Variation of contact resonance frequency during domain switching in PFM measurements for ferroelectric materials

Abstract

Piezoresponse Force Spectroscopy (PFS) is a powerful method widely used for measuring the nanoscale ferroelectric responses of the materials. However, it is found that certain non-ferroelectric materials can also generate similar responses from the PFS measurements due to many other factors, hence, it is believed that PFS alone is not sufficient to differentiate the ferroelectric and non-ferroelectric materials. On the other hands, this work shows that there are distinct differences in contact resonance frequency variation during the PFS measurements for ferroelectric and non-ferroelectric materials.Therefore, a new, simple and effective method is proposed to differentiate the responses from the ferroelectric and non-ferroelectric materials, this new analysis uses contact resonance frequency responses during the PFS measurements as a new parameter to differentiate the PFS measured responses from 2 different materials. Development and applications of the ferroelectric materials have been one of the most active topics for decades. Due to the unique characteristics of spontaneous polarization, ferroelectric materials have been used in a wide range of applications, such as sensors, actuators and memory devices. 1 Developing new ferroelectric materials has great significances for research and applications in the area of functional materials. 2 Comparing with the common dielectric materials with a linear polarization response, ferroelectric materials demonstrate a nonlinear and nonzero polarization response. 3 To study the ferroelectric phenomena at nanoscale, such as at domain level, Piezoresponse Force Microscopy (PFM) and its spectroscopy form, Piezoresponse Force Spectroscopy (PFS), are widely used in the last decades. As the premier characterization tools for domain structures, orientation and properties of the ferroelectric materials, PFM and PFS techniques can probe time-or voltage-dependent phenomena withhigh spatial resolution. 4 In the PFS measurements, the surface of the sample contacts with a sharp conductive tip at the end of PFM cantilever. After applying excitation of DC voltage and scanning of the sample surface with the same tip, local polarization switching may occur and can be detected by the same tip. However, due to the principle of probing method in PFS, 5,6 the measurements of the local ferroelectric responses can be affected by a number of factors. Besides the polarization-electric field (P-E) relationship, the electrostatic force between the tip and sample surface, 7 surface charging, 8-10 Vegard effect 11 and ionic mechanisms 12-14 can also induce the hysteresis-like loops in which are similar to the P-E loops obtained in ferroelectric materials during the PFS measurements. In addition, it is also noted that such hysteresis-like loop can also be observed in a broad variety of non-ferroelectric materials during the PFS measurements, for example, glass, 15 LiCoO2, 12 TiO2 16 and even banana peel. 5 It was therefore believed that the hysteresis loops obtained by PFS is insufficient as the only pr...

Better, Faster, and Less Biased Machine Learning: Electromechanical Switching in Ferroelectric Thin Films

“…We note that the resonance frequencies at positive voltages in N 4 could be well-described by the non-ferroelectric phenomena, similar to that seen in glass ( Figure S9, Supporting Information) superimposed with a small amount of ferroelectric softening at coercive values. The asymmetric response at negative voltages is tentatively assigned to Schottky barrier [47] formation between tip and sample surface in addition to possible conductive phenomena. [45] The piezoresponse curve can similarly be well-described by a superposition of different conduction-like, non-ferroelectric behaviors.…”

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

“…In the previous study by Liu et al, 29 it was found that, during the SS-PFM measurements conducted on the ferroelectric materials, f 0 rose to a peak value around the coercive bias where the local effective piezoresponse is zero. In contrast, the non-ferroelectric materials, glass and banana peel, also showed a hysteresis loop in the bias spectroscopic measurements, while the signals of f 0 fluctuated differently.…”

“…Note that, for the second and third loadings, two similar peak-shaped fluctuations occur regularly. Referring to the previous study, 29 we consider that these field; (d-f) the score maps for the first three principal components at the off-field; and (g-i) the loadings for the first three principal components at the on-/off-field. The percentages of variance explained by the first, the second, and the third on-field principal components are 83.58%, 4.70%, and 3.87%, respectively; at the off-field, they are 90.80%, 2.88%, and 1.27%, respectively.…”

The Piezoresponse in WO3 Thin Films Due to N2-Filled Nanovoids Enrichment by Atom Probe Tomography

“…The piezoelectric effect is usually measured by piezoresponse force microscopy (PFM), through the estimation of the piezoelectric coefficient d 33 , the obtention of hysteresis loops and switching imaging of the topography showing piezo-active domains [ 17 , 18 ]. However, non-piezoelectric effects [ 10 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ] can induce electromechanical (EM) responses in PFM measurements that resemble the piezoresponse. These can be electrostatic effects [ 25 , 26 , 27 ], electrochemical strain [ 28 , 29 , 30 , 31 ], induced polarization (electrostriction) [ 32 ], flexoelectricity [ 33 , 34 , 35 , 36 ], or thermal expansion due to Joule heating [ 37 ].…”