scanning Kelvin probe force microscopy

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/.

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

Please follow this external link to read the full article: https://rdcu.be/dzddh

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/.