In Search of Pure Ferroelectricity

BSC-Ursa Minor 40

In this study we explore methods to differentiate ferroelectric and non-ferroelectric signal origins with an atomic force microscope via piezoresponse force microscopy (PFM). Ferroelectric materials are of interest due to their potential applications in computer memory, tunable capacitors, actuators, and RFID cards. Due to symmetry considerations these materials are also required to be piezoelectric and pyroelectric which enhance the potential for new and innovative applications. The advent of piezoresponse force microscopy (PFM) and spectroscopy has allowed us to probe the electromechanical interactions of ferroelectric materials including, but not limited to, polymers, thin films, and organic-inorganic compounds by observing hysteretic polarization vs. electric field curves. Unfortunately, other mechanisms unrelated to ferroelectricity can give rise to hysteretic P-E artifacts. Mechanisms such as electrostatics, charge injection, and capacitive sample-tip interactions can convolute results by also displaying hysteretic behavior. The significance of these artifacts, when published, are detrimental to the understanding of ferroelectric behavior in materials. Here, we report three techniques that can be used to minimize these other mechanisms to reveal ferroelectric behavior clearly which include: varying the tip-sample contact stiffness, on- and off- field hysteresis measurements, and top electrode placement. Cantilever force constant of 17 N/m reduced electrostatic effects by an order of magnitude on barium titanate (BaTiO3). The increased contact force reduced the size of on- and off- field hysteresis loops when probed under voltage range of ⁺/-8Vac. Top electrode placement reduced the capacitive tip-sample interaction on BaTiO3 when probed under voltage range of ⁺/- 5Vac. Techniques show effectiveness when compared to PFM results of a new material “Red” tested under identical conditions.