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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–(Cx)–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. [ABSTRACT FROM AUTHOR]

Mechanical contacts in dry conditions are often characterized by an interfacial layer called “third body”, which generally originates from the degradations of the surfaces, but which can exhibit strongly different material properties. This layer is a direct consequence of past wear, but also exerts a control on the rate at which surfaces in contact will keep getting worn. A comprehensive understanding of mechanical contacts therefore relies on a theory describing the interplay between this sheared layer and the moving surfaces which confine it. In this paper, we make a step towards such a theory by quantitatively investigating the link between the flow regime of the third body and the mechanical loading it applies to the surfaces. For that purpose, a previously developed local model of solid flow based on the Multibody Meshfree Approach is employed, in order to simulate characteristic flow regimes identified in experiments. Typical stress concentration patterns endured by the surfaces are then described and quantified, and a simple damage model is used to demonstrate how such a model could lead to wear prediction. We demonstrate that agglomerated flow regimes are prone to enhance large and deep damaging of surfaces, while granular third body flows have a more limited and shallow damaging effect. [ABSTRACT FROM AUTHOR]

Hydrocarbon adsorption at the contact interface of nano-electromechanical switches is the main cause of device failure. This study simulated the approaching and separation process between two Pt(111) surfaces with adsorbed benzene molecules by Reactive molecular dynamics (ReaxFF-MD) simulations, to investigate the influence of benzene molecular coverage and relative orientation of substrate crystal surfaces on the adsorption structure of interfacial benzene molecules and substrate surface damage. During the approaching process, the interfacial benzene molecules form horizontal top and hollow adsorption structures in the sub-monolayer and monolayer coverage models, yet tilted adsorption structures in the multilayer coverage model. The formation of top and hollow adsorption structures is significantly affected by the relative crystallographic orientation. When two substrate surface atoms are aligned with each other, the interfacial benzene molecule is easy to form top adsorption structure, otherwise it tends to form hollow adsorption structure. However, the formation of the tilted adsorption structure is independent of the relative crystallographic orientation. Benzene molecules in horizontal hollow adsorption are usually bonded with two surfaces simultaneously. During the separation process, these bridging benzene molecules, simultaneously bonded with two substrates, lead to atomic detachment and other forms of damage on the metal surface. This feature may cause much more substrate damage in the monolayer coverage model than in the other two coverage models. This work provides a deeper insight into the damage mechanism of the contact surface of nano-electromechanical devices. [ABSTRACT FROM AUTHOR]

Material transfer during scratching is a direct result of adhesion and abrasive processes. In this work, molecular dynamics simulations are performed to quantify the individual effect of adhesive strength and abrasion depth on material transfer during nanoscratching of Tungsten. It is found that while the influence of adhesion and abrasion is tightly coupled at small scratching depths, the coupling decreases by increasing the scratching depth. Furthermore, it is shown that there exists a critical adhesive strength as a function of scratching depth at which the material removal mechanism transitions from the atom-by-atom to the wear fragment removal. This study confirms that the contribution of the atom-by-atom removal mechanism is suppressed when ploughing dominates the process of material removal. [ABSTRACT FROM AUTHOR]