Metal-free phthalocyanine (H2Pc) molecule adsorbed on the Au(111) surface: formation of a wide domain along a single lattice direction.

Using low-temperature scanning tunneling microscopy (STM), we observed the bonding configuration of the metal-free phthalocyanine (H2Pc) molecule adsorbed on the Au(111) surface. A local lattice formation started from a quasi-square lattice aligned to the close-packed directions of the Au(111) surface. Although we expected the lattice alignment to be equally distributed along the three crystallographically equivalent directions, the domain aligned normal to the ridge of the herringbone structure was missing in the STM images. We attribute this effect to the uniaxial contraction of the reconstructed Au(111) surface that can account for the formation of a large lattice domain along a single crystallographical direction.