The lattice mismatch between a monolayer of MoS2 and its Au(111) substrate induces a moiré superstructure. The local variation of the registry between sulfur and gold atoms at the interface leads to a periodic pattern of strongly and weakly interacting regions. In consequence, also the electronic bands show a spatial variation. We use scanning tunneling microscopy and spectroscopy (STM/STS), x-ray photoelectron spectroscopy (XPS) and x-ray standing wave (XSW) for a determination of the geometric and electronic structure. The experimental results are corroborated by density functional theory (DFT). We obtain the geometric structure of the supercell with high precision, identify the fraction of interfacial atoms that are strongly interacting with the substrate, and analyze the variation of the electronic structure in dependence of the location within the moiré unit cell and the nature of the band.

We studied the effect of alkali metal intercalation (Cs and Li) on the geometry of graphene on Ir(111) using the X-ray standing waves technique. For both alkali metals, the increase in the mean height of the carbon layer does not depend on the lateral structure or the density of the intercalated layer. For Li, full delamination of graphene from the metal substrate is found already for a small amount of intercalant. Even though lithium lifts graphene to a smaller height, it is much more efficient in ironing out the corrugation of pristine graphene on Ir(111).

The structure of graphene on Ru(0001) has been extensively studied over the last decade, yet with no general agreement. Here, we analyze graphene's valleys and hills using a combination of X-ray standing wave (XSW) and density functional theory (DFT). The chemical specificity of XSW allows an independent analysis of valleys and hills, which, together with the DFT model, results in the precise determination of the distance between the flat, strongly bounded valleys of graphene and the substrate as well as the corrugation presented in the weakly bounded hills. From the theoretical viewpoint, the good agreement with the experiment validates the choices regarding the unit cell size and the nonlocal correlation functional.

Growth of 2D materials under ultrahigh-vacuum (UHV) conditions allows for an in situ characterization of samples with direct spectroscopic insight. Heteroepitaxy of transition-metal dichalcogenides (TMDs) in UHV remains a challenge for integration of several different monolayers into new functional systems. In this work, we epitaxially grow lateral WS 2 −MoS 2 and vertical WS 2 /MoS 2 heterostructures on graphene. By means of scanning tunneling spectroscopy (STS), we first examined the electronic structure of monolayer MoS 2 , WS 2 , and WS 2 /MoS 2 vertical heterostructure. Moreover, we investigate a band bending in the vicinity of the narrow one-dimensional (1D) interface of the WS 2 −MoS 2 lateral heterostructure and mirror twin boundary (MTB) in the WS 2 /MoS 2 vertical heterostructure. Density functional theory (DFT) is used for the calculation of the band structures, as well as for the density of states (DOS) maps at the interfaces. For the WS 2 −MoS 2 lateral heterostructure, we confirm type-II band alignment and determine the corresponding depletion regions, charge densities, and the electric field at the interface. For the MTB, we observe a symmetric upward bend bending and relate it to the dielectric screening of graphene affecting dominantly the MoS 2 layer. Quasi-freestanding heterostructures with sharp interfaces, large built-in electric field, and narrow depletion region widths are proper candidates for future designing of electronic and optoelectronic devices.