Selective Observation of Edge-Specific Electronic States and Chemical Reactivity of Laser-Cut MoS₂ Surfaces

The edge sites of molybdenum disulfide (MoS2) are recognized as active sites for various catalytic reactions. However, selective spectroscopic investigation of edge-specific electronic states and surface reactions has been challenging due to the difficulty in preparing edge surfaces with sufficiently large and well-defined areas. In this study, we report a novel method for fabricating MoS2 edge surfaces by the ultrashort laser pulse cutting of bulk crystals. This approach enables selective spectroscopic characterization of the edge surface via microscopic X-ray photoelectron spectroscopy (XPS) under ultrahigh-vacuum and ambient-pressure (AP) conditions. Valence band photoelectron spectra show a density of states at the Fermi level only on the edge surface. van der Waals density functional theory calculations indicate that the zigzag-structured edge surfaces exhibit metallic properties regardless of sulfur defects. Moreover, the Mo 3d XPS spectra of the edge surface reveal components corresponding to coordinatively unsaturated Mo atoms. Using AP-XPS under water vapor, we demonstrate that water molecules dissociate on the edge surface at room temperature, where the unsaturated Mo atoms serve as the active sites for water dissociation. The present edge preparation method offers a versatile platform for studying the intrinsic physical and chemical properties of edge surfaces of van der Waals-layered materials.