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Atomic-scale friction between single-asperity contacts unveiled through in situ transmission electron microscopy

Nature Nanotechnology volume 17, pages 737–745 (2022)Cite this article

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A Publisher Correction to this article was published on 08 June 2022

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Abstract

Friction and wear are detrimental to functionality and reduce the service life of products with mechanical elements. Here, we unveil the atomic-scale friction of a single tungsten asperity in real time through a high-resolution transmission electron microscopy investigation of a nanocontact in countermotion, induced through a piezo actuator. Molecular dynamics simulations provide insights into the sliding pathway of interface atoms and the dynamic strain/stress evolution at the interface. We observe a discrete stick–slip behaviour and an asynchronous process for the accumulation and dissipation of the strain energy together with the non-uniform motion of interface atoms. Our methodology allows for studying in situ atomic-friction phenomena and provides insights into friction phenomena at the atomic scale.

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Fig. 1: In situ atomic observation of stick–slip behaviour between single-tungsten asperity nanocontacts.
Fig. 2: Discrete stick–slip behaviour between tungsten asperities revealed by MD simulations.
Fig. 3: In situ TEM observation of atomic friction with 11 contact atoms.
Fig. 4: Strain evolution on the top layer of the tip during friction.
Fig. 5: Dynamic evolution of shear stress field on the bottom layer of the substrate using MD simulation.

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Data availability

All data needed to evaluate the conclusions have been included in the paper/or the Supplementary Materials. Source data are provided with this paper. Additional data related to this paper can be requested from the corresponding authors S.X.M. (sxm2@pitt.edu) or G.W. (guw8@pitt.edu).

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Acknowledgements

S.X.M. acknowledges support from the National Science Foundation (NSF CMMI 1824816) through the University of Pittsburgh. G.W. acknowledges the computational resources provided by the University of Pittsburgh Center for Research Computing.

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Author notes

  1. These authors contributed equally: Xiang Wang, Zhenyu Liu.

Authors and Affiliations

  1. Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, USA

    Xiang Wang, Zhenyu Liu, Yang He, Guofeng Wang & Scott X. Mao

  2. Petersen Institute of Nanoscience and Engineering, University of Pittsburgh, Pittsburgh, PA, USA

    Susheng Tan

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Contributions

S.X.M. conceived the project. X.W. designed the experiment and performed in situ TEM tests and associated result analysis. Y.H. contributed to the experiment design and the result discussion. S.T. contributed to the TEM observation. Z.L. and G.W. carried out MD simulations. X.W., Z.L., G.W. and S.X.M. wrote the manuscript with the contribution of all authors.

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Correspondence to Guofeng Wang or Scott X. Mao.

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Nature Nanotechnology thanks the anonymous reviewers for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1

Three force components of the interface atoms in MD simulation with 7 contact atoms. (Fig. 2) When the interface atoms completed the second slipping along the zig-zag route, the accumulated stress along z-direction in the first slipping would release, leading to the drop of the friction force. In experiments, since the shear force was obtained by measuring shear strains of seven/eleven atoms along x-direction in contact, the effect from the stress release along z-direction on the friction force might not be noticed.

Extended Data Fig. 2

The friction process within one period in MD simulation. (a-g) The structure evolution of the single asperity W-W contacts during friction, corresponding to the points of numbers 1–7 in Fig. 2a.

Extended Data Fig. 3

Variation of normal force with the displacement of the tip in the experiment (Fig. 1). The error bars represent the standard deviation of the normal force.

Source data

Extended Data Fig. 4

Discrete stick-slip behavior between tungsten asperities revealed by molecular dynamics (MD) simulation (The width of the contact region is 11 atoms’ space). (a) The function of the lateral force with the sliding displacement of the tip. (b-h) The snapshots of the dynamic movement of atoms in the top layer of the tip with respect to the substrate. The cyan balls represent the atoms in the bottom of the substrate. Four selected atoms were colored in yellow, orange, red, dark respectively. (i) The motion traces of the selected four atoms marked by the broken circles within one friction period.

Extended Data Fig. 5

The shear strain evolutions measured from two selected atoms marked by 1 and 7 in Fig. 4 during friction within one period.

Source data

Extended Data Fig. 6

Dynamic evolution of shear stress field on the bottom layer of the substrate in MD simulation. (a-e) The evolution of σxy (σzy) distribution on the bottom layer of the substrate and the corresponding sequences are indicated by red Roman numbers in Extended Data Fig. 4a.

Extended Data Fig. 7

Variation of normal force with the displacement of the tip in the case with 11 contact atoms. The error bars represent the standard deviation of the normal force.

Source data

Supplementary information

Supplementary Information

Supplementary Figs. 1–6, Discussion 1–3, Tables 1 and 2 and references.

Supplementary Video 1

In situ TEM observation of atomic friction.

Supplementary Video 2

In situ TEM observation of atomic friction containing 11 contact atoms.

Supplementary Video 3

Another in situ atomic friction test.

Supplementary Video 4

In situ TEM observation of contact between two tungsten asperities.

Source data

Source Data Fig. 1a

Statistical Source Data.

Source Data Fig. 3a

Statistical Source Data.

Source Data Extended Data Fig. 3

Statistical Source Data.

Source Data Extended Data Fig. 5

Statistical Source Data.

Source Data Extended Data Fig. 7

Statistical Source Data.

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Wang, X., Liu, Z., He, Y. et al. Atomic-scale friction between single-asperity contacts unveiled through in situ transmission electron microscopy. Nat. Nanotechnol. 17, 737–745 (2022). https://doi.org/10.1038/s41565-022-01126-z

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