Dynamic Contact Electrostatic Force Microscopy Research Articles

Electrospinning and characterization of magnetoelectric NdFeO3–PbZr0.52Ti0.48O3 Core–Shell nanofibers

A core–shell nanofiber with a neodymium orthoferrite (NdFeO3) core and lead zirconium titanate (PbZr0.52Ti0.48O3) shell was prepared in this study using the sol-gel electrospinning method. Structural properties of the nanofiber were analysed using the X-ray diffraction (XRD) method, which revealed that a perovskite structure was formed. The strain was calculated using Williamson-Hall (W–H) plot. Functional groups of the nanofiber were studied using Fourier transform infrared (FTIR) spectroscopy. Morphological studies revealed the core diameter of the nanofiber to be 65 nm and its shell diameter to be 128 nm. The elemental analysis of core-shell nanofiber was made using Energy Dispersive X-ray Spectroscopy (EDS) which proved the formation of NdFeO3 and PbZr0.52Ti0.48O3 composite in the stoichiometric ratio. Topography analysis using atomic force microscopy found the average fibre diameter to be 135 nm. The nanofiber exhibited antiferromagnetic behaviour, with a saturation magnetization of 0.48 emu/g. Dynamic contact electrostatic force microscopy (DC-EFM) studies revealed that the nanofiber showed domain-switching behaviour. The ferroelectric hysteresis plots showed that the nanofiber exhibited a maximum polarization of 5.45 μC/cm2 at 20 kV/cm. Also, its dielectric constant was 268 at 100 Hz. The leakage current study revealed a butterfly-shaped J-E loop, which further proved the ferroelectric behaviour of the nanofiber. The mechanism behind the leakage current was identified to be the Schottky emission. The P-E loops recorded under external magnetic fields of different strengths exhibited variations in the polarization, indicating the presence of cross-coupling between electric and magnetic order parameters. Because of the high dielectric constant displayed by the magnetoelectrically active NdFeO3–PbZr0.52Ti0.48O3 core–shell nanofiber, it can be a promising candidate for a number of applications, such as data storage devices, multimedia devices, spintronics and magnetic field sensors.

Energy harvesting performance of magnetoelectric poly(vinylidene fluoride)/NiFe2O4 nanofiber films

Flexible nanocomposite films of poly(vinylidene fluoride)(PVDF)/nickel ferrite (NiFe2O4) fiber were made using solvent casting method. The NiFe2O4 fibers with a diameter of 400 nm were synthesized initially by means of electrospinnig technique. Studies of XRD and FTIR confirmed the formation of both α and β phases in the composite films. The presence of α-phase was diminished with the incorporation of NiFe2O4 and a maximum β-phase percentage (68%) was obtained. SEM and AFM analyses also demonstrated the transformation of the microstructures from α to β phase. The ferroelectric properties were tested with respect to NiFe2O4 loading and the composite film with 10 wt% NiFe2O4 exhibited a high Pmax value of 1.46 μC/cm2. VSM studies revealed the ferrimagnetic behaviour of the films and exhibited a maximum saturation magnetization value of 4.2 emu/cm3. Local ferroelectric properties were investigated through their domain switching behavior using dynamic contact electrostatic force microscopy (DC-EFM), and magnetic force microscopy (MFM) was used to analyze the magnetic properties. The magnetoelectric cross-coupling between ferroelectric and ferrimagnetic orderings is verified through the variations in ferroelectric parameters under different magnetic fields. Then a nanogenerator was fabricated using the composite films and generated an open circuit voltage of 10 V (peak-peak). Additionally, these films were made into magneto-mechano-electric (MME) generator, which could generate a 4.8 V (peak-peak) output voltage under a weak AC magnetic field of 10 Oe at 50 Hz.

Multifunctional films of poly(vinylidene fluoride)/ZnFe2O4 nanofibers for nanogenerator applications

A two-step synthesis method was used to prepare a flexible PVDF/ZnFe2O4 multiferroic nanocomposite film. ZnFe2O4 nanofibers synthesized using electrospinning technique were incorporated into a PVDF matrix to form PVDF/ZnFe2O4 composite films through the solution-casting process. XRD patterns confirmed the formation of the polar β-phase in films, which is responsible for ferroelectricity. The percentage of the β-phase, calculated by FTIR analysis, reached 88% with the incorporation of ZnFe2O4 in PVDF. The transformation of α to β-phase microstructure were examined using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The dielectric constant and tangent loss of the composites with respect to ZnFe2O4 loading were measured. The dielectric constant increase with the increasing concentration of ZnFe2O4, and a maximum value of 30 was obtained for a ZnFe2O4 concentration of 15 wt%. Ferroelectric properties were analyzed by taking into consideration the domain switching behavior, which was investigated by dynamic contact electrostatic force microscopy (DC-EFM), whereas the magnetic properties were analyzed using magnetic force microscopy (MFM). The as-synthesized composite films were further used to fabricate a nanogenerator, which was capable of generating up to 7 V (peak–peak) as a maximum open circuit voltage for a 15 wt% ZnFe2O4-loaded film at 1.5 N of applied force. In addition, the nanogenerator delivered an output power of 4 μW at a load resistance of 500 kΩ, and the results were compared with previous results.

Nanohydroxyapatite embedded blends of ethylene‐co‐vinyl acetate and millable polyurethane as piezoelectric materials: dielectric, viscoelastic and mechanical features

AbstractWe report the piezoelectric, dielectric and dynamic mechanical features of nanohydroxyapatite (nHA) embedded ethylene‐co‐vinyl acetate (EVA)/millable polyurethane (MPU) elastomer blends. The EVA/MPU/nHA systems were prepared by two‐roll milling followed by compression moulding. The piezoelectric features were probed by dynamic contact electrostatic force microscopy (EFM).The neat EVA/MPU blend was not found to exhibit ferroelectric properties. However, upon incorporation of nHA, butterfly loops of EFM amplitude signals as well as complementary hysteresis curves were obtained, confirming the introduction of ferro‐piezoelectric properties. The ferro‐piezoelectric features were found to be improved with an increase in nHA loading which recorded highest signals for 8 parts per hundred parts of rubber (phr) loaded composites. The fabricated devices generated a peak voltage of 4.02 V and 4.89 V respectively with 6 phr and 8 phr nHA loaded composites. Electrical properties such as dielectric constant, volume resistivity and loss factor as well as dynamic mechanical properties were examined. The viscoelastic features of the systems support the reinforcing feature with filler loading. TEM analysis of the composites indicated a uniform distribution of filler particles in the blend matrix, complementing the observed ferro‐piezoelectric, dielectric and dynamic mechanical properties. The simultaneous modulation of piezoelectric and viscoelastic properties is a preferred feature for fast‐responsive dielectric elastomers for their applications in various piezoelectric devices. © 2020 Society of Chemical Industry

Local ferroelectric studies on interconnected PVDF nano-dot thin films using piezo force microscopy

The local ferroelectric domain structure of interconnected PVDF nano-dots with applied DC voltages of ± 10 V to ± 100 V is evaluated using various Piezo force microscopy (PFM) methods such as conventional PFM and Dynamic contact electrostatic force microscopy (DC-EFM). The self-assembled PVDF nano-dots are fabricated by using a spin coater method with 2 wt% of PVDF-DMSO solution. The polar gamma phase is found to be induced by the microstructural confinement of PVDF monomers and also reveals a strong ferroelectric nature after poling at different DC bias voltages. Poling with altered directions of the voltages renders a 180° phase reversal of PVDF domains. The local domain study depicts that each nano-dot is functioning as a single domain and switches as a whole. The single nano-dot switching signifies the potential of using the nano-dots for organic ferroelectric memory devices.

Nano P(VDF-TrFE) doped polyimide alignment layers for twisted nematic liquid crystal devices

ABSTRACTThe rapid development of consumer electronics and portable devices imposes a great demand for energy efficient information display systems. Among the information display devices, liquid crystal display (LCD) devices stands in the front. The fabrication of energy-efficient LCD systems demands new material and techniques. In this work, the conventional polyimide alignment layer of twisted nematic liquid crystal device (TNLCD) was replaced with ferroelectric polymer nanoparticle doped alignment layer. Morphology of the alignment layer was analysed using field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The ferroelectric nature of the polymer alignment layer was studied using dynamic contact electrostatic force microscopy (DC-EFM). TNLCD cells are fabricated with this modified alignment layer and the switching characteristics are compared with the conventional TNLCD devices. The TNLCD with modified alignment layer has shown a reduction of 50% in threshold (Vthr) and 47% reduction in saturation voltage (Vsat).

Ferroelectric polymer nanocomposite alignment layer in twisted nematic liquid crystal devices for reducing switching voltage

ABSTRACTTwisted nematic liquid crystal device (TNLCD) was fabricated using a ferroelectric zinc oxide (ZnO)-doped polyimide alignment layer. The ferroelectric nanoparticle can produce a local electric field, which can trigger the orientation of liquid crystal molecule and reduces the switching voltage. The uniform dispersion of ferroelectric ZnO nanoparticles in the alignment layer was studied using field emission scanning electron microscopy and atomic force microscopy. The ferroelectric property of ZnO-doped polyimide was investigated using dynamic contact electrostatic force microscopy. An increased local electric field due to the presence of nano ZnO was confirmed with the help of scanning tunnelling microscopy. An augmentation of capacitance was observed with an increase in concentration, which substantiates the reduction of switching voltage of TNLCD with the modification of ferroelectric nanoparticle-doped alignment layer.

Flexible, ferroelectric nanoparticle doped polymer dispersed liquid crystal devices for lower switching voltage and nanoenergy generation

Flexible polymer dispersed liquid crystal (F-PDLC) devices were fabricated using transparent conducting ITO/PET film. Polymerization induced phase separation (PIPS) method was used for pure and ferroelectric BaTiO3 (BTO) and ZnO doped PDLC devices. The distribution of nanoparticles in the PDLC and the formation of micro cavities were studied using field emission scanning electron microscopy (FESEM). It was observed that the addition of ferroelectric BTO nanoparticles has reduced the threshold voltage (Vth) and saturation voltage (Vsat) of FNP-PDLC by 85% and 41% respectively due to the spontaneous polarization of ferroelectric nanoparticles. The ferroelectric properties of BTO and ZnO in the fabricated devices were investigated using dynamic contact electrostatic force microscopy (DC EFM). Flexing the device can generate a potential due to the piezo-tribo electric effect of the ferroelectric nanomaterial doped in the PDLC matrix, which could be utilized as an energy generating system. The switching voltage after multiple flexing was also studied and found to be in par with non-flexing situations.

Study on the enhancement of ferroelectric β phase in P(VDF-HFP) films under heating and poling conditions

Free-standing, flexible films of poly(vinylidene fluoride–hexafluoropropylene) (P(VDF-HFP)) were prepared by spin coating technique, and the effects of heat treatment and poling on the formation of electroactive β phase were studied. The X-ray diffraction, Fourier-transform infrared spectroscopy, Field emission scanning electron microscopy and Atomic force microscopy studies proved that the melt-quenching process influences the transformation of non-ferroelectric α phase to ferroelectric β-phase, when compared to heat-drying process. The variation in the β-phase content resulted in the enhanced ferroelectric response in the melt-quenched samples, which was proved by the dynamic contact electrostatic force microscopy (DC-EFM) studies and also by the ferroelectric hysteresis. The polarization switching behavior of the films was also investigated with DC-EFM. The electrical poling at 30MV/m further enhanced the ferroelectric nature of the films by 29–30%. The films exhibited high dielectric constant, low dielectric loss, and low-leakage current, and it was identified that the leakage current in the films was originated due to the Schottky emission.

Studies on Field Dependent Domain Structures in Multi-Grained 0.85PbMg1/3Nb2/3O3–0.15PbTiO3 Thin Films by Scanning Force Microscopy

0.85PbMg1/3Nb2/3O3–0.15PbTiO3 (0.85PMN–0.15PT) ferroelectric relaxor thin films have been deposited on La0.5Sr0.5CoO3/(111) Pt/TiO2/SiO2/Si by pulsed laser ablation by varying the oxygen partial pressures from 50 mTorr to 400 mTorr. The X-ray diffraction pattern reveals a pyrochlore free polycrystalline film. The grain morphology of the deposited films was studied using scanning electron microscopy and was found to be affected by oxygen pressure. By employing dynamic contact-electrostatic force microscopy we found that the distribution of polar nanoregions is majorly affected by oxygen pressure. Finally, the electric field induced switching in these films is discussed in terms of domain wall pinning.

Effect of oxygen pressure on the grain and domain structure of polycrystalline 0.85PbMg1/3Nb2/3O3–0.15PbTiO3 thin films studied by scanning probe microscopy

0.85PbMg1/3Nb2/3O3–0.15PbTiO3 ferroelectric–relaxor thin films have been deposited on La0.5Sr0.5CoO3/(1 1 1) Pt/TiO2/SiO2/Si by pulsed laser ablation at various oxygen partial pressures in the range 0.05 to 0.4 Torr. All the films have a rhombohedral perovskite structure. The grain morphology and orientation are drastically affected by the oxygen pressure, studied by x-ray diffraction and scanning electron microscopy. The domain structure investigations by dynamic contact electrostatic force microscopy have revealed that the distribution of polar nanoregions and their dynamics is influenced by the grain morphology, orientation and more importantly, oxygen vacancies. The correlation length extracted from autocorrelation function images has shown that the polarization disorder decreases with oxygen pressure up to 0.3 Torr. The presence of polarized domains and their electric field induced switching is discussed in terms of internal bias field and domain wall pinning. Film deposited at 0.4 Torr presents a curious case with unique triangular grain morphology and large polarization disorder.

Deterministic domain formation observed in ferroelectrics by electrostatic force microscopy

The effect of crystalline defects on the formation of ferroelectric domains in triglycine sulfate (TGS) crystals has been investigated using a dynamic contact electrostatic force microscopy. This detection method, based on the Coulomb interaction between the charge on the tip and the surface charge on the sample, yields a good spatial resolution as well as a complete separation between the topography and the domain image. The crystal imperfections, degraded surface, and strain in the crystal affect strongly the static domain configuration. Comparison of the topography to the domain image reveals a deterministic behavior in the formation of the equilibrium domain configuration, which is determined by twin boundaries in the crystal. Surface imperfections appear different depending on the polarization direction. Positively polarized regions show circular islands, whereas negatively polarized region shows circular holes as well as islands of various shapes. When TGS samples were cooled below the Curie temperature from a paraelectric state, the relaxation rate of the domains from the nonequilibrium configuration to the equilibrium configuration is substantially decreased forthe sample that contains many defects, indicating a pinning effect by the crystal imperfections such as the degraded surface and stress in the crystal.

Studies of the effects of ion irradiation on ferroelectric domains of triglycine sulfate single crystals on a nanometer scale

The effects of low dose (10 9/cm 2) ion irradiation on the ferroelectric domains and on the ferroelectric↔paraelectric phase transition of triglycine sulfate (TGS) single crystals has been studied by using variable temperature dynamic contact electrostatic force microscopy. The evolution with temperature of ferroelectric domains of virgin and ion irradiated samples was observed in situ. In general, the phase transition of ion unirradiated samples is similar to that of virgin samples, which can be well described by Landau's mean field theory. However, on ion irradiated samples, there is a strong asymmetry of spontaneous polarization P for positive and negative domains. This asymmetry is due to the defects produced by ion implantation.