Molecular assemblies on silicon surfaces via Si-O linkages

Monolayer assemblies on silicon surfaces are of interest for a number of te chnological reasons. Here, we present a novel, two-step strategy for assemb ly formation directly on silicon surfaces. In the first step, a H-terminate d Si(100) or Si(111) surface reacts with Cl-2 to give a Cl-capped surface. In the second step, the CI-Si surface is immersed in an alcohol/isooctane s olution for monolayer formation via Si-O linkages, with the removal of surf ace 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 i nfrared spectroscopy and water contact angle measurements suggest that the alkyl chains within the monolayer possess, to a limited degree, conformatio nal order. Atomic force microscopy image with molecular lattice resolution shows intermolecular distance corresponding to close packing of alkyl chain s. The monolayer coatings show both chemical and mechanical stability. The possible mechanism for monolayer assembly formation on covalent Si surfaces is discussed.