Orbital-selective chemical functionalization of MoS₂ by Fe

Abstract

The occupied electron energy bands of monolayer MoS₂ are composed from out-of-plane d orbitals at the Brillouin zone (BZ) center and from in-plane d orbitals at the BZ corner. If a dopant would interact in an orbital selective manner with the MoS₂ bands, it could provide a tuning knob to modulate the MoS₂ energy bands according to the electron wave vector. Here we directly show by angle-resolved photoemission spectroscopy (ARPES) that Fe doping of epitaxial MoS₂ is orbital selective. That is, Fe doping causes a larger energy upshift of the valence band at the BZ center compared to the BZ corner. The optical properties of Fe-doped MoS₂ are investigated by ultrahigh vacuum photoluminescence and reveal a loss of photoluminescence upon Fe doping. The sample morphology is investigated by scanning tunneling microscopy and shows a two-dimensional core-shell structure with Fe chemisorbed along the edge of MoS₂ islands. This structural determination is consistent with core-level spectroscopy measurements. Realistic ab initio calculations and tight-binding calculations of the electronic band structure fully explain ARPES and photoluminescence experiments and highlight that dopants with complex d-orbital structure interact with MoS₂ in an orbital-sensitive manner. Our approach opens opportunities in band-structure engineering of two-dimensional materials.