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(Color online) (a) Contact stiffness strongly depends on surface topography via variations in contact area and local mechanical properties. (b) Amplitude at a constant frequency provides information on electromechanical activity on homogeneous surface. (c) On inhomogeneous surfaces, changes in the contact resonant frequency can result in strong variations in the signal even on piezoelectrically uniform surfaces. (d) The phase of the response is opposite for antiparallel domains and changes by 180° across the resonance. This local phase dependence precludes the use of feedback loops based on phase detection.
(Color online) (a) Experimental setup for PFM measurements with resonance enhancement. (b) Map of the resonant PFM amplitude signal across a PZT surface. (c) Response spectra and fits using Eq. (1) at selected locations within the domains and at a domain wall.
(Color online) (a) Surface topography and (b) PFM amplitude images of the PZT surface. Region (I) shows a strong enhancement of the PFM signal at the grain boundary, (II) the presence of 180° domain walls within the grains, and (III) a region with low response amplitude. (c) Phase images of polycrystalline PZT. Arrows indicated 180° domain walls. (d) Map showing locations where the data fitting to Eq. (1) was successful (white) and unsuccessful (black). Maps of (e) the electromechanical response at the local resonant frequency (a.u.), (f) the resonant frequency (MHz), and (g) the factor of the same region. Note the good agreement between (b) and (e), indicative of the veracity of the electromechanical data.
Dependence of the eigenfrequency on resonance number.
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