DEFORMATION MECHANISMS IN NANOGRAINED METAL FILMS

Miniaturized electronic and mechanical components (e.g., airbag sensors) have contributed significantly to the backbone of our civilization today. These components have many metal structures such as wires that are at submicro to nanometer scale (human hair diameter is about 100 micrometers). These metals are mostly polycrystalline in nature, with nanoscale grains connected to each other by grain boundaries.

We currently lack a fundamental understanding of the role of grain boundaries in determining the thermomechanical properties of metals, largely because of the limitations of instrumentation to study ultrasmall specimens. Professor Saif and his students have developed a micromechanical apparatus (size: 10mm x 3mm x 0.1mm) that makes it possible, for the first time, to study the mechanical behavior of metal films as thin as 20nm inside scanning or transmission electron microscopes. Such study should reveal the fundamental microstructural mechanisms involved in determining metal behavior. The group used the apparatus to study aluminum films with thicknesses of 30-350nm at room temperature. They observed that the elastic modulus of aluminum decreases as the grains become smaller than 50nm and that, contrary to current thinking, aluminum behaves as a nonlinear elastic material when its grain size decreases below 50nm.

During his Center appointment, Professor Saif will explore the mechanisms of grain boundaries to explain these experimental observations. His study will advance the state of our fundamental understanding of nanograined metal films.