Waveguide ultrasonic force microscopy at 60 MHz

We present measurements using ultrasonic force microscopy at similar to 60 MHz, operating in a "waveguide" mode in which the cantilever base is vibrat ed and flexural ultrasonic vibrations are launched down the cantilever with out exciting any particular cantilever resonance. The nonlinearity of the t ip-sample force-distance curve allows the conversion of a modulated ultraso nic frequency into a low frequency vibration of the cantilever, detected in a conventional atomic force microscope. Images of Ge quantum dots on a Si substrate show contrast related to elasticity and adhesion differences, and this is interpreted with the Johnson-Kendall-Roberts model of the force-di stance curve. (C) 2000 American Institute of Physics. [S0003-6951(00)03114- 4].