title: Site-Specific Reactivity of Ethylene at Distorted Dangling-Bond Configurations on Si(001).
abstract: Differences in adsorption and reaction energetics for ethylene on Si(001) are reported with respect to distorted dangling-bond configurations induced by hydrogen precoverage, as obtained by DFT calculations. This can help to understand the influence of surface defects and precoverage on the reactivity of organic molecules on semiconductor surfaces in general. The results show that the reactivity of surface dimers fully enclosed by hydrogen-covered atoms is essentially unchanged compared to the clean surface. This is confirmed by scanning tunneling microscopy measurements. On the contrary, adsorption sites with partially covered surface dimers show a drastic increase in reactivity. This is due to a lowering of the reaction barrier by more than 50 % relative to the clean surface, which is in line with previous experiments. Adsorption on dimers enclosed by molecule (ethylene)-covered surface atoms is reported to have a strongly decreased reactivity, as a result of destabilization of the intermediate state due to steric repulsion; this is quantified through periodic energy decomposition analysis. Furthermore, an approach for the calculation of Gibbs energies of adsorption based on statistical thermodynamics considerations is applied to the system. The results show that the loss in molecular entropy leads to a significant destabilization of adsorption states.
authors.affiliation: Faculty of Chemistry and Material Sciences Centre, Philipps-Universität Marburg, Hans-Meerwein-Str. 4, 35032, Marburg, Germany.
authors.forename: Josua
authors.identifier: http://orcid.org/0000-0001-7130-0287
authors.initials: J
authors.lastname: Pecher
authors.affiliation: Faculty of Physics and Material Sciences Centre, Philipps-Universität Marburg, Renthof 5, 35032, Marburg, Germany.
authors.forename: Gerson
authors.identifier: http://orcid.org/0000-0001-7561-3264
authors.initials: G
authors.lastname: Mette
authors.affiliation: Faculty of Physics and Material Sciences Centre, Philipps-Universität Marburg, Renthof 5, 35032, Marburg, Germany.|Institute of Applied Physics, Justus Liebig University Giessen, Heinrich-Buff-Ring 16, 35392, Giessen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Dürr
authors.affiliation: Faculty of Chemistry and Material Sciences Centre, Philipps-Universität Marburg, Hans-Meerwein-Str. 4, 35032, Marburg, Germany.
authors.forename: Ralf
authors.identifier: http://orcid.org/0000-0002-6759-8559
authors.initials: R
authors.lastname: Tonner
keywords: density functional calculations; ethylene; scanning probe microscopy; silicon; surface analysis