Future electronic devices could use self-assembling molecules

Organic molecules that self assemble into nanoscale circuits could herald the next generation of electronic devices, following a proof-of-concept study at Cambridge University.

The research team created a ‘pavement’ of pentagonal cyclopentadienyl (C5H5) ‘tiles’ — resulting in a stable and highly conductive film.

As project lead Dr Holly Hedgeland of Cambridge explained to The Engineer, it represents an important step in the ‘bottom-up’ manufacture of nanoscale devices.

‘Obviously you can manufacture things on a one-off basis, using things such as probe microscopy — pushing things around with a tip basically — but that’s not going to be scaled up to anything that’s realistic,’ she said. ’We’re really trying to look at the fundamental properties and see how we can use them.’

Currently, commercial electronics use a top-down approach, with the milling or etching away of inorganic material, such as silicon. For many years, the computing power of a given size of computer chip has been doubling every 18 months (a phenomenon known as Moore’s law) but a limit in this growth is soon expected. 

At the same time, the efficiency of coupling electronic components to incoming or outgoing light (either in the generation of electricity from sunlight or in the generation of light from electricity in flat-screen displays and lighting) is also fundamentally limited by the scale of the circuitry.

Some progress has been made with nanoscale circuits, but the process still relies on top-down processes such as scanning probe microscopy that do not result in stable and reproducible components.

Hedgeland and her team turned their attention to cyclopentadienes, whose fivefold symmetry makes them amenable to self assembling onto a copper surface with triangular, threefold symmetry. The result is a high-density film with potential applications in computing, solar power and novel display technologies. 

In its recent work, the team studied the dynamic behaviour of the self-assembly process and found that the molecules remain highly mobile and yet strongly bound to the surface, with a large degree of thermal stability.

‘It’s the first time this particular effect, in terms of the interactions and the direction of the work function change, has been seen for this kind of extended molecule — it’s putting up a flag in terms of investigating these prototypical devices,’ Hedgeland said.

Hedgeland said her team, which carried out its latest work with Rutgers University in the US, is now investigating the use of graphene substrates for nanoscale circuits.