Two-Dimensional Rare-Earth\nMetal Phosphides: From\nWeyl Semimetal to Semiconductor

Two-dimensional (2D) nanomaterials have garnered extensive\nattention\nowing to their unique properties and versatile application. Here,\na family of 2D rare-earth metal phosphides (M<sub>2</sub>P, M = Sc,\nY, La) and their derivatives M<sub>2</sub>POT (T = F, OH) is developed\nto find their topological and electronic properties on the basis of\ndensity functional theory simulations. We show that the 2D M<sub>2</sub>P compounds are most possibly obtained from thermodynamically stable\nM<sub>2</sub>InP by chemical exfoliation. The In with a substantial\natomic radius of 156 pm exhibits weak polarization ability, resulting\nin homogeneity of the electron cloud and a weakening of the M-In bond\nrelative to the M-P bond. Upon exfoliation of the In layer, the M<sub>2</sub><sup>2+</sup>P<sup>3–</sup>:<i>e</i><sup><i>–</i></sup> emerges as an electride with surface\nelectrons, which is attributed to the larger ion radius and lower\nelectronegativity of M<sup>2+</sup> ions in M<sub>2</sub>P. The metallic\nM<sub>2</sub>P is found to be a Weyl semimetal derived from the contribution\nof surface electrons. Further, by leveraging the high reactivity of\nsurface electrons, surface functionalization can produce M<sub>2</sub>POT compounds with the increased valence state of M<sup>3+</sup>,\nwhich results in their semiconducting properties characterized by\nhigh carrier mobilities and strong built-in electronic fields. These\ndistinct topological and electronic characteristics position the 2D\nM<sub>2</sub>P and M<sub>2</sub>POT as promising candidates for a\nwide range of applications.