Detection of short X-ray pulses excited by an atmospheric-pressure discharge of nanosecond duration in air

The X-ray radiation of gas-filled diodes has been studied with the use of a multichannel detection unit based on microstrip GaAs ionizing-radiation detectors. It has been shown that a detector responses to X-ray pulses of subnanosecond duration and allows studies of the characteristics of X rays to be performed at short pulse durations and small exposure doses. Data on X rays formed in various diodes filled with atmospheric-pressure air have been obtained.     

Efficiency enhancement of a dielectric barrier plasma discharge by dielectric barrier optimization

The characteristic feature of a dielectric barrier discharge (DBD) is the dielectric barrier placed between the electrodes. In the present work, the influence of the dielectric barrier to the properties of a DBD in air was investigated. Spectroscopic characterization of the DBD and electrical measurements were carried out. It was shown that the efficiency of a DBD can be considerably improved by optimizing the dielectric barrier. The dielectric material should possess an appropriate relative permittivity and thickness. For thin dielectric barriers, a high secondary emission coefficient becomes important. Additionally, the use of only one dielectric barrier is advantageous.     

Detection of x-ray emission in a nanosecond discharge in air at atmospheric pressure

Measurement of x-ray emission is an important parameter to investigate runaway behavior of fast electrons produced in nanosecond-pulse gas discharge. An online detection system of x rays is described in this paper, and the system consists of an x-ray detector with NaI (Tl) scintillator and photomultiplier tube, and an integrated multichannel analyzer. The system is responsible for detecting x-ray emission signal, processing the detected signals, and scaling the energy distribution. The calibration results show that every channel of the detection system represents a given x-ray energy and various x rays can be divided into different energy ranges between 10 and 130 keV. For a repetitive nanosecond-pulse breakdown between highly nonuniform gaps in open air, an energy distribution is obtained using the online detection system. It shows that the x-ray emission is a continuous spectrum and the x rays of above 60 keV dominate in the detected energy distribution.     

纳秒激光等离子体光源的光谱测量技术

提出了一种新的探测和测量激光等离子体软X射线源光谱强度的方法。此方法使用通道电子倍增器和定标过的硅光电二极管为探测器,前者是非标准探测器,后者为标准探测器。应用电荷灵敏前置放大器和峰值探测器测量探测器产生的电量,并以高分辨率的光谱仪为分光元件,在已知光栅效率、通道电子倍增器增益、硅光电二极管能量响应的条件下,给出了计算激光等离子体软X射线源在某一波长光谱强度的公式。     

Modifying the surfaces of fluorocarbon polymer implants in the plasma of a high-voltage nanosecond discharge

The possibility in principle is shown for rapidly and efficiently modifying the surface of medical articles made of polytetrafluoroethylene (PTFE) by placing them in a bulk plasma discharge formed in a highly overvoltage gap. As an example, by processing PTFE films with nanosecond discharges at a frequency of 3 kHz over a few seconds, it is possible to substantially improve the conditions for cytoadherence and increase the permeability of an implant, which is an important factor for its integration into adjacent tissues.     

Development of dielectric barrier discharge plasma processing apparatus for mass spectrometry and thin film deposition

Cost effective and a very simple dielectric barrier discharge plasma processing apparatus for thin film deposition and mass spectroscopic analysis of organic gas mixture has been described. The interesting features of the apparatus are the construction of the dielectric electrodes made of aluminum oxide or alumina (Al(2)O(3)) and glass and the generation of high ignition voltage from the spark plug transformer taken from car. Metal capacitor is introduced in between ground and oscilloscope to measure the executing power during the discharge and the average electron density in the plasma region. The organic polymer films have been deposited on Si (100) substrate using several organic gas compositions. The experimental setup provides a unique drainage system from the reaction chamber controlled by a membrane pump to suck out and remove the poisonous gases or residuals (cyanogens, H-CN, CH(x)NH(2), etc.) which have been produced during the discharge of CH(4)N(2) mixture.     

Adjustment of the nanosecond laser pulse duration by using a carbon nanotube suspension

It is shown that the scanning of an optical cell with an aqueous suspension of carbon nanotubes along the optical axis of a focused laser beam leads to a smooth change in the duration of nanosecond laser pulses transmitted through the suspension. Pulses shorten owing to the pulse trailing edge cutoff, when the cell approaches the beam waist. In experiments, pulses of a YAG:Nd³⁺ laser with passive Q-switching and duration of 16 ns were continuously controlled in the range 16–10 ns.     

Simple method of determining plasma impedance of streamer discharge in atmospheric air

For atmospheric streamer discharges using a lightning impulse generator, we demonstrate a method of determining the plasma impedance in a streamer region by analyzing the periodic attenuated discharge waveforms having high-frequency components. When the streamer region in the plasma can be treated as an equivalent series circuit model including resistance and inductance elements, the regression waveforms obtained by reducing and smoothing the discharge waveforms are analyzed in the equivalent circuit. We found that the streamer resistance increased exponentially with time after the discharge, whereas the streamer inductance and series impedance were constant at 4.0 Ω for longer than the first period of the discharge waveforms. Moreover, the slope of the regression curve increases more rapidly for the positive streamer resistance than for the negative resistance. Finally, the absolute values of the streamer impedance versus time were 3.3-19 Ω and 3.5-9.0 Ω for positive and negative discharges, respectively.     

Fundamental study of NOx removal from diesel exhaust gas by dielectric barrier discharge reactor

Journal of Mechanical Science and Technology - Due to increasingly stringent emission legislation, it is essential to find a solution of eliminating nitrogen oxides (NOx) from diesel exhaust gas....     

A compact repetitive high-voltage nanosecond pulse generator for the application of gas discharge

Uniform and stable discharge plasma requires very short duration pulses with fast rise times. A repetitive high-voltage nanosecond pulse generator for the application of gas discharge is presented in this paper. It is constructed with all solid-state components. Two-stage magnetic compression is used to generate a short duration pulse. Unlike in some reported studies, common commercial fast recovery diodes instead of a semiconductor opening switch (SOS) are used in our experiment that plays the role of SOS. The SOS-like effects of four different kinds of diodes are studied experimentally to optimize the output performance. It is found that the output pulse voltage is higher with a shorter reverse recovery time, and the rise time of pulse becomes faster when the falling time of reverse recovery current is shorter. The SOS-like effect of the diodes can be adjusted by changing the external circuit parameters. Through optimization the pulse generator can provide a pulsed voltage of 40 kV with a 40 ns duration, 10 ns rise time, and pulse repetition frequency of up to 5 kHz. Diffuse plasma can be formed in air at standard atmospheric pressure using the developed pulse generator. With a light weight and small packaging the pulse generator is suitable for gas discharge application.     

Correlation of wettability and superficial cleaning of 2024 aluminium alloy with air cold plasma treatment time

The subject of this study, 2024 aluminium alloy, is widely used in the aeronautic field for its high mechanical properties. In order to solve corrosive problems, where Al2024 is involved in critical applications such as aeronautic ones, it is necessary to paint aluminium alloy: the applied paint film protects the aluminium alloy from corrosion. To improve the adhesion of the paint film it is necessary to pretreat the manufactured surface: pretreatments develop a cleaned, uniform and wettable surface. Cold plasma is an efficient, economic and environmentally attractive alternative to the traditional pretreatment. An air cold plasma treatment improves the wettability of aluminium alloy and also cleans organic contaminants from the surface. This work aims to value the possible correlations between: (1) the wettability and the cold plasma treatment time, (2) the superficial cleaning and the cold plasma treatment time and (3) the superficial cleaning and the wettability.     

Changes in the biomechanical properties of a single cell induced by nonthermal atmospheric pressure micro‐dielectric barrier discharge plasma

Mechanical properties of a single cell are closely related to the fate and functions of the cell. Changes in mechanical properties may cause diseases or cell apoptosis. Selective cytotoxic effects of nonthermal atmospheric pressure micro‐dielectric barrier discharge (DBD) plasma have been demonstrated on cancer cells. In this work, changes in the mechanical properties of a single cell induced by nonthermal atmospheric pressure micro‐DBD plasma were investigated using atomic force microscopy (AFM). Two cervical cancer cell lines (HeLa and SiHa) and normal human fibroblast cells (HFBs) were exposed to micro‐DBD plasma for various exposure times. The elasticity of a single cell was determined by force–distance curve measurement using AFM. Young's modulus was decreased by plasma treatment for all cells. The Young's modulus of plasma‐treated HeLa cells was decreased by 75% compared to nontreated HeLa cells. In SiHa cells and HFBs, elasticity was decreased slightly. Chemical changes induced by the plasma treatment, which were observed by Raman spectroscopy, were also significant in HeLa cells compared to SiHa cells and HFBs. These results suggested that the molecular changes induced by micro‐DBD plasma were related to cell mechanical changes.     

Preparation of cultured cells for SEM: air drying from organic solvents.

Air evaporation from organic solvents of differing polarities and surface free energies was used in the preparation of cultured murine peritoneal macrophages for scanning electron microscopy (SEM). The surface structural features of these cells were compared to the surfaces of similar cells prepared by the critical-point procedure. In general, all organic solvents produced a marked collapse of cell structure resulting in an increase in surface irregularity. Fracture surfaces and sharply defined contours including numerous flaps and ridges were characteristic of the non-polar solvent dehydrated samples. Polar solvent dehydrated samples, including those dried from solvents of low surface free energy, exhibited a secondary flowing and settling of the cell membrane. Primary collapse was apparent but cell contours were smoothed and rounded. Overall cell shape and cell-to-cell relationships were retained regardless of solvent type. It is suggested that solvent evaporation may prove useful in certain cases, though investigators are advised to use caution when interpreting the results obtained by such procedures.     

飞秒激光诱导的空气等离子体冲击波探究

一定强度的飞秒激光聚焦于空气能生成空气等离子体并诱导生成冲击波。为了观察该冲击波传播特性,引入了超快时间分辨涡旋滤波成像技术,并对观测到的冲击波动力学过程进行了分析。实验探测到泵浦能量为1.5 mJ的飞秒激光经过透镜聚焦到空气中产生等离子体空气冲击波,分析了在3~15 μs时间段冲击波的动态演化过程。结果表明,飞秒激光等离子体空气冲击波在传输时以不对称的球形形状向外扩散,且沿着激光传播方向的传播速度与背着激光传播方向的传播速度不同,分别为372 m/s和341 m/s。这一观察结果与传统的点爆炸模型的对称情形不同,尝试对该不对称动力学过程进行了合理解释。     

Detection limits for glow discharge mass spectrometry (GDMS) analyses of impurities in solar cell silicon

The measurement of both doping elements and trace elements in solar cell silicon plays a key role for achieving high conversion efficiency of the solar cell device. Doping element concentrations in the range of few hundreds part per billions (ppb) and trace elements in the ppb or sub-ppb concentration range are typically present in multicrystalline silicon wafers for solar cells. Accurate and reliable measurements of these small amounts are not straightforward. The present work describes a fast-flow direct-current high resolution glow discharge mass spectrometer (GDMS). Detection limits for a number of impurities (B, Al, P, Ca, Ti, V, Cr, Mn, Fe, Ni, Co, Cu, Mo, Sn, W and Pb) of interest for solar cell applications have been investigated by GDMS. These detection limits are approximately 1 ppba or below, except for B, Al, P, Ca and Pb. All concentrations reported are quantitative since calculated relative sensitivity factors (RSF‘s) for Si matrix have been used. The detection limits have been achieved with minimum sample preparation and short analysis time.     

Assessment of the cleaning effect of HF cold plasma by statistical processing of photographic image

The assessment of cultural heritage objects cleaning by HF cold plasma treatment is hard to quantify. One method is based on direct comparison of photographic images acquired before and after treatment, a subjective evaluation, depending on the rigor and visual accuracy of the observer.     

Note: Measuring dezincification of brass by Schottky barrier diodes formed between semiconductor corrosion products and brass

A newly developed method is presented for measuring dezincification on the surface of brass from a consideration of the forward and reverse bias potential drop across a Schottky barrier diode formed between n-type zinc oxide or p-type copper (I) oxide corrosion products and the brass substrate. Electrical connection to the corrosion product is made with zinc and platinum tipped probes, approximately 1 mm diameter. Comparison with x-ray photoelectron spectroscopy shows the difference between the forward and reverse bias potential drop to be dependent on the relative abundance of the corrosion products and the work function of the metal probe. This difference, for a zinc tipped probe, gives a statistically significant correlation to the surface zinc to copper ratio and the degree of dezincification. Details of the setup, operation, and testing of a portable instrument designed to measure dezincification of brass by this method are given.     

Determination of volatile organic compounds in air by a surface acoustic wave array

This article reports the design and performance of a portable volatile organic compound detection system implemented with a surface acoustic wave array. The system employed electrospray technology for the determination of acetone and methanol. The novel part of this study was the design of the 433 MHz surface acoustic wave array. The sensor oscillators were operated at higher frequencies to reduce space and power consumption. The higher frequency also improved the response resolution; however, it created problems including interferences, crosstalk, signal degradation, and noise. Crosstalk was the most important problem and was minimized by the operation of one sensor at a time while the others were muted. Analog and digital circuitry served as the transducer to obtain analyte signals that were processed to produce bar and principal component analysis plots. The system was extensively tested and good results were obtained for qualitative and quantitative measurements.     

利用图像处理技术评价硅片表面清洗率

介绍了一种基于Matlab图像处理工具箱技术的评价硅片表面污染颗粒激光清洗率的新方法。借助Matlab图像处理工具箱,对清洗前后硅片表面光学显微镜照片进行处理,编写硅片表面激光干法清洗率的评价程序,统计清洗前后硅片表面评价区域的污染颗粒个数,对清洗效果进行定量评价。研究结果证明,利用此方法统计的颗粒数准确度达97.6%,得到的激光清洗率准确度达99.2%。结果表明,借助图像处理技术评定清洗效果是一种高效、快速、准确的新方法。     

Residual stress analysis of the thermal barrier coating system by considering the plasma spraying process

The residual stress is the key factor causing the reliability problem of thermal barrier coating (TBC). The failure of plasma spray coatings due to residual stresses is a serious and recurring problem of TBC. The difference of thermal expansion coefficient between the substrate and each coating combined with temperature evolution and temperature gradients during deposition process determine the residual stress for the whole TBC system. The magnitudes and distributions of the residual stresses are affected by deposition process and deposition characteristics. Most of FEA (finite element analysis) has been performed under the assumption that the multilayer coating system is stacked at once without considering the deposition process during plasma spraying. In this research, FEA for a coupled heat transfer and elastic-plastic thermal stress was performed to obtain the more detailed and reliable result of residual stress of the TBC system using the element activation/deactivation technique. The residual stress variation from the start of plasma spraying to cooling stage with room temperature was obtained systematically considering the deposition process. It can be used as reference data to improve the performance of TBC. In addition, the relationship between residual stress and coating conditions such as cooling rate and time is also examined thoroughly.