Evaluation of local elasticity and inelasticity with nonoscale spatial resolution with scanning ultrasonic force microscope

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In this research, we develop the scanning ultrasonic probe microscope with lateral resolution < 1 nm and study the physics involved in it. The contributions of elasticity, viscosity, surface energy at the sample-tip interface to the sample and cantilever dynamics are analyzed distinctively in order to carry out the quantitative measurement on the surface and subsurface local complex elasticity.A commercial AFM is modified by attaching the PZT transducer at the cantilever base or on the scanner to make the scanning ultrasonic probe microscopy which is capable to apply the ultrasonic vibration to the cantilever or the sample. At various frequency below and above the cantilever resonance frequency and at various ultrasonic amplitude, we carry out the force curve measurement on Si and GaAs single crystals. The vibration amplitude is calibrated with Michelson enterferomenter. The obtained force curve has the following common features : 1)In case of no applied vibration, small "jump-in" in the approach phase and large "jump-out" in the retraction phase are observed. 2)Within creasing the vibration amplitude, the "jump-out" position rapidly approaches to the "jump-in" position. 3)At above certain vibration amplitude, a new "repulsive jump' is observed for both approach and retraction phase.These results are analyzed by considering the cantilever motion numerically with the finite difference method. In the analysis, we give the elasticity of the tip and sample, damping, adhesion, and assume the JKR model for the tip-sample interaction. The result explains the features 1)and 2)quantitively and proves the validity of the analysis.