Asperity contacts at the nanoscale: Comparison of Ru and Au

Fortini, Andrea; Mendelev, Mikhail I.; Buldyrev, Sergey V.; Srolovitz, David J.

doi:10.1063/1.2991301

Cited by 51 publications

(56 citation statements)

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“…The functional forms and parameters for V (r ij ), F (ρ i ), and Φ(r ij ) can be found in Ref. 22 . The interatomic potential adopted for the Ru atoms in this work reproduces the elastic constants and cohesive energy of Ru, and also gives stacking fault energy and surface energies that are in reasonable agreement with the experiment (for a comparison between experiment and model for several quantities of interest see Ref.…”

Section: Methodsmentioning

confidence: 99%

“…This behavior is typical of ductile materials. On the other hand, a Ru nanoasperity contact was reported 22 to show a behavior which is more typical for brittle materials like glasses. Namely, the contact separation is characterized by crack formation and a sharp drop-to-zero of the tensile force during the unloading stage.…”

Section: -5mentioning

confidence: 99%

“…In Ref. 22 , it was hypothesized that Ru contacts are more brittle than Au contacts due to the fact that the HCP lattice of Ru has fewer slip systems than the FCC lattice of Au and also due to the fact that Ru stacking fault energy (which is activated in plastic deformations) is 16 times larger than that of Au, while the Ru surface energy (which is activated during fracture formation) is only 3 times larger than that of Au. Our present study which shows the variability of the behavior of Ru contacts on separation does not contradict this hypothesis.…”

Section: -5mentioning

confidence: 99%

“…Ruthenium contacts have proven to be more reliable than gold contacts, routinely surviving millions of cycles without significant degradation. The behavior of Ru single asperity contacts has recently been studied by molecular dynamic simulations and compared to that of gold contacts 22 . In that work, a new embedded atom potential 23,24 was developed which accurately reproduces several key structural, thermodynamic and mechanical properties of ruthenium, including its hexagonal close packed lattice structure, elastic constants, work of adhesion, and stacking fault energy.…”

Section: -5mentioning

confidence: 99%

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

et al. 2011

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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.

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Section: Methodsmentioning

confidence: 99%

Section: -5mentioning

confidence: 99%

Section: -5mentioning

confidence: 99%

Section: -5mentioning

confidence: 99%

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

et al. 2011

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“…The performance and reliability of these devices depends on the contact physics that govern the pullout force required to open the switch and on the defect generation that leads to an increase in contact resistance. The interaction between surfaces depends on the materials involved [3], surface chemistry, and roughness as well as operating conditions. In this Letter we focus on clean platinum slabs with nanoscale surface roughness where the interaction is dominated by the metallic bridges that form when surface asperities come into contact.…”

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confidence: 99%

Nanoscale Metal-Metal Contact Physics from Molecular Dynamics: The Strongest Contact Size

Kim

Strachan

2010

Phys. Rev. Lett.

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Using molecular dynamics we find that the tensile strength of the contacts between two clean platinum surfaces with nanoscale asperities is strongly size dependent with a maximum strength for contact lengths of approximately 5 nm. This is the first time a strongest size is observed in single crystals. The strengthening with decreasing size down to 5 nm results from a decrease in the initial density of mobile dislocations available for plastic deformation and the subsequent weakening originates from a reduction in the constraint to mechanical deformation inside the contact by the bulk. DOI: 10.1103/PhysRevLett.104.215504 PACS numbers: 62.25.Àg, 62.20.FÀ, 62.20.Qp, 81.07.Lk Processes resulting from the interaction between contacting surfaces including friction and stiction (static friction) are ubiquitous in traditional and emerging technologies including micro-and nanoscale contacting switches for communications [1] and low-power electronics [2]. The performance and reliability of these devices depends on the contact physics that govern the pullout force required to open the switch and on the defect generation that leads to an increase in contact resistance. The interaction between surfaces depends on the materials involved [3], surface chemistry, and roughness as well as operating conditions. In this Letter we focus on clean platinum slabs with nanoscale surface roughness where the interaction is dominated by the metallic bridges that form when surface asperities come into contact. In actual micro-and nanoswitches a large number of nanoscale contacts will form with a size distribution and local forces that depend on surface roughness and chemistry and external closing force [4]. The mechanical response of materials with such nanoscale dimensions is size dependent and the sub-100 nm range remains vastly unexplored. This factor contributes to the current lack of an understanding in the area of nanoscale contacts. Here we report on a molecular dynamics study of the strength of nanoscale contacts (tensile stress required to open the contact) between clean platinum surfaces as a function of their size. Our simulations shed light into the atomic mechanisms that govern size effects in contact physics and indicate that nanocontact experiments between clean surfaces would be a powerful tool to interrogate mechanical properties at extremely small scales that are difficult to explore by other means. A thin layer of adsorbates is always present in real microelectromechanical systems (MEMS) surfaces and contributes to surface adhesion; our work focuses on the interaction via metallic bridges that form due to large local forces and heating caused by electrical currents.Size effects in mechanical properties were first characterized by Hall and Petch in polycrystalline materials and by Brenner in metallic whiskers in the 1950s, with the general observation that smaller is stronger. More recently, size effects in strength have been observed in micropillars [5,6], thin films [7], and nanoindentation [8]. In the case of polycr...

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Case Studies

Bazu

Băjenescu

2011

Failure Analysis

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Asperity contacts at the nanoscale: Comparison of Ru and Au

Cited by 51 publications

References 46 publications

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

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

Nanoscale Metal-Metal Contact Physics from Molecular Dynamics: The Strongest Contact Size

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