On 22nd September, the members of Café Scientifique met to discuss Graphene.
Everyone has heard of carbon. It is an element on the periodic table. 6 protons, 6 electrons. Carbon based compounds are found in all living things. From the blue whale to the tardigrade and every living animal in between. There are many different allotropes of carbon. Diamond is one of the hardest substances known and is often used in cutting as the tip of drills. Graphite is soft and slippery and is used as a lubricant. Buckminster fullerene is in the shape of a football and is used in drug delivery systems. How can carbon atoms form structures that have such a wide range of uses? The answer lies in the bonding and structure of each allotrope. In diamond each carbon atom forms strong covalent bonds to four other carbon atoms in a tetrahedral arrangement. In graphite each carbon atom forms covalent bonds to three other atoms to give layers of hexagons. In Buckminster fullerene, each carbon atom bonds to four others to give a spherical structure. However, the most interesting of the allotropes of carbon is graphene. A two-dimensional substance that is one atom thick. Graphene is one layer of graphite. The chances are we have all made it at some point in our lives – just by writing with a graphite pencil. It was first isolated at the University of Manchester in 2004 by two professors. They removed some flakes from a lump of bulk graphite with sellotape. They soon noticed that some of the flakes of graphite were thinner than others. By separating the graphite fragments repetitively, they managed to create flakes which were just one atom thick therefore creating graphene! You may be wondering why this matters, how can a one atom thick substance have any use to us? It is important to remember some of graphene’s properties. It conducts electricity, it conducts heat, it is a 100x stronger than steel, it is the lightest material known to man. Still unsure? Graphene is one of the most in demand materials of today. In the beginning graphene was just integrated into a huge number and range of applications. It is expected to be used as efficient bioelectric sensory devices for example measuring glucose levels. Another idea is a graphene screen in your phone. At 97% transparent it is more than capable to be used as a material to replace the current glass screens. Perhaps a more surprising potential use of graphene is in ultrafiltration. This is due to a bizarre, but marvellous, property. Graphene allows water to pass through it but is almost completely impervious to other liquids and gases. Many people will have seen the adverts, whether it be Samsung or LG, for a graphene TV. Samsung have managed to produce a 30-inch sheet of pure graphene – one which is capable of being used as a TV screen. However, whilst these uses of graphene remain highly intriguing, the most exciting part of graphene is the fact that it is two dimensional. Imagine a 40cm by 20cm sheet of graphene. Length = 40cm Width = 20cm Height =? Now we know that graphene is one atom thick. So surely graphene’s height is the height of one carbon atom. But that gives graphene three dimensions – so that must make graphene 3D? No. You can only see graphene in two dimensions. Its length and its width. A human eye is not capable of seeing a height of one atom. Therefore, graphene is said to have three dimensions but be two dimensional and that is the real beauty of grapheme.
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June 2020
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