Sulfur Structures on Bare and Graphene-Covered Ir(111)

We present a study of sulfur adsorption on bare Ir(111). Two well-defined superstructures are found: a (root 3 x root 3)R30 degrees and a c(4 x 2) S-adlayer. Moreover, we also investigate sulfur intercalation of graphene on Ir(111). For adsorption, sulfur is provided either in the form of the precursor molecule H2S or as elemental sulfur through sublimation from FeS2 heated in a Knudsen cell. On the basis of scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED), as well as density functional theory calculations (DFT), we present a model for the c(4 x 2) superstructure consistent with surface relaxations. We show that above a graphene coverage threshold, when islands of the two-dimensional (2D) material start to coalesce, the sulfur superstructure intercalated below graphene depends on the form in which sulfur is provided: c(4 x 2) forms in the case of exposure to elemental sulfur, while the (root 3 x root 3)R30 degrees superstructure forms in the case of H2S exposure. The two intercalation structures influence the graphene moire ' corrugation in different ways. We have used DFT calculations to determine sulfur adsorption energies, surface relaxations, and the influence of sulfur intercalation on the density of electronic states of graphene on Ir(111)

Step-induced faceting and related electronic effects for graphene on Ir(332)

Modifications of graphene's electronic band structure can be achieved through periodic bending strain and related potential in samples grown on stepped substrates, opening a viable route to implement the periodicity effects in this ultimate two-dimensional (2D) material. We studied graphene grown on stepped Ir(332), which can be benchmarked to a well-known graphene on flat Ir(111) recognized for a weak van der.Waals (vdW) interaction. The structural characterization indicated that graphene growth induces reversible, well defined faceting of iridium surface into alternating terraces and step bunches, while spectroscopy techniques revealed substantial changes of graphene's electronic structure. Crucially, highly concentrated Ir step edges, resulting in locally strong chemical bonding of graphene, introduce a dominant energy parameter which overwhelms the induced strain and presents a driving force for the surface faceting. This sets a general framework for the understanding of graphene mediated faceting of stepped substrates whenever the corresponding low index surface exhibits dominantly vdW interaction with graphene, which can be also supplemented to other 2D materials. Interestingly, the graphene band becomes pronouncedly anisotropic due to the presence of a periodic potential originating from steps, and lateral variation of the charge carrier concentration enabling a straightforward electronic band engineering in graphene. (C) 2016 Elsevier Ltd. All rights reserved