Arunachalam’s Weblog

In the quest to turn the vision of molecular electronics into reality, the fundamental problem of charge transport through molecular wires is currently being investigated in many labs all over the world. However, the experiments face a dilemma. On the one hand, we know that the contacts to the wire are extremely important for its conductance properties, on the other hand there is – within conventional approaches – no way to obtain atomic-scale information about them. Harnessing the power of surface science for molecular electronics, scientists at the Forschungszentrum Jülich have recently reported a proof-of-principle experiment that overcomes this dilemma.

The experiment utilizes a two-step approach based on ordered molecular layers on metals. In step 1, the powerful armoury of surface science is employed to characterize the structural and electronic properties of the molecule-substrate bond. In step 2, the tip of a low-temperature scanning tunnelling microscope (STM) is covalently connected to a single molecule in the ordered layer. Because of the STM’s excellent imaging properties, the tip can accurately contact a predefined part of the molecule. In this way a molecular wire with two structurally well-defined contacts is realized. Moreover, it is possible to gate the wire mechanically by retracting the tip and gradually peeling the molecule off the surface. The experiment is a breakthrough for the comparison with ab initio simulations of transport, because such detailed structural information on a tunable single-molecule transport junction is hardly ever available. A detailed simulation programme is currently under way. Molecular electronics is a visionary concept conceived in 1973 by Aviram and Ratner, according to which purpose-designed molecules embody the full functionality of electronic switches in their chemical structure. Molecular electronics not only promises ultimate miniaturization of electronic devices, but may also allow easy-to-use bottom-up assembly strategies for making electronic circuitry.