Two-Dimensional Rare-Earth Metal Phosphides: From Weyl Semimetal to Semiconductor

Two-dimensional (2D) nanomaterials have garnered extensive attention owing to their unique properties and versatile application. Here, a family of 2D rare-earth metal phosphides (M2P, M = Sc, Y, La) and their derivatives M2POT (T = F, OH) is developed to find their topological and electronic properties on the basis of density functional theory simulations. We show that the 2D M2P compounds are most possibly obtained from thermodynamically stable M2InP by chemical exfoliation. The In with a substantial atomic radius of 156 pm exhibits weak polarization ability, resulting in homogeneity of the electron cloud and a weakening of the M-In bond relative to the M-P bond. Upon exfoliation of the In layer, the M2 2+P3-:e - emerges as an electride with surface electrons, which is attributed to the larger ion radius and lower electronegativity of M2+ ions in M2P. The metallic M2P is found to be a Weyl semimetal derived from the contribution of surface electrons. Further, by leveraging the high reactivity of surface electrons, surface functionalization can produce M2POT compounds with the increased valence state of M3+, which results in their semiconducting properties characterized by high carrier mobilities and strong built-in electronic fields. These distinct topological and electronic characteristics position the 2D M2P and M2POT as promising candidates for a wide range of applications.