Assessing the stability of Cd3As2 Dirac semimetal in humid environments: the influence of defects, steps and surface oxidation

Abstract

The presence of a Dirac cone in bulk cadmium arsenide (Cd₃As₂) has triggered the interest of the scientific community, considering its technological potential related to the ultrahigh mobility of charge carriers and the observed giant magnetoresistance. Definitely, the stability of Cd₃As₂ in humid environments is crucial for a successful technology transfer. Here, we study the interaction of Cd₃As₂ with water by means of density functional theory and surface-science experimental tools. Metastable water adsorption is feasible for both pristine and defective surfaces with Cd and As vacancies. Water decomposition is energetically favorable only at steps, although with a rate of only ∼0.1 s⁻¹ at atmospheric pressure, with H and OH fragments forming bonds with As and Cd atoms, respectively. Interestingly, surface oxidization notably increases the reactivity towards water, also enabling water decomposition on the oxidized Cd₃As₂(112) surface with a rate of ∼10⁸ s⁻¹ and an energy barrier of only 0.29 eV. Our study clarifies the key role of surface oxidation in the interaction of Cd₃As₂ with water molecules, and, consequently, also in the stability of Cd₃As₂ in humid environments (including air). Moreover, our results elucidate the need of encapsulation in order to protect the surface of Cd₃As₂ topological semimetal from oxidation and hydroxylation. Correspondingly, it is evident that the wetting properties of this topological material drastically depend on the presence of surface oxide phases.