Coverage effects on phenol adsorption on Si(100)2 x 1 as: A first principle calculation

We investigated the adsorption of a 6-dimers Si(100)2 x 1 surface as a function of coverage and adsorption type (molecular/dissociative) by first principle calculations. in particular, we performed calculations on models with 2, 3, 4 and 6 phenol molecules, corresponding to coverage Theta = 0.34, 0.5, 0.67 and 1. We found that total adsorption energy, when at least one phenol is in a molecular state is lower than the sum of the corresponding singly adsorbed molecules. The dissociative adsorption of multiple molecules, both in parallel and switched configuration is most favoured for a coverage Theta = 0.34 (2.6 eV per adsorbed molecule). This values decreases to 2.0 eV and remains constant till the coverage 1 is reached. The energy barrier for the molecular-to-dissociated transition of a phenol molecule, in presence of another dissociatively adsorbed molecule is similar to 0.008 eV and it is similar to the value in case of single adsorption. Possible hydrogen displacements were also considered. (C) 2008 Elsevier B.V. All rights reserved.