pubs.acs.org/Langmuir © 2010 American Chemical Society
Formation of Multilayer Ultrathin Assemblies Using Chemical Lithography Chuanzhen Zhou and Amy V. Walker* Department of Chemistry and Center for Materials Innovation, Washington University in St. Louis, Campus Box 1134, One Brookings Drive, St. Louis, Missouri 63130 Received December 28, 2009. Revised Manuscript Received March 3, 2010 Ultrathin complex multilayer structures have many potential applications in molecular and organic electronics, sensing, biotechnology and other areas. Reported here is a method by which to construct multifunctional, multilayer, patterned structures, using alkanethiolate SAMs adsorbed on Au, UV photopatterning, and chemoselective covalent bond formation. We demonstrate that amide coupling is efficient for producing multilayer structures on -COOHterminated SAMs, while oxime coupling is efficient for producing multilayer structures on -CHO-terminated SAMs. Reaction yields obtained are ∼67% and ∼84% for the coupling of the first layer (bilayer formation) for amide and oxime coupling, respectively. Subsequent adlayer formation occurs with ∼100% yield in both cases. The resulting adlayers are chemically robust and are suitable for subsequent chemical processing. Finally, both chemistries are used to produce a complex multilayer structure atop a UV photopatterned SAM. The resulting construct is well-defined and has the same lateral resolution as the photopatterned SAM substrate. The method demonstrated here is synthetically flexible and allows for the assembly of functionally complex surfaces and, in principle, the incorporation of biomolecules and metals.
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Published on Web 04/19/2010
DOI: 10.1021/la904891h
8441
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many ways to pattern SAMs including UV photopatterning,42-48 electron beam lithography,49-55 nanoimprinting,56 dip pen nanolithography,56-58 and microcontact printing.56,59 The assembly of multilayers on SAMs using electrostatic interactions has been studied previously.37,60,61 Chemistries employed include the interaction of Zr4þ and Hf4þ ions with phosphonate functionalized layers,34,62-65 Co2þ with diisocyanide,36 Cu2þ with thiols,39 pyrazines with Ru2þ,66 sulfonates with Hf 4þ and Zr4þ,34 and carboxylates with Hf 4þ, Zr4þ, and Cu2þ ions.37,60,61 Films 20-30 layers thick can easily be grown using these methods.36,63 However, the resulting assemblies are not necessarily well-ordered because the adlayers are often incomplete.36,60,62,67 For example, Anderson et al.,68 and McCarty et al.69 have demonstrated that Cu-mercaptoalkanoic acid “molecular ruler” films can be employed as resists to produce
