Graphene: Materials in the Flatland
I’ve been invited to be part of Applied Materials’ distinguished Engineering and Technology (ET) speaker series to meet with employees and give a talk on graphene.
When one writes by a pencil, thin flakes of graphite are left on a surface. Some of them are only one angstrom think and can be viewed as individual atomic planes cleaved away from the bulk. This strictly two dimensional material called graphene was presumed not to exist in the free state and remained undiscovered until a few years ago. In fact, there exists a whole class of such two-dimensional crystals. The most amazing things about graphene probably is that its electrons move with little scattering over huge (submicron) distances as if they were completely insensitive to the environment only a couple of angstroms away. Moreover, whereas electronic properties of other materials are commonly described by quasiparticles that obey the Schrodinger equation, electron transport in graphene is different: It is governed by the Dirac equation so that charge carriers in graphene mimic relativistic particles with zero rest mass. The very unusual electronic properties of this material as well as the possibility for its chemical modification make graphene a promising candidate for future electronic applications.
Recent progress in graphene samples production allowed for a dramatic improvement in quality. Thus, mobilities of the order of 106 cm2/Vs can be routinely achieved in mono-and bi-layer graphene samples. This brought an influx of novel phenomena, previously non-observable in this material. The influence of electron-electron interaction become dominant and exhibit itself in spectrum modification, fractional quantum Hall effect, etc.
Micromechanical or chemical exfoliation can also be successfully applied to other layered materials such as Bi2Sr2CaCu2Ox, NbSe2, BN, MoS2, Bi2Te3 and other dichalcogenides, and epitaxial growth has been applied to grow monolayers of boron-nitride. As with graphene, the crystal quality of the obtained monolayer samples is very high. Many of the 2D materials conduct and even demonstrate field effects (changes of the resistance with gating). The properties of the obtained 2D materials might be very different from those of their 3D precursors.
Furthermore, as we have full control over the 2D crystals, we can also create stacks of these crystals according to our requirements. Here, we are not merely talking about stacks of the same material: we can combine several different 2D crystals in one stack. Insulating, conducting, probably superconducting and magnetic layers can all be combined in one layered material as we wish, the properties of such heterostructures depending on the stacking order and easily tuneable, introducing a new concept in material engineering – Materials on Demand.
If there are any questions about this material I encourage you to leave them below on this blog post.