Advanced in the search for graphene-based electronics

In theory, graphene can be modified to perform many different tasks, e.g. electronics, photonics or sensors by simply cutting out tiny patterns, which fundamentally alter its quantum properties. A "simple" task, which has proved surprisingly difficult, is to induce a band gap essential for the fabrication of transistors and optoelectronic devices. However, since graphene is only an atom, all atoms are important and even very small irregularities can destroy their properties.

"Graphene is a fantastic material that, in my opinion, will play a crucial role in the fabrication of new electronics at the nanoscale.The problem is that it is extremely difficult to design the electrical properties", says Peter Bøggild, professor at DTU Physics.

The Center for Nanostructured Graphs DTU and the University of Aalborg were created in 2012 with the aim of studying how to adapt the electrical properties of graphene by changing its shape on a very small scale. When modeling graphene, the team of researchers at DTU and Aalborg experienced the same thing as other researchers around the world: it did not work.

"When you create patterns in a material such as graphene, you do it in order to modify its properties in a controlled way – to fit your design, but we have seen over the years that we can drill holes, but not without introducing so much mess and contamination that it no longer behaves like graphene.It's a bit like making a water pipe partially obstructed due to poor workmanship.Outside, it may sound good, but the water can not flow freely, it's obviously disastrous, "says Peter Bøggild.

Now, the team of scientists has solved the problem. The results are published in Nature NanotechnologyTwo postdoctoral researchers from DTU Physics, Bjarke Jessen and Lene Gammelgaard, first inserted the encapsulated graphene into another two-dimensional material: hexagonal boron nitride, a non-conductive material often used to protect the properties of graphene.

Then they used a technique called electron beam lithography to carefully model the protective layer of boron nitride and graphene below with a dense network of ultra-small holes. The holes have a diameter of approx. 20 nanometers, with only 12 nanometers between them – however, the roughness at the edge of the holes is less than 1 nanometer, one billionth of a meter. This allows 1000 times more electrical current to flow than what was reported in such small graphene structures. And not only that.

"We have shown that we can control the graphene band structure and design its behavior.When we control the structure of the band, we have access to all the properties of graphene – and we were surprised to see that some of the electronic effects Subtle quantum patterns survive dense patterns – this is extremely encouraging – our work suggests that we can sit in front of the computer and design components and devices – or imagine something completely new – then go to the lab and to achieve them in practice, "says Peter Bøggild. He keeps on:

"Many scientists have long since abandoned nanolithography in graphene at this scale, and it is a pity that nanostructuring is an essential tool for exploiting the most interesting features of graphene electronics and photonics. We've now figured out how to do it, we could say that the curse is lifted, there are other challenges, but the fact that we can adapt the electronic properties of graphene is a big step forward in creating a new electronics of very small dimensions, "said Peter Bøggild.

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More information:
Bjarke S. Jessen et al. Graphene lithographic web structure engineering, Nature Nanotechnology (2019). DOI: 10.1038 / s41565-019-0376-3