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 bulk modulus B 0 ؍ 290(5) GPa and its first pressure derivative B 0 ؍ 4.9(6) were obtained for c-Si 3 N 4 from volume versus pressure dependence. Measurements were performed under quasi-hydrostatic conditions in a diamond anvil cell to 53 GPa using synchrotron radiation and energy dispersive X-ray powder diffraction. This combined with nanoindentation measurements determined the shear modulus G 0 of c-Si 3 N 4 to be 148(16) GPa. The Vickers microhardness H V (0.5) for dense, oxygen-free c-Si 3 N 4 was estimated to be between 30 and 43 GPa. Both the elastic moduli and microhardness of c-Si 3 N 4 exceed those of the hexagonal counterparts, ␣-and -phases.
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