Surface Of Dielectric Material Research Articles

Substrate surface processing in gas vacuum arc discharge

Problem. Preparation of the surface before the deposition of vacuum arc coatings is of great importance, as it affects not only the adhesive properties of the obtained coatings, but also the physical and mechanical properties of the substrate surface layer. The processes of ions interaction with the substrate surface during its ionic cleaning, before the deposition of coatings, have been relatively little studied and are almost not described in the literature. Goal. In this work, some of their features are considered in relation to the surface preparation of materials before the deposition of vacuum arc coatings. Methodology. The nature of the plasma interaction with the substrate material is determined by the ions energy and their flow density, other things being equal. The energy of the ions treating the substrate consists of their initial energy and the energy acquired in the Debye layer adjacent to the substrate when a negative potential is applied to it. The value of the potential at which the processes of condensation or sputtering are balanced is determined mainly by the nature of the vaporized material. When the value of the substrate potential increases, the deposited particles and its material are sputtered. At the same time, atoms on the substrate that are weakly connected to it, various impurities are removed, substrate temperature increases, especially in its surface layers. Results. The work investigates the influence of various metals and gases used to clean the surface of substrates made of cubic boron nitride PcBN and steels on the surface morphology. It was established that the use of gases (argon, nitrogen) for cleaning the surface of dielectric materials, in particular PcBN, showed the best results, which subsequently leads to an increase in the adhesion of the vacuum arc coating to the substrate. Practical value. The obtained results of investigation are of great practical importance. They can be used for the increasing of tool life and productivity of mechanical engineering.

Nano-TiO2/MWCNT composite coating with high DC flashover strength and super hydrophobicity

Epoxy resin (EP) materials are frequently used in high voltage power equipment because of their excellent electricity, force, and heat properties. However, under the condition of DC high voltage, the surface of EP insulation material is more likely to accumulate charge, which distorts the nearby electric field and causes flashover along the surface. In this article, a nanocomposite coating was prepared by spraying through the nanoparticles (TiO2 with carbon nanotubes) dispersed in the polydimethylsiloxane (PDMS) elastomers solution. Micro-nano porous structures are introduced in the spraying process, which hinders the development of collision ionization and increases the flashover strength of the coating. At the same time, the change in surface morphology makes the hydrophobic properties of the coating improve and enhances the anti-icing and anti-fouling capacity. Spraying nano filler provides a general method for improving hydrophobicity and flashover strength.

INCREASING THE ACCURACY OF DETERMINING THE WORKING PARAMETERS OF THE RIBBON-SHAPED ELECTRONIC FLOW IN THE ELECTRON-BEAM MICRO-PROCESSING OF DIELECTRICS

The article shows the possibility of increasing the accuracy of determining the operating parameters of the ribbon-shaped electron flow during electron beam micromachining of dielectric materials in a vacuum (using the example of Kp0 grade polycrystalline silicon and K8 grade optical glass) as a result of the analysis and selection of the most acceptable energy modes of operation of the Pierce wire electron-beam gun. The purpose of the work is to study the influence of the volt-current characteristics of the Pierce wire electron-beam gun on the quality and repeatability of the process of processing dielectric materials with a ribbon-shaped electron flow, which allows choosing the most rational modes of determining the operating parameters of the electron flow with higher accuracy.
 The paper proposes a technological experiment on electron-beam micromachining of dielectric surfaces, as well as defined and investigated the working parameters of the process of such processing, depending on the possible energy characteristics of the main working node of the electron-beam equipment, namely, the Pierce electron-beam gun.
 The operating parameters of the ribbon-shaped electron flow obtained as a result of the experimental study made it possible to ensure the highest quality processing of the surfaces of dielectric materials due to the improvement of such indicators of the accuracy of determining these parameters as precision (for example, the standard deviation of the repeatability of Sr decreased from 8.33% to 4.95%, and the standard the SR reproducibility deviation decreased from 13.28% to 6.18%), which confirms the representativeness of the working parameters, as well as the correctness (the bias of the method of determining the working parameters in the electronic flow is statistically insignificant under the conditions of the confidence interval on the axis d = 0 at the significance level a = 0.05). The analysis of the obtained results regarding the electron-beam microprocessing of the surfaces of dielectric materials according to the selected operating parameters proves the improvement of quality and the increase in the reproducibility of the results of the processing of these surfaces in terms of purity, as well as the reduction of the residual nanorelief by 18-25%.
 A comparison of the results of experimental electron-beam microprocessing of dielectrics with the results of their laser surface treatment made it possible to establish a reduction in residual micro-uniformities of the surface, as in electron-beam microprocessing (for optical glass K8 by 17-27 times; for silicon Kp0 - by 14-22 times) , as well as during surface laser treatment (for both types of material – 12-14 times). At the same time, surface laser treatment does not allow to eliminate surface waviness, which is related to the specifics of the interaction of the laser beam with the surface of the optical material, while when processing with an electron flow of the ribbon form, the occurrence of such waviness is not observed.
 The conclusions and analyzed data obtained in the article based on the results of experimental research can be used to optimize the technological regimes of electron-beam micromachining in the production of products of microoptics, integrated optics, nanoelectronics, etc.

MODELING OF THE TEMPORAL BEHAVIOR OF THE SURFACE TEMPERATURE OF AN ISOLATION MATERIAL TEST SAMPLE UNDER AN AC LOW CURRENT ARC

In this article, a computational model is presented which can be used to predict the heating of insulating material surfaces by low-current high-voltage arcs. The discharge is represented by a so-called three-cylinder model. Based on this, the heat flows onto the insulating material surface and its heating by means of thermal conduction and convection are calculated. The calculation results are compared to the measurements of the surface temperature on a model arrangement. The overall model reproduces the dynamic behavior of the heating very well. The quantitative deviations from the measurement are only in the range of a few percent.

Thermal radiation resonating with longitudinal optical phonon from surface micro-stripe structures on metal-gallium nitride and sapphire

Thermal emissions from metal/dielectric-material stripe structures on the surface of dielectric materials are observed. These emissions are attributed to electric-dipole emissions induced by coherent thermal lattice vibrations in the surface structures of a few micrometers. Thermal emission based on coherent lattice vibrations has been reported via surface phonon polariton (SPhP), where metal ingredients have been excluded, whereas the present emission is independent of SPhP. The structures on undoped GaAs shows the emission close to the longitudinal optical (LO) phonon energy, while the peak energy of the emission from the structures on GaN is located in between the LO and transverse optical (TO) mode energies. The present studies on several vibration modes of α-Al2O3 and the dependence of the emission peak energy on geometrical conditions of surface structures reveal that modification of electric permittivity by the local depolarization field induces additional zero points of the real part of the permittivity, which yields additional local LO-like modes and the shift of the main emission peak energy from the original LO mode. This shift is significant for materials with a large energy difference between the LO and TO modes, such as 270 cm−1 for a mode of α-Al2O3 and 170 cm−1 for GaN. This is contrasted with the case of GaAs with 30 cm−1 difference.

초전도케이블용 Stop Joint Box 설계를 위한 연면방전 특성에 관한 연구

A study on the development of a superconducting cable has been conducted actively due to its ‘0’ resistance characteristics. A superconducting cable consists of three parts: termination, core, and joint box. A joint box could be classified into normal joint box (NJB) and stop joint box (SJB) according to its structure. In this paper, a study on the development of the design technology of SJB where a bulkhead is installed to maintain a constant pressure and temperature of a cryogenic system is conducted. In an SJB system, a bulkhead is installed at a superconducting core system and impregnated with epoxy resin, and then wound with polypropylene laminated paper (PPLP) in order to insulate the superconducting core system. The creepage discharge characteristics along the surface of a solid insulation material in liquid nitrogen (LN₂) are investigated through dielectric experiments and the criterion to perform electrical insulation design of an SJB system for a distribution superconducting cable is proposed.

Contact‐free dielectric response measurement based on limit fitting by neural network

Frequency domain spectroscopy (FDS) is widely used in analysis of insulation condition of dielectric material. The traditional contact method is susceptible to the impact of the contact state between the test sample and the electrode, which is also difficult to ensure the accuracy and repeatability of the test results. Using the method of sputtering gold on the surface of the sample is an effective way to avoid this problem though, this processing method is time-consuming and high-cost. This paper presents a method based on limit fitting by neural network to realize contact-free dielectric response measurement, which can eliminate the distortion effect of the air gap introduced by the uneven surface of dielectric material. Cross linked polyethylene (XLPE) is chosen as the test object to verify this method: in the domain of frequency = 1–1000 Hz, comparing with the test results of sample treatment by gold sputtering, the average error of frequency domain spectroscopy data in traditional method is 10%, while the new method is only 1%. Meanwhile, this paper analyses the cause of the errors in each method.

Nanofriction characteristics of h-BN with electric field induced electrostatic interaction

The nanofriction properties of hexagonal boron nitride (h-BN) are vital for its application as a substrate for graphene devices and solid lubricants in micro- and nano-electromechanical devices. In this work, the nanofriction characteristics of h-BN on Si/SiO2 substrates with a bias voltage are explored using a conductive atomic force microscopy (AFM) tip sliding on the h-BN surface under different substrate bias voltages. The results show that the nanofriction on h-BN increases with an increase in the applied bias difference (Vt−s) between the conductive tip and the substrate. The nanofriction under negative Vt−s is larger than that under positive Vt−s. The variation in nanofriction is relevant to the electrostatic interaction caused by the charging effect. The electrostatic force between opposite charges localized on the conductive tip and at the SiO2/Si interface increases with an increase in Vt−s. Owing to the characteristics of p-type silicon, a positive Vt−s will first cause depletion of majority carriers, which results in a difference of nanofriction under positive and negative Vt−s. Our findings provide an approach for manipulating the nanofriction of 2D insulating material surfaces through an applied electric field, and are helpful for designing a substrate for graphene devices.

Immobilizing a π-Conjugated Catecholato Framework on Surfaces of SiO2 Insulator Films via a One-Atom Anchor of a Platinum Metal Center to Modulate Organic Transistor Performance.

Chemical modification of insulating material surfaces is an important methodology to improve the performance of organic field-effect transistors (OFETs). However, few redox-active self-assembled monolayers (SAMs) have been constructed on gate insulator film surfaces, in contrast to the numerous SAMs formed on many types of conducting electrodes. In this study, we report a new approach to introduce a π-conjugated organic fragment in close proximity to an insulating material surface via a transition metal center acting as a one-atom anchor. On the basis of the reported coordination chemistry of a catecholato complex of Pt(II) in solution, we demonstrate that ligand exchange can occur on an insulating material surface, affording SAMs on the SiO2 surface derived from a newly synthesized Pt(II) complex containing a benzothienobenzothiophene (BTBT) framework in the catecholato ligand. The resultant SAMs were characterized in detail by water contact angle measurements, X-ray photoelectron spectroscopy, atomic force microscopy, and cyclic voltammetry. The SAMs served as good scaffolds of π-conjugated pillars for forming thin films of a well-known organic semiconductor C8-BTBT (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene), accompanied by the engagements of the C8-BTBT molecules with the SAMs containing the common BTBT framework at the first layer on SiO2. OFETs containing the SAMs displayed improved performance in terms of hole mobility and onset voltage, presumably because of the unique interfacial structure between the organic semiconducting and inorganic insulating layers. These findings provide important insight into creating new elaborate interfaces through installing coordination chemistry in solution to solid surfaces, as well as OFET design by considering the compatibility between SAMs and organic semiconductors.

A New Pathway for Liquid–Solid Triboelectric Nanogenerator Using Streaming Flow by a Novel Direct Charge Transfer

Herein, a new triboelectric energy‐harvesting method by a direct transfer‐triboelectric nanogenerator (DT‐TENG) in a streaming flow is proposed. Previously, most of the fluid‐based‐triboelectric nanogenerators (Flu‐TENGs) generate the electricity by electrostatic induction, which is one of the indirect charge transfer methods. To enhance the triboelectric effect of liquid from the surface of dielectric material, negative dielectric surface treatment is focused. The significance of a novel direct charge transfer method to generate high output power of Flu‐TENG is first reported herein. From the experiment, the maximum power of DT‐TENG reaches up to 28.4 μW. The findings not only enhance the output power in the streaming flow but also provide a paradigm‐shifting technique to harvest mechanical energy in the flow electrification.

Effect of Humidity Adsorption on Mixed Valence Dielectric Material LaFe1−xAlxO3

In mixed‐valence colossal dielectric materials, the room temperature Maxwell–Wagner response is commonly assigned, in the past literature, to the electrode effect, grain boundary effect, or internal barrier layer capacitor effect. Another underlying phenomenon is brushed aside, and that is of adsorbance of the hydroxyl ions onto the defect centers on the surface of dielectric material. The properties of dielectric materials, especially those having oxygen vacancies, are sensitive to the atmospheric moisture and easily degrade in the humid environment. To study this effect, a series of LaFe1 − xAlxO3 samples (x = 0, 0.1, 0.2, …, 0.8, and 1) are prepared by the sol–gel method, and the effect of humidity sensitivity on their dielectric properties is seen. The samples with greater Fe concentration show distinct humidity‐sensitive properties with both metal electrodes (Pt and Ag) with a very miniscule difference in their measurement values. The effect of hydroxyl ions is further confirmed by the dielectric measurements after the thermal quenching of the samples that verify the adsorbance of water molecules on the surface of dielectric material.

Дослідження вольт-амперних характеристик дротяної електронної гармати Пірса для електронно-променевої мікрообробки діелектриків

The main energy characteristics of Pierce wire electron beam gun, which is used for treatment of dielectric materials in vacuum, are considered. The modes of operation of such a gun depending on their energy characteristics are studied. It is established that at a fixed width of the anode gap of 2.0 mm it is possible to implement the main technological modes of low-energy EBT dielectrics (including optical glass). The results of electron beam treatment of dielectrics with the results of their laser surface treatment are compared. The reduction of residual surface microroughnesses for optical glass K8 up to 26 times with EBT and up to 14 times with surface laser treatment was established. It is shown that the electron beam treatment of the tape shape, in contrast to the surface laser treatment, allows to completely eliminate the waviness of the optical surface. On the example of plates made of optical glass K8 it is proved that electron beam treatment of surfaces of dielectric materials allows to increase the reproducibility of the results of such micromachining by purity and residual nanorelief by 18 ... 25 %.

Triboelectricity-based self-charging droplet capacitor for harvesting low-level ambient energy

Abstract In this study, we propose a self-charging droplet capacitor for harvesting low-level mechanical energy. The capacitor comprises of a conductive liquid droplet, which is placed on a heterogeneous and hydrophobic surface of dielectric materials coated onto a conductive substrate. The substrate and the droplet, along with the dielectric materials in between, form a parallel-plate type capacitor. The droplet is free to move on the surface, and thus, enables the position-dependent variation of capacitance. The surface consists of two regions, each with a different material and thickness. The different strengths of solid-water contact electrification of the two materials give rise to a self-charging mechanism. The variation in thickness allows for the capacitance change required for energy harvesting. A device is fabricated with two droplet capacitors and one ceramic capacitor. Passive diode switches are used to enable reconfiguration of the connectivity of the capacitors, which leads to a geometrical growth of the energy in the system. With a 450 μL water drop in each capacitor, the device can effectively harvest energy from low ambient vibrations. The energy harvested grows by 100 times within 11 cycles, sufficient to illuminate 30 LEDs connected in series.

Increase of capacitance of thick dielectrics by fringe effect

For a capacitor with defined geometry, dimensions, and dielectric material, the capacitance normally cannot be changed. In this work, we found the apparent capacitance can be significantly increased by adding one or more electrodes to the lateral surfaces of dielectric materials, especially for the materials with large thickness/width ratio. The increase of capacitance is attributed to the capacitance formed by the small gaps between the lateral and top or bottom electrodes, which can response to the applied field due to the fringe effect. For a capacitor with thick dielectric material, the capacitance of the fringe capacitors, which are in parallel to the capacitor formed between the top and bottom electrodes, can be larger than the capacitance without lateral electrode, and increases the apparent capacitance.

An automated approach for real time diagnostics of electrical and optical parameters for ESD events at triple junction

Abstract Environment consisting of charged particles leads to an electrostatic discharge (arcs) on the surface of dielectric material. Simulating such environment in laboratory requires the expertise of plasma physics, vacuum technology and advanced instrumentation. Various electrical and optical discharge parameters are important for understanding arc behavior and developing a mitigation technique against it’s deteriorating effects like change in material properties and decrease in substrate’s life. A real time controller can be used for measuring all these parameters. In order to measure feeble arcs of few microseconds, its voltage and current signals are measured using high speed digitizer. Arc voltage signal is used to trigger a CCD camera for capturing arc image and hence locating its position on the substrate’s surface. Both electrical and optical signals are measured simultaneously with high precision. Gradual rise in surface potential which is responsible for ESD, can be measured by scanning entire substrate’s surface at regular time intervals. A non-contact capacitive Trek probe which is carried by a stage controller is used for this measurement. For these measurements, an advanced data acquisition, logging and analysis system is developed using LabVIEW platform. The scope of this paper is limited to on-line measurement of electrical and optical signals of an ESD event using RT and transferring them to host system. A specific case of discharges on solar panel is considered for experimental validation of the developed algorithm.

Characteristics of streamer propagation along insulation surface: quantitative influence of permittivity and surface properties

An investigation into the quantitative influence of permittivity and surface properties on characteristics of streamer propagation along insulation surface was presented. In the three-electrode arrangement, the variation of the streamer stable propagation electric field and streamer propagation velocity along the dielectric materials was measured through three photomultipliers. The measured dielectric materials were consisted of two different dielectric materials with the thickness of 5 mm piled by the side of each other. The influence of the permittivity (the capacitive effect) and the surface properties on the characteristic of streamer propagation along the surface of dielectric materials were obtained by varying the ratio of two material volumes. The streamer propagation velocity and electric field for streamer stable propagation along two combinations of nylon and PTFE, silicone rubber and PTFE were measured, respectively. The conclusion was that the surface properties of dielectric materials had large effect on streamer propagation. Furthermore, surface properties of silicone rubber were most unfavorable for streamer propagation in the three dielectric materials.

Gas Heating and Streamer-to-Leader Transition of Impulse Surface Discharge on Quartz Glass in Atmospheric Air

Flashover on the surface of dielectric materials often causes extensive damage to the insulation system, resulting in reduced withstand voltage and system downtime as the damaged component is located and replaced. Therefore, understanding the flashover mechanism on dielectrics is of great significance to reduce incidences. In this work, the change in gas temperature in an impulse surface discharge during streamer-to-leader transition was measured in atmospheric air by the spectroscopic method. In the experiment, a quartz glass having a conductive indium tin oxide-coated back-surface was used as an insulation material having a back electrode. As a result, the increase in gas temperature in a discharge channel was confirmed when the discharge phase transformed into a leader.

Multi-dimensional modelling of electrostatic force distance curve over dielectric surface: Influence of tip geometry and correlation with experiment

Electric Force-Distance Curves (EFDC) is one of the ways whereby electrical charges trapped at the surface of dielectric materials can be probed. To reach a quantitative analysis of stored charge quantities, measurements using an Atomic Force Microscope (AFM) must go with an appropriate simulation of electrostatic forces at play in the method. This is the objective of this work, where simulation results for the electrostatic force between an AFM sensor and the dielectric surface are presented for different bias voltages on the tip. The aim is to analyse force-distance curves modification induced by electrostatic charges. The sensor is composed by a cantilever supporting a pyramidal tip terminated by a spherical apex. The contribution to force from cantilever is neglected here. A model of force curve has been developed using the Finite Volume Method. The scheme is based on the Polynomial Reconstruction Operator—PRO-scheme. First results of the computation of electrostatic force for different tip–sample distances (from 0 to 600 nm) and for different DC voltages applied to the tip (6 to 20 V) are shown and compared with experimental data in order to validate our approach.

Effects of accelerated repetitive impulse voltage aging on performance of model stator insulation of wind turbine generator

A high reliability is essential for the insulation system of wind turbine generator because of its high repairing cost. In this paper, three experimental methods based on accelerated aging under repetitive impulse voltage and multi-environmental factors are established to (i) investigate the failure or degradation mechanism during the aging, and (ii) make recommendations on how to assess the functional life and reliability of insulation systems for wind turbine generator. Repetitive impulse voltage stress combined with thermal stress, change of temperature, steady damp heat and salt mist was, in turn, applied to model specimens with different length and section sizes. Some of non-destructive characteristic parameters such as dissipation factor, insulation resistance, and partial discharge inception voltage were measured periodically during the aging. In addition to the residual breakdown voltage, the appearance features and infrared spectrum analysis of specimens were carried out after aging. It has been found that the surface partial discharge generated under repetitive impulse voltage resulted in the degradation of surface insulating material near the slot end. The change of temperature also caused the delaminating of stator insulation from the core slot especially when massimpregnated insulation used in long slot of practical stator. The increase of dissipation factor of insulation system was largely contributed by salt mist and moisture factors especially when the surface or interface of insulation material was damaged. The electrically accelerated aging under about triple maximum repetitive impulse voltage for 1000 h was an effective and feasible method to assess the insulation system of wind turbine generator.

Environmental Analysis on Insulation Resistance Reduction Case

An insulation resistance reduction case was studied in this paper. An electrical component composed with metal panel, screw and insulation panel occurred flashover after 2-year service. Environment assessment, dust analysis and material analysis were done to find the reduction reason. The result shows that the reduction is caused by conductive dust aggraded on insulation panel surface; the aged surface of insulation material is favor for the conductive dust aggradation; humid air and high-hygroscopic dust accelerate this aggradation. It is suggested to improve the hydrophobicity and anti-aging property of insulation materials as well as increase the creepage for avoiding the kind of failure.