W. C. Gan

Hot Plate Annealing at a Low Temperature of a Thin Ferroelectric P(VDF-TrFE) Film with an Improved Crystalline Structure for Sensors and Actuators

Ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer 70/30 thin films are prepared by spin coating. The crystalline structure of these films is investigated by varying the annealing temperature from the ferroelectric phase to the paraelectric phase. A hot plate was used to produce a direct and an efficient annealing effect on the thin film. The dielectric, ferroelectric and pyroelectric properties of the P(VDF-TrFE) thin films are measured as a function of different annealing temperatures (80 to 140 °C). It was found that an annealing temperature of 100 °C (slightly above the Curie temperature, Tc) has induced a highly crystalline β phase with a rod-like crystal structure, as examined by X-ray. Such a crystal structure yields a high remanent polarization, Pr = 94 mC/m2, and pyroelectric constant, p = 24 μC/m2K. A higher annealing temperature exhibits an elongated needle-like crystal domain, resulting in a decrease in the crystalline structure and the functional electrical properties. This study revealed that highly crystalline P(VDF-TrFE) thin films could be induced at 100 °C by annealing the thin film with a simple and cheap method.

Theoretical and experimental approach on dielectric properties of ZnO nanoparticles and polyurethane/ZnO nanocomposites

ZnO nanoparticles (ZnO-NPs) were synthesized by a new, simple sol-gel method in gelatin media (particle size of ZnO ≈ 30 to 60 nm). Polyurethane/ZnO nanocomposites thin films (PU/ZnO-NPs) were prepared by mixing the ZnO-NPs into PU prepolymer. The nanocomposites were structurally characterized using Fourier transmission infrared (FTIR) spectroscopy. The interaction between ZnO-NPs and PU matrix is studied by analyzing the differences in C=O region and N-H region of FTIR spectra. The morphology of ZnO and PU/ZnO nanocomposites were assessed using transmission electron micrograph, TEM, and field emission scanning electron microscope, FESEM, respectively. The dielectric properties of ZnO-NPs were attributed to the interfacial and orientation polarization. Measurement is reported for the real and imaginary parts of the ac conductivity of ZnO-NPs in the frequency range of 10 to 106 Hz in the temperature range 298–478 K. The experimental results are interpreted in terms of the classical correlated-barrier hoppi...

Pyroelectricity enhancement of PVDF nanocomposite thin films doped with ZnO nanoparticles

A thin film of pyroelectric composite with 0–3 connectivity was fabricated from zinc oxide (ZnO) nanopowder and polyvinylidene fluoride (PVDF) with different volume fraction from 0–0.25 wt%. The dielectric and pyroelectric properties of the samples were investigated. It was found that the presence of a small amount of ZnO nanoparticles (0.25 wt%) has significantly increased the pyroelectric coefficient of the PVDF by 25%. Furthermore, the nanocomposite films required lower poling field to form polar-δ phase compared to pure PVDF thin films. Analysis of the complex permittivity in a wide range of frequency was carried out indicating that the dielectric constant and loss of PVDF/ZnO nanocomposite thin films increase when doped with ZnO. Havriliak-Negami (HN) empirical function has been employed to obtain the αrelaxation time of the nanocomposite thin films before and after poling. The α-relaxation time does not vary with the increase of ZnO wt%; however, the effect of poling has lengthened the relaxation time of the thin films. FTIR and XRD results supports the fact that the addition of ZnO nanoparticles into PVDF polymer thin films do not cause any significant effect on the structure of the PVDF thin films. In fact, ZnO nanoparticle has enhanced the overall pyroelectricity of PVDF by facilitating the poling process in the composites and led to phase transformation of PVDF from α -t oδ-phase as supported by a marked reduction of (100) x-ray diffraction intensities.

Phase sensitive molecular dynamics of self-assembly glycolipid thin films: A dielectric spectroscopy investigation

Glycolipid, found commonly in membranes, is also a liquid crystal material which can self-assemble without the presence of a solvent. Here, the dielectric and conductivity properties of three synthetic glycolipid thin films in different thermotropic liquid crystal phases were investigated over a frequency and temperature range of (10(-2)-10(6) Hz) and (303-463 K), respectively. The observed relaxation processes distinguish between the different phases (smectic A, columnar/hexagonal, and bicontinuous cubic Q) and the glycolipid molecular structures. Large dielectric responses were observed in the columnar and bicontinuous cubic phases of the longer branched alkyl chain glycolipids. Glycolipids with the shortest branched alkyl chain experience the most restricted self-assembly dynamic process over the broad temperature range studied compared to the longer ones. A high frequency dielectric absorption (Process I) was observed in all samples. This is related to the dynamics of the hydrogen bond network from the sugar group. An additional low-frequency mechanism (Process II) with a large dielectric strength was observed due to the internal dynamics of the self-assembly organization. Phase sensitive domain heterogeneity in the bicontinuous cubic phase was related to the diffusion of charge carriers. The microscopic features of charge hopping were modelled using the random walk scheme, and two charge carrier hopping lengths were estimated for two glycolipid systems. For Process I, the hopping length is comparable to the hydrogen bond and is related to the dynamics of the hydrogen bond network. Additionally, that for Process II is comparable to the bilayer spacing, hence confirming that this low-frequency mechanism is associated with the internal dynamics within the phase.

Pyroelectricity in Synthetic Amphitropic Glycolipid for Potential Application of IR Sensor Device

Synthetic pure β-anomer glycolipid with large pyroelectric coefficient (∼80 μC/m2K under zero applied bias field) is reported. The pyroelectric and dielectric properties of glycolipid prepared in thin films, annealed at various temperatures have been investigated. The induced polarization in the glycolipid thin films systems remains stable up to 100°C, thus this material is appropriate for sensor materials for pyroelectric application. The real part of the dielectric constant is also low as compared to that of the other ferroelectric ceramic materials used in pyroelectric devices; therefore these new materials have significant potential application for infrared sensing devices.

Different surface morphology of annealed PVDF-TrFE thin films and the effect on its ferroelectric properties

The different morphology of 250 nm PVDF-TrFE (70:30 mol%) thin films were observed in relation to its ferroelectricity. The annealing temperatures were varied from solvent evaporation (Ts), Curies transition (Tc), up to melting temperature (Tm). It was found that the annealing process promoted the development of elongated crystallite structure also known as ferroelectric crystal, which significantly improved the ferroelectric properties of PVDF-TrFE (70:30 mol%) thin films. However, the presence of nanoscale separations on the thin film annealed over Tm (AN160) suggested high possibility of defects, and hence a reduction in ferroelectric properties of thin films.

Effect of various annealing temperature on the morphological and dielectric properties of Polyvinylidenefluoride-Trifluoroethylene thin film

The morphology of PVDF-TrFE (70/30) thin film at various annealing temperature were investigated using non-contact mode Atomic Force Microscopy (AFM). Differential Scanning Calorimetry (DSC) technique was used to obtain T_C, T_m, and T_Crys of PVDF-TrFE. The prepared spin coated PVDF-TrFE (70/30) thin films were annealed at T_C (113°C), T_m (154°C), T_Crys (135°C) and T_c at cooling (55°C) in accordance to the DSC thermogram observed. Impedance Spectroscopy were conducted to study the dielectric characteristic of the thin films in order to substantiate the electrical behavior of the thin films From the results obtained, the thin films exhibited different morphologies depending on the annealing temperatures utilized. Formation of needle-like crsytallite structure was observed film annealed at and over T_m. Thin film re-crystallized at T_C has an optimized dielectric constant of ~7.8 at 10⁴ hz.

Preparation of PVDF-TrFE layer-based bilayer composite PbTiO3/PVDF-TrFE films for MIM capacitor

The capacitor device has evolved from a simple device to an innovative and complex device. The capability of a capacitor is very much dependent on capacitance performance. Currently, researchers have shown interest in hybrid composites, which are capable of improving performance and increase reliability of devices. Thus, there is a need to fabricate thin films of hybrid dielectric materials such as polymer (PVDF-TrFE) and ceramic (PbTiO3). This study presents the preparation of the PVDF-TrFE layer for bilayer composite PbTiO3/PVDF-TrFE configured as metal–insulator–metal films capacitor. The deposition process utilised two methods: solvent casting and spin coating. The ceramic layer (first layer), PbTiO3, has optimum dielectric permittivity and tangent loss of about 138 and 0.9 taken at 1 kHz. The polymeric spin-coated layer (second layer) PVDF-TrFE films produced good dielectric property as compared to solvent casting prepared films. This provides an opportunity for further investigation of the dielectric property for enhanced understanding of capacitor-based devices.

Ferroelectric Properties of Polyvinylidenefluoride-Trifluoroethylene (PVDF-TrFE) Annealed Thin Film

The annealing temperature for 250nm PVDF-TrFE (70:30 mol %) spin coated thin films were varied at solvent evaporation (Ts = 79°C), Curies transition (Tc= 113°C) till melting temperature (Tm = 154°C). From the XRD measurement, there was an improvement in the crystallinity of the annealed films, consistent with the increased in the annealing temperatures. Morphological studies of the annealed PVDF-TrFE thin films as observed with Field Emission Scanning Electron Microscope (FESEM) (100k magnification), showed enhanced development of elongated crystallite structures better known as ferroelectric crystal. However, the AN160 thin film showed fibrous-like structure with appearance of nanoscale separations, which suggested to posed high possibility of defects. Ferroelectric characterization indicated an improvement in the remnant polarization of annealed PVDF-TrFE thin films with the exception to AN160 in which leakage of current was inevitable due to the presence of cracks on the film surface.