Mechanical Properties of Thin Polymer Films At the Nanometer Scale

Nanometer-thin polymer films are critical to a variety of technologies, such as microelectronics, optics, energy production, and biomedical devices.  These thin films must retain a high degree of mechanical durability for the best performance under their operating conditions.  In particular, the dependence of mechanical properties on film thickness is of fundamental importance and practical interest with rapidly growing nanotechnologies.  The mechanical behavior of materials can be described by a full set of key mechanical properties, such as stiffness, strength, and ductility.  However, there is a dearth of knowledge about these key mechanical properties of thin polymer films due to the lack of appropriate measurement tools at the nanometer scale.  In this presentation, we describe a measurement technique of a combined wrinkling and cracking that enables the determination of the modulus, fracture strength, and onset fracture strain of thin films.  We first demonstrate the general applicability of our methodology to a diverse range of thin films, and then apply it to investigate the effect of film thickness on the collective mechanical properties of polystyrene thin films with thickness ranging from 10 nm to 300 nm.