Graphene

Graphene is a unique form of the element carbon. It is a carbon allotrope, which means it is a version of carbon with a different structure. Specifically, it is a single layer of atoms arranged in a two-dimensional honeycomb planar nanostructure. This material is considered the thinnest two-dimensional material in the world. While carbon is commonly found in forms like diamond or graphite, graphene exists as a single-atom-thick sheet.

The structure of graphene is defined by how its atoms are bonded. Each carbon atom is connected to three nearest neighbors through sigma bonds, or σ-bonds. These bonds are formed by the overlap of sp2 hybrid orbitals. The remaining outer-shell electron occupies a pz orbital that points perpendicularly away from the sheet. These orbitals create delocalized pi bonds, or π-bonds, which extend over the entire sheet. This bonding creates a valence band that touches a conduction band. Because of this, graphene acts as a semimetal with very unusual electronic properties.

Graphene is characterized by several extraordinary physical properties. On a microscopic scale, it is the strongest material ever measured. It also possesses exceptionally high electrical conductivity and high tensile strength. Despite being a solid material, a single sheet is nearly transparent. It only absorbs approximately 2.3% of visible light. In contrast, graphite is made of many graphene layers stacked together. Because graphite absorbs all visible light wavelengths, it appears black to the eye.

The history of graphene involves many decades of theoretical and experimental work. In 1947, the Canadian physicist P. R. Wallace first suggested that carbon could exist in sheets. He did this while researching the electronic properties of 3D graphite. Later, in 1986, the German chemist Hanns-Peter Boehm and his coworkers isolated single sheets from graphite. They gave these sheets the name "graphene," derived from "graphite" and the suffix "-ene." This suffix indicates the presence of double bonds within the carbon structure.

A major breakthrough occurred in 2004 at the University of Manchester in England. Scientists Andre Geim and Konstantin Novoselov successfully isolated and characterized graphene. They used a method called micro-mechanical cleavage, often called the "Scotch tape technique." They used adhesive tape to pull thin layers from a piece of graphite. They then transferred these flakes onto a silicon wafer with a thin silicon dioxide layer. This setup allowed them to study the material's properties effectively. For these groundbreaking experiments, Geim and Novoselov received the Nobel Prize in Physics in 2010.

Measuring graphene reveals just how small and light it is. The molecular bond length in the lattice is 0.142 nanometers. A single hexagonal unit of graphene has an area of 0.052 square nanometers. Each unit contains two carbon atoms with a combined mass of 0.000000000000000000000036 milligrams. This means the two-dimensional density is 0.77 milligrams per square meter. To visualize this, one kilogram of graphene would cover 131.2 hectares.

Today, scientists are working to move graphene from the lab to the real world. In 2012, the global graphene market was valued at $9 million. Most of this demand comes from research into semiconductors, electronics, electric batteries, and composites. In 2014, the National Graphene Institute was established at the University of Manchester with £60 million in funding. While small amounts are easy to produce, making large quantities is difficult. Companies struggle with cost-effectiveness and quality control during mass production. However, the search for commercial uses continues in many different scientific fields.