| AVS 54th International Symposium | |
| Nanometer-scale Science and Technology | Tuesday Sessions |
| Session NS-TuM |
| Session: | Imaging of Nanostructures |
| Presenter: | B.J. Rodriguez, Oak Ridge National Laboratory |
| Authors: | B.J. Rodriguez, Oak Ridge National Laboratory S. Jesse, Oak Ridge National Laboratory A.P. Baddorf, Oak Ridge National Laboratory S.V. Kalinin, Oak Ridge National Laboratory |
| Correspondent: | Click to Email |
Electromechanical activity is a universal feature of molecular and biological systems, ranging from piezoelectricity in calcified tissues to voltage-controlled ion channels and the functionality of cardiac miocytes and cells for auditory signal transduction. Here, we study the mechanisms of electromechanical imaging by Piezoresponse Force Microscopy (PFM) in liquid environments using model ferroelectric systems. The effects of the conductive properties of the liquid on the localization of the dc electric field are studied from the polarization patterns created by the voltage pulses applied to the tip. Under ambient conditions, the biased tip establishes a highly-localized electric field that decays rapidly with distance from the tip-surface junction, resulting in small, well-defined domains. For solvents with intermediate conductivities, the electric field is localized, but the characteristic length scale is significantly larger than the tip size and is mediated by pulse length via the mobile ion diffusion length. The switching in this case results in the formation of irregular fractal domains. In conductive solvents, the solution is uniformly biased, resulting in a homogeneous electric field across the film thickness and partial or complete uniform switching. Notably, high resolution imaging is possible even in polar solvents because of the high excitation frequencies, minimization of the diffusion paths, and high localization of the strain that transmit predominantly through the mechanical (rather than electrical) contact. The same screening effect in solution enables a mechanically modulated approach for intermittent-contact PFM in solution. In air, this mode is dominated by electrostatic forces, which are screened in solution, allowing the electromechanical signal to dominate. These results elucidate a strategy for high resolution imaging of electromechanical activity in biological and molecular systems in liquid environments.
Research sponsored by the Laboratory Directed Research and Development (BJR, SJ, SVK) and SEED (BJR, SVK) Programs of Oak Ridge National Laboratory, managed by UT-Battelle, LLC for the U. S. Department of Energy, and The Center for Nanophase Materials Sciences (BJR, APB, SVK), at Oak Ridge National Laboratory, which is managed by UT-Battelle, LLC.