Structurally Driven Environmental Degradation of Friction in MoS2 Films
John F. Curry, Taisuke Ohta, Frank W. DelRio, Philip Mantos, Morgan R. Jones, Tomas F. Babuska, N. Scott Bobbitt, Nicolas Argibay, Brandon A. Krick, Michael T. Dugger, Michael Chandross
Abstract
Abstract We report an investigation of the friction mechanisms of MoS 2 thin films under changing environments and contact conditions using a variety of computational and experimental techniques. Molecular dynamics simulations were used to study the effects of water and molecular oxygen on friction and bonding of MoS 2 lamellae during initial sliding. Characterization via photoelectron emission microscopy (PEEM) and Kelvin probe force microscopy (KPFM) were used to determine work function changes in shear modified material within the top few nanometers of MoS 2 wear scars. The work function was shown to change with contact conditions and environment, and shown by density functional theory (DFT) calculations and literature reports to be correlated with lamellae size and thickness of the basally oriented surface layer. Results from nanoscale simulations and macroscale experiments suggest that the evolution of the friction behavior of MoS 2 is linked primarily to the formation or inhibition of a basally oriented, molecularly thin surface film with long-range order.