This week in cond-mat

Two recent arxiv papers caught my eye. I'm not working on graphene, but these are both pretty interesting results.

arxiv:0905.0923 - Mak et al., Observation of an Electric-Field Induced Band Gap in Bilayer Graphene by Infrared Spectroscopy
The authors, from Tony Heinz's group at Columbia, make a field-effect device out of bilayer graphene (identified optically thanks to its particular Raman spectrum) and an electrolyte. As I'd mentioned once before, by using electrolytes it is possible to achieve very large gated charge densities in transistor-style devices. In this case, the authors find that they can turn bilayer graphene from a semimetal-like system (with touching valence and conduction bands at the charge neutrality point) to a semiconductor (as determined via optical measurements), with a band gap induced and controlled by the gate. I need to read more carefully just how this works, but it shows how these kinds of experiments (moving a good fraction of a charge per unit cell around) can alter band structure profoundly.

arxiv:0905.1712 - Li et al., Large-Area Synthesis of High-Quality and Uniform Graphene Films on Copper Foils
This paper, published this week online in Science, may end up being quite important. The authors show that they can grow mostly single-layer graphene on copper supports. Copper can be annealed to produce large (several mm) crystallites, so significant areas of graphene can be made this way, templated with comparatively few defects. The big step here compared to earlier work on growing graphene using Ru or Ni substrates is that the resulting material seems to be self-limiting in thickness because of the mutual solubility limits of C in Cu and Cu in C. The authors can also transfer the graphene to other substrates, including Si chips, a necessary step for any would-be electronics applications.