[PDF] Encapsulation of Molecules in Single-Walled Carbon Nanotube

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Encapsulation of Molecules in

Single-Walled Carbon Nanotube

- A Novel Nanodevice Material - Single-walled carbon nanotube (SWNT) is the most promising materialformolecular electronics because ofitsuniquestructural andelectronic properties.

Molecularelectronics isanemerging areainwhich

thegoalisusing molecular materials ascore device components.Anadvantageofmolecular electronics isobviouslythesmallsize ofthecore components, surpassing structures attainableby top-down lithography,andcouldthereforebeessentialfor miniaturization. SWNTs arewireswithmolecular- scalediameters (~1nm),andindividualsemiconducting

SWNTshavebeenactively explored inorder to

construct nanotube field-effecttransistors(FETs).For thefurtheradvancement ofmolecularelectronics,the abilitytoobtainbothp-and n-typeFETsis important forconstructing complementaryelectronics whose performance isbetter(for example,lowpower consumption)thanthatofdevicesconsistingof unipolar p-orn-typetransistors. SWNT-FETsbuilt fromas-grown tubesarefoundto beunipolar p-type.

Severaldopingmethods havebeen developedfor

nanotubes,although stabilityinairwasnotsufficient for the n-type doping.

Ontheotherhand, dueto their sizeand geometry,

SWNTs also provide a unique opportunity for nanoscale en gineering of novelone-dimensional systems, createdbyself-assemblyofmoleculesinsidethe

SWNT'shollowcore.Ithas beenexperimentally

shownthat fullerenescanbeinserted intoSWNTs, forming apeapod-like structure[1].Thecomposite natureofpeapod materials raises anexciting possibilityofananoscalematerialhavingatunable structure that canbetailoredtoaparticular electronic functionality.Inthiswork,weclarify the structure of organics/SWNT compounds,andinvestigate the chargetransfer betweenSWNT andorganic molecules.

Sinceorganicmolecules predominantlyoccupy the

innerspace ofSWNTs,thedopingstateis rather stable in air.

SWNTsweremanufacturedbylaservaporization

ofcarbon rodsdopedwithCo/Niinanatmosphere of

ArandsubsequentlypurifiedwithH

2 O 2 ,HCland

NaOH[2]. SWNTswerereacted withvaporoforganic

molecules,whichare shown inFig.1,inamanner similartothecase oftheC 60
-peapod[3].For structural characterization,synchrotron X-raypowder

Fig.1.Singlewalled carbon nanotube

encapsulating TCNQ molecules. diffractiondata wereobtainedatroomtemperature at beamlineBL02B2.Figure2showstypicaldiffraction profilesforpristine, TCNQ-dopedandTMTSF-doped

SWNT materials.Themostobviousdifference between

dopedandundopedSWNTsisthestrongreduction of peak intensityatapproximatelyQ~0.4(Å -1 ), whichis indexedas(10)reflection.Suchabehavior provides evidence ofencapsulation oforganicmoleculesinside

SWNTs,asobservedinseveralpeapodmaterialsand

gas-adsorbedSWNTs [4].

Intensity reductionofthe (10)peak allows usto

estimate thechemical concentration ratio of encapsulated organic molecules tocarbon atoms of

SWNT.First,theparameters ofpristineSWNTswere

determined soastoreproduce theobserved diffraction pattern shown inFig.2(a),takingthe

Gaussian distribution ofthe tube diameterinto

account.By usingtheobtained parameters,the intensitydistributionsofthediffractionpatternforthe organic/SWNT compounds were well accounted for by inserting anuniformrodofcharge withthediameter of7Åinside thetubes. Fromthedensityofuniform

charge,thecarbonnumberofSWNTperorganic 77777777777373737373737373737373737373737373737373737373737373737373737373737373733333333333333333373737373737373737373737373333333333333333333333333

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