We estimate the conductance of molecular junctions composed of an oligo(phenylene ethynylene) (OPE) molecule sandwiched between a metallic gold or carbon nanotube on one end and a semiconducting silicon contact on the other end. Two very well defined, low and high, states of conductance (logic “0” and “1”) are obtained through changes in conformation or charge states of the OPE when two metallic contacts address the molecule. However, when a combination of a semiconducting and metallic contacts are used, the bistable states are lost at low bias voltages where a flat region of nearly zero current in the current-voltage characteristic is predicted regardless of the conformation or charge state.

• Received 30 July 2006

DOI:https://doi.org/10.1103/PhysRevB.76.115316