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DFT investigation of oligothiophenes on the Si(001) surface.

Francesca Costanzo , Elisabetta Venuti, Raffaele Guido Della Valle, Aldo Brillante, Pier Luigi Silvestrelli, Washington (2010)

The nature of the interaction of a series of -oligothiophenes (1T up to 6T) with the Si(001) surface was studied by means of density functional theory (DFT) structural optimizations. For 1T, we found that the products of the [4+2] cycloaddition are more thermodynamically stable than those of the [2+2] cycloaddition, in agreement with previous cluster approach calculations. Since there are many possible ways of placing the nT molecule on the Si(001) surface, we have tested a number of possible conformations; in particular, starting from simple geometric considerations, we built the 6T molecule from 1T as a result of [2+2] cycloadditions. The binding energy of oligomers with n from 2 to 6 displays a steady drop, attributable to an increased deformation energy. Our study sheds light on the chemisorption of oligothiophenes on Si(001) showing, in particular, that molecular chemisorption is possible for oligothiophenes with up to four thiophene units. For 6T, we estimated the van der Waals contribution to the binding energy, being of the order of 1 eV for molecule-surface distances > 4 A, in agreement with the experimental evidence of the presence of 6T physisorbed states on the Si(111) surface. Finally, the calculated work function for 6T on Si(001) is in very good agreement with the experimental estimate.

Partners : UNIBO

Place of Publication : Washington

Date of Publication : 2010/11/10

Link to the online version of the article.