We combine experimental and theoretical methods to understand the impact of long-range Coulomb interactions on phonons and excitons in ZrSxSe2−x.

A thorough understanding of native oxides is essential for designing semiconductor devices. Here, we report a study of the rate and mechanisms of spontaneous oxidation of bulk single crystals of ZrS x Se 2−x alloys and MoS 2 . ZrS x Se 2−x alloys oxidize rapidly, and the oxidation rate increases with Se content. Oxidation of basal surfaces is initiated by favorable O 2 adsorption and proceeds by a mechanism of Zr−O bond switching, that collapses the van der Waals gaps, and is facilitated by progressive redox transitions of the chalcogen. The rate-limiting process is the formation and out-diffusion of SO 2 . In contrast, MoS 2 basal surfaces are stable due to unfavorable oxygen adsorption. Our results provide insight and quantitative guidance for designing and processing semiconductor devices based on ZrS x Se 2−x and MoS 2 and identify the atomistic-scale mechanisms of bonding and phase transformations in layered materials with competing anions.