Electronic Structure and Stacking Arrangement of Tungsten Disulfide at the Gold Contact.

There is an intensive effort to control the nature of attractive interactions between ultrathin semiconductors and metals and to understand its impact on the electronic properties at the junction. Here, we present a photoelectron spectroscopy study on the interface between WS films and gold, with a focus on the occupied electronic states near the Brillouin zone center (i.e., the Γ point). To delineate the spectra of WS supported on crystalline Au from the suspended WS, we employ a microscopy approach and a tailored sample structure, in which the WS/Au junction forms a semi-epitaxial relationship and is adjacent to suspended WS regions. The photoelectron spectra, as a function of WS thickness, display the expected splitting of the highest occupied states at the Γ point. In multilayer WS, we discovered variations in the electronic states that spatially align with the crystalline grains of underlying Au. Corroborated by density functional theory calculations, we attribute the electronic structure variations to stacking variations within the WS films. We propose that strong interactions exerted by Au grains cause slippage of the interfacing WS layer with respect to the rest of the WS film. Our findings illustrate that the electronic properties of transition metal dichalcogenides, and more generally 2D layered materials, are physically altered by the interactions with the interfacing materials, in addition to the electron screening and defects that have been widely considered.