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O: Fachverband Oberflächenphysik

O 86: Nanostructure at Surfaces: Molecular Assembly

O 86.3: Vortrag

Donnerstag, 19. März 2015, 15:45–16:00, HE 101

Self-assembly of NC-Ph3-CN molecules on Cu(111): an unusual alignment with respect to the substrate — •Giulia E. Pacchioni, Marina Pivetta, and Harald Brune — Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.

The self-assembly of dicarbonitrile polyphenyl molecules (NC-Phn-CN) on metal surfaces is a widely studied subject. These molecules on Ag(111) are in most cases aligned along the first or second nearest neighbors directions of the substrate. For NC-Ph5-CN molecules on Cu(111) the alignment along the second nearest neighbors is the only one observed. On Cu(111) the alignment along this direction is particularly favorable, since it allows an almost perfect epitaxial fit of the molecules with respect to the substrate. The behavior of NC-Ph3-CN molecules on Cu(111) is in this respect rather bizarre: while for purely organic assemblies the alignment is, as expected, along the high symmetry directions, when the network is metal coordinated the molecules align along a bunch of directions deviating from the second nearest neighbors ones by 4, 11 and 18 degrees. The resulting networks have a strongly reduced degree of order compared to NC-Ph5-CN on Cu(111) assemblies. We explain this peculiar behavior through the interplay between the gain in energy obtained by forming a straight CN-Cu bond at the molecule ends, and the one given by having the hydrogen and nitrogen atoms placed on favorable adsorption sites on the surface. We show that these two preferences cannot be satisfied at once, so depending on the length of the molecule one or the other will prevail, giving rise to different dispositions on the substrate.