Tip bluntness transition measured with atomic force microscopy and the effect on hardness variation with depth in silicon dioxide nanoindentation

Abstract

Depth-sensing indentation measurements of surfaces and structures with indentation depths less than 100 nm necessitate the use of accurate area functions for correct property evaluation. Here, the effect of a blunt nanoindenter tip geometry is characterized using atomic force microscopy to measure the direct tip geometry and modeled by a power law profile shape. Direct measurement of tip geometry is a method to observe changes in the tip curvature and transition from the blunt tip region to an ideal tip geometry. The tip shape, curvature, and transition to ideal geometry is found to correspond with the increase in hardness observed experimentally in SiO2 using a self-similar contact model. For a Berkovich indenter, tip bluntness was found to have a power law degree of 1.5 near the tip apex with a continuously varying degree of bluntness until an ideal pyramidal shape was reached at a depth of 160 nm.