Graphene, a sheet of carbon just one atom thick, is promising for making molecular electronic devices of the future due to its unique electronic, mechanical and thermal properties that include extremely high electrical conductivity and exceptional strength. It is tougher than diamond, but stretches like rubber. It is virtually invisible, conducts electricity and heat better than any copper wire and weighs next to nothing. It could lead to mobile phones high definition televisions as thin as wallpaper, and bent electronic newspapers that readers could fold away into a tiny square. It could transform medicine, and replace silicon as the raw material used to make computer chips. The chemistry of the surface on which graphene is deposited plays a key role in shaping the material’s conductive properties.
Research results show that when deposited on a surface treated with oxygen, graphene exhibits semiconductor properties. When deposited on a material treated with hydrogen, however, graphene exhibits metallic properties.
Graphene stacks
Recently, researchers have also turned their attention to multilayer graphene because they expect it to have even more astonishing characteristics due to enhanced electronic interactions between the layers making up the structure.
Triple layer graphene comes in two types; with different layer stacking orders: ABA and ABC. The difference is that the top layer is shifted by the distance of one carbon atom in the sheet relative to another. In such multilayer systems, the stacking order dramatically affects the electronic properties of the structures. The effect in graphene is expected to be particularly pronounced as ABA-stacked triple layers are predicted to be semi-metals with tunable band overlaps, and ABC-stacked triple layers are predicted to be semiconductors with tunable band gaps. ABA-stacked triple layer graphene is metallic and that ABC-stacked triple layer is insulating where as theory predicts both types of triple layers to be conducting.
The results indicate that ABC triple layer graphene has an intrinsic band gap, which likely comes from the enhanced electronic interactions in this multilayer system. A band gap, however small, is important for making electronic devices from graphene which normally lacks a band gap. The findings suggest that graphene's electronic properties can be tuned, in principle, by simply changing the stacking order of the layers.