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Nanoscale Chemical Patterns Fabricated by Using Colloidal Lithography and Self-Assembled Monolayers Fre´de´ric A. Denis,† Per Hanarp,‡ Duncan S. Sutherland,‡ and Yves F. Dufreˆne*,† Unite´ de Chimie des interfaces, Universite´ Catholique de Louvain, Croix du Sud 2/18, B-1348 Louvain-la-Neuve, Belgium, and Department of Applied Physics, Chalmers University of Technology, S-412 96 Go¨ teborg, Sweden Received March 30, 2004. In Final Form: August 4, 2004 A method for preparing surfaces with well-defined nanoscale chemical patterns is described. The fabrication strategy involves creating nanoscale Au pits surrounded by a TiO2 matrix, or vice versa, using colloidal lithography, followed by selective functionalization of the Au areas by CH3-terminated alkanethiols. Using AFM force spectroscopy with chemically modified tips (OH, CH3), we show that the nanopatterned surfaces display strong chemical contrast, in the form of hydrophobic CH3 nanopatches surrounded by a hydrophilic TiO2 surface, or vice versa. The nanofabrication approach presented here offers several advantages over existing patterning technologies, among which are easiness (no sophisticated instrumentation is required), versatility (patterns with a range of surface functionalities can be prepared), and the possibility to produce patterns over large areas at low cost.
Introduction The fabrication of surfaces displaying nanoscale variations of chemical properties is an important challenge of current nanotechnology and represents a key toward the development of new applications in biomaterial science and biotechnology,1,2 electronics,3 and catalysis.4,5 A variety of methods have been developed for fabricating nanoscale chemical patterns,6-8 among which are electron lithography,9,10 photolithography,11 replication by stamping,12,13 dip-pen14 and scanning15 probe nanolithography, and molecular self-assembly16 or dewetting.17 * Corresponding author. Phone: (32) 10 47 36 00. Fax: (32) 10 47 20 05. E-mail:
[email protected]. † Universite ´ Catholique de Louvain. ‡ Chalmers University of Technology. (1) Roco, M. C. Curr. Opin. Biotechnol. 2003, 14, 337-346. (2) Curtis, A.; Wilkinson, C. Trends Biotechnol. 2001, 19, 97-101. (3) Hoeppener, S.; Maoz, R.; Cohen, S. R.; Chi, L.; Fuchs, H.; Sagiv, J. Adv. Mater. 2002, 14, 1036-1041. (4) Kasemo, B.; Johansson, S.; Persson, H.; Thormahlen, P.; Zhdanov, V. P. Top. Catal. 2000, 13, 43-53. (5) Barteau, M. A.; Lyons, J. E.; Song, I. K. J. Catal. 2003, 216, 236-245. (6) Xia, Y.; Rogers, J. A.; Paul, K. E.; Whitesides, G. M. Chem. Rev. 1999, 99, 1823-1848. (7) Seebohm, G.; Craighead, H. G. In Quantum Semiconductor Devices and Technologies; Electronic Materials Series, Vol. 6; Kluwer Academic: Boston, 2000; pp 97-138. (8) Chen, Y.; Pe´pin, A. Electrophoresis 2001, 22, 187-207. (9) (a) Golzhauser, A.; Geyer, W.; Stadler, V.; Eck, W.; Grunze, M.; Edinger, K.; Weimann, Th.; Hinze, P. J. Vac. Sci. Technol., B 2000, 18, 3414-3418. (b) Geyer, W.; Stadler, V.; Eck, W.; Zharnikov, M.; Golzhauser, A.; Grunze, M. Appl. Phys. Lett. 1999, 75, 2401-2403. (c) Golzhauser, A.; Eck, W.; Geyer, W.; Stadler, V.; Weimann, T.; Hinze, P.; Grunze, M. Adv. Mater. 2001, 13, 806-809. (10) Pallandre, A.; Glinel, K.; Jonas, A. M.; Nysten, B. Nano Lett. 2004, 4, 365-371. (11) Sun, S.; Chong, K. S. L.; Legget, G. J. J. Am. Chem. Soc. 2002, 124, 2415-2416. (12) Odom, T. W.; Love, J. C.; Wolfe, D. B.; Paul, K. E.; Whitesides, G. M. Langmuir 2002, 18, 5314-5320. (13) Biebuyck, H. A.; Larsen, N. B.; Delamarche, E.; Michel, B. IBM J. Res. Dev. 1997, 41, 159-170. (14) Piner, R. D.; Zhu, J.; Xu, F.; Hong, S.; Mirkin, C. A. Science 1999, 283, 661-663. (15) Liu, G.-Y.; Xu, S.; Qian, Y. Acc. Chem. Res. 2000, 33, 457-466. (16) Cox, J. K.; Eisenberg, A.; Lennox, R. B. Curr. Opin. Colloid Interface Sci. 1999, 4, 52-59. (17) Dupont-Gillain, C. C.; Jaquemart, I. Surf. Sci. 2003, 53, 145154.
Many patterning technologies rely on the use of selfassembled monolayers (SAMs).18 SAMs are formed by the spontaneous chemisorption and vertical close-packed positioning of molecules onto some specific substrata, exposing only the end-chain group(s) at the interface.19 The most widely used SAMs are alkanethiols on gold (and some other noble metals)19,20 and alkylsilanes on hydroxylated surfaces.19,21 SAMs with well-defined and tunable chemistries are increasingly used in basic research to investigate interfacial processes such as protein adsorption22,23 and cellular interactions23,24 and to develop new bioanalytical applications.25,26 There are two important issues to consider regarding nanofabrication methods: (i) precise control of the chemical composition, size, shape, and distribution of the created nanofeatures and (ii) low-cost, high-throughput production of the nanopatterned material. Usually, these two aspects are antagonistic, meaning it is very challenging to produce well-defined nanopatterned surfaces at low cost over large areas. In this context, colloidal lithography has recently emerged as a versatile approach for producing nanoscale features over large surface areas.27 Basically, electrostatic assembly of nanoparticles by random sequential adsorption on smooth surfaces is used to create sparse monolayers of nanoparticles, the characteristic spacing between particles being controlled by the ionic strength of the colloidal solution. The particle size can be varied between (18) Smith, R. K.; Lewis, P. A.; Weiss, P. S. Prog. Surf. Sci. 2004, 75, 1-68. (19) Ulman, A. Chem. Rev. 1996, 96, 1533-1554. (20) (a) Bain, C. D.; Troughton, E. B.; Tao, Y. T.; Evall, J.; Whitesides, G. M.; Nuzzo, R. G. J. Am. Chem. Soc. 1989, 111, 321-335. (b) Bain, C. D.; Whitesides, G. M. Science 1988, 240, 62-63. (21) Sagiv, J. J. Am. Chem. Soc. 1980, 102, 92-98. (22) Ostuni, E.; Chapman, R. G.; Holmlin, R. E.; Takayama, S.; Whitesides, G. M. Langmuir 2001, 17, 5605-5620. (23) Ostuni, E.; Yan, L.; Whitesides, G. M. Colloids Surf., B 1999, 15, 3-30. (24) Mrksich, M. Chem. Soc. Rev. 2000, 29, 267-273. (25) Liedberg, B.; Cooper, J. M. In Immobilized Biomolecules in Analysis; Cass, T., Ligler, F. S., Eds.; Oxford University Press: New York, 1998; pp 55-78. (26) Gooding, J. J.; Mearns, F.; Yang, W.; Liu, J. Electroanalysis 2003, 15, 81-96. (27) Hanarp, P.; Sutherland, D.; Gold, J.; Kasemo, B. Nanostruct. Mater. 1999, 12, 429-432.
10.1021/la049188g CCC: $27.50 © 2004 American Chemical Society Published on Web 09/16/2004
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20 and 500 nm, and surface coverages ranging from 0 to 45% have been demonstrated.28 By combining colloidal lithography with various treatments (metal film precoating or postcoating, substratum heating, ionic etching, and particle removal), different kinds of nanoscale features can be produced including hemispheres, pillars, pits, rings, or cups.29 For instance, using the nanoparticle film as an imprint for metal film vapor-deposition allows one to produce surfaces showing well-defined nanoprotrusions and homogeneous chemistry.30,31 Such nanostructured surfaces are valuable systems to investigate the effect of substratum nanotopography on interfacial events such as protein adsorption30,32 and cell adhesion.33,34 Surfaces showing metallic nanopillars have also been produced and further exploited for producing biologically relevant nanopatterns35 and fabricating planar model catalysts.36 In this paper, we report on the use of colloidal lithography combined with self-assembled monolayers to chemically pattern metal surfaces on the nanoscale. Atomic force microscopy (AFM) imaging and X-ray photoelectron spectroscopy (XPS) are used to characterize the morphology and chemical composition of the patterned surfaces, while the spatial arrangement of the chemical groups is mapped using chemically modified AFM tips. Materials and Methods The first step of the fabrication process involved the adhesion of polymer nanoparticles onto metallic surfaces, as described previously.27-36 To this end, silicon wafers (∼5 cm diameter) coated with a 30 nm thick Au or Ti layer using thermal evaporation were coated with a triple layer precursor film (∼1 nm thick)37 to make them positively charged and immersed in an aqueous suspension (pH ) 6) of polystyrene beads of 107 ( 5 nm diameter, at a concentration of 0.1 wt % (Sulfate Latex, Interfacial Dynamics Corp. (IDC), Portland, OR; 60 s adsorption time,
