Local Piezoelectric Properties Research Articles

Piezoelectric domains in BiFeO3 films grown via MOCVD: Structure/property relationship

Metal-Organic Chemical Vapor Deposition (MOCVD) has been applied to the fabrication of BiFeO3 on dielectric SrTiO3 and conducting SrTiO3:Nb (100) substrates. Films have been deposited using a mixed bi-metallic source, consisting of Bi(phenyl)3 and Fe(tmhd)3, (phenyl=-C6H5, H-tmhd=2,2,6,6-tetramethyl-3,5-heptandione) precursor mixture. The chemical, structural and morphological characterizations of films have been carried out by energy dispersive X-ray analysis, X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Local piezoelectric properties have been investigated by piezoresponce force microscopy (PFM) and piezoelectric force spectroscopy (PFS). Structural and morphological characterizations point to the formation of homogeneous and flat surfaces for BiFeO3 films. Different ferroelectric/piezoelectric domains have been observed depending on the structure/morphology of the samples.

The Microstructure and Local Piezoelectric Response in Polymer Nanocomposites with Different Ferroelectric Crystalline Additions

ABSTRACTIn this work, we report on local ferroelectric and piezoelectric properties of nanostructured polymer composites P(VDF-TrFE)+x(Ba,Pb)(Zr,Ti)O3 (x = 0 - 50 %). High-resolution imaging of ferroelectric domains, local polarization switching, and polarization relaxation dynamics were studied by piezoresponse force microscopy. In particular, we found that (Ba,Pb)(Zr,Ti)O3 inclusions usually show a strong unipolar piezoresponse signal, as compared to the polymer matrix. By scanning under high dc voltage the films can be polarized uniformly under both positive and negative electric fields. Stability of the polarized state is discussed.

Nanoscale piezoresponse and magnetic studies of multiferroic Co and Pr co-substituted BFO thin films

Piezoresponse Force Microscopy (PFM) technique has been employed to acquire out-of-plane (OPP) piezoresponse images and local piezoelectric hysteresis loop in rhombohedrally distorted Bi1−xPrxFe1−yCoyO3 [x=0, 0.05; y=0.05] polycrystalline thin films fabricated via chemical solution deposition method. PFM images revealed that piezoelectric contrast is dependent upon the film composition. Furthermore, negative self-polarization effect was observed in the cobalt substituted BFO film. Well saturated local piezo-hysteresis loops were monitored and an increase was noticed in the piezoelectric coefficient (d33) value with cobalt doping (25.1pm/V) whereas with Pr co-substitution in BFCO film, the piezoelectric behavior was almost suppressed. Pr and cobalt co-substituted film exhibited the lowest leakage current density. Magnetic behavior (M–H curves) exhibited nearly eight times enhancement in the saturation magnetization values in the Co- and Co–Pr substituted films. The present study provides the different elements’ substitution effect on the local piezoelectric and magnetic properties of BiFeO3 multiferroic thin film.

Local piezoelectric response of single poly(vinylidene fluoride) electrospun fibers

AbstractIt is shown that electrospun poly(vynilidene fluoride) nanofibers are fully poled right after preparation and show β‐phase contents of ∼70%, therefore being able to be implemented into electroactive devices without further processing steps. Further, the local piezoelectric properties of individual electrospun fibers have been studied by piezoresponse force microscopy. Piezoelectric response, polarization switching, and nanoscale patterning of the fibers have been demonstrated.magnified image

Local piezoelectric activity of single poly(L-lactic acid) (PLLA) microfibers

Local piezoelectric properties of the poly(L-lactic acid) individual electrospun fibers have been studied by Piezoresponse Force Microscopy. Piezoelectric response, polarization switching, and nanoscale patterning of the fibers have been demonstrated in this important biomaterial, thus opening interesting possibilities for tissue engineering and sensing/actuating applications.

Ferroelectric-Paraelectric Phase Transition in Triglycine Sulphate via Piezoresponse Force Microscopy

Triglycine sulphate (TGS) is a widely studied ferroelectric material due to its high pyroelectric coefficients and pure 2nd order phase transition of the order-disorder type. In this work, we report local piezoelectric properties and domain evolution in TGS via piezoresponse force microscopy (PFM) where the ferroelectric-paraelectric phase transition and its domain structure are visualized in a single image while slowly heating the crystal during scanning. Thus, the y-coordinate of the scan represents the temperature and serves as a temperature “lens” to zoom in peculiarities of the domain evolution and paraelectric-ferroelectric phase boundary. Strong shift of the Curie point and broad peak of the second harmonic PFM signal are rationalized in terms of the stabilization of ferroelectric phase at the surface and large contribution of the dielectric constant to the local electromechanical measurements.

Piezoresponse force microscopy studies of the triglycine sulfate-based nanofibers

Local ferroelectric and piezoelectric properties of triglycine sulfate (TGS) nanocrystals embedded into poly(ethylene) oxide (PEO) electrospun fibers were examined by piezoresponse force microscopy (PFM). Piezoresponse contrast was found to be strongly dependent on the position being much stronger at the fiber periphery. A model of the distribution of TGS crystals inside the core-shell PEO-TGS fiber structure was proposed. TGS nanocrystals were unevenly distributed along the fiber axis and tend to grow near the surface of the fiber. The volume fraction distribution of the TGS crystals extracted from PFM measurements is in a good agreement with the data obtained from the dielectric constant measurements.

Local piezoelectric properties of ZnO thin films prepared by RF-plasma-assistedpulsed-laser deposition method

Zinc oxide (ZnO) thin films were grown on uncoated and zinc-coated Corning glasssubstrates by pulsed-laser deposition (PLD). X-ray diffraction measurements revealed thatthe as-deposited films are polycrystalline having preferential orientation along the [0002]and [] directions. Transmittance spectroscopy verified that the as-deposited films aretransparent with a direct bandgap of about 3.28 eV at room temperature. Piezoresponseimaging and local hysteresis loop acquisition were performed to characterize thepiezoelectric and possible ferroelectric properties of the films. The out-of-plane (effectivelongitudinal, ) and in-plane (effective shear, ) coefficients were estimated from the local piezoresponse based on the comparison withLiNbO3 single crystals. Measurements of all three components of piezoresponse (one longitudinaland two shear signals) allowed constructing piezoelectric maps for polycrystalline ZnO andto relate the variation of piezoelectric properties to the crystallographic and grain structureof the films. A shifted piezoresponse hysteresis loop under high voltages hints at thepossible pseudoferroelectricity, as discussed recently by Tagantsev (2008 Appl. Phys. Lett. 93202905).

Nanoscale characterization and local piezoelectric properties of lead-free KNN-LT-LS thin films

We report the observation of domain structure and piezoelectric properties of pure and Mn-doped (K0.44,Na0.52,Li0.04)(Nb0.84,Ta0.1,Sb0.06)O3 (KNN-LT-LS) thin films on SrTiO3 substrates. It is revealed that, using piezoresponse force microscopy, ferroelectric domain structure in such 500 nm thin films comprised of primarily 180° domains. This was in accordance with the tetragonal structure of the films, confirmed by relative permittivity measurements and x-ray diffraction patterns. Effective piezoelectric coefficient (d33) of the films were calculated using piezoelectric displacement curves and shown to be ∼53 pm V−1 for pure KNN-LT-LS thin films. This value is among the highest values reported for an epitaxial lead-free thin film and shows a great potential for KNN-LT-LS to serve as an alternative to PZT thin films in future applications.

Modeling Piezoresponse Force Microscopy for Low-Dimensional Material Characterization: Theory and Experiment

Piezoresponse force microscopy (PFM) is an atomic force microscopy-based approach utilized for measuring local properties of piezoelectric materials. The objective of this study is to propose a practical framework for simultaneous estimation of the local stiffness and piezoelectric properties of materials. For this, the governing equation of motion of a vertical PFM is derived at a given point on the sample. Using the expansion theorem, the governing ordinary differential equations of the system and their state-space representation are derived under applied external voltage. For the proof of the concept, the results obtained from both frequency and step responses of a PFM experiment are utilized to simultaneously identify the microcantilever parameters along with local spring constant and piezoelectric coefficient of a periodically poled lithium niobate sample. In this regard, a new parameter estimation strategy is developed for modal identification of system parameters under general frequency response. Results indicate good agreements between the identified model and the experimental data using the proposed modeling and identification framework. This method can be particularly applied for accurate characterization of mechanical and piezoelectric properties of biological species and cells.

Special Issue on Dynamic Modeling, Control and Manipulation at the Nanoscale

Special Issue on Dynamic Modeling, Control and Manipulation at the Nanoscale

Large-scale fabrication of titanium-rich perovskite PZT submicro/nano wires and their electromechanical properties

We report a 2-step approach to prepare tetragonal perovskite PbZr(0.1)Ti(0.9)O(3) submicro/nano wires in gram scale and with over 95% wire content. Non-perovskite precursor wires were first fabricated by hydrothermal processing. A subsequent annealing in a PbO atmosphere at 600 degrees C converted these wires into perovskite structures which retain the one-dimensional shape. Binding of the perovksite nanowires to a conductive substrate could be achieved by a similar heat treatment of the non-perovskite precursor wires on a flat Pt coated substrate. Taking advantage of the strong mechanical attachment and good electrical contact between the wires and the metallic layer, piezoresponse force microscopy (PFM) was used to measure the local piezoelectric and ferroelectric properties of the individual wires. Enhanced piezoelectric response relative to sputtered epitaxial PbZr(0.2)Ti(0.8)O(3) film and squared hysterisis loop with sharp switching indicate pronounced electro-mechanical and ferroelectric behavior. The 90 degree domain structure of the as-prepared perovskite PZT wires was confirmed by both PFM and transmission electron microscopy investigations.

Strained Rhombohedral Stripe Domains in BiFeO3 (001) Thin Films

This is a copy of the slides presented at the meeting but not formally written up for the volume. Stripe domains in ferroelectric thin films form in order to minimize the total energy of the film. It has been known for some time that a stable configuration is reached when the decrease in elastic energy from domain formation is balanced by the energetic costs of domain wall formation, local elastic strains in the substrate, and internal electric field formation from domain polarizations. The size and strain of each domain is determined by the lattice mismatch and the energetic costs of interface formation. Recent piezoelectric force microscopy measurements have shown that BiFeO3 (BFO) films on SrRuO3/SrTiO3 (001) substrates form striped polarization domains. Since the details of the local structure and polarization cannot be measured at the same time with conventional techniques, we have used synchrotron x-ray microdiffraction to study these effects. Probing only a few domains at a time with the submicron x-ray spot resulted in a diffraction pattern near the substrate (103) reflection consisting of several BFO peaks. We have unambiguously assigned these peaks to individual structural variants. Based on these results, we propose a physical model that includes the striped domains. The structural variants within the stripes are similar to those predicted by striped patterns in rhombohedral films which minimize elastic energy. The local piezoelectric properties were measured using time-resolved microdiffraction in order to examine the role of the striped domains in the linear responses of the film. The out of plane piezoelectric coefficient d33 was approximately 50 pm/V and the piezoelectric strain was proportional to electric field was up to 0.55%, the maximum strain we have measured. The projection of the in-plane piezoelectric coefficients onto the reciprocal space maps for different structural variants had vastly different values due to the differences in orientation of the domains.

Ferroelectric and piezoelectric properties of bismuth layered thin films grown on (100) Pt electrodes

The effect of film orientation on piezoelectric and ferroelectric properties of bismuth layered compounds deposited on platinum coated silicon substrates was investigated. Piezo-force microscopy was used to probe the local piezoelectric properties of Bi4Ti3O12, CaBi4Ti4O15 and SrBi4Ti4O15 films. Our measurements on individual grains clearly reveal that the local piezoelectric properties are determined by the polarization state of the grain. A piezoelectric coefficient of 65 pm/V was attained after poling in a grain with a polar axis very close to the normal direction. The piezoelectric coefficient and the remanent polarization were larger for a–b axes oriented than for c-axis-oriented films.

Manufacture and measurement of combinatorial libraries of dielectric ceramics: Part II. Dielectric measurements of Ba 1− xSr xTiO 3 libraries

Applying combinatorial methods to materials science offers the opportunity to accelerate the discovery of more efficient dielectric ceramics. High-throughput methods have the potential to investigate the effects of a wide range of dopants on the dielectric properties, and to optimise existing systems, encouraging the short innovation cycles that the communications technology industry requires. The London University Search Instrument (LUSI) is a fully automated, high-throughput combinatorial robot that has the potential capability to produce large numbers of sintered bulk ceramic samples with varying composition in 1 day, as combinatorial libraries on alumina substrates. Ba 1− x Sr x TiO 3 (BST) libraries were produced by LUSI as a proof-of-principle, with x = 0–1 in steps of 0.1, and fired to 1350 and 1400 °C for 1 h. Part I of this paper described the manufacture and physical characterisation of BST libraries, showing a regular change in composition with x across the libraries. In this second part, the dielectric properties of BST libraries produced by LUSI are assessed at frequencies between 100 Hz and 1 MHz, and at temperatures between 150 and 500 K. Local piezoelectric properties were also characterised by scanning probe microscope (SPM). All measurements showed evidence of a clear functional gradient varying with x across the library, with measured ɛ r corresponding to expected values for BST.

Local Piezoelectric Properties of Oriented PZT Based Ferroelectric Thin Films

A series of PZT based ferroelectric thin films obtained by multitarget sputtering with different preferential orientations are studied by piezoresponse force microscopy (PFM). The modification of the substrate by the deposition of an extra TiO x layer, and the use of MgO-based substrates instead of the usual Si-based ones, change the preferential orientation of the films. The results of the analysis of the local piezoelectric properties allow us to discuss the origin of some special features observed, like the appearance of protruding grains in films with specific orientations, and the homogeneity of the piezoelectric performance at the nanoscale.

AFM based polarization nanolithography on PZT sol–gel films

In this work, the possibility to create the inverted domain patterns on the surface of sol–gel derived ferroelectric PbTiO 3–PbZrO3 (PZT) thin films are demonstrated. Surface microstructure and local piezoelectric properties were investigated by piezoresponse atomic force microscopy. Macroscopic piezoelectric properties are investigated by laser Doppler vibrometry. PZT films exhibits high d 33 (93 pm/V in unpoled and 419 pm/V in poled state). Piezoresponse atomic force microscope (AFM) measurements were carried out by applying AC voltage (frequency 25 kHz and amplitude of 2 V) coupled with DC bias voltage between the grounded tip of AFM and Pt bottom electrode of the sample, and detecting first harmonics of resulting surface vibration by lock-in amplifier. The possibility to write and read the polarization patterns on the PZT thin film by piezoresponse AFM was confirmed.

Local piezoelectric and ferroelectric responses in nanotube-patterned thin films of BaTiO3synthesized hydrothermally at 200 °C

Piezoresponse atomic-force microscopy (PFM) has been used to characterize the local piezoelectric properties of a novel, nanotube-patterned (“honeycomb”) thin film of BaTiO3on Ti substrate synthesized hydrothermally at 200 °C. PFM amplitude and phase images, prior to the application of any direct current (dc) field, show ring-shaped piezoelectric regions that correspond to the nanostructure of this film. These results show clearly that the as-synthesized nanotube-patterned BaTiO3thin film is piezoelectric, with a net spontaneous polarization perpendicular to the film–substrate interface. In addition, polarization switching and hysteresis were observed as a function of applied dc field, confirming that this novel fabrication procedure results in unique configurations of BaTiO3film that are also ferroelectric.

RF magnetron sputtering ferroelectric PbZr0.52Ti0.48O3 thin films with (001) preferred orientation on colossal magneto-resistive layers

Deposition by RF magnetron sputtering of PbZr0.52Ti0.48O3 (PZT) ferroelectric thin films on two types of colossal magneto-resistive (CMR) oxide electrodes, La0.67Sr0.33MnO3 (LSMO) and La0.67Ca0.33MnO3 (LCMO), is demonstrated in this work. The multiferroic heterostructure is grown on a STO substrate, which causes a 〈001〉 preferred orientation to develop. Ferroelectric, retention of polarisation and local piezoelectric properties were measured for assessing the success of the integration from the ferroelectric point of view. Remnant polarisation Pr and coercive field Ec were found to be ∼40 μC/cm2 and ∼100 kV/cm, respectively. Films presented good retention of polarisation and piezoresponse loops. These results show that ferroelectric layers with good functionality can be grown on CMR oxide films, and open the possibility of designing a piezoelectrically driven spin valve memory cell device based on this heterostructure.

Domain populations in lead zirconate titanate thin films of different compositions viapiezoresponse force microscopy

Pb (ZrxTi1−x)O3 (PZT) thin films with (111) texture were deposited onto commercially availablePt/Ti/SiO2/Si substrates via the sol–gel technique. Piezoforce microscopy (PFM) was then usedto analyse the evolution of domain populations as a function of the Zr contentx. Domain structures of virgin films, local piezoelectric properties of individual grainsand piezoelectric histograms were studied in films with different compositions(x = 0.2–0.6), which cover both the tetragonal and rhombohedral sides of the phase diagram. In filmswith low Zr content mainly single-domain grains were observed. As the Zr content increased, alarger fraction of polydomain grains was found. The local piezoelectric response measured insidesufficiently big grains indicated that the strongest piezoelectric effect occurs in PZT30/70(x = 0.3) films. This was attributed to two different effects: high out-of-plane polarization achieveddue to the (111) texture and influence of the dielectric constant. In tetragonal filmswith their lower dielectric constants the electric field seen by a ferroelectric ishigher as compared to other compositions, giving rise to an apparent increaseof the effective piezoelectric response measured by PFM. The analysis of thedomain images indicated that sol–gel derived PZT films are slightly self-polarizednear the free surface. With increasing Zr/Ti ratio, the variation of domainpopulations resulted in reversing the sign of the average piezoelectric response atx≈0.3. It is demonstrated that PFM histograms are extremely sensitive to PZT composition andcan be used as a signature of complex domain structures in ferroelectric thin films.