A comparison of the uniaxial deformation of copper and nickel (1 1 19) surfaces: a molecular dynamics study

Nuša Pukšič,Monika Jenko,Paul J. McGuiness,Matjaž Godec

doi:10.1038/srep42234

Abstract

While a lot is known about the deformation of metallic surfaces from experiments, elasticity theory and simulations, this investigation represents the first molecular-dynamics-based simulation of uniaxial deformation for the vicinal surfaces in a comparison of copper and nickel. These vicinal surfaces are composed of terraces divided by equidistant, mono-atomic steps. The periodicity of vicinals makes them good candidates for the study of the surface steps’ influences on surface dynamics. The simulations of tensile and compressive uniaxial deformations were performed for the (1 1 19) vicinal surfaces. Since the steps on the surfaces serve as stress concentrators, the first defects were expected to nucleate here. In the case of copper, this was found to be the case. In the case of nickel, however, dislocations nucleated beneath the near-surface layer affected by the displacement field generated by the steps. Slip was hindered at the surface step by the vortex in the displacement field. The differences in the deformation mechanisms for the Ni(1 1 19) and Cu(1 1 19) surfaces can be linked to the differences in their displacement fields. This could lead to novel bottom-up approaches to the nanostructuring of surfaces using strain.

Highlights

In the past 20 years investigations of stress and strain effects in the field of surface physics have become increasingly important as the manufacture of nanoscale materials and devices has become more widespread, leading to studies based on a combination of theoretical, computational and experimental investigations[1]
In the case of the vicinal surfaces this minimal energy arrangement of atoms leads to a complex displacement field, stretching several layers into the bulk specific for each surface orientation and material[2,8]
We conclude that the displacement fields of vicinal surfaces play a role in their deformation mechanisms

Summary

Introduction

In the past 20 years investigations of stress and strain effects in the field of surface physics have become increasingly important as the manufacture of nanoscale materials and devices has become more widespread, leading to studies based on a combination of theoretical, computational and experimental investigations[1]. Elasticity provides pressure maps that can help to predict the stress release resulting from atomic rearrangements[1]; on the subject of vicinal surfaces under an externally applied stress the data from both experiments and simulations is scarce. These vicinal surfaces are defined by terraces divided by equidistant, monoatomic steps, and can be exposed by cutting a crystal at a small angle to one of the low-index planes. The substrates are thin films[18,19,20], with controlled impurities, i.e., vacancies[21], voids[22], grain boundaries[23] and steps[24,25,26,27], added in some cases

Methods

Results

Discussion

Conclusion