Oct 1, 2010
Mica pairs up with graphene
Graphene could be ideal for making a host of electronic devices, such as ultrafast transistors and single-molecule detectors, thanks to its unique electronic and mechanical properties. However, for real-world applications, the material needs to be deposited on a substrate first and many of these can seriously degrade graphene. Now, researchers in Germany and the Netherlands have discovered that graphene's electronic structure seems to remains intact when it is deposited on mica.
"Wonder material" graphene consists of a planar single sheet of carbon arranged in a honeycombed lattice. It is currently attracting a lot of interest in the scientific community and many believe that it could be the ideal replacement for silicon in future electronics. This is because charge carriers, electrons and holes, travel ballistically through the material at extremely high speed, which leads to an extremely high conductivity – perfect for making ultrafast devices.
One drawback with graphene, however, is that it contains ripples, or wrinkles, similar to those seen on tightly pulled plastic cling film. These occur because of pre-existing strains in the material, and are possibly caused by the contours of underlying substrates. The corrugations are roughly 1 nm high and spread over distances of between 10 and 25 nm. They can adversely affect the material's electronic properties by inducing effective electromagnetic fields and changing local potentials that limit how fast charge carriers can travel.
Mica is a silicate-based mineral and it is relatively flat and smooth. It is widely used in electronics because it has good physical, chemical and thermal properties, shows low power losses and has a high dielectric constant and dielectric strength – that is, it can withstand high voltages.
Mikhail Katsnelson of Radboud University in the Netherlands and colleagues from Hamburg in Germany have calculated that graphene's electronic structure remains virtually unchanged when the material is deposited on a mica substrate. The researchers found that the interaction between graphene and mica is not purely of a Van der Waals nature, as expected, but that charge transfer occurs between graphene and differently charged regions of mica. This charge transfer significantly increases the interactions between the surfaces of the two materials, which may help to suppress, or smooth out, the ripples in graphene.
The team obtained its results using one of the most widely used theoretical approaches in computational solid-state and molecular physics – namely density functional theory. The calculations were done at the high-performance computer cluster of the Hamburg University of Technology.
"Mica shows many advantages as a substrate for graphene in electronic devices," team member Alexander Rudenko told nanotechweb.org. "These include its relatively flat surface, its good dielectric properties and its strong interaction with graphene."
The researchers now plan to study how graphene behaves when it comes into contact with other promising substrates, such as silicon dioxide and boron nitride.
The paper in which these results appear can be seen for free at arXiv.
About the author
Belle Dumé is contributing editor at nanotechweb.org