View Picture Gallery
Watch the Lecture

The advent of microelectronic, magnetic and optical thin film materials, which are artificially structured on a fine scale, has brought about the need for mechanical testing on the scale of microstructure. This, in turn, has led to the development of new experimental techniques for studying mechanical properties of materials in small dimensions. These emerging techniques provide not only technical solutions to the problem of characterizing artificially structured device materials, but also the opportunity to study mechanical properties of bulk structural materials at the microstructural level. These studies are providing a basis for linking the continuum-scale modeling of structural materials, familiar to engineers, to the microstructural-scale treatment of mechanical properties, familiar to materials scientists. Here we describe recent progress in studying microstructure-mechanical property relationships in materials using newly developed experimental techniques applicable to materials with small dimensions. These include nanoindentation for studying the elastic and plastic properties of thin films and multilayers and for probing plasticity on the scale of individual defects. The well-known size dependence of the hardness of metals is described in terms of the geometrically necessary dislocations created in small indentations. This can be related to the continuum theory of strain gradient plasticity. We also discuss substrate curvature techniques that are being used to study the basic mechanisms of plasticity in thin metal films on substrates. We show that the small dimensions of thin films lead not only to very high yield strengths, but also to very high rates of strain hardening. Bulge testing of thin films in the form of free-standing membranes is also briefly discussed as a technique for determining the full stress-strain curves for thin film materials. Newly developed microbeam bending techniques for determining isothermal stress-strain relations for metal films still attached to their substrate are also described. These experiments also reveal high strengths and high rates of strain hardening for thin metal films on substrates. All of these newly developed techniques provide a basis for monitoring and controlling the mechanical properties of materials at small length-scales.