AVS 52nd International Symposium
    Nanometer-Scale Science and Technology Monday Sessions
       Session NS1-MoA

Paper NS1-MoA10
Quantitative Elastic and Electromechanical Imaging: The Probe Dynamics of Vector Piezoresponse Force Microscopy

Monday, October 31, 2005, 5:00 pm, Room 204

Session: Nanotribology
Presenter: S. Jesse, Oak Ridge National Laboratory
Authors: S. Jesse, Oak Ridge National Laboratory
A.P. Baddorf, Oak Ridge National Laboratory
S.V. Kalinin, Oak Ridge National Laboratory
Correspondent: Click to Email
Piezoresponse Force Microscopy (PFM) is a nanoscale probe of the local coupling of electronic and mechanical properties, including domain imaging, polarization switching, hysteresis measurement, and orientation imaging of ferroelectric and piezoelectric materials. The image formation mechanism in PFM is controlled by the voltage dependent mechanics of the tip surface junction and the dynamics of the cantilever. A detailed analysis of the nanoscale tip-surface junction electromechanics junction shows that, for a conductive tip, the PFM signal is independent of tip shape, as in case for Atomic Force Acoustic Microscopy (AFAM). We analyze the frequency and DC bias dependent dynamic response of vector PFM, in particular, the transmission of vertical, lateral, and longitudinal surface vibrations to the tip, using modeling and 2D frequency-bias spectroscopy. We demonstrate that for an electrical tip excitation, the contact resonances are determined solely by the elastic properties of the material. Therefore, the tracking of contact resonance frequency permits local mechanical characterization, absent the numerous stray resonances inherent to piezo-actuators used in AFAM. The frequency dispersion of the nulling bias, the DC bias at which the measured response to AC excitation is zero, yields a measurement of electrostatic vs. electromechanical contrast. The differences between transduction for vertical and in-plane response components are analyzed. It is shown that lateral PFM imaging is optimal at low frequencies, while vertical PFM is best at high frequencies where dynamic stiffening reduces the electrostatic and longitudinal contributions. Finally, we discuss the measurements of all three components of the electromechanical response vector using a single PFM scan. Implications for molecular orientation imaging are also discussed. Research was performed as a Eugene P. Wigner Fellow (SVK) at ORNL, managed by UT-Battelle, LLC under DOE contract DCE-AC05-00OR22725.