pubs.acs.org/Langmuir © 2010 American Chemical Society
Nanolithography of Single-Layer Graphene Oxide Films by Atomic Force Microscopy Gang Lu,† Xiaozhu Zhou,† Hai Li,† Zongyou Yin,† Bing Li,† Ling Huang,‡ Freddy Boey,†,§ and Hua Zhang*,†,§ † School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore, ‡School of Chemical and Biomedical Engineering, Nanyang Technological University, 70 Nanyang Drive, Singapore 637457, Singapore, and §Centre for Biomimetic Sensor Science, Nanyang Technological University, 50 Nanyang Drive, Singapore 637553, Singapore
Received March 17, 2010. Revised Manuscript Received April 4, 2010 Atomic force microscopy-based nanolithography is used to generate the single-layer graphene oxide (GO) patterns on Si/SiO2 substrates. In this process, a Si tip is used to scratch GO films, resulting in GO-free trenches. Using this method, various single-layer GO patterns such as gaps, ribbons, squares, triangles, and zigzags can be easily fabricated. By using the GO patterns as templates, the hybrid GO-Ag nanoparticle patterns were obtained. Our study provides a flexible, simple, convenient method for generating GO patterns on solid substrates, which could be useful for graphene materialbased device applications.
Graphene, a single layer of graphite, has been widely studied in recent years because of its unique electronic properties and potential applications in the fields of electronics and sensing.1-8 Among its applications, specifically in electronics, it is of importance to obtain patterned graphene. Until now, many methods8-19 such as the “scratching” method,8 plasma etching,9 microcontact printing,10 dip-pen nanolithography (DPN),11 photolithography,12 e-beam lithography,13 nanosphere lithography,14 and soft transfer printing15 have been used to pattern graphene-related materials. Alternatively, the patterned catalyst *Author to whom correspondence should be addressed. Tel: þ6567905175. Fax: þ65-67909081. E-mail:
[email protected], hzhang166@ yahoo.com. Website: http://www.ntu.edu.sg/home/hzhang/. (1) Castro Neto, A. H.; Guinea, F.; Peres, N. M. R.; Novoselov, K. S.; Geim, A. K. Rev. Mod. Phys. 2009, 81, 109–162. (2) Enoki, T.; Kobayashi, Y.; Fukui, K. I. Int. Rev. Phys. Chem. 2007, 26, 609– 645. (3) Geim, A. K. Science 2009, 324, 1530–1534. (4) Ostrovsky, P. M.; Gornyi, I. V.; Mirlin, A. D. Phys. Rev. B 2006, 74, 235443. (5) Geim, A. K.; Novoselov, K. S. Nat. Mater. 2007, 6, 183–191. (6) Yin, Z. Y.; Wu, S. X.; Zhou, X. Z.; Huang, X.; Zhang, Q. C.; Boey, F.; Zhang, H. Small 2010, 6, 307–312. (7) Wang, Z. J.; Zhou, X. Z.; Zhang, J.; Boey, F.; Zhang, H. J. Phys. Chem. C 2009, 113, 14071–14075. (8) Li, B.; Cao, X. H.; Ong, H. G.; Cheah, J. W.; Zhou, X. Z.; Yin, Z. Y.; Li, H.; Wang, J.; Boey, F.; Huang W.; Zhang, H. Adv. Mater.; DOI: 10.1002/ adma.201000736. (9) Zhou, X. Z.; Lu, G.; Qi, X. Y.; Wu, S. X.; Li, H.; Boey, F.; Zhang, H. J. Phys. Chem. C 2009, 113, 19119–19122. (10) Li, H.; Zhang, J.; Zhou, X. Z.; Lu, G.; Yin, Z. Y.; Li, G. P.; Wu, T.; Boey, F.; Venkatraman, S. S.; Zhang, H. Langmuir; DOI: 10.1021/la9039144. (11) Li, B.; Lu, G.; Zhou, X. Z.; Cao, X. H.; Boey, F.; Zhang, H. Langmuir 2009, 25, 10455–10458. (12) Tung, V. C.; Allen, M. J.; Yang, Y.; Kaner, R. B. Nat. Nanotechnol. 2009, 4, 25–29. (13) Duan, H. G.; Xie, E. Q.; Han, L.; Xu, Z. Adv. Mater. 2008, 20, 3284–3288. (14) Cong, C. X.; Yu, T.; Ni, Z. H.; Liu, L.; Shen, Z. X.; Huang, W. J. Phys. Chem. C 2009, 113, 6529–6532. (15) Allen, M. J.; Tung, V. C.; Gomez, L.; Xu, Z.; Chen, L. M.; Nelson, K. S.; Zhou, C. W.; Kaner, R. B.; Yang, Y. Adv. Mater. 2009, 21, 2098–2102. (16) Staley, N.; Wang, H.; Puls, C.; Forster, J.; Jackson, T. N.; McCarthy, K.; Clouser, B.; Liu, Y. Appl. Phys. Lett. 2007, 90, 143518. (17) Meyer, J. C.; Girit, C. O.; Crommie, M. F.; Zettl, A. Appl. Phys. Lett. 2008, 92, 123110. (18) Tapaszto, L.; Dobrik, G.; Lambin, P.; Biro, L. P. Nat. Nanotechnol. 2008, 3, 397–401. (19) Song, L.; Ci, L. J.; Gao, W.; Ajayan, P. M. ACS Nano 2009, 3, 1353–1356.
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was used to directly grow patterned graphene in CVD.20 Recently, nanowires have been used as etching masks to fabricate graphene nanoribborns.21 In addition, metal and nonmetal nanoparticles were used to tailor graphene at elevated temperature.22-25 In the last few decades, scanning probe lithography (SPL)26-39 has been widely used for the fabrication of patterns on various substrates from the micrometer to nanometer scale. As one kind of SPL method, local anodic oxidation (LAO) lithography has (20) Lee, Y. H.; Lee, J. H. Appl. Phys. Lett. 2009, 95, 143102. (21) Bai, J. W.; Duan, X. F.; Huang, Y. Nano Lett. 2009, 9, 2083–2087. (22) Campos, L. C.; Manfrinato, V. R.; Sanchez-Yamagishi, J. D.; Kong, J.; Jarillo-Herrero, P. Nano Lett. 2009, 9, 2600–2604. (23) Gao, L. B.; Ren, W. C.; Liu, B. L.; Wu, Z. S.; Jiang, C. B.; Cheng, H. M. J. Am. Chem. Soc. 2009, 131, 13934–13936. (24) Datta, S. S.; Strachan, D. R.; Khamis, S. M.; Johnson, A. T. C. Nano Lett. 2008, 8, 1912–1915. (25) Severin, N.; Kirstein, S.; Sokolov, I. M.; Rabe, J. P. Nano Lett. 2009, 9, 457– 461. (26) Giesbers, A. J. M.; Zeitler, U.; Neubeck, S.; Freitag, F.; Novoselov, K. S.; Maan, J. C. Solid State Commun. 2008, 147, 366–369. (27) Weng, L. S.; Zhang, L. Y.; Chen, Y. P.; Rokhinson, L. P. Appl. Phys. Lett. 2008, 93, 093107. (28) Masubuchi, S.; Ono, M.; Yoshida, K.; Hirakawa, K.; Machida, T. Appl. Phys. Lett. 2009, 94, 082107. (29) (a) Ginger, D. S.; Zhang, H.; Mirkin, C. A. Angew. Chem., Int. Ed. 2004, 43, 30–45. (b) Zhang, H.; Amro, N. A.; Disawal, S.; Elghanian, R.; Shile, R.; Fragala, J. Small 2007, 3, 81–85. (c) Li, B.; Goh, C. F.; Zhou, X. Z.; Lu, G.; Tantang, H.; Chen, Y. H.; Xue, C.; Boey, F. Y. C.; Zhang, H. Adv. Mater. 2008, 20, 4873–4878. (d) Zhou, X. Z.; Chen, Y. H.; Li, B.; Lu, G.; Boey, F. Y. C.; Ma, J.; Zhang, H. Small 2008, 4, 1324– 1328. (e) Huo, F. W.; Zheng, Z. J.; Zheng, G. F.; Giam, L. R.; Zhang, H.; Mirkin, C. A. Science 2008, 321, 1658–1660. (30) (a) Garno, J. C.; Yang, Y. Y.; Amro, N. A.; Cruchon-Dupeyrat, S.; Chen, S. W.; Liu, G. Y. Nano Lett. 2003, 3, 389–395. (b) Liu, G. Y.; Xu, S.; Qian, Y. L. Acc. Chem. Res. 2000, 33, 457–466. (31) Kenseth, J. R.; Harnisch, J. A.; Jones, V. W.; Porter, M. D. Langmuir 2001, 17, 4105–4112. (32) Kramer, S.; Fuierer, R. R.; Gorman, C. B. Chem. Rev. 2003, 103, 4367– 4418. (33) Ross, C. B.; Sun, L.; Crooks, R. M. Langmuir 1993, 9, 632–636. (34) Piner, R. D.; Zhu, J.; Xu, F.; Hong, S. H.; Mirkin, C. A. Science 1999, 283, 661–663. (35) Lee, K. B.; Park, S. J.; Mirkin, C. A.; Smith, J. C.; Mrksich, M. Science 2002, 295, 1702–1705. (36) Zhang, H.; Chung, S. W.; Mirkin, C. A. Nano Lett. 2003, 3, 43–45. (37) Xu, S.; Miller, S.; Laibinis, P. E.; Liu, G. Y. Langmuir 1999, 15, 7244–7251. (38) Amro, N. A.; Xu, S.; Liu, G. Y. Langmuir 2000, 16, 3006–3009. (39) Liu, J. F.; Cruchon-Dupeyrat, S.; Garno, J. C.; Frommer, J.; Liu, G. Y. Nano Lett. 2002, 2, 937–940.
Published on Web 04/06/2010
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Figure 1. (A) SEM and (B) AFM images of single-layer GO films on Si/SiO2 substrates fabricated by the Langmuir-Blodgett method.
been used to fabricate graphene nanoribbons.26-28 Although the methods mentioned above have shown the capability to pattern graphene, it is still necessary and urgent to develop a simple, convenient, flexible method to pattern single-layer graphene from the micrometer to nanometer scale on various substrates. Herein, we used the atomic force microscopy (AFM)-based lithographic method to fabricate patterns of graphene oxide (GO) on Si/SiO2 surfaces. Importantly, this method is very flexible and can be used to fabricate GO patterns on various substrates. After the GO sheets were synthesized using the modified Hummers method from graphite powder,40-44 they were assembled onto a Si/SiO2 substrate using the Langmuir-Blodgett (LB) technique.45 Figure 1 shows the obtained single-layer GO films on Si/SiO2. The height of the GO film, ca. 1.2 nm, was measured by AFM (Figure 1B), confirming that a single-layer GO film was obtained, which is consistent with our previous reports. 9,43 Note that few double-layer GO sheets existed on Si/SiO2, arising from the irreversible stacking of the size-mismatched GO sheets as a result of face-to-face interactions during the LB process.45 By using the NSCRIPTOR DPN system (Nanoink Inc., IL),46 the GO patterns can be easily generated in contact mode. The Si AFM tip was used in the experiments. The force between the Si AFM tip and substrate, used to scratch the GO film, can be easily adjusted by changing the set point of the NSCRIPTOR DPN system (2 to 4 V). At a set point of 3 V, when the Si tip moves on the substrate, the GO film is scratched, resulting in a GO-free gap. If a smaller force (set point=1 V) is used, the GO film cannot be completely scratched whereas a larger force (set point = 5 V) will destroy the Si/SiO2 substrate. Note that the set-point value might be different if another AFM and a different AFM tip are used. A series of experiments need to be studied in order to get the optimized experimental conditions for scratching the GO film. Our method shows the flexibility and convenience for the fabrication of different kinds of GO patterns. For example, GO gaps as narrow as 70 nm can be easily generated (Figure 2). Also, it can be been used to fabricate GO ribbons. By controlling the spacing between the parallel scratching lines, GO ribbons with (40) Hummers, W. S.; Offeman, R. E. J. Am. Chem. Soc. 1958, 80, 1339–1339. (41) Stankovich, S.; Piner, R. D.; Chen, X. Q.; Wu, N. Q.; Nguyen, S. T.; Ruoff, R. S. J. Mater. Chem. 2006, 16, 155–158. (42) Gilje, S.; Han, S.; Wang, M.; Wang, K. L.; Kaner, R. B. Nano Lett. 2007, 7, 3394–3398. (43) Zhou, X. Z.; Huang, X.; Qi, X. Y.; Wu, S. X.; Xue, C.; Boey, F. Y. C.; Yan, Q. Y.; Chen, P.; Zhang, H. J. Phys. Chem. C 2009, 113, 10842–10846. (44) Li, D.; Muller, M. B.; Gilje, S.; Kaner, R. B.; Wallace, G. G. Nat. Nanotechnol. 2008, 3, 101–105. (45) Cote, L. J.; Kim, F.; Huang, J. X. J. Am. Chem. Soc. 2009, 131, 1043–1049. (46) Haaheim, J.; Eby, R.; Nelson, M.; Fragala, J.; Rosner, B.; Zhang, H.; Athas, G. Ultramicroscopy 2005, 103, 117–132.
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Figure 2. AFM image of GO nanogaps fabricated by AFM-based lithography.
Figure 3. AFM images of fabricated GO ribbons with widths of (A) 110 and (B) 56 nm. (Inset in A) Height profile of GO ribbons. (C) AFM image of GO-Ag nanoparticle composite patterns.
different widths were fabricated. Figure 3A,B shows the AFM images of thus-fabricated GO ribbons with widths of 110 and 56 nm, respectively. Different from our scratching method, LAO lithography26-28 is another SPL-based method used for the fabrication of graphene nanoribbons. When LAO lithography is used, the substrate needs to be conductive in order to generate the current between the AFM tip and the substrate when a bias is applied. The area of the graphene sheets in contact with the AFM tip was oxidized, and a bumpy structure was formed on both side of the trench generated by the AFM tip. However, in our experiment, the choice of substrates is flexible and it is not necessary to use conductive substrates, which is one of the advantages of our method. Besides ribbons, other GO pattern shapes can also be fabricated using our method. Figure 4 shows the fabricated GO squares, triangles, and zigzags. This further demonstrates that our method is flexible and convenient for fabricating GO patterns with various shapes. The obtained GO patterns can be reduced by many methods, such as hydrazine vapor reduction9,43,47 and hightemperature annealing48,49 to achieve single-layer rGO patterns. Our method used for the fabrication of single-layer GO/rGO patterns might be beneficial to the fabrication of graphene-based electronics. (47) Gomez-Navarro, C.; Weitz, R. T.; Bittner, A. M.; Scolari, M.; Mews, A.; Burghard, M.; Kern, K. Nano Lett. 2007, 7, 3499–3503. (48) Wang, X.; Zhi, L. J.; Mullen, K. Nano Lett. 2008, 8, 323–327. (49) Becerril, H. A.; Mao, J.; Liu, Z.; Stoltenberg, R. M.; Bao, Z.; Chen, Y. ACS Nano 2008, 2, 463–470.
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Figure 4. SEM images of fabricated GO patterns. (A) Squares, (B) triangles, and (C) zigzags. (Inset) Corresponding AFM images.
As known, Ag nanoparticles can grow on a GO surface by immersing a single-layer GO film adsorbed on a solid substrate into a AgNO3 aqueous solution at a certain temperature.9,43 After the fabricated GO patterns on Si/SiO2 reacted with AgNO3 in an aqueous solution at 75 °C for half an hour, the patterns of Ag nanoparticles were obtained (Figure 3C), which is consistent with our previous reports.9,43 This method can also be used to generate other GO-metal nanoparticle patterns on solid substrates. Thuspatterned GO-metal nanoparticle composites might have applications in many fields, such as electronics, thermal conductivity, catalysis, biosensing, and so forth. In summary, a flexible, convenient, simple AFM-based lithography method was used to fabricate GO patterns on Si/SiO2. By using a Si tip to scratch the single-layer GO film on a substrate, various patterns with different shapes and dimensions were fabricated. Because of the flexibility and convenience of this method, it might be useful in fabricating graphene-based electronic devices.
Experimental Section Synthesis of Graphene Oxide (GO) and Its Assembly on a Si/SiO2 Substrate by the Langmuir-Blodgett (LB) Technique. Graphite oxide was synthesized from natural graphite by
the modified Hummers method.40-44 Synthesized GO was redispersed in a mixed solution of water and methanol (1:5) and assembled on a Si/SiO2 substrate using the LB method.45 GO
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solution (8-12 mL) was dropped at a rate of 100 μL/min onto a water surface in the LB trough. After compression of the GO film on the water surface, a freshly piranha-solution-cleaned Si/SiO2 substrate was vertically dipped into the solution and then slowly pulled out (2 mm/min) to form single-layer GO film on the Si/SiO2 substrate.
Generation of Single-Layer GO Patterns by AFM-Based Lithography. The assembled single-layer GO film on Si/SiO2 via
the LB technique was heated and maintained at 60 °C for more than 10 h. The GO film was scratched on the NSCRIPTOR DPN system (Nanoink Inc., IL)46 in contact mode by using a Si AFM tip (spring constant, 42 N/m; resonance frequency, 320 kHz). The set point was varied to control the force between the Si tip and the substrate. All patterning experiments were carried out under ambient conditions. Characterization. All AFM images were obtained by using Dimension 3100 (Veeco, Santa Barbara, CA) in tapping mode with a Si tip (Veeco; spring constant, 42 N m-1; resonance frequency, 320 kHz) under ambient conditions. A JEOL JSM6700 field-emission scanning electron microanalyzer (JEOL Ltd., Tokyo, Japan) was used to obtain scanning electron microscopy (SEM) images at an accelerating voltage of 5 kV.
Acknowledgment. This work was supported by a start-up grant from NTU, AcRF Tier 1 (RG 20/07) from MOE, CRP (NRF-CRP2-2007-01) from NRF, an A*STAR SERC grant (no. 092 101 0064) from A*STAR, and the Centre for Biomimetic Sensor Science at NTU, Singapore.
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