Functionalization of silicon step arrays II: Molecular orientation of alkanes and DNA

Alkanes and DNA are adsorbed via thiol groups on ultrathin gold films that have been templated on stepped Si(111)7×7 surfaces. The orientation of the adsorbed molecules is determined by polarization-dependent near edge x-ray absorption fine structure spectroscopy from the C 1s and N 1s core levels. An anisotropy in the polar distribution is found which is consistent with models in which the molecules have a preferred tilt angle with respect to normal but a random azimuthal distribution. In order to obtain maximum coverage and an oriented overlayer it is necessary to deposit more than 3 nm of Au (12 monolayers).