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Epitaxial films of BiAl x Fe 1 − x O 3 (xBAFO) were grown on SrTiO 3 (STO) and SrRuO 3 buffered STO substrates using pulsed laser deposition. To understand the effects of Al substitution at the Fe-site of BFO, we systematically investigated its impact on the material's crystal structure, surface morphology, ferroelectric properties, and magnetic properties. Our x-ray diffraction analysis revealed that phase-pure xBAFO films can be stabilized for Al concentrations between 0% and 35%, without the formation of secondary phases, due to the isotypic crystal structures of BiAlO 3 and BiFeO 3. This allowed the rhombohedral structure of BAFO to be preserved. We then characterized the ferroelectric properties of xBAFO (0 ≤ x ≤ 0.25) by analyzing polarization-voltage hysteresis loops, which exhibited a transition from a nearly square shape to a more slanted shape with increasing Al substitution. Additionally, piezoresponse force microscopy revealed that the domain growth mode, shape, size, dimension, and nucleation play a crucial role in the switching behavior of ferroelectric materials. Furthermore, we observed a modest enhancement in magnetization due to the modified spin ordering of Fe atoms with Al substitution. Notably, the optimal ferroelectric and magnetic properties were achieved at an Al concentration of 15%. These findings suggest that BAFO is a promising magnetoelectric material with desired functionalities for realizing BFO-based next-generation non-volatile memory devices. [ABSTRACT FROM AUTHOR]

Recent advances in electron, scanning probe, optical, and chemical imaging and spectroscopy yield bespoke data sets containing the information of structure and functionality of complex systems. In many cases, the resulting data sets are underpinned by low-dimensional simple representations encoding the factors of variability within the data. The representation learning methods seek to discover these factors of variability, ideally further connecting them with relevant physical mechanisms. However, generally, the task of identifying the latent variables corresponding to actual physical mechanisms is extremely complex. Here, we present an empirical study of an approach based on conditioning the data on the known (continuous) physical parameters and systematically compare it with the previously introduced approach based on the invariant variational autoencoders. The conditional variational autoencoder (cVAE) approach does not rely on the existence of the invariant transforms and hence allows for much greater flexibility and applicability. Interestingly, cVAE allows for limited extrapolation outside of the original domain of the conditional variable. However, this extrapolation is limited compared to the cases when true physical mechanisms are known, and the physical factor of variability can be disentangled in full. We further show that introducing the known conditioning results in the simplification of the latent distribution if the conditioning vector is correlated with the factor of variability in the data, thus allowing us to separate relevant physical factors. We initially demonstrate this approach using 1D and 2D examples on a synthetic data set and then extend it to the analysis of experimental data on ferroelectric domain dynamics visualized via piezoresponse force microscopy. [ABSTRACT FROM AUTHOR]

Piezoresponse force microscopy (PFM) is one of the most widespread methods for investigating and visualizing ferroelectric domain structures down to the nanometer length scale. PFM makes use of the direct coupling of the piezoelectric response to the crystal lattice, and hence, it is most often applied to spatially map the three-dimensional (3D) near-surface domain distribution of any polar or ferroic sample. Nonetheless, since most samples investigated by PFM are at least semiconducting or fully insulating, the electric ac field emerging from the conductive scanning force microscopy (SFM) tip penetrates the sample and, hence, may also couple to polar features that are deeply buried into the bulk of the sample under investigation. Thus, in the work presented here, we experimentally and theoretically explore the contrast and depth resolution capabilities of PFM, by analyzing the dependence of several key parameters. These key parameters include the depth of the buried feature, i.e., here a domain wall (DW), as well as PFM-relevant technical parameters such as the tip radius, the PFM drive voltage and frequency, and the signal-to-noise ratio. The theoretical predictions are experimentally verified using x-cut periodically poled lithium niobate single crystals that are specially prepared into wedge-shaped samples, in order to allow the buried feature, here the DW, to be "positioned" at any depth into the bulk. This inspection essentially contributes to the fundamental understanding in PFM contrast analysis and to the reconstruction of 3D domain structures down to a 1 μ m-penetration depth into the sample. [ABSTRACT FROM AUTHOR]

Switching Spectroscopy Piezoresponse Force Microscopy (SSPFM) stands out as a powerful method for probing ferroelectric properties within materials subjected to incremental polarization induced by an external electric field. However, the dense data processing linked to this technique is a critical factor influencing the quality of obtained results. Furthermore, meticulous exploration of various artifacts, such as electrostatics, which may considerably influence the signal, is a key factor in obtaining quantitative results. In this paper, we present a global methodology for SSPFM data processing, accessible in open-source with a user-friendly Python application called PySSPFM. A ferroelectric thin film sample of potassium sodium niobate has been probed to illustrate the different aspects of our methodology. Our approach enables the reconstruction of hysteresis nano-loops by determining the PR as a function of applied electric field. These hysteresis loops are then fitted to extract characteristic parameters that serve as measures of the ferroelectric properties of the sample. Various artifact decorrelation methods are employed to enhance measurement accuracy, and additional material properties can be assessed. Performing this procedure on a grid of points across the surface of the sample enables the creation of spatial maps. Furthermore, different techniques have been proposed to facilitate post-treatment analysis, incorporating algorithms for machine learning (K-means), phase separation, and mapping cross correlation, among others. Additionally, PySSPFM enables a more in-depth investigation of the material by studying the nanomechanical properties during poling, through the measurement of the resonance properties of the cantilever–tip–sample surface system. [ABSTRACT FROM AUTHOR]

The current focus in Autonomous Experimentation (AE) is on developing robust workflows to conduct the AE effectively. This entails the need for well-defined approaches to guide the AE process, including strategies for hyperparameter tuning and high-level human interventions within the workflow loop. This paper presents a comprehensive analysis of the influence of initial experimental conditions and in-loop interventions on the learning dynamics of Deep Kernel Learning (DKL) within the realm of AE in scanning probe microscopy. We explore the concept of the "seed effect," where the initial experiment setup has a substantial impact on the subsequent learning trajectory. Additionally, we introduce an approach of the seed point interventions in AE allowing the operator to influence the exploration process. Using a dataset from Piezoresponse Force Microscopy on PbTiO3 thin films, we illustrate the impact of the "seed effect" and in-loop seed interventions on the effectiveness of DKL in predicting material properties. The study highlights the importance of initial choices and adaptive interventions in optimizing learning rates and enhancing the efficiency of automated material characterization. This work offers valuable insights into designing more robust and effective AE workflows in microscopy with potential applications across various characterization techniques. [ABSTRACT FROM AUTHOR]

Piezoresponse Force Microscopy (PFM) is capable of detecting strains in piezoelectric materials down to the picometer range. Driven by diverse application areas, numerous weaker electromechanical materials have emerged. The smaller signals associated with them have uncovered ubiquitous crosstalk challenges that limit the accuracy of measurements and that can even mask them entirely. Previously, using an interferometric displacement sensor (IDS), we demonstrated the existence of a special spot position immediately above the tip of the cantilever, where the signal due to body-electrostatic (BES) forces is nullified. Placing the IDS detection spot at this location allows sensitive and BES artifact-free electromechanical measurements. We denote this position as x I D S / L = 1 , where x I D S is the spot position along the cantilever and L is the distance between the base and tip. Recently, a similar approach has been proposed for BES nullification for the more commonly used optical beam deflection (OBD) technique, with a different null position at x O B D / L ≈ 0.6 . In the present study, a large number of automated, sub-resonance spot position dependent measurements were conducted on periodically poled lithium niobate. In this work, both IDS and OBD responses were measured simultaneously, allowing direct comparisons of the two approaches. In these extensive measurements, for the IDS, we routinely observed x I D S / L ≈ 1 . In contrast, the OBD null position ranged over a significant fraction of the cantilever length. Worryingly, the magnitudes of the amplitudes measured at the respective null positions were typically different, often by as much as 100%. Theoretically, we explain these results by invoking the presence of both BES and in-plane forces electromechanical forces acting on the tip using an Euler–Bernoulli cantilever beam model. Notably, the IDS measurements support the electromechanical response of lithium niobate predicted with a rigorous electro-elastic model of a sharp PFM tip in the strong indentation contact limit [ d e f f ≈ 12 pm / V , Kalinin et al., Phys. Rev. B 70, 184101 (2004)]. [ABSTRACT FROM AUTHOR]

Size effect is a fundamental phenomenon in ferroelectric materials and grain size dependence of the dielectric and piezoelectric properties of BaTiO3 (BTO) ceramics has been observed. However, the dependence of flexoelectric response on grain size has not been reported, thus far. In this work, BTO ceramics with grain sizes ranging from 0.59 to 8.90 μm were prepared by a two-step sintering method. We found that with increasing grain size, the flexoelectric coefficient of BTO ceramics increases from less than 20 μC/m (grain size 0.59–0.69 μm) to more than 300 μC/m (grain size 8.90 μm), but the grain size dependence of the flexoelectric response is different from that of the dielectric and piezoelectric properties. Observation by piezoresponse force microscopy reveals that the surface regions of BTO ceramics are spontaneously polarized. Strong inhomogeneous strain is measured by grazing incidence x-ray diffraction and the resultant flexoelectric effect is enough to polarize the surface regions. Fitting of the flexoelectric data indicates that the grain size effect of the flexoelectric response can be well explained by the polarized surface layer mechanism. [ABSTRACT FROM AUTHOR]

Piezoresponse force microscopy (PFM) has been widely used for the nanoscale analysis of piezoelectric properties and ferroelectric domains. Although PFM is useful because of its simple and nondestructive features, PFM measurements can be obscured by non-piezoelectric effects that could affect the PFM signals or lead to ferroelectric-like behaviors in non-ferroelectric materials. Many research studies have addressed related technical issues, but they have primarily focused on vertical PFM. Here, we investigate significant discrepancies in lateral PFM signals between the trace and the retrace scans, which are proportional to the scan angle and the cantilever lateral tilting discrepancy. The discrepancies in PFM signals are analyzed based on intrinsic and extrinsic components, including out-of-plane piezoresponse, electrostatic force, and other factors. Our research will contribute to the accurate PFM measurements for the visualization of ferroelectric in-plane polarization distributions. [ABSTRACT FROM AUTHOR]

κ-Ga2O3 has been predicted to be a potential ferroelectric material. In this work, undoped Ga2O3 films were grown by either plasma-enhanced atomic layer deposition (PEALD) or metal organic chemical vapor deposition (MOCVD) on platinized sapphire substrates. 50 nm thick PEALD films with a mixture of κ-Ga2O3 and β-Ga2O3 had a relative permittivity of ∼27, a loss tangent below 2%, and high electrical resistivity up to ∼1.5 MV/cm. 700 nm thick MOCVD films with predominantly the κ-Ga2O3 phase had relative permittivities of ∼18 and a loss tangent of 1% at 10 kHz. Neither film showed compelling evidence for ferroelectricity measured at fields up to 1.5 MV/cm, even after hundreds of cycles. Piezoresponse force microscopy measurements on bare κ-Ga2O3 showed a finite piezoelectric response that could not be reoriented for electric fields up to 1.33 MV/cm. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate the ability of polarity inversion of sputtered aluminum scandium nitride thin films through post-fabrication processes with domain widths as small as 220 nm at a periodicity of 440 nm. An approach using photo- and electron-beam lithography to generate sub-quarter micrometer feature size with adjustable duty cycle through a lift-off process is presented. The film with a coercive field Ec+ of 5.35 MV/cm was exercised first with a 1 kHz triangular double bipolar wave and ultimately poled with a 0.5 kHz double monopolar wave using a Radiant Precision Premier II tester. The metal polar (M-polar) and nitrogen polar (N-polar) domains were identified and characterized through potassium hydroxide wet etching as well as piezoresponse force microscopy (PFM). Well-distinguished boundaries between the oppositely polarized domain regions were confirmed through the phase diagram of the PFM results. The relationship between the electrode width, poling voltage, and domain growth was experimentally studied and statistically analyzed, where 7.96 nm/V domain width broadening vs escalating poling voltage was observed. This method produces extremely high domain spatial resolution in III-nitride materials via poling and is transferable to a CMOS-compatible photolithography process. The spatial resolution of the periodically poled Al0.68Sc0.32N is suitable for second-harmonic generation of deep ultraviolet through quasi-phase-matching and RF MEMS operating in the X-Band spectrum. [ABSTRACT FROM AUTHOR]

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. Here 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. [ABSTRACT FROM AUTHOR]

The bulk photovoltaic effect (BPVE) in ferroelectrics, wherein spontaneous polarization can be reversed within crystals lacking centrosymmetry, encompasses the significant contribution of ferroelectric domain walls (DWs), known as DW‐PVE. Nevertheless, the separation between intrinsic BPVE within the domain and DW‐PVE remains unexplored in 2D ferroelectrics, notwithstanding its significant importance. In this study, sizable crystals of 2D ferroelectric SnS are successfully grown, facilitating a comprehensive yet intricate examination of domain configurations utilizing polarized optical microscopy and piezoresponse force microscopy. By properly selecting the large ferroelectric single domain within SnS crystals, uniform intrinsic BPVE across the domain is unequivocally demonstrated. Furthermore, to further enhance intrinsic BPVE, manipulation of strain poling increased photocurrent, suggesting that locally distributed polarizations due to imperfection introduced in SnS crystals are aligned by strain. These results will offer a new avenue for rigorous comprehension of DW‐PVE in 2D ferroelectrics. [ABSTRACT FROM AUTHOR]

Although 2D Bi2O2Se plays an important role in the electronics and optoelectronics based on its in‐plane property, its out‐of‐plane electrical transport behavior remains unclear, especially in fabricating vertical devices with high integration density for novel functionality. Here, a solution‐processed method is developed to prepare 2D Bi2O2Se with mass production (e.g., hundreds of milliliter scale). The out‐of‐plane ferroelectric property of 2D Bi2O2Se is observed by piezoresponse force microscopy and the ferroelectric dipole map atom‐by‐atom at the Bi2O2Se surface, which shows an atomically resolved dipolar displacement of Se ions. The out‐of‐plane resistant switching property of 2D Bi2O2Se is revealed by conductive atomic force microscopy. Moreover, the electric field on the local polarization of Bi2O2Se is addressed by using ab initio simulations, which shows a broken inversion symmetry along the z‐axis of Bi2O2Se. The working mechanism of resistant switching behavior in Bi2O2Se is attributed to the diffusion and shuttle of Se ions. Besides, a controllable wet‐assembled method is developed to prepare Bi2O2Se thin film with centimeter scale and explores its application on photodetectors under 808 nm laser light. This work reveals the unique out‐of‐plane transport behavior of 2D Bi2O2Se, providing the basis for fabricating multifunctional devices with high integration based on this 2D material. [ABSTRACT FROM AUTHOR]

The recent discovery of sliding ferroelectricity opens up the field of 2D ferroelectricity. However, the limitation to switching the polarization due to the topological protection of the domain walls limits the potential of these heterostructures. Here, the switching of sliding ferroelectric bulk misfit layer compound (PbS)1.11VS2 crystals is studied using switching spectroscopy piezoresponse force microscopy. A large number of measured hysteresis loops can be efficiently analyzed using unsupervised machine‐learning tools. Different switching behavior of the domains is observed on different types of domain structures, and it is shown that full domain switching can be observed for the right type of dislocation structure in the PbS layer. [ABSTRACT FROM AUTHOR]

As a class of clean oxidants, the hydrogen peroxide (H2O2) has shown great application potential in a variety of fields due to its high energy density and convenient storage condition, while the synthesis of H2O2 by the utilization of green energy technology has currently become one of the attentions in energy field. In this paper, the CdxZn1‐xS (x = 0, 0.2, 0.4, 0.6, 0.8, 1) solid solutions with different zinc‐cadmium molar ratios are prepared by a simple solvothermal route, and the H2O2 evolution performances of materials under illumination and ultrasound conditions are explored. The results show that Cd0.4Zn0.6S has the highest H2O2 yield rate of 2866 µmol/g/h under the synergistic effect of ultrasound and illumination without any sacrificial agent, which is higher than those in ultrasonic or light condition alone, showing piezo‐photocatalytic coupling characteristic. The characterizations including piezoresponse force microscopy (PFM), finite element simulation, in situ electron spin resonance (ESR) reveal that the excellent H2O2 production property of the material should be mainly ascribed to its nanorod structure and e−‐h+ dual‐channel reactivity formed by the bending of its energy band under the piezoelectric effect. This work provides reference and enlightenment for the preparation of H2O2 through the green energy avenue. [ABSTRACT FROM AUTHOR]

One of the exceptional features of the van der Waals (vdW) ferroelectrics is the existence of stable polarization at a level of atomically thin monolayers. This ability to withstand a detrimental effect of the depolarization fields gives rise to complex domain configurations characterized, among others, by the presence of layered "antipolar" head‐to‐head (H‐H) or tail‐to‐tail (T‐T) dipole arrangements. In this study, tomographic piezoresponse force microscopy (TPFM) is employed to study the 3D polarization arrangement in vdW ferroelectric α‐In2Se3. Sequential removal of thin layers from the polar surface using the PFM tip reveals a complex 3D profile of the domain walls in the α‐In2Se3 crystals. Antiparallel domain layers stacked along the polar direction are also observed by PFM imaging of the non‐polar surfaces showing that H‐H and T‐T domain boundaries are commonly present in α‐In2Se3. Application of TPFM to the electrically written domains allows evaluation of their geometrical lateral‐to‐vertical size aspect ratio, which shows a strong prevalence for the sidewise expansion in comparison to the forward growth. Local I–V measurements reveal a strong polarization direction dependence of conductivity due to the modulation of the energy barrier height as corroborated by theoretical modeling. [ABSTRACT FROM AUTHOR]

One of the exceptional features of the van der Waals (vdW) ferroelectrics is the existence of stable polarization at a level of atomically thin monolayers. This ability to withstand a detrimental effect of the depolarization fields gives rise to complex domain configurations characterized, among others, by the presence of layered "antipolar" head‐to‐head (H‐H) or tail‐to‐tail (T‐T) dipole arrangements. In this study, tomographic piezoresponse force microscopy (TPFM) is employed to study the 3D polarization arrangement in vdW ferroelectric α‐In2Se3. Sequential removal of thin layers from the polar surface using the PFM tip reveals a complex 3D profile of the domain walls in the α‐In2Se3 crystals. Antiparallel domain layers stacked along the polar direction are also observed by PFM imaging of the non‐polar surfaces showing that H‐H and T‐T domain boundaries are commonly present in α‐In2Se3. Application of TPFM to the electrically written domains allows evaluation of their geometrical lateral‐to‐vertical size aspect ratio, which shows a strong prevalence for the sidewise expansion in comparison to the forward growth. Local I–V measurements reveal a strong polarization direction dependence of conductivity due to the modulation of the energy barrier height as corroborated by theoretical modeling. [ABSTRACT FROM AUTHOR]

The dielectric gap between the scanning probe microscopy (SPM) tip and the surface of a ferroelectric using conductive atomic force microscopy and piezoresponse force microscopy (PFM) is investigated. While the gap functions as a dielectric layer, it also allows tunneling current to inject charges into the ferroelectric when a critical loading force between 10–20 µN is applied to a tip with a radius of 25 nm under a bias voltage of 0.5 V. It is observed that the permittivity of the dielectric gap determines the coercive voltage measured by the piezoresponse hysteresis loop. While such studies done in air often produce coercive voltages much larger than those studied for the same materials in capacitor‐based studies, the use of high permittivity media such as water (ɛr = 79) or silicone oil (ɛr = 2.1‐2.8) produces coercive fields that more closely match those measured in conventional capacitor‐based polarization hysteresis loop measurements. Furthermore, using water as a dielectric medium in PFM imaging enhances the accuracy in extracting the amplitude and phase data from periodically poled lithium niobate crystals. These findings provide insight into the nanoscale phenomena of polarization switching instigated by the SPM tip and provide a pathway to improved quantitative studies. [ABSTRACT FROM AUTHOR]

Harnessing low ultrasonic vibration energy to initiate piezocatalytic-based reactions is increasingly becoming a significant focus due to the current environmental energy crisis. In this study, we report on the potential of heterovalent ion substitution in improving piezocatalytic degradation of Rhodamine B dye (RhB) under the application of low-power ultrasonic vibration. For this purpose, bismuth ions Bi3+ are substituted into the lead-free ferroelectric BaTi 0 · 89 Sn 0 · 11 O 3 (BTSn 11 -xBi, x = 0, 0.02, 0.04) submicrocubes synthesized using sol-gel method. The structural, morphological, optical and piezocatalytic properties of the prepared materials appear to be significantly influenced by the substituting content. Compared to pure BTSn 11 and BTSn 11 -0.04Bi, BTSn 11 -0.02Bi exhibits the lowest band gap energy value of 3.22 eV, the smallest particle size value of 283 nm, the strongest piezoelectric current of about 8 μA/cm2, and the lowest required applied field for piezoresponse force microscopy hysteresis loops. The degradation efficiency and the kinetic rate constant are substantially higher for BTSn 11 -0.02Bi, indicating its enhanced piezocatalytic efficiency. Total organic carbon (TOC) measurements revealed good RhB mineralization using BTSn 11 -xBi piezocatalysts. Furthermore, the BTSn 11 -0.02Bi sample demonstrates good reusability and stability by maintaining effective RhB dye degradation for five consecutive cycling tests. These findings suggest that the BTSn 11 -0.02Bi piezocatalytic system holds significant potential for environmental remediation applications. [ABSTRACT FROM AUTHOR]

Layered perovskite-structured thin films of SrBi2Ta2O9 (SBT) were successfully deposited onto highly oriented pyrolytic graphite substrates using a pulse laser deposition technique, resulting in an atomic structure identical to that of the graphene surface. The SBT thin films exhibited enhanced ferroelectric and dielectric properties when the substrate temperature was slightly lowered, attributed to the improvement in a-oriented crystallinity. Due to the enhancement in a-oriented crystallinity, the SBT thin films exhibited an improved remanent polarization of approximately 12.3 μC/cm2 and an enhanced remanent piezoelectric coefficient of approximately 13.6 pm/V. The observations of ferroelectric domain structures using piezoresponse force microscopy confirmed a slight increase in domain boundary energy for SBT thin films with enhanced a-oriented crystallinity. [ABSTRACT FROM AUTHOR]

Over the past years, the application potential of ferroelectric nanomaterials with unique physical properties for modern electronics is highlighted to a large extent. However, it is relatively challenging to fabricate inorganic ferroelectric nanomaterials, which is a process depending on a vacuum atmosphere at high temperatures. As significant complements to inorganic ferroelectric nanomaterials, the nanomaterials of molecular ferroelectrics are rarely reported. Here a low‐cost room‐temperature antisolvent method is used to synthesize free‐standing 2D organic–inorganic hybrid perovskite (OIHP) ferroelectric nanosheets (NSs), that is, (CHA)2PbBr4 NSs (CHA = cyclohexylammonium), with an average lateral size of 357.59 nm and a thickness ranging from 10 to 70 nm. This method shows high repeatability and produces NSs with excellent crystallinity. Moreover, ferroelectric domains in single NSs can be clearly visualized and manipulated using piezoresponse force microscopy (PFM). The domain switching and PFM‐switching spectroscopy indicate the robust in‐plane ferroelectricity of the NSs. This work not only introduces a feasible, low‐cost, and scalable method for preparing molecular ferroelectric NSs but also promotes the research on molecular ferroelectric nanomaterials. [ABSTRACT FROM AUTHOR]

The electrical signals generated by an electromechanical coupling mechanism in biomaterials have significant potential applications in the field of biomedical engineering. For example, the piezoelectric- or flexoelectric-induced electrical signals in bone biomaterials play an important role in facilitating self-repair, remodeling, and reshaping processes. Polyetheretherketone (PEEK) has been found to possess excellent mechanical properties and biocompatibility with bone, making it an outstanding choice as an implantable polymer material. It is particularly important to investigate the electromechanical response performance of PEEK materials. In this study, we experimentally examine the flexoelectricity of PEEK and evaluate its effective out-of-plane direct and converse flexoelectric coefficients. Using the piezoresponse force microscopy module of atomic force microscopy, we observe a clear converse flexoelectric effect in a PEEK disk-shaped sample. The effective out-of-plane converse flexoelectric coefficient of the PEEK disk-shaped sample is about μ 3333 eff = 0.21 ± 0.02 nN / V. The effective out-of-plane direct flexoelectric coefficient, determined through the bending experiment of a PEEK cantilever, is f 3113 eff = 17.61 nC/m, which is larger than that of polyvinylidene fluoride and is nearly two orders of magnitude superior over other biomaterials such as bone and hydroxyapatite. This indicates that PEEK materials have even greater potential for development and research in biomedical engineering applications such as intervertebral fusion, bone joint replacement, bone rehabilitation and regeneration, etc. [ABSTRACT FROM AUTHOR]

Heterovalent ion doping has influenced the further development of piezoelectric applications. Pr3+ doping in relaxor ferroelectrics is rarely focused on piezoelectric performance enhancement. 0.51 Pb(Ni 1/3 Nb 2/3)O 3 -0.49 Pb(Hf 0.3 Ti 0.7)O 3 (PNN-49PHT) ceramics with Pr3+ doping ceramics were designed and fabricated by a two-step precursor method. Excellent dielectric diffusion coefficient (γ) of 1.96 was achieved at the low Pr3+ doping concentration of 0.2 %. Increased relaxation enhanced the nanoscale domains formation, resulting in a giant strain response (d* 33) of 1400 pm/V at 10 kV/cm, and a total strain (S tol) of 0.27 % at 20 kV/cm. Structural refinement unveiled that the high piezoelectricity originated from the mainly substitution of Pr3+ for Pb2+ at the A-site, inducing lattice distortion and phase transitions. Local domain switching and long-range ordered destruction were investigated by piezoresponse force microscopy (PFM) and Scanning Electron Microscopy (SEM). These findings contribute to the advancement of piezoelectric devices and provide valuable insights for the design and optimization of high-performance piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Photonic devices based on ferroelectric domain engineering in thin film lithium niobate are key components for both classical and quantum information processing. Periodic poling of ridge waveguide can avoid the selective etching effect of lithium niobate, however, the fabrication of high-quality ferroelectric domain is still a challenge. In this work, we optimized the applied electric field distribution, and rectangular inverted domain structure was obtained in the ridge waveguide which is beneficial for efficient nonlinear frequency conversions. Second harmonic confocal microscope, piezoresponse force microscopy, and chemical selective etching were used to characterize the inverted domain in the ridge waveguide. In addition, the performance of nonlinear frequency conversion of the periodically poled nano-waveguide was investigated through second harmonic generation, and the normalized conversion efficiency was measured to be 1,720 % W−1 cm−2, which is close to 60 % that of the theoretical value. The fabrication technique described in this work will pave the way for the development of high-efficiency, low-loss lithium niobate nonlinear photonic devices. [ABSTRACT FROM AUTHOR]

Knowledge of the statics and dynamics of ferroelectric domains is of immense importance since they are directly correlated with macroscopic polarization and strain. For the present work, piezoresponse force microscopy (PFM) is used to afford insight into field-induced phase transitions and local switching properties of a (1–2x)Na0.5Bi0.5TiO3–xBiFeO3–xPbTiO3 system for compositions, x = 0.01, 0.03, 0.05, and 0.07. Rietveld analysis of x-ray diffraction data reveals crystallization of the compound in single and dual phases in the chosen compositions. Upon the application of a local electric field, a phase transition from relaxor to normal ferroelectric (FE) is observed for all samples. A decrease in degree of non-ergodicity is realized within this composition range, which is found by analyzing the stability of field-induced ferroelectric domains. The field-induced FE domains for lower concentrations of x are found to be irreversible and a reversible nature was found for higher values of x. In addition, spatial variations of local switching parameters are investigated with the help of switching spectroscopic-PFM and a maximum local d 33 was found for compositions having dual phases. [ABSTRACT FROM AUTHOR]

CaBi2Nb2O9 (CBN) ceramic is a promising sensing element to convert vibration to electrical signal at temperatures higher than 600°C. However, conventionally sintered ceramics suffer from poor piezoelectric coefficient (d33) and low electrical resistivity (ρdc). Here, we report that CBN ceramics can be prepared by microwave sintering (MS) to mitigate volatilization issue of Bi2O3 and thus suppress the generation of oxygen vacancies usually seen in conventional sintering (CS) as demonstrated by X‐ray photoelectron spectroscopy (XPS) analysis and mass‐loss measurement. As compared to the CS, the MS is more favorable for reducing the sintering time, and obtaining a dense, fine, and uniform grain morphology as revealed by scanning electron microscopy (SEM) characterizations of both surface and interior of the CBN ceramics, leading to an enhancement of 86% and 75% in d33 and ρdc, respectively. Piezoresponse force microscopy (PFM) as combined with Rayleigh law analysis clearly revealed that the enhancement of piezoelectric properties was attributed to the thinner domains, the higher domain wall density, and the enhanced domain wall motion in the MS‐940 samples. This study paves an important road to simultaneously improve both d33 and ρdc in CBN ceramics for developing high‐temperature vibration sensors. [ABSTRACT FROM AUTHOR]

Because of their full compatibility with CMOS technology, HfO2-based ferroelectrics, and especially Hf0.5Zr0.5O2 (HZO), attract a lot of attention. However, the overwhelming majority of measurement techniques provides only information about the cumulative electrical response of many domains of HZO, i.e., at the macroscopic level. So far, only piezoresponse force microscopy technique was applied to visualize distinct ferroelectric domains in HZO and to analyze the local switching behavior in the microscopic level. This work introduces the possibility of using electron beam-induced current (EBIC) technique in the scanning electron microscope to visualize the gradual polarization reversal of HZO and to obtain the local polarization dynamics. We show that although the local EBIC signal is affected by surrounding domains, studying the variations in the ferroelectric response of individual domains as well as the spread of the local stiffness and local imprint is possible by this method. Besides, we show the connection between the EBIC current and an electric field across passive non-ferroelectric layers at interfaces between HZO and metal electrodes, which opens up additional opportunities to use the EBIC technique for investigations of interface-dependent properties of HZO ferroelectrics in the future. [ABSTRACT FROM AUTHOR]

Because of their full compatibility with CMOS technology, HfO2-based ferroelectrics, and especially Hf0.5Zr0.5O2 (HZO), attract a lot of attention. However, the overwhelming majority of measurement techniques provides only information about the cumulative electrical response of many domains of HZO, i.e., at the macroscopic level. So far, only piezoresponse force microscopy technique was applied to visualize distinct ferroelectric domains in HZO and to analyze the local switching behavior in the microscopic level. This work introduces the possibility of using electron beam-induced current (EBIC) technique in the scanning electron microscope to visualize the gradual polarization reversal of HZO and to obtain the local polarization dynamics. We show that although the local EBIC signal is affected by surrounding domains, studying the variations in the ferroelectric response of individual domains as well as the spread of the local stiffness and local imprint is possible by this method. Besides, we show the connection between the EBIC current and an electric field across passive non-ferroelectric layers at interfaces between HZO and metal electrodes, which opens up additional opportunities to use the EBIC technique for investigations of interface-dependent properties of HZO ferroelectrics in the future. [ABSTRACT FROM AUTHOR]

The (K , Na) Nb O 3 (KNN)-based ceramics have been deemed one of the most promising lead-free piezoelectric materials replacing lead-containing ones. In our study, we have prepared both undoped and Mn-doped KNN nanofibers via the electrospinning method and investigated how the thermal annealing process affects their structural, crystallographic, and piezoelectric properties. X-ray diffraction measurements suggest that the crystallization occurs around 450 ° C in these fibers, and with increasing annealing temperature, both undoped and Mn-doped nanofibers become granular with small grains forming along the fiber, accompanying the crystallization. Both exhibit increasing piezoelectric properties with annealing temperature based on the piezoresponse force microscopy measurements with Mn-doping, leading to a higher piezoelectric response. [ABSTRACT FROM AUTHOR]

Utilizing vector PFM (piezoresponse force microscopy) on high-density nanodot arrays, ferroelectric nanodots and domain structure in nanodot arrays were investigated in the current study. Accordingly, we identified four types of topological domain states based on the measurements of spontaneous polarization vectors vs writing results in nanodots. In addition to convergent and divergent domains with upward and downward polarization, double-center domains and triple-center domains were also identified. In addition, center domains could be reversibly switched under the electric field produced by the biased PFM tip, and their stability could be maintained by compensating the polarization charge with the accumulated charge. These stable topological domain states in discrete nanodots present an opportunity to further investigate their new properties in high-density memory devices. [ABSTRACT FROM AUTHOR]

Recently, HfO2‐based ferroelectric thin films have attracted widespread interest in developing next‐generation nonvolatile memories. To form a metastable ferroelectric orthorhombic phase in HfO2, a post‐annealing process is typically necessary. However, the microscopic mechanism underlying the effect of annealing temperature on ferroelectric domain nucleation and growth is still obscure, despite its importance in optimizing the operation speed of HfO2‐based devices. In this study, the ferroelectric properties and polarization switching of Hf0.5Zr0.5O2 thin films annealed at different temperatures (550–700 °C) are systematically investigated. Evidently, the crystal structure, remnant polarization, and dielectric constant monotonically change with annealing temperature. However, microscopic piezoresponse force microscopy images as well as macroscopic switching current measurements reveal non‐monotonic changes in the polarization switching speed with annealing temperature. This intriguing behavior is ascribed to the difference in the ferroelectric‐domain nucleation process induced by the amount of oxygen vacancies in the Hf0.5Zr0.5O2 thin films annealed at different temperatures. This work demonstrates that controlling the defect concentration of ferroelectric HfO2 by tuning the post‐annealing process is critical for optimizing device performance, particularly polarization switching speed. [ABSTRACT FROM AUTHOR]

Magnetoelectric nanoparticles (NPs) present an important class of nanomaterials with a wide interest in piezocatalytic and biomedical applications. Herein, the results of magnetoelectric and magnetization measurements performed on core–shell NPs having magnetic core (MnFe2O4, MFO) and ferroelectric shell (Ba0.85Ca0.15Ti0.5Zr0.5O3, BCZT) synthesized by the microwave hydrothermal method are reported. Magnetic results are compared with the measurements on reference MFO NPs prepared under identical conditions. Detailed SQUID magnetometer measurements of the magnetization hysteresis loops M(H) down to 2 K reveal the existence of a clear exchange bias effect in pure MFO NPs attributed to the coexistence of ferromagnetic and antiferromagnetic short‐range interactions. When the magnetic core is covered by the thin ferroelectric BCZT shell, it is observed that 1) the shell suppresses the apparent bias effect and 2) induces an “extra” ferromagnetic magnetization at T < 20 K. The results indicate that this “extra” ferromagnetism has a 2D character and it is most likely related to the interface interactions between the MFO core and BCZT shell. Ferroelectric properties and strong magnetoelectric effect in core–shell NPs are revealed via piezoresponse force microscopy under magnetic field. The mechanisms of the observed effects are discussed. [ABSTRACT FROM AUTHOR]

The LiNbO3 (LNO) single crystal receives wide applications in nonvolatile memories, surface acoustic wave devices, and electro-optic modulators. However, engineering of antiparallel domain patterns within micrometer-sized devices generally requires a poling voltage more than a few thousands of volts. The high poling voltage could invoke dielectric breakdown. Here, we found an effective method to increase the local electric field significantly for domain nucleation at the interfaces of an etched LNO mesa in contact to two concave side electrodes, while the electric field across the protruding intra-electrode area can be lower by 10 times after the metal diffusion at the surface. Subsequent piezoresponse force microscopy mapping shows the nucleating domains to grow up through the entire intra-electrode area. This method is universal and analogous to other ferroelectric devices for the realization of low-voltage operations. [ABSTRACT FROM AUTHOR]

In this paper, using a combination of pulse testing measurements and piezoresponse force microscopy (PFM), an investigation of the polarization reversal behavior and the accompanying resistive switching in the Al0.72Sc0.28N thin film capacitors is reported. The obtained results reveal a transition from the nucleation‐limited switching (NLS) in the low field range toward the more uniform switching described by the Kolmogorov–Avrami–Ishibashi (KAI) model in the high field range. It is found that the Al0.72Sc0.28N capacitors exhibit an unusually steep change in the switching time– it decreases by five orders of magnitude with a moderate increase of the applied field. This feature is caused by a significantly higher activation field value (≈126 MV cm−1) in comparison with the conventional perovskite ferroelectrics. PFM visualization of the field‐induced domain dynamics has allowed the evaluation of the nucleation rate and domain wall velocity. Furthermore, capacitors in the polydomain state generated by partial switching of polarization exhibit a significant (up to two orders of magnitude) increase in the steady‐state conductance. This effect is likely caused by the injection of strongly inclined conducting 180° domain walls. Resistance tunability offers additional functionalities to the Al1‐xScxN devices where conductive domain walls are used as active elements. [ABSTRACT FROM AUTHOR]

The amelioration of atomically thin ferroelectric materials is imperative for next‐generation outperformed two‐dimensional (2D) electronics, which is elusive by their bulk counterparts. These remarkable materials' ferroelectric and piezoelectric features are the fundamental urges in optoelectronics, electronics, and energy harvesting. In this work, 2D ferroelectric Bi2O2Se flakes have been synthesized using a modified chemical vapor deposition technique. The 6 nm thick Bi2O2Se flake provides a robust ferroelectric switching under an applied voltage of ±10 V by piezoresponse force microscopy, further confirmed by first principles. Leveraging the successful growth, the high‐quality Bi2O2Se flakes permit the fabrication of a field‐effect transistor (FET) with state‐of‐the‐art performance. The FET device rewards a high current on–off ratio of 108 and field effect mobility of almost 131 cm2 V−1 s−1, owing to the small carrier effective mass of 0.2 m0. Combined, the electric field‐induced local polarization of ferroelectric switching and unprecedented device performance of Bi2O2Se semiconductors are certified for their utilization in advanced nanoelectronics and miniaturization of multifunctional devices with multifunctionalities. [ABSTRACT FROM AUTHOR]

Bismuth ferrite (BiFeO3) thin films were epitaxially grown on (110)- and (001)-oriented NdGaO3 single crystal orthorhombic substrates by pulsed laser deposition. The films grown on NdGaO3(110) are fully strained and show two ferroelectric variants that arrange in a stripe domain pattern with 71° domain walls, as revealed by piezoresponse force microscopy. We explored their antiferromagnetic textures using scanning nitrogen-vacancy magnetometry. Surprisingly given the large compressive strain state, the films still show a spin cycloid, resulting in a periodic zig-zag magnetic pattern due to the two ferroelastic variants. The films grown on NdGaO3(001) are also fully strained, but the (001) orthorhombic substrate imposes a strongly anisotropic in-plane strain. As a consequence, the ferroelectric polarization exhibits a uniaxial in-plane component, parallel to the b-axis of the substrate. The ferroelectric domain pattern consists of 109° charged domain walls between the two selected ferroelastic variants. This anisotropic strain impacts the magnetic state of BiFeO3 and leads to a simpler spin texture defined by a single propagation vector for the spin cycloid. In both cases, electric-field control of ferroelectric domains tends to favor a transition to a canted antiferromagnetic order. These results reveal that the cycloidal structure of BiFeO3 can undergo large compressive strain and open further electrical means to tune the magnetic state of this room-temperature multiferroic compound. [ABSTRACT FROM AUTHOR]

Ferroelectric Bi2SiO5 (BSO) thin films were deposited by pulsed laser deposition on Nb‐doped (100), (110) and (111) SrTiO3 (Nb:STO) substrates, resulting in (001)‐, (113)‐ and (204)‐oriented epitaxial films. Due to the crystallinity of BSO, in which the Bi2O2 layers are formed perpendicular to the c‐axis direction, the (001)‐oriented epitaxial BSO thin film showed the lowest remanent polarization and the best leakage current characteristics. On the other hand, the (113)‐ and (204)‐oriented films showed an increase in remanent polarization due to the improvement of a‐oriented crystallinity. Through experiments using vertical and lateral piezoresponse force microscopy, it has been confirmed that the distribution of in‐plane‐oriented domains reducing remanent polarization decreases in the order of (001)‐, (113)‐ and (204)‐oriented epitaxial BSO thin films. The epitaxial BSO thin films that exhibit ferroelectric hysteresis loops similar to the relaxor ferroelectric thin films tended to have improved energy storage characteristics as a result of improved remanent polarization and saturation polarization. In particular, the (113)‐oriented epitaxial BSO thin film showed a high recoverable energy density of about 41.6 J cm−3 and an energy storage efficiency of about 85.6%. [ABSTRACT FROM AUTHOR]

Electrocaloric refrigeration technology has garnered significant attention due to its potential for next-generation solid-state cooling, which is miniaturized and efficient. However, achieving a substantial electrocaloric effect (ECE) and a wide working temperature range at low electric fields remains a challenge. In this study, a synergistic approach combining domain and defect engineering was used in transparent 0.88 Pb(Mg 1/3 Nb 2/3)O 3 -0.12PbTiO 3 - x Sm(0.88PMN-0.12 PT- x Sm) ceramics to improve ECE and temperature stability. Finally, a notable adiabatic temperature change (ΔT) of 2.07 K in the x = 0.01 ceramic, with ΔT exceeding 1.0 K across a broad temperature range from 30 to 180 °C was achieved. Piezoresponse force microscopy (PFM) and X-ray photoelectron spectroscopy revealed the presence of small domains and appropriate oxygen vacancies as contributors to the enhanced ECE and broad operation temperature range. This work introduces a promising candidate material for electrocaloric refrigeration. [ABSTRACT FROM AUTHOR]

Interfacial engineering is important for ferroelectric thin-film heterostructures because of the modulation of boundary conditions of the spontaneous polarizations and their switching behaviors, which are essential for ferroelectric electronics. In this work, we study the effects of interfacial buffering layer, 5-nm-thick SrTiO3 (STO), on the imprint and domain switching of epitaxial Pt/Pb(Zr,Ti)O3/SrRuO3 (SRO) thin-film heterostructures and capacitors. By buffering the ultrathin SrTiO3 layer at the Pb(Zr,Ti)O3 surface, the imprint effect can be dramatically alleviated as observed in the piezoresponse force microscopy (PFM)-measured domain structures and polarization–electric field hysteresis loops in thin-film capacitors. However, when the SrTiO3 layer is buffered at the Pb(Zr,Ti)O3/SrRuO3 interface, the imprint effect is slightly increased. These phenomena are explained based on the band alignments among the Pt and SrRuO3 electrodes and the Pb(Zr,Ti)O3 layer associated with the existence of oxygen vacancies in the SrTiO3 layer. With the reduction of imprint effect, the domain switching dynamics are also improved in the SrTiO3-buffered Pb(Zr,Ti)O3 capacitor, in which the switching activation field is decreased by about 45.3% in comparison with that of the pristine capacitor. These results facilitate the design and optimization of ferroelectric devices with the improvements in domain configurations, switching behaviors and band alignments. [ABSTRACT FROM AUTHOR]

The study of the properties of ferroelectric materials against irradiation has a long history. However, anti−irradiation research on the ferroelectric domain has not been carried out. In this paper, the irradiation of switched domain structure is innovatively proposed. The switched domain of 700 nm lithium niobate (LiNbO3, LN) thin film remains stable after gamma irradiation from 1 krad to 10 Mrad, which was prepared by piezoresponse force microscopy (PFM). In addition, the changing law of domain wall resistivity is explored through different sample voltages, and it is verified that the irradiated domain wall conductivity is still larger than the domain. This domain wall current (DWC) property can be applied to storage, logic, sensing, and other devices. Based on these, a ferroelectric domain irradiation resistance model is established, which explains the reason at an atomic level. The results open a possibility for exploiting ferroelectric materials as the foundation in the application of space and nuclear fields. [ABSTRACT FROM AUTHOR]

Topological polar structures are attracting attention as potential applications of next-generation high-density memories. We investigate how the ferroelectric domain evolves with film thickness in c-axis oriented epitaxial Bi2WO6 thin films grown on (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates. In addition to the general thickness scaling effect on domain size, we find that 3- or 4-variant domains appear in a sample thicker than 120 nm, whereas ⟨100⟩-type domains compete with the ⟨110⟩ ones in thinner samples, resulting in a variety of nontrivial topological structures. By visualizing the spatial distribution of electric polarizations through angle-resolved piezoresponse force microscopy, we provide direct evidence for the spontaneous emergence of nontrivial topological polar structures. These results provide useful insights into the domain behavior of layered ferroelectric thin films. [ABSTRACT FROM AUTHOR]

Quantitative converse piezoelectric coefficient (d33) mapping of polymer ultrafine fibers of poly(acrylonitrile) (PAN), as well as of poly(vinylidene fluoride) (PVDF) as a reference material, obtained by rotating electrospinning, was carried out by piezoresponse force microscopy in the constant-excitation frequency-modulation mode (CE-FM-PFM). PFM mapping of single fibers reveals their piezoelectric activity and provides information on its distribution along the fiber length. Uniform behavior is typically observed on a length scale of a few micrometers. In some cases, variations with sinusoidal dependence along the fiber are reported, compatibly with a possible twisting around the fiber axis. The observed features of the piezoelectric yield have motivated numerical simulations of the surface displacement in a piezoelectric ultrafine fiber concerned by the electric field generated by biasing of the PFM probe. Uniform alignment of the piezoelectric axis along the fiber would comply with the uniform but strongly variable values observed, and sinusoidal variations were occasionally found on the fibers laying on the conductive substrate. Furthermore, in the latter case, numerical simulations show that the piezoelectric tensor's shear terms should be carefully considered in estimations since they may provide a remarkably different contribution to the overall deformation profile. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate ferroelectricity in high-quality monocrystalline quaternary alloy ScAlGaN. Sc0.2Al0.45Ga0.35N films are grown by plasma-assisted molecular beam epitaxy and exhibit a surface roughness of 0.5 nm, limited by the roughness of the underlying molybdenum template. Polarization-electric field and positive-up-negative-down measurements reveal unambiguous ferroelectric switching with a coercive field of ∼5.5 MV cm−1 at 10 kHz and high remanent polarization of ∼150 μC cm−2. Time-dependent measurements suggest that the polarization reversal behavior adheres to the Kolmogorov–Avrami–Ishibashi model and follows a scheme of domain nucleation and growth. Detailed piezoresponse force microscopy studies further elucidate the evolution of polarity reversal domains in wurtzite nitride ferroelectrics and support the notion that the growth of inversion domains occurs via an in-plane motion of the domain walls. The realization of functional ferroelectric quaternary alloys in the wurtzite nitride family extends beyond being a technical demonstration. The additional degree of bandgap, band alignment, lattice parameter, and piezoelectric constant tunability achievable through quaternary alloys unveils a vast dimension through which wurtzite nitride ferroelectrics can be optimally engineered for a broad variety of high-performance electronic, optoelectronic, and acoustic devices and systems. [ABSTRACT FROM AUTHOR]

(1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–PT) has attracted attention due to its excellent electrical properties as a typical relaxor ferroelectric material. High‐quality Mn–Sm co‐doped 0.68PMN–0.32PT thin films were synthesized on the Pt/Ti/SiO2/Si substrates by sol–gel based on spin coating method. The results show that 1 mol% Mn–2 mol% Sm co‐doped PMN–PT thin films have high dielectric constant (εr ∼ 1895) and relatively low dielectric loss (tanδ ∼.039) at 1 kHz. They also show superior ferroelectric polarization (Pmax ∼ 53.71 μC/cm2, Pr ∼ 30.85 μC/cm2) and high dielectric breakdown strength (∼1656.6 kV/cm), which are primarily due to the low leakage current density (∼10−7 A/cm2). This work suggests a practical approach to enhance the dielectricity, piezoelectricity, and ferroelectricity of PMN–PT thin films. [ABSTRACT FROM AUTHOR]

(Pb0.96La0.04)(Zr0.95Ti0.05)0.99O3 ceramics were successfully elaborated by the solid‐sate reaction method. The pure perovskite phase was obtained, comprising both rhombohedral (R3c) and orthorhombic (Pbam) crystallographic structures, as determined by x‐ray diffraction and Raman spectroscopy analyses. The rhombohedral and orthorhombic structures were carefully attributed to the ferroelectric (FE) and antiferroelectric (AFE) phases, respectively. The room temperature electromechanical performances of the samples were particularly investigated at the nanoscale level by using piezoresponse force microscopy (PFM). The measurement of PFM domain patterns evidenced spontaneous piezoelectric and ferroelectric activities as well as regions with no piezoresponse, in agreement with the coexistence of FE and AFE phases. By means of the spectroscopic mode of the PFM used in on‐ and off‐field methods, very specific piezoloops were recorded. Square‐shaped hysteresis loops for phase signal and butterfly‐like shape loops for amplitude activity were obtained under and at zero bias when probing ferroelectric regions, while on‐field piezoloops displaying double hysteresis for phase signal were detected and assigned to the stable antiferroelectric phase. Finally, the signature of metastable antiferroelectric phase was also identified through in‐field and remnant loops measurements. These results further provided the phases coexistence, concurrently unveiling intricate nanoscale electrical characteristics (both stable and metastable AFE behaviors) at room temperature. Furthermore, these data suggest that PFM proves to be a robust technique for investigating local antiferroelectricity in such complex ceramic oxides. [ABSTRACT FROM AUTHOR]

During the past decade, Scanning Probe Microscopy (SPM) based surface strain detection techniques have been extensively used in the characterization of functional materials, structures, and devices. Here, we refer these techniques as Surface Strain Force Microscopy (SSFM), which mainly includes the Piezoresponse Force Microscopy, Atomic Force Acoustic Microscopy, Atomic Force Microscopy-Infrared spectroscopy (or photothermal induced resonance), Piezomagnetic Force Microscopy, and Scanning Joule Expansion Microscopy. The inception of SSFM opens up a pathway to study the nanoscale physical properties by using a sharp tip to detect the local field-induced surface strain. Through measuring the signals of the surface strain, multiple physical properties, such as the electromechanical, mechanical, photothermal, magnetic, thermoelastic properties, can be characterized with an unprecedented spatial resolution. In order to further develop and overcome the fundamental issues and limitations of the SSFM, the multi-frequency SPM technology has been introduced to the SSFM-based techniques, leading to the emerging of multi-frequency SSFM (MF-SSFM). As a technical breakthrough of the SSFM, MF-SSFM has demonstrated substantial improvements in both performance and capability, resulting in increased attentions and numerous developments in recent years. This Perspective is, therefore, aimed at providing a preliminary summary and systematic understanding for the emerging MF-SSFM technology. We will first introduce the basic principles of conventional SSFM and multi-frequency SPM techniques, followed by a detailed discussion about the existing MF-SSFM techniques. MF-SSFM will play an increasingly important role in future nanoscale characterization of the physical properties. As a result, many more advanced and complex MF-SSFM systems are expected in the coming years. [ABSTRACT FROM AUTHOR]

Epitaxial films of multiferroic BiFe 1 − x Co x O 3 (BFCO) with 0 ≤ x ≤ 0.35 are grown on (001)-oriented SrTiO 3 and SrRuO 3 buffered SrTiO 3 substrates using the pulsed laser deposition technique. The effect of structural transformation from rhombohedral to tetragonal phase with increasing cobalt substitution on the magnetic, electrical, and piezo-/ferroelectric properties is investigated. Piezoresponse force microscopy is used to quantify the coercive voltage from the phase hysteresis loops for different thickness films to investigate the semi-empirical Kay–Dunn scaling law with varying cobalt concentrations. For the rhombohedral structure, a reduction of the coercive voltage is observed with increasing substitution of Fe by Co. The coercive voltage of a 10 nm BFCO (x = 0.35) film is found to be 0.63 V, which is 67% lower than that of a pure BiFeO 3 (BFO) (1.9 V) film of the same thickness. Cobalt substitution also leads to changes in the magnetic and electrical properties due to modification of spin ordering and reduction of the bandgap, respectively. Further, to validate the experimental results, we have performed theoretical calculations using density functional theory. The theoretical results indicate a reduction in unit cell volume and enhancement in net magnetization can be achieved with cobalt substitution, in agreement with experimental results. Partial Co substitution can, thus, provide a pathway to realize BFO-based nonvolatile magnetoelectric devices with reduced operating voltage. [ABSTRACT FROM AUTHOR]

Triple-cation mixed-halide perovskite Cs0.05(FA0.85MA0.15)0.95Pb(I0.85Br0.15)3 (CsFAMA) has emerged as one of the most promising candidates for future high-efficiency solar cells. Ferroelectricity has been recognized as a critical issue in perovskite photovoltaics, although its existence and influence on photovoltaic performance remain controversial. We verify the ferroelectric polarization and reveal that it can suppress local photocurrent in CsFAMA through photoconductive atomic force microscopy (pc-AFM) and piezoresponse force microscopy (PFM). The time evolution of pc-AFM and PFM mappings first demonstrates that the photocurrents decreased with increasing electromechanical responses. Systematic characterization based on the first and second harmonic pointwise measurement as well as mappings shows that piezoelectricity primarily contributes to the measured electromechanical responses, while the ionic activity takes a back seat. Clear hysteresis loops and relaxation behaviors further confirm that the piezoresponse originates from ferroelectric polarization. Finally, based on temperature-dependent studies, we conclude that it is the ferroelectric polarization that weakens local photocurrent. This work provides insights into optimizing the photovoltaic performance of triple-cation mixed-halide perovskite solar cells. [ABSTRACT FROM AUTHOR]

Detecting ferroelectricity at micro- and nanoscales is crucial for advanced nanomaterials and materials with complicated topography. Switching spectroscopy piezoresponse force microscopy (SSPFM), which involves measuring piezoelectric hysteresis loops via a scanning probe microscopy tip, is a widely accepted approach to characterize polarization reversal at the local scale and confirm ferroelectricity. However, the local hysteresis loops acquired through this method often exhibit unpredictable shapes, a phenomenon often attributed to the influence of parasitic factors such as electrostatic forces and current flow. Our research has uncovered that the deviation in hysteresis loop shapes can be caused by spontaneous backswitching occurring after polarization reversal. Moreover, we've determined that the extent of this effect can be exacerbated when employing inappropriate SSPFM waveform parameters, including duration, frequency, and AC voltage amplitude. Notably, the conventional 'pulse-mode' SSPFM method has been found to intensify spontaneous backswitching. In response to these challenges, we have redesigned SSPFM approach by introducing the positive up-negative down (PUND) method within the 'step-mode' SSPFM. This modification allows for effective probing of local piezoelectric hysteresis loops in ferroelectrics with reversible piezoresponse while removing undesirable electrostatic contribution. This advancement extends the applicability of the technique to a diverse range of ferroelectrics, including semiconductor ferroelectrics and relaxors, promising a more reliable and accurate characterization of their properties. [ABSTRACT FROM AUTHOR]

Ferroelectric wurtzite‐type aluminum scandium nitride (Al1−xScxN) presents unique properties that can enhance the performance of non‐volatile memory technologies. The realization of the full potential of Al1−xScxN requires a comprehensive understanding of the mechanism of polarization reversal and domain structure dynamics involved in the ferroelectric switching process. In this work, transient current integration measurements performed by a pulse switching method are combined with domain imaging by piezoresponse force microscopy (PFM) to investigate the kinetics of domain nucleation and wall motion during polarization reversal in Al0.85Sc0.15N capacitors. In the studied electric field range (from 4.4 to 5.6 MV cm−1), ferroelectric switching proceeds via domain nucleation and wall movement. The currently available phenomenological models are shown to not fully capture all the details of the complex dynamics of polarization reversal in Al0.85Sc0.15N. PFM reveals a non‐linear increase of both domain nucleation rate and lateral wall velocity during the switching process, as well as the dependency of the domain pattern on the polarization reversal direction. A continuously faster N‐ to M‐polar switching upon cycling is reported and ascribed to an increasing number of M‐polar nucleation sites and density of domain walls. [ABSTRACT FROM AUTHOR]