Negative resistance in organic monomolecular layers sandwiched between metal electrodes

Metal–insulator–metal sandwiches can exhibit low-frequency differential negative resistance (DNR) if they are placed in vacuum and formed by applying a few volts. This effect was till now established only for amorphous or polycrystalline insulators (mostly oxides). In attempts to explain the DNR phenomenon it is important to know whether it occurs also for other insulators and therefore monomolecular multilayers of cadmium arachidate are investigated. It is shown that such organic films can exhibit DNR very similar to that observed in amorphous and polycrystalline insulators. The striking difference, however, is that for monomolecular multilayers the DNR occurs at temperatures below about 225 °K, and not at room temperature as for the above-mentioned insulators. Moreover, multilayer sandwiches can be formed at 77 °K. The dependence of the DNR on the number of monomolecular layers is reported and the way in which electrode material and voltage polarity affect the forming process. The results will be discussed in relation to the various existing models proposed to explain the DNR phenomenon.