Flat out: being two-dimensional isn’t always a bad thing

The future is flat, and things will never be the same, according to 180 scientists who are attending a conference in Dublin. The latest flat technology will find its way into electronics, replacement hips, new kinds of batteries, lighter aircraft and a host of other applications.

Trinity College Dublin is hosting the packed three-day meeting, Flatlands: Beyond Graphene. Here, scientists and nanotechnology experts will hear about the latest two-dimensional materials that are going to cause big changes.

These remarkable new materials form sheets that are very thin – not thin in the common sense, but really thin: just one atom thick. When it comes to flat, it doesn’t get much flatter than the diameter of a single atom.

Graphene – sheets of pure carbon exfoliated from graphite – is one such 2D material. It has been the focus of much scientific attention over the past 10 years as researchers have rushed to study and find uses for such an unusual material.

It has caught the attention of the European Commission, which has agreed a €1 billion graphene research budget, including €500 million in EU funds and matching money from member states willing to take part. It is important enough to be considered a "flagship" initiative, and Prof Andrea Ferrari, the chair of its executive board, who is in Dublin for the event.

"The title of the flagship is graphene, but it was always the mission of the flagship to look at all these other two-dimensional materials," says Ferrari, who is also the director of the graphene centre at Cambridge University. He presented his own research yesterday at the conference.

World leader

The world's top scientists on 2D materials are in Dublin because Trinity itself is a world leader in this field. Prof Jonathan Coleman and Prof Valeria Nicolosi and their teams are leading the charge in the Amber research centre at Trinity, funded by Science Foundation Ireland.

Coleman developed the first cheap and effective way to exfoliate graphene in 2011, and then began stripping sheets off other 2D materials. His work was published in Science and was its most cited paper in 2011.

Both scientists are also European Research Council grant holders and have international reputations for their work. They published a review of the field in Science last year, which included about 550 materials that produced sheets.

“They come with a host of different chemical species,” says Nicolosi, who is chairing the Flatlands conference. “Each has specific properties – for example, metallic, semiconductor – some are brittle or mechanically robust, some have thermal properties. This conference is going to be focused on all of these two-dimensional materials but not graphene.”

Trinity has been involved in this research since early on. “Amber would be regarded as one of the leading research centres in two-dimensional materials,” says Coleman. “That gives us a great advantage in that we can attract leading researchers to the meeting.”

He likens materials that form these sheets to a deck of cards. His method to separate these cards from the deck one by one in order to make them usable was very low-cost: a kitchen blender and a bit of washing-up liquid.

His work with Nicolosi has shown there are limitless options to pursue in terms of applications. “For every application you can think of, there will be a two-dimensional material for you.”

Some of the best and most commercially important ones are in the area of energy, he says. Solar cells that produce electricity directly from the sun are layered, but because they include platinum, they are “horribly expensive”, but sheets including molybdenum could be used to replace the platinum to deliver cells “for a fraction of the price”.

Chemical reaction

Amber is working with Alcatel-Lucent's research arm, Bell Labs, using these thin sheets as electrodes in batteries to make them smaller and able to store more energy. They are also being used as catalysts, which are substances that speed up chemical reactions without being consumed in the process.

“Some of these two-dimensional materials are among the most efficient catalysts known,” says Coleman, who is also deputy director of the materials component of the graphene flagship. In this case, the sheets would be used to split the strong bond that holds hydrogen and oxygen together as water. It would deliver a cheap and plentiful supply of hydrogen for use as an alternative energy for fuelling vehicles.

Their review showed there were hundreds of these materials and there will likely be more. “There will be many new materials, but with so many existing ones, we have only scratched the surface of what we can do with them. We are going to be very busy over the next 10 years,” he says.

SMALL WORLD: NO SUCH THING AS TOO THIN

Miniature is too big a word to describe the two-dimensional world that has material scientists around the world buzzing. When they talk about 2D, they mean really thin, a sheet of flat carbon or forms of tungsten or nickel just one atom thick.

Scientists at Trinity College Dublin have been world-beaters in developing ways to “exfoliate” these two-dimensional sheets, work that originated with graphite used to produce carbon sheets of graphene. These sheets were a huge deal but now graphene has been overtaken, part of a much bigger pool of 2D options.

“We are talking about hundreds of nanomaterials,” says Prof Valeria Nicolosi, professor of chemistry and physics and a European Research Council grant holder in Crann and Amber nanotech centres at Trinity.

“We counted more than 550 different materials. They come with all kinds of different chemical species – molybdenum, nickel, tungsten – mixed with other elements,” she says. “The nice thing is that all these different types of materials can be synthesised in the same way we synthesise graphene.”

What does it means for the scientists? Option shock. Each sheet offers different properties and characteristics, depending on how you plan to use them.

“You suddenly have a zoo of different materials opening up a whole world in front of you and a world of applications,” says Nicolosi.

They can be used to produce batteries that last longer and give more power, bio-compatible versions can be used as a scaffold to grow new bone for hip replacements and others offer new methods of separating valuable hydrogen from water.

“The applications are almost infinite,” she says.