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Properties of many layered materials, including copper-and iron-based superconductors, topological insulators, graphite and epitaxial graphene, can be manipulated by the inclusion of different atomic and molecular species between the layers via a process known as intercalation. For example, intercalation in graphite can lead to superconductivity and is crucial in the working cycle of modern batteries and supercapacitors. Intercalation involves complex diffusion processes along and across the layers; however, the microscopic mechanisms and dynamics of these processes are not well understood. Here we report on a novel mechanism for intercalation and entrapment of alkali atoms under epitaxial graphene. We find that the intercalation is adjusted by the van der Waals interaction, with the dynamics governed by defects anchored to graphene wrinkles. Our findings are relevant for the future design and application of graphene-based nano-structures. Similar mechanisms can also have a role for intercalation of layered materials.

The quantum wells formed by ultra-thin metallic films on appropriate metallic substrates provide a real example of the simple undergraduate physics problem in quantum mechanics of the 'particle in a box'. Photoemission provides a direct probe of the energy of the resulting quantized bound states. In this review the relationship of this simple model system to the real metallic quantum well (QW) is explored, including the way that the exact nature of the boundaries can be taken into account in a relative simple way through the 'phase accumulation model'. More detailed aspects of the photoemission probe of QW states are also discussed, notably of the physical processes governing the photon energy dependence of the cross sections, of the influence of temperature, and the processes governing the observed peak widths. These aspects are illustrated with the results of experiments and theoretical studies, especially for the model systems Ag on Fe(100), Ag on V(100) and Cu on fcc Co(100).

Angle resolved photoelectron spectroscopy (ARPES) is extensively used to characterize the dependence of the electronic structure of graphene on Ir(111) on the preparation process. ARPES findings reveal that temperature programmed growth alone or in combination with chemical vapor deposition leads to graphene displaying sharp electronic bands. The photoemission intensity of the Dirac cone is monitored as a function of the increasing graphene area. Electronic features of the moir\'e superstructure present in the system, namely minigaps and replica bands are examined and used as robust features to evaluate graphene uniformity. The overall dispersion of the pi-band is analyzed. Finally, by the variation of photon energy, relative changes of the pi- and sigma-band intensities are demonstrated.Comment: 8 pages, 6 figures in published for

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SignificanceSurfaces are gates to control the transport of energy and materials between the gas phase and bulk. For the hydrogen storage, the transport of hydrogen across the surface is recognized as the bottleneck, e.g., 1 H2 in 1,000 impinging a Pd surface penetrates the surface. Here, we demonstrate that alloying the Pd(110) surface with submonolayer amounts of Au dramatically accelerates the hydrogen absorption, by a factor of more than 40. This discovery will lead to enhancement of hydrogen absorption kinetics, thereby improving the performance of hydrogen-purifying membranes and hydrogen-storage materials, which is a key for utilizing hydrogen as a carbon-free energy carrier.

We analyze renormalization of the π * band of n-doped epitaxial graphene on Ir(111) induced by electronphonon coupling. Our procedure of extracting the bare band relies on recursive self-consistent refining of the functional form of the bare band until the convergence. We demonstrate that the components of the self-energy, as well as the spectral intensity obtained from angle-resolved photoelectron spectroscopy (ARPES) show that the renormalization is due to the coupling to two distinct phonon excitations. From the velocity renormalization and an increase of the imaginary part of the self-energy we find the electron-phonon coupling constant to be ∼ 0.2, which is in fair agreement with a previous study of the same system, despite the notable difference in the width of spectroscopic curves. Our experimental results also suggest that potassium intercalated between graphene and Ir(111) does not introduce any additional increase of the quasiparticle scattering rate.