Graphene is just the beginning

Many new materials are emerging to revolutionise technology and Brazil is on the front line of this research, says Antonio Castro Neto, who heads Singapore's Centre for Advanced 2D Materials and Graphene Research Centre.

By Heitor Shimizu, in Barcelona

Agência FAPESP – Graphene has been in the news a good deal in recent years, as the harbinger of a technological wave set to lead to the development of ultrafast computers, one-atom-thick transistors, safer medical implants, and flexible electronic devices that can fold to fit in a pocket. All this and much more.

The extraordinary potential of this graphite-derived material is explained by its unusual properties: for example, it is light, 200 times stronger than steel, and extremely thin – a million times thinner than a human hair. Moreover, it conducts heat and electricity better than any other known material.

But graphene is not alone. It is only one of many new two-dimensional materials, so called because they consist of a single layer of atoms or molecules. Together these 2D materials could potentially signal the advent of a major scientific and technological revolution. What is more, the vast majority are still practically unexplored, according to Antônio Hélio de Castro Neto, a Brazilian physicist who heads the National University of Singapore’s Centre for Advanced 2D Materials and Graphene Research Centre.

“Many of these materials have yet to be discovered and studied. It can’t even be said we’ve found the tip of the iceberg. The number of 2D systems is immense and we’re only just starting to look at them,” Castro Neto said during FAPESP Week Barcelona, which took place on May 28-29 in the Catalan capital.

“Then there are 3D heterostructures, which are still in their infancy but will also become a huge field with enormous economic value because of the many potential applications,” he said.

Castro Neto is also a visiting professor at the Mackenzie Presbyterian University’s Centre for Advanced Research in Graphene, Nanomaterials & Nanotechnology (MackGrafe) in São Paulo, Brazil. Unveiled in 2014, MackGrafe is supported by FAPESP.

“The university is investing US$20 million in the centre,” he said. “FAPESP is providing another US$5 million through the São Paulo Excellence Chairs Programme. I’m proud to be the lead investigator for this project. In sum, the entire field has a lot to offer.”

MackGraphe and the Singapore centre collaborate under an agreement between Mackenzie Presbyterian University and the National University of Singapore.

Complementary materials

Andre Geim and Konstantin Novoselov, both from the University of Manchester in England, won the 2010 Nobel Prize in Physics in recognition of their research leading to the development of graphene, whose theoretical existence had been described decades before.

“Graphene is obtained from graphite, which is nothing more than a handful of layers of graphene stacked on top of one another. We exfoliate graphite to obtain a material that’s only one atom thick, made of pure carbon,” Castro Neto explained.

In 2005, he went on, Geim and Novoselov had already highlighted the potential not just of graphene but of all 2D crystals in an article published by the journal Proceedings of the National Academy of Sciences.

“They realised graphene wasn’t the only material that could be isolated in this way. In a fantastic article entitled Two-dimensional atomic crystals they showed that the process used to obtain graphene could also be applied to other materials.

“That article opened up the new field of 2D crystals, although in a sense graphene is a field apart because it’s been more explored and researched than the rest,” he said. Many of the new materials have complementary properties and could be used in conjunction with graphene in a theoretically unlimited number of combinations.

One of these new materials is molybdenum disulphide, Castro Neto said. Another is phosphorene, basically a single layer of black phosphorus. Phosphorene has semiconductive properties and is being studied with great emphasis by Castro Neto’s group in Singapore. Transition metal dichalcogenide (TMDC) is yet another, and many more are starting to appear in laboratories around the world.

“These new materials have non-trivial optical properties. They’re thin and soft like membranes, so they aren’t like known solids. Their softness is reflected by their electronic properties,” he said.

“Indeed, the most particular characteristic of these 2D materials is the fact that they’re membranes. They have pure surfaces without irregularities, and their electronic properties can be modified by the application of forces. We can stretch them or modify them chemically. One of the most significant benefits of working with these materials is chemical functionalisation.”

Castro Neto also spoke about some of the challenges faced by the scientists who are researching these new materials, such as the difficulty of producing them in the laboratory, let alone on an industrial scale.

“Exfoliation takes a long time. We’re hopeful that engineers will create new technologies capable of manipulating these 2D crystals mechanically. I expect robotics to be very helpful in this regard,” he said.

“Without doubt computer science will also play a key role in this exploration. They’re complex materials so we can’t do simple modelling. Without sufficient computational power, we won’t know what’s happening.

“This is an exciting field with many surprises, unlike many others. I think science is especially fascinating when there are surprises.”