Making devices with graphene necessarily involves making contacts with metals. We use density functional theory to study how graphene is doped by adsorption on metal substrates and find that weak bonding on Al, Ag, Cu, Au, and Pt, while preserving its unique electronic structure, can still shift the Fermi level with respect to the conical point by 0:5 eV. At equilibrium separations, the crossover from p-type to n-type doping occurs for a metal work function of 5:4 eV, a value much larger than the graphene work function of 4.5 eV. The numerical results for the Fermi level shift in graphene are described very well by a simple analytical model which characterizes the metal solely in terms of its work function, greatly extending their applicability. DOI: 10.1103/PhysRevLett.101.026803 PACS numbers: 73.63.ÿb, 73.20.Hb, 73.40.Ns, 81.05.Uw Recent progress in depositing a single graphene sheet on an insulating substrate by micromechanical cleavage enables electron transport experiments on this twodimensional system [1,2]. Such experiments demonstrate an exceptionally high electron mobility in graphene, quantization of the conductivity, and a zero-energy anomaly in the quantum Hall effect, in agreement with theoretical predictions [3][4][5][6][7]. The spectacular effects arise from graphene's unique electronic structure. Although it has a zero band gap and a vanishing density of states (DOS) at the Fermi energy, graphene exhibits metallic behavior due to topological singularities at the K points in the Brillouin zone [3,4] where the conduction and valence bands touch in conical (Dirac) points and the dispersion is essentially linear within 1 eV of the Fermi energy.In a freestanding graphene layer the Fermi energy coincides with the conical points but adsorption on metallic (or insulating) substrates can alter its electronic properties significantly [8][9][10][11][12][13][14][15]. Since electronic transport measurements through a graphene sheet require contacts to metal electrodes [2,12,16,17], it is essential to have a full understanding of the physics of metal-graphene interfaces. In this Letter we use first-principles calculations at the level of density functional theory (DFT) to study the adsorption of graphene on a series of metal substrates. The (111) surfaces of Al, Co, Ni, Cu, Pd, Ag, Pt, and Au, covering a wide range of work functions and chemical bonding, form a suitable system for a systematic study.Our results show that these substrates can be divided into two classes. The characteristic electronic structure of graphene is significantly altered by chemisorption on Co, Ni, and Pd but is preserved by weak adsorption on Al, Cu, Ag, Au, and Pt. Even when the bonding is weak, however, the metal substrates cause the Fermi level to move away from the conical points in graphene, resulting in doping with either electrons or holes. The sign and amount of doping can be deduced from the difference of the metal and graphene work functions only when they are so far apart that there is no wave function overlap. At the e...

In the past decade, Resonant Inelastic X-ray Scattering (RIXS) has made remarkable progress as a spectroscopic technique. This is a direct result of the availability of highbrilliance synchrotron X-ray radiation sources and of advanced photon detection instrumentation. The technique's unique capability to probe elementary excitations in complex materials by measuring their energy-, momentum-, and polarization-dependence has brought RIXS to the forefront of experimental photon science. We review both the experimental and theoretical RIXS investigations of the past decade, focusing on those determining the low-energy charge, spin, orbital and lattice excitations of solids. We present the fundamentals of RIXS as an experimental method and then review the theoretical state of affairs, its recent developments and discuss the different (approximate) methods to compute the dynamical RIXS response. The last decade's body of experimental RIXS data and its interpretation is surveyed, with an emphasis on RIXS studies of correlated electron systems, especially transition metal compounds. Finally, we discuss the promise that RIXS holds for the near future, particularly in view of the advent of x-ray laser photon sources.

Measuring the transport of electrons through a graphene sheet necessarily involves contacting it with metal electrodes. We study the adsorption of graphene on metal substrates using firstprinciples calculations at the level of density functional theory. The bonding of graphene to Al, Ag, Cu, Au and Pt(111) surfaces is so weak that its unique "ultrarelativistic" electronic structure is preserved. The interaction does, however, lead to a charge transfer that shifts the Fermi level by up to 0.5 eV with respect to the conical points. The crossover from p-type to n-type doping occurs for a metal with a work function ∼ 5.4 eV, a value much larger than the work function of free-standing graphene, 4.5 eV. We develop a simple analytical model that describes the Fermi level shift in graphene in terms of the metal substrate work function. Graphene interacts with and binds more strongly to Co, Ni, Pd and Ti. This chemisorption involves hybridization between graphene pz-states and metal d-states that opens a band gap in graphene. The graphene work function is as a result reduced considerably. In a current-in-plane device geometry this should lead to n-type doping of graphene.