AFM nanoindentation: tip shape and tip radius of curvature effect on the hardnessmeasurement

Abstract

AFM nanoindentation is nowadays not so widespread for the study of mechanicalproperties of materials at the nanoscale. ‘Nanoindenter’ machines are presentlymore accurate and more standardized. However, AFM could provide interestingfeatures such as imaging the indentation impression right after the load application.In this work a new method for nanoindentation via AFM is proposed. The use of AFMallows hardness measurement with standard sharp AFM probes and a simultaneoushigh-resolution imaging (which is not achievable with standard indenters—cube corner andBerkovich). How the shape of the indenter and the tip radius of curvature affect thehardness measurement is here analysed with three different approaches: experiments,numerical simulations and theoretical models. In particular the effect of the tip radius ofcurvature, which is not negligible for the real indenters, has been considered both in thenature of the indentation process, than in the practice of imaging with AFM.A final theoretical model has been developed, that includes the effect of the tipradius of curvature as well as variable corner angle. Through this model we havebeen able to define a correction factor which permits us to evaluate the actualhardness of the material, once the radius of curvature of the tip is measured.