Piezoresponse Force Microscopy Studies Research Articles

Ferroelectric properties and piezoresponse force micoroscopy study of Bi3TaTiO9 thin films

We investigate the ferroelectric properties and crystal structures of Bi3TaTiO9 (BTTO) thin films deposited on single-crystal Nb-doped (100) SrTiO3 substrates via pulsed laser deposition. The BTTO films exhibited either a (001)-epitaxial crystalline structure or a mixed a- and c-oriented polycrystalline structure depending on the substrate temperature. The ferroelectric polarization and piezoelectric coefficient of the mixed a- and c-oriented film were larger than those of the (001)-epitaxial film because its polar axis was perpendicular to the c-axis. Vertical and lateral piezoresponse force microscopy studies indicate that the ferroelectric domains of the (001)-epitaxial film were all parallel to the in-plane orientation, whereas the mixed a- and c-oriented film comprised both square grains with in-plane-oriented ferroelectric domains and longish grains with ferroelectric domains out of orientation with the plane.

Sequential piezoresponse force microscopy and the \u2018small-data\u2019 problem

The term big-data in the context of materials science not only stands for the volume, but also for the heterogeneous nature of the characterization data-sets. This is a common problem in combinatorial searches in materials science, as well as chemistry. However, these data-sets may well be ‘small’ in terms of limited step-size of the measurement variables. Due to this limitation, application of higher-order statistics is not effective, and the choice of a suitable unsupervised learning method is restricted to those utilizing lower-order statistics. As an interesting case study, we present here variable magnetic-field Piezoresponse Force Microscopy (PFM) study of composite multiferroics, where due to experimental limitations the magnetic field dependence of piezoresponse is registered with a coarse step-size. An efficient extraction of this dependence, which corresponds to the local magnetoelectric effect, forms the central problem of this work. We evaluate the performance of Principal Component Analysis (PCA) as a simple unsupervised learning technique, by pre-labeling possible patterns in the data using Density Based Clustering (DBSCAN). Based on this combinational analysis, we highlight how PCA using non-central second-moment can be useful in such cases for extracting information about the local material response and the corresponding spatial distribution.

Enhanced Piezoelectric Response in Hybrid Lead Halide Perovskite Thin Films via Interfacing with Ferroelectric PbZr0.2Ti0.8O3.

We report a more than 10-fold enhancement of the piezoelectric coefficient d33 of polycrystalline CH3NH3PbI3 (MAPbI3) films when interfacing them with ferroelectric PbZr0.2Ti0.8O3 (PZT). Piezoresponse force microscopy (PFM) studies reveal [Formula: see text] values of 0.3-0.4 pm/V for MAPbI3 deposited on Au, indium tin oxide, and SrTiO3 surfaces, with small phase angle fluctuating at length scales smaller than the grain size. In sharp contrast, on samples prepared on epitaxial PZT films, we observe large-scale polar domains exhibiting clear, close to 180° PFM phase contrasts, pointing to polar axes along the film normal. By separating the piezoresponse contributions from the MAPbI3 and PZT layers, we extract a significantly higher [Formula: see text] of ∼4 pm/V, which is attributed to the enhanced alignment of the MA molecular dipoles promoted by the unbalanced surface potential of PZT. We also discuss the effect of the interfacial screening layer on the preferred polar direction.

Two-phase dielectric polar structures in 0.1NBT-0.6ST-0.3PT solid solutions

In this work we address the peculiarities of the macroscopic responses in ternary 0.1Na0·5Bi0·5TiO3-0.6SrTiO3-0.3PbTiO3 (0.1NBT-0.6ST-0.3PT) solid solutions. These solid solutions exhibit a spontaneous first order relaxor to normal ferroelectric phase transition. The phase transition is accompanied by a broad dielectric relaxation which expands over 10 orders of magnitude in frequency just above the phase transition temperature. The temperature dependence of polarization shows that non-zero net polarization persists above the phase transition temperature. Below the phase transition temperature, it is not possible to describe the temperature dependence of polarization with a power law function which is valid in normal ferroelectrics. The piezoresponse force microscopy studies reveal that 0.1NBT-0.6ST-0.3PT solids solutions display several local polarization patterns which arise due to the bimodal distribution of grains in the ceramics. We associate the peculiar macroscopic responses to these complex polar structures and their different temperature behaviours.

The local cationic configurations in the K2Sr4Nb10O30 lattice and peculiarities of its surface piezoresponse

ABSTRACTBasing on the X-ray diffraction studies, a possibility of six local cationic configurations was established for K2Sr4Nb10O30 (KSN) having a tetragonal tungsten bronze-type structure. The association of these locally charged configurations may lead to the formation of the electrically active nanoregions. The piezoresponse force microscopy studies revealed at the KSN surface the presence of a subsystem of nano- or meso-size regions, which may be electrically active. Distribution and reference size of these regions have been estimated using the Fourier filtering of the source piezoresponse image.

Deep UV-Vis photodetector based on ferroelectric/semiconductor heterojunction

Herein, we develop a ferroelectric/semiconducting heterostructure for deep UV-Vis photo detection as a new approach to enhance the photocurrent by introducing the polarization-dependent interfacial coupling effect. The deep UV-Vis photo detection efficiency of the heterostructure device is improved as compared with BaTiO3 and ZnO devices. The polarization-dependent interfacial coupling effect has been demonstrated by resistive switching and piezoresponse force microscopy study. The present work provides an efficient and novel way in designing highly efficient ferroelectric-based photodetector and new optoelectronic memory devices.

Surface anchoring of bi-functional organic linkers on piezoelectric BiFeO3 films and particles: Comparison between carboxylic and phosphonic tethering groups

The functionalization of piezoelectric/ferroelectric bismuth ferrite (BiFeO3, BFO) films and particles with bi-functional organic monolayers is reported. BFO films, grown by MOCVD adopting a bi-metallic mixed source, and BFO particles, synthetized by a sol-gel route, were functionalized either with the benzene-1,4-dicarboxylic acid (BDC) or with the phosphonobenzoic acid (PBA). The proposed functionalization route is based on an activation step of the BFO surface followed by the treatment with a BDC or PBA solution. The structural and morphological characterizations of functionalized BFO samples were carried out using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The chemical composition and the anchoring mode of the grafted monolayers were investigated by X-ray photoelectron spectroscopy (XPS) and FT-IR. Comparison of XPS and FT-IR results, obtained from BDC and PBA functionalized surfaces, gave indications on the role of the nature of the anchoring group in the functionalization process. Finally, piezoresponse force microscopy (PFM) and PFM spectroscopy studies demonstrated that the ferroelectric properties of the material are retained after the functionalization.

PFM studies of hydroxyapatite-reduced graphene oxide nanocomposite

ABSTRACTWe present the nanoscale piezoresponse of ultrasonically synthesized reduced graphene oxide-hydroxyapatite (rGO-HAP) nanocomposite using Piezoresponse Force Microscopy (PFM). The piezoresponse in rGO (thickness ∼ 12 nm) is homogeneous in the unfolded region than that of the folded region. Variation in the confined piezo response of rGO-HAP nanocomposite studied at different regions having pure rGO, HAP nanorod (NR) and HAP NR intercalated rGO sheets. Under biasing, the polarization switching of the HAP NR intercalated rGO nanosheets is examined. Based on the PFM data analysis, it is implied that piezoelectricity of HAP intercalated rGO nanosheets is mainly created through the hydroxyl ions along the c-axis which prompts noncentrosymmetry in the structure.

Ferroelectric domain structure and polarization switching speed of highly (111)-oriented polycrystalline YMnO3 thin films on glass substrates

Polycrystalline YMnO3 (YMO) thin films were deposited on (111) Pt/Ta/glass substrates via pulsed laser deposition (PLD). The low PLD deposition rate made it possible to reduce the leakage currents of the YMO thin film due to the resulting high level of crystallinity. The YMO thin film exhibited a strong ferroelectric response, including a remnant polarization of 4.2μC/cm2. The piezoresponse force microscopy study revealed that the YMO thin films had a mosaic domain structure and a ferroelectric domain wall energy lower than that of PbTiO3 thin films. It is suggested that the fast switching speed of YMO capacitors, which is below 85ns, originates from this low domain wall energy.

Physical properties and reentrant behavior in PLZT thin films

ABSTRACTLa-modified lead zirconate titanate (PLZT) thin films were prepared to study their physical properties at macro- and nanoscale. Piezoresponse force microscopy (PFM) studies suggest a local imprint behavior at room temperature. Confirmed by P-E hysteresis loops recorded at 180-300 K, the imprint effect at room temperature tends to disappear at lower temperatures. In addition, the remanent polarization gradually increases and then decreases after reaching a maximum at around 243 K. This behavior suggests the occurrence of a reentrant dipole glass or an activated electric field effect in the studied PLZT films.

Combined theoretical and nanoscale experimental study of Pb(Ca,Ba)TiO3, Pb(Sr,Ba)TiO3, and Pb(Sr,Ca)TiO3 complex perovskite structures: An investigation of the ferroelectric and electronic properties

Combined experimental and first-principles studies have been conducted to obtain a fundamental understanding of the effect of A-site chemical doping on the electronic structure and ferroelectric behavior of Pb(Ca,Ba)TiO3, Pb(Sr,Ba)TiO3, and Pb(Sr,Ca)TiO3 perovskite complex solid solutions. Rietveld refinement of powder X-ray diffraction data shows that the crystal structure of all the three compounds is distorted from the ideal cubic perovskite structure. At the nanoscale, piezoresponse force microscopy (PFM) studies show low-performance ferroelectric properties of Pb(Sr,Ca)TiO3 thin films when compared to Pb(Ca,Ba)TiO3 and Pb(Sr,Ba)TiO3 films. Theoretical analysis of the electronic band structure performed on the basis of density functional theory (DFT) allows to elucidate the origin of the different ferroelectric behaviors observed in Pb(Ca,Ba)TiO3, Pb(Sr,Ba)TiO3, and Pb(Sr,Ca)TiO3 thin films. DFT-based computational calculations reveal that there is a strong correlation between the effects of Ti 3d non-bonding orbitals (responsible for π TiO bonding) and the ferroelectric polarization behavior of A(A′A″)BO3 complex perovskite solid solutions. In our study, very low Ti 3dxy, dxz, and dyz non-bonding electronic density state contributions were observed and the presence of mainly ionic CaO and SrO bonds. These effects are the reason for the unusually weak polarization, low tetragonality, and poor ferroelectricity of Pb(Sr,Ca)TiO3 thin films. This is in contrast to the observed behaviors of Pb(Ca,Ba)TiO3 and Pb(Sr,Ba)TiO3 thin films. However, our first-principles calculations agree well with the PFM-based experimental results obtained in the nanometer scale.

High Resolution Piezoresponse Force Microscopy Study of Self-Assembled Peptide Nanotubes

ABSTRACT Peptide nanotubes based on short dipeptide diphenylalanine (FF) attract a lot of attention due to their unique physical properties ranging from strong piezoelectricity to extraordinary mechanical rigidity. In this work, we present the results of high-resolution Piezoresponse Force Microscopy (PFM) measurements in FF microtubes prepared from the solution. First in-situ temperature measurements show that the effective shear piezoelectric coefficient d15 (proportional to axial polarization) significantly decreases (to about half of the initial value) under heating up to 100 oC. The piezoresponse becomes inhomogeneous over the surface being higher in the center of the tubes. Further, PFM study of a composite consisting of FF microtubes and reduced graphene oxide (rGO) was performed. We show that piezoelectric properties of peptide microtubes are significantly modified and radial (vertical) piezoresponse appears in the presence of rGO as confirmed via PFM analysis. The results are rationalized in terms of molecular approach in which π – π molecular interaction between rGO and dipeptide is responsible for the appearance of radial component of polarization in such hybrid structures.

High-sensitivity piezoresponse force microscopy studies of single polyvinylidene fluoride nanofibers

We report piezoresponse force microscopy (PFM) studies of single electrospun polyvinylidene fluoride (PVDF) nanofibers on the Pt/Ti electrode substrate. The out-of-plane piezoelectric response is much stronger than the in-plane, which is dependent on the parameters of the electrospinning technique. Further, the local polarization switching of the thin nanofibers can be quantitatively characterized by the amplitude-voltage butterfly loop and phase-voltage hysteresis loop. The piezoelectric coefficient (d33) of the nanofibers is diameter-dependent. The thinnest nanofiber studied here is 30nm and has the maximal |d33| of 38.5pmV−1. The excellent piezoelectric properties of these low-dimensional nanofibers can facilitate the development in sensing and energy harvesting applications.

Re-entrant relaxor ferroelectricity of methylammonium lead iodide

We have performed a piezoresponse force microscopy (PFM) study on methylammonium lead iodide (MAPbI3) thin films in normal (non-resonance, non-band-excitation) contact mode. In contrast to the ferroelectric Pb0.76Ca0.24TiO3 (PCT) control sample, a typical ferroelectric response was not observed. However, a nonlinear electric field dependence of the local PFM amplitude was found in MAPbI3, similar to PCT. An analysis combining results on structure, dielectric dispersion, and weak ferroelectricity demonstrates that MAPbI3 is actually a re-entrant relaxor ferroelectric which, upon cooling, enters into a relaxor phase below its ferroelectric phase transition at ∼327 K, due to the balance between the long range ferroelectric order and structural methylammonium group orientational disorder. The ferroelectricity at room temperature is compromised due to the re-entrant relaxor behavior, causing the poor polarization retention or weak ferroelectricity. Our findings essentially conciliate the conflicting experimental results on MAPbI3's ferroelectricity and are beneficial both for basic understanding as well as for device applications.

RETRACTED: A study approach on ferroelectric domains in BaTiO3

Abstract Atomic Force Acoustic Microscopy (AFAM) and Piezoresponse Force Microscopy (PFM) were used to study local elastic and electromechanical response in BaTiO 3 ceramics. A commercial multi-mode Scanning Probe Microscopy (SPM) and AFAM mode to image contact stiffness were employed to accomplish the aforementioned purposes. Stiffness parameters along with Young's moduli and piezo coefficients were quantitatively determined. PFM studies were based on electrostatic and electromechanical response from localized tip-surface contact. Comparison was made regarding the Young's moduli obtained by AFAM and PFM. In addition, phase and amplitude images were analyzed based on poling behavior, obtained via the application of − 10 V to + 10 V local voltage.

Piezoelectric and Dielectric Properties of Multilayered BaTiO3/(Ba,Ca)TiO3/CaTiO3 Thin Films.

Highly oriented multilayered BaTiO3-(Ba,Ca)TiO3-CaTiO3 thin films were fabricated on Nb-doped (001) SrTiO3 (Nb:STO) substrates by pulsed laser deposition. The configurations of multilayered BaTiO3-(Ba,Ca)TiO3-CaTiO3 thin films are designed with the thickness ratio of 1:1:1 and 2:1:1 and total thickness ∼300 nm. Microstructural characterization by X-ray diffraction indicates that the as-deposited thin films are highly c-axis oriented and large in-plane strain is determined in BaTiO3 and CaTiO3 layers. Piezoresponse force microscopy (PFM) studies reveal an intense in-plane polarization component, whereas the out-of-plane shows inferior phase contrast. The optimized combination is found to be the BaTiO3-(Ba0.85Ca0.15)TiO3-CaTiO3 structure with combination ratio 2:1:1, which displays the largest domain switching amplitude under DC electric field, the largest room-temperature dielectric constant ∼646, a small dielectric loss of 0.03, and the largest dielectric tunability of ∼50% at 400 kV/cm. These results suggest that the enhanced dielectric and tunability performance are greatly associated with the large in-plane polarization component and domain switching.

Ferroelectric InMnO3: Growth of single crystals, structure and high-temperature phase transitions

To understand the origin of the ferroelectricity in InMnO3, single crystals with average size of 1mm were grown in PbF2 flux at 950°C. The results of single crystal X-ray diffraction, second harmonic generation and piezoresponse force microscopy studies of high-quality InMnO3 single crystals reveal that the room-temperature state in this material is ferroelectric with P63cm symmetry. The polar InMnO3 specimen undergoes a reversible phase transition from non-centrosymmetric P63cm structure to a centrosymmetric P63/mmc structure at 700°C as confirmed by the in situ high-temperature Raman spectroscopic and synchrotron X-ray diffraction experiments.

Mixed grains and orientation-dependent piezoelectricity of polycrystalline Nd-substituted Bi4Ti3O12 thin films

Polycrystalline Bi3.15Nd0.85Ti3O12 (BNT) thin films were prepared on Pt/Ta/glass substrates by a pulsed laser deposition method. X-ray diffraction measurements revealed that the BNT thin films were preferentially oriented along the (117) direction although they possessed a polycrystalline structure. Good ferroelectric properties of the BNT thin film were observed with a remnant polarization of 13 μC/cm2 (2Pr ~26μC/cm2). The fatigue resistance test exhibited that the ferroelectric polarization of the BNT thin film degraded significantly after around 109 switching cycles, which can be attributed to its crystal structure. We investigated the surface morphology and ferroelectric domain structure by atomic force microscopy (AFM) and piezoresponse force microscopy (PFM), respectively. Interestingly, mixed grains consisting of long and circular shapes were observed on the BNT film surface, which corresponded to a- and c-axes orientations of crystal growth, respectively. The PFM study revealed that the piezoelectric coefficient (d33) of the long grains was much larger than that of the circular grains.

Strain effect on ferroelectric polarization of epitaxial LuFeO3 thin films

Epitaxial LuFeO3(LFO) thin films were deposited on La0.5Sr0.5MnO3(LSMO)/LaAlO3(LAO) substrates by pulsed laser deposition method. The LFO thin film with a thickness of 100 nm exhibited tetragonally strained structure on the LSMO/LAO substrate, in which the film showed c/a ratio of 1.045 based on X-ray diffraction experiment. The LFO thin film had a remnant polarization of about 15.2 μC/cm2, which was higher than the previously reported values. By using piezoresponse force microscopy study, it was confirmed that the LFO thin films had mosaic ferroelectric domain structure and that their domain wall energy was estimated to be lower than that of PbTiO3 thin films.

Spontaneous growth of GaN nanowire nuclei on N- and Al-polar AlN: A piezoresponse force microscopy study of crystallographic polarity

The polarity of gallium nitride (GaN) nanowire nuclei grown on AlN layers was studied by piezoresponse force microscopy (PFM). N- or Al-polar AlN layers were grown by molecular beam epitaxy (MBE) on Si (111) substrates by use of Al- or N-rich growth conditions, respectively. Short and low density GaN nanowires were then grown on each AlN polarity type. PFM measurements verified the expected AlN layer polarity and further indicated that predominantly N-polar nanowires are produced for growth on both AlN polarity types. Cross-section scanning transmission electron microscopy (STEM) images further reveal that the nanowires on Al-polar AlN films are nucleated on regions in the AlN layer that contain inversion domains, which propagate into the GaN nanowire nuclei. PFM measurements were found to be a convenient technique for mapping the polarity of a statistically significant number of individual GaN nanowires.