posted on 2007-04-25, 00:00authored byPawan Tyagi, Dongfeng Li, Stephen M. Holmes, Bruce J. Hinds
Producing reliable electrical contacts of molecular dimensions has been a critical challenge in
the field of molecule-based electronics. Conventional thin film deposition and photolithography techniques
have been utilized to construct novel nanometer-sized electrodes on the exposed vertical plane on the
edge of a thin film multilayer structure (metal/insulator/metal). Via thiol surface attachment to metal leads,
an array of paramagnetic, cyanide-bridged octametal complexes, [(pzTp)FeIII(CN)3]4[NiII(L)]4[O3SCF3]4 (1)
[(pzTp) = tetra(pyrazol-1-yl)borate; L = 1-S(acetyl)tris(pyrazolyl)decane], were covalently linked onto the
electrodes forming a dominant conduction pathway. A series of molecule-based devices were fabricated
using Ni, NiFe, Ta, and Au as metal electrodes separated by insulating Al2O3 spacers, followed by treatment
with 1. A series of control experiments were also performed to demonstrate that the conduction path was
through tethered metal clusters. The molecular current was analyzed via the Simmons tunnel model, and
calculations are consistent with electron tunneling through the alkane ethers to the central metal core.
With a Ni/Al2O3/Au molecular electrode, the tether binding was found to be reversible to the top Au layer,
allowing for a new class of chemical detection based on the steric bulk of coordinating analytes to disconnect
the molecular current path. Simple and economical photolithography/liftoff/self-assembly fabrication
techniques afford robust molecular junctions with high reproducibility (>90%) and long operational lifetimes
(>1 year).