Elastic recovery measurements performed by atomic force microscopy and standard nanoindentation on a Co(10.1) monocrysta
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M. Zamfirescu LASMEA-UMR 6602 du CNRS, Avenue des Landais, 63177 AUBIERE Cedex, France
H. Pelletier Laboratoire d’Ingénierie des Surfaces de Strasbourg, ENSAIS, 24, bld de la Victoire, 67084 Strasbourg Cedex, France (Received 22 January 2002; accepted 28 February 2002)
Atomic force microscopy (AFM) nanoindentation experiments were performed on a Co(10.1) monocrystal. Using AFM line scans, we deduced the elastic recovery, which is an intrinsic parameter of the studied material. The comparison of these elastic recovery values with those calculated by standard nanoindentation shows a fair agreement for forces higher than 400 N with an important discrepancy for lower forces. This difference is attributed to tip shape effects and to the AFM cantilever elastic deformation. Furthermore, the material hardness was measured from AFM images of the imprint by considering the lateral dimension L. In this case, the obtained values are practically independent from the applied load. Moreover, a simple model based on geometrical considerations is proposed to correct hardness values calculated from the residual depth. I. INTRODUCTION
Atomic force microscopy (AFM) is a powerful technique for studying local interaction of a tip with a surface at a nanoscale level. Tribological properties such as friction, stiffness, wear, adhesion or plasticity could be measured using AFM.1–3 Such experiments can be carried out in different environments [ultrahigh vacuum (UHV), controlled atmosphere, ambient air] on a wide range of materials: monocrystalline surfaces,4–6 thin deposited films,7,8 and adsorbed molecules.9,10 Adhesion, nanoindentation, and fracture of an AFM tip with a surface have been modeled by molecular dynamics simulations.11 An AFM diamond tip has been used to indent surfaces.5,12 Because of the small radius of curvature of the tip, the interaction tip-surface is more localized than standard indentation so that weaker forces can be applied. A tremendous difference for the force resolution was reported, close to 1 nN compared to 100 nN for the better classical home built indenters.13 Moreover, using AFM, indentations could be imaged just after the indentation
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J. Mater. Res., Vol. 17, No. 6, Jun 2002 Downloaded: 09 Feb 2015
and the indentation’s topography can be obtained. However, it has been claimed that AFM nanoindentation does not provide quantitative data due to the tip geometry and the calibration of the piezo scanner.14 In the case of hard materials such as silicon, which exhibit high elastic recovery, AFM measurements lead to mistaken hardness values.15 The surface is indeed imaged immediately after the indentation and the nano-hardness is then calculated by dividing the applied load by the residual projected contact area. On the other hand, standard indentation gives access to the deformation behavior of indented material during the indentation via load-displacement curves. However, some a
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