Ultrasonic atomic force microscope with overtone excitation of cantilever

We propose a novel atomic force microscope (AFM) combined with ultrasonic frequency vibration of a cantilever excited at its support. This method enables both topography and elasticity imaging of stiff samples such as metals and ceramics, without a need for bonding a transducer to the sample. When the sample surface is contacted with a tip attached to the cantilever, the cantilever vibration mode is changed according to the sample properties. It is theoretically predicted that the amplitude and resonant frequency of vibration at higher-order modes are useful parameters for elasticity evaluation of stiff samples. A preliminary experimental verification of this principle is presented using a glass-fiber-reinforced plastic sample. Clear elastic contrast was successfully obtained using a soft cantilever only when it was vibrated at MHz frequency higher-order modes.