3D06

C60 – SWNT Based Ultrathin Films Stepwise Grafted onto aSelf-Assembled Monolayer on ITO㧔᧲㇌ᄢⶄว‛ᕈ⎇ⓥ࠮ࡦ࠲࡯‫᧲ޔ‬㇌ᄢℂ 㧕٤ ₺ ᄸⷰ  ᫪ጊᐢᕁ A step-by-step method was used to prepare homogeneous ultrathin films composed of [60]-fullerene (C60) andsingle-walled carbon nanotubes (SWNTs), grafted onto the functional surface of an alkylsilane self-assembledmonolayer (SAM) on an ITO substrate with an ITO–C60–SWNT sequence using amine addition across a doublebond in C60 followed by amidation coupling with acid-functionalized SWNTs. Atomic force microscope andscanning electron microscope images of the resulting composite film showed two-component ball–tube
microstructures with high-density coverage, where C60 was homogeneously distributed in the SWNT forest. The
attachment of SWNTs to the residual amine units in the SAM on the ITO substrate (SAM–ITO) as well as on theC60 sphere results in the C60 molecules in the aggregated clusters being more separately dispersed, which forms a
densely packed composite film as a result of the !–! interaction between the C60 buckyballs and the SWNT walls.
It was found using ferrocene as an internal redox probe that the oxidative and reductive processes at thefilm–solution surface were effectively retarded because of obstruction from the densely packed film and theelectronic effect of SWNT and C60. In addition, the electrochemical properties of C60 on SAM–ITO plates
observed by cyclic voltammetry were significantly modified by chemical anchorage using SWNTs. X-ray
photoelectron spectroscopy (XPS) analysis also indicated the successful grafting of C60 and SWNT. The XPS
chemical shift of the binding energy showed the presence of electronic interactions between C60, SWNT, and ITO
components. AFM images of these thin films are shown in Fig. 1.
Carbon nanotubes and fullerenes, composed of fascinating cylindrical and spherical graphitic structures
respectively, have been studied extensively, with the aim of applying them in many fields as a result of theirunique physical and chemical characteristics. Because carbon nanotubes and fullerenes both show photocurrent
generation effects, the combination of these two carbon allotropes, which may give rise to novel structures andproperties, has been extensively investigated by different methods, such as encapsulation of C60 by single-walledcarbon nanotubes to fabricate the so-called peapods, covalent linkage of C60 clusters to the surfaces of carbon
nanotubes, and physical attachment of C60 derivatives through !–! interactions with the surfaces of SWNTs.
Although there are several examples of combined C60–SWNT ball–tube materials showing photoelectrochemical
behaviors, in which the single-walled carbon nanotubes are treated as electron donors or electron-transfer
networks, the preparation of their composite films, especially those having stable covalent interactions withsubstrates, has attracted less attention.
It is easy to obtain C60 or SWNT films on an opticallytransparent electrode using electrophoretic deposition;
however, for the C60–SWNT two-component film, thistechnique results in a layer-by-layer structure because of thefaster deposition of SWNT than of C60.
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Fig. 1 AFM Images of two different thin layer a) and b)  1!

To increase the lifetime of excitons during the photoexcitation, the bundling of SWNT and the clustering of C60
should be decreased. Therefore, designing a more uniformly distributed C60–SWNT film on a solid substrate isrequired for future research. Encouragingly, an increasing number of different techniques have been developed toprepare ultrathin SWNT or fullerene films besides electrophoretic deposition, including drop-drying from solvent,the Langmuir–Blodgett technique, and self-assembled monolayers (SAMs), which pave the way to fabricating
SWNT- and fullerene-based composite films for use in different types of devices. Compared with other techniques,
the method of chemically SAMs showing high stability is considered an especially promising approach. Recently,
SWNT SAMs have been prepared on a Au substrate by a surface condensation reaction, and also, fullerene C60
molecules as models have been covalently attached to an amine-terminated SAM on a Si(111) substrate. In thelatter case, the experimental XPS data showed the presence of both primary amine groups –NH2 of the SAM onSi(111) and secondary amine groups –NH– during the C60 attachment, which indicates the low reaction efficiencyof this attachment with a considerable number of amine groups left unreacted, supporting the possibility ofintroducing other functional molecules. More recently, a stable electroactive SWNT monolayer endcapped by aconductive oligomer was prepared in our group that showed potential application in electrochemicalnanoarchitectures.1) In view of the intriguing electrochemical properties of C60, introducing C60 in the SWNT film
may be a good way to modify SWNTs. From the viewpoint of morphology control, here, we report a morehomogeneous SWNT–C60 film covalently grafted onto an optically transparent SAM–ITO surface using astep-by-step method, by integration of the above preparations of C60 SAM and SWNT SAM,2) in which theSWNTs were anchored to the unreacted amines of the SAM–ITO as well as to C60 aggregates functionalized byamine groups.

Scheme 1.
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Schematic illustration of thepreparation route to C60–SWNT
ultrathin film grafted on ITO
step-by-step.
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In conclusion, A C60 layer was successfully grafted onto a silanized SAM–ITO surface using amine addition
across a double bond in C60, which showed a loosely packed spherical morphology with a low coverage becauseof the low grafting efficiency. To make the C60 clusters more separately distributed, a step-by-step strategy wasused. After further tethering by a layer of SWNTs functionalized with carboxylic acid, a homogeneous ultrathin
film composed of C60 and SWNT with a high-density coverage was obtained from the AFM images. (Fig. 1) This
uniform ultrathin hybrid film of C60 and SWNT may open a route for applications in electrochemical andphotoelectronic research.
Acknowledgments. We are grateful to the Sumitomo Corporation for donating the HiPco of the SWNTs from CNI(Texas, USA). We thank Mr. R. Osada, Chiba Institute of Technology, Japan, for measuring the FE–SEM and XPS data,and Mr. A. Kogure, Shimadzu Corporation, Japan, for measuring the AFM. We thank Prof. K. Terada, Faculty of
Pharmaceutical Sciences, Toho University, for measuring the NIR, and Mr. M. Fujimoto, JASCO Corporation, Japan,
for measuring the FTIR–RAS.
(1) Wang, Q.; Moriyama, H. Bull. Chem. Soc. Jpn. 2009, 82, 743–749.
(2) Wang, Q.; Moriyama, H. Langmuir 2009, in press.
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