Switching Spectroscopy Piezoresponse Force Microscopy Research Articles

Enhancing ferroelectric characterization at nanoscale: A comprehensive approach for data processing in spectroscopic piezoresponse force microscopy

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.

Defining ferroelectric characteristics with reversible piezoresponse: PUND switching spectroscopy PFM characterization

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.

The effect of charged defects on the local effective piezo-electric response for the polycrystalline lead-free BCZT bulk ceramic versus thin film

The current work presents the d33,eff evaluation for Ba0·9Ca0·1Ti0·9Zr0·1O3 (BCZT) thin film (TF) prepared by RF magnetron sputtering over Pt (111) substrate by switching spectroscopy piezo-response force microscopy (SS-PFM). Our results reveal an d33.eff approximately of 70 p.m. V−1. This value was compared with the bulk ceramic counterpart (d33.eff = 72 p.m. V−1), and it is comparable with other similar lead-free TF compositions. To understand the d33.eff value for the TF, the influence of mixed-valence Ti (Ti3+ and Ti4+) states and oxygen chemical ions is elucidated by x-ray photoelectron spectroscopy (XPS). The component analysis for Ti 2p and O 1s XPS regions confirmed a less presence of oxygen O− ions in the TF. X-ray diffraction corroborates the tetragonal perovskite structure with P4mm space group, which is desired to obtain ferroelectric properties. The good piezo-response for the TF is very promising as a storage device for the electronic industry.

Enhanced piezoelectricity in 0.7BiFeO3-0.3BaTiO3 lead-free ceramics: Distinct effect of poling engineering

BiFeO3-BaTiO3 based ceramics are considered to be the most promising lead-free piezoelectric ceramics due to their large piezoelectric response and high Curie temperature. Since the piezoelectric response of piezoelectric ceramics just appears after poling engineering, in this work, the domain evolution and microscopic piezoresponse were observed in-situ using piezoresponse force microscopy (PFM) and switching spectroscopy piezoresponse force microscopy (SS-PFM), which can effectively study the local switching characteristics of ferroelectric materials especially at the nanoscale. The new domain nucleation preferentially forms at the boundary of the relative polarization region and expands laterally with the increase of bias voltage and temperature. The maximum piezoresponse (Rs), remnant piezoresponse (Rrem), maximum displacement (Dmax) and negative displacement (Dneg) at 45 V and 120 °C reach 122, 69, 127 pm and 75 pm, respectively. Due to the distinct effect of poling engineering in full domain switching, the corresponding d33 at 50 kV/cm and 120 °C reaches a maximum of 205 pC/N, which is nearly twice as high as that at room temperature. Studying the evolution of ferroelectric domains in the poling engineering of BiFeO3-BaTiO3 ceramics provides an insight into the relationship between domain structure and piezoelectric response, which has implications for other piezoelectric ceramics as well.

Effect of poling direction on microhardness and indentation fracture toughness in PMN-0.28PT and PMN-0.32PT single crystals

The relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) has been considered to be a potential choice for high performance actuators and sensors owing to their ultrahigh electromechanical properties. Their devices are often subjected to contact loading which may nucleate surface cracks leading to catastrophic failure. Therefore, in order to understand the deformation and fracture behavior, Vickers micro-indentation experiments are performed on [001] oriented poled PMN-0.28PT and PMN-0.32PT single crystals along parallel and perpendicular to the poling direction. Results show that the hardness, H is primarily governed by the orientation of domains with respect to the loading direction. The finite element simulations demonstrated that H increases with rise in piezoelectric coupling coefficient, d33. Further, the length of crack parallel to poling direction is found to be larger than that of perpendicular to poling direction when indentation load is perpendicular to the poling direction. This behavior is in contrast to the trend reported for Pb(ZrxTi1−x)O3 (PZT), BaTiO3, and lead-free piezoelectric materials in the past. The Switching spectroscopy piezoresponse force microscopy (SS-PFM) performed along the cracks shows different patterns of d33* for crack parallel and perpendicular to the poling direction. Motivated from the observed trend in d33*, the mechanism of crack propagation is presented and the reasons for anisotropy in KIC is also explained.

Non-centrosymmetric features in nanostructured MoS2 and WS2 exfoliated in liquid phase

Exfoliation in liquid phase of Transition Metal Dichalcogenides promotes the industrialization of low dimensional structures in photonic and material science applications, due to its high nonlinear optical and piezoelectric responses on monolayers and few odd layers. Here, we report piezoelectricity and prospects of non-linear optics through Switching Spectroscopy Piezoresponse Force Microscopy (SS-PFM) and Fluorescence spectroscopy on MoS2 - and WS2 - flakes exfoliated in liquid phase. These features are intrinsically related to non-centrosymmetric structures and depend on the number of layers. SS-PFM signal in a small region reveals that the strength of AFM tip deflection was considerable just for an odd number of layers and negligible for even layers. Thin films were evaluated with ellipsometric measurements by constructing models mixing mono and few layers, resulting in a detailed description of the optical and surface properties of the nanostructures studied.

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

Contact mode voltage modulated scanning probe microscopy (SPM) techniques, such as switching spectroscopy piezoresponse force microscopy (SS-PFM), are powerful tools for detecting local electromechanical behaviors. However, interpreting their signals, especially the contact resonance frequency (f0), is difficult due to the complexity of the tip-sample contact and the signal tracking system. In a previous study, an interesting phenomenon on the variation of f0 was observed, showing distinctions between ferroelectric and non-ferroelectric materials. Therefore, it is believed that f0 conveys important information about the tip-sample contact which is real-timely affected by charge accumulation or polarization switching. In this study, principal component analysis (PCA) and correlation analysis are applied to decompose the signal of f0. The first and second principal components successfully restore most information of the original data, and they describe different features which are related to the surface morphology and electromechanical behavior, respectively. In addition, a customized method based on the PCA and correlation analysis of f0 can well distinguish the responses from different materials of which the amplitude and phase signals show "ferroelectric like" phenomena during the SS-PFM measurements.

Exploring Charged Defects in Ferroelectrics by the Switching Spectroscopy Piezoresponse Force Microscopy.

Monitoring the charged defect concentration at the nanoscale is of critical importance for both the fundamental science and applications of ferroelectrics. However, up-to-date, high-resolution study methods for the investigation of structural defects, such as transmission electron microscopy, X-ray tomography, etc., are expensive and demand complicated sample preparation. With an example of the lanthanum-doped bismuth ferrite ceramics, a novel method is proposed based on the switching spectroscopy piezoresponse force microscopy (SSPFM) that allows probing the electric potential from buried subsurface charged defects in the ferroelectric materials with a nanometer-scale spatial resolution. When compared with the composition-sensitive methods, such as neutron diffraction, X-ray photoelectron spectroscopy, and local time-of-flight secondary ion mass spectrometry, the SSPFM sensitivity to the variation of the electric potential from the charged defects is shown to be equivalent to less than 0.3 at% of the defect concentration. Additionally, the possibility to locally evaluate dynamics of the polarization screening caused by the charged defects is demonstrated, which is of significant interest for further understanding defect-mediated processes in ferroelectrics.

Depolarization field tuning of nanoscale ferroelectric domains in (001)PbZr0.4Ti0.6O3/SrTiO3/PbZr0.4Ti0.6O3 epitaxial heterostructures

The effect of tuning the depolarization field in (001)-oriented ultrathin epitaxial PbZr0.4Ti0.6O3/SrTiO3/PbZr0.4Ti0.6O3 ferroelectric heterostructures is investigated. The thickness of the dielectric spacer (SrTiO3) is maintained constant at 2 unit cells. The ferroelectric layer thickness in the heterostructure (each PbZr0.4Ti0.6O3) layer varied from 8 to 15 nm is exploited as the parameter to tune the depolarization field. Piezoresponse force microscopy reveals a domain evolution from continuous labyrinthine domains to individual nanoscale bubble domains under the influence of an increasing depolarization field. A statistical analysis of the domain features (i.e., domain wall length and domain fraction) reveals that this change in domain morphology also affects the wall roughness and its associated disorder. The local coercive voltage obtained using switching spectroscopy piezoresponse force microscopy finds the 15 nm film to have the lowest coercive voltage. This is attributed to both a strain-induced increase in tetragonality and the depolarization field-induced changes in the domain morphology.

Multiferroic response in bismuth ferrite doped heterostructures: A buffer layer inference

Multiferroic heterostructures of doped-BiFeO3 were prepare by RF magnetron sputtering over FTO substrates. Barium-nickel co-doped BiFeO3 (Bi0.75Ba0.25Fe0.975Ni0.025O3) and Praseodymium-Manganese co-doped BiFeO3 (Bi0.85Pr0.15Fe0.97Mn0.03O3) were used as a source for ferroelectric (FE) and ferromagnetic (FM) layers in a two-layer heterostructure architecture. The arrangement of FE and FM layers were switch in order to study the effect of the previous layer consider as a buffer layer on the overall multiferroic properties of the system. X-ray diffraction in two different geometries (BBXRD and GIXRD) were implemented to study the structural effect of the heterostructures demonstrating two different tetragonal-type structures. Scanning electron microscopy showed two different morphologies and thicknesses. Magnetic hysteresis loops were obtained from both samples obtaining a major magnetization on the sample where the FE layer was on top and switching spectroscopy piezoresponse force microscopy (SSPFM) showed an improved on the ferroelectric properties for the sample where the FM layer was on top, attributing the enhancing of the multiferroic properties to the buffer layer used on top of the substrate.

Ferroelectric Instability Induced Ultralow Thermal Conductivity and High Thermoelectric Performance in Rhombohedral p-Type GeSe Crystal.

The orthorhombic phase of GeSe, a structural analogue of layered SnSe (space group: Pnma), has recently attracted attention after a theoretical prediction of high thermoelectric figure of merit, zT > 2. The experimental realization of such high performance in orthorhombic GeSe, however, is still elusive (zT ≈ 0.2). The rhombohedral phase of GeSe, a structural analogue of GeTe (space group: R3m), previously stabilized at high pressure (2 GPa) and high temperature (1600 K), is promising due to its theoretically predicted ferroelectric instability and the higher earth abundance of Se compared to Te. Here, we demonstrate high thermoelectric performance in the rhombohedral crystals of GeSe, which is stabilized at ambient conditions by alloying with 10 mol % AgBiSe2. We show ultralow lattice thermal conductivity (κL) of 0.74-0.47 W/mK in the 300-723 K range and high zT ≈ 1.25 at 723 K in the p-type rhombohedral (GeSe)0.9(AgBiSe2)0.1 crystals grown using Bridgman method. First-principles density functional theoretical analysis reveals its vicinity to a ferroelectric instability which generates large anomalous Born effective charges and strong coupling of low energy polar optical phonons with acoustic phonons. The presence of soft optical phonons and incipient ferroelectric instability in (GeSe)0.9(AgBiSe2)0.1 are directly evident in the low temperature heat capacity (Cp) and switching spectroscopy piezoresponse force microscopy (SS-PFM) experiments, respectively. Effective scattering of heat carrying acoustic phonons by ferroelectric instability induced soft transverse optical phonons significantly reduces the κL and enhances the thermoelectric performance in rhombohedral (GeSe)0.9(AgBiSe2)0.1 crystals.

Determination of polarization states in (K,Na)NbO3 lead-free piezoelectric crystal

Polarization switching in lead-free (K0.40Na0.60)NbO3 (KNN) single crystals was studied by switching spectroscopy piezoresponse force microscopy (SS-PFM). Acquisition of multiple hysteresis loops on a closely spaced square grid enables polarization switching parameters to be mapped in real space. Piezoresponse amplitude and phase hysteresis loops show collective symmetric/asymmetric characteristics, affording information regarding the switching behavior of different domains. As such, the out-of-plane polarization states of the domains, including amplitudes and phases can be determined. Our results could contribute to a further understanding of the relationships between polarization switching and polarization vectors at the nanoscale, and provide a feasible method to correlate the polarization hysteresis loops in a domain under an electric field with the polarization vector states.

Characterization of domain structure and imprint of Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 (PZN-4.5%PT) single crystals by using PFM and SS-PFM techniques

In this study, the underlying physical mechanisms of imprint are addressed in order to obtain a better understanding of the imprint phenomenon of relaxor Pb(Zn1/3Nb2/3)O3-x%PbTiO3 (PZN-x%PT) ferroelectric single crystals. The local domain structure and imprint of Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 (PZN-4.5%PT) single crystals are investigated by using Piezoresponse Force Microscopy (PFM) and Switching Spectroscopy PFM (SS-PFM) techniques, respectively. The results show that the imprint depends on polarization states. It is also found that surface charge accumulation shows no significant effects on the imprint behaviour of the PZN-4.5%PT single crystals. By studying the annealed samples in the oxygen and argon atmospheres respectively, it is found that the alignment of oxygen vacancy related defect dipoles is one of the origins for the occurrence of imprint. This study provides a better understanding of the imprint phenomenon in ferroelectric materials, which is crucial for the enhancement of the reliability and the advancement of ferroelectric relaxors into the application of ferroelectric devices.

Correlation of resistance switching and polarization rotation in copper doped zinc oxide (ZnO:Cu) thin films studied by Scanning Probe Microscopy

This paper presents multiple-modes Scanning Probe Microscopy (SPM) studies on characterize the correlation of resistance switching (RS) and polarization rotation (PR) in copper doped ZnO (ZnO:Cu) thin films. Firstly, the bipolar RS behavior is confirmed by conductive Atomic Force Microscopy (c-AFM). The PR with almost 180° phase angle is confirmed by using the Piezoresponse Force Microscopy (PFM) on the same location. In addition, it elucidates that obvious PR behavior can be observed in the sample with increasing Cu concentration by combining Kelvin Probe Force Microscopy (KPFM). Furthermore, it is found that the region with downward polarization has low resistance state (LRS), whereas the region with upward polarization has high resistance state (HRS). Moreover, the Piezoresponse Force Spectroscopy (PFS) and Switching Spectroscopy PFM (SS-PFM) measurements further confirm that the existence of the built-in voltage, Vbuilt-in is largest in the ZnO:Cu (8 at.%) film deposited at the oxygen partial pressure of 2 × 10−4 Torr. The schematic diagrams of energy band diagram with varied built-in field, Ebuilt-in, polarization directions and redistributed charges are presented to explain the correlation between RS and PR behavior.

Phase distribution and corresponding piezoelectric responses in a morphotropic phase boundary Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal revealed by confocal Raman spectroscopy and piezo-response force microscopy

Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) single crystals exhibit ultrahigh piezoelectric property and have already been applied in various industrial fields. Here, spatial distribution of coexistent phases and corresponding local piezoelectric responses in a morphotropic phase boundary (MPB) PMN-xPT single crystal are thoroughly investigated by confocal Raman spectroscopy coupled with piezo-response force microscopy (PFM). Different from previous studies on MPB crystals, spatial distribution of coexistent phases is exhibited intuitively in an image obtained by confocal Raman mapping. Via in-situ PFM measurements, domain morphology of each coexistent phase is observed. Moreover, local piezoelectric responses of each coexistent phase are obtained by switching spectroscopy PFM measurements, indicating that Ma and Mc phases behave like PNRs and polar matrix in PMN-xPT crystals Our work clarifies the contribution from different phases to the giant piezoelectric performance, which can deepen the understanding on the ultrahigh piezoelectricity in PMN-xPT crystals and provide the key point for developing novel high piezoelectricity materials.

Micro-Area Ferroelectric, Piezoelectric and Conductive Properties of Single BiFeO₃ Nanowire by Scanning Probe Microscopy.

Ferroelectric nanowires have attracted great attention due to their excellent physical properties. We report the domain structure, ferroelectric, piezoelectric, and conductive properties of bismuth ferrite (BFO, short for BiFeO3) nanowires characterized by scanning probe microscopy (SPM). The X-ray diffraction (XRD) pattern presents single phase BFO without other obvious impurities. The piezoresponse force microscopy (PFM) results indicate that the nanowires possess a multidomain configuration, and the maximum piezoelectric coefficient (d33) of single BFO nanowire is 22.21 pm/V. Poling experiments and local switching spectroscopy piezoresponse force microscopy (SS-PFM) demonstrate that there is sufficient polarization switching behavior and obvious piezoelectric properties in BFO nanowires. The conducting atomic force microscopy (C-AFM) results show that the current is just hundreds of pA at 8 V. These lay the foundation for the application of BFO nanowires in nanodevices.

Nanoscale insight of high piezoelectricity in high-TC PMN-PH-PT ceramics

The piezoelectric properties of the high-Curie temperature (high-TC) 0.15Pb(Mg1/3Nb2/3)O3-0.38PbHfO3-0.47PbTiO3 (0.15PMN-0.38PH-0.47PT) ceramics prepared by three different methods were compared. The 0.15PMN-0.38PH-0.47PT ceramics synthesized by the partial oxalate route exhibit the optimum properties, in which d33* = 845.3 pm/V, d33 = 456.2 pC/N, Kp = 67.2%, and TC = 291 °C. The nanoscale origin of the high piezoelectric response of the 0.15PMN-0.38PH-0.47PT ceramics was investigated by piezoresponse force microscopy (PFM) using the ceramics synthesized by the partial oxalate route. Large quantities of fine stripe submicron ferroelectric domains are observed, which form large island domains. In order to give further insights into the piezoelectric properties of the 0.15PMN-0.38PH-0.47PT ceramics from a microscopic point of view, the local poling experiments and local switching spectroscopy piezoresponse force microscopy (SS-PFM) were investigated, from which the local converse piezoelectric coefficient d33*(l) is calculated as 220 pm/V.

Orientation of Ferroelectric Domains and Disappearance upon Heating Methylammonium Lead Triiodide Perovskite from Tetragonal to Cubic Phase

We study the spontaneous polarization of the archetypal semiconducting halide perovskite methylammonium lead triiodide (CH3NH3PbI3) that is currently being investigated for use in thin film solar cells and light-emitting diodes. Using both lateral and vertical piezoresponse force microscopy (PFM) to image polycrystalline thin films, we observed domains in the piezoresponse that reversibly appear and disappear below and above the tetragonal-to-cubic phase transition temperature. Importantly, we observe these domains to exhibit a piezoresponse that is predominantly in-plane for films with the (110) plane oriented parallel to the substrate, providing a measure of the polarization associated with specific crystal planes. We characterize the polarization and its temporal response using both local switching spectroscopy and time-dependent PFM spectra. These data show hysteresis loops with the polarization switching with bias but relaxing back on time scales of several minutes. Our results suggest the existence ...

Local piezo-response for lead-free Ba0.9Ca0.1Ti0.9Zr0.1O3 electro-ceramic by switching spectroscopy

The purpose of this work is to determine the effective piezoelectric coefficient (d33) and the macro ferroelectric hysteresis behavior for the Ba0.9Ca0.1Ti0.9Zr0.1O3 (BCZT). The sample was prepared by the modified Pechini method and it was sintered at 1250 oC for 5 h. The refinements of X-ray diffraction (XRD) patterns obtained by the Rietveld method suggest a slight degree of tetragonality (c/a = 1.0025) in the perovskite structure. High counting statistics was performed in the two-dimensional grazing incidence 2D-GIXRD characterization by using synchrotron radiation. These results and the Raman spectrum analysis support the XRD interpretation. The morphology reveals a non-homogeneous terrace-type shape with a grain size distribution centered at 13 microns. The switching spectroscopy piezo-response force microscopy was used to obtained the effective d33 = 142 pm/V. The soft ferroelectric hysteresis shows a coercive field Hc = 1.3 kV/cm with a saturation polarization Ps = 15.7 µC/cm2.

Sol-gel processing and nanoscale characterization of (Bi0.5Na0.5)TiO3-SrTiO3 lead-free piezoelectric thin films

(1-x)(Bi0.5Na0.5)TiO3-xSrTiO3 (BNT-xST) (0 ≤ x ≤ 0.4) thin films were fabricated using a sol-gel technique on Pt(111)/Ti/SiO2/Si(100) substrates, which were investigated by piezoresponse force microscopy (PFM) and Raman spectroscopy. The composition-induced phase transition was analyzed by acquiring structural variations and the domain distribution on a local scale. Raman spectra showed phonon anomalies with peak broadening and shifting when increasing SrTiO3 (ST) concentrations were used. Changes in the domain morphology with changes in the composition were observed, and grains smaller than 0.5µm were observed at lower concentrations of x = 0–0.25, while larger grains appeared with increasing ST contents. The switching spectroscopy PFM (SS-PFM) results supported a ferroelectric (FE) to relaxor ferroelectric (RFE) phase transition at approximately x ≈ 0.3 by means of analyzing the parameters as a function of the composition including the piezoresponse parameters of hysteresis loops (Dmax, Drem) and amplitude butterfly loops (Stotal, Sneg). Hence, these results demonstrated that the composition-driven FE to RFE phase transition behavior, which is consistent with the localized response behavior, is dependent on the ST content in bulk BNT-xST ceramics.