1. Could you explain the significance of your article to the non-specialist?

Aviram & Ratner provided the theoretical basis for molecular rectification more than thirty years ago when they proposed a donor-(bridge)-acceptor sequence as the organic counterpart of the p-n junction. Rectification arises because electrons can more readily tunnel from the cathode to acceptor on one side of the device and from the donor to anode on the opposite side. 

However, current rectification ratios obtained from these ultra-thin films are typically less than 30 at ±1 V: they are too small to have any practical significance but those reported in this paper are in excess of 3000 at ±1 V. The enhancement was achieved by improving the donor/acceptor combination, in this case by using an ionically coupled bilayer arrangement that comprised a cationic donor-(pi-bridge)-acceptor molecule and an anionic phthalocyanine donor: Au|Au-S-C₁₀H₂₀-A⁺-pi-D|D^-|Au.

 

2. What has motivated you to conduct this work?

I have been interested in the diode since 1990 when collaborative studies with Roy Sambles at the University of Exeter provided tentative evidence of molecule-induced rectification. The discovery was at first treated with curiosity but, in the last five years, there has been renewed interest and three of the early papers have been cited in total about 600 times. The motivation at first was to verify the molecular origin of the electrical asymmetry and then to improve the rectification ratio from ultra-thin films.

 

3. Where do you see this work developing in the future?

There is now widespread interest in molecular scale electronics and this discovery has important implications in the design and synthesis of components with even higher rectification ratios. There is still a long way to go but these self-assembling molecules appear to provide a link to the ultimate challenge of electronic device miniaturisation.

 

4. Are there any particular challenges facing future research in this area?

The main challenge involves the nano-to-macro interface: methods are needed to contact single molecules, which may involve the sculpting of nanometer-scale device structures with electrode gaps of predetermined size to locate electro-active molecules.