Insulator Materials Research Articles

Study on Influencing Factors of Insulators Flashover Characteristics on the 110 kV True Tower Under the Lightning Impulse

Lightning strike is the main reason for the transmission line tripping. Studies on the insulator flashover characteristics and the accurate flashover criteria under the lightning impulse are the basis for correctly evaluating the lightning resistance performance of the transmission line. In this paper, an experimental study on the flashover characteristics of the insulators with different materials was carried out on the 110-kV double-circuit transmission line tower. The insulators were hung on the umbrella-shaped tower and the drum-shaped tower in the test, and both the standard lightning impulse (1.2/ $50~\mu \text{s}$ ) and the short-tail lightning impulse (1/ $10~\mu \text{s}$ ) were used. The flashover test of a single composite insulator was also carried out for comparatively analyzing the influence of the true tower on the insulator flashover performance. According to the test results on the true tower, the lightning flashover criteria of the insulators with different materials are given. The influencing factors of the insulator flashover characteristics, including the impulse waveform, the insulator material, the tower type, and the insulator suspension position, were further compared and analyzed. Meanwhile, the results of the single insulator test proved that the true tower has great influence on the insulator flashover characteristics and that the flashover test on the true tower can reflect actual situation better and obtain more accurate results. In addition, based on the simulation analysis results of the electric-field distribution around the insulators, the difference of 50% impulse flashover voltage ( $U_{\mathrm {50\%}}$ ) of the insulators in different conditions was partly explained.

Investigating PMMA as a potential insulator material for metal-insulator-metal diode

The metal-insulator-metal (MIM) diodes are considered very promising for high frequency applications because of its tunnelling-based ultrafast charge transport mechanism. A wide variety of materials are being explored in quest of developing these thin film devices. Recently, organic insulator-based MIM diodes have attracted significant attention to the researchers due to its several advantages and have become a promising alternative of conventional inorganic insulators. In the present work the feasibility of an organic polymer polymethyl methacrylate (PMMA) is investigated for insulating material of MIM junction. It is a transparent resin which is able to produce uniform and thin insulating layer with low defect density. In this work, an Al/PMMA/Cr structure is fabricated by optimising different process parameters in order to develop high performance, reproducible organic MIM diodes. The as fabricated device exhibited fairly asymmetric and nonlinear current-voltage characteristics, which reveals the viability of PMMA as candidate material for insulator layer in MIM diodes.

Enhancement of field electron emission in topological insulator Bi2Se3 by Ni doping.

Nanostructures of bismuth selenide (Bi2Se3), a 3D topological insulator material, and nickel (Ni) doped Bi2Se3 samples were prepared by a hydrothermal method to explore the field emission properties. An enrichment in the field electron emission (FE) properties in terms of the threshold and turn-on field values of Bi2Se3 and Ni doped Bi2Se3 nanostructures was measured at a base pressure of ∼1 × 10-8 mbar. Using the background of the Fowler-Nordheim (FN) theory a field enhancement factor (β) of 5.7 × 103 and a threshold field value of 2.5 V μm-1 for 7.5% Ni doped Bi2Se3 were determined by investigating the J-E plot of the FE data. The value of β is three times higher than that of pure Bi2Se3 confirming the superior FE properties. The emission current was found to be very stable with the property of long standing durability as a negligible amount of variation was observed when measured at a constant value of 5 mA for 3 hours. The experimental results signify many opportunities for potential applications of Ni doped Bi2Se3 as a source of electrons in scanning as well as transmission electron microscopy, flat panel displays and as an X-ray generator, etc.

Effects of the TiO2 high-k insulator material on the electrical characteristics of GaAs based Schottky barrier diodes

The effects of the TiO2 high-k insulator material on Au/n-GaAs/Ti/Au Schottky barrier diodes have been studied by means of the numerical simulation and experimental results at room temperature. The Atlas-Silvaco-TCAD numerical simulator has been used to explain the behavior of different physical phenomena of Schottky diode. The experimental values of ideality factor, barrier height, and series resistance have been determined by using the various techniques such as Cheung’s method, forward bias lnI–V and reverse capacitance–voltage behaviors. The experimental ideality factor and barrier height values have been found to be 4.14 and 0.585 eV for Au/n-GaAs/Ti/Au Schottky barrier diode and 4.00 and 0.548 eV for that structure with 16 nm thick TiO2 film and 3.92, 0.556 eV with 100 nm thick TiO2 film. The diodes show a non-ideal current–voltage behavior that of the ideality factor so far from unity. The extraction of Nss interface distribution profile as a function of Ec–Ess is made using forward-bias I–V measurement by considering the bias dependence of ideality factor, the effective barrier height, and series resistance for Schottky barrier diodes. The Nss calculated values with consideration of the series resistance are lower than the calculated ones without series resistance. The current–voltage results of diodes reveal an abnormal increase in leakage current with an increase in thickness of high-k interfacial insulator layer. However, the simulation agrees in general with the experimental results.

Performance optimization of single-layer and double-layer high-k gate nanoscale ion-sensitive field-effect transistors

The use of high-k dielectric materials for the gate insulator of nanoscale Ion-Sensitive Field-Effect Transistor (ISFET) has been demonstrated to generally improve the ISFET performance. High-k gate insulator reduces the gate leakage current and increases the gate capacitance, which lead to higher trans-conductance and higher current sensitivity. The best high-k material for ISFET sensors is not simply the material of highest dielectric constant because high-k ISFET performance depends on many conflicting factors such as dissociation properties with electrolytes and linearity of voltage/current variation with pH change. In this work, a comparative simulation study is presented for six high-k gate insulators (Si3N4, Al2O3, ZrO2, Ta2O5, HfO2, and TiO2), along with SiO2 for comparison, for nanoscale ISFET sensors, comparing their sensitivity and linearity. The simulation tool used (NIST) is based on the numerical solution of nanoscale ballistic MOSFET equations along with Gouy-Chapman-Stern model equations. The study presents a guideline for the determination of the optimum insulator material and insulator thickness used for nanoscale ISFETs. The study included single-layer as well as double–layer insulators in which two layers of different dielectric materials are used.

Current Status and Future Trends of Photonic-Integrated FBG Interrogators

In this paper, we present an overview of the current efforts toward integration on chip of fiber Bragg grating (FBG) sensor interrogators. Different photonic-integration platforms are discussed, including monolithic planar lightwave circuit technology, silicon on insulator (SOI), indium phosphide, and gallium arsenide material platforms. Furthermore, various possible techniques for wavelength metering and methods for FBG multiplexing are discussed and compared in terms of resolution, dynamic performance, multiplexing capabilities, and reliability. The use of linear filters, array waveguide gratings (AWG) as multiple linear filters, and AWG-based centroid signal processing techniques are presented as well as interrogation techniques based on tunable microring resonators and Mach-Zehnder interferometers for phase sensitive detection. FBG sensor interrogation based on SOI platform using active and passive phase sensitive detection is also described, demonstrating specifically the potential of passive phase demodulation for high-speed dynamic strain measurements. This paper finally presents the challenges and perspectives of photonic integration to address the increasing requirements of several industrial applications.

Photo-oxidation-modulated refractive index in Bi2Te3 thin films

We report on an 800 nm femtosecond laser beam induced giant refractive index modulation and enhancement of near-infrared transparency in topological insulator material Bi2Te3 thin films. An ultrahigh refractive index of up to 5.9 was observed in the Bi2Te3 thin film in near-infrared frequency. The refractive index dramatically decreases by a factor of ~3 by an exposure to the 800 nm femtosecond laser beam. Simultaneously, the transmittance of the Bi2Te3 thin films markedly increases to ~96% in the near-infrared frequency. The Raman spectra provides strong evidences that the observed both refractive index modulation and transparency enhancement result from laser beam induced photooxidation effects in the Bi2Te3 thin films. The Bi2Te3 compound transfers into Bi2O3 and TeO2 under the laser beam illumination. These experimental results pave the way towards the design of various optical devices, such as near-infrared flat lenses, waveguide and holograms, based on topological insulator materials.

Ab-initio study of electronic and elastic properties of Mg(BH4)(NH2) complex hydride

Structural and electronic properties of complex hydride Mg(BH4)(NH2), applicable in hydrogen storage, were studied in framework of pseudopotential-density functional theory. This compound shows an indirect band gap of 4.95 eV which is categorized in insulator materials. The calculated total and partial density of states of this compound show that the hydrogen bonding in BH4 anion is mainly covalent and the hydrogen-hydrogen repulsion is more in anion BH4 than in anion NH2. The calculated bulk modulus from Birch-Murnaghan equation of state is in close agreement with that obtained from the elastic constants. The obtained bulk modulus (19.27 GPa) shows this compound is more ductile than binary and ternary hydrides and it does not have a brittle structure. Therefore, it is a good candidate for hydrogenation and dehydrogenation cycles. The stability of the structure in ambient pressure is also declared by calculating the elastic coefficients. However, the existence of elastic anisotropy in the compound demonstrates the less compressibility of it along the c axis than a and b axes. The small amount of Poisson ratio indicates that it is more stable against shear compared to common borohydrides. This point is important for hydride stability in hydrogenation and dehydrogenation cycles.

Assessing Local Structure Motifs Using Order Parameters for Motif Recognition, Interstitial Identification, and Diffusion Path Characterization

Structure-property relationships form the basis of many design rules in materials science, including synthesizability and long-term stability of catalysts, control of electrical and optoelectronic behavior in semiconductors as well as the capacity of and transport properties in cathode materials for rechargeable batteries. The immediate atomic environments (i.e., the first coordination shells) of a few atomic sites are often a key factor in achieving a desired property. Some of the most frequently encountered coordination patterns are tetrahedra, octahedra, body and face-centered cubic as well as hexagonal closed packed-like environments. Here, we showcase the usefulness of local order parameters to identify these basic structural motifs in inorganic solid materials by developing classification criteria. We introduce a systematic testing framework, the Einstein crystal test rig, that probes the response of order parameters to distortions in perfect motifs to validate our approach. Subsequently, we highlight three important application cases. First, we map basic crystal structure information of a large materials database in an intuitive manner by screening the Materials Project (MP) database (61,422 compounds) for element-specific motif distributions. Second, we use the structure-motif recognition capabilities to automatically find interstitials in metals, semiconductor, and insulator materials. Our Interstitialcy Finding Tool (InFiT) facilitates high-throughput screenings of defect properties. Third, the order parameters are reliable and compact quantitative structure descriptors for characterizing diffusion hops of intercalants as our example of magnesium in MnO2-spinel indicates. Finally, the tools developed in our work are readily and freely available as software implementations in the pymatgen library, and we expect them to be further applied to machine-learning approaches for emerging applications in materials science.

Signal enhancement due to high-Z nanofilm electrodes in parallel plate ionization chambers with variable microgaps.

We developed a method for measuring signal enhancement produced by high-Z nanofilm electrodes in parallel plate ionization chambers with variable thickness microgaps. We used a laboratory-made variable gap parallel plate ionization chamber with nanofilm electrodes made of aluminum-aluminum (Al-Al) and aluminum-tantalum (Al-Ta). The electrodes were evaporated on 1mm thick glass substrates. The interelectrode air gap was varied from 3μm to 1cm. The gap size was measured using a digital micrometer and it was confirmed by capacitance measurements. The electric field in the chamber was kept between 0.1kV/cm and 1kV/cm for all the gap sizes by applying appropriate compensating voltages. The chamber was exposed to 120kVp X-rays. The current was measured using a commercial data acquisition system with temporal resolution of 600Hz. In addition, radiation transport simulations were carried out to characterize the dose, D(x), high-energy electron current, J(x), and deposited charge, Q(x), as a function of distance, x, from the electrodes. A deterministic method was selected over Monte Carlo due to its ability to produce results with 10nm spatial resolution without stochastic uncertainties. Experimental signal enhancement ratio, SER(G) which we defined as the ratio of signal for Al-air-Ta to signal for Al-air-Al for each gap size, was compared to computations. The individual contributions of dose, electron current, and charge deposition to the signal enhancement were determined. Experimental signals matched computed data for all gap sizes after accounting for several contributions to the signal: (a) charge carrier generated via ionization due to the energy deposited in the air gap, D(x); (b) high-energy electron current, J(x), leaking from high-Z electrode (Ta) toward low-Z electrode (Al); (c) deposited charge in the air gap, Q(x); and (d) the decreased collection efficiency for large gaps (>~500μm). Q(x) accounts for the electrons below 100eV, which are regarded as stopped by the radiation transport code but which can move and form electron current in small gaps (<100μm). While the total energy deposited in the air gap increases with gap size for both samples, the average high-energy current and deposited charge are moderately decreasing with the air gap. When gap sizes are smaller than ~20μm, the contribution to signal from dose approaches zero while contributions from high-energy current and deposited charges give rise to an offset signal. The measured signal enhancement ratio (SER) was 40.0±5.0for the 3μm gap and rapidly decreasing with gap size down to 9.9±1.2 for the 21μm gap and to 6.6±0.3 for the 100μm gap. The uncertainties in SER were mostly due to uncertainties in gap size and data acquisition system. We developed an experimental method to determine the signal enhancement due to high-Z nanolayers in parallel plate ionization chambers with micrometer spatial resolution. As the water-equivalent thicknesses of these air gaps are 3nm to 10μm, the method may also be applicable for nanoscopic spatial resolution of other gap materials. The method may be extended to solid insulator materials with low Z.

Formulation of a composite of date palm wood‐cement

This work reports the results of an experimental study on the incorporation of woodwaste date palm reduced in particles for the manufacture of wood – cement composites. Thesematerials are chipper than the conventional insulator material and environmental friendly. Fivetypes of wood – cement composites with various concentrations of the wood particles, ie. 2, 4, 6, 8and 10% of total volume, were made according to defined protocol and mix design. Their thermaland mechanical properties were measured and compared to other conventional materials. Theobtained results show that the thermal conductivity is positively correlated to the content ofparticles in the mixture. The compressive strength of composites decreases where the content ofparticles increase. However, taking account of the ASTM C 109 / C109‐95 standard, the wood –cement composite contained 10% of wood particles, considered as lightweight concrete, could beused as non‐structural material in construction.

Investigation of Environmental Conditions Using Artificial Polluted Conditions for Selection of Insulator Material

The aim of this research is to find out suitable material for insulator and their flashover performance to withstand the high pollution degree in different environmental conditions. The experimental investigation was carried out on various insulating material like porcelain, glass, and rubber to find out the artificial effluence to examine alternate current flashover potentials. The result shows that the polluted flashover voltage is affected by equivalent salt deposit density and non soluble deposit density, the authorities of which are autonomous of each one on another. The correction formulae of the flashover voltage of various insulators at various salt deposit density and non soluble deposit density levels have pointed out by means of the flashover voltages examination. Also the dissimilarity existing between the flashover voltages of various types of polluted insulators. From this we are able to conclude which insulating material withstands the pollution degree better amongst the above three.

Chemical Intercalation of Topological Insulator Grid Nanostructures for High-Performance Transparent Electrodes.

2D layered nanomaterials with strong covalent bonding within layers and weak van der Waals' interactions between layers have attracted tremendous interest in recent years. Layered Bi2 Se3 is a representative topological insulator material in this family, which holds promise for exploration of the fundamental physics and practical applications such as transparent electrode. Here, a simultaneous enhancement of optical transmittancy and electrical conductivity in Bi2 Se3 grid electrodes by copper-atom intercalation is presented. These Cu-intercalated 2D Bi2 Se3 electrodes exhibit high uniformity over large area and excellent stabilities to environmental perturbations, such as UV light, thermal fluctuation, and mechanical distortion. Remarkably, by intercalating a high density of copper atoms, the electrical and optical performance of Bi2 Se3 grid electrodes is greatly improved from 900 Ω sq-1 , 68% to 300 Ω sq-1 , 82% in the visible range; with better performance of 300 Ω sq-1 , 91% achieved in the near-infrared region. These unique properties of Cu-intercalated topological insulator grid nanostructures may boost their potential applications in high-performance optoelectronics, especially for infrared optoelectronic devices.

Tunable spin-polarized edge transport in inverted quantum-well junctions

Inverted HgTe/CdTe quantum wells have been used as a platform for the realization of 2D topological insulators, bulk insulator materials with spin-helical metallic edges states protected by time-reversal symmetry. This work investigates the spectrum and the charge transport in HgTe/CdTe quantum well junctions both in the topological regime and in the absence of time-reversal symmetry. We model the system using the BHZ effective Hamiltonian and compute the transport properties using recursive Green's functions with a finite differences' method. Specifically, we have studied the material's spatially-resolved conductance in a set-up with a gated central region, forming monopolar (n-n$^{\prime}$-n) and heteropolar (n-p-n, n-TI-n) double junctions, which have been recently realized in experiments. We find regimes in which the edge states carry spin-polarized currents in the central region even in the presence of a small magnetic field, which breaks TRS. More interestingly, the conductance displays spin-dependent, Fabry-Per\'ot-like oscillations as a function of the central gate voltage producing tunable, fully spin-polarized currents through the device.

Evaluation of calcium oxide in Rhodamine 6G photodegradation

The effect of the thermal decomposition of calcium hydroxide, in the 500–800°C range, for CaO production was studied. The produced materials were characterized by X-ray powder diffraction, thermogravimetric analysis, N2 adsorption-desorption at −196°C, Scanning Electron Microscopy and Diffuse Reflectance Spectroscopy. The produced materials were evaluated in Rhodamine 6G (Rh6G) photodegradation and the effect of annealing temperature, catalyst amount and Rh6G concentration were determined.It was evidenced by the X-ray diffraction analysis that upon annealing an average crystal size was achieved which was in accordance with the Scanning Electron Microscopy and specific surface area results. The badgap values of the samples (5.35–5.53eV) corroborated their insulator nature. Materials evaluation indicated CaO produced at 700°C was the most active material. Samples were taken after adsorption and the photocatalytic reaction, respectively; indicating that CaO was not the effective active phase but Ca(OH)2. Being both CaO and Ca(OH)2 insulator materials, the photocatalytic activity was attributed to an indirect dye sensitization.

Geometric effect in a vertical stack-up metal-insulator-metal tunnel diode

The geometric effect was investigated in a vertically designed metal-insulator-metal (MIM) tunnel diode for which a narrow tunneling distance can be controlled easily and reliably, with the goal of enhancing rectifying efficiency, based on the angle of a pointed shape electrode and various thicknesses of insulator material. Although MIM tunneling diodes can provide ultra- high working speeds (&amp;gt;THz), the very low contrast ratio between forward and reverse currents results in poor rectifying efficiency. An asymmetric geometry design with two metal electrodes can be an effective approach for enhancing the contrast ratio between the tunneling currents. Using a sharp electrode with a pointed shape, it was determined that the rectifying efficiency and tunneling probability could be increased impressively depending on the angle of the pointed shape of the electrode. Moreover, the selection of insulation material was also important for improving efficiency. Although the band gap of Al2O3 is larger than that of HfO2, the rectifying efficiency was significantly improved by blocking reverse current well. In general, large band gap insulator materials are inappropriate for a tunneling device, due to the low tunneling current. However, in our approach, since the issue of low tunneling probability is compensated by the sharp tip structure, the larger band gap insulator produced better rectifying efficiency with the appropriate current density. The results of this study demonstrated that geometric design could be a possible solution to increase rectifying efficiency. If the geometric effect in the tunneling diode structures will be optimized more, it can improve the applicability of vertical stack-up MIM tunnel diode to THz switching devices, tunneling transistors and ultra-high speed electronics.

Electrical Properties of Solution-Processed Nanolaminates of ZrO2 and Al2O3 as Gate Insulator Materials for Thin-Film Transistors

Electrical Properties of Solution-Processed Nanolaminates of ZrO₂ and Al₂O₃ as Gate Insulator Materials for Thin-Film Transistors

Experimental study on surface properties of the PMMA used in high power spark gaps

This paper studies the surface properties of the Polymethylmethacrylate (PMMA) insulator samples used in high power spark gaps. Experiments on surface morphology, surface profile, surface chemical composition and surface leakage current were performed. Metal particles ejected in tangent direction of discharge spots were researched on the sample surface. Three kinds of distinct bands were found on the surface after 1500 shots: colorless and transparent sinking band, black band, and grey powdered coating band. The thickness of the coating band was tens of microns and the maximum radial erosion rate was about 10 μm/C. Surface content analysis indicated that the powdered coating was a mixture of decomposed insulator material and electrode material oxides. In addition, leakage current significantly depended on water content in the chamber and presented an U-shape curve distribution along the insulator surface, in keeping with the amount of powdered coating due to shock waves. Possible reasons of the surface property changes were discussed. Electroconductive oxides of low valence states of Cu and W produced by the reactions between electrode materials and arc plasmas were considered to be the cause of dielectric performance degradation.

Outstanding Performance as Cu Top Gate IGZO TFT With Large Trans‐Conductance Coefficient by Adopting Double‐Layered Al2O3/SiNx Gate Insulator

Gate insulator (GI) materials in top gate structured InGaZnO thin‐film transistor (TFT) with copper gate electrode are examined for the application to the large area display. To overcome the problems with hydrogen diffusion, which can influence the number of carriers in oxide semiconductor and to gain large trans‐conductance coefficient, a double‐layered GI of 30 nm Al2O3/120 nm SiNxis adopted. The TFT showed field‐effect mobility, Von, SS, and hysteresis of 12.8 cm2 V−1 s−1, −0.7 V, 0.17 V decade−1, and almost 0 V, respectively, and the ΔVon under the positive bias stress of 20 V and negative bias stress of −20 V at 60 C for 10 000 s are +0.1 and −0.4 V, respectively.

Incorporation of Lead Containing TV Tube Glass Waste in Aluminous Porcelain

The aim of this work was to study the incorporation of lead containing TV tube glass waste as a method to provide alternative raw material for aluminous electrical porcelain. For this purpose, aluminous porcelain formulations containing up to 30 wt.% of TV tube glass waste as a replacement for traditional flux material (sodium feldspar) were pressed and fired in air at 1300 oC using a fast-firing cycle (< 60 min). X-ray diffraction (XRD), scanning electron microscopy (SEM), linear shrinkage, apparent density, water absorption, and electrical resistivity have been carried out. The results indicated that the aluminous porcelain pieces containing up to 30 wt.% of TV tube glass waste rich in PbO with water absorption between 0.42 and 0.45% and volume electrical resistivity between 1.91 and 2.93 x 1011 Ω.cm have high potential to work as electrical insulator material. This use of lead containing TV tube glass waste can contribute greatly to reducing the environmental impacts related to it, and also save the sources of non-renewable raw materials used in the electrical porcelain sector.