ELECTRONIC JUNCTION DEVICES FEATURING REDOX ELECTRODES

摘要

The electronic properties of molecular junctions of the general type carbon/molecule/TiO₂/Au as examples of "molecular heterojunctions" consisting of a molecular monolayer and a semiconducting oxide. Junctions containing fluorene bonded to pyrolyzed photoresist film (PPF) were compared to those containing AI₂O₃ instead of fluorene, and those with only the TiO₂ layer. The responses to voltage sweep and pulse stimulation were strongly dependent on junction composition and temperature. A transient current response lasting a few milliseconds results from injection and trapping of electrons in the TiO₂ layer, and occurred in all three junction types studied. Conduction in PPF/TiO₂/Au junctions is consistent with space charge limited conduction at low voltage, then a sharp increase in current once the space charge fills all the traps. With fluorene present, there is a slower, persistent change in junction conductance which may be removed by a reverse polarity pulse. This "memory" effect is attributed to a redox process in the TiO₂ which generates Ti^III and/or Ti^II, which have much higher conductance than TiO₂ due to the presence of conduction band electrons. The redox process amounts to "dynamic doping" of the TiO₂ layer by imposed electric field. The memory effect arises from a combination of the properties of the molecular and oxide layers, and is a special property of the molecular heterojunction configuration.