Characterization of the structural, electronic and tribological properties of metal dichalcogenides by scanning probe microscopies

Abstract

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) have been used to characterize the structural and electronic properties of single-crystal MoS 2, nickel-substituted MoS 2 (Ni x Mo 1− x S 2), and chalcogenide-substituted MoS 2 (MoS 2− x Ch x , Ch ≡ Se, Te) at the atomic level. Images of Ni 0.1Mo 0.9S 2 demonstrate that nickel substitution causes localized changes in the electronic states, although the structure of the surface sulfur layer is unchanged compared with MoS 2. Investigations of MoS 1.75Se 0.25 also show that within the detection limits of AFM selenium substitution does not perturb the sulfur surface structure, and STM data further indicate that the substituted selenium is electronically delocalized. In contrast, AFM studies of MoS 1.75Te 0.25 show that tellurium substitution produces atomic-sized structural protrusions that may modify significantly the tribological properties of MoS 2. In addition, we demonstrate that material wear can be characterized on an atomic scale by AFM. These studies indicate that the microscopic origin of material wear as well as the local structure and electronic properties should be considered to develop further models of friction and wear in metal dichalcogenide materials.