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Portrait of Graphene

Science · Chemistry

Graphene

2004

Chemistry — carbon allotropes and materials science

Graphene is a single layer of carbon atoms arranged in a honeycomb lattice — one atom thick, and the two-dimensional sheet from which graphite, nanotubes and fullerene cages are all built. Theorists had long argued that a strictly two-dimensional crystal could not survive at room temperature, so the surprise of 2004 was not just that Andre Geim and Konstantin Novoselov at Manchester made it, but how: by repeatedly peeling flakes off a lump of graphite with ordinary adhesive tape. The material turned out to be extraordinary — stronger than steel by weight, an excellent conductor of heat and electricity, almost transparent, and host to electrons that behave as though they have no mass. Geim and Novoselov shared the 2010 Nobel Prize in Physics.

How to spot them

  • ▸A single atomic layer of carbon in a honeycomb lattice
  • ▸Isolated with sticky tape in a Manchester laboratory in 2004
  • ▸Electrons in it behave like massless relativistic particles
  • ▸About 200 times stronger than steel by weight, and nearly transparent
  • ▸Millions of layers stacked together make the graphite in a pencil

Key facts

A honeycomb sheet of carbon one atom thick — the thinnest material there is

Carbon–carbon bonds 142 pm long; each atom bonded to three others in a flat hexagonal net.

Andre Geim and Konstantin Novoselov isolated it in Manchester in 2004 using ordinary adhesive tape (2004)

The 'Scotch tape method': peel a flake off graphite, fold the tape, peel again, and repeat until one layer is left.

Its isolation won the 2010 Nobel Prize in Physics (2010)

Awarded 'for groundbreaking experiments regarding the two-dimensional material'.

Electrons travel through it as if they had no mass, behaving like relativistic particles

Its conduction and valence bands meet at points, so charge carriers act as massless Dirac fermions — and it shows the quantum Hall effect even at room temperature.

A one-square-metre sheet weighs about 0.77 milligrams yet could in principle hold up a four-kilogram cat

The Nobel committee's illustration of a hammock a million times thinner than a human hair.

Millions of these layers stacked on top of one another make the graphite in a pencil

Every time you write, you are probably shedding a few single layers.

It was long thought impossible, because a strictly two-dimensional crystal was supposed to be destroyed by thermal fluctuations

The Mermin–Wagner argument; real sheets survive by rippling slightly in the third dimension.

Key ideas

  • One atom thick and yet it absorbs about 2.3 per cent of the light passing through it — enough that a single layer is visible on a silicon wafer of the right thickness, which is how the Manchester group spotted theirs.
  • It is a zero-gap semiconductor: superb at carrying current, but hard to switch off, which is the central obstacle to replacing silicon with it in transistors.

Quick-fire facts

  • •The isolation was published in Science in October 2004, as 'Electric Field Effect in Atomically Thin Carbon Films'.
  • •Geim and Novoselov shared the 2010 Nobel Prize in Physics; Novoselov had been Geim's PhD student, and both had come to Manchester via the Netherlands from Russia.
  • •The work came out of Geim's 'Friday night experiments', deliberately speculative projects run outside the main research programme.
  • •Geim also won the 2000 Ig Nobel Prize in Physics for magnetically levitating a live frog — the only person to hold both an Ig Nobel and a Nobel.
  • •The name was coined by Hanns-Peter Boehm and colleagues in 1986, from graphite plus the -ene suffix.
  • •It is about 200 times stronger than steel by weight and conducts heat better than any other known material.
  • •The UK opened the National Graphene Institute in Manchester in 2015; commercial uses so far are mostly composites, coatings and batteries rather than electronics.
  • •Common misconception: graphite is not a different substance from it — graphite is simply a stack of these sheets held together by weak van der Waals forces, which is why pencils write.

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