| 摘要 |
The electronic properties of molecular junctions of the general type carbon/molecule/TiO<SUB>2</SUB>/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 Al<SUB>2</SUB>O<SUB>3 </SUB>instead of fluorene, and those with only the TiO<SUB>2 </SUB>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 TiO<SUB>2 </SUB>layer, and occurred in all three junction types studied. Conduction in PPF/TiO<SUB>2</SUB>/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 TiO<SUB>2 </SUB>which generates Ti<SUP>III </SUP>and/or Ti<SUP>II</SUP>, which have much higher conductance than TiO<SUB>2 </SUB>due to the presence of conduction band electrons. The redox process amounts to "dynamic doping" of the TiO<SUB>2 </SUB>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.
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