A spin-polarized first-principles calculation of the atomic and electronic structure of the graphene/Ni(111) interface is presented. Different structural models have been considered, which differ in the positions of the carbon atoms with respect to the nickel topmost layer. The most probable structure, which has the lowest energy, has been determined. The distance between the floating carbon layer and the nickel surface is found smaller than the distance between graphene sheets in bulk graphite, in accordance with experimental measurements. The electronic structure of the graphene layer is strongly modified by interaction with the substrate and the magnetic moment of the surface nickel atoms is lowered in the presence of the graphene layer. Several interface states have been identified in different parts of the interface two-dimensional Brillouin zone. Their influence on the electron energy loss spectra has been evaluated.

A simple fluorescence recovery after photobleaching (FRAP) apparatus using a fluorescence microscope with a conventional mercury arc lamp, working under conditions of "uniform disk illumination" is described. This set-up was designed essentially for the use of anthracene as fluorescent probe, which is bleached (photodimerization reaction) by illumination in the near ultraviolet range (360 nm). It is shown that the lateral diffusion coefficients D can be readily calculated from fluorescence recovery curves using a finite differentiate method in combination with statistical analysis of the data. In contrast to the analytical solutions so far described, this numerical approach is particularly versatile. With a minimization algorithm, D and the probe mobile fraction can be readily calculated for any recovery time under various experimental conditions. These include different probe concentration profiles in the illuminated area after the bleaching step, and situations of infinite or noninfinite reservoir in the diffusion area outside the illuminated area.

We present the results of a calculation of zero-temperature elastic conductance through a finite ''atomic wire'' between Au pads, all supported by a Si͑001͒-͑2ϫ1͒-H surface. The atomic wire consists of a line of dangling bonds which can be fabricated by removing hydrogen atoms by applying voltage pulses to a scanning tunneling microscopy ͑STM͒ tip along one side of a row of H-passivated silicon dimers. Two different line configurations, without and with Peierls distortion, have been considered. We find that the nondistorted line behaves like a single ballistic transmission channel. Conversely, with Peierls distortion present, tunneling occurs through the small resulting energy gap (0.2 eV), leading to inverse decay length of the current of 0.09 Å Ϫ1 . The conductance of the substrate between the pads without the defect line has also been calculated. In this case, tunneling occurs through a much wider energy gap and a larger inverse decay length of 0.41 Å Ϫ1 . These fully three-dimensional atomistic computations represent an application of the electron-scattering quantum-chemistry method which was previously used to calculate the conductance of ''molecular wires'' and of STM junctions with various adsorbates. Compared to molecular wires previously investigated by the same method, the atomic wire studied here exhibits the smallest inverse decay length. ͓S0163-1829͑99͒09123-7͔ PHYSICAL REVIEW B 15 JUNE 1999-II VOLUME 59, NUMBER 24 PRB 59 0163-1829/99/59͑24͒/15910͑7͒/$15.00 15 910