Electron transport through single phthalocyanine molecules studied using scanning tunneling microscopy

Using low-temperature scanning tunneling microscopy, electron transport across single H₂- or Co-phthalocyanine molecules was studied. The molecules were adsorbed onto clean Cu(111) surface and Co nanostructures on Cu(111) and were contacted through a controlled approach of the tip. Soft phonons from the molecular side groups promote a discrete jump to contact followed by bond formation. Molecular conductances strongly depend on the substrate but not on the central atom of the molecules. This is explained by charge transfer and hybridization of the molecular orbitals with the substrate states as seen by scanning tunneling spectroscopy.