Molecular Simulation of Contact/Separation Behavior of Platinum Surfaces with Adsorbed Acetylenes

Ambient hydrocarbons adsorbed on the contact surface of nanoelectromechanical (NEM) switches would impact its performance. In this study, we utilized reactive molecular dynamics simulations to investigate the cyclic contact/separation process of Pt(111)/C₂H₂/Pt(111) systems. Our results demonstrate that substrate damage decreases as acetylene coverage increases from sub-monolayer to multilayer. This suppression occurs due to the presence of acetylene molecules, which can suppress direct (Pt–Pt connection) and indirect (Pt–(C_x)–Pt-like connection) interfacial bonding between the two substrates, depending on their coverage. Moreover, we observed the formation of chain-like oligomers after multiple contact/separation simulations in the monolayer model, much more significantly compared with the sub-monolayer and multilayer models. These oligomers arise from polymerization reactions among fragmented acetylene molecules, primarily formed through acetylene dehydrogenation. In the sub-monolayer model, numerous transferred Pt atoms at the interface hinder bonding between acetylene fragments, whereas in the multilayer model, only a few acetylene fragments form during the contact process, due to the well-organized and dense acetylene layer adsorbed on the substrate surfaces. These insights shed light on the atomic-scale mechanisms underlying substrate damage and chain-like oligomers formation in metal NEM switches.