Probing linear and non-linear tip-sample interaction forces by atomic force acoustic microscopy

The cantilever-sample system of an atomic force acoustic microscope is exci ted in the frequency range from 10 kHz to 3 MHz. By analysing the cantileve r vibration in the frequency domain, one obtains information about the stif fness and the damping of the whole mechanical system, consisting of the fle xural beam clamped at one end and the sensor tip at the other end in force interaction with the sample surface. Variation of the cantilever-sample dis tance or of the excitation amplitude changes the range of the tip-sample di stance covered during the vibration cycles and consequently the section of the non-linear force interaction curve that is probed. Starting from high s tatic loads and small excitation amplitudes, the contact resonance frequenc ies shift to lower values when the excitation amplitude is increased or whe n the static cantilever force is decreased. A further increase of the excit ation amplitude leads to asymmetric resonance peaks, showing hysteresis whe n the direction of the frequency scan is changed, We present experimental s pectra in the linear and non-linear regime and compare them to theoretical results. Copyright (C) 1999 John Wiley & Sons, Ltd.