Dislocation nucleation at nano-scale mechanical contacts

The plastic deformation of metals in highly localized stress fields is critical to macroscopic phenomena such as fracture, surface wear and adhesion where crack tips and surface asperities concentrate the applied stress. Controlled-probe contact techniques can be used to measure forces and displacements on the atomic scale, thereby directly exploring elastic and plastic deformation of solids al the nanometer level. In this study we use interfacial force microscopy to quantitatively examine the nano-scale elastic and plastic response of single crystal Au(111) surfaces using controlled-probe contacts with a range of radii extending down to 500 Angstrom. Our results show that the stress at the plastic threshold increases with decreasing probe-tip radius. We apply a model for dislocation nucleation which reproduces the scaling behavior with tip radius and discuss deficiencies in the model and plausible reasons for the underestimation in quantitative stress values. (C) 1998 Acta Metallurgica Inc.