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)7x7 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 m odels in which the molecules have a preferred tilt angle with respect to no rmal but a random azimuthal distribution. In order to obtain maximum covera ge and an oriented overlayer it is necessary to deposit more than 3 nm of A u (12 monolayers). (C) 2001 American Institute of Physics.