Comparison of Depth-Sensing Indentation at Ultramicroscopic Contacts by Single- and Multiple-Partial-Unload Cycles

Abstract

Abstract Thin films typically exhibit variations in modulus and hardness with increasing indentation depth during depth-sensing indentation experiments at ultramicroscopic contacts (“nanoindentation”) because the measured stiffness response is affected by the substrate. There are three techniques commonly used to sample this variation in properties with depth: multiple indentations with increasing peak load, a single indentation with multiple-partial-unload cycles, and continuous stiffness measurement during a single indentation event. Experiments using the first two options were performed on a series of thin film systems and the method of multiple-partial-unloading found to have significant drawbacks when used at the sub-micron length scale that lead to erroneous conclusions.