Electronic structure and magnetism of ultrathin transition metal-graphene layered systems

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Subject of the present research-project is an investigation of the structural and electronic properties of graphene-layers on metallic substrates, modified (i) by intercalation of noble- and transition metals between graphene and substrate and (ii) adsorption of respective metals on top of the graphene overlayer. Graphene layers, i.e. monolayers of hexagonally ordered carbon atoms, have attracted considerable interest in the recent past due to peculiarities of the electronic properties caused by almost vertical Fermi-level crossings of bands as characteristic for two-dimensional Dirac-fermions. These properties are strongly influenced by chemical environment, i.e. by charge-transfer, spin polarization, and dimensionality of bonding, and possible applications of graphene-based structures as spin filters and spin field-effect transistors were discussed in the literature. On the other hand, even monolayers of graphene act as effective protection layers for the chemical passivation of surfaces and thin films, while the surface of graphene may be used as nanomesh substrate for the growth of metallic clusters. All these aspects will be investigated in the framework of the present project. Graphene layers will be prepared in situ under ultra-high vacuum conditions by thermal cracking of propene adsorbed on non-reactive W(110), Rh(111), and Ni(111) surfaces. Subsequently, the graphene layers will be modified by thermal deposition of noble (Cu, Ag, Au) and late transition metals (Fe, Co, Ni) followed by thermal annealing, where as a function of temperature either intercalation of metal layers between graphene and substrate or growth of ordered films and clusters on top of the graphene surface are expected. Structural characterization will be made by means of scanning tunnel microscopy (STM) and electron diffraction. The electronic structure will be studied by means of angle- and spin-resolved photoemission and x-ray absorption (near-edge structure, NEXAFS, as well as magnetic dichroism, XMCD) focusing particularly on the magnetic properties of the layered structures. These experimental investigations will be accompanied by theoretical studies: On the basis of density functional theory (DFT) band structures, local densities of states, magnetic moments and total energies will be calculated for different sample geometries.