Comparing the conductivity of molecular wires with the scanning tunneling microscope

Current–voltage characteristics as measured by scanning tunneling microscopy for several different molecular backbones are presented. It is demonstrated that isolated oligo(phenylene ethynylene) molecules have the same measured conductance as oligo(phenylene ethynylene) molecules in a crystalline self-assembled monolayer. This result suggests that previous studies involving relatively large surface areas of self-assembled monolayers can be applied to molecular electronics devices employing small numbers of molecules. In addition, gap resistance measurements are used to rank the molecular conductance of oligo(phenylene ethynylene), oligo(phenylene vinylene), and dodecanedithiol. The observed trend for isolated molecules agrees with earlier large-scale measurements.