Spatially Resolved Electronic Properties of Single-Layer WS₂ on Transition Metal Oxides

There is a substantial interest in the heterostructures of semiconducting transition metal dichalcogenides (TMDCs) among each other or with arbitrary materials, through which the control of the chemical, structural, electronic, spintronic, and optical properties can lead to a change in device paradigms. A critical need is to understand the interface between TMDCs and insulating substrates, for example, high-κ dielectrics, which can strongly impact the electronic properties such as the optical gap. Here, we show that the chemical and electronic properties of the single-layer (SL) TMDC, WS₂, can be transferred onto high-κ transition metal oxide substrates TiO₂ and SrTiO₃. The resulting samples are much more suitable for measuring their electronic and chemical structures with angle-resolved photoemission than their native-grown SiO₂ substrates. We probe the WS₂ on the micron scale across 100 μm flakes and find that the occupied electronic structure is exactly as predicted for free-standing SL WS₂ with a strong spin-orbit splitting of 420 meV and a direct band gap at the valence band maximum. Our results suggest that TMDCs can be combined with arbitrary multifunctional oxides, which may introduce alternative means of controlling the optoelectronic properties of such materials.