Impact of external screening on the valence and core level photoelectron spectra of monolayer WS₂

Transition metal dichalcogenides (TMDs) represent an emerging class of layered materials with applications in microelectronics, optoelectronics, photonics, and catalysis. The confinement of charge carriers within the highly anisotropic, quasi-two-dimensional geometry of one-layer (1L) TMDs leads to reduced, variable dielectric screening, giving rise to a quasiparticle band gap that is highly susceptible to the surrounding dielectric environment. Exploiting the contrasting external dielectric environments of gold-supported and suspended 1L WS₂, we show how the electronic states of WS₂ under the effective and ineffective screening environments align at a junction made within the same sheet of material. Photoelectron spectra point to the close alignment of the charge neutrality levels of WS2 in both environments, and the breakdown of rigid shifts between the valence states and core levels with the core levels shifting more than twice as much as the valence states. Furthermore, the effectively screened WS₂ exhibits a valence state with the photoemission linewidth twice as large as the ineffectively screened suspended WS₂, presumably originated from the locally varying WS₂-Au distance and substrate disorders. Collectively, these findings provide key insights into the electronic behavior of WS₂ and its photoemission process with the electronic states renormalized according to the external screening environments.