Mechanisms of Contact, Adhesion, and Failure of Metallic Nanoasperities in the Presence of Adsorbates: Toward Conductive Contact Design

Abstract

The properties of contacting interfaces are strongly affected not only by the bulk and surface properties of contacting materials but also by the ubiquitous presence of adsorbed contaminants. Here, we focus on the properties of single asperity contacts in the presence of adsorbates within a molecular dynamics description of metallic asperity normal contact and a parametric description of adsorbate properties. A platinum-platinum asperity contact is modeled with adsorbed oligomers with variable properties. This system is particularly tailored to the context of nanoelectromechanical system (NEMS) contact switches, but the results are generally relevant to metal-metal asperity contacts in nonpristine conditions. Even though mechanical forces can displace adsorbate out of the contact region, increasing the adsorbate layer thickness and/or adsorbate/metal adhesion makes it more difficult for metal asperity/metal surface contact to occur, thereby lowering the electrical contact conductance. Contact separation is a competition between plastic necking in the asperity or decohesion at the asperity/substrate interface. The mechanism which operates at a lower tensile stress dominates. Necking dominates when the adsorbate/metal adhesion is strong and/or the adsorbate layer thickness is small. In broad terms, necking implies larger asperity deformation and mechanical work, as compared with decohesion. Optimal NEMS switch performance requires substantial contact conductance and minimal asperity deformation; these results indicate that these goals can be achieved by balancing the quantity of adsorbates and their adhesion to the metal surface.

Review: Electrostatically actuated nanobeam-based nanoelectromechanical switches – materials solutions and operational conditions

“…The switch contact can become electrically insulating due to the oxidation of the switching material or build-up of a non-conductive tribopolymer layer under repetitively applied load in the contact [ 63 , 156 , 188 ]. Oxidation and tribopolymer formation issues were discussed previously.…”

Effect of Surface Energy on Shearing of Metal Asperities Contact at the Nanoscale

“…Recent year development of near-field, analytical, and simulation technologies has provided new methods for studying the fundamentals of friction and wear. Among them, experiments at the mesoscale give us some unprecedented insights. − However, due to the multi-physical influences and the limitations of experimental manipulation and observation techniques, the real-time details at the interface are difficult to access with high accuracy. Molecular dynamics (MD) simulation, another powerful method used in studying nanoscale tribology, makes up for the shortcomings of experiments.…”

The Influence of Lubrication and the Solid–Fluid Interaction on Thermodynamic Properties in a Nanoscopic Scratching Process

“…Lubricated scratching processes where two solid bodies are in direct contact under the influence of a fluid, on the other hand, have not been investigated as systematically. Results on the influence of the chain length of the lubricant molecules, , the surface roughness, , adsorbates, ,− the squeeze-out of lubricant molecules, ,, and the surface chemistry , have been reported in the literature. In most of these studies, lubrication was only considered by single adsorbed layers of fluid molecules on the substrate surface in the simulation, while studies in which the contact is truly immersed in a liquid are still rare. ,,, Also, small systems with state-of-the-art ab initio molecular dynamics simulations − have been reported recently.…”