Significant excitonic effects were observed in graphene by measuring its optical conductivity in a broad spectral range including the two-dimensional π-band saddle-point singularities in the electronic structure. The strong electron-hole interactions manifest themselves in an asymmetric resonance peaked at 4.62 eV, which is redshifted by nearly 600 meV from the value predicted by ab initio GW calculations for the band-to-band transitions.

We have examined the interfacial thermal conductance GK of single and multilayer graphene samples prepared on fused SiO2 substrates by mechanical exfoliation of graphite. By using an ultrafast optical pump pulse and monitoring the transient reflectivity on the picosecond time scale, we obtained an average value of GK of GK = 5000 W/ cm2 K for the graphene/ SiO2 interface at room temperature. We observed significant variation in GK between individual samples, but found no systematic dependence on the thickness of the graphene layers. © 2010 American Institute of Physics.