Using scanning tunneling microscopy, we observe an adlayer structure that is dominated by short rows of S atoms, on unreconstructed regions of a Au(111) surface. This structure forms upon adsorption of low S coverage (less than 0.1 monolayer) on a fully reconstructed clean surface at 300 K, then cooling to 5 K for observation. The rows adopt one of three orientations that are rotated by 30 • from the close-packed directions of the Au(111) substrate, and adjacent S atoms in the rows are separated by √ 3 times the surface lattice constant, a. Monte Carlo simulations are performed on lattice-gas models, derived using a limited cluster expansion based on density functional theory energetics. Models which include long-range pairwise interactions (extending to 5a), plus selected trio interactions, successfully reproduce the linear rows of S atoms at reasonable temperatures.

Sulfur-metal complexes, containing only a few atoms, can open new, highly efficient pathways for transport of metal atoms on surfaces. For example, they can accelerate changes in the shape and size of morphological features, such as nanoparticles, over time. In this study, we perform STM under conditions that are designed to specifically isolate such complexes. We find a new, unexpected S-Cu complex on the Cu(111) surface, which we identify as Cu 2 S 3 . We propose that Cu 2 S 3 enhances mass transport in this system, which contradicts a previous proposal based on Cu 3 S 3 . We analyze bonding within these Cu-S complexes, identifying a new principle for stabilization of sulfur complexes on coinage metal surfaces. Introduction.It has been proposed that metal-adsorbate complexes can greatly accelerate rearrangements of metal nanostructures and surfaces. This issue is of importance for stability of catalysts or nanostructures, and has been the subject of prolonged speculation given that the complexity of such systems typically precludes definitive analysis [1,2]. Nonetheless, evidence continues to accumulate supporting the presence of mobile complexes on surfaces and, by implication, their role in metal transport. Recently, for instance, Parkinson et al. have shown that CO interacts with Pd atoms adsorbed on a Fe 3 O 4 surface, forming a highly-mobile Pd-CO complex [3]. Other adsorbates that form mobile surface complexes with metals include hydrogen [4,5], oxygen [6,7], alkylsulfides [8], and-the subject of this study-sulfur [9][10][11][12][13][14]. The soft metals Cu, Ag, and Au, which are of great interest because of their catalytic and plasmonic properties, are expected to be particularly susceptible to this effect.The challenge in identifying such complexes is their high mobility, plus their potential condensation into extended ordered structures at moderate to high coverage. Together, these considerations mean that conditions of low temperature and low coverage offer the best chance for isolating and observing such species. The present work is a search for S-Cu complexes under these conditions. Previously, Feibelman [9] proposed that a Cu 3 S 3 complex can enhance metal transport on Cu(111), not because of high mobility (relative to metal adatoms), but rather because of high population (reflecting high stability), combined with moderate mobility (cf. Ref. [1]). The stability of the cluster was attributed to the fact that S atoms could adsorb at pseudo-4-fold-

The scattering of the oxygen molecule from a graphite surface has been studied using a molecular beam scattering technique. The angular intensity distributions of scattered oxygen molecules were measured at incident energies from 291 to 614 meV with surface temperatures from 150 to 500 K. Every observed distribution has a single peak at a larger final angle than the specular angle of 45° which indicates that the normal component of the translation energy of the oxygen molecule is lost by the collision with the graphite surface. The amount of the energy loss by the collision has been roughly estimated as about 30-41% based on the assumption of the tangential momentum conservation during the collision. The distributions have also been analyzed with two theoretical models, the hard cubes model and the smooth surface model. These results indicate that the scattering is dominated by a single collision event of the particle with a flat surface having a large effective mass. The derived effective mass of the graphite surface for the incoming oxygen is 9-12 times heavier than that of a single carbon atom, suggesting a large cooperative motion of the carbon atoms in the topmost graphene layer.

We report nonuniform and long-range electronic perturbation of graphite near the Fermi level by the point defect based on the measurements with scanning tunneling spectroscopy. The states propagate with threefold symmetry perpendicular to the zigzag edges at the point defect, indicating the formation of the nonbonding states. The propagation continues for 3-4 nm from the defect and is accompanied by oscillations in the state energy and state intensity with a periodicity of ͑ ͱ 3 ϫ ͱ 3͒R30°. The oscillation in the state intensity is ascribed to the disruption in the-conjugated system in graphite around the defect, i.e., edge-states propagation from the defect while the oscillation in the state energy is ascribed to electron-electron interactions between the nonbonding electronic states and the standing-wave caused by bands of graphite.

Arich menagerie of structures is identified at 5Kfollowing adsorption of lowcoverages (≤0.05 monolayers) of S on Cu(111) at room temperature. This paper emphasizes the reconstructions at the steps. The A-type closepacked step has 1 row of S atoms along its lower edge, where S atoms occupy alternating pseudo-fourfoldhollow (p4fh) sites. Additionally, there are 2 rows of S atoms of equal density on the upper edge, bridging a row of extra Cu atoms, together creating an extended chain. The B-type close-packed step exhibits an even more complex reconstruction, in which triangle-shaped groups of Cu atoms shift out of their original sites and form a base for S adsorption at (mostly) 4fh sites. We propose a mechanism by which these triangles could generate Cu-S complexes and short chains like those observed on the terraces. PHYSICS 142, 194711 (2015) Reconstruction of steps on the Cu(111) surface induced by sulfur A rich menagerie of structures is identified at 5 K following adsorption of low coverages (≤0.05 monolayers) of S on Cu(111) at room temperature. This paper emphasizes the reconstructions at the steps. The A-type close-packed step has 1 row of S atoms along its lower edge, where S atoms occupy alternating pseudo-fourfold-hollow (p4fh) sites. Additionally, there are 2 rows of S atoms of equal density on the upper edge, bridging a row of extra Cu atoms, together creating an extended chain. The B-type close-packed step exhibits an even more complex reconstruction, in which triangle-shaped groups of Cu atoms shift out of their original sites and form a base for S adsorption at (mostly) 4fh sites. We propose a mechanism by which these triangles could generate Cu-S complexes and short chains like those observed on the terraces. C 2015 AIP Publishing LLC.[http://dx