Nanometer-scale elastic modulus of surfaces and thin films determined using an atomic force microscope

A versatile acoustic method using a commercial atomic force microscope (AFM) was developed to measure surface stiffness at nanometer-scales. Calibrated measurements of acoustic reflections at interfaces between the AFM tip and the surfaces of reference and test materials yielded near-surface interfacial stiffness, from which the elastic modulus was determined using a simple contact mechanics model. The utility and versatility of this method were demonstrated by determining elastic modulus relaxation for surfaces and thin films, including a freshly exposed, reconstructing epoxy surface, and by probing depth-dependent elastic modulus for thin polystyrene films on oxidized silicon substrates.