Measuring Substrate-Independent Young’s Modulus
Publication Number: 5990-6507EN
Publication Date: 2014.07.31
Language: English
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Measuring Substrate-Independent Young’s Modulus

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The problem of determining intrinsic ilm properties from indentation data that are inluenced by both ilm and substrate is an old one. If the ilm is thick enough to be treated as a bulk material, then the analysis of Oliver and Pharr (1992) is typically used 1 . When the ilm is so thin that indentation results at all practical depths are substantially affected by the substrate, the inluence of the substrate must be accurately modeled in order to extract the properties of the ilm alone. Since 1986, many such models have been proposed 2-12 .

In 1992, Gao, Chiu, and Lee proposed a simple approximate model for substrate inluence. They derived two functions, I0 and I1, to govern the transition in elastic properties from ilm to substrate 5 . Beginning with his Ph.D. dissertation in 1999, Song and his colleagues took an alternate solution path which was originally suggested by Gao et al. but not followed 7-9. This alternate path yielded a simpler model which is called the “Song-Pharr model” in the literature. The Song-Pharr model predicts substrate effect reasonably well when the ilm is more compliant than the substrate. Unfortunately, none of the available models works well when the ilm is stiffer than the substrate. This shortcoming motivated the present work.