Differential Conductance Switching of Planar Tunnel Junctions Mediated by Oxidation/Reduction of Functionally Protected Ferrocene

Planar tunnel junctions were fabricated by self-assembling 1,1‘- ferrocenedicarboxylic acid (FDCA) onto native oxides of thermally deposited aluminum films and subsequently depositing a second aluminum film. Junctions were characterized using Reflection−Absorption Fourier Transform Infrared Spectroscopy (RAIRS) and current−voltage (I−V) spectroscopy. Before deposition of the second aluminum film, RAIRS of FDCA and ferrocenecarboxylic acid (FCA) films revealed COO-, CO, and Fc ring stretching modes, indicating that both types of molecules can interact strongly with the oxide and remain intact. After deposition, systems exhibited prominent COO- modes and weakened CO modes, indicating further reaction with aluminum/aluminum oxide. Fc ring modes persisted in FDCA systems but disappeared in FCA systems, suggesting that the second COOH group in the FDCA molecule can act as a protecting group for the ferrocene moiety. Cyclic I−V measurements of FDCA tunnel junction systems revealed very strong (∼10-fold) hystere...