Graphene: Tying ribbons of graphene

04/25/2016

Extremely thin ribbons of graphene grown on copper could open applications for the ‘miracle material’

A topographic scanning tunneling microscopy image showing graphene nanoribbons (green) grown on a copper substrate (blue).
A topographic scanning tunneling microscopy image showing graphene nanoribbons (green) grown on a copper substrate (blue).

© 2016 Patrick Han

A method that produces tiny units of graphene and joins them together to form highly connected stripes has been found by AIMR researchers. This ‘bottom-up’ fabrication technique could unleash graphene’s potential for use in high-speed, low-power electronic devices.

Since its discovery in 2004, graphene has generated much excitement due to its remarkable electronic and mechanical properties. But for it to become useful in applications, scientists need a way to combine graphene nanostructures such that they form macroscale components while still preserving graphene’s excellent properties.

Extremely narrow (thinner than 50 nanometers) stripes of graphene, known as graphene nanoribbons, promise to achieve this, but current processing methods produce either well-connected nanoribbons that contain defects or entangled bundles of nanoribbons that are defect free.

Now, Patrick Han of the AIMR at Tohoku University and his co-workers have found a way to produce well-connected strings of nanoribbons without defects1. Their method produces good-quality graphene nanoribbons and connects their ends so that they form chemically and electronically connected structures (see image).

The researchers found that, on applying heat, a copper substrate guides precursor molecules to form and connect graphene ribbons. The lengths and growth directions of the nanoribbons could be controlled by varying the substrate properties and the temperature.

“There are two outstanding questions regarding how graphene can be applied in electronics,” comments Han. “One is how to fabricate atomically precise graphene structures with high aspect ratios at desired locations, while the other is how to make electronic connections between these structures to access graphene’s properties.”

The method provides answers to both questions. “If precursor molecules are allowed enough time and space to align, graphene nanoribbons with very high aspect ratios can be produced without defects. Moreover, graphene nanoribbon interconnections yield smooth electronic connections, showing that bottom-up strategies can access graphene’s amazing properties.”

Han notes that while other two-dimensional materials have recently been stealing the spotlight from graphene, it still has a unique advantage ― organic chemistry can be used to fabricate defect-free structures from designer precursors. “In this regard, our method is a significant advance ― the use of bottom-up graphene fabrication strategies may lead not only to the production of future graphene nanodevices, but also to the integration of non-graphitic materials.”

Since copper substrates limit growth to six directions, growing graphene nanoribbons inevitably collide, limiting their length. The team intends to overcome this restriction by finding strategies to limit growth to a single direction.

References

  1. Han, P., Akagi, K., Federici Canova, F., Shimizu, R., Oguchi, H., Shiraki, S., Weiss, P. S., Asao, N. & Hitosugi, T. Self-assembly strategy for fabricating connected graphene nanoribbons. ACS Nano 9, 12035–12044 (2015). | article

This research highlight has been approved by the author of the original article and all empirical data contained within has been provided by said author.