NANO LETTERS
A Surface Modification Approach to the Patterned Assembly of Single-Walled Carbon Nanomaterials
2003 Vol. 3, No. 9 1239-1243
Jin Zhu,*,† Masako Yudasaka,† Minfang Zhang,† Daisuke Kasuya,‡ and Sumio Iijima†,‡,§ Carbon Nanotube Project, Japan Science and Technology Corporation, c/o NEC, 34 Miyukigaoka, Tsukuba 305-8501, Japan, NEC Corporation, 34 Miyukigaoka, Tsukuba 305-8501, Japan, and Department of Physics, Meijo UniVersity, Tenpaku-ku, Nagoya 468-8502, Japan Received July 1, 2003; Revised Manuscript Received July 28, 2003
ABSTRACT A surface modification strategy has been employed for the patterned assembly of single-walled carbon nanomaterials onto oxide surfaces. The method relies on distinct molecular recognition properties of different functional groups toward the carbon graphitic structure. The surface modification starts with reactions between bifunctional molecules 1 (with amino and silane groups) and hydroxyl groups on an oxide substrate, generating an amine-covered surface. This is followed by a coupling step where bifunctional molecules 2 (with succinimidyl ester and pyrene groups) react with amines. With one area covered with pyrenyl groups and the other one covered with hydroxyl groups, the patterned assembly of a single layer of single-walled carbon nanohorns (SWNHs) has been demonstrated. The strategy employed herein is quite generic and applicable to a variety of oxide substrates, including quartz, SiO2 layer on Si, and indium tin oxide (ITO). Because silane chemistry is compatible with soft or lift-off lithography, an extension of this methodology to micrometer-scale patterning has been achieved, and a further reduction of the size feature should be possible. In addition, the patterned assembly of single-walled carbon nanotubes (SWNTs) has also been realized. These surface-immobilized structures should open up new possibilities in such areas as nanoelectronics, chemical sensing, field-emission displays, nanotribology, and cell adhesion/biorecognition investigations.
Self-assembly is emerging as a powerful approach to the fabricationofcomplexsupramolecularormaterialsarchitecture.1-4 Monolayer structures of nanoscale building blocks constructed of solid surfaces through such a strategy often display new types of collective functionalities. For example, their uses in surface-enhanced Raman scattering,1 DNA detection,2 and as superlattices displaying interesting physical properties3 have been demonstrated. Nanoscale carbonaceous materials, with applications ranging from field-emission displays and field-effect transistors to gas adsorption and chemical sensors, have attracted much attention recently.5-9 Surface immobilization, allowing easy interfacing and integration of these materials with other material components, is a key to probing some of their fundamental properties further and extending their applications. So far, no method has been available for the directed placement of single-walled carbon nanorhorns (SWNHs) because the catalytic chemical vapor deposition (CCVD) method, which has been well developed for single-walled carbon nanotubes (SWNTs), is * Corresponding author. E-mail:
[email protected]. † Japan Science and Technology Corporation. ‡ NEC Corporation. § Meijo University. 10.1021/nl034459d CCC: $25.00 Published on Web 08/23/2003
© 2003 American Chemical Society
notably absent for this class of materials.9 Herein, we report a surface modification approach to the patterned assembly of a single layer of SWNHs on oxide surfaces. In addition, an extension of this strategy to the immobilization of SWNTs will also be briefly discussed. The employed surface modification strategy is depicted in Scheme 1. The methodology utilizes the strong interaction between the pyrenyl functional group and the sidewall of the single-walled carbon nanomaterials.10 Specifically, it starts with an acid treatment of oxide surfaces, which is used to maximize the number of surface hydroxyl groups.11 After this, bifunctional molecule 1, with an amine on one end and silane on the other side, is used to react with surface hydroxyl groups. This will result in a surface covered with amino functional groups. These amino groups are then reacted with bifunctional molecule 2, which has a succinimidyl ester on one end and pyrene on the other side. The pyrene-covered surface is then reacted with SWNHs in aqueous solutions. Patterning of the surface functional groups could be carried out in either step A or B. With part of the substrate immersed in the solution in step A, a patterned surface, covered with amino and hydroxyl groups, could be generated. Then the
Scheme 1
whole substrate could be kept in the solution in step B, generating pattern I. To generate pattern II, the whole slide was first reacted with a solution of molecule 1 in step A. After this, part of the substrate was immersed in the solution of 2 in step B, and only this part was derivatized by reaction with succinimidyl ester. Soft lithographic methods have been developed for silane chemistry.12 As a result, the proof-ofconcept patterning experiment described here is ready to 1240
be applied at the micrometer or submicrometer scale (vide infra). To prove that the reaction in step A had indeed taken place, a quartz slide produced from this step was immersed in a Au nanoparticle solution, and a pink color was clearly imparted onto the substrate, confirming the presence of amino functional groups on the surface.1c To prove that the reaction in step B was successful, a quartz surface with pattern II Nano Lett., Vol. 3, No. 9, 2003
Figure 1. Assembly of SWNHs onto oxide substrates. Patterned immobilization onto (A) a quartz substrate, (B) a SiO2/Si substrate, and (C) an ITO substrate modified with pattern I (left side covered with SWNHs in all cases) and SEM images of (D) a monolayer of SWNHs on a SiO2/Si substrate, (E) a monolayer of SWNHs on an ITO substrate, and (F) D after thermal treatment at 1000 °C in vacuum. (Bright spots are SWNHs.)
was immersed in an as-grown SWNH solution. SWNHs were immobilized only onto the area functionalized with pyrene (Supporting Information).13 The difference in the interaction strength between the functional groups in pattern I with as-grown SWNHs is also significant enough that a patterned assembly has been realized. Alternatively, if SWNHs were treated in an oxygen atmosphere, resulting in their functionalization with surface polar groups,14 then the interaction strengths between those groups with pyrenes and amines would be so similar that the whole slide modified with pattern II would be covered with SWNHs. However, if a quartz slide with pattern I was used to react with oxidized SWNHs, then patterned immobilization could be achieved (Figure 1A). Because of the aggregate nature of the SWNHs, the structure of the materials on the surface was irregular, and the thickness and roughness were difficult to control. In those applications where SWNH monolayer structures are desirable, a better method for dispersing the materials in H2O, preferably to the singleparticle level, is needed. To this end, oxidized SWNHs were sonicated in H2O for an extended period of time and centrifuged at high speed before the supernatant was filtered through submicrometer filter paper.15 After these three steps, the dispersions of SWNHs are relatively stable for at least several weeks. The patterned assembly of SWNHs with such a dispersion on a SiO2/Si substrate has been realized (Figure Nano Lett., Vol. 3, No. 9, 2003
1B).16 The generality of the methodology was further demonstrated by a patterned immobilization of SWNHs on indium tin oxide (ITO), a conductive substrate (Figure 1C). Characterization of the materials by scanning electron microscopy (SEM) indeed reveals the formation of SWNH monolayer structure on the pyrene areas of SiO2/Si and ITO surfaces (Figure 1D and E). Importantly, soft lithography could be used to derivatize the substrate with molecule 1, and patterned assembly at the micrometer level has thereby been achieved (Supporting Information).17 To immobilize the SWNH layer permanently on oxide surfaces, which is of critical importance for a variety of applications, a more robust interface is necessary. The initial set of experiments was focused on SiO2/Si because the organic barrier between SWNHs and the substrate may be detrimental to such applications as field-emission displays. A SiC interface is critical to the formation of ohmic contact between SWNHs and the substrate. To realize this, a solidstate reaction between SWNHs and the SiO2/Si substrate was carried out at 1000 °C in vacuum.18 Significantly, no change in the monolayer structure was observed (Figure 1F), indicating that SWNH particles were pinned on the surface during the reaction. Raman spectroscopy carried out on this surface confirmed that SWNH graphitic structure remained there (Supporting Information). 1241
Figure 2. Tapping-mode AFM image of immobilized SWNTs on a pyrene-patterned area of a SiO2/Si substrate.
The surface modification strategy could be applied to the patterned assembly of SWNTs, which is important for their potential applications in many areas. Although the CCVD method has been successfully used for the direct placement of SWNTs and the construction of electronic components,6d in applications where postsynthesis purification or manipulation is necessary or desirable, the self-assembly strategy developed here provides an attractive alternative. An initial experiment was carried out on purified HiPco SWNTs.19 Unlike SWNHs, HiPco SWNTs form unstable dispersions in H2O, making their immobilization onto the substrate relatively difficult. To overcome this, a sodium dodecyl sulfate surfactant (SDS) was used to stabilize the dispersion. Even in the presence of SDS, the patterned assembly of SWNTs was successful, suggesting that the surfactant did not significantly interfere with the interaction between pyrenyl groups and SWNT graphitic basal planes.20 Characterization of the surface with atomic force microscopy (AFM) confirmed that SWNTs could be observed only in the area functionalized with pyrenyl groups. A representative tapping-mode AFM image of immobilized SWNTs on SiO2/ Si is shown in Figure 2. Although not demonstrated, patterned alignment of SWNTs onto oxide substrates should be possible with the application of an electrical field during the surface immobilization process.21 In summary, a general methodology for the patterned assembly of single-walled carbon nanomaterials onto oxide surfaces has been demonstrated. These surface-immobilized structures should open up new possibilities in the fields of nanoelectronics, chemical sensing, field-emission displays, nanotribology, and cell adhesion/biorecognition investigations. Supporting Information Available: Patterned immobilization of as-grown SWNHs onto a modified quartz substrate and oxidized SWNHs onto a modified Si/SiO2 substrate. 1242
Raman spectroscopy of a SWNH monolayer on SiO2/Si. This material is available free of charge via the Internet at http:// pubs.acs.org. References (1) (a) Freeman, R. G.; Grabar, K. C.; Allison, K. J.; Bright, R. M.; Davis, J. A.; Guthrie, A. P.; Hommer, M. B.; Jackson, M. A.; Smith, P. C.; Walter, D. G.; Natan, M. J. Science 1995, 267, 1629. (b) Grabar, K. C.; Smith, P. C.; Musick, M. D.; Davis, J. A.; Walter, D. G.; Jackson, M. A.; Guthrie, A. P.; Natan, M. J. J. Am. Chem. Soc. 1996, 118, 1148. (c) Musick, M. D.; Pena, D. J.; Botsko, S. L.; McEvoy, T. M.; Richardson, J. N.; Natan, M. J. Langmuir 1999, 15, 844. (2) (a) Cao, Y. C.; Jin, R.; Mirkin, C. A. Science 2002, 297, 1536. (b) Taton, T. A.; Mirkin, C. A.; Letsinger, R. L. Science 2000, 289, 1757. (c) Taton, T. A.; Lu, G.; Mirkin, C. A. J. Am. Chem. Soc. 2001, 123, 5164. (d) Taton, T. A.; Mucic, R. C.; Mirkin, C. A.; Letsinger, R. L. J. Am. Chem. Soc. 2000, 122, 6305. (3) (a) Black, C. T.; Murray, C. B.; Sandstrom, R. L.; Sun, S. Science 2000, 290, 1131. (b) Sun, S.; Murray, C. B.; Weller, D.; Folks, L.; Moser, A. Science 2000, 287, 1989. (4) (a) Gittins, D. I.; Bethell, D.; Nichols, R. J.; Schiffrin, D. J. AdV. Mater. 1999, 11, 737. (b) Brust, M.; Bethel, D.; Kiely, C. J.; Schiffrin, D. J. Langmuir 1998, 14, 5425. (5) (a) Iijima, S. Nature 1991, 354, 56. (b) Iijima, S.; Ichihashi, T. Nature 1993, 363, 603. (6) (a) Iijima, S. Physica B 2002, 323, 1. (b) Ouyang, M.; Huang, J.; Lieber, C. M. Acc. Chem. Res. 2002, 35, 1018. (c) Dai, H.; Kong, J.; Zhou, C.; Franklin, N.; Tombler, T.; Cassell, A.; Fan, S.; Chapline, M. J. Phys. Chem. B 1999, 103, 11246. (d) Dai, H. Acc. Chem. Res. 2002, 35, 1035. (e) Carbon Nanotubes: Synthesis, Structure, Properties, and Applications; Dresselhaus, M. S.; Dresselhaus, G.; Avouris, Ph., Eds.; Springer-Verlag: Berlin, Germany, 2001. (7) (a) Jo, S. H.; Tu, Y.; Huang, Z. P.; Carnahan, D. L.; Wang, D. Z.; Ren, Z. F. Appl. Phys. Lett. 2003, 82, 3520. (b) Wind, S.; Appenzeller, J.; Martel, R.; Derycke, V.; Avouris, Ph. Appl. Phys. Lett. 2002, 80, 3817. (8) (a) Liu, C.; Fan, Y. Y.; Liu, M.; Cong, H. T.; Cheng, H. M.; Dresselhaus, M. S. Science 1999, 286, 1127. (b) Kong, J.; Franklin, N. R.; Zhou, C.; Chapline, M. G.; Peng, S.; Cho, K.; Dai, H. Science 2000, 287, 622. (9) (a) Iijima, S.; Yudasaka, M.; Yamada, R.; Bandow, S.; Suenaga, K.; Kokai, F.; Takahashi, K. Chem. Phys. Lett. 1999, 309, 165. (b) Kasuya, D.; Yudasaka, M.; Takahashi, K.; Kokai, F.; Iijima, S. J. Phys. Chem. B 2002, 106, 4947. (c) Nisha, J. A.; Yudasaka, M.; Nano Lett., Vol. 3, No. 9, 2003
(10) (11)
(12) (13) (14)
Bandow, S.; Kokai, F.; Takahashi, K.; Iijima, S. Chem. Phys. Lett. 2000, 328, 381. (d) Bekyarova, E.; Kaneko, K.; Yudasaka, M.; Murata, K.; Kasuya, D.; Iijima, S. AdV. Mater. 2002, 14, 973. (e) Magnie, A.; Kasuya, D.; Yudasaka, M.; Iijima, S. Unpublished results. For the use of 2 in the immobilization of proteins onto the side walls of carbon nanotubes, see Chen, R. J.; Zhang, Y.; Wang, D.; Dai, H. J. Am. Chem. Soc. 2001, 123, 3838. (a) For a procedure to modify the oxide slides with silane molecules, see Chrisey, L. A.; Lee, G. U.; O’Ferrall, C. E. Nucleic Acids Res. 1996, 24, 3031. (b) Reaction step A follows the procedure in the above reference. For step B, typically the substrate is immersed in a mixed solution of 500 µL of sodium tetraborate aqueous buffer (0.1 M, pH 8.5) and 400 µL of dimethylforamide with 1 mg of 2. The concentration of the aqueous solution of carbonaceous materials 3 in step C could be varied over a wide range without affecting the surface immobilization process. The reaction in step B typically takes 12 h, and the surface assembly in step C is finished within 2 h for both SWNHs and SWNTs. For example, Pompe, T.; Fery, A.; Herminghaus, S.; Kriele, A.; Lorenz, H.; Kotthaus, J. P. Langmuir 1999, 15, 2398. The optical characterization of the surface functionalization process is currently underway and will be reported in due course. (a) Oxygen treatment is critical for opening nanosized windows on SWNHs and for such applications as gas adsorption. (b) The presence of polar functional groups is supported by the evolution of oxygenrelated species H2O, CO2, CO after O2 treatment from the thermogravimetric-mass spectrum analysis.
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(15) Typical experimental conditions for dispersing oxidized SWNHs are sonication for 1 h, centrifugation at 10 000 rpm for 5 min, and filtration through a 0.45-µm filter paper. (16) SWNHs could barely be observed in the hydroxyl area of the substrate (ref Figure S2B). (17) A pipet was used to transfer the solution of 1 along an open end of the microchannels of a poly(dimethylsiloxane) stamp, and the reaction was allowed to proceed for 20 min. The rest of the procedure is the same as that described previously. (18) Zhang, Y.; Ichihashi, T.; Landree, E.; Nihey, F.; Iijima, S. Science 1999, 285, 1719. (19) (a) Nikolaev, P.; Bronikowski, M. J.; Bradley, R. K.; Rohmund, F.; Colbert, D. T.; Smith, K. A.; Smalley, R. E. Chem. Phys. Lett. 1999, 313, 91. (b) HiPco SWNTs were purified through a two-step procedure: (1) heating in an O2 atmosphere at 300 °C and (2) removal of metal catalysts in HCl at 60 °C for 2 h. After that, SWNTs were washed with a substantial amount of H2O and cut into short strands with ultrasonication. (20) Because of the presence of the SDS surfactant and the high aspect ratio of SWNTs, compared with that of SWNHs, the process of the surface immobilization of SWNTs is different, and the surface density of SWNTs is not as high as that of SWNHs. (The assembly of both SWNHs and SWNTs is finished within 2 h, and the surface density is not increased afterwards.) (21) Zhang, Y.; Chang, A.; Cao, J.; Wang, Q.; Kim, W.; Li, Y.; Morris, N.; Yenilmez, E.; Kong, J.; Dai, H. Appl. Phys. Lett. 2001, 79, 3155.
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