AFM evidence of perpendicular orientation of cylindrical craters on hybrid silica thin film templated by triblock copolymer

A simple method for elaborating mesoporous thin films with patterns normal to the substrate has been studied. The structured thin films were prepared by deposition of thin silica film templated by the so-called P123 (EO)20-(PO)69-(EO)20 (poly-[ethyleneoxide-co-propyleneoxide-co-ethyleneoxide]) triblock copolymer on monolayers of n-octadecyltrichlorosilane (OTS) assembled onto a silicon wafer. Surface morphologies of films deposited onto silicon wafers modified by this hydrophobic monolayer or cleaned hydrophilic bare silicon wafer were characterized by using atomic force microscopy (AFM). We evidenced that, in the case of hydrophobic modified substrate, organic-inorganic hybrid thin films made of P123 species embedded in a silica matrix exhibit regularly-shaped craters in the direction normal to the surface. Our investigation has shown that the diameter of the craters agrees fairly well with the length of the fully extended organic chains of the triblock copolymer. The specific interfacial interactions between both the hydrophilic part of the shell of the surfactant, the native silicon oxide of the silicon wafer and the silanized surface are discussed.