Determining Amplitudes of Standing Surface Acoustic Waves via Atomic Force Microscopy

Abstract

Atomic force microscopy is a tool for characterizing surface acoustic waves, in particular for high frequencies, where the wavelength is too short to be resolved by laser interferometry. A caveat is, that the cantilever deflection is not equal to the amplitude of the surface acoustic wave. We show that the energy transfer from the moving surface to the cantilever instead leads to a deflection exceeding the surface modulation. We present a method for an accurate determination of surface acoustic wave amplitudes based on comparing force-curve measurements with the equation of motion of a driven cantilever. We demonstrate our method for a standing surface acoustic wave on a $\mathrm{Ga}\mathrm{As}$ crystal confined in a focusing cavity with a resonance frequency near 3 GHz.