Engineering Borophene Band Structure Through Thickness.

Borophene, the 2D allotrope of boron, exhibits electronic properties that strongly depend on the supporting substrate and film thickness. Understanding how interlayer and substrate interactions jointly regulate borophene's electronic properties remains a key challenge for the future exploitation of this emerging material. Here, monolayer and bilayer borophene are synthesized on W(110) to probe thickness-induced changes in their band structure. In situ low-energy electron microscopy and diffraction, combined with x-ray photoelectron spectroscopy and angle-resolved photoemission spectroscopy, reveal distinct borophene-derived valence-band fingerprints for the two thicknesses. While the monolayer adopts an ordered, epitaxial arrangement with substrate-hybridized metallic states, the bilayer exhibits reduced visibility of these substrate-hybridized features, long-range order, and distinct valence-band states. These results reveal a thickness-induced electronic reorganization governed by structural reconstruction and interlayer interactions that accompany the formation of the second boron layer, which collectively shape the band structure of this emerging material.