Subsurface-Controlled Angular Rotation: Triphenylene Molecules on Au(111) Substrates

Molecular self-assembly can be used for the bottom-up fabrication of nanoscale electronic devices. For this, polycyclic aromatic hydrocarbons are particularly suited due to their extended π-system. Besides, these compounds can serve as precursors for fabricating graphene-like material. To design future electronic devices it is essential to be able to reproducibly predict the structure formation of these molecules after adsorption on solid surfaces. Here we studied the self-assembly of triphenylene molecules on a reconstructed Au(111) substrate in the submonolayer regime by scanning tunneling microscopy. Only two different orientations of the planar adsorbed molecules are observed. At intermediate coverages self-assembly is mainly determined by repulsive molecule–molecule interactions, leading to a one-to-one ratio of molecular orientations. At 1.0 monolayer coverage, however, a reorientation into close-packed domains occurs, which significantly shifts the ratio of molecular orientations. It is found that this reorientation is controlled by molecule–subsurface interactions, opening new avenues in assembling molecules on surfaces.