Resonant tunnelling diodes based on molecular wires incorporating saturated spacers:: a quantum-chemical study

The demand for increased miniaturization of integrated circuits has opened the way to the emerging field of molecular electronics. Recent experimental studies have established that single molecules or a finite ensemble of self-assembled molecules can perform the basic functions of conventional electronic components (i.e., transistors, wires and diodes). In particular, it has been demonstrated that molecular wires inserted into nanopores can be used as active elements for the fabrication of resonant tunnelling diodes (RTDs), whose I/V characteristics reveal a negative differential resistance (NDR) behaviour (i.e., a negative slope in the I/V curve). Here, we provide a detailed quantum-chemical description of a possible mechanism leading to NDR in polyphenylene-based molecular wires incorporating saturated spacers. This mechanism can be understood from the evolution of the molecular wire one-electron structure upon application of a static electric field aligned along the molecular axis, which simulates the driving voltage applied between the two electrodes in the RTD devices. The main parameters controlling the NDR behaviour can be fine tuned through molecular engineering of the wires.