Newly Discovered Pile Up Effects During Nanoindentation

Abstract

This work focuses on clearly defining the effects of pile up during nanoindentation of thin films deposited on substrates. Thin film behavior is important to understand in order to prevent failure in nano- and microscale mechanical devices utilized in computers or cell phones. During nanoindentation tests, phenomena such as sink-in or pile-up can occur depending on the mismatch of elastic moduli and Poisson’s ratios. This, in turn, alters the projection of the indent on the sample. While others have tried to measure and account for the pile up through changes in contact area, we have found that the pile up area does not affect the extracted elastic mechanical properties of the film or substrate materials. By depositing different thicknesses of gold on various plastically deforming substrates, pile up trends are visualized. Accounting for pile up is not necessary, as demonstrated through experimental data matched with models and images from scanning electron microscopy. These findings will help future experiments to correctly calculate elastic mechanical properties that have pile up issues.