Spatially resolved tunneling along a molecular wire

We have spatially resolved the electronic penetration of metallic electroni c states through a molecular wire connected to an atomically clean contact. The molecular wire, which is 0.3 nm wide and 1.7 nm long, was electronical ly connected on one side, and a scanning tunneling microscope tip was used as a second movable electronic counterelectrode. The results reveal a clear exponential decay in the transparency (conductance) of the wire with dista nce from the contacted end. Analysis of the data shows that electrons are t ransported along the molecular wire by virtual resonance tunneling with an inverse decay length of 3 nm(-1), in excellent agreement with theoretical c alculations.