Circuit characteristics of molecular electronic components

Electronic devices based on single molecules, or small assemblies of molecules, are attracting much attention as intrinsically nanoscale devices that can add functionality such as optical emission and nonvolatile storage to silicon-based electronics. One of the key issues in these devices is the nature of the microscopic contacts to the active molecules and the need to develop well-controlled interfaces in order to achieve low-resistance contacts. We describe the formation of suitable contact structures in the form of nanometer scale "break junctions" in gold lines, formed by lithographic or electrical means. The structure provides a lead frame for realizing high-quality contacts to nanometer-size molecules and nanoparticles with selective docking achieved by end-groups such as thiol (-SH). Metal-molecule-metal junctions can be formed by chemisorbing short molecules such as 1,4-benzenedithiol on the two electrodes. Current-voltage (I-V) characteristics have been measured for configurations including small numbers of molecules directly bonded in the junction and molecule/nanocluster/molecule assemblies. These junctions are being used as test beds to study electrical conduction through different types of engineered-molecules, and to subsequently develop circuit level models. By integrating these molecules with electrical contacts, selective microscopic events (e.g. doping events or gas docking) can be coupled to external circuitry.