Two evaluation methods of nano-scale internal defects by ultrasonic atomic force microscopy (UAFM) is reviewed. The first one is a linear vibration analysis of the contact stiffness calculated from a finite element method analysis of a model including a subsurface gap. The second one is a nonlinear vibration analysis of a stiffening or softening spring representing the opening-and-closing behavior of the gap. These methods were verified by the resonance frequency mapping, the load dependence of the resonance frequency and the resonance spectra in UAFM on a subsurface gap in highly oriented pyrolytic graphite. It was proved that the proposed methods are useful for evaluating the crack closure/opening on the nano-scale.
Ultrasonic atomic force microscopy (UAFM) is a new scientific tool realizing reliable measurement of nano-scale elasticity from resonance vibration of cantilever in the contact mode AFM. The elasticity is evaluated from the resonance frequency, and the loss modulus may be evaluated from Q the factor. This paper describes recent progress on the theoretical model, subsurface imaging, inverse analysis, nonlinearity due to a dislocation, and theory and experiment of Q control for improving resolution and stability.