Reactivity of the ZnS(10(1)over-bar0) Surface to Small Organic Ligands by Density Functional Theory

The adsorption process of small organic molecules that represent reactive groups in amino acids (H2O, H2S, NH3, and HCOOH) on the nonpolar ZnS(10 (1) over bar0) surface was investigated by van der Waals corrected density functional theory calculations. At the accomplished interfaces, the oxygen, sulfur and nitrogen atoms of the adsorbates point toward the zinc atoms of the substrate, realizing electronic hybridization of their p lone pairs with the s and d bands of Zn. This electronic hybridization that involves surface cations is accompanied by H-bond formation that involves surface anions: this concerted mechanism enhances the interface strength and stability. On the basis of our results, we distinguish two classes of adsorption modes: molecular adsorption pertains to H2O, NH3, and HCOOH independently of the coverage and to H2S at low coverage, while concurrent adsorption/dissociation pertains to H2S at saturation coverage as a compromise between steric repulsion and H-bond-like interactions. Our results shed light on the passivation and modification of ZnS substrates (quantum dots and flat surfaces) in the prospect of technological and biomedical applications.