Engineering of Neutral Excitons and Exciton Complexes in Transition Metal Dichalcogenide Monolayers through External Dielectric Screening

In order to fully exploit the potential of transition metal dichalcogenide monolayers (TMD-MLs), the well-controlled creation of atomically sharp lateral heterojunctions within these materials is highly desirable. A promising approach to create such heterojunctions is the local modulation of the electronic structure of an intrinsic TMD-ML via dielectric screening induced by its surrounding materials. For the realization of this non-invasive approach, an in-depth understanding of such dielectric effects is required. We report on the modulations of excitonic transitions in TMD-MLs through the effect of dielectric environments including low-k and high-k dielectric materials. We present absolute tuning ranges as large as 37 meV for the optical band gaps of WSe 2 and MoSe 2 MLs and relative tuning ranges on the order of 30% for the binding energies of neutral excitons in WSe 2 MLs. The findings suggest the possibility to reduce the electronic band gap of WSe 2 MLs by 120 meV, paving the way towards dielectrically defined lateral heterojunctions.Comment: 11 pages + 6 pages supporting informatio

Thermodynamic stability and control of oxygen reactivity at functional oxide interfaces: EuO on ITO

As a prototypical all-oxide heterostructure, the ferromagnetic insulator europium monoxide (EuO) issynthesized on transparent and conductive indium tin oxide (ITO) virtual substrates. Non-destructivehard X-ray photoelectron spectroscopy is employed to depth profile the chemical composition of themagnetic layer and the buried oxide–oxide interface. We find that thermally activated oxygen diffusionfrom ITO affects the EuO growth process. We present how to control the oxygen reactivity at the interfaceand discuss its origin in a thermodynamic analysis. Our complementary methodical strategy allowsfor a significant improvement of the EuO chemical quality with sizeable magnetic properties. Generally,our approach derives guidelines for the proper choice of oxide substrates and buffer layer materials forfunctional all-oxide heterostructures