Electronic dynamics in unoccupied states of graphene

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In this project the dynamics in unoccupied electronic states of graphene nanoribbons and graphene sheets grown on Ni(111), intercalated with Au, and on SiC(0001) will be investigated. Measurements of the lifetimes are performed as a function of energy above the Fermi level in the vicinity of the K and of the M points. Due to the high parallel momentum of the electrons in these parts of the Brillouin zone ultrashort XUV pulses obtained from high harmonic generation of Ti:sapphire laser radiation have to be employed for the photoemission out of the excited states. A two-dimensional delay-line detector with time-of-flight option enables us to measure also the momentum relaxation in the unoccupied bands. We expect a different behavior near the K and M points of the Brillouin zone. A temporal delay of the XUV probe pulses with respect to visible or UV pump pulses enables us to trace these dynamics. The effect of doping the graphene, which shifts the unoccupied bands with respect to the Fermi level, shall also be studied for substrates which only weakly interact with the graphene. Various co-operation partners within the Priority Program contribute to reach these goals by providing chemicals for the defined growth of nanoribbons, Gr/SiC samples and theoretical insight into the dynamic behavior.