Carbon Nanofilm with a New Structure and Property

JpnJ．AppI Phys．Vol．42（2003）pp・LlO73−L1076 Part2，No．9A／B，15September2003 1⑤2003TheJapanSocietyofApplledPhysICS

CarbonNanommwithaNewStructureandProperty ShigeoHoRIUCHT＊，TakuyaGoTOU，MasahiroFUJTWARA，RyujiSoTOAKA，MasukazuHIRATA， KojiKIMOTOl，ToruAsAKAl，TadahiroYoKOSAWAl，YoshioMATSUl一，KenjiWATANABElandMasamiSEKITAI CoIpOrateResearchLabomto7y，MllsubtshtGaL∼ChemlCalCo・Inc・，22Wt7daLTukuba，Ibarak1300−4247，Japan lAdvancedMaterlalsLaboratoly，NatzonalTn▲Stitulef，rMaterlalsScience，1−1Namtkt，Tukuba，lbaraki305−0044，Japan

（ReceivedMay16，2003；aCCePtedforpubllCationJuly2．2003）

Wehavepreparedacarbon刷mofnanometerthickness，Whichiscalledhereacarbonnano別m（CNF），Startingflomthe oxidation ofgraphite・The structure andthickness oftheCNF are determinedby high−reSOlut10ntranSmission electron

microscopyandelectrond冊action・Thestructureisofanewtype（S・G∴P3），inwhichcarbonsix一membered−ringplanesare stackedwlththesequenceof‥・AA…・Accordingtoelectronenergylossspectroscopy，aSubstantialamountofoxygenis

detectedbutthemolarratioofoxygentocarbonispossiblydecreasedtoIessthanO工TheCNFchangesfromaninsulatortoa

semiconductorwhenreducedonheatingat2500C．lDOI‥10・1143／JJAP・42・LlO73］ KEYWORDS：Carbonnanofiim，HRTEM，ED，StruCtureanaIysiS，thiCkness，StaCkingsequence，EELS，○／C，SemiCOnductor

Manystudiesongraphiteoxide，Whichisoneofgraphite intercalatedcompoundsandaninsulator，havebeencarried

醒闇 聾 該 ∴： ∴

讃

out．Different models have been proposedlbrits struc−

∴ ＼疑 ∴：

ture．1−3）Theinterlayer spaclngbetween carbonplanesis

indennite and reported to bein the range from O・60to

l・lnm，dependingonthepreparationmethod・415）Themolar ratioofoxygentocarbon，0／C，isintherangebetweenO・3 andO．6．5）Ithasbeennotedthatthe separationoflayers easily occursin an aqueous∴SOlution・6・7）After strong

exfbliation，Verythinparticleshavebeenformed・8）

Wehavepreparedaverythin皿mbylinkingtheparticles

∴∴： ∴∴ 「；∴ 一∴∴

；：∴ ∴∴言．∴∴∴子．∴∴∴一∴∴  ∴∴∴

andanalyzedits structurebytransmissionelectron micro−

SCOpy（TEM）andelectrondimaction（ED）・Herewereport

：b：

thatitis not the graphite oxidebuta substance，Whichis COmPOSed mostly of carbon，With a new structure and

PrOPerty・ ）達蓑築く摂

Thestartingmaterialusedwasanaturalgraphite（SN0− ∴∴ 綴 ／裟

25，SEC Corp．）with a purity better than99・97wt％・We

OXidizedthismaterialbythemethodproposedbyHummers

∴5∴∩∴m    ：∴       「       ：∴

／醗

andOffeman，9）inwhichpotassiumpermanganate，Sulfuric acidandsodiumnitrateareusedaschemicalreagents．The

PrOduct was puri丘ed uslng an aqueOuS SOlution of5wt％ sulfuricacidandwatertoobtainablack，Viscousliquid．It

was then diluted with methanol，tO Obtain alight brown， colloidalsuspension・Thin particlesin the colloid do not

COagulate，becausetheirinterfacialenergywithmethanolis ∵

Small．A droplet of the suspensionis put on a carbon

microgrid（3mmindiameter）．Whenmethanolevaporates，

thecolloidalparticlesarelinkedtoeachotherandathinmm

繍＼製鞘諷 灘纂鷺纂真裏薫親           ）（麗綴

is formed continuously atthe Hame areaas wellas atthe OPen pOrtion of the microgrid・The more dilute the

SuSpenSion，the thinneris the resultant刷m A very thin

Fig．1．（a）TEMimage of a carbon nanonlm（CNF（l））・Darklines representpuckerslnthemm．AnEDpattemlSlnSelted（b）HRTEM imageofthedarkllne，markedbyanarrowin（a）・HonzontalstrlpeSShow

釦mistransparentandbarelydiscriminatedunderanoptlCal

thatthemmlSCOmPOSedoftenhexagonalplanes．（C）HRTEMlmageOf

microscope・In a relatively thick case，a mm of some

CNF（2），ShowlngthathexagonalplanesarestronglydLSturbcd・Atthe

Centimetersindiameterispossiblyfomed．

arrowedsites，thelrlocalseparationoccurs・ThecorrespondlngEDpattern

As wi11be shown below，the nlm has ananometer−level

thickness andis composed mostly ofcarbon．Wecallita

Carbonnano創m（CNF）hereafter． The CNF was examined uslng a high−VOltage TEM （HVEM，mOdel H−1500）at an acceleration voltage of

800kV and an analyticalTEM（ATEM，mOdelHF−3000） of300kV．The HVEM was used to take high−reSOlution ＊coITeSPOndlngauthor Presentaddress：2−13−1Sakura，Tsukuba，Ibaraki つIヽくIヽIヽIヽつ  丁へ．，、．．、．、 t⊃∴．＿、ハ言l 〈」」＿へ．、．、．ハ1、／、．二，，〈1、．1万1il、＿．．．、l′：／、●、一、／、．1．、∠、：．へ

TEM（HRTEM）images．Figurel（a）showsaTEMimageof a cNF言n which darklines are seen．Theirlengthis indennite・They onglnatefrom thepuckers formedin the

創m，aSeXplainedbelow． In the corresponding electron di冊action（ED）pattem insertedinFig．1（a），StrOngdi組action“spotswithasixfold

S．HoRIUCHI etal．

LlO74  JpnJ Appl．Phys・Vo142（2003）Pt2，No・9A／B

tothecarbonsix一membered−ringplane，Whichiscalledthe

fromthespectrumtobeintherangebetweenO・13andO・27，

Carbonhexagonalplanehereafterforsimpliclty・Innermost

dependingonthesiteexamined・Itislowerforthethinner

di血action spots are from the（100）planes，While second

site・This suggests that some oxygens are removed血om

innermostones丘omthe（110）planes．

interlayerspaceswiththeadvancementofexfoliation・

Figurel（b）isanHRTEMimageofarelativelythick，dark

According to X−ray photoemission spectroscopy（XPS）

line，marked by an arrowin Fig・1（a）・Strong，horizontal

usingmonochromaticAl−KαX−ray（V・G・ESCALAB250）言t

strlPeS．Whichconsistofabouttendarklines，arethelattice

was clarined that beside a m劉Or Chemical bond of C−C

image ofthe carbon hexagonalplanes・When apuckeris

（E＝284．5eV），thereareminorbondslikeC−0（C−OHand

formedin a刷m，a Part Of the hexagonalplanes，being

C一〇一C，E＝286．2eV），C＝0（E＝287．6eV）and COOH

accidentallyalmostpara11eltotheincidentelectronbeam言s

（E＝289．1eV），Where Eis the binding energy・These

reHected as a darkline．In addition，We nOte Weaklines，

functionalgroupsexistatbothsidesofhexagonalplanesor

which are thelatticeimage ofthe（100）planes，running

attheiredges・AnyelementsotherthanCandOarescarcely

almostnormaltothestrlPeS．

detected．

Thehorizontaldarklines are wa、′y，SuggeStlng thatthe

InordertoexaminethestructureoftheCNF，thesameED

carbonhexagonalplanes are undulated・Theundulationis

pattemasthatinFlg．1（a）watrecordedtoanimagingplate

notperiodicanditsmagnitudevariesaccordingtothearea

（IP）system（FujiFDL5000）．whichenabledustomeasure

examined．Intheareas，markedbyarrowsinFig・l（b），the

theintensltyquantitati、▼elv・Asaresult，theintensltyratioof

interlayerspaclnglSreadouttobeintherangebetweenO・43

the（100）tothe（110）spotsisknowntobel・2forthestrong

andO．50nm・Thisisclearlysmallerthanthatofthegraphite

SpOtS・

oxide mentioned above，Whilelargerthan thatofgraphite

Asanapproximation，Weneglecttheoxygen，remainlngln

（0．334nm）．The occurrence of the undulation may be

theinterspacesbetweenhexagonalplanes・Therearethree

attributedtothatsubstancesexistlngattheinterlayerspaces

possiblemodelsfortheirstackingsequence；1）・‥AA…・2）

Huctuateinspeciesandquantities・

Itis di冊cultto obtainHRTEMimagefromthe areato

…ABAB…and3）…ABCABC…，Where A，B and C denotethehexagonalplanesatd肝erentpositions・Wehave

whichelectronbeamisincidentnormaltohexagonalplanes，

kinematicallycalculatedthedi冊actionintensity（Icl00and

becausetheimagecontrastisveryweakand，aCCOrdingly・1t

IcllO）forthesemodels，aSafunctionofnforverythincases

takestimetoachievetheoptlmumdefocuslngCOndition・

（n＝1∼20）．TheresultisshowninTableIintemsofthe

Weak spots are also observedin the ED pattem This

intensityratioIc100／IcllO．Itisnotedthattheratioisconstant

indicatesthatthepresentCNFisconstitutedbythestackof

independentofnformodell），Whilevarieswithrelatiヽely

themm，eXhibitingthepuckershowninFig・1（b），andtwo

lowvaluesformodels2）and3）．Adynamicalcalculationfbr

thinner mms，glVlng Weak spots・These component nlms

thedi冊actionintenslty，uSlngaCOmPuterSOftware’“MacH−

apparently orlglnate Hom different tine particlesin the

REM”，gaVe areSultessentially similartothat shoWnin

colloidal solution mentioned above．Theintenslty Of ED

TableLComparlngthiswiththeresultobtainedfromtheED

spotsalsoshowsthehighsixfoldsymmetry・Thismustbe

patternin Fig．1（a），We may COnSider that the stacking

duetothefactthateachcomponentmmissu範cientlythin

sequenceinthepresent創mcorrespondstothatofmodell）・

toexcitedi血actionstreaks，elongatlngnOrmaltothe創m，SO

Inthediscussionabove，Wehaveneglectedthee諒tence

thattheintensltyishardlyaffectedbytheslighttiltofthec

ofoxygen・However，thecalculatedintensltyagreeSfairly

axis fromthedirection ofincidentelectrons．

Similar ED pattems are observedin diHerent areas，

although the combination of strong and weak ED spots variesandtherotationdegreeaboutthecaxisisdi任erent・

wellwiththeobservedone・Apossibleexplanationforthisis

thatmostofthefunctionalgroups，Whichconlainoxygen， arraylrregularly，thustheyhardlyaffecttheEDintenSlty・

Asstatedabove，VerythincomponentfilmscoeXistinthe

Thepattem showlng anidenticalorientation appears over

present CNF・We have then tried to di、Tide them from

theareaoflOto20いmaSfarasstrongspotsareconcerned・

relativelythickonesinthestageofthecolloidalsolution・

Thiscorrespondstothelateralextentofarelativelythick

uslng the differencein weight，aS folloWS・l The black，

componentnlm・Theareas，Whereanidenticalarrayofweak

viscousliquidwasdilutedwithwatertoobtainacolloidal

spotsisexcited，areSmallerandHuctuatedinsize・

suspension．2）After the centr血gation（5（XOrpm）ofthe

ItisnotedinHRTEMimagesthatthestackingnumberof

suspension，thesupernatantwasobtained・3〉B、aStrOnger

hexagonal planes，n，isless than about30・When nis

centrifugation（7000rpm）ofthesupematant・、eIT thin，血e

between10and30，along strlPe Of hexagonal planes

particleswerecollectedasasediment，Which、、aSnOlonger

appears・The magnitude of undulation of the strlPeS

viscous．Thevolumeofthesedimentisroughlヽ1−100fthat

decreaseswithanincreaseinn，WhilethespaclnglnCreaSeS，

ofthe black，Viscousliquid・Wehereafkrreftrthe CNF，

althoughitseldomexceedsO・55nm・Inthecaseofnsmaller

thanlO，HRTEMimages are severely disturbed言・e・言he

Table T．Calculatedintenslty rat10，IclOO／］cllO．rOr三田Cture mOdelsl）

magnitude of undulationislarge and strlPeS are Partly

‥．AA…、2）．ABAB．and3）‥ABCABC．種、d run”On Ofthe

apparent，aSWillbeshownbelow・

numberofstackingplanes．

An electron energyloss spectroscopy（EELS）spectrum

wasobtainedusinganapparatus（GatanGIF2002）attached

Structure

NumberofstacklngPlaneミ（n一

model l Z∴∴∴3   4   5   1り

2 8

1 鴇 00

9

3） 110．28 0．0 0．069 0．0＋l OOll

1   0   0

（284eV）and the dther to that of the oxygen K−Shell

2）  Ll 0．28 0．37 0．28 031 0ニ8

、−▲∴∴ヽ− 0−

1） 1．1111111 11 11

corresponds tothe absorptlOnedge ofthe carbon K−Shell

−1 0 0

to an ATEM．Two core−loss slgnals are detected；One

JpnJ Appl Phys・Vo142（2003）Pt．2．No9A／B

S．HoRIUCHIelal

LlO75

Whichis constituted ofonly the丘ne particles，aS CNF（2），

WhiletheoriginalCNFasCNF（1），Whenclassityingthem．

ATEMimageofCNF（2）observedatlowmagnincation SeemSaPparentlysimilartothatshowninFig．1（a），butthe

darklinesduetopuckersareshortandweakincontrast．An

HRTEMimage of a puckeris shownin Fig．1（C）．The COrreSPOndingEDpatteminsertedshowsthattheCNF（2）is COmPOSedoftwocomponent創ms・ThestrlPeSOfhexagonal Planesarestronglydisturbed，i・e・darklinesquicklychange

innumberbetween2and4alongthem．Atthesitesmarked byarrows，darklinesareseparatedintobranches・Thesemay

be atthbutedtothefactthathexagonalplanes arelocally Separated．Itis generally observedin the CNF（2）that the

灘畿羅

localseparationofhexagonalplanesoftenoccursandmost

諾／＼＼諒鸞羅爆溺

COmPOnent乱ms∴Seem tO be composed ofless than5 hexagonalplanes． TheintensityratioIolOO／Iol10islargerthanl．5inmost

CaSeS・Thereasonforthismaybetheeffectofthe‘‘apparent

＼／醒聞

temperaturefactor”，i・e・，Carbonatoms aredisplacedfrom idealpositions，While the stacking sequenceisessentially

／

unchanged・TheresultofquantitativeanalysISOnthiswillbe reportedelsewhere．

AnEELS spectrum wastaken Hom CNF（2）．Theresult

i醒

ShowsthattheratioO／CisintherangebetweenO．082and O・17，dependingonthe sitemeasured．Thedecreaseinthe

amountofoxygenascomparedtoCNF（1）maybeattributed to the release ofthe functionalgroups and water，having existedattheinterlayerspaces．

Fig・2・（a）TEMlmageOfCNF（1）（n＝15）heatedat250uCfor30min． ThecorrespondlngEDpattemlSLnSerted・（b）EnlargedlmageOfapartof

CNF（1）was heatedin vacuum（10￣lpa）．Weightloss

（a）afterremovingthebackgroundnoISe．Acomputer−Slmulatedimageof

StartedatlOOCCandcontinuedwithinincreaseinheatlng

themultiplycondensedbenzenerlngSisinserted Therealandcalculated

temperatureupto500ccwithapeakat200cc・Darkening

lmageSfitlndomain−1ikeareas．

OCCurred ataround1200C andCNF（1）becameopaqueon heating a1250＝C for30min．Itis clear that a reduction

Pr00eS OeCurredduringheatlng．

In the XPS pronle from CNF（1）heated at2500C for 30min．the peak related to the C一〇bond decreased the height・SuggeStlngthatthereductionisattributedmainlyto

the release ofOH．

The spaclng between neighboring hexagonalplanesin

…AA…tyPe．At the same time言tis conErmed that the remainlngOXygenSarraylrregularly，Sincetheyhardlya能ct theimagecontrast．

Ithasbeenreportedthatthecarbonhexagonalplanesin graphite sulfate13）orin graphite nitrate，14）which are intercalated compounds，have the stacking sequence of

CNF（l）slightlydecreasesonheatingat2500Cfor30min．

…iALAI…tyPe，Wheretheverticallinesimplyintercalated

AccordingtoanHRTEMimage言tisintherangebetween

layers・Thepresentresultsuggests thatasimilarstacking

O．47andO．43nmin the創m withn＝15．

We have then obtained the HRTEMimage from the CNF（l）With theincident beam nomalto the丘1m（Fig． 2（a））・Weaklines corresponding to the（100）planes are

SequenCemayariseingraphiteoxide，althoughtherehave beennosuchreportssofar・

Theareas，inwhichtheobservedimageagreeswellwith thesimulatedone，arelimitedinsmall（∼2nm）domains，aS

faintlynotedunderhighbackgroundnoise・Acorresponding

OutlinedinFig・2（b）・Theyseemtohaveaslightdifference

EDpatternisinserted，ShowlngStrOngSPOtS，eXCitedfrom

in orientation・At the boundary areas，SOme defects must

themaincomponent創mwithn＝15，andweakones．The

have been fomedin order to accommodate the orientation

ratioIolOO／IollOforthestrongspotsisl．1，indicatingthat

diHerence・Infact，WenOte丘ve−andseven一membered−rings

the stacking sequence ofhexagonalplanesis of…AA．‥

atthesitemarkedbyanarrowinFig．2（b）．Surroundingsix一

type・

membered−ringsseemtobedefbrmedstrongly・

Figure2（b）is an enlargedimage ofapart of（a）after

Hexagonal planes must have been severely disturbed

eliminatlngthebackgroundnoise・10）Acomputer−Simulated

duringtheoxidation，Purificationand／orexfoliation．Some

image fbr the st…Cture Of…AA…type With n＝15is

fractionofadefectivechemicalbondisrestoredonheatlng・

inserted，in which carbon sites are denoted by small

Thisisthereasonwhythedamageduetoelectronirradiation

circles・11）Theobservedandcalculatedimagesapparently

hasbeendecreasedintheheatedspecimen・

Showsimilarpatternsandcontrasts・Ithasbeenreported12）

According toEELSIbrthe CNF（2）heatedat2500C fbr

thatathinplateofgraphiteexhibitsasimilarlatticeimage・

30min，theO／CvaluesvaryintherangebetweenO．075and

However，based on the present results obtained Hom

O．15−

HRTEMimages and ED pattems，We Can COnClude that

ThepreliminarymeasurementofelectricconductivltyWaS

L1076  Jpn．J．Appl．Phys．Vo142（2003）Pt．2，No．9A／B

The resistivlty at rOOm temPerature WaS Verylarge （→500【2・cm）for the nonheated nlm・After heating at

2500C fbr30min，it was around O．151・cm．It decreased

Withanincreaseintemperatureintherangebetween30and 1500C，andtheactivationenergywasestimatedtobeabout

S．HoRIUCHIetal．

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O・05eV・A similar conductivlty WaS Observed also for

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thinner創msplayanessentialroleinelectricconduction．

A CNF can be prepared on a substrate with alarge （3mmQinthepresentwork）areaandcomplicatedshape．It

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usefulmaterialfornanotechnology．

We wouldlike to thank T．Kawaki，M．Takeda，A．

AmagalandM．OhbaofMGC，andC．Tsumta，H．Nozaki， M・OnodaandT・MitsuhashiofNIMSfortheirsupport．

ObtaineddiffractlOnSpOtSWeremteredandinverselytransfomed．

11）ThespacegrouplSPj．TheatomcoordlnateSare2／3，1／3，Oandl／3， 2／3，0（hexagonalnotation）．

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767．

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