Novel growth of naphthalene overlayer on Cu(111) studied by STM, LEED, and 2PPE

Adsorbed structures of naphthalene on Cu(111) have been studied using low temperature scanning tunneling microscope (LT-STM) and low energy electron diffraction (LEED). Starting from single molecules, three kinds of long-range ordered superstructures, (5√3 - 5√3)R30°, (2√3 - 3)rect-1C₁₀H₈, and (-411-4) are observed depending on the molecular concentrations and the substrate temperatures during molecular adsorption. One of the self-assembled ordered phases with a (5√3 - 5√3) R30° periodicity is chiral in adsorption-induced arrangement though a single naphthalene molecule itself has no inherent chirality. In STM images, isolated single molecules appear as depressions whereas the molecules are seen as protrusions in self-assembled layers. Coverage dependent two-photon photoemission (2PPE) spectra show that the adsorption-induced occupied states is formed at around Cu 3d bands, and this results in the enhanced tunneling of occupied state images in assembled layers.