Buckyballs and diamondoids combined to create molecule-sized diode

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Molecule-sized "buckydiamondoids" have been created that exhibit similar electrical properties to a simple rectifier diode (Image: Manoharan Lab/Stanford University)

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Scientists working at the Stanford Institute for Materials and Energy Sciences (SIMES) claim to have created a molecule-sized electronic component just a few nanometers long that conducts electricity in only the one direction. In essence, a rectifier diode, but one so small that it may one day help replace much bulkier diodes and other semiconductors found on today's integrated circuits to produce incredibly compact, super-fast electronic devices.

Created using two unconventional types of carbon – Buckminsterfullerene (aka buckyballs, spherical molecules of carbon in a fused-ring structure) and diamondoids (microminiature nanoscale carbon cage molecules that are incredibly strong) – the resultant "buckydiamondoids" exhibit asymmetric conductance when an electric current is applied. That is, they act just like diodes in conducting electricity in one direction, but block it if it is applied from the other direction.

"We wanted to see what new, emergent properties might come out when you put these two ingredients together to create a 'buckydiamondoid,'" said Hari Manoharan, Associate Professor at Stanford and researcher at SIMES. "What we got was a basically a one-way valve for conducting electricity – clearly more than the sum of its parts."

Building on previous work by a team of scientists from SLAC (Stanford Linear Accelerator Center) and Stanford University, which demonstrated that a layer of diamondoids on a metal surface – with a small bias voltage applied – can be made to efficiently emit a beam of electrons, the latest research arose from the idea of pairing such electron-emitting devices with a molecule that attracted electrons.

The diamondoids were produced in the SLAC laboratory by extracting these tiny molecules from petroleum, where they naturally occur. These were then sent to Justus-Liebig University in Germany, where the chemists there attached them to the buckyballs.

The resultant buckydiamondoids were then sent back to Professor Manoharan and his team to test an electrical current flowing through these combined molecules. What they discovered was that electron flow was up to 50 times stronger in one direction (from the diamondoid to the buckyball) than in the opposite direction.

Though not the first molecular rectifier diode ever created, this is the first one constructed from just atoms of carbon and hydrogen, unlike others that have used such metals as gold and platinum. The simplicity of construction and of the elements used also offers hope in constructing more complex electronic components, such as transistors.

"Buckyballs are easy to make – they can be isolated from soot – and the type of diamondoid we used here, which consists of two tiny cages, can be purchased commercially," said Professor Manoharan. "And now that our colleagues in Germany have figured out how to bind them together, others can follow the recipe. So while our research was aimed at gaining fundamental insights about a novel hybrid molecule, it could lead to advances that help make molecular electronics a reality."

The team reported the results of their research in the journal Nature Communications.

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