Nanoindentation of Thin Films and Small Volumes of Materials

Abstract

One of the most popular applications of nanoindentation is the determination of the mechanical properties of thin films. In nanoindentation tests, the properties of the film may be measured without removing the film from the substrate as is done in other types of testing. The spatial distribution of properties, in both lateral and depth dimensions, may be measured, and a wide variety of films are amenable to the technique, from ion-implanted surfaces to optical coatings and polymer films. Apart from testing films in-situ, nanoindentation techniques can also be used for films made as free-standing microbeams or membranes [1]. 8.2 Testing of Thin Films Both quantitative and qualitative information can be obtained from nanoindentation experiments on thin film systems. For example, comparison of load-displacement curves between coated and uncoated substrates often reveals changes in the elastic and plastic response of a system due to differences in surface treatment. The pres-ence of discontinuities in the load-displacement response reveals information about cracking, delamination, and plasticity in the film and substrate. Some properties of thin films tested using nanoindentation techniques are given in Sect. 13.5. The chief difficulty encountered in nanoindentation of thin films is to avoid un-intentional probing of the properties of the substrate. To achieve this, it is common to restrict the maximum depth of penetration in a test to no more than 10% of the film thickness, although research suggests that this rule has no physical basis [2]. For indentations with a conical or pyramidal indenter, the indentation depth increas-es at the same rate as the radius of the circle of contact. Thus, for an indentation test on a thin film, the indentation scales with the ratio of the radius of the circle of contact divided by the film thickness a/t. The ratio of the penetration depth and the film thickness, h/t, can also be used as a scale parameter. The former is probably a more useful parameter for hard films on soft substrates since the contact radius