Orbital Mediated Tunneling in Vanadyl Phthalocyanine Observed in both Tunnel Diode and STM Environments

For the first time orbital mediated tunneling spectroscopy (OMTS) is reported for the same species, vanadyl phthalocyanine (VOPc), in both the tunnel diode and STM environments. IETS and OMTS for a junction of the form [Al−Al2O3−VOPc−Pb] show both the expected bias symmetry of vibrational and electronic inelastic electron tunneling spectroscopy (IETS) bands and the highly bias asymmetric OMTS band associated with tunneling via direct occupation of the Pc ring π* orbital. STM studies of submonolayer coverage of VOPc on Au(111) produce well-resolved submolecular images of the molecule. Current imaging tunneling spectroscopy (CITS) allows one to easily identify VOPc islands, and the resulting I−V curves can be used to generate dI/dV spectra for VOPc and for bare gold regions. An intense band seen near +1.4 V bias (Au+) is identified as the same OMTS band as seen in the tunnel diode: resonance-like tunneling through the Pc ring π* orbital.