Wetting driven self-assembly as a new approach to template-guided fabrication of metal nanopatterns.

Wetting driven self-assembly (WDSA) of appropriate materials in their liquid state on organic monolayer nanopatterns consisting of wettable (lyophilic) surface features surrounded by a nonwettable (lyophobic) monolayer background is shown to provide the basis of a versatile new approach to template-guided fabrication of metal nanopatterns. Monolayer nanopatterns with planned distributions of lyophilic/lyophobic surface regions are conveniently generated by constructive nanolithography upon local electrochemical oxidation of the top -CH3 groups of a highly ordered OTS (n-octadecyltrichlorosilane) monolayer self-assembled on silicon to -COOH (Adv. Mater. 2000, 12, 725-731). Retraction of such a patterned monolayer from a liquid that does not wet its nonpolar -CH3 surface (lyophobic) results in selective, site-defined immobilization of nanosized volumes of the liquid on the locally generated polar -COOH groups (lyophilic). Examples are given of WDSA of organic materials that offer further options for post-assembly chemical processing, such as nonvolatile low-melting olefins, acids, or thiols, the former being in situ reacted to generate polar functions like -COOH or -SH. Loading surface patterns created in this manner with silver or gold ions followed by further chemical processing results in elemental metal nanoparticles generated within the ion-binding organic material, which thus functions as a guiding template for planned metal deposition at predefined surface sites. WDSA is particularly versatile, as any nonvolatile material with appropriate melting temperature and surface wetting characteristics or solubility in a liquid displaying such properties may in principle be utilized to fabricate potentially useful surface nanostructures.