Experimental determination of the mechanical impedance of atomic force microscopy cantilevers in fluids up to 70 kHz

The high-frequency dynamical response of cantilevers used in atomic force microscopy (AFM) to an external force is important for applications such as dynamic AFM modes and dynamic mechanical measurements on biological tissues. In this paper we present a novel method for experimentally determining the mechanical driving-point impedance of an AFM cantilever up to frequencies of at least 70 kHz. A frequency-independent, point force was achieved by applying an electric field between the cantilever and a sharpened steel electrode positioned near (10 mu m) the tip of the cantilever. The velocity of the cantilever in response to the force was measured with a laser interferometer. The method was tested in air and in tetrachloromethane (CCl4), a nonpolar, nondissociating fluid. The results agree with theoretical predictions. In addition, the mechanical impedance of a cantilever near a flat surface was measured. (C) 2000 American Institute of Physics. [S0021- 8979(00)05717-0].