Thursday, April 18, 2013

Graphene: The Next Wonder Material?

By Michael Tinnesand

There is a new wonder material in town that might change our future. Imagine a coffee cup that streams the day’s headlines in real time. Or a cooking pot that can detect the presence of E. coli bacteria that could make you sick. Or a television screen that is as flexible and thin as a piece of paper. All of these applications could be a reality if the wonder material, named graphene, lives up to its hype.

Chicken wire made of carbon

Graphene rocked the world of chemistry in 2004 when scientists discovered that it had remarkable properties: It conducted electricity better than any other common substance, it was the thinnest known material—only one-atom thick—and it was stronger than steel!
After all, carbon is one of the most common and most familiar of the known chemical elements, so scientists were surprised to find that this new form of carbon had such amazing properties.
Carbon comes in many crystalline forms, called allotropes, the most well-known being diamond and graphite. Allotropes are different forms of the same element with different bonding arrangements between atoms, resulting in structures that have different chemical and physical properties. The way atoms are connected to each other in solid materials has a huge impact on their overall properties.
A diamond and a piece of coal are so different that you would never guess that they are both made of the same element—carbon. Diamond is a hard and transparent mineral that is ejected to the surface from deep within the Earth’s interior through volcanic eruptions, while graphite is a black and lightweight material extracted from coal.
In diamond, each carbon atom is connected to four other carbons. This is a very strong arrangement that makes diamond one of the hardest known materials. In graphite, each atom is linked to three others in layers of hexagonal (six-sided) shapes that look like chicken wire (Fig. 2, p. 8). The bonds within the hexagonal sheets are strong, but each layer is only weakly attracted to the next, which allows the layers to slip by one another.
In 2004, Andre Geim and Konstantin Novoselov, two chemists at the University of Manchester, United Kingdom, used this property to produce samples of graphene and discover its remarkable properties. They used sticky tape to separate the layers of carbon in graphite. To get an idea of how their technique worked, think of pressing sticky tape onto a piece of graphite and pulling it away, leaving the sticky surface covered with graphite flakes. Then, press the sticky tape to itself and pull it apart. Repeat, and after a few rounds of this, some flakes on the tape will be only a single one-atom thick layer—pure graphene.
Sticky tape can be used to peel off powdered graphite, leaving a single layer of graphene
Sticky tape can be used to peel off powdered graphite, leaving a single layer of graphene.

The initial samples of graphene were very small—only a couple of square millimeters in size each—but large enough to test. Because graphene is only one-atom thick, it is considered to be a two-dimensional material, the first example of such a thing in the real world. Despite being the thinnest material known to exist, it is also the strongest material ever tested—100 times stronger than steel.
Even more amazing: Electrons do not scatter as much when they move as they do in other materials, such as silicon. This led researchers to make graphene-based transistors that are twice as fast as traditional silicon transistors, which could make computers run much faster.

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