Permittivity Of Films Research Articles

Highly Porous Particles of Cellulose Derivatives for Advanced Applications.

A chemical modification of cellulose diacetate by phthalate and nitrate was performed to increase solubility in organic solvents and change the electrical properties. The role of substituents on the conductivity, permittivity, and polarizability of cellulose films is revealed. It has been shown that highly porous micro particles can be obtained from cellulose derivatives by a simple and technological freeze-drying method. The resulting micro sized aerogels have a predominantly spherical morphology and amorphous structure. Suspensions of porous particles of nitro- and phthalylated cellulose derivatives in silicone oil have an increased dielectric permittivity compared to cellulose diacetate particles. Produced particles are novel promising material with tunable electrical properties for advanced applications in composites, including for electrorheological fluids.

Tunable thermal conductivity of surface phonon polaritons in SiC thin film

As an additional heat carrier besides phonons and electrons, the surface phonon polariton (SPhPs) possesses a large potential to increase the thermal conductivity. In this work, the influences of SPhP frequency, film thickness and film permittivity on the SPhP-contributed thermal conductivity of SiC thin films were probed. Results show that: there are two frequency zones which could lead to a much high thermal conductivity, i. e. the frequency which approaching zero and the frequency in singularity zone. The thermal conductivity decreases with the increase of the film thickness, following a power-function relationship, and a thin film with a thickness of 10-nm could have a thermal conductivity higher than 1×104 W·m−1·K−1. However, the experimental observation of this high thermal conductivity is still difficult because of the size effect of the film length. The thermal conductivity will increase with the decrease of the imaginary part of the film permittivity and/or increase of the real part of the film permittivity, and there is approximately a reciprocal dependence of thermal conductivity on the imaginary part of the film permittivity. The thermal conductivity could be tuned by several times with tailoring its permittivity through adding fillers in it or adding dopant in it. This work provides some potential methods to tune the SPhP thermal conductivity in SiC thin film, which could help its application in microscale heat dissipation.

Ferromagnetic semiconductor EuO thin films characterized by vacuum electrochemical process with ionic liquid

In this study, the electrochemical impedance analysis was demonstrated for thin film EuO, a ferromagnetic semiconductor, by taking the advantage of our original instrument, which enables to perform the entire process from thin film deposition to electrochemical measurement with ionic liquid in a vacuum. Effects of whether surface protecting layers were insulative or metallic, as well as their thickness on the electrochemical measurement of EuO thin films were examined by comparing the choices of amorphous alumina and Ag metal as the protecting layer. As a result, the relative permittivity of EuO films, even with a thickness of 2 nm, was successfully estimated and the averaged value was 6.6 within an error of 10 %. Furthermore, the donor density accordingly estimated was found well correlated with the Curie temperature TC of the EuO films.

A novel double-gate trench SOI LDMOS with double-dielectric material by TCAD simulation study

In this paper, a novel double-gate trench silicon-on-insulator lateral double-diffused metal oxide semiconductor field-effect transistor (LDMOS) with double-dielectric material (DGDK-LDMOS) is proposed. DGDK-LDMOS has two dielectric materials: a reverse-L-shaped high-k (HK) thin film and an low-k (LK) buried oxide layer. The HK thin film optimizes the electric field distribution on the drift region surface, attracting electric flux, and the excellent withstand voltage of the LK buried oxide layer can significantly improve the breakdown voltage (BV) and reduce specific on-resistance (R on,sp) of the device. The modulation mechanism of LDMOS by HK thin film and LK buried oxide layer is analyzed. The results show that compared with conventional LDMOS, when the permittivity of HK thin film is 25 and the permittivity of LK buried oxide is 3, the BV of DGDK-LDMOS is increased by 89.6%, the R on,sp is decreased by 26.4%, and the figure of merit (FOM, FOM = BV2/R on,sp) is increased by 397.2% from 3.6 MW cm−2 to 17.9 MW cm−2. Meanwhile, the output characteristics, transfer characteristics, lattice temperature, AC characteristics and switching characteristics of DGDK-LDMOS are also discussed and compared.

Dielectric Characterization of H2O and CO2 Uptake by Polyethylenimine Films.

The absorption of CO2 by polyethylenimine polymer (PEI) materials is of great interest in connection with proposed carbon capture technologies, and the successful development of this technology requires testing methods quantifying the amount of CO2, H2O, and reaction byproducts under operating conditions. We anticipate that dielectric measurements have the potential for quantifying both the extent of CO2 and H2O absorption within the PEI matrix material as well as insights into subsequent reaction byproducts that can be expected to occur in the presence of moisture. The complexity of the chemistry involved in this reactive binding process clearly points to the need for the use of additional spectroscopic techniques to better resolve the multiple components involved and to validate the model-dependent findings from the dielectric measurements. Here, we employed noncontact resonant microwave cavity instrumentation operating at 7.435 GHz that allows for the precise determination of the complex dielectric permittivity of CO2 films exposed to atmospheres of controlled relative humidity (RH), and N2:CO2 compositions. We find that the addition of CO2 leads to a considerable increase in dielectric loss of the PEI film relative to loss measured in nitrogen (N2) atmosphere across the same RH range. We attribute this effect to a reaction between CO2 and PEI generating a charged dielectrically active species contributing to the dielectric loss in the presence of moisture. Possible reaction mechanisms accounting for these observations are discussed, including the formation of carbamate-ammonium pairs and ammonium cations stabilized by bicarbonate anions that have sufficient local mobility to be dielectrically active in the investigated microwave frequency range. Understanding of these reaction mechanisms and the development of tools to quantify the amount of reactive byproducts are expected to be critical for the design and optimization of carbon capture materials.

Design and synthesis of low‐dieclectric polyaryl ethers containing bulky tetraphenyl vinyl pendant group

AbstractA tetraphenylethylene‐containing bisphenol monomer 5‐[4‐(triphenylvinyl)phenyl]benzene‐1,3‐diol (TPE‐OH) was designed and synthesized by Suzuki coupling and nucleophilic substitution reaction. By adjusting the proportion of TPE‐OH, a series of rigid polyaryl ether, namely PPTES, were facilely synthesized by homopolymerization or copolymerization with 4‐(4‐hydroxyphenyl)‐2,3‐diazepine‐1‐one (DHPZ) and 4,4′‐difluorodiphenyl sulfone (DFS). The following characterization of their structures with nuclear magnetic resonance and infrared spectroscopy confirmed successful synthesis of both monomers and polymers. Large, volume‐twisted and non‐coplanar rigid tetraphenylethylene could effectively increase the molecular chain spacing and reduce the regularity of the molecular chain, as evidenced by molecular dynamics simulation with Materials Studio, in turn to form an amorphous nature of PPTES phase state. In addition, such PPTESs have excellent solubility, heat resistance, and other comprehensive properties. Their glass transition temperature (Tg) is between 219 and 300°C, and the 5% thermogravimetric temperature of PPTESs locates at 490–539°C under N2 atmosphere. At 1 GHz, the intrinsic dielectric permittivity of polymer films is between 2.32 and 2.61, gradually decreases with TPE‐OH content. This work would provide new idea and choice for the selection of polyaryl ether resin bisphenol monomer, and promote the development and application of low‐dielectric polyarylether materials.

Explaining the thickness-dependent dielectric permittivity of thin films

Explaining the thickness-dependent dielectric permittivity of thin films

Tailoring dielectric permittivity of epitaxial Gd-doped CeO2−x films by ionic defects

Engineering materials with highly tunable physical properties in response to external stimuli is a cornerstone strategy for advancing energy technology. Among various approaches, engineering ionic defects and understanding their roles are essential in tailoring emergent material properties and functionalities. Here, we demonstrate an effective approach for creating and controlling ionic defects (oxygen vacancies) in epitaxial Gd-doped CeO2−x (CGO)(001) films grown on Nb:SrTiO3(001) single crystal. Our results exhibit a significant limitation in the formation of excess oxygen vacancies in the films during high-temperature film growth. However, we have discovered that managing the oxygen vacancies in the epitaxial CGO(001) films is feasible using a two-step film growth process. Subsequently, our findings show that manipulating excess oxygen vacancies is a key to the emergence of giant apparent dielectric permittivity (e.g. ε′ ≈ 106) in the epitaxial films under electrical field control. Overall, the strategy of tuning functional ionic defects in CGO and similar oxides is beneficial for various applications such as electromechanical, sensing, and energy storage applications.

High frequency permittivity of rare-earth Er-doped MoS2 films

Two-dimensional (2D) MoS2 has attracted considerable attention for their significant potential application in high-frequency electronic devices. In this work, erbium doped MoS2 (Er:MoS2) film is prepared by chemical vapor deposition. The structures and binding energy are studied by X-ray photoelectron spectroscopy indicating the substitution of Er atoms into MoS2 lattices. The complex permittivity of the film is measured by the microstrip line up to the frequency of 4 GHz. The high frequency permittivity ε′ of MoS2 film is 4.11 and ε′ increases about 28% when the Er doping amount is 0.83 at% (atomic percentage). The permittivity of Er:MoS2 film is higher than that of MoS2 film, which is mainly due to the enhanced polarization of Er:MoS2 film. The permittivity ε′ of Er:MoS2 film increases with the increase of Er doping (0∼0.83 at%). It is believed that Er:MoS2 film has great potential application in tunable electromagnetic devices.

An Adaptation of the Split-Cylinder Resonator Method for Measuring the Microwave Properties of Thin Ferroelectric Films in a “Thin Film—Substrate” Structure

The split-cylinder resonator method was adapted to measure the microwave properties (dielectric permittivity and loss tangent) of thin ferroelectric films on a dielectric substrate. The mathematical model for calculating the resonance frequency of the split-cylinder resonator was adjusted for the “ferroelectric film—substrate” structure. An approach for correcting the gap effect based on calibrating with a single-layer dielectric was introduced and used to study two-layer dielectrics. The prototype of a split-cylinder resonator designed to measure single-layer dielectric plates at a frequency of 10 GHz was presented. The resonator calibration was performed using dielectric PTFE samples and fused silica, and an example of the correction function was suggested. The measurement error was estimated, and recommendations on the acceptable parameter range for the material under investigation were provided. The method was demonstrated to measure the microwave properties of a ferroelectric film on a fused silica substrate.

Terahertz dielectric properties of Fe3O4 thin films deposited on Si (100) substrate

Fe3O4 is considered to be a promising material for terahertz spintronic applications as well as for stealth technology. However, the optical properties of Fe3O4 in the thin film form at terahertz frequencies are not reported in literature. In this article, we present the frequency and temperature dependence of dielectric permittivity (ε 1) and optical conductivity (σ 1) of Fe3O4 films deposited on Si substrate. The σ 1 of these films show absorption peaks related to charge localization and shallow impurities. It is also observed that the Fe2O3/Fe3O4 composite films have large σ 1 and ε 1 indicating their potential use for stealth technology applications. The overall optical properties are found to depend strongly on the microstructure and defects, such as, the grain size and the presence of grain boundaries, anti-phase boundaries, strain disorder due to lattice mismatch and/or the Fe+2/Fe+3 ratio.

Estimation of Permittivity of Films Using the Free-Space Measurement Method at Ka-Band

Estimation of Permittivity of Films Using the Free-Space Measurement Method at Ka-Band

Perovskite stannate La-doped BaSnO3 films for near- and mid-infrared plasmonic applications

La-doped BaSnO3 (LBSO) epitaxial thin films were grown on (001) MgO substrates by pulsed laser deposition using a La0.04Ba0.96SnO3 target. The structural, electrical, and optical properties of the LBSO films were investigated as a function of oxygen pressure during deposition. The carrier mobility can be tuned from 13 cm2V−1s−1 to 44 cm2V−1s−1 by varying oxygen partial pressure from 2 Pa to 12 Pa, respectively. This improved mobility is attributed to the reduced film strain via reducing oxygen defect concentration or reducing off-stoichiometry in the film. The optical permittivity of LBSO films can also be modified as a function of the oxygen pressure during deposition, allowing tuning of their epsilon-near-zero wavelength from 1.9 µm to 5.6 µm. These results demonstrate that LBSO thin films grown on MgO can be used for plasmonic devices at mid-wave infrared wavelengths.

Size effects of polydopamine-coated BaTiO3 nanoparticles on the piezoelectric performance of P(VDF-TrFE)/BaTiO3 composite

The size effect of the polydopamine (PDA)-coated BaTiO3 (BTO) (BTO@PDA) nanoparticles (NPs) on the interfacial compatibility between BTO NPs and the polymer matrix and the resultant piezoelectric performance of the composite films remain elusive. In this study, BTO and BTO@PDA NPs of various sizes were incorporated into a P(VDF-TrFE) matrix to prepare two series of P(VDF-TrFE)/BTO and P(VDF-TrFE)/BTO@PDA composites. Subsequently, the effects of the NP size on the dielectric, ferroelectric, and piezoelectric properties of the composite films were comprehensively studied. As the size of the BTO@PDA NPs increased, residual hole defects were clearly observed in the cross section of the composite film. The deteriorated interfacial compatibility due to the large size of the BTO@PDA NPs was also confirmed by the increased dielectric permittivity of the composite film, which was induced by the intensified interfacial polarisation. The P(VDF-TrFE)/BTO@PDA composite with NPs of the smallest size (100 nm) exhibited superior piezoelectric performance owing to the excellent interfacial compatibility between the fillers and the matrix. The piezoelectric performance was significantly enhanced by the reduced leakage current during electrical poling and reduced trap charges. Finally, the pulse waveform originating from the radial artery was precisely measured using the optimised P(VDF-TrFE)/BTO@PDA composite film.

High frequency characterization of PZT thin-films deposited by chemical solution deposition on SOI for integrated high speed electro-optic modulators

The increasing demand for high data rates and low power consumption puts silicon photonics at the edge of its capabilities. The heterogeneous integration of optical ferro-electric materials on silicon enhances the functionality of the silicon on insulator (SOI) platform to meet these demands. Lead zirconate titanate (PZT) thin films with a large Pockels coefficient and good optical quality can be directly integrated on SOI waveguides for fast electro-optic modulators. In this work, the relative permittivity and dielectric loss of PZT thin films deposited by chemical solution deposition on SOI substrates are analyzed at high frequencies. We extract ε r =1650−2129 and tan (δ) = 0.170 − 0.209 for the PZT thin films in the frequency range 1-67GHz. We show the possibility of achieving bandwidths beyond 60GHz via a Mach-Zehnder modulator with V π = 7V, suitable for next generation data communication systems.

Large-scale fabrication and performance improvement of polyvinylidene fluoride piezoelectric composite films

Sensing applications such as wearable electronics, electronic skin, and soft robotics using flexible piezoelectric films have received extensive attention. In this study, we fabricate large-scale 0–3 type composite films of polyvinylidene fluoride (PVDF)-doped modified lead zirconate titanate (PZT) particles (PZT@UP) through an extrusion-casting process to enhance piezoelectric properties and explain the piezoelectric performance mechanism. The introduction of PZT@UP particles improved the dielectric permittivity of the composite films and promoted the polarization of PVDF, which positively affected the piezoelectric properties of PVDF/PZT@UP films. The composite film with 25 wt% PZT@UP possessed an excellent piezoelectric coefficient (d33) of 29 pC/N, which was 93% higher than that of neat PVDF (15 pC/N). Moreover, the addition of PZT@UP particles effectively inhibited the movement of PVDF molecular chains and improved the mechanical modulus stability of the composite films. The law of electrostrictive effect of the PVDF/PZT@UP composite films is clarified from the aspects of the movement of PVDF molecular chains, the principle of electric field distribution, and the construction of the internal electric field. Further, the similarities and differences between the piezoelectric and electrostrictive mechanisms of the PVDF/PZT@UP composite films are summarized. The extrusion-casting process combined with modified fillers shows promising potential in improving wear and tear of and electricity generation from PVDF-based composite films, leading to a profound impact on the development of large-scale fabrication of piezoelectric sensors.

Disordering of Starch Films as a Factor Influencing the Release Rate of Biologically Active Substances.

The release of a spin probe (nitroxide radical) from polymer films was studied by electron paramagnetic resonance (EPR). The films were fabricated from starch having different crystal structures (A-, B-, and C-types) and disordering degrees. Film morphology (analysis of the scanning electron microscopy (SEM)) depended on the presence of dopant (nitroxide radical) to a larger extent rather than on crystal structure ordering or polymorphic modification. The presence of nitroxide radical led to additional crystal structure disordering and reduced the crystallinity index from the X-ray diffraction (XRD) data. Polymeric films made of amorphized starch powder were able to undergo recrystallization (crystal structure rearrangement), which manifested itself as an increase in crystallinity index and phase transition of the A- and C-type crystal structures to the B-type one. It was demonstrated that nitroxide radical does not form an individual phase during film preparation. According to the EPR data, local permittivity of starch-based films varied from 52.5 to 60.1 F/m, while bulk permittivity did not exceed 17 F/m, which demonstrates that local concentration of water is increased in the regions near the nitroxide radical. The mobility of the spin probe corresponds to small stochastic librations and is indicative of the strongly a mobilized state. The application of kinetic models made it possible to find out that substance release from biodegradable films consists of two stages: matrix swelling and spin probe diffusion through the matrix. Investigation of the release kinetics for nitroxide radical demonstrated that the course of this process depends on the type of crystal structure of native starch.

Numerical evaluation of an external environment effectiveness to the surface plasmon mode in Au slot waveguide for design the sensor simulation

The effective permittivity of gold thin films with an external thin dielectric layer on the top and core of the slot waveguide was evaluated as an effective compound semi-metal layer of the surface plasmonic polariton slot waveguide that will vary due to some environmental factors. By uses simple parallel and series permittivity of compound material, this value need for the computation of the effective propagating vector βsp. This takes for a sensor model designing which the external environment effectiveness was changed by the surface plasmonic mode in its slot waveguide. So the resonance length and grating period are evaluated for the sensor model in the first. Further, the propagation of the SPP surface wave mode along the interface between the compound cladding and Si dielectric waveguide is computed, while the effective refractive index of the compound cladding of the slot waveguide is increased from 1 − 1.50. The computation results showed that the TM0 mode power transfer and propagation length seem to vary with this effective refractive index of the compound cladding on the surface plasmonic polariton waveguide. The 140 nm gap width and 3.70 mm long waveguide is also simulated by the finite different time domain method in the optiwave program, where the TM0 mode transition output is corrected, while the refractive index of the environment layer is changed. The results of the simulation showed good agreement with the computation in that the TM0 mode depends on the external refractive of index and input wavelength. This result shows that loss peak ships vary with the external refractive index thin film layer and input wavelength. Thus, they seem to be useful for sensor applications such as the solution concentration analytic.

Enhancing the output of triboelectric nanogenerator by embedding SrTiO3 nanoparticles into polydimethylsiloxane films

To improve the output power of polydimethylsiloxane (PDMS)-based triboelectric nanogenerators (TENGs), SrTiO3 (STO), which is a high-k material, nanoparticles (NPs) was embedded into the PDMS films because the relative permittivity of triboelectric films is proportional to the output power. The STO NPs/PDMS composite films showed a maximum output power density of approximately 3.6 W m−2 at the content of the STO NPs of 20 vol%. To further boost the output power, we measured the output power at a contact/separation tapping frequency of 5 Hz. The maximum output power density was approximately 32.4 W m−2. This method is expected to be applicable to various material combinations for TENGs.

Laser sintering of electrophoretically deposited Si2N2O radiative cooling films for densification and its potential application in low-k and passive thermoelectric devices

In this study, Si2N2O films were prepared from a Si2N2O suspension via pulsed electrophoretic deposition. The resulting Si2N2O electrophoretically deposited films were sintered by applying laser irradiation at a wavelength of 460 nm. Laser sintering caused the film to shrink by approximately 60% in the direction normal to the substrate. The cooling capacity of the laser-sintered film was approximately 1.5 times higher than that of the electrophoretically deposited film, and the temperature of the former was 1.2 °C lower than that of a reference device at an ambient temperature of 90 °C. The relative permittivity of the laser-sintered Si2N2O film was in the range of 7–8, indicating its potential application to the development of low-k radiative cooling devices. We fabricated a device that combined a laser-sintered Si2N2O film with a Peltier element. This device was observed to have an electromotive force of 0.286–0.727 mV in an ambient temperature range of 30–90 °C. The thermoelectromotive force generated by this composite device suggests the possibility of passive power generation.