Promising material graphene is now also easy to switch on or off

Graphene has been a promising material for a long time. It is only one atomic layer thin and consists of carbon atoms arranged in a hexagonal pattern. This atomic chicken wire has special properties that make smaller and faster computers possible.

But graphene lacked a crucial property: you can’t easily switch it on and off. An international group presented on Wednesday in Nature graphene with which this is possible.

Graphene makes more efficient electronics possible because electrons can move through it very quickly. It is also robust. You can drive large electrical currents through it without it heating up or breaking down. That makes it an ideal successor to silicon, which is starting to reach its limits.

For electronics you need semiconductors, such as silicon. These are materials that may or may not conduct electricity, depending on the circumstances. Semiconductors can therefore be used as switches (transistors) that you can turn on and off. This is possible thanks to the so-called band gap – the difference between two energy bands in which electrons can move in the material. If electrons have enough energy, they are in the high band and the semiconductor behaves like a conductor. With less energy they are in the low band and it is an insulator.

To let grow

“Of band gap is like a dam in a river,” emails Walter de Heer from the American university Georgia Tech, who is leading the research. “If the water level (electron energy) is lower than the dam, the water stops. If the water level is higher, it can flow through.” By applying an electric field you can change the position of the energy bands to turn the switch on or off. With that electric field you can, as it were, make the dam higher or lower.

You can make a semiconductor from graphene by growing it on the material silicon carbide. This technique has been around for some time, but usually produces a messy layer. The Lord and his group developed a technique to create an impeccable layer. To do this, they gradually heated silicon carbide to 1,600°C. This produces a single layer of graphene in which electrons move ten times faster than in silicon.

Mazhar Ali and Herre van der Zant from TU Delft, who were not involved in the research, call the result a great and important step. “I think it’s a surprise,” says Van der Zant. “I thought everything had already been tried, but this shows that it is possible.”

They emphasize that further steps are needed. “For example, if you want to make computer chips from it, you have to connect it with other materials,” says Ali. “This now ensures that the electrons are much slower than in loose graphene.”

According to De Heer, it will be a long time before you can buy a computer with graphene chips. “To me, this is like the moment the Wright brothers made the first flight (in 1903). It then took about 35 years until the first commercial flight across the Atlantic Ocean took place.”

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