Molecule/Metal Surface Interactions Evidenced Quantum Mechanically via Tip-Induced CS2 Interaction with Friedel Oscillations on Au{111}

Submonolayer coverages of CS 2 adsorbed on Au{111} at 4 K were studied using scanning tunneling microscopy. The molecule forms well-ordered islands on the terraces and molecular chains at the bottoms of the steps. The adsorption of the CS 2 molecule at specific surface sites is explained in terms of the substrate electron density. Strong tip/molecule interactions are shown to be prevalent in this system at negative tip biases and yield images showing reversed corrugation. At low positive tip bias, the tip again perturbs the molecules, but in this regime, the tip/molecule interaction is comparable to the molecule/surface interaction and higher residence times at certain surface sites are observed. This effect is explained fully in terms of the CS 2 molecule having increased interactions with the areas of high electron density on the peaks of standing waves arising from electrons close to the Fermi energy. The importance of this result is discussed in terms of the fundamental surface physics of adsorbate/metal bonding.