In atomic force acoustic microscopy (AFAM) the cantilever of an atomic force microscope (AFM) is vibrated at ultrasonic frequencies while a sample surface is scanned with the sensor tip contacting the sample. As a consequence, the amplitude and phase of the cantilever vibration as well as the shift of the cantilever resonance frequencies contain information about local tip-sample contact stiffness and can be used as imaging quantities. An appropriate theoretical description of the transfer of ultrasound in an AFM enables the measurement of the local mechanical material parameters of the sample surface by evaluating experimental cantilever vibration spectra. In the experiments presented here, we examine the sensitivity of the technique using silicon single crystals. Furthermore we show that the ferroelectric domains of lead zirconate-titanate (PZT) ceramics can be imaged by atomic force acoustic microscopy and that local elastic constants of the sample surface can be determined quantitatively. The lateral resolution of the technique is given by the contact area formed by the sensor tip and the sample surface, which can have a diameter of less than 10 nm

The local elastic properties and the ferroelectric domain configuration of piezoelectric ceramics have been examined by atomic force acoustic microscopy and by ultrasonic piezoelectric force microscopy. The contrast mechanisms of the two techniques are discussed. From the local contact stiffness which is obtained by evaluation of the contact resonance spectra, the elastic constants of the sample surface can be calculated. In the case of anisotropic materials these elastic constants correspond to the indentation moduli. Indentation moduli for barium titanate and for a lead zirconate-titanate ceramics were calculated theoretically and are in reasonable agreement with experiments. The non-linearity of the tip–sample interaction becomes noticeable at large vibration amplitudes or large mechanical tip loads.

[1] The presence of clay minerals, hydrous aluminosilicates that are smaller than 2 mm can alter the elastic and plastic behavior of materials significantly. We have used Atomic Force Acoustic Microscopy (AFAM) to measure elastic properties of clay minerals. We demonstrate the AFAM technique for measuring elastic properties of soft materials. Using this technique, we present first-ever quantitative measurements of Young's modulus in clay. The Young's modulus of dickite was measured as 6.2 GPa.

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