Molecular Assemblies on Silicon Surfaces via Si−O Linkages

Monolayer assemblies on silicon surfaces are of interest for a number of technological reasons. Here, we present a novel, two-step strategy for assembly formation directly on silicon surfaces. In the first step, a H-terminated Si(100) or Si(111) surface reacts with Cl2 to give a Cl-capped surface. In the second step, the Cl−Si surface is immersed in an alcohol/isooctane solution for monolayer formation via Si−O linkages, with the removal of surface Cl likely in the form of HCl. This reaction mechanism is confirmed by X-ray photoelectron spectroscopy. X-ray reflectivity measurement shows that the thickness of the monolayer film is close to molecular dimension and the density is about 85% of that in crystalline paraffine. Fourier transform infrared spectroscopy and water contact angle measurements suggest that the alkyl chains within the monolayer possess, to a limited degree, conformational order. Atomic force microscopy image with molecular lattice resolution shows intermolecular distance corresponding to close packing of alkyl chains. The monolayer coatings show both chemical and mechanical stability. The possible mechanism for monolayer assembly formation on covalent Si surfaces is discussed.