The effects of chlorine-containing species on cinnabar: A density functional theory investigation into the surface adsorption reactivity of mercury sulfide

Abstract

First-principles computations can be used to noninvasively probe semiconductor surfaces and describe mechanisms and transformations that occur on those surfaces. One such material of interest is the chalcogenide mercury sulfide (HgS), also known as cinnabar. Cinnabar (α-HgS) and its synthetic counterpart (vermilion) have been used as bright red pigments since antiquity and are important sulfide materials in the field of art conservation. However, it has been known since Roman times that these pigments can darken when exposed to light. It has been hypothesized that Cl2 and other chlorine-containing materials are involved in the photodegradation of cinnabar surfaces. Here we use first-principles density functional theory (DFT) to probe the adsorption reactivity of Cl-containing adsorbates on HgS surfaces, as DFT yields information at the atomistic level and can link changes in surface structure to changes in electronic states. Specifically, we model single adsorbates interacting with corrugated and flat HgS surfaces to probe the initial step in the photodegradation mechanism. This allows us to not only assess the strength of adsorption and any corresponding adsorbate dissociations, but also link these adsorption and dissociation events to key changes in the electronic band structure that may act as spectroscopic identifiers in the degradation pathway of chalcogenide semiconductors that contain photoreactive metals.