Templated Assembly of Semiconductor and Insulator Nanoparticles at the Surface of Covalently Modified Multiwalled Carbon Nanotubes Toby Sainsbury and Donald Fitzmaurice* Department of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland Received May 28, 2004. Revised Manuscript Received July 12, 2004 Reported is the preparation and characterization of phosphonic acid-modified and alkoxy silane-modified multiwalled carbon nanotubes (MWCNTs). Also reported is the use of these modified MWCNTs to template the assembly of titanium dioxide and silica nanoparticles, respectively. Some potential applications of these findings are considered. Introduction The demand for integrated circuits that will allow information to be processed at even faster speeds is as great as ever. This is despite the fact that scaling has led to a doubling of the density of the wires and switches that comprise such circuits every 18 months for 4 decades, giving rise to Moore’s Law. 1 While it is expected that Moore’s Law will continue to hold true for another decade, it is not expected that it will hold true there- after. 2 In order for Moore’s Law to hold true even for another decade, major advances in existing fabrication and materials technologies will be required. Specifically, the development of new short wavelength light sources, masks and resists, and materials with high and low dielectric constants are all requirements. The scientific and engineering advances, not to mention the invest- ment, which will be required to secure these advances, are very significant. Even assuming these advances can be secured, and the sizes of the wires and switches that comprise integrated circuits be reduced still further, they will eventually approach sizes where the materials of which they are composed no longer exhibit bulk properties, but exhibit properties that are dominated by surface and confinement effects. For these reasons it is necessary to contemplate alternative fabrication and materials technologies that offer the prospect of still smaller wires and switches at lower cost and new circuit architectures that can ac- commodate or even exploit the novel properties exhib- ited by nanoscale components. When considering alternative fabrication technolo- gies, one is immediately attracted to the self-assembly in solution and the self-organization at technologically relevant substrates of nanoscale architectures. 3 When considering alternative materials technologies, one is immediately attracted to high information content molecules, 4 and to the growing number of nanomaterials that are becoming available. 5 It is noted that there are a growing number of reports that demonstrate the potential of this and related approaches. 6-10 One particularly active area has been research into the use of carbon nanotubes (CNTs) as wires and as nanoscale building blocks for switches. Accordingly, there are a growing number of reports that describe the structure-dependent electrical properties of CNTs and that demonstrate their use as wires and as nanoscale building blocks for switches. 11 A limitation of CNTs, however, is that their electrical properties are very sensitive to the local environment, to the extent that the local environment alters their physical or chemical properties. For example, the pu- rification or modification of CNTs may lead to the introduction of defects, which alter the structure of the CNT and their electronic properties. 12 It is in this context that we have explored the potential of CNTs, not as wires, but as templates for the self-assembly of wires. * To whom correspondence should be addressed. E-mail: donald- .fitzmaurice@ucd.ie. (1) Moore, G. E. Electronics 1965, 38. (2) International Technology Roadmap for Semiconductors. http:// public.itrs.net/ (2003). (3) Parviz, B.; Ryan, D.; Whitesides, D. IEEE Trans. Adv. Packag. 2003, 26, 233. (4) Niemeyer, C. Angew. Chem., Int. Ed. 2001, 40, 4128. (5) Parak, W. J.; Gerion, D.; Pellegrino, T.; Zanchet, D.; Micheel, C.; Williams, S. C.; Boudreau, R.; Le Gros, M.; Larabell, C.; Alivisatos, P. Nanotechnology 2003, 14, 15. (6) Braun, E.; Eichem, Y.; Sivan, U.; Ben-Yoseph, G. Nature 1998, 391, 775. (7) Collier, C.; Wong, E.; Belohradsky, M.; Raymo, F.; Stoddart, F.; Kuekes, P.; Williams, R.; Heath, J. Science 1999, 285, 391. (8) Keren, K.; Krueger, M.; Gilad, R.; Ben-Yoseph, G.; Sivan, U.; Braun, E. Science 2002, 297, 72. (9) Yan, H.; Park, S.; Finkelstein, G.; Reif, J.; La Bean, T. Science 2003, 301, 1882. (10) Xin, H.; Woolley, A. T. J. Am. Chem. Soc. 2003, 125, 8710. (11) (a) Aviram, A.; Ratner, M. A. Chem. Phys. Lett. 1974, 29, 277. (b) Dai, H.; Wong, E. W.; Lieber, C. M. Science 1996, 272, 523. (c) Bachtold, A.; Henny, M.; Tarrier, C.; Strunk, C.; Scho ¨nenberger, C.; Salvetat, J.-P.; Bonard, J.-M.; Forro ´ , L. Appl. Phys. Lett. 1998, 73, 274. (d) Ebbesen, T. W.; Lezec, H. J.; Hiura, H.; Bennett, J. W.; Ghaemi, H. F.; Thio, T. Nature 1996, 382, 54. (e) Frank, S.; Poncharal, P.; Wang, Z. L.; de Heer, W. A. Science 1998, 280, 1744. (f) Tans, S. J.; Devoret, M. H.; Dai, H.; Thess, A.; Smalley, R. E.; Geerligs, L. J.; Dekker, C. Nature 1997, 386, 474. (g) Collins, P. G.; Arnold, M. S.; Avouris, P. Science 2001, 292, 706. (h) Tans, S. J.; Verschueren, A. R. M.; Dekker, C. Nature 1998, 393, 49. (i) Fuhrer, M. S.; Nyga ˚ rd, J.; Shih, L.; Forero, M.; Yoon, Y. G.; Mazzoni, M. S. C.; Choi, H. J.; Ihm, J.; Louie, S. G.; Zettl, A.; McEuen, P. L. Science 2000, 288, 494. (j) Collins, P. G.; Bradley, K.; Ishigami, M.; Zettl, A. Science 2000, 287, 1801. (k) Kong, J.; Franklin, N. R.; Zhou, C.; Chapline, M. G.; Peng, S.; Cho, K.; Dai, H. Science 2000, 287, 622. 3780 Chem. Mater. 2004, 16, 3780-3790 10.1021/cm049151h CCC: $27.50 © 2004 American Chemical Society Published on Web 08/27/2004