First-Principles Investigation of Surface Mechanochemistry of Transition Metal Phosphides under Oxygen and Benzene Atmospheres

Transition metal phosphides (TMPs) have aroused widespread research interest in the past decade due to their excellent electrical and mechanical properties. Nonetheless, their application in micro- and nanoelectromechanical systems (MEMS and NEMS) has not been investigated. Here, we use density functional theory (DFT) to explore the potential of four transition-metal phosphides to act as contact materials of MEMS/NEMS switches. Specifically, we first investigate the thermodynamic stability of Ru₂P, RuP, Rh₂P, and TiP under an oxygen environment. Then, using benzene as the background gas, the mechanical contact cycle is modeled to examine the process of tribopolymer formation on the surface of the contacts, which has been reported as the major reason for conductance loss after repeated actuation. The results show that Ru₂P and Rh₂P are excellent choices for avoiding friction-induced polymerization, making them promising contact materials for MEMS/NEMS switches.