| This thesis explores molecule-doped planar tunnel junctions; in particular, the role molecules play in influencing junction electrical characteristics. In Chapter 2, we describe a solution phase method to generate phenyl-based azomethine oligomer assemblies on quartz and silicon oxide surfaces. The method is based on a controlled iminization reaction in which aromatic aldehydes and amines (1,4-terepthaldicarboxaldehyde, TPDA, and 1,4-phenylenediamine, PPDA) are sequentially assembled onto amino-functionalized substrates. Using UV-Visible and polarized ATR-FTIR spectoscopies, we explored the roles of temperature, acid catalyst, and monomer concentration on the rate of film formation. Observed rate constants for TPDA assembly grew linearly with monomer concentration, while those for PPDA assembly were independent of monomer concentration. Fully formed films were found to be remarkably stable to repeated sonication and exposure to solvents at elevated temperatures.; In Chapter 3 we investigate electrical properties of planar aluminum aluminum oxide/silver tunnel junctions modified with phenyl-based azomethine oligomes. Normalized differential conductance, NDC (NDC = sigmaV/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.; In Chapter 4, we investigate planar tunnel junctions that were fabricated by self-assembling 1,1'-ferrocenedicarboxylic acid (FDCA) onto native oxide 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. RAIRS of FDCA after deposition of a second 20A aluminum film reveal Fc-ring mode peaks, 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) hysteretic conductance switching that was both reversible and stable. Control measurements revealed only very weak (∼10%) conductance changes. We attribute FDCA junction switching to barrier profile modifications induced by oxidation/reduction of the functionally protected ferrocene moieties. |
