Electronic Decoupling of Monolayer MoSe₂ from Au(111) Substrate by Selenium Intercalation

Monolayer two-dimensional (2D) materials grown on metal surfaces form a particular set of van der Waals heterostructures with strong interlayer interactions. Unveiling the interaction mechanism may shed light on the issues associated with metal contacts on 2D materials. By using scanning tunneling microscopy/spectroscopy (STM/STS) and angle-resolved photoemission spectroscopy (ARPES), we investigated the electronic structures of MoSe₂ epitaxially grown on Au(111) with and without Se intercalation. For MoSe₂/Au(111), the STM can visualize the moiré pattern with a periodicity of ~2.3 nm. STS measurements reveal a remnant metallic characteristic with significant conductance in the gap region, indicating a strong 2D-metal interaction. By intercalating Se, a significantly increased gap at the interface, absence of moiré pattern, and recovery of a well-defined semiconducting gap, indicating that the 2D-metal interaction was blocked. Our STS and ARPES results show a significantly increased work function (~0.3 eV) and a remarkably reduced K-Γ energy difference (~0.4 eV) after intercalation. Intriguing, the STS resolved Γ point in the valence band only shows a ~0.1 eV energy modulation within the moiré supercell. Calculations based on density functional theory for the full moiré supercell show reasonable agreements with experimental results. The modification in different electronic bands can be understood from the interactions of different orbital characters of Mo and Se with the Au surface atoms.