Nanostructures of Octadecyltrisiloxane Self-Assembled Monolayers Produced on Au(111) Using Particle Lithography

Abstract

Preparing high-quality self-assembled monolayers (SAMs) of organosilanes on conductive metal substrates such as gold is problematic because of the hydrophobic nature of the surface under ambient conditions. Trace amounts of water are required for a surface hydrolysis reaction to form siloxane bridges to the metal substrate. We describe an approach using sequential steps of ultraviolet (UV) irradiation, particle lithography, and chemical vapor deposition of octadecyltrichlorosilane (OTS) to successfully prepare silane nanostructures on Au111 surfaces. Pretreatment of gold films with UV irradiation renders the surface to be sufficiently hydrophilic for particle lithography. Close-packed films of monodisperse latex mesospheres provide an evaporative mask to spatially direct the placement of nanoscopic amounts of water on surfaces. Vapor-phase organosilanes deposit selectively at areas of the surface containing water residues to produce millions of nanopatterns with regular thickness, geometry, and periodicity. Atomic force microscopy (AFM) images reveal that OTS binding is localized to areas defined by water residues. The spacing between adjacent nanopatterns is determined by the periodicity of the latex mask; however, the dimensions of the nanostructures are confined to a narrow contact area of the water meniscus, which surrounds the base of the latex spheres. The siloxane nanostructures on Au111 furnish an excellent model surface for AFM characterizations, as demonstrated with current-sensing measurements.