Electrostatic effect on off-field ferroelectric hysteresis loop in piezoresponse force microscopy

Abstract

Piezoresponse force microscopy (PFM) has been extensively utilized as a versatile and an indispensable tool to understand and analyze nanoscale ferro-/piezoelectric properties by detecting the local electromechanical response on a sample surface. However, it has been discovered that the electromechanical response originates not only from piezoelectricity but also from other factors such as the electrostatic effect. In this study, we explore the dependence of off-field PFM hysteresis loops on the surface-potential-induced electrostatic effect in a prototypical ferroelectric thin film by applying an external voltage to the bottom electrode during the measurement. We simplify the situation by equating the surface potential to the direct current voltage waveform variations and predicting the contribution of the surface-potential-induced electrostatic effect to the PFM hysteresis loops. The experimental results approximately match our prediction—the coercive voltage linearly decreases with the surface potential, whereas the saturated amplitude and piezoresponse remain nearly constant owing to the relatively large piezoelectric coefficient of the ferroelectric thin film.

Nanoscale Ferroelectric Characterization with Heterodyne Megasonic Piezoresponse Force Microscopy

“…The existence of the electrostatic force can give rise to significant artifacts or misinterpretations in PFM‐based ferroelectric studies, resulting large numbers of ferroelectric‐like observations in many non‐ferroelectric materials. [ 6–8,14–19 ] Meanwhile, due to the pronounced contribution of the electrostatic force, researchers usually measure the ferroelectric hysteresis loop by using the pulsed DC method in which the electrostatic force effect can be minimized but the polarization back‐switching effect is involved inevitably. [ 3,15,20,21 ] Therefore, a large amount of research work has been implemented to eliminate or quantify the electrostatic force contribution in PFM measurements.…”

“…Moreover, there may be multiple other electric field‐induced effects which can directly or indirectly induce responses in PFM measurements, including electrochemical dipoles, charge injection, field effect, electrochemical reactions, flexoelectricity and Joule heating and so on. [ 6–8,19,22,37,40,42,43,44–46 ] Obviously, the issue on signal sources causes large complexity and uncertainty in current PFM measurements, which greatly challenges its application especially for the materials with unknown properties. For example, the ongoing hot debate about the ferroic nature of methylammonium lead triiodide (CH 3 NH 3 PbI 3 or MAPbI 3 ) perovskite is such a striking illustration of the challenges faced by conventional PFM, since the true origin of the PFM signal observed on MAPbI 3 is remaining unclear.…”

“…On the other hand, PFM is based on inverse piezoelectric effect and thereby detects the piezoelectric deformation of the sample in response to an external electric field applied between the tip and sample, thus a concomitant electrostatic force will be always involved in the final PFM signal, causing large ambiguity to the interpretation of the measurement (8,12,15,19,20,44,45). Due to the great importance, a large amount of research work has been continuously implemented to eliminate or quantify the electrostatic force contribution in the PFM measurements (3,8,12,15,20,22,(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57), but nearly all of the proposed solutions, including using stiff cantilever, applying DC compensation voltage, imaging in liquid environment, using higher eigenmode and interferometric detection as well as off-line analysis strategies, are subject to many specific limitations (12,48,51,(54)(55)(56)(57)(58)(59)(60).…”

Recent Progress in the Nanoscale Evaluation of Piezoelectric and Ferroelectric Properties via Scanning Probe Microscopy

“…[94,95] Moreover, the electrostatic effect caused by charge injection could change the surface potential from the equilibrium state. [95][96][97][98][99] Consequently, ferroelectric-like PFM image contrast and hysteresis loop can be induced by the electrostatic effect associated with the charge injection. Nonetheless, several previous studies have demonstrated how to minimize the electrostatic force, for example, increasing the spring constant of the SPM cantilever, [41,100] conducting measurements at higher AC frequencies [101] and compensating the surface potential by applying an external voltage.…”

Decomposing and analyzing contact resonance frequency in contact mode voltage modulated scanning probe microscopies

“…14,15 In addition, the electrostatic effects between the tip and sample also contribute to the ''ferroelectric-like'' behavior in the voltage-modulated SPM. [16][17][18][19] Similar to that of the SS-PFM technique, SM-ESM also cannot thoroughly eliminate the electrostatic effects in the output signals. 18 In order to obtain accurate and stable responses, multifrequency techniques, for example, the dual AC resonance tracking (DART) mode and the band excitation (BE) mode, were developed to track the variation of the contact resonance frequency ( f 0 ) of the tip-sample system during the image scanning.…”