pubs.acs.org/Langmuir © 2009 American Chemical Society
Catalytic Microcontact Printing on Chemically Functionalized H-Terminated Silicon Alexander A. Shestopalov,† Robert L. Clark,*,‡ and Eric J. Toone*,† †
Department of Chemistry, Duke University, Durham, North Carolina 27708 and ‡Hajim School of Engineering and Applied Sciences, University of Rochester, Rochester, New York 14627 Received September 14, 2009. Revised Manuscript Received October 23, 2009
We report a novel inkless soft lithographic fabrication protocol that permits uniform parallel patterning of hydrogenterminated silicon surfaces using catalytic elastomeric stamps. Pattern transfer is achieved catalytically via reaction between sulfonic acid moieties covalently bound to an elastomeric stamp and a Boc-functionalized SAM grafted to passivated silicon. The approach represents the first example of a soft lithographic printing technique that creates patterns of chemically distinctive SAMs on oxide-free silicon substrates.
Microcontact printing (μCP) is a micro- and nanopatterning technique that uses elastomeric stamps to pattern various solid surfaces with inorganic, organic, and biological molecules.1-3 First reported by Whitesides and co-workers in the early 1990s,4 the technique has become a mainstay of surface science and is routinely used to create micropatterns of self-assembled monolayers (SAMs) of thiols and silanes on metal and oxide surfaces.1-3,5-11 Traditional μCP is restricted to surfaces that undergo rapid irreversible reaction with molecular inks and suffers from several limitations that preclude the accurate replication of submicrometer features. Processes that include diffusive spreading of molecular inks1,6,12 and the deformation of elastomeric stamps13,14 permit only a limited number of organic SAMs to be successfully patterned at resolutions below 500 nm. Moreover, traditional μCP methods are largely restricted to thiol/metal and silane/oxide systems and cannot pattern many important hard substrates such as polycrystalline silicon and germanium. The formation of monolayers on these surfaces usually requires prolonged reaction times and harsh conditions (high temperature, inert atmosphere, and UV irradiation), which are incompatible with the traditional stamp materials and μCP conditions. Recently, we have developed several inkless μCP techniques that transfer pattern from an elastomeric stamp bearing an *To whom correspondence should be addressed. E-mail: eric.toone@ duke.edu;
[email protected]. (1) Perl, A.; Reinhoudt, D. N.; Huskens, J. Adv. Mater. 2009, 21, 2257–2268. (2) Smith, R. K.; Lewis, P. A.; Weiss, P. S. Prog. Surf. Sci. 2004, 75, 1–68. (3) Xia, Y.; Whitesides, G. M. Angew. Chem., Int. Ed. 1998, 37, 550–575. (4) Kumar, A.; Whitesides, G. M. Appl. Phys. Lett. 1993, 63, 2002–4. (5) Biebuyck, H. A.; Larsen, N. B.; Delamarche, E.; Michel, B. IBM J. Res. Dev. 1997, 41, 159–170. (6) Delamarche, E.; Schmid, H.; Bietsch, A.; Larsen, N. B.; Rothuizen, H.; Michel, B.; Biebuyck, H. J. Phys. Chem. B 1998, 102, 3324–3334. (7) Gates, B. D.; Xu, Q.; Stewart, M.; Ryan, D.; Willson, C. G.; Whitesides, G. M. Chem. Rev. 2005, 105, 1171–1196. (8) Michel, B.; Bernard, A.; Bietsch, A.; Delamarche, E.; Geissler, M.; Juncker, D.; Kind, H.; Renault, J. P.; Rothuizen, H.; Schmid, H.; Schmidt-Winkel, P.; Stutz, R.; Wolf, H. IBM J. Res. Dev. 2001, 45, 697–719. (9) Rogers, J. A.; Nuzzo, R. G. Mater. Today 2005, 8, 50–56. (10) Weibel, D. B.; DiLuzio, W. R.; Whitesides, G. M. Nat. Rev. Microbiol. 2007, 5, 209–218. (11) Zhao, X.-M.; Xia, Y.; Whitesides, G. M. J. Mater. Chem. 1997, 7, 1069– 1074. (12) Larsen, N. B.; Biebuyck, H.; Delamarche, E.; Michel, B. J. Am. Chem. Soc. 1997, 119, 3017–3026. (13) Bietsch, A.; Michel, B. J. Appl. Phys. 2000, 88, 4310–4318. (14) Delamarche, E.; Schmid, H.; Michel, B.; Biebuyck, H. Adv. Mater. 1997, 9, 741–746.
Langmuir 2010, 26(3), 1449–1451
Figure 1. Catalytic μCP on Boc-modified SAMs on silicon.
immobilized catalyst to a preformed functionalized SAM.15-17 By employing a biochemical or chemical reaction between a catalyst immobilized on the stamp and the corresponding substrate immobilized as a SAM on gold, the diffusive limitations of traditional μCP are obviated and the accurate replication of pattern features with sub-50-nm edge resolution (limited by the size of gold grains) is possible. Moreover, the use of readily functionalized, rigid polyurethane-acrylate (PU) polymers as stamp materials18,19 circumvents the deformation behavior of PDMS-based stamps, and features with extremely low aspect ratios (
