I’ve been a professional organic chemist for over ten years, and one of the most exciting developments I’ve seen during that time was the discovery of graphene. Graphene (not to be confused with graphite) is a thin molecular sheet made entirely from carbon molecules. The compound resembles a flat layer of hexagons, all fused to each others edges, kind of like a hexagonal grid map. The molecule has a large array of overlapping electron orbitals which means that it’s very easy for an electron to pass freely over the surface of the material and travel large distances. This high conductivity of graphene makes it very attractive for use in thin film electronics such as transistors and displays.
While graphene is very exciting for a large number of chemists and physicists, it’s only been in the last two years that advances have been made in it’s production. While crude graphene is actually pretty simple to make, there are huge difficulties in making large amounts that also have a uniform thickness. Graphene is only useful if it can be isolated in extremely thin layers (ideally, one atom thick). So far, methods have ranged from the use of Scotch tape to lift single layers of carbon to a more complicated process called chemical vapor deposition, or CVD. CVD. By taking a thin sheet of hot metal and exposing it to a natural gas atmosphere, the hydrogen is removed from the methane molecules and a thin layer of carbon is deposited on the hot metal.
However, current graphene production techniques using CVD have hit a snag. While metal objects may look shiny, smooth, and reflective, such appearances can be deceiving. On the atomic level, the surface can be very rough. These microscopic crevices and crannies can fill up with the deposited graphene from the vapor deposition. The result is sort of a “positive” carbon impression of the “negative” metal surface. While technically the entire material is made up of graphene sheets, it can’t be separated into separate sheets of uniform thickness. Therefore, it’s not very useful. There is an additional complication: CVD techniques only succeed when most of the air inside the sample chamber has been evacuated. This requires powerful vacuum pumps which are susceptible to leaks, and which are difficult to manage over a large surface area.
As an organic chemist who would love to get his hands on graphene (I’ve been active in the organic electronics area for over a decade), this synthetic limitation has always irked me. That’s why I was excited to read a very recent publication in the American Chemistry Society journal, Chemistry of Materials. The researchers reveal that graphene can be produced by CVD over a large surface area, and with atmospheric pressure (not vacuum). The key is using a simple copper foil which can be purchased from any supplier. The foil is electropolished, which is a technique that dissolves peaks and surface roughness from a metal material by immersing the metal in an electrolytic bath. Metal from the rough surfaces dissolves faster than recessed metal, meaning that the smoothness of the surface increases over time.
The resulting polished copper foil allows the production of graphene from methane at normal atmospheric pressure, which avoids the use of the troublesome vacuum systems, and it also allows for a large amount of the graphene to produced at once. I’ve seen numerous developments in organic chemistry come and go that were sunk by the lack of a large scale, practical synthesis. Thankfully, graphene production will not follow down the roads of these other failed technologies. Using this new method will allow chemists and physicists access to large amount of quality graphene at a low cost, which will translate into cheaper, better electronic devices.
The source of this article can be found at:
Luo, Z., et al. “Effect of substrate roughness and feedstock concentration on the growth of wafer-scale graphene at atmospheric chemistry”. Chem. Mater 2011, 23, 1441-1447.