Columbia Engineering researchers have designed a new technique to build a single-molecule diode. Their results achieved rectification ratios as high as 250, fifty times higher than earlier designs.

The molecule itself acts as a rectifier, a one-way conductor of electric current. Since the diode acts as an electricity valve, its structure needs to be asymmetric so that electricity flowing in one direction experiences a different environment than electricity flowing in the other direction.

In order to develop a single-molecule diode, researchers have designed molecules that have asymmetric structures. The asymmetric molecular designs, however, have typically suffered from very low current flow in both "on" and "off" directions, and the ratio of current flow in the two has typically been low.

The new design from the Columbia team allows current to flow in one direction — at up to more than 0.1 microamps. The technique can be applied to nanoscale devices of all types, including those that are made with graphene electrodes.

In order to overcome the challenges associated with asymmetric molecular design, the researchers developed an asymmetry in the environment around the molecular junction. The team surrounded the active molecule with an ionic solution and used gold metal electrodes of different sizes to contact the molecule.

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