Nanoscale patterning of organic monolayers by catalytic stamp lithography: scope and limitations

Developing a method to pattern organic molecules, particularly on the sub-100-nm scale, is of wide interest in current nanoscience for a broad range of technological applications. Because of the efficiency and simplicity of soft lithography, here we describe in detail the process for synthesizing and applying catalytic stamp lithography, a process that can easily produce sub-100-nm patterns on surfaces; in this work, the approach is demonstrated on silicon. Catalytic stamps were fabricated through a two-step procedure in which the nanoscale pattern of catalysts is produced via a self-assembled block-copolymer-templated synthesis of metallic nanostructures on SiO(x)/Si supports, followed by the production of the poly(dimethylsiloxane) (PDMS) stamp on top of the as-patterned metals. Simply peeling off the as-formed PDMS stamp removes the metallic nanostructures, leading to the functional stamp. Two different patterns, pseudohexagonal and linear Pt nanoarrays, were produced from a single block copolymer, PS(125000)-b-P2VP(58500), by controlling the morphology of thin-film templates through tetrahydrofuran vapor annealing. When terminal alkenes, alkynes, or aldehydes with different functionalities were used as molecular inks, these Pt nanopatterns on catalytic stamps were translated into corresponding molecular arrays on Si(111)-H and Si(100)-H(x) surfaces because catalytic hydrosilylation took place exclusively underneath patterned Pt nanostructures. With this straightforward approach, the resolution limit of conventional microcontact printing (approximately 100 nm) could be downsized to a sub-20-nm scale, while maintaining the advantages of stamp-based patterning (i.e., large-area, high-throughput capabilities and low cost).