Resonane Raman Sattering: Nondestrutive and
Noninvasive Tehnique for Strutural and Eletroni
Charaterization of Isolated Single-Wall
Carbon Nanotubes
A. Jorio a;e
, F. M. Matinaga a
, A. Righi a
, M. S.S. Dantas a
,
M. A. Pimenta a
, A. G. SouzaFilho b;e
,J. Mendes Filho b
, J.H. Hafner
,
C. M. Lieber
, R.Saito d
,G. Dresselhaus f
,and M.S. Dresselhaus e;g
a
Departamento deFsia,UniversidadeFederaldeMinasGerais,BeloHorizonte,MG,30123-970 Brazil
b
Departamentode Fsia, UniversidadeFederaldoCeara,Fortaleza-CE,60455-760, Brazil
Department ofChemistry,HarvardUniversity,Cambridge,MA02138 USA
d
Department ofEletroni-Engineering,UniversityofEletro-Communiations,Tokyo, 182-8585Japan
e
DepartmentofPhysis, f
FranisBitterMagnetLaboratory,
g
Department ofEletrialEngineering andComputer Siene,Massahusetts InstituteofTehnology,
Cambridge,MA02139-4307 USA
Reeivedon10May,2002
Wedisusshowresonanemiro-Ramanspetrosopyandeterminetheeletroni andstrutural
propertiesofindividualisolatedsingle-wallarbonnanotubes(SWNTs)thatanbefurtherusedfor
potentialnanodeviesorstudiedbydierentexperimentaltehniques. Weshowthatitispossibleto
markthesurfaeoftheSi/SiO2substrateforloalizationoftheisolatedSWNTsbyusingadiamond
tip. Bytimingthegrowthproedure,alowdensityofSWNTsonthesubstrateanbeobtainedso
that theSWNTloalization byatomiforemirosopy (AFM)istrivial. Wealsoharaterizea
SWNTbyresonaneRamanspetrosopyattheedgeofaSi-SWNT-AFMtip. Thereresultsshow
thatitispossibletomakejointexperimentsonthesameisolatedSWNT.
Single wall arbon nanotubes (SWNTs)[1℄ have
been intensively studied for their interesting
one-dimensional(1D)physialproperties,andfortheirhigh
potential for tehnologial appliations.[2, 3℄ SWNTs
have been onsidered as a andidate for post-Si
nan-otehnology, due to their interesting eletroni
prop-erties, and for appliations suh as atomi fore
mi-rosopy(AFM)tips,beauseoftheirspeialstrutural
andmehanialproperties.[3℄
TheremarkableeletronipropertiesofSWNTsare
uniquelydened by theirdiameter d
t
and hiral angle
, that are speied by the twointegers(n;m) whih
desribetheroll-upvetorC
h =na
1 +ma
2 (a
1 anda
2
aretheunitvetorsofthegraphenesheet).[2℄Resonant
Ramansattering an beused toassign (n;m)indies
to isolatedSWNTs basedontheanalysis oftheradial
breathing mode (RBM).[4 ℄ Furthermore, it has been
shown that eah of the several harateristi features
observedin theRamanspetrafrom isolatedSWNTs,
namelytheG-band,theDbandandG 0
band,ishighly
sensitiveto the detailed nanotube struture, hanging
the(n;m)indies of theresonant SWNT.Conversely,
thesespetralfeaturesanalsobeusedtoprovide
stru-turalandeletroniharaterizationinformationabout
isolatedSWNTs (seeRefs. [5,6, 7℄). Thegoalof this
paperistoshowthat resonaneRamansatteringan
beused to haraterizenanotubesthat will befurther
studiedbydierentexperimentaltehniques. This
pro-edureanalsobeusedtoharaterizeSWNTsfor
po-tentialuse in nano-devies,oreven SWNTs builtinto
nano-devies. We here disuss theharaterization of
isolatedSWNTsonSi/SiO
2
substratesthat are
gener-allyused for transport measurements[8℄, and also the
haraterization of one SWNT nano-devie, that is a
Si-SWNTAFMtip.[3, 9℄
Figure 1 shows Raman spetra taken from an
iso-latednanotubeonaSi/SiO
2
substrate. TheSipeakat
521m 1
is known as astrong Raman feature and is
learlyobservedin thespetraof Fig.1. In this
spe-trum we found a strong Raman signal oming from
an isolated SWNT, where several SWNT Raman
seond-Fig. 1(b) showthat adetailed lineshape analysis an
beperformedon thedisorder-indued D band andon
the graphite-like G band. A doublet is observed for
theD-bandproleformed bypeaks withfullwidth at
half maximum intensity (FWHM) of about 12m 1
.
The G-band exhibits the lineshape usually observed
for semionduting SWNT bundles, but with a muh
sharperFWHMofabout11m 1
. Thesignalintensity
of theSWNTis omparableto thestrongRaman
sig-nal fromsilion, although thenumberof arbonatom
satterersinthe1DSWNTisabout10 6
timessmaller
than the number of atoms on the illuminated 3D Si
substrate. This extremely large Raman ross setion
of SWNTs under resonane onditions is due to the
quantum onnement of the eletroni states in this
1D material, resultingin an unusually high densityof
eletronistatesattheenergieswherethe1DvanHove
singularitiesour.[10℄
1260
1300
100
300
500
Frequency (cm
−1
)
0
2e+06
4e+06
6e+06
8e+06
Intensity
(a)
1500
1650
400
800
1200 1600 2000
Frequency (cm
−1
)
(b)
237(5)
Si
Si
G−band
D−band
RBM
2
nd
Figure1. ResonantRamanspetraofaSWNTonaSi/SiO
2
substrate. (a)AstronglyresonantRBMfeature,and(b)a
stronglyresonantG-bandfeature.TheRamanspetrawere
obtainedwithE
laser
=1:58eV.
ResonaneRamanspetrosopyanbeusedto
har-aterize isolated SWNTs in nano-devies. Fig. 2(a)
showsanoptialimage(100)obtainedfromaSiAFM
tip ontaining a SWNT at the edge [upper left inset
shows a transmission eletronmirosope (TEM)
im-ageofaSi-SWNTAFMtip,takenfromRef. [9℄℄. Fig.
2(b) shows Raman spetra obtained by fousing the
laserat theedge oftheAFMtip. FromtheRBM
fre-queny !
RBM
, we an obtain the nanotube diameter
(d
t
=248=!
RBM
).[4℄Theinter-bandeletroni
transi-tion energy E
ii
involved in the resonant Raman
sat-tering proessofthe measuredSWNT analso be
ob-tained,sinetheRamanintensityisproportionaltothe
squareofthejointdensityofstates(JDOS).[10,11℄In
thisase,resonanewiththeSWNTwasfoundusingan
Ar:Krlaser. Fig. 2(b)showstheRamanspetrawith
E
laser
= 2:18, 2.41 and 2.54eV. The SWNT shows a
resonanenear E
laser
=2:41eVand!
RBM
=196m 1
(d
t
=248=196=1:27nm).[4℄ TheSWNT atthe AFM
tip an be assigned as a semionduting(16;0) tube,
thathasd
t
=1:27nmandE S
=2:40eV.
1200
1450
1700
Frequency (cm
−1
)
430
630
830
Raman Intensity
150
250
2.18eV
2.41eV
2.54eV
196cm
−1
laser spot
AFM tip
10nm
(a)
(b)
Figure 2. (a)The optialimage of a Si-SWNTAFM tip.
OneisolatedSWNTisattahedtotheedgeoftheSitipby
theproeduredisussedinRef. 9.Upperleftinsetshowsa
TEMimageofanotherSi-SWNTAFMtip,takenfromRef.
9. (b)The SWNT G-bandRaman spetra obtained with
threelaserlinesfoused attheedgeofthe Sitipshownin
the optial image (a). Theinset shows the orresponding
RBMfrequenyregion.
Itisimportantto ommentthat the(n;m)
assign-ment is based on the experimental determination of
the tight binding overlap integral,
0
= 2:90eV and
the atomi distane between arbons atoms a
C C =
0:142nm. This
0
valueisfoundtodesribeoptial
ex-perimentswithhigh auray, as,forexample,optial
absorption studies on SWNT bundles[12℄, the
asym-metriesin theStokesvs. anti-StokesRaman
measure-mentsonSWNTs[11,13,14,15℄,theosillatory
behav-ior of the RBM spetral moments[16℄, the osillation
in the dispersive D-band frequenies for SWNT
bun-dles[5℄, and unusual G-band[6℄ and G 0
-band[7℄
spe-tral features. Sanning tunneling spetrosopy (STS)
experiments arebetter desribed with
0
2:6eV[3℄,
and the originof the dierent
0
valuesneeds further
researh.
TheeletronitransitionenergyE
ii
anbeobtained
withhighauray(3meV)byusingafrequeny
tun-ablelaser. InRef.10aSWNTwith!
RBM
=173:6m 1
(d
t
= 1:43nm)[4℄ and E
ii
= 1:6550:003eV was
measured with a tunable Ti:Sapphire laser, uniquely
identifying the resonantSWNTasthe metalli (18;0)
SWNT.ThestrutureoftheloalizedSWNTis
deter-mined and the measurement is non-destrutive. This
SWNT wassitting on a Si/SiO
2
substrate ontaining
lithographimarkers,andthesameSWNTanbe
fur-therimagedbyAFM(seeRef.10),orusedfortransport
measurements.[3,8℄
Thegeneral problem of performing morethan one
experimenton thesameSWNT isto loalizethetube
spatially. Fig.3showsanexperimentalproedure,
sim-ilartotheonedisussedinRef.10,butusingasimpler
method forspatially loalizingtheSWNTs. Fig. 3(a)
substrate with a diamond tip. AFM images an be
taken onsuh asampleto desribethesurfaeandto
identifythepreseneofisolatedSWNTs[seeFig.3(b)℄.
The density of tubes an be ontrolled by timing the
atalyst formationand SWNTgrowthproedure. The
verylowdensity of isolatedSWNTs on thesurfaeof
this sample makes it trivial to identify the tube that
is resonant with E
laser
. Ramanspetrawere taken at
the position shown in Fig.3(b) to obtaintheresonant
RamansignalfromtheisolatedSWNTlosetothe
dia-mondmarker. Fig.3()showstheG-bandRaman
spe-trafromthisSWNT,obtainedwithdierentlaserlines
fromaDCMdyelaser. WithRamanspetrosopyand
AFM, we analyzedthree other nanotubeslose to the
diamondmarkersonthesampleshowninFig.3.
There-fore,theuseofalownanotubedensitysamplewith
di-amond markersmakesitrelativelyeasytoanalyzethe
same SWNTwith dierenttehniques, i.e., AFMand
Ramanspetrosopy.
m
µ
1
1500
1550
1600
1650
Frequency (cm
−1
)
25
75
125
Intensity
672.4 (1.844)
661.3 (1.875)
643.3 (1.927)
649.3 (1.909)
638.7 (1.941)
630.7 (1.966)
619.7nm (2.000eV)
700.0 (1.771)
a
c
b
diamond
SWNT
marker
Figure3. (a)AnoptialimageofaSi/SiO2 substratewith
markersmadebyadiamondtip. (b)AnAFMimageofthe
edgeofonemarker,indiatingthepreseneofoneisolated
SWNT. ()G-bandRaman spetra ofthe isolatedSWNT
shownin(b)forvariouslaserexitationenergies.
It is important to disuss the experimental
lim-itation of the (n;m) assignment proedure, related
to the energy ranges aessible by the experimental
set up. Fig.3() shows a resonant proess at about
E
laser
= 1:909eV. The spetrain the RBM region do
notshowanyRamanfeatures,indiatingthatthis
res-onane proessours with satteredphotons, and
in-volves G-band phonons, so that a preise d
t
determi-nationannotbeperformedusingthe!
RBM
harater-izationapproah.[4℄However,theinter-bandeletroni
transition energy an still be evaluated approximately
by E
ii = E
laser E
phonon
= 1:91 0:20 = 1:71eV.
The RBM spetrashould beobservedusing alaserat
E
laser
=1:71eV,weresuhalaserlineavailable.
Theuseof atunable laseris importantforthe
de-one laser line an be used to selet spei SWNTs.
To build a SWNT devie using only semionduting
SWNTs withagivenE
ii
, it ispossibleto selet those
tubes from a marked Si/SiO
2
substrate that are in
resonane with a xed laser line E
laser ' E
ii .
Res-onant metalli orsemionduting SWNTs an be
dif-ferentiatedaordingtotheirdiameters(obtainedfrom
!
RBM
)[4℄andfromanalysisoftheirharateristi
spe-tralfeatures.[5,6,7℄
TheadvantageofRamanspetrosopyasa
hara-terizationtoolis that thetehniqueisnon-destrutive
andrelativelyeasytoperform. Ramansetupsare
read-ilyavailableandtheexperimentanbedoneunder
am-bienttemperatureandpressureonditions. Duetothe
large density of states at the 1D van Hove
singulari-ties,RamansignalfromoneisolatedSWNTisobserved
withoutusing thesurfae enhanedRaman sattering
(SERS)tehnique. Therefore,Ramanspetrosopyisa
veryaurateandnon-invasivespetrosopitehnique
forusing light as aweakly interating probe, and the
resonantinter-bandeletronitransitionsanbe
deter-minedwithhigh auray(about3meV).[10℄
Insummary, weshowherehowto haraterizethe
strutureofaSWNTthatanbefurtherusedforother
measurements. Weshowthatitispossibletomarkthe
surfaeof theSi/SiO
2
substrate forloalizationof the
isolated SWNTs by using a diamond tip. By timing
thegrowthproedure,alowdensityofSWNTs onthe
substrateanbeobtainedso thattheSWNT
loaliza-tionbyAFMistrivial. Thisproedureiseasyand
non-expensive,andmightbeadoptedforresearhwork. We
alsoshowthatitispossibletoharaterizeaSWNTby
resonaneRamanspetrosopyattheedgeofanAFM
tip. Theseresultsshowthatitispossibletomakejoint
experiments on the same isolated SWNT. Future
di-ameter haraterization of oneisolated SWNT at the
edge of an AFM tip by using the Raman and TEM
tehniques would giveus a denitiverelation between
!
RBM andd
t
,andtheappropriate
0
valueforthe
sys-tem.
Theexperimentalworkwasperformedatthe
miro-Ramanlaboratory, Department of Physis-
Universi-dadeFederaldeMinasGerais(UFMG),Brazil. We
a-knowledgetheNSF/CNPqjointollaborationprogram
that makespossible exhange trips between MIT and
UFMG researhers (No. NSF INT 00-00408and No.
CNPq910120/99-4). A. J. andA.G.S.F. aknowledge
nanialsupportfromtheBrazilianagenyCNPq,
un-derProx(350039/2002-0)and DCR(301322/2001-5)
ontrats,respetively. TheMITauthors aknowledge
support under NSF Grants DMR 01-16042, INT
98-15744,andINT 00-00408. R.S.aknowledgesa
Referenes
[1℄ S.Iijima,Nature(London)354,56(1991).
[2℄ R.Saito,G.Dresselhaus,andM.S.Dresselhaus,
Phys-ialProperties ofCarbonNanotubes(ImperialCollege
Press,London,1998).
[3℄ M. S. Dresselhaus, G. Dresselhaus, and Ph. Avouris,
Carbon Nanotubes: Synthesis, Struture,
Proper-ties and Appliations (Springer-Verlag, Berlin, 2001),
Vol.80ofSpringerSeriesinTopisinAppl.Phys.
[4℄ A. Jorio, R. Saito, J. H. Hafner, C. M. Lieber,
M. Hunter, T. MClure, G. Dresselhaus, and M. S.
Dresselhaus,Phys.Rev.Lett.86,1118(2001).
[5℄ A. G. Souza Filho, A. Jorio, G. Dresselhaus, M. S.
Dresselhaus, R.Saito, A.K.Swan, M.S.
Unlu,B.B.
Goldberg, J. H. Hafner, C.M. Lieber, and M. A.
Pi-menta,Phys.Rev.B65,035404 (2002).
[6℄ A. Jorio, A. G. Souza Filho, G. Dresselhaus, M. S.
Dresselhaus, A. K. Swan, B. Goldberg, M. S.
Unlu,
M. A. Pimenta, J. H. Hafner, C. M. Lieber, and
R.Saito,Phys.Rev.B65,155412 (2002).
[7℄ A. G. Souza Filho, A. Jorio, Anna K. Swan, M. S.
Unlu,B. B.Goldberg, R. Saito, J.H. Hafner, C. M.
Lieber,M.A.Pimenta,G.Dresselhaus, M.S.
Dressel-[8℄ S. J. Tans, M. H. Devoret, H. Dai, A. Thess, R. E.
Smalley, L. J. Geerligs and C. Dekker, Nature
(Lon-don)386,474(1997).
[9℄ J. H. Hafner, C. L. Cheung, T. H. Oosterkamp, and
C.M.Lieber,J.Phys.Chem.B105,743(2001).
[10℄ A. Jorio, A. G. Souza Filho, G. Dresselhaus, M. S.
Dresselhaus,R.Saito,J.H.Hafner,C.M.Lieber,F.M.
Matinaga,M.S.S.Dantas,andM.A.Pimenta,Phys.
Rev.B63,245416(2001).
[11℄ A.G.SouzaFilho,A.Jorio,J.H.Hafner,C.M.Lieber,
R. Saito, M. A. Pimenta, G. Dresselhaus, and M. S.
Dresselhaus,Phys.Rev.B63,241404R(2001).
[12℄ H. Kataura, A. Kimura, Y. Ohtsuka, S. Suzuki,
Y. Maniwa, T.Hanyu,and Y. Ahiba, Jpn. J. Appl.
Phys.37,L616(1998).
[13℄ S.D.M. Brown, P.Corio, A.Marui, M.S.
Dressel-haus, M. A. Pimenta, and K.Kneipp, Phys. Rev. B
Rapid61,R5137(2000).
[14℄ P.-H.Tan, Y. T.ans C.Y.Hu, F.Li, Y. L. Weiand
H.M.Cheng,Phys.Rev.B62,5186(2000).
[15℄ Z. Yu and L. E. Brus, J. Phys. Chem. B 105, 1123
(2001).
[16℄ M. Milnera, J. Kurti, M. Hulman, and H. Kuzmany,
