Analysis of dynamic characteristic for ultra-thin coating layer with Ultrasonic Atomic Force Microscopy

Ultrasonic Atomic Force Microscopy (Ultrasonic-AFM) was applied to characterize the mechanical properties of an ultra-thin coating layer in a nanoscale thin film system. The modified Hertzian theory was adopted for accurate theoretical analysis of the dynamic characteristics of the ultra-thin coating layer. Aluminum and Titanium thin films with 200 nm thickness were coated on the substrate using the DC Magnetron sputtering method. When the cantilever tip approaches and couples with a sample surface, the interaction forces and boundary conditions change in response to the sample contact stiffness. As a result, the contact resonance frequency of the vibrating cantilever shifts according to the local contact stiffness. This research demonstrates that Ultrasonic-AFM is a potential technique for nondestructively characterizing the mechanical properties of the ultra-thin coating layer.