Papers by Keyword: Piezoresponse Force Microscopy

Abstract: Atomic force microscopy techniques (conductive-AFM, I-V spectroscopy and PFM) were used for characterisation of the local electrical properties of bilayer polyaniline-polystyrene/P(VDF-TrFE) polymer nanocomposite. Observed hysteresis of current-voltage characteristics confirms its memristive properties. It was caused by the influence of the ferroelectric polarization of P(VDF-TrFE) layer, the domain structure of which was visualised by piezoelectric force microscopy on the transport of charge carriers at the interface.

Abstract: An experimental study of low temperature domain dynamics could provide information on a mechanism of domain wall motion at low temperatures in thin ferroelectric films. For this purpose we use a piezoresponse force microscopy (PFM) technique and investigate the 180⁰ ferroelectric domains growth in the temperature range 5 K – 295 K. Domains were created by applying a dc voltage pulses between an atomic force microscopy (AFM) tip and a bottom electrode of a thin epitaxial PbZr_0.3Ti_0.7O₃ film. Two different types of tips were used, a semiconducting tip with dopant conductivity and a tip with metallic coating to clarify an influence of poling procedure on the domain dynamics. Created domains were then visualized and their in-plane sizes were measured with out-of-plane PFM. Dependences of lateral domain size on the duration and amplitude of dc voltage pulse were obtained. Received experimental dependences were then fitted with logarithmic function with good accuracy. This circumstance indicates on the thermally activated mechanism of domain growth and formation. Temperature dynamics of the 180⁰ ferroelectric domains growth does not depend on the AFM tip used in a poling procedure what allows us to conclude that the voltage transfer to the ferroelectric film does not significantly depend on the tip-film local contact properties.

Abstract: Ferroelectric-relaxor behavior on highly epitaxial Barium Zirconium Titanate (Ba (Zr_0.2Ti_0.8)O₃) thin film was investigated using the Piezoresponse Force Microscopy specifically to investigate the onset of relaxor behavior. The surface roughness, microstructure and the grain size of the film were systematically studied. Ferroelectric switching at random localized points were observed at room temperature though it has been previously reported that the phase transition in BZT-20 occurs at 285K. Phase reversal with the reversal of the applied voltage was also seen. Scanning Capacitance Microscope has been employed to interrogate the localized change in the capacitance with change in voltage. The thin film sample showed the presence of ferroelectric nanoregions at room temperature unlike its bulk counterparts which is paraelectric at room temperature.

Abstract: Large area film deposition was performed by means of multitarget reactive magnetron sputtering from metallic targets (Pb, Ti, Zr) with a diameter of 200 mm onto Cu-coated Kapton® HN substrates. High-power pulse sputtering has been employed for the Zr-target (or alternatively for the Ti-target). Film composition profiles were evaluated by XPS and RBS. Piezoelectric properties were investigated by PFM.

Abstract: The poling and local piezoresponse mechanism has been investigated in ferroelectric polymers. Isotropic 94/6 composition vinylidenefluoride and tetraflouroethylene copolymer films is formed from acetone at room temperature by slow evaporation of solvent. The copolymer crystallization results in metastability (nonequilibre) form at high overcooling temperatures. IR spectroscopy shows occurrence of isomers with conformation TGTG^-, T₃GT₃G^- and (TT)_n. The local piezoresponse shows that ferroelectric domains include crystals areas as well as nonordered phase. After annealing by heating to 150 oC was found conformation changes in polymer chain: T₃GT₃G^- TGTG^- and T₃GT₃G^- (TT)_n. It is show that the regular conformation chains length rising after annealing. Polarization value decreasing kinetic was investigated by piezoresponse force microscopy method.

Abstract: Single crystalline BaTiO₃ nanocubes, which were synthesized by hydrothermal reaction with organic surfactants and additives, were assembled in order and directly on the substrates by dip-coating method using the dispersed solution. After evaporation of solvent, the orderly assembly of the nanocubes was developed over the large region in about several tens of micrometers square. It can cover whole surface of the substrate. The microstructures of the nanocube assemblies were evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Electrical property of the nanocube-assembled film was characterized by piezoresponse force microscopy (PFM). The d₃₃-V curve showed ferroelectric hysteresis and saturation behaviors under high applied voltage.

Abstract: Barium titanate (BT) and strontium titanate (ST) nanocubes which have been synthesized by hydrothermal method with surfactants were assembled in order directly on the substrates by using capillary-force-assisted self-assembly method. The ordered structures, crystallinity and orientation of the nanocubes were evaluated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning probe microscopy (SPM) and X-ray diffraction (XRD). The piezoresponse properties of the nanocubes ordering structures characterized by Piezoresponse Force Microscopy (PFM) seemed to depend on the constituents and their interface.

Abstract: Top-seeded solution growth method under high-oxygen-pressure atmosphere has been developed for obtaining high-performance and large-sized single crystals of ferroelectric (Bi_0.5Na_0.5)TiO₃ (BNT). Crystals grown at 1000 °C at a Po₂ of 0.9 MPa exhibited a well-saturated hysteresis with a remanent polarization of 34 μC/cm² and a coercive field of 22 kV/cm along <100>_cubic. The spontaneous polarization of BNT along <111>_cubic is estimated to be 59 μC/cm² from the measured polarization properties along <100>_cubic of the crystals obtained. Domain observations using piezoresponse force microscopy revealed that the degraded performance of BNT crystals grown at a low Po₂ is attributed to unswitched 71° domains remaining even after applying a high electric field to the crystals .

Abstract: This work analyzes the processing of Pb(Zr,Ti)O3 (PZT) thin films directly on copper-coated polymer films. PZT thin film deposition was performed onto the metallized Kapton® films using a single RF plasma jet. In order to reduce the interaction of PZT and Cu during the initial growth stage, an ultrathin amorphous TiO2-x seeding layer was sputter-deposited prior to PZT deposition. The film texture was a mixture of (111)-oriented perovskite nanocrystals, rutile and pyrochlore. Topography and piezoelectric in-plane and out-of-plane response of the films were evaluated using a commercial AFM adapted for piezoforce measurements. The as-deposited films were self-polarized with polarization pointing at the surface of the sample. Polarization was switchable and a piezoelectric hysteresis was obtained.

Abstract: Ferroelectrics are among the most advanced materials for non-volatile storage applications. Their two thermodynamically equivalent groundstates of spontaneous polarization can be toggled between by an external electric field. We present recent progress in the fabrication, registration, manipulation and characterization of nanoscale ferroelectrics. Chemical solution deposition is adapted to a pre-registration process by e-beam lithography to fabricate registered ferroelectric nanostructures below 100 nm width. A post-processing by chemical mechanical polishing either for embedded or free grains modifies the aspect ratio thus controlling the coercive field distribution of nanoferroelectrics. We also discuss some very recent findings of the complex interaction of field and piezoelectric tensor in a real piezoresponse force microscope. This method requires a comprehensive treatment of all contributions to tell apart extrinsic from intrinsic effects.