The Physics of the Graphene Revolution

The Graphene lattice. Image from: https://singularityhub.com/2018/08/05/beyond-graphene-the-promise-of-2d-materials/

It is a poorly kept secret that graphene is a material with the potential to revolutionise the world of electronics. Alongside its optical transparency, its flexibility and its unparalleled physical strength, it is among the most efficient conductors of electricity known to science.

In some ways, it is remarkable that graphene conducts electricity at all. It is, after all, a lattice of carbon, which occupies the “non-metal” bin of high-school chemistry, so we might expect that it would be a poor conductor of electricity like, say, crystalline sulfur or phosphorus. And indeed diamond, a crystal of carbon, is an extremely good insulator. So why is graphene any different?

The electrons around any atom occupy distinct regions of space known as orbitals. These can come in a wide range of different shapes and sizes, but for carbon there are only two types of orbital present: two spherical s-orbitals and one dumbbell shaped p-orbital. Each of these contain two of the carbon atom’s six electrons.

Examples of s and p atomic orbitals. The p orbital shown is in the z direction, which is the orbital left unhybridised in the carbon atoms of the graphene lattice. Image from the Encylcopaedia Brittanica https://www.britannica.com/science/orbital/images-videos

More exciting is what happens when atoms bond. To do this, orbitals combine in a process known as hybridisation, and this can happen in a few different ways. In diamond, the…