Dynamics of the contact between a ruthenium surface with a single nanoasperity and a flat ruthenium surface: Molecular dynamics simulations

Abstract

We study the dynamics of the contact between a pair of surfaces (with properties designed to mimic ruthenium) via molecular dynamics simulations. In particular, we study the contact between a ruthenium surface with a single nanoasperity and a flat ruthenium surface. The results of such simulations suggest that contact behavior is highly variable. The goal of this study is to investigate the source and degree of this variability. We find that during compression, the behavior of the contact force displacement curves is reproducible, while during contact separation, the behavior is highly variable. Examination of the contact surfaces suggest that two separation mechanism are in operation and give rise to this variability. One mechanism corresponds to the formation of a bridge between the two surfaces that plastically stretches as the surfaces are drawn apart and eventually separates in shear. This leads to a morphology after separation in which there are opposing asperities on the two surfaces. This plastic separation/bridge formation mechanism leads to a large work of separation. The other mechanism is a more brittle-like mode in which a crack propagates across the base of the asperity (slightly below the asperity/substrate junction) leading to most of the asperity on one surface or the other after separation and a slight depression facing this asperity on the opposing surface. This failure mode corresponds to a smaller work of separation. those in which a single mechanism operates. Furthermore, contacts made from materials that exhibit predominantly brittle-like behavior will tend to require lower work of separation than those made from ductile-like contact materials.

An atomic interaction-based adhesive contact model for shallow nanoindentation and nanoscratch

“…Such type of load-displacement discontinuity was found particularly evident for the contact pair with larger adhesion work, and very different from the indentation behavior of no adhesion case, of which load-displacement curve is continuous and smooth. Note that similar load-displacement behaviors have been found in past not only with the AFM-based nanoscale experiment, [21] but also with the molecular dynamics simulation [22][23][24][25] and the multi-scale analysis. [26] Where, the results of molecular dynamics simulation show that the load drop behaviors are closely associated with the generation and development of dislocations.…”

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

“…Asperity contact in the absence of adsorbates was discussed in our earlier studies. ,,− To understand the effect of adsorbates on the contact process, we systematically vary adsorbate layer thickness, adhesion between metal and adsorbates, and cohesion between oligomer adsorbates (see Methods). We simulate adsorbate layer thicknesses h = 0, 0.12, 0.36, 0.73 nm, where h = 0 implies no adsorbates; this covers the adsorbate layers from submonolayer to several layers (see Figure S1 and Methods).…”

A Combined Molecular Dynamics and Finite Element Analysis of Contact and Adhesion of a Rough Sphere and a Flat Surface

“…A proper averaging would require extensive simulation work. Nonetheless, as demonstrated by de Oliveira, et al (30), different asperity realizations share the same type of plastic behavior. Furthermore, simulations have been conducted corresponding to the (1122) planes and show very similar results to those conducted for the (0001) planes.…”

“…Nonetheless, the MD simulations in de Oliveira, et al (30) included a case with 7,000 atoms in the asperity, which is almost two and a half times as many as used here and corresponds to a 34% increase in the linear dimensions such as radius. This increased size led to an approximately 25% increase in the maximum load.…”

“…Finally, we compare these results to those from a smooth sphere model. Figure 1 shows the atomistic configuration for a typical MD cell used to simulate the contact formation and separation of a single Ru nano-asperity and an Ru flat (de Oliveira, et al (30)). Molecular dynamics simulations of the contact of individual Ru nano-asperities and a flat Ru substrate were originally performed by Fortini, et al (31).…”