TEM lattice imaging of the nanostructure of early-growth sputter-deposited MoS2solid lubricant films

Abstract

Transmission electron microscopy (TEM) was used to investigate the nanostructure of sputter-deposited MoS2films; these films represent the early stages of growth under deposition conditions that produce a zone 2 columnar morphology. Analysis reveals that the early-growth film morphology consists of anisotropic (plate-like) islands in which the (001) basal planes are generally perpendicular to the substrate (forming “edge islands”) or parallel to the substrate (forming “basal islands”). Within the context of an active-sites nucleation model, localized regions of the substrate surface can lack the active sites needed to induce edge orientation. The edge islands evolve into the zone 2 morphology, shadowing and inhibiting the continued growth of the basal islands. Basal plane (002) lattice image curvature and kinking were observed in the edge islands. Dark-field analysis showed intensity variations within the edge islands. The edge island plates appear to be imperfect crystals of aligned basal planes. These crystals can bend, kink, or twist, apparently because of variations in local growth conditions. The ability of crystal growth to deviate has implications for the morphological evolution of thicker films. The ability of the MoS2crystal lattice to bend supports the idea that localized deviation can occur during sliding wear.