Dual character of excited charge carriers in graphene on Ni(111)

The dynamics of excited charge carriers at the graphene/Ni(111) interface has been investigated by means of time-resolved two-photon photoemission spectroscopy, employing femtosecond-XUV pulses with an energy of 39.2 eV produced by high-order-harmonic generation. Due to the interplay of substrate and adsorbate band structures, the dependence of the lifetimes on the energy (E − EF ) of the excited carriers was found to be similar to that of Ni 3d electrons measured for clean Ni in the energy range (E − EF ) < 1 eV, while it resembled that of graphite from 1 eV above EF onwards. This result is suggested to be the effect of the peculiar electronic structure of the interface, which still possesses features belonging to the pristine graphene layer, such as a residual saddle point.