Tag: Piezoresponse Force Microscopy

Ultralow Strain-Induced Emergent Polarization Structures in a Flexible Freestanding BaTiO3 Membrane

Until now, diverse polarization structures and topological domains are obtained in ferroelectric thin films or heterostructures, and the polarization switching and subsequent domain nucleation are found to be more conducive to building energy-efficient and multifunctional polarization structures.*

In the article “Ultralow Strain-Induced Emergent Polarization Structures in a Flexible Freestanding BaTiO3 Membrane” Jie Wang, Zhen Liu, Qixiang Wang, Fang Nie, Yanan Chen, Gang Tian, Hong Fang, Bin He, Jinrui Guo, Limei Zheng, Changjian Li, Weiming Lü and Shishen Yan introduce a continuous and periodic strain in a flexible freestanding BaTiO3 membrane to achieve a zigzag morphology. *

The authors successfully fabricated freestanding BTO membranes with a zigzag morphology using the water-solvation process. *

These films exhibited remarkable curvature-dependent long-range coherence and periodic distributions of polarization. Through experiments and phase-field simulations, Jie Wang et al. observed the presence of H–H and T–T polarization boundaries as well as the formation of large-scale chiral vortex domains. *

Interestingly, these singular polar structures could be induced by ultralow uniaxial and biaxial strains (≈0.5%), which is significantly lower than the previously reported values. The accumulation of charge was found to reduce the formation energy, making the singular polar structures more stable. *

This complicated polarization structure resulting from the morphological variation of the ferroelectric domain provides useful insights into the polarization structure and ferroelectric domain under strain engineering. *

The wrinkled ferroelectric oxides with different strained regions and correlated polarization distributions as well as tunable ferroelectricity can pave the way toward novel flexible electronics. *

Understanding the 3D polarization configuration of a wrinkled BTO membrane is crucial for revealing the relationship between the polarization structure and strain distribution.

To evaluate the polarization configuration, piezoresponse force microscopy (PFM) was employed to obtain the piezoresponse under both vertical and lateral modes (referred to as V-PFM and L-PFM, respectively), and the results are shown in Figure 2a from the article by Jie Wang et al. cited in this blogpost. *

The polarization structures in the freestanding wrinkled BTO membrane were characterized by a commercial scanning probe microscope (SPM).

When the conductive AFM probe (NanoWorld Arrow-EFM) with AC bias was in contact with the sample, the sample underwent regular expansions and contractions due to the inverse piezoelectric effect, which caused the AFM probe to oscillate with the sample.

The oscillation amplitude and phase signals were recorded, which corresponded to the piezoresponse strength and polarization orientation, respectively.

Dual AC resonance tracking PFM (DART-PFM) was used to track the shift in the contact resonance frequency caused by the surface roughness, avoid signal crosstalk, obtain more stable piezoelectric signals with higher sensitivity, and ensure the accuracy of data. The vertical deflection and torsional motion of the probe cantilever were used to detect the deformation of the sample, and the IP and OOP polarization components of the sample were obtained.

To determine the domain structures, both the vertical and lateral PFM images were recorded at different sample rotation angles. The local piezoresponse hysteresis loops were measured by fixing the PFM probe on the selected position and then applying a triangular-square waveform, accompanied with a small AC-driven voltage from the probe.

Electrostatic force microscopy (EFM) and scanning Kelvin probe force microscopy (SKPFM) are widely applied to obtain the surface potential of materials through a dual-channel method.

In the Nap mode, the first-line scanning is used to obtain the surface morphology information of the sample, and then the probe is lifted to a certain height to detect the long-range force (electrostatic force) signal. The operating principle of EFM can be simply interpreted as the phase difference imaging of probe vibration caused by the electrostatic force between the probe and sample. In SKPFM, a DC bias is applied to the conductive tip to balance the surface potential of the sample. The DC bias is equal to the potential difference between the tip and sample, thereby obtaining the relative surface potential distribution of the material. Therefore, EFM qualitatively reflects the potential properties of samples, and SKPFM quantifies the potential of samples.*

Figure 2 from Jie Wang et al. (2024), Ultralow Strain-Induced Emergent Polarization Structures in a Flexible Freestanding BaTiO3 Membrane:Domain structures of zigzag-wrinkled BTO film. a) Topographic image of wrinkled BTO film, giving rise to zigzag pattern. V-PFM and L-PFM amplitude and phase images for two different sample rotation angles of 0° and 90°. b) Line profiles of the height, OOP phase, and IP phase (0° and 90°) data (average over 6 pixels) along the red dotted lines in (a). c) Typical OOP and IP phase images overlapped on 3D morphology. The red and blue dotted curves indicate the position of the peak and valley, respectively. NanoWorld Arrow-EFM conductive AFM probes were used.
Figure 2 from Jie Wang et al. (2024), Ultralow Strain-Induced Emergent Polarization Structures in a Flexible Freestanding BaTiO3 Membrane:
Domain structures of zigzag-wrinkled BTO film. a) Topographic image of wrinkled BTO film, giving rise to zigzag pattern. V-PFM and L-PFM amplitude and phase images for two different sample rotation angles of 0° and 90°. b) Line profiles of the height, OOP phase, and IP phase (0° and 90°) data (average over 6 pixels) along the red dotted lines in (a). c) Typical OOP and IP phase images overlapped on 3D morphology. The red and blue dotted curves indicate the position of the peak and valley, respectively.

*Jie Wang, Zhen Liu, Qixiang Wang, Fang Nie, Yanan Chen, Gang Tian, Hong Fang, Bin He, Jinrui Guo, Limei Zheng, Changjian Li, Weiming Lü and Shishen Yan
Ultralow Strain-Induced Emergent Polarization Structures in a Flexible Freestanding BaTiO3 Membrane
Advanced Science, Volume 11, Issue 25, July 3, 2024, 2401657
DOI: https://doi.org/10.1002/advs.202401657

Open Access  The article “Ultralow Strain-Induced Emergent Polarization Structures in a Flexible Freestanding BaTiO3 Membrane” by Jie Wang, Zhen Liu, Qixiang Wang, Fang Nie, Yanan Chen, Gang Tian, Hong Fang, Bin He, Jinrui Guo, Limei Zheng, Changjian Li, Weiming Lü and Shishen Yan 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 http://creativecommons.org/licenses/by/4.0/.

Lateral Piezoelectricity of Alzheimer‘s Aβ Aggregates

Alzheimer’s disease (AD) is the most frequent neurodegenerative disorder in the elderly aged over 65.*

The extracellular accumulation of beta-amyloid (Aβ) aggregates in the brain is considered as the major event worsening the AD symptoms, but its underlying reason has remained unclear.

In the article „Lateral Piezoelectricity of Alzheimer‘s Aβ Aggregates“ by Jinhyeong Jang, Soyun Joo, Jiwon Yeom, Yonghan Jo, Jingshu Zhang, Seungbum Hong and Chan Beum Park the piezoelectric characteristics of Aβ aggregates are revealed.

The vector piezoresponse force microscopy (PFM) analysis results exhibit that Aβ fibrils have spiraling piezoelectric domains along the length and a lateral piezoelectric constant of 44.1 pC N-1. Also, the continuous sideband Kelvin probe force microscopy (KPFM) images display that the increment of charge-induced surface potential on a single Aβ fibril is allowed to reach above +1700 mV in response to applied forces.

These findings shed light on the peculiar mechano-electrical surface properties of pathological Aβ fibrils that exceed those of normal body components.*

Both KPFM and nanoindentation measurements were performed using a chemically inert conductive diamond AFM tip. (NanoWorld Pointprobe CDT-FMR).

Vertical and lateral PFM images of Aβ fibrils were obtained by scanning probe microscopy with a platinum/iridium-coated silicon cantilever ( NanoWorld Pointprobe® CONTPt ). The scanning angle of the PFM cantilever was set to zero, with scan rate of 0.5 Hz and loading force of 10 nN. This setup minimized electrostatic contributions to the torsional movement of the tip, allowing measurements to focus on the shear electromechanical effects of Aβ fibrils. Vertical and lateral drive frequencies were 53 kHz and 309 kHz, respectively.*

Figure S10 from „Lateral Piezoelectricity of Alzmeiner‘s Aβ Aggregates by Jinhyeong Jang et al.:
Nanoindentation test result of Aβ fibrils. Direct piezoelectric effects are tested by measuring the surface potential change before and after nano-indentation of Aβ fibrils.
(A) Schematic illustration of the nanoindentation test for Aβ fibrils coated on an Au/Cr substrate.
(B) Topgraphy of Aβ fibrils acquired before and after applying nanoindentation. The post-indentation image shows white spots resulting from physical interactions between the AFM tip and the sample, while the approximate structure of the Aβ fibrils remains intact. Height and potential line sections obtained fom the (c) blue and (d) red lines are shown in the topgraphy of Aβ fibrils. The height remains unchanged, while electrical voltage increment and decrement were observed at the blue and red lines, respectively.
(D) During the nanoindentation the Young‘s modulus of Aβ – fibrils was measured to be 3.17 GPa, closely approxmating the literature (Nanoscale 4, 4426-4429 (2012). Both KPFM and nanoindentation measurements were performed using a chemically inert conductive diamond AFM tip (CDT-FMR, NanoWorld, Switzerland). Collected force curves were analyzed using the Hertz model to estimate the elastic moduli.

*Jinhyeong Jang, Soyun Joo, Jiwon Yeom, Yonghan Jo, Jingshu Zhang, Seungbum Hong and Chan Beum Park
Lateral Piezoelectricity of Alzheimer‘s Aβ Aggregates
Advanced Science, Volume 11, Issue 39, October 024, 2406678
DOI: https://doi.org/10.1002/advs.202406678

Open Access The article “Lateral Piezoelectricity of Alzheimer‘s Aβ Aggregates” byJinhyeong Jang, Soyun Joo, Jiwon Yeom, Yonghan Jo, Jingshu Zhang, Seungbum Hong and Chan Beum Park 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 http://creativecommons.org/licenses/by/4.0/.

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/.