We have investigated electrical properties of planar aluminum/aluminum oxide/silver tunnel junctions modified with phenyl-based azomethine oligomers. Normalized differential conductance, NDC (NDC=sigma(V)/sigma(V=0), where sigma=dI/dV), of the junctions increases with oligomer length. At a bias of 2 V, azomethines with three phenyl rings exhibit NDCs that are on average more than an order of magnitude greater than those of unmodified oxide junctions. Differential conductances of junctions modified with azomethines increase more rapidly with temperature than those of plain oxide junctions. Our results are consistent with a model in which both increased conjugated length of the sandwiched organic layer and a molecule/metal interface lead to a lowering of the barrier profile outside the aluminum oxide tunnel region. (C) 2003 American Institute of Physics.