Piezoresponse Force Microscopy

Electrically and mechanically driven rotation of polar spirals in a relaxor ferroelectric polymer

Flux-closure structures, vortices/antivortices, skyrmions, and merons in oxides, metals and polymers represent non-trivial topologies in which a local polar/magnetic order undergoes quasi-continuous spatial variations in a host crystal lattice. These structures are now extensively studied due to emergent functionalities, but the application of electrical/mechanical fields has so far only served to destroy the polar topologies of interest. *

Topology created by quasi-continuous spatial variations of a local polarization direction represents an exotic state of matter, but field-driven manipulation has been hitherto limited to creation and destruction. *In the article “Electrically and mechanically driven rotation of polar spirals in a relaxor ferroelectric polymer” Mengfan Guo, Erxiang Xu, Houbing Huang, Changqing Guo, Hetian Chen, Shulin Chen, Shan He, Le Zhou, Jing Ma, Zhonghui Shen, Ben Xu, Di Yi, Peng Gao, Ce-Wen Nan, Neil. D. Mathur and Yang Shen report that relatively small electric or mechanical fields can drive the non-volatile rotation of polar spirals in discretized microregions of the relaxor ferroelectric polymer poly(vinylidene fluoride-ran-trifluoroethylene).*

These polar spirals arise from the asymmetric Coulomb interaction between vertically aligned helical polymer chains, and can be rotated in-plane through various angles with robust retention. *

Given also that their manipulation of topological order can be detected via infrared absorption, Mengfan Guo et al.’s work suggests a new direction for the application of complex materials. *

Mengfan Guo et al. produced a 100-nm-thick monolayer of face-on lamellae with vertically aligned polymer chains by melt-recrystallizing spin-coated thin films of P(VDF-TrFE).

The resulting melt-recrystallized thin film of the relaxor ferroelectric polymer was characterized by the authors using a commercial atomic force microscope for in-plane piezo-response force microscopy (IP-PFM).

NanoWorld Platinum Iridium coated Arrow-CONTPt AFM probes (typical resonant frequency: 14 kHz, typical force constant: 0.2 N/m, typical AFM tip radius 25 nm) were used for the in-plane (IP) PFM tests and the PFM lithography tests.

For piezo-response force microscopy (PFM) imaging, Vector mode was used where AFM tips were modulated at around 240 kHz for IP imaging, with the AC voltage set at 2 V. The images obtained by Vector Mode were double checked by using dual AC resonance tracking (DART) mode and the patterns could be reproduced. *

For angle-resolved IP-PFM tests, the rotation of sample was controlled by a protractor. To ensure identical position was imaged after rotating the sample, the authors made cross-scratches as a mark on the sample surface in advance. This method was applied to locate the scanning position in other situations if Mengfan Guo et al. had to move the sample in between the scanning probe microscopic studies.

For electric-field-induced manipulations using PFM lithography, the DC voltage on AFM tip was previously edited in the software. The scan speed was set at 1.95 Hz and no AC voltage was applied during the scanning. The DC voltage was divided by film thickness (100 nm) to obtain the electric field value. And an electric field with downward direction is defined with a positive sign.

For stress-induced manipulations, the deflection value of the PFM cantilever, which is a signal from photodetector, was preset to control the stress/force applied onto the sample. The difference in deflection value between a pressed AFM cantilever and a free AFM cantilever reflects how hard the AFM tip and sample surface are pressed to each other.*

To obtain the force value F, Mengfan Guo et al. first calibrated the AFM tips by the thermal noise method, and obtain the inverse optical lever sensitivity (InvOLS) and the spring constant k of the AFM tips.

The authors also conducted a polarization analysis based on their PFM measurements. *

To obtain the nominal toroidal order evaluated by the local curvature, the obtained IP-PFM amplitude image was firstly divided into 33 × 33 arrays, and each region was then subjected to a recognition of potential domain walls and measurement of an averaged curvature radius. *

To obtain polarization maps, angle-resolved IP-PFM images were first aligned to correct spatial distortion in nanoscale measurement. Positions with specific morphological characteristics were selected as reference points to determine the coordinate. After the correction, improved angle-resolved IP-PFM phase images would be divided into 64 × 64 arrays for deriving polarization maps. *

Fig. 1 from Mengfan Guo et al. (2024) “Electrically and mechanically driven rotation of polar spirals in a relaxor ferroelectric polymer”:Observation of a microregion containing an in-plane polar spiral. a Morphology of a melt-recrystallized thin film of the relaxor ferroelectric polymer. The scale bar is 2 μm. IP-PFM phase (b) and amplitude (c) images of the same area in a exhibiting concentric ring-shaped domains in curly stripe domains. d Distribution of domain wall curvatures in the same area in a–c evidencing nominal toroidal order. It is assumed that the local polarization is parallel to the nearest domain wall so that larger curvature (denoted red) reflects stronger toroidal order. IP-PFM phase images of identical concentric ring-shaped domains with the axis along vertical (e) and horizontal (f) measurement directions. The scale bar is 0.3 μm. The curl (g) and the divergence (h) of local polarization in the same area as e and f, revealing the polar spiral topology. i Schematic stereoscopic view of a CCW polar spiral, arrows represent regions of polarization. The red/blue arrows denote the polar source/sink that spirals in/out. The white arrows represent Néel rotation along the radial direction, as shown in more detail via the inset. NanoWorld Platinum Iridium coated Arrow-CONTPt AFM probes (typical resonant frequency: 14 kHz, typical force constant: 0.2 N/m, typical AFM tip radius 25 nm) were used for the in-plane (IP) PFM tests and the PFM lithography tests. — Fig. 1 from Mengfan Guo et al. (2024) “Electrically and mechanically driven rotation of polar spirals in a relaxor ferroelectric polymer”:
Observation of a microregion containing an in-plane polar spiral.
a Morphology of a melt-recrystallized thin film of the relaxor ferroelectric polymer. The scale bar is 2 μm. IP-PFM phase (b) and amplitude (c) images of the same area in a exhibiting concentric ring-shaped domains in curly stripe domains. d Distribution of domain wall curvatures in the same area in a–c evidencing nominal toroidal order. It is assumed that the local polarization is parallel to the nearest domain wall so that larger curvature (denoted red) reflects stronger toroidal order. IP-PFM phase images of identical concentric ring-shaped domains with the axis along vertical (e) and horizontal (f) measurement directions. The scale bar is 0.3 μm. The curl (g) and the divergence (h) of local polarization in the same area as e and f, revealing the polar spiral topology. i Schematic stereoscopic view of a CCW polar spiral, arrows represent regions of polarization. The red/blue arrows denote the polar source/sink that spirals in/out. The white arrows represent Néel rotation along the radial direction, as shown in more detail via the inset.

*Mengfan Guo, Erxiang Xu, Houbing Huang, Changqing Guo, Hetian Chen, Shulin Chen, Shan He, Le Zhou, Jing Ma, Zhonghui Shen, Ben Xu, Di Yi, Peng Gao, Ce-Wen Nan, Neil. D. Mathur and Yang Shen
Electrically and mechanically driven rotation of polar spirals in a relaxor ferroelectric polymer
Nature Communications volume 15, Article number: 348 (2024)
DOI: https://doi.org/10.1038/s41467-023-44395-5

The article “Electrically and mechanically driven rotation of polar spirals in a relaxor ferroelectric polymer” by Mengfan Guo, Erxiang Xu, Houbing Huang, Changqing Guo, Hetian Chen, Shulin Chen, Shan He, Le Zhou, Jing Ma, Zhonghui Shen, Ben Xu, Di Yi, Peng Gao, Ce-Wen Nan, Neil. D. Mathur and Yang Shen is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third-party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.

Active self-assembly of piezoelectric biomolecular films via synergistic nanoconfinement and in-situ poling

Piezoelectric biomaterials have attracted great attention owing to the recent recognition of the impact of piezoelectricity on biological systems and their potential applications in implantable sensors, actuators, and energy harvesters. However, their practical use is hindered by the weak piezoelectric effect caused by the random polarization of biomaterials and the challenges of large-scale alignment of domains.*

In the article “Active self-assembly of piezoelectric biomolecular films via synergistic nanoconfinement and in-situ poling” Zhuomin Zhang, Xuemu Li, Zehua Peng, Xiaodong Yan, Shiyuan Liu, Ying Hong, Yao Shan, Xiaote Xu, Lihan Jin, Bingren Liu, Xinyu Zhang, Yu Chai, Shujun Zhang, Alex K.-Y. Jen and Zhengbao Yang present an active self-assembly strategy to tailor piezoelectric biomaterial thin films.*

The nanoconfinement-induced homogeneous nucleation overcomes the interfacial dependency and allows the electric field applied in-situ to align crystal grains across the entire film. The β-glycine films exhibit an enhanced piezoelectric strain coefficient of 11.2 pm V−1 and an exceptional piezoelectric voltage coefficient of 252 × 10−3 Vm N−1. Of particular significance is that the nanoconfinement effect greatly improves the thermostability before melting (192 °C). *

This finding offers a generally applicable strategy for constructing high-performance large-sized piezoelectric bio-organic materials for biological and medical microdevices.*

The piezoelectric properties of the as-prepared β-glycine nanocrystalline films were evaluated by piezoresponse force microscopy (PFM) measurements.*

For all piezoresponse force microscopy (PFM) measurements and SKPM (scanning Kelvin probe force microscopy) measurements mentioned in this article, conductive NanoWorld Arrow-EFM AFM probes with PtIr coating on both AFM cantilever and AFM tip were used. The nominal resonance frequency and the nominal stiffness of the AFM probe are 75 kHz and 2.8 N m−1, respectively.

Figure 3 from “Active self-assembly of piezoelectric biomolecular films via synergistic nanoconfinement and in-situ poling” by Zhuomin Zhang et al.:PFM measurements and polarization alignment studies of β-glycine nanocrystalline films. a The PFM OOP amplitude mapping overlaid on the 3D topography of as-prepared films in a 1.5 × 1.5 µm2 area. The applied AC voltage is 2 V. b The corresponding PFM OOP phase mapping overlaid on the 3D topography. c Histogram calculated from the PFM OOP phase mapping in (b) showing that the β-glycine nanocrystalline films are dominated by domains with the unique polarization direction. d PFM OOP phase mapping of the β-glycine microcrystals obtained by electrohydrodynamic focusing deposition through heterogeneous nucleation. e Histogram calculated from the phase mapping in (d). f Comparison of statistics of the piezoelectric phase for the as-prepared β-glycine nanocrystalline films via synergistic nanoconfinement and in-situ poling (left), and β-glycine microcrystals grown by heterogeneous nucleation in the absence of nanoconfinement effect (right). NanoWorld conductive Arrow-EFM AFM probes were used for the piezoresponse force microscopy (PFM) and scanning Kelvin probe force microscopy (SKPFM) measurements mentioned in this article. — Figure 3 from “Active self-assembly of piezoelectric biomolecular films via synergistic nanoconfinement and in-situ poling” by Zhuomin Zhang et al.:
PFM measurements and polarization alignment studies of β-glycine nanocrystalline films.
a The PFM OOP amplitude mapping overlaid on the 3D topography of as-prepared films in a 1.5 × 1.5 µm2 area. The applied AC voltage is 2 V. b The corresponding PFM OOP phase mapping overlaid on the 3D topography. c Histogram calculated from the PFM OOP phase mapping in (b) showing that the β-glycine nanocrystalline films are dominated by domains with the unique polarization direction. d PFM OOP phase mapping of the β-glycine microcrystals obtained by electrohydrodynamic focusing deposition through heterogeneous nucleation. e Histogram calculated from the phase mapping in (d). f Comparison of statistics of the piezoelectric phase for the as-prepared β-glycine nanocrystalline films via synergistic nanoconfinement and in-situ poling (left), and β-glycine microcrystals grown by heterogeneous nucleation in the absence of nanoconfinement effect (right).

*Zhuomin Zhang, Xuemu Li, Zehua Peng, Xiaodong Yan, Shiyuan Liu, Ying Hong, Yao Shan, Xiaote Xu, Lihan Jin, Bingren Liu, Xinyu Zhang, Yu Chai, Shujun Zhang, Alex K.-Y. Jen and Zhengbao Yang
Active self-assembly of piezoelectric biomolecular films via synergistic nanoconfinement and in-situ poling
Nature Communications volume 14, Article number: 4094 (2023)
DOI: https://doi.org/10.1038/s41467-023-39692-y

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The article “Active self-assembly of piezoelectric biomolecular films via synergistic nanoconfinement and in-situ poling” by Zhuomin Zhang, Xuemu Li, Zehua Peng, Xiaodong Yan, Shiyuan Liu, Ying Hong, Yao Shan, Xiaote Xu, Lihan Jin, Bingren Liu, Xinyu Zhang, Yu Chai, Shujun Zhang, Alex K.-Y. Jen and Zhengbao Yang is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third-party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.

Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy

Nano-piezoelectric materials such as 1D piezoelectric nanofibers, nanowires, and nanobelts have attracted a lot of research interest in recent years. *

Because of their active property that can transform strain energy into electricity, 1D piezoelectric nano-materials can be building blocks for nano-generators, strain sensors, acoustic sensors, force sensors, biosensors, self-powered drug delivery systems, piezoelectric transistors and other intelligent systems. *

The most important property of these active materials is their ability to convert mechanical energy into electrical energy and vice versa. *

Therefore, researchers started developing nano-sized piezoelectric materials in hope of achieving better piezoelectric properties. *

The characterization of these piezoelectric properties, especially measuring the piezoelectric strain coefficients, remains a challenge. *

The Atomic Force Microscopy (AFM)-based method to directly measure nano-materials’ piezoelectric strain coefficients is widely used.

However, several factors such as the extremely small piezoelectric deformation, the influence from the parasitic electrostatic force, and the environmental noise can make the measurement results questionable. *

In the article “Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy” Guitao Zhang, Xi Chen, Weihe Xu, Wei-Dong Yao, and Yong Shi address these issues by introducing a resonant piezo-force microscopy method and describing how it was used to accurately measure the piezoelectric deformation from 1D piezoelectric nanofibers. *

During the measurement the AFM tip was brought into contact with the piezoelectric sample and set to work close to the AFM tip’s first resonant frequency. *

The AFM probe used in this test was a platinum iridium coated NanoWorld Arrow-CONTPt (typical force constant 0.2 N/m, typical resonant frequency 14 KHz. The PtIr coating makes the AFM tip conductive and at the same time enhances the laser reflection from the detector facing side of the AFM cantilever to the photodetector. *

A lock-in amplifier was used to pick up the sample’s deformation signal at the testing frequency. By using this technique, the piezoelectric strain constant d33 of the Lead Zirconate Titanate (PZT) nanofiber with a diameter of 76 nm was measured. The result showed that d33 of this PZT nanofiber was around 387 pm/V. Meanwhile, by tracking the piezoelectric deformation phase image, domain structures inside PZT nanofibers were identified. *

Figure 5 from “Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy” by Guitao Zhang et al. : Piezoelectric deformation amplitude image from a PZT nanofiber on a silicon dioxide substrate (a) and its cross-sectional view along the horizontal direction (b). Conductive NanoWorld Arrow-CONTPt AFM probes were used for the resonant piezo-force microscopy — Figure 5 from “Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy” by Guitao Zhang et al. :
Piezoelectric deformation amplitude image from a PZT nanofiber on a silicon dioxide substrate (a) and its cross-sectional view along the horizontal direction (b).

Figure 6 from “Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy” by Guitao Zhang et al. : (a) Piezoelectric deformation phase image from a PZT nanofiber on the silicon dioxide substrate and its 3D image (b). NanoWorld Arrow-CONTPt platinum iridium 5 coated AFM probes were used. — Figure 6 from “Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy” by Guitao Zhang et al. :
(a) Piezoelectric deformation phase image from a PZT nanofiber on the silicon dioxide substrate and its 3D image (b).

*Guitao Zhang, Xi Chen, Weihe Xu, Wei-Dong Yao and Yong Shi
Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy
AIP Advances 12, 035203 (2022)
DOI: https://doi.org/10.1063/5.0081109

The article “Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy” by Guitao Zhang, Xi Chen, Weihe Xu, Wei-Dong Yao and Yong Shi is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.