Electron transport through aluminum oxide tunnel barriers and OPE-based molecular junctions

This work presents results of a study of electron transport through aluminum-oxide based tunnel barriers and single-molecule transistors. Both systems have the potential for a dramatic increase of the density and performance of integrated circuits with critical dimensions well below the scaling limits of the conventional semiconductor technology. Studies of these two systems are also united by a common experimental approach - measurement of very small (down to 10 --14 A) currents within a broad temperature range (from 4.2 K to 350 K).;Electron transport through single molecular devices has been studied for structures of three types: (i) co-planar Au electrodes with 5-nm-scale gaps formed by e-beam lithography, (ii) co-planar Au electrodes with 1--2 nm-scale gaps formed by electromigration, and (iii) nanowires crosspoints with vertical gaps of 3 to 5 nm formed by under-etched aluminum oxide layers. Two types of Oligo(Phenylene Ethynylene) based molecules (with or without naphthalene diimide groups working as acceptors), capped with isocyanide terminal groups, have been investigated. For both molecules, nonlinear current-voltage curves with discrete current steps, due to tunneling through one or a few molecules, have been observed, and their dependences on the gate voltage and temperature have been studied in detail.;Key Words: electron transport, aluminum oxide, crested barrier, rapid thermal annealing, single-electron transistor, electromigration, molecular junction.;Transport properties of (Nb/)Al/AlOx/Nb tunnel barriers have been studied for structures formed by (i) thermal oxidation and (ii) plasma oxidation, before and after their rapid thermal post-annealing at temperatures up to 650°C. The post-annealing results in a substantial increase of the barrier height of the thermally formed aluminum oxide, which (within a broad range of RTA temperatures) may be substantially higher than that of the plasma-grown AlOx barriers. This fact, together with high endurance of annealed barriers under electric stress, may eventually lead to the fabrication of AlOx and SiO2/AlOx layered ("crested") barriers for advanced floating-gate memories.