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Graphene intercalation is a novel way to control graphene's band structure and generate two-dimensional quantum materials with unusual spintronic and electronic properties. Despite its importance, information about the intercalation mechanism is lacking, especially the role of low density domain boundaries between regions of graphene of different thickness. With high resolution surface diffraction we have systematically studied Pb intercalation on epi-graphene grown on SiC, with domain boundaries between buffer and single layer graphene. By examining the evolution of different diffraction spots as a function of tempertature, the location of Pb and stability of the intercalated phases underneath were determined.

Despite its importance in theoretical studies of surface diffusion there has been limited experimental progress in developing methods to measure the dynamic structure factor S(q,t). In this work we study gases adsorbed on single-crystal surfaces and show that their equilibrium dynamics is measurable in a diffraction experiment through density fluctuations described by the dynamic correlation function . Using a lattice-gas model with nearest-neighbor repulsive interaction, we demonstrate how to separate out the microscopic dynamics caused by diffusion and adsorption-desorption from the form of . Our analytical results show that decays as an exponential with a time constant {tau}(q). Significant deviations from the hydrodynamic dependence of 1/{tau}(q)=D{sub c}q{sup 2} are found with and without desorption. These deviations have important consequences in extracting diffusion constants from experiments. (c) 2000 The American Physical Society.

We present low-energy electron-diffraction evidence showing that the W(210) surface irreversibly facets into two different orientations: a near-(310) facet and a (530) facet. While the near-(310) facet consists of primarily single-atomic-height steps, the (530) facet is made up of a mixture of single- and double-atomic-height steps. Step doubling is predicted on the basis of existing free-energy models, while faceting has important implications on the nature of the step-step interaction.

We present evidence for equilibrium temporal fluctuations in a high resolution low energy electron diffraction (LEED) experiment. These fluctuations are the reciprocal space analog of current fluctuations in field emission microscopy and therefore can be used to extract surface kinetic information. We show that even when the electron beam illuminates an area larger than its correlation length, time correlated data can be extracted from LEED. To demonstrate this, we present time dependent data from a W(430) surface, which reflects thermal step fluctuations. Our results illustrate the potential of LEED as a real time, ultrafast probe. {copyright} {ital 1998} {ital The American Physical Society }

The understanding of metal nucleation on graphene is essential for promising future applications, especially of magnetic metals which can be used in spintronics or computer storage media. A common method to study the grown morphology is to measure the nucleated island density n as a function of growth parameters. Surprisingly, the growth of Fe on graphene is found to be unusual because it does not follow classical nucleation: n is unexpectedtly high, it increases continuously with the deposited amount θ and shows no temperature dependence. These unusual results indicate the presence of long range repulsive interactions. Kinetic Monte Carlo simulations and density functional theory calculations support this conclusion. In addition to answering an outstanding question in epitaxial growth, i.e., to find systems where long range interactions are present, the high density of magnetic islands, tunable with θ, is of interest for nanomagnetism applications.

We present energy filtered electron emission spectromicroscopy with spatial and wave-vector resolution on few-layer epitaxial graphene on SiC$(000\overline{1})$ grown by furnace annealing. Low-energy electron microscopy shows that more than 80% of the sample is covered by 2--3 graphene layers. C1s spectromicroscopy provides an independent measurement of the graphene thickness distribution map. The work function, measured by photoelectron emission microscopy (PEEM), varies across the surface from 4.34 to 4.50 eV according to both the graphene thickness and the graphene-SiC interface chemical state. At least two SiC surface chemical states (i.e., two different SiC surface structures) are present at the graphene/SiC interface. Charge transfer occurs at each graphene/SiC interface. $k$-space PEEM gives 3D maps of the $|{\mathrm{k\ifmmode \bar{}\else \={}\fi{}}}_{\ensuremath{\parallel}}|$ $\ensuremath{\pi}\ensuremath{-}{\ensuremath{\pi}}^{*}$ band dispersion in micron-scale regions showing that the Dirac point shifts as a function of graphene thickness. Bragg diffraction of the Dirac cones via the superlattice formed by the commensurately rotated graphene sheets is observed. The experiments underline the importance of lateral and spectroscopic resolution on the scale of future electronic devices in order to precisely characterize the transport properties and band alignments.

High resolution low-energy electron diffraction measurements are reported that demonstrate the existence of semiordered islands on the clean Pd(110) surface. The islands are stable up to 1000 °C and are approximately 90 atoms long in the 001 direction. A simple model is presented that makes use of step-step interactions to generate the periodic island structure. This model predicts that ordered islands form below the roughening temperature if the step creation energy is small compared to the step-step interaction. A justification for this condition is given for the Pd(110) surface. © 1993 The American Physical Society.

The inability to grow large well-ordered ultra high vacuum (UHV) graphene with a specific number of layers on SiC(0001) is well known. The growth involves several competing processes (Si desorption, carbon diffusion, island nucleation, etc.) and because of the high temperatures, it has not been possible to identify the growth mechanism. Using scanning tunneling microscopy and a vicinal 6H-SiC(0001) sample, we determine that the Si desorption from steps is the main controlling process. Adjacent steps retract with different speeds and the released carbon produces large areas of bilayer graphene with characteristic ``fingers'' emanating from steps. If faster heating rates are used, the different Si desorption rates are avoided and single-layer graphene films extending over many microns are produced.

We present a structural analysis of the graphene-4HSiC(0001) interface using surface x-ray reflectivity. We find that the interface is composed of an extended reconstruction of two SiC bilayers. The interface directly below the first graphene sheet is an extended layer that is more than twice the thickness of a bulk SiC bilayer (~1.7A compared to 0.63A). The distance from this interface layer to the first graphene sheet is much smaller than the graphite interlayer spacing but larger than the same distance measured for graphene grown on the (000-1) surface, as predicted previously by ab intio calculations., Comment: 1 tex file plus 6 figures

We show experimentally that multilayer graphene grown on the carbon terminated SiC(0001[over ]) surface contains rotational stacking faults related to the epitaxial condition at the graphene-SiC interface. Via first-principles calculation, we demonstrate that such faults produce an electronic structure indistinguishable from an isolated single graphene sheet in the vicinity of the Dirac point. This explains prior experimental results that showed single-layer electronic properties, even for epitaxial graphene films tens of layers thick.

We present a structural analysis of the multilayer graphene/$4H\mathrm{Si}\mathrm{C}(000\overline{1})$ system using surface x-ray reflectivity. We show that graphene films grown on the C-terminated $(000\overline{1})$ surface have a graphene-substrate bond length that is very short $(1.62\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}})$. The measured distance rules out a weak van der Waals interaction to the substrate and instead indicates a strong bond between the first graphene layer and the bulk as predicted by ab initio calculations. The measurements also indicate that multilayer graphene grows in a near turbostratic mode on this surface. This result may explain the lack of a broken graphene symmetry inferred from conduction measurements on this system [C. Berger et al., Science 312, 1191 (2006)].