MoS₂ Nanoclusters Grown on TiO₂: Evidence for New Adsorption Sites at Edges and Sulfur Vacancies

Abstract

MoS2 clusters have been grown on a TiO2(110) substrate to provide a model surface for better understanding the adsorbate interactions and chemical activity on titania-supported MoS2 clusters. Scanning tunneling microscopy experiments show that clusters with elongated shapes and flat tops are formed, and the long axes of the clusters have specific orientations with respect to the [001] direction on TiO2(110). In contrast, deposition of Mo in the absence of H2S results in a high density of smaller, round clusters that cover the majority of the surface. The morphologies of the MoS2 clusters do not change after exposure to various gases (D2, CO, O2, H2O, and methanol) in ultrahigh vacuum. However, exposure to higher pressures of O2, H2O, or methanol (10 Torr), as well as exposure to air, causes the clusters to disintegrate as Mo in the clusters becomes oxidized. Temperature-programmed desorption studies with CO on the MoS2 clusters show a distinct desorption peak at 280 K, which is not observed on metallic Mo or titania. Density functional theory calculations suggest that these new adsorption sites for CO are at the edges of the elongated MoS2 clusters, particularly along the (101̅0) edge containing sulfur vacancy sites.