Lithiation of Epitaxial Monolayer Borophene

Functionalization of borophene offers a viable route to modify its properties and create advanced boron-based 2D derivatives. For tuning the electronic structure of borophene, an aspect of both fundamental and applicative importance, alkali metals are particularly attractive because of their efficient charge donation. In light of this, we study morphological and electronic modifications of the borophene monolayer on Ir(111) after Li deposition in an ultra-high vacuum. By combining micro-probe low-energy electron microscopy and diffraction with X-ray spectroscopy and comprehensive density functional theory calculations, we are able to disentangle the complex interaction between Li, B, and Ir atoms. It is found that adsorbed Li distorts the crystal lattice of borophene, especially after sample annealing, and that Li intercalation is unfavorable. Charge redistribution within the system is governed by the high chemical reactivity and efficient electron donation of Li atoms, which bind strongly to B and Ir atoms and disrupt the preset energy balance of the epitaxial borophene layer. Our study showcases the advantages and challenges of alkali-metal decoration of borophene and provides guidelines for future borophene functionalization strategies.