Substrate dependent electronic structure variations of van der Waals heterostructures of MoSe2 or MoSe2(1−x)Te2x grown by van der Waals epitaxy

Abstract

Substrate induced variation of the electronic structure of MoSe2 monolayers is studied. MoSe2 is directly grown by van der Waals epitaxy on MoS2 and highly ordered pyrolytic graphite (HOPG). In this article, we give a review of growth of transition metal dichalcogenides (TMDCs) by van der Waals epitaxy and discuss previously found evidence for the modifications of the electronic structure of TMDCs by van der Waals substrates. Using angle resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy we determine the dispersion of the valence band and the band gap, respectively. For MoSe2 on graphite the valence band resembles that expected for free standing single layer MoSe2, however, the substrate induces a narrowing of the overall band gap. For MoSe2 on MoS2 evidence for hybridization of the valence band maximum between the monolayer and the substrate are presented. Such hybridization, results in an alignment of the valence band maximum (VBM) of MoSe2 with the binding energy of the VBM of the MoS2-substrate at the Γ-point. Furthermore, the VBM at the Γ-point is very close in energy to that of the VBM at the K-point. The effective electron mass around the Γ-point is also much decreased for MoSe2 on MoS2- compared to HOPG-substrates or free standing MoSe2 monolayers. This indicates that in TMDC heterostructures interlayer interactions significantly modify the electronic structure and the resulting properties are in between those of free-standing monolayer and bulk materials. In an attempt to control the electronic states incorporation of Te by formation of MoSe2(1−x)Te2x has been investigated. While shifts in the core level position are observed, the VBM states are found to be very similar to those of pure MoSe2.