultra-thin polymericﬁlms discussedin this paper were

obtainedbyanoriginalCVDprocess.First,theoriginalitycomes

fromthephotonactivationofthegasphase(Photo-CVD)without

irradiatingthethinlayergrowingonthesubstrate.Uptonowthis

techniquewasreportedtodepositinorganicmaterials[16].

Sec-ondly,sincethepolymerizationinvolvesaliquidmonomerasCVD

precursoranovelapproachwastouseDLI-CVD.Thisdual

inno-vationresultedinthedepositionofultra-thin(nanometric)poly

(methylmethacrylate)(PMMA)ﬁlmsthat,underparticular

condi-tions,encapsulatedaliquidphaseofitsmonomer.PMMAthinﬁlms

werepreviouslydepositedbyiCVDandevidencesforafree-radical

mechanismwerefound[13].TheapproachoftheDLIPhoto-CVD

processisbasedonthephotonactivationofthegasphase.Ithas

theadvantageofdepositingatroomtemperature(orlower),

with-outdirectsubstrateirradiationanditallowstoobtainaconformal

coverageatlowpressures(oversolidandliquidsurfaces).

Becausetheﬁlmsarenanometricthicktheircharacterization

requires speciﬁc tools and methodologies. This paper gives an

insightintothemeansofcharacterizingsuchpolymericultra-thin

ﬁlms.Theexperimentalresultsdeducedfromthetechniquesused

givedirectand indirectevidencesofthemainfeaturesof these

PMMAthinﬁlms.

2. Materialsandmethods

ThecoreofthePhoto-CVDsystemstandsinavertical

align-mentperpendiculartothesubstratesurfaceofanInjectionSystem,

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Table1

ExperimentalparametersusedforDLIPhoto-CVDofPMMAﬁlms.

Parameters Inj-1 Inj-2

Depositiontemperature(◦_C) ₁₈ ₁₈

Totalpressure(Torr) 9.5 9.5

Injectorconditions

fliq(Hz) 1 1

ton(ms) 1 1

N2carriergasininjector(sccm) N/A 150

N2carriergasinvaporizationchamber(sccm) 108 N/A

Setpoint(%) N/A 10

fgas(Hz) N/A 1

andaSampleReactor.Theinjectorsystemsﬂashvaporizesthe liq-uidmonomerusedasprecursor.Fortheexperimentsreportedin thispaper,twocommercialinjectionsystemsprovidedby Kem-stream(www.kemstream.com)wereused.

Inthecaseofinjectionsystem1(Inj-1)aliquidinjector

commu-nicatesdirectlytoavaporizationchamber.Theamountofliquid

injectedis computercontrolledbyanopeningtime (ton)and a

repeatingfrequency(fliq)oftheprocess.Inthevaporization

cham-berthesprayoftheliquidisvaporizedandmixedwithacontinuous

streamofN2usedascarriergasmonitoredbyamassﬂowmeter.

Theinjectorsystem2(Inj-2)isanewgenerationdesignedto

improvetheatomizationandthegasﬂowrateoftheprecursor.It

hastwo-stagecomponents.Itcontainsaﬁrstliquidinjectorthat

pulsesthemonomertoamixingchamber.Theamountofliquid

injectedatthisﬁrststageiscontrolledbyanopeningtime(ton)and

arepeatingfrequency(fliq)oftheprocess.Thisﬁrstliquid

injec-torcommunicateswithasecondgasinjectoractingalsoasmixing

chamberwiththecarriergas.Thegasinjectormixesthespraywith

N2ascarriergasandthenpulsestheliquid/carriergasmixtureinto

theﬂashvaporizationchamber.Thegasinjectionismonitoredby

amassﬂowmeter.Theamountofgasinjectediscontrolledbythe

softwarethatconvertsagivensetpoint(percentofsccm)inopening

time.Therecurringpulsedopeningtimeofthegasinjectorisgiven

bya gasfrequency(fgas).Bothinjectionsystemsproducesprays

withdifferentcharacteristicsintermsofaveragesizeofdroplets

andsizedistribution.

For Inj-1 setup, the monomer waspushed by a pressure of

3.8barofN2towardstheinjectorwhichoperatedatfliq=1Hzand

ton=1ms.IntheInj-2setup,themonomerwaspushedwitha

pres-sureof3.5barandtheN2carriergaspressurewasof2bar,with

Setpoint=10%and fgas=1Hz.Theexperimentalparameterswith

respecttotheinjectingconditionsaresummarizedinTable1.

TheUVchamberconsistsoffourHglowpressurelamps

emit-tingat254nm(HeraeusmodelNNI60/35XL).Foreachlamp,the

radiativeﬂuxat254nminairatroomtemperaturewas20Wand

theirradianceatthiswavelengthwas150␮W/cm2_at_a_distance_of

1m.Theyare38cmlongandplacedaroundaquartztubeof5cmin

diameterand40cmlong.Thelampsandthetubearesurroundedby

ashellandapolishedaluminumreﬂector.Thetemperatureofthe

lampsandthequartztubearemaintainedaround80◦Cbyastream

ofcompressedair.Thevaporphaseisphoto-activatedwhenpassing

intothisquartztubeandiscarriedtowardsthesamplereactor.For

thedeposition,themonomermethylmethacrylate(MMA)

(con-taining∼0.004%hydroquinoneasstabilizer) wasmixedwith2%

1-hydroxycyclohexylphenylketoneasphoto-initiator(PI)inorder

toaidthepolymerization.TheywerebothpurchasedfromSigma

Aldrichandusedasreceived.

The substrates in the growth reactor were placed

perpen-dicularly tothemain gasstreamon asample holder equipped

witha temperaturecontrolsystem.Theywerekeptatambient

temperature(18◦C).Theyweredegreased andcleanedin

ultra-sonicbathwithacetoneand thenethanol. During deposition,a

substrateareawasmaskedinordertoallowadirectcomparison

between a deposited and an undeposited zone. The masking

was performedby placing the polished face of a Si(100) chip

(10mm×5mm×0.4mmdirectlyonthepolishedsurfaceofa

rect-angular Si(100) wafer (30mm×5mm×0.4mm). The intimate

contactbetweenthetwopolishedsurfacespreventsthediffusion

ofreactivegasbetweenthemandthereforethecontaminationof

themaskedsurfaceofthesubstrateduringtheCVDrun.Inorder

tohaveadifferenttypeofsurfaces,a25mm×25mm×1mmglass

substratewasalsousedneartheSi(100)substrate.

TheAtomicForceMicroscopy(AFM)datawasobtainedbyan

AgilentTechnology5500AFMoperatinginacousticmodewith

sil-iconTypeVIIMACLeverfromAgilent.TheAFMmeasurementswere

madeataspeedof5nm/satroomtemperatureinambientair.The

RamanspectraandinsituOpticalMicrographieswereobtainedat

roomtemperaturebyaHoribaLabRAMRamanConfocal

Spectrom-eterwitha5mWlaseremittingat532nm.Bothtechniquesoffer

directcharacterizationofthesamples.However,withrespectto

ultra-thinnanometriclayers,thesecharacterizationscanprovide

direct and indirect experimentalresults. TheAFM offers direct

resultsovertheultra-thinﬁlmduetotheatomicforceinteractions

thatitmeasures;itisreallyasurfaceanalysistechnique.

TheRamanConfocal Microscopy(RCM)analysisofultra-thin

polymericﬁlmsprovidesbothdirect andindirectresultsinthe

sensethatitisnotreallyasurfaceanalysistechniqueanditcan

beinvasiveforthematerialanalyzed.Thesamplescanbeanalyzed

as-depositedandaftersubsequenttreatmentseitherinsituduring

theRamananalysisasaresultoftheinteractionbetweenthelaser

beamandthematerial,orvariouspost-treatments.Inthiswork,we

focusonpost-thermaltreatmentintheambientairofaMemmert

Model550ovenat115◦C.

3. Resultsanddiscussion

ThetwoDLIsystemsallowedencapsulatingdifferentvolumes

ofliquidinsideapolymericthinmembraneonthesurfaceofa

sub-strate.Thetwoinjectionsystemswithcontinuous(Inj-1)orpulsed

(Inj-2)carriergasofferedthepossibilitytoinvestigateultra-thin

ﬁlmswithdifferentmorphologiesandproperties.

Inaﬁrstseriesofdepositionexperiments,theInj-1 injection

systemwasusedtoobtainverythin polymericﬁlmbytheDLI

Photo-CVDprocess.Theformationofananometricthickmembrane

isdifﬁculttoidentifyandcharacterize,inparticulartodetermine

itsthicknessandstructuralfeaturesbecauseorganicpolymersare

generally nonconductive and thermally fragile materials.

Infor-mationwithrespecttothepresenceofanultra-thinﬁlmcanbe

obtaineddirectlybyAFMorindirectlybyextrapolatingRCMdata.

TheAFMtopographyofanuncoatedarea(Fig.1a)andacoated

area(Fig.1b)overthesamesubstrateisshown inFig.1.Itcan

beobservedthatthemaximumheightforacoatedareaincreased

byapproximately30nmwithrespecttotheuncoatedone,which

revealsthepresenceofanultra-thinﬁlmcoveringthesurfaceofthe

substrate.Bymappingthephaseofthecantileveroscillations,the

AFMoffersthepossibilitytoidentifyvariationsinthesample

com-position.InFig.1c,thephaseimagingofthecoatedareashowssuch

aphasechangeandrevealstwotypesofstructures.First,whatcan

beregardedasencapsulatedliquiddroplets(structure#1),looking

asblistersca.1␮mindiameterspreadoutoverthesurfaceofthe

sampleand,secondly,smallerheterostructureslookingasagood

conformalcoverageofsolidnanoparticlesthatcontaminatedthe

surfaceoftheSisubstratebyathinﬁlm.

Afterthedeposition,theblistersobservedonthesurface

pre-servetheirshape,sizeanddistributiononthesurfaceevenafter2

monthsinambientairandindark.Theydonotshowanychange

duetoeitherchemicalreactivityforinstancewithairorto

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Fig.1.AFMtopographyforanuncoatedarea(a)andforacoatedarea(b)withtheInj-1system.Thephaseimageofthedepositedareaisalsopresented(c)withpossible liquidencapsulationasblisters(1)andinhomogeneitiesresultingfromconformalcoverageofparticlescontaminatingthesurfaceoftheSi(100)substrate(2).

monomer,itsvaporpressureissufﬁcientlyhigh(29.5Torrat20◦C)

tobecompletelyevaporated.Thisindicatestheliquiddropletsare

protectedfromtheenvironmentbyaverythinpolymeric

mem-brane.Atthisstage,thebestassumptionistoconsiderthatthese

blisterslikestructurescontainaliquidthatshouldbethemonomer

andthephotoinitiatormoleculesincetheyarethesoleliquid

com-poundsinvolvedintheCVDprocess.

Raman analysis of an as-deposited droplet-like structure

approximately10␮mwide, revealsthe C C bonds ofboth the

monomer(notpresentinthepolymer)andthephotoinitiatorwith

bandsat1640cm−1 and1660cm−1,respectively.Thisresultsin

abroadcumulativeC Cpeakinthisspectralrange(Fig.2).Even

iftherewereonly2%ofPIintheinitialsolutioninjected,itcan

bepresent in anamount signiﬁcantly greater in theseblisters.

Indeed,thevolatilityofMMA(29.5Torrat20◦C)comparedtoPI

(2.2×10−3Torr)suggeststhatapartofthemonomerislikely

evap-oratedduring thedepositionunderreduced pressure (9.5Torr),

whichenrichestheproportionofPIintheliquidcondensedonthe

substratesurface.

Theissueofseparatingthetwospeciestodeterminethe

compo-sitionoftheliquidinthedropletswillberesolvedbyasubsequent

post-treatmentofthesample.TheRamantechniquewasreported

asa tool for estimating theextentof polymerizationof PMMA

after a thermal treatment, highlightingthe 115◦C temperature

as optimum temperaturefor monomer polymerization[17].As

observedinFig.2,thebandassociatedtothemonomerdecreases

graduallywiththeincreaseofthetimeofathermalpost-treatment

at115◦Cin air.Thisindicatesthepresenceofliquid MMAinto

theobserveddrop-likestructurethatprogressivelypolymerizeby

Fig.2.Ramanspectraofa10␮mencapsulateddropletsobtainedwithInj-1system afteranthermal(115◦_C)_{post-treatment.}

thermal activation.Duringand afteralloftheRaman

measure-ments,theﬁlmandthedropletsdepositedusingtheInj-1system

werepreservedintact.

ThefurtheruseoftheInj-2injectionsystemwillprovide

poly-mericthinﬁlmswithsimilarfeatures,butwithdifferentproperties.

Largerdropletswereincorporatedintoathinﬁlmgrownusingthe

Inj-2injectionsystem.TheAFMforcemicroscopywasperformed

ontothreepointsindicatedintheAFMtopographicalimage(Fig.3).

TheAtomicForceSpectroscopyinvolvesthreestepsof theAFM

cantileverbehavior:(i)anapproachhalfcycle,whenthecantilever

tipapproachesthesurface,(ii)acontactwiththesampleand(iii)a

retractinghalfcyclewhenthecantileverretracts.Fig.3bshowsthat

thebareSisubstrate(thereference)hasashortapproach/retracting

cycle(∼0.5s).Duetotheultra-thinpolymericﬁlmcoveringthe

sub-strate,theapproach/retractcyclesarelonger(∼1.5s)thatindicates

amoreelasticbehaviorcomparedtothebareSisubstrate.Ifpure

liquidwerepresentontothesurfaceasfreedroplets,i.e.without

encapsulationinanultra-thinmembraneasblisters,theAFMtip

wouldhavepenetratedtheliquideasily,indicatingthusadifferent

retractingcyclefortheregion3comparedtoregions1and2.

ItiswellknownthatthefocusedRamanlasergeneratesheat

thatcandamagematerialsiftheyabsorbthephotons.Forinstance,

thelaser-inducedthermaleffectswerestudiedoncarbon

nano-tubesandonmagnetiteoxidation[18,19].Also,theoptimizedlaser

energycanbeusedtoachieveweldingofPMMAsheets[20].Here,

duringtheRamanMicroscopyanalysesoflayersobtainedby

Inj-2system,theultra-thinﬁlm ontheSisubstrate wasirradiated

insitubythelaserbeam.Duringthislaserirradiationfor

approx-imately15s,bothadestructiveanda constructiveeffectcanbe

extrapolated.

Firstly,theas-depositedblisterapproximately30␮min

diam-eter(Fig.4a)onwhichthelaserfocusshowsacatastrophicfailure

of the ﬁlm bythe presence of a crater-like structure (Fig.4b).

Thefocal diameterof theRCMlaserwas430nm.Theresulting

crater-like geometry after the exposure to laser beam reaches

approximately5␮mindiameter.Thedegradationprocesscanbe

essentiallydescribedbythefollowingsteps:(i)laserenergy

absorp-tionatthethin ﬁlminterfacewiththeSisubstrateleadingtoa

suddentemperatureincreaseoriginatingessentiallyfrom

absorp-tionoftheSi,(ii)initialthermalstrainandpossiblymelting(suchas

depolymerizationofPMMA[21])and/orvaporizationoftheliquid

species(MMA),and(iii)thermallyinducedpolymerizationfrom

encapsulatedmonomerinthelowtemperatureareas(attheedges

ofthecrater)[22].InFig.4aandb,thelaserbeamwasfocusedon

aheterogeneityembeddedintheblister.Thisheterogeneitylikely

originatingfromthesurfacecontaminationoftheSisubstrateis

uncoveredafterlaserirradiationatthecenterofthecraterasshown

inFig.4b.Forblisterswithoutsuchcontaminationthebottomof

thecrateriscleanafterlaserexposureandnoparticleisobserved

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Fig.3.TheAFMtopography(a)witharrowsindicatingtheareaswheretheforcespectroscopydata(b)wereobtainedforthePMMAﬁlmpolymerizedwiththeInj-2system andforthebareSisubstrate.

Fig.4. InsituopticalmicroscopyimageofﬁlmsdepositedwiththeInj-2systemacquired(a)(c)beforeand(b)(d)afterirradiationbyfocusinga5mWlaserbeamemitting atawavelengthof532nmoftwoblister-likestructuredepositedover(a)(b)glassand(c)(d)Si(100)substratesduringRamananalysis.

Thepresenceofsuchcrater-likestructuresafterseveralRaman

analysessupportsthisdegradationprocess.Ramanlaserprovides

a heatgradient acrossthe surfaceof thesample, witha

maxi-mumtemperatureatthecenterofthespotandasharpdecrease

towardsambienttemperature attheperiphery. Shebanova and

LazorobservedthatRamanlaserirradiation(at512nm)induced

theoxidationofmagnetite[18].Thisoxidationcouldoccurat

tem-peraturescloseto240◦C[18].Theirstudywasorientedtowardsthe

determinationofthelocaltemperatureforthelaser-heatedspot.It

involvedthevariationofthepowertothesample(7–60mW)over

aspotsizeofaround5–10_␮m,forinstance50mW/5_␮m.Forthe

opticalobjectiveusedinourexperimentsthecalculatedspotsizeof

our5mWlaserisaround0.5␮m.Thereforetheapproximatepower

persurfaceareaoftheRCMusedinourexperimentsisofthesame

orderofmagnitude(5mW/0.5␮m).At50mWthetemperaturewas

correlatedbyShebanovaandLazorataround410◦Cformagnetite

[18].Sisubstratestronglyabsorbsirradiationat532nmanditcan

readilytransmititslocalheattothepolymericﬁlm.Therefore,itcan

besuspectedthatattheobservedradiusof2.5␮mfromthecenter

ofthecrater(i.e.edgeofthecrater)thetemperaturecouldreachan

optimumvaluenear100◦Cthatleadstoaself-healingmechanism

oftheblisterbythermalpolymerization.Thesealingattheedgeof

theexposedareacanbeconsideredasaconstructiveeffectoflaser

irradiation(Fig.4c).

ThedifferentbehaviorofthesamplespreparedusingtheInj-1

andInj-2 systemsobservedduringRamananalysesmaybedue

to a different composition of the liquid (for instancethe ratio

MMA/PI)encapsulatedinthepolymerﬁlm.Thenanometer-thick

PMMAﬁlmsthatencapsulatepolymerizablemonomericspecies

showself-healingproperties,withtheabilitytore-sealthearea

thatsufferedacatastrophicfailure.Thisisachievedunderparticular

conditionsdictatedbytheactivationparametersofthe

polymer-izationsuchasthetemperatureinducedbylaserheating.

4. Conclusions

AnoriginalPhoto-CVDprocess wasusedtoobtainultra-thin

nanometric PMMA ﬁlms. After the photo-excitation of thegas

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surfaces.Twocommercialinjectorsystemsallowedliquid

encap-sulationasblisterswithdifferentmorphologiesandproperties.A

partoftheliquidmonomerwasencapsulatedasmicrodropletsin

theultra-thinpolymericﬁlm.AFMandRCMtechniqueswereused

tocharacterizesuchﬁlmsandevidencesforliquidencapsulation

weregiven.Theﬁlmpresentsself-healingbehavioratmicrometric

scale,apropertythathasthepotentialtobealsoexploitedatlarger

scales.

Acknowledgements

The work has been funded by the Sectoral Operational

Programme Human Resources Development 2007–2013 of the

RomanianMinistryofLabour,FamilyandSocialProtectionthrough

theFinancialAgreementPOSDRU/88/1.5/S/61178.

References

[1]R.K.Sahoo,V.Daramalla,C.Jacob,Mater.Sci.Eng.B177(2012)79–85.

[2]S.-J.Cho,I.-S.Bae,J.-H.Boo,ThinSolidFilms518(2010)6417–6421.

[3]L.Cao,H.Jiang,H.Song,Z.Li,G.Miao,J.AlloysCompd.489(2010)562–565.

[4]D.Barreca,D.Bekermann,E.Comini,A.Devi,R.A.Fischer,A.Gasparotto,M. Gavagnin,C.Maccato,C.Sada,G.Sberveglieri,E.Tondello,Sens.ActuatorsB: Chem.160(2011)79–86.

[5]F.-D.Duminica,F.Maury,S.Abisset,ThinSolidFilms515(2007)7732–7739.

[6]A.Douard,C.Bernard,F.Maury,Surf.Coat.Technol.203(2008)516–520.

[7]M.E.A.Warwick,C.W.Dunnill,J.Goodall,J.a.Darr,R.Binions,ThinSolidFilms 519(2011)5942–5948.

[8]M.G.Nolan,J.A.Hamilton,S.O’Brien,G.Bruno,L.Pereira,E.Fortunato,R. Mar-tins,I.M.Povey,M.E.Pemble,J.Photochem.Photobiol.A:Chem.219(2011) 10–15.

[9]A.Douard,F.Maury,Surf.Coat.Technol.200(2006)6267–6271.

[10]A.Shanaghi,A.R.S.Rouhaghdam,S.Ahangarani,P.K.Chu,T.S.Farahani,J. Non-Cryst.Solids258(2012)3051–3057.

[11]N.Yoshida,S.Terazawa,K.Hayashi,T.Hamaguchi,H.Natsuhara,S.Nonomura,J. Non-Cryst.Solids(2012),http://dx.doi.org/10.1016/j.jnoncrysol.2012.03.028. [12]K.Chan,K.K.Gleason,Langmuir21(2005)11773–11779.

[13]K.Chan,K.K.Gleason,Chem.Vap.Deposit.11(2005)437–443.

[14]T.B.Casserly,K.K.Gleason,Chem.Vap.Deposit.12(2006)59–66.

[15]V.Santucci,F.Maury,F.Senocq,ThinSolidFilms518(2010)1675–1681.

[16]A.M.Boies,J.T.Roberts,S.L.Girshick,B.Zhang,T.Nakamura,A.Mochizuki, Nanotechnology20(2009)295604.

[17]F.Pallikari,G.Chondrokoukis,M.Rebelakis,Y.Kotsalas,Mater.Res.Innov.4 (2001)89–92.

[18]O.N.Shebanova,P.Lazor,J.RamanSpectrosc.34(2003)845–852.

[19]Y. Zhang,H.Son, J. Zhang,J. Kong, Z.Liu, J. Phys.Chem. C111 (2007) 1988–1992.

[20]I.Jones,J.Rudlin,Proceedingsofthe2ndInternationalConferenceonJoining Plastics,NationalPhysicalLaboratory,2006,pp.25–26.

[21]B.B.Troitskii,G.A.Domrachev,L.V.Khokhlova,L.I.Anikina,DokladyPhys.Chem. 375(2000)268–270.

[22]J.Bovatsek,A.Tamhankar,R.Patel,N.M.Bulgakova,J.Bonse,Proc.SPIE7201 (2009)720116.