Imaging molecules and metals on metal surfaces by scanning tunneling microscopy

Using an ultrahigh vacuum scanning tunneling microscope (STM), we have imaged naphthalene molecules adsorbed on Pt(111) and submonolayer metal coverages of Ni, Fe, Ag, and Au on Au(111). The STM is able to observe atomic scale features on both types of systems, giving information on the ordering and binding sites of atoms and molecules on the surface. High resolution STM images of naphthalene on Pt(111) show the molecules as bi-lobed features with three discrete molecular orientations on the surface, 120° apart, as shown for the ordered layer in Fig. 1. The absolute orientation of the long axis of the molecules is observed to be parallel to the near-neighbor directions of the Pt(111) lattice. The sketch of the observed features, shown in Fig. 2, with the molecules overlayed arbitrarily onto on-top sites of a Pt(111) lattice, demonstrates that the molecules are located on 3x3 lattice sites, with separation of 4 lattice constants between domains. Although the (6x3) LEED pattern reported previously was reproduced, the proposed unit cell is seldom observed in the STM images.