Ma, Lianxi (2008-05). Electron tunneling studies of Mn12-Acetate. Doctoral Dissertation. Thesis uri icon


  • We used self-assembling tunnel junctions (SATJs) to study the electron transport

    through films of the molecular magnets, Mn12-Acetate. Pulse laser deposition

    (PLD) was used to deposit two monolayers of Mn12-Acetate on thin Pt wires (diameter

    0.001 in). The electron tunneling current was measured with typical bias voltages

    from -1 to 1 V at liquid helium temperature, 4.2 K. I, dI/dV , and d2I/dV 2 signals

    were directly acquired with the aid of a current amplifier and two lock-in-amplifiers.

    Results show that the differential conductance is approximately 10? 6 S for bias voltages

    0.04 V < or =| V |< or = V and exhibits a strong voltage dependence. In the region

    | V |< or = 0.04 V, we find a zero-bias feature (ZBF) in which the differential conductance

    is suppressed. In some samples, we observe I -V staircases which we attribute to

    electrons "hopping" between the electrodes and the molecules. The observed hysteresis

    was attributed to the slow relaxation of molecules re-orienting within the junction.

    Abrupt conductance jumps at a bias voltage of -0.12 V were also observed and may

    indicate state transitions in the Mn12-Acetate molecules. Furthermore, we observed

    that the zero bias feature (ZBF) can switch from an enhancement to a suppression

    of the differential conductance.

    A dip and dry (DAD) method was also used to form films of Mn12-Acetate on

    Al and Pt wires. Although the conductances were similar to those obtained using the PLD method, there were some subtle differences. In particular, we did not observe

    the I -V staircases and the state jumps were more ambiguous. The differential

    conductance for the Mn12-Acetate films on Al wires were typically 10- 7 S, which we

    attributed to the oxide layer on Al surfaces.

    We have also found substantial changes in the I - V characteristics when the

    Pt wires coated with the Mn12-Acetate films were stored in 10-2 Torr for 6 months.

    In particular, we observed many new features such as peaks in the conductance as a

    function as the bias voltage. We believe that these effects may be caused by the slow

    oxidation of the Mn12-Acetate molecules.

publication date

  • May 2008
  • May 2008