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

Abstract

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-Al 2 O 3 -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.

Controlled Reorientation of CuPc Molecules in Ordered Structures Assembled on the TiO2(011)‐(2×1) Surface

“…Phase I is dominated by the ordered molecular stripes running along the surface rows (see Figure 2 c). The planar stacking molecules within the stripes are slightly rotated (by approximately 108) to minimize the intermolecular interactions similarly to previously observed rotation in ordered CuPc layers on several different metallic and semiconducting substrates [on graphite, [14] VOPc on Au(111), [15] CuPc on graphite and alkane adlayer, [16] on Cu(111), [17] on Au(111) [18][19][20] ]. The neighboring molecular chains are separated by approximately 2.7 nm, that is, a triple surface unit cell dimension.…”

Anisotropic Crystalline Organic Step-Flow Growth on Deactivated Si Surfaces

“…The Si spectrum reveals that the surface has been deactivated with the unoccupied state at about 1.5 eV above the Fermi level and an occupied back-bond state at about 1.5 eV below the Fermi level, consistent with the previous study [31]. Spectrum on ZnPc shows the available density of states near +2.5 V, corresponding to the resonant tunneling through the lowest unoccupied molecular orbital (LUMO) [33,34].…”

Establishing the Molecular Basis for Molecular Electronics

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Several examples are noted. Hipps and co-workers reported orbital-mediated tunneling through phthalocyanins and porphyrins that contain metal centers.…”

“…Hipps and co-workers reported orbital-mediated tunneling through phthalocyanins and porphyrins that contain metal centers. [5][6][7][8] Tour, Bard, and co-workers displayed peak shaped I-V curves in phenylene ethynylene oligomers (OPEs) by using a tuning-fork STM. [9,10] We have studied negative differential resistance in patterned, electroactive SAMs by using STM.…”