Improving the surface insulation of epoxy resin by plasma etching

Epoxy resin (EP) tends to accumulate a large amount of charge on its surface when exposed to a high-voltage DC electric field,which leads to a reduction in its insulative performance and an increase in potential safety risks in power systems.To suppress charge accumulation,improve the flashover voltage of the EP,and reduce the risk of gas insulated switchgear (GIS)/gas insulated transmission line (GIL) failure,we used two plasma-etching methods,i.e.,atmospheric-pressure dielectric barrier discharge (DBD) and the atmospheric-pressure plasma jet(APPJ),to modify the surface of the EP.The surface morphology and electrical properties of the modified materials were explored as a function of time.The results show that after DBD treatment,the roughness of the sample increases by 103.9 nm,the conductivity increases by3.9?×?10~(–18)S,and the flashover voltage increases by 14.4%;after APPJ treatment,the roughness of the sample increases by 223.5 nm,the conductivity increases by 3.4?×?10~(–17)S,and the flashover voltage increases by 18%.This shows that both plasma-etching methods can improve the insulation properties of materials by improving the surface-charge characteristics.The two methods are compared with each other:the APPJ treatment method is better at improving the surface roughness and electrical properties of materials,and this flexible treatment method has greater potential in industrial applications.     

Improving the surface flashover performance of epoxy resin by plasma treatment:a comparison of fluorination and silicon deposition under different modes

This work treats the Al2O3-ER sample surface using dielectric barrier discharge fluorination(DBD-F),DBD silicon deposition(DBD-Si),atmospheric-pressure plasma jet fluorination(APPJ-F)and APPJ silicon deposition(APPJ-Si).By comparing the surface morphology,chemical components and electrical parameters,the diverse mechanisms of different plasma modification methods used to improve flashover performance are revealed.The results show that the flashover voltage of the DBD-F samples is the largest(increased by 21.2％at most),while the APPJ-F method has the worst promotion effect.The flashover voltage of the APPJ-Si samples decreases sharply when treatment time exceeds 180 s,but the promotion effect outperforms the DBD-Si method during a short modified time.For the mechanism explanation,firstly,plasma fluorination improves the surface roughness and introduces shallow traps by etching the surface and grafting fluorine-containing groups,while plasma silicon deposition reduces the surface roughness and introduces a large number of shallow traps by coating SiOx film.Furthermore,the reaction of the DBD method is more violent,while the homogeneity of the APPJ modification is better.These characteristics influence the effects of fluorination and silicon deposition.Finally,increasing the surface roughness and introducing shallow traps accelerates surface charge dissipation and inhibits flashover,but too many shallow traps greatly increase the dissipated rate and facilitate surface flashover instead.     

Cleaning of nitrogen-containing carbon contamination by atmospheric pressure plasma jet

Atmospheric pressure plasma jet (APPJ) was used to clean nitrogen-containing carbon films (C–N) fabricated by plasma-assisted chemical vapor deposition method employing the plasma surface interaction linear device at Sichuan University (SCU-PSI). The properties of the contaminated films on the surface of pristine and He-plasma pre-irradiated tungsten matrix, such as morphology, crystalline structure, element composition and chemical structure were characterized by scanning electron microscopy, grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy. The experimental results revealed that the removal of C–N film with a thickness of tens of microns can be realized through APPJ cleaning regardless of the morphology of the substrates. Similar removal rates of 16.82 and 13.78 μm min−1 were obtained for C–N films deposited on a smooth pristine W surface and rough fuzz-covered W surface, respectively. This is a remarkable improvement in comparison to the traditional cleaning method. However, slight surface oxidation was found after APPJ cleaning, but the degree of oxidation was acceptable with an oxidation depth increase of only 3.15 nm. Optical emission spectroscopy analysis and mass spectrometry analysis showed that C–N contamination was mainly removed through chemical reaction with reactive oxygen species during APPJ treatment using air as the working gas. These results make APPJ cleaning a potentially effective method for the rapid removal of C–N films from the wall surfaces of fusion devices.     

Trap distribution of polymeric materials and its effect on surface flashover in vacuum

The surface trap parameter can significantly affect the development of surface flashover in vacuum, but the effective mode and mechanism are not very clear yet. The trap parameters of three polymeric materials were tested and calculated by means of isothermal surface potential decay. The flashover experiment was developed under different applied voltages. The results show a positive correlation between the withstand voltage and the deep trap, i.e., the deeper trap energy level is, the higher flashover voltage is. The dynamics process of charge trapping and detrapping was analyzed based on the charge transport model in dielectrics with a single trap level and two discrete trap levels. The time of charge trapping was compared with that of the discharge development. The results show that the charge trapping time is longer than the flashover development time. The way to influence flashover for a trap is not to decrease the secondary electrons in single discharge development, but to change the electric field distribution on the dielectric surface by charge capture.     

Surface modification of silicone rubber by CF4 radio frequency capacitively coupled plasma for improvement of flashover

The flashover performance of insulating materials plays an important role in the development of high-voltage insulation systems. In this paper, silicone rubber(SIR) is modified by CF₄ radio frequency capacitively coupled plasma (CCP) for the improvement of surface insulation performance. The discharge mode and active particles of CCP are diagnosed by the digital single-lens reflex and the spectrometer. Scanning electron microscopy and x-ray photoelectron spectroscopy are used for the surface physicochemical properties of samples, while the surface charge dissipation, charge accumulation measurement, and flashover test are applied for the surface electrical characteristics. Experimental results show that the fluorocarbon groups can be grafted and the surface roughness increases after plasma treatment. Besides, the surface charge dissipation is decelerated and the positive charge accumulation is inhibited obviously for the treated samples. Furthermore, the surface flashover voltage can be increased by 26.67% after 10 min of treatment. It is considered that strong electron affinity of C–F and increased surface roughness can contribute to deepening surface traps, which not only inhibits the development of secondary electron emission avalanche but also alleviates the surface charge accumulation and finally improves the surface flashover voltage of SIR.     

Non-Thermal Equilibrium Atmospheric Pressure Glow-Like Discharge Plasma Jet

Non-thermal equilibrium atmospheric pressure plasma jet (APPJ) is a cold plasma source that promises various innovative applications,and the uniform APPJ is more favored.Glow discharge is one of the most effective methods to obtain the uniform discharge.Compared with the glow dielectric barrier discharge (DBD) in atmospheric pressure,pure helium APPJ shows partial characteristics of both the glow discharge and the streamer.In this paper,considering the influence of the Penning effect,the electrical and optical properties of He APPJ and Ar/NH3 APPJ were researched.A word "Glow-like APPJ" is used to characterize the uniformity of APPJ,and it was obtained that the basic characteristics of the glow-like APPJ are driven by the kHz AC high voltage.The results can provide a support for generating uniform APPJ,and lay a foundation for its applications.     

Effect of plasma step gradient modification on surface electrical properties of epoxy resin

In this paper, plasma fluorination is combined with plasma silicon deposition to achieve step gradient modification on an epoxy resin surface. The physicochemical characteristics of samples are investigated and the electrical performances measured. The obtained results show that compared with untreated and single treated samples, the samples treated by step gradient modification significantly improve the flashover performance. According to experiment and simulation, the mechanism explanations are summarized as follows. First, it is found that the step gradient conductivity can effectively optimize the electric field distribution of a needle-needle electrode. Then, step gradient modification suppresses the accumulation of surface charge at the triple junction and makes the charge distribution more uniform. Furthermore, it can accelerate the surface dissipation on a high electrical field region and control the dissipation rate on a low electrical field region. All these results can restrain surface discharge and increase the flashover voltage. The step gradient modification method proposed in this paper provides a new idea for improving the surface insulation performance.     

Deposition of stain resistance coating by non-thermal plasma brush application to dental whitening

A non-thermal plasma brush is employed to deposit stain-resistant SiO₂-like coatings on resin composite fillings and bovine teeth. With post-treating by plasma, the hardness of the coating increases from H to 8H and the water contact angle decreases from 98.8° to 61.7°. The Fourier transform infrared spectroscopy (FTIR) results show that, after plasma post-treating, the Si–O–Si and Si–OH bonds of the coating increase. Scanning electron microscope (SEM) images show the coatings to be uniform, without cracks. The coatings present outstanding performance in a stain resistance test both on resin composite and bovine teeth. Being easy to handle and less time consuming than traditional methods, with a body-friendly temperature and material, this plasma brush provides a promising in-situ coating method on patient teeth in dental clinics.     

The influence of grounded electrode positions on the evolution and characteristics of an atmospheric pressure argon plasma jet

An atmospheric pressure plasma jet (APPJ) in Ar with various grounded electrode arrangements is employed to investigate the effects of electrode arrangement on the characteristics of the APPJ.Electrical and optical methods are used to characterize the plasma properties.The discharge modes of the APPJ with respect to applied voltage are studied for grounded electrodepositions of 10 mm,40 mm and 80 mm,respectively,and the main discharge and plasma parameters are investigated.It is shown that an increase in the distance between the grounded electrode and high-voltage electrode results in a change in the discharge modes and discharge parameters.The discharges transit from having two discharge modes,dielectric barrier discharge (DBD) and jet,to having three,corona,DBD and jet,with increase in the distance from the grounded to the high-voltage electrodes.The maximum length of the APPJ reaches 3.8 cm at an applied voltage of 8 kV.The discharge power and transferred charges and spectral line intensities for species in the APPJ are influenced by the positions of the grounded electrode,while there is no obvious difference in the values of the electron excited temperature (EET) for the three grounded electrode positions.     

Aging Characteristics on Epoxy Resin Surface Under Repetitive Microsecond Pulses in Air at Atmospheric Pressure

Research on aging characteristics of epoxy resin(EP) under repetitive microsecond pulses is important for the design of insulating materials in high power apparatus.It is because that very fast transient overvoltage always occurs in a power system,which causes flashover and is one of the main factors causing aging effects of EP materials.Therefore,it is essential to obtain a better understanding of the aging effect on an EP surface resulting from flashover.In this work,aging effects on an EP surface were investigated by surface flashover discharge under repetitive microsecond pulses in atmospheric pressure.The investigations of parameters such as the surface micro-morphology and chemical composition of the insulation material under different degrees of aging were conducted with the aid of measurement methods such as atomic force microscopy(AFM),scanning electron microscopy(SEM),and X-ray photoelectron spectroscopy(XPS).Results showed that with the accumulation of aging energy on the material surface,the particles formed on the material surface increased both in number and size,leading to the growth of surface roughness and a reduction in the water contact angle; the surface also became more absorbent.Furthermore,in the aging process,the molecular chains of EP on the surface were broken,resulting in oxidation and carbonisation.     

The Effect of Plasma Surface Treatment on a Porous Green Ceramic Film with Polymeric Binder Materials

To reduce time and energy during thermal binder removal in the ceramic process, plasma surface treatment was applied before the lamination process.The adhesion strength in the lamination films was enhanced by oxidative plasma treatment of the porous green ceramic film with polymeric binding materials.The oxygen plasma characteristics were investigated through experimental parameters and weight loss analysis.The experimental results revealed the need for parameter analysis,including gas material,process time,flow rate,and discharge power,and supported a mechanism consisting of competing ablation and deposition processes.The weight loss analysis was conducted for cyclic plasma treatment rather than continuous plasma treatment for the purpose of improving the film’s permeability by suppressing deposition of the ablated species.The cyclic plasma treatment improved the permeability compared to the continuous plasma treatment.     

制备工艺对自支撑薄膜粗糙度的影响

利用磁过滤等离子沉积技术,以甜菜碱、油酸钾、抛光NaCl单晶基片、自支撑火棉胶膜和自支撑SiN薄膜为衬底制备了自支撑Ni膜。采用原子力显微镜和场发射扫描电子显微镜对薄膜表面形态和粗糙度进行了分析。结果表明：自支撑Ni膜的粗糙度与衬底材料密切相关,等离子体的沉积角度直接影响纳米薄膜的微观结构,采用60°倾斜沉积在自支撑火棉胶膜衬底上,可获得表面粗糙度为1.5nm的自支撑Ni膜。     

Surface morphology influence on deuterium retention in beryllium films prepared by thermionic vacuum arc method

In a plasma-confinement device, material eroded from plasma facing components will be transported and re-deposited at other locations inside the reaction chamber. Since beryllium from the first wall of the ITER fusion reactor will be eroded, ionized in the scrape-off layer plasma and finally re-deposited on divertor surfaces flowing along the magnetic field, it is important to study the properties of divertor armour materials (C, W) coated with beryllium.By applying different bias voltages (−200 V to +700 V) to the substrates during deposition, the morphology of the obtained films was modified. The films’ morphology was characterized by means of AFM and SEM, and it was found that the coatings prepared using negative bias voltage at the substrate during deposition are more compact and have a smoother surface compared to the samples prepared with positive bias voltage. The thickness and composition of each film were measured using Rutherford backscattering spectrometry (RBS). A study of deuterium implantation and retention into the prepared films was performed at IPP Garching in the high current ion source.     

感应耦合等离子体源制备硬质类金刚石膜的研究

采用感应耦合等离子体源(ICPS)成功地实现化学气相沉积硬质类金刚石(DLC)膜,并考察了基片负偏压对类金刚石膜沉积过程和薄膜性质的影响。薄膜的微观形貌、显微硬度、沉积速率以及结构成分分析表明感应耦合等离子体源适于制备硬质类金刚石膜,并且在相对较低的基片负偏压条件就可以获得高硬度的类金刚石膜。基片负偏压对类金刚石膜化学气相沉积过程和薄膜性质都有显著影响。     

Silicone-coated polyimide films deposited by surface dielectric barrier discharges

Hybrid dielectric barrier discharges are investigated for plasma generated on the surface of a dielectric layer, where two conducting electrodes of high voltage and ground are formulated on the upper and bottom surfaces. Using a flexible thin polyimide-film of a thickness ranging from 25 to 125 μm, a plasma is generated with a voltage of about 1 kV and a frequency of 40 kHz.However, the surface of the dielectric layer was etched through a chemical reaction involving plasma oxygen radical species, and thus the polyimide films failed readily, resulting in dielectric breakdown within short operating time ranging from a few minutes to several tens of minutes,based on the film thicknesses of 25 μm and 125 μm, respectively. These plasma erosions were prevented by coating the polyimide surface with a 25 μm thick silicone paste. The siliconecoated film surface was then reinforced remarkably against plasma erosion as the organic polymer was vulnerable to chemical reaction of the plasma species, while the inorganic silicone exhibited a high chemical resistance against plasma erosion.     

Experimental Study of Electron Emission Characteristics of a Surface Flashover Trigger in a Low Pressure Environment

Characteristics of electron emission induced by a surface flashover trigger device in a low-pressure trigger switch were investigated. A test method to measure the emitted charges from the trigger device was developed, and the factors affecting the emitted charges were analyzed. The results indicated that the major emitted charges from the trigger device were induced by surface plasma generated by surface flashover occurring on the trigger dielectric material. The emitted charges and the peak emission current increased linearly with the change in the trigger voltage and bias voltage. The emitted charges collected from the anode were affected by the gap distance. However, the emitted charges were less affected by the anode diameter. Furthermore, the emitted charges and the peak emission current decreased rapidly with the increase in gas pressure in a range from 0 to 100 Pa, and then remained stable or changed slightly when the increase in gas pressure up to 2400 Pa.     

XPS characterization of different thermal treatments in the ITO–Si interface of a carbonate-textured monocrystalline silicon solar cell

In this work we have applied the X-ray photoelectron spectroscopy (XPS) in depth to study, for the first time, the influence of different thermal treatments in the ITO–Si interface of a monocrystalline Si-based solar cell where the Si surface is carbonate-textured and covered by an ITO sputtered layer. The efficiency of the solar cells significantly increases when thermal treatments are applied just after the ITO deposition. The efficiency is also dependent on the characteristics of the pyramidal relief of the silicon surface previously obtained by immersion of the Si wafers in a sodium carbonate/bicarbonate solution. An efficiency of 15.5% has been obtained with an optimized texturization of the silicon substrates and an annealing treatment of the solar cells at 400 °C just after the ITO deposition.     

Atomic layer deposition of copper thin film and feasibility of deposition on inner walls of waveguides

Copper thin films were deposited by plasma-enhanced atomic layer deposition at low temperature, using copper(I)-N,N′-di-sec-butylacetamidinate as a precursor and hydrogen as a reductive gas. The influence of temperature, plasma power, mode of plasma, and pulse time, on the deposition rate of copper thin film, the purity of the film and the step coverage were studied.The feasibility of copper film deposition on the inner wall of a carbon fibre reinforced plastic waveguide with high aspect ratio was also studied. The morphology and composition of the thin film were studied by atomic force microscopy and x-ray photoelectron spectroscopy,respectively. The square resistance of the thin film was also tested by a four-probe technique. On the basis of on-line diagnosis, a growth mechanism of copper thin film was put forward, and it was considered that surface functional group played an important role in the process of nucleation and in determining the properties of thin films. A high density of plasma and high free-radical content were helpful for the deposition of copper thin films.     

Study on deposition of Al2O3 films by plasma-assisted atomic layer with different plasma sources

In this paper,A12O3 thin films are deposited on a hydrogen-terminated Si substrate by using two home-built electron cyclotron resonance (ECR) and magnetic field enhanced radio frequency plasma-assisted atomic layer deposition (PA-ALD) devices with Al(CH3)3 (trimethylaluminum,TMA) and oxygen plasma used as precursor and oxidant,respectively.The thickness,chemical composition,surface morphology and group reactions are characterized by in situ spectroscopic ellipsometer,x-ray photoelectric spectroscopy,atomic force microscopy,scanning electron microscopy,a high-resolution transmission electron microscope and in situ mass spectrometry (MS),respectively.We obtain that both ECR PA-ALD and the magnetic field enhanced PA-ALD can deposit thin films with high density,high purity,and uniformity at a high deposition rate.MS analysis reveals that the A12O3 deposition reactions are not simple reactions between TMA and oxygen plasma to produce alumina,water and carbon dioxide.In fact,acetylene,carbon monoxide and some other by-products also appear in the exhaustion gas.In addition,the presence of bias voltage has a certain effect on the deposition rate and surface morphology of films,which may be attributed to the presence of bias voltage controlling the plasma energy and density.We conclude that both plasma sources have a different deposition mechanism,which is much more complicated than expected.