ja408652h_si_002.avi (2.61 MB)
Defining the Value of Injection Current and Effective Electrical Contact Area for EGaIn-Based Molecular Tunneling Junctions
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posted on 2013-12-04, 00:00 authored by Felice
C. Simeone, Hyo Jae Yoon, Martin M. Thuo, Jabulani R. Barber, Barbara Smith, George M. WhitesidesAnalysis of rates of tunneling across
self-assembled monolayers
(SAMs) of n-alkanethiolates SCn (with n = number of carbon atoms) incorporated
in junctions having structure AgTS-SAM//Ga2O3/EGaIn leads to a value for the injection
tunnel current density J0 (i.e., the current
flowing through an ideal junction with n = 0) of
103.6±0.3 A·cm–2 (V = +0.5 V). This estimation of J0 does
not involve an extrapolation in length, because it was possible to
measure current densities across SAMs over the range of lengths n = 1–18. This value of J0 is estimated under the assumption that values of the geometrical
contact area equal the values of the effective electrical contact
area. Detailed experimental analysis, however, indicates that the
roughness of the Ga2O3 layer, and that of the
AgTS-SAM, determine values of the effective electrical
contact area that are ∼10–4 the corresponding
values of the geometrical contact area. Conversion of the values of
geometrical contact area into the corresponding values of effective
electrical contact area results in J0(+0.5
V) = 107.6±0.8 A·cm–2, which
is compatible with values reported for junctions using top-electrodes
of evaporated Au, and graphene, and also comparable with values of J0 estimated from tunneling through single molecules.
For these EGaIn-based junctions, the value of the tunneling decay
factor β (β = 0.75 ± 0.02 Å–1; β = 0.92 ± 0.02 nC–1) falls within
the consensus range across different types of junctions (β =
0.73–0.89 Å–1; β = 0.9–1.1
nC–1). A comparison of the characteristics of conical
Ga2O3/EGaIn tips with the characteristics
of other top-electrodes suggests that the EGaIn-based electrodes provide
a particularly attractive technology for physical-organic studies
of charge transport across SAMs.