Graphene and Graphite


Graphene
is the mother system of all the carbon-based materials.  It is made out of a single planar sheet of carbon atoms (sp2 bonded) located along the corner of an hexagon.  From an electronic point of view, graphene is an exciting novel material because of the presence of Dirac quasiparticles, e.g. quasiparticles with a linear E vs. k dispersion and a zero density-of-states at the Fermi level.  The presence of Dirac quasiparticles is considered to be the main cause for several of the peculiar properties of graphene and for the failure of the Fermi liquid picture in the description of the Dirac quasiparticles. 

 

A part of our research activity focuses on establishing new methods for the synthesis of single-layer graphene.  So far we have used an approach similar to one that is already well known in the literature, and have recently succeeded in synthesizing epitaxial graphene films less than two layers in thickness by the solid-state decomposition of 6H-SiC.

 

Here are LEED patterns from SiC during the process of graphitization, and a SEM image of one graphitized surface:

 

For us, this is the first step toward the study of the electronic structure in a pure 2D system, and an exploration of the fascinating physics of Dirac quasiparticles.

 

For more information about this project, please look for our upcoming publication in J. Phys. Chem. Solids (2005).

 

 

Graphite is a layered material made up of many graphene layers stacked with the ABAB type of stacking.  The large layer separation, compared to the in plane C-C distance, makes graphite an ideal quasi two dimensional system.

 

Graphite is a semimetal or zero-gap semiconductor with the π bands crossing the Fermi level at the corners of the hexagonal Brillouin zone.   The layer interaction in graphite lifts the degeneracy of the π bands and results in small electron and hole pockets near the zone corners.  In contrast to Fermi Liquid theory, the energy dependence of the quasiparticle lifetime in graphite is unconventional.  

 


 

We are interested in studying the electronic properties of graphite using high resolution angle-resolved photoemission spectroscopy and understanding how this is effected by the interlayer coupling.  Also, our focus is on the quasiparticle lifetime, the effects of disorder, and the electron-phonon coupling.   We are also interested in studying the electronic properties and the effect of localization in 2D graphene (a single layer of graphite). 

 

Below is our work on HOPG, where the coexistence of single crystalline and disorder features in graphite demonstrated the possibility of using ARPES to study layered materials with azimuthal disorder.  See our publication in Phys. Rev. B 71, 161403 (2005) for details.  For a color version of the figures, see cond-mat/0506238.

 

 

For more information, please see our selected publications list.