The carbon molecules in graphene (top) each possess only three bonds, leaving free electrons to conduct charge. Adding hydrogen (bottom) creates a fourth bond, locking up the free electrons and converting the sheet to an insulating state (Image: Science)

Computer processors may soon have one fundamental aspect in common with their owners – a structure composed largely of carbon, rather than silicon.

Graphene, carbon arranged in atom-thick sheets, is already known to be an excellent conductor, but electronics requires the ability to insulate too, as well as electrical properties in between those two extremes.

Now research has shown that the material can be easily modified to act as an insulator, paving the way for efficient all-carbon electronics (see our feature What happens when silicon can shrink no more?).


The semiconductor industry exploits the “whole periodic table” to manufacture its components, says Konstantin Novoselov at the University of Manchester, UK. “But what if a single material is modified so that it covers the entire spectrum needed for electronics?” Graphene could be that material, he says.

Using a single material could simplify construction and allow near-seamless interconnections between conductors and semiconductors – currently as much of a headache for the chip manufacturers as the need to constantly shrink transistors.

Just add hydrogen

Discovered in 2004, graphene is made from sheets of carbon atoms in a hexagonal “chicken wire” arrangement. The material is an ideal conductor – electrons whiz through the layers at near the speed of light.

Novoselov and colleagues have shown the material can be easily modified to act as an insulator by adding hydrogen atoms to its surface. The new material – called graphane – is made by exposing a graphene sheet to ionised hydrogen gas for two hours.

The carbon-hydrogen bonds created lock away electrons that in graphene are free to move as current.

Alex Savchenko at the University of Exeter in the UK thinks the new find is significant. “In electronics, all digital elements – transistors – switch signals on and off, so they should have a large difference between the open and closed-state resistances,” he says.

Graphene ordinarily lacks that “band gap”, and finding a way to add it has kept physicists busy in recent years.

One-sheet wonder

“The new study offers perhaps [the most] practical solution,” Savchenko says. Using the technique, it is possible to tune the graphene to be conductor, insulator, or anything in between.

That paves the way for a sheet of graphene to be transformed into a working chip with conductive interconnections and semiconducting transistors simply by changing its chemistry in different areas.

Novoselov’s study comes a week after Philip Shemella and Saroj Nayak at the Rensselaer Polytechnic Institute in Troy, New York, reported a similar insulating effect by depositing pure graphene on a silicon-dioxide substrate (Applied Physics Letters, DOI: 10.1063/1.3070238).

The researchers found that the oxygen atoms in the substrate form covalent bonds with the graphene, which has the same effect as bonding with hydrogen – it turns the graphene into an insulator.

“The discovery of graphane and our results are related,” says Shemella. “Both studies are interesting for extending the versatility of graphene-based structures.”

Journal reference: Science (DOI: 10.1126/science.1167130)