OS5-1-2 Characterization of Small-volume Materials with Nanocontact Images

Abstract

Conventional nanoindentation testing generally uses a peak penetration depth of less than 10 % of thin-film thickness in order to measure film-only mechanical properties, without considering the critical thickness for a given thin film-substrate system. The uncertainties in this testing condition make the measurement of film mechanical property more difficult. Thus, we estimated the critical relative thickness of Au thin film by adopting the mechanism-based strain gradient plasticity theory. Au film's critical relative thickness was determined by 0.17 and subsequent strength evaluations were carried out for nanoindentations shallower than 204 nm. The yield strength of thin film was estimated by considering the force equilibrium around an indentation-induced plastic zone; the plastic zone dimension is a key information for this analysis. However, conventional approach has analogized the plastic zone radius from few cross-sectional line profiles of the remnant indent and yielded erroneous strength result. Thus, we tried to extract a two-dimensional closed boundary of the plastic zone in this study by plotting a contour graph for the surface pile-up. This image processing was applied to the strength characterization of 1.2 μm-thick Au film on Si substrate. However, the analyzed indentation data produced strength overestimations compared to the microtensile results. This discrepancy in the yield strength was discussed from a viewpoint of microstructural anisotropy in the Au thin film.