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 $(E\ensuremath{-}{E}_{F})$ of the excited carriers was found to be similar to that of Ni $3d$ electrons measured for clean Ni in the energy range $(E\ensuremath{-}{E}_{F})l1$ eV, while it resembled that of graphite from 1 eV above ${E}_{F}$ 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.