Analysis of subsurface imaging and effect of contact elasticity in the ultrasonic force microscope

We examined, both theoretically and experimentally, the characteristics of subsurface imaging with nanometer resolution and the effect of contact elasticity in the ultrasonic force microscope (UFM). In particular, the effect of the surface energy and effective elasticity on the maximum tip-sample force and the shift of the averaged tip-sample distance were examined. Furthermore, kink formation in the cantilever deflection (z_a) against the ultrasonic frequency vibration (UFV) amplitude (a) characteristics was predicted. This model was used to explain experimental observations in UFM, such as the features of the measured z_a a) curve and the damping of the cantilever torsion vibration by the UFV. Moreover the previously reported lateral ultrasonic force microscope image of subsurface features was explained by the response of subsurface edge dislocation to a large instantaneous force enhanced by the UFV.