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 10รข 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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/85957 |
| Date | 10 October 2008 |
| Creators | Ma, Lianxi |
| Contributors | Agnolet, Glenn |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation, text |
| Format | electronic, born digital |
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