Hydrocarbon molecules deposited onto monolayer steps on Si(100): A study of adsorption and conductance

In this study, the interactions of small hydrocarbon molecules with monolayer SA steps are considered. The purpose of the calculations is a systematic description of the adsorption capability of the silicon steps in dependence of the type of the incident molecule. The study deals with both the electronic configuration of the deposited system and with its transport properties and the flat, dimerized surface is used as reference. The calculations are based on a semi-empirical Hamiltonian which is applied to the evaluation of the total energy and of the conductance and this last quantity is obtained from the scattering theory. It has been found that, though the step is a weaker sink than the flat surface, adsorption is possible and the molecules are bonded to the step. The functional relationship between the binding energy and the type of the adsorbed molecule is reminiscent of the intrinsic binding energy of the molecule itself and is therefore similar for the flat surface and for the step. The transmission function depends on the type of molecule and of the substrate and on the allowed energy levels of the deposited system. Depending on the channel type, a direct, or reverse, proportionality exists between the conductance and the binding energy.