Molecular Orbitals Gating for a Single Long, Rigid, Planar Molecular Wire

摘要

We have reported that carbon-bridged oligo(phenylenevinylene)s (COPVn) serve as effective molecular wires as demonstrated by photoinduced electron transfer because of their rigid structures to achieve effective π-conjugation.1-2 In this presentation, we demonstrate that resonant tunneling through molecular orbitals for SAuSH device, in which COPV5(SH)2 molecular wire (Figure 1) is one-side chemical bonded to electrodes. Due to improved nanogap electrodes of our electroless Au-plated (ELGP) nanogap Pt electrodes with the top radius of a few nm, we report that resonant tunneling is modulated by application of gate voltage. The initial structures of the source, drain, and two side gate electrodes of Ti/Pt were fabricated on a SiO2/Si substrate via electron beam lithography (EBL) and lift-off processes. Electroless Au-plating was carried out to reduce the electrode gaps to ~3 nm (Figure 2), followed by the introduction of a COPV5(SH)2 molecule between the nanogap electrodes by immersing into a solution of COPV5(SH)2. We then measured the current-voltage (I-V) characteristics at 9 K using a mechanical He-refrigerator-type prober station, and differential conductance is numerically calculated in Figure 3. Negative second dI/dV peak have been observed largely shifted by application of gate bias at -8 V (Figure 3, red lines). We suggest that the transport mechanism of this single molecular wire is resonant tunneling phenomena under the alignment of a molecular orbital with Fermi energy of a source or drain electrode.