Optical spatio-temporal optical control of electron-induced processes at graphene-supported metal cluster nano-structures

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In this proposal we wish to explore the potential of optimal control with shaped ultrafast laser pulses to localize the electromagnetic field in metal nano-cluster arrays consisting of graphene-supported size-selected silver clusters with extensions from a few atoms to the nanometer scale. Nothing is known so far about the optical properties of such arrays and we expect to find interesting new phenomena in particular also because of the intriguing electronic propensities of the 2D-material graphene. Graphene is employed as a substrate to provide a geometric template, i.e., to define the cluster distances – its potential to also provide electronic coupling between the clusters will be a subject of investigation. Size-selected clusters will be employed to obtain perfectly monodisperse samples and to investigate the effect of the transition from discrete to plasmonic electronic cluster structure on the possibility of field localization. Optical excitation will be provided by modulated (frequency, phase, polarization) ultrafast laser pulses. In a new experimental approach, the effect of the electromagnetic field localization will be probed by detecting the effectiveness of the electron-emission-induced dissociation of physisorbed adsorbate molecules (CH3Br, CH3Cl) on the metal clusters. Thus, the molecular fragment (CH3) mass signal will be employed as feedback signal in the control loop to obtain the optimal electromagnetic field. The investigation of the field localization will be performed by scanning tunnelling microscopic detection of the spatial extent of the metal cluster halogenation as a function of the parameters cluster size and cluster separation.