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EEE9.02 - Atomically-Defined Indentation: Bridging the Length-Scale Gap with Simulations 
April 25, 2014   9:00am - 9:15am

Using a combination of scanning probe microscopy (SPM) and field ion microscopy (FIM) in ultra-high vacuum (UHV), indentation can be carried out with atomically-defined indenters at a length scale which is directly comparable with atomistic simulations. Starting with a spherical tungsten indenter of radius ~3-12 nm, we have investigated indentation response on Au(111) at the atomic scale. Scanning tunneling microscopy (STM), using the same tip, provides high resolution imaging of defect structures on the surface after indentation.In this talk, we will discuss results of recent indentation experiments on Au(111) single crystals with an emphasis on phenomena which are unique to the atomic length scale (tips of radius < 10 nm and penetration depths < 2 nm). This length scale is intrinsically interesting because it is at these low penetration depths that plastic deformation is initiated in the substrate [1]. We find evidence for heterogeneous dislocation nucleation in these experiments, a feature which is suggested by molecular dynamics simulations with atomically rough W(111) tips [2].Molecular dynamics simulations support numerous experimental observations including adhesion and tip wetting, material pileup, and indent morphology. Some behaviors are not well reproduced, however: Notably, the maximum adhesive pull-off force is significantly higher in simulation than in experiment, and varies in experiments as the tungsten tip wets with gold from the substrate [3]. We believe that the disparity in adhesive forces may point to the need to close not only the length scale, but also the time scale gap.[1] W. Paul, D. Oliver, Y. Miyahara and P. H. Grütter, Phys. Rev. Lett. 110, 135506 (2013)[2] D. Oliver, W. Paul, M. El Ouali, T. Hagedorn, Y. Miyahara, Y. Qi, and P. Grütter, Nanotechnology (in press for Nov 2013)[3] W. Paul, D. Oliver, Y. Miyahara, and P. Grütter, Nanotechnology (in press for Oct 2013)

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