Quantitative nanomechanical measurements and imaging with atomic force microscopy methods

Abstract

We describe our work to evaluate the nanomechanical properties of surfaces, thin films, and nanostructures using the atomic force microscope (AFM). Our approach is based on atomic force acoustic microscopy (AFAM) and involves the resonant vibrations of an AFM cantilever in contact with a sample. We first describe the basic principles of AFAM, in which local elastic‐property values are determined from the contact‐resonance frequencies using models for the cantilever dynamics and for the tip‐sample contact mechanics. Quantitative results for a variety of thin supported films ranging in stiffness from 50 to 250 GPa and as thin as 50 nm are given to illustrate our methods. Studies related to measurement accuracy involving the effects of film thickness and tip shape are also presented. Finally, we discuss new frequency‐tracking electronics for rapid (typically 20 min per image), quantitative imaging of nanoscale elastic properties. We describe how such methods not only provide modulus mapping capabilities, but also have enabled us to detect variations in adhesion between a thin film and substrate.