IRG3 and International Partnership: How Do Electrons Cross Si-Bound Alkyl Monolayers? (DMR-0213706) David Cahen (Weizmann Institute) and Antoine Kahn (Princeton)

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IRG3 and International Partnership How Do
Electrons Cross Si-Bound Alkyl Monolayers?
(DMR-0213706)David Cahen (Weizmann Institute)
and Antoine Kahn (Princeton)
Electron flow through ultra-small wires made of
single molecules is a fascinating, but poorly
understood, area of study. Here, we investigate
an ideal system consisting of a well ordered
monolayer of alkyl chains (CnH2n1, n12,14,16,
18) attached to a Si wafer and contacted with a
mercury droplet (Fig. a). The electronic
structure of the system is determined by electron
spectroscopy (Fig. b). Current-voltage (J-V)
measurements (Fig. c) reveal two dominant
transport mechanisms. At low bias (lt0.5 V), the
current is limited by thermionic emission over
the barrier in the Si substrate, yielding a
current that is independent of the molecular
chain length. The inset shows a
temperature-dependent measurement that confirms
this mechanism. At high bias, the current shows
an exponential dependence on chain length,
signaling a current dominated by tunneling across
the molecular layer. The combination of
spectroscopic and detailed J-V data allows a
realistic investigation of the meaning of
charge-carrier effective mass in these
systems. References A. Salomon, T. Boeckling,
C.K. Chan, F. Amy, O. Girshevitz, D. Cahen, and
A. Kahn, Phys. Rev. Lett., 95, 266807 (2005).