Vector Piezoresponse Force Microscopy

Abstract

A novel approach for nanoscale imaging and characterization of the orientation dependence of electromechanical properties-vector piezoresponse force microscopy~Vector PFM!-is described. The relationship between local electromechanical response, polarization, piezoelectric constants, and crystallographic orientation is analyzed in detail. The image formation mechanism in vector PFM is discussed. Conditions for complete three-dimensional~3D! reconstruction of the electromechanical response vector and evaluation of the piezoelectric constants from PFM data are set forth. The developed approach can be applied to crystallographic orientation imaging in piezoelectric materials with a spatial resolution below 10 nm. Several approaches for data representation in 2D-PFM and 3D-PFM are presented. The potential of vector PFM for molecular orientation imaging in macroscopically disordered piezoelectric polymers and biological systems is discussed.

Dynamic behaviour in piezoresponse force microscopy

“…17,18,19 Imaging ferroelectric materials in the vicinity of a phase transition at small probing biases or imaging of biological systems with weak electromechanical coupling require optimal imaging conditions to be established, and a number of approaches based on using contact resonances in PFM have been suggested. 20,21 Finally, it is recognized that the use of the cantilever coupled with a beam-deflection detection system typical for most commercial AFM s does not allow longitudinal and normal force components to be unambiguously distinguished, 12,22 and it has been suggested that operation at specific frequencies would allow these components to be differentiated. 22 In our previous publications, we presented in-depth analysis of the static (low frequency) PFM imaging mechanism and demonstrated approaches for data interpretation and visualization.…”

Vortex ferroelectric domains

“…On the other hand, the vortex-type domains represent non-steady polarization state with the in-plane components appearing only during dynamic switching. Second, during PFM measurements through the top electrodes, the lateral PFM signal is inevitably affected by the contribution of d 31 and d 32 constants of the piezoelectric tensor of tetragonal PZT, which makes unambiguous detection of the in-plane polarization difficult [17].…”

Electromechanical imaging of biological systems with sub-10nm resolution

“…Vertical PFM ͑VPFM͒ measurements were performed at frequencies 50-100 kHz, which minimizes the longitudinal contribution to measured vertical signal. 12 For lateral PFM ͑LPFM͒, the optimal conditions for contrast transfer were ϳ10 kHz; for higher frequencies, the onset of sliding friction minimizes in-plane oscillation transfer between the tip and the surface. Custom LABVIEW software was developed for simultaneous acquisition of VPFM and LPFM phase and amplitude data, emulating additional SPM data acquisitions channels.…”