Electron microscopy
 
Piezoresponse Atomic-Force Microscopy (PFM)
- Practical Electron Microscopy and Database -
- An Online Book -
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This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
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Piezoresponse atomic-force microscopy (PFM) is a near-field, contact-mode-derived microscopy technique and has been developed for probing electromechanical interaction in domain structures of ferroelectric materials and local electromechanical hysteresis through local imaging and polarization in nanoscale. The PFM technique was initially created to visualize the polar regions in ferroelectric films. This application is based on the electrical modulation (e.g. AC voltage) technique using the inverse piezoelectric effect, which corresponds to a linear coupling between the electrical and mechanical properties of a material and reflect the expansion and contraction of a material subjected to an electrical field. Therefore, the amplitude and phase of the piezoresponse signal depend on the magnitude of the piezoelectric coefficient and the direction of local polarization, respectively, and thus, PFM allows the measurement of the mechanical response of a specimen when an electrical voltage is applied to its surface by the conductive PFM tip.

PFM can be performed on coated specimen surfaces. In this case, the coating on piezoelectric structure acts as electrode, and then the electrical field between the AFM tip and specimen surface causes relatively uniform deformation in the structure along the field direction. The thickness change of the film can be given by,
          Piezoresponse Atomic-Force Microscopy ----------------------- [2348a]
where,
          z -- The film thickness.
          Ez -- The component of the electric field intensity along the thickness direction.
          ± -- Related to the effective piezoelectric coefficient of antiparallel domains.

When an electrical modulation of V0cos(ωt) is applied, resulting in inelastic deformation due to mechanical and dielectric losses, Equation 2348a becomes,
          Piezoresponse Atomic-Force Microscopy ----------------------- [2348b]
where,
          α-- The film thickness.          
          α -- A constant depending on the energy loss in the dynamic deformation.
          ϑ  -- The phase difference between the applied electrical voltage and the surface oscillation.

 

 

 

 

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