We describe a dynamic atomic force microscopy (AFM) method to measure the nanoscale elastic properties of surfaces, thin films, and nanostructures. Our approach is based on atomic force acoustic microscopy (AFAM) techniques and involves the resonant modes of the AFM cantilever in contact mode. From the frequencies of the resonant modes, the tip-sample contact stiffness k* can be calculated. Values for elastic properties such as the indentation modulus M can be determined from k* using appropriate contact-mechanics models. We present the basic principles of AFAM and explain how it can be used to measure local elastic properties with a lateral spatial resolution of tens of nanometers. Quantitative results for a variety of films as thin as 50 nm are given to illustrate our methods. Studies related to measurement accuracy involving film thickness effects and tip wear are also described. Finally, we discuss techniques to rapidly locate the contact-resonance frequencies at each image position. This extension of AFAM methods will enable rapid quantitative imaging of nanoscale elastic properties.
Citation: Measurement Science & Technology
Pub Type: Journals
atomic force acoustic microscopy, atomic force microscopy, elastic properties, thin films