Self-Assembly Evolution of Metal-Free Naphthalocyanine Molecules on Ag(111) at the Submonolayer Coverage

Structures of self-assembled films play essential roles in the performance of potential organic molecular electronics; therefore, detailed knowledge of molecular adsorption and structural evolution is fundamental for the implementation of molecular electronics. Here, we systematically investigated the initial adsorption and structure evolution of metal-free naphthalocyanine (H2Nc) on the Ag(111) surface from dimers to ordered self-assembled structures in the submonolayer range. H2Nc molecules deposited on Ag(111) at 100 K accumulate into clusters dominated by dimers. Subsequent sample annealing induces the emergence of two ordered self-assembled structures, denoted by Sl and Sll. Molecule-resolved scanning tunneling microscopy images confirm that structure Sl is more stable with six rotation domains lying in two chiralities. Deviations of the lattice parameters from a threefold symmetry indicate non-neglectable intermolecular interactions in self-assembled patterns. Combined with density functional theory calculations, orientations of the two inner hydrogens of H2Nc in the self-assembled film are revealed.