Particularities of ignition of the non-self-sustained discharge with a thermoemission cathode in crossed fields

The experimental results of use of a thermoemission cathode as the cathode-compensator when working with the Hall electroreactive thruster are presented. The operation particularities of the thruster with the thermoemission cathode are investigated, and the technical requirements for the cathodes in use are adjusted. Data making it possible to specify the technical requirements on the power supplies for the Hall reactive thrusters (HRTs) are obtained. The study of the discharge ignition process in the crossed fields inside the Hall electroreactive thruster shows that, at the moment of ignition, the total discharge current may exceed by 10–20 times that of the stationary regime; here, the value and the duration of the current “spike” depend directly on the emissive ability of the cathode-compensator. The influence of the magnetic field value in the accelerator channel on the ignition potential is discovered.     

Recombination instability of a dusty plasma of non-self-sustained discharge

The stability of a dusty plasma of low pressure non-self-sustained discharge is studied. It is shown that aperiodic recombination instability can be developed in plasma in a wide wavenumber range. The physical mechanism of instability is discussed. The dependence of conditions of instability development and its increment on discharge parameters is analyzed.     

Methane conversion in a plasma created by a periodic-pulsed electron beam and non-self-sustained discharge

The process of methane conversion in a mixture modeling the natural gas under the action of a periodic nanosecond pulsed electron beam and an electron-beam-induced non-self-sustained discharge has been numerically simulated and studied in experiment. The possibility of methane conversion under the action of electric pulses without significant heating of the processed gas mixture is demonstrated for the first time. The main conversion products in experiment were hydrogen, ethylene, and acetylene.     

Periodic plasma structures in nanosecond discharge with a slit cathode

The spatial structure of optical emission from a transverse nanosecond pulsed electric discharge with a hollow (slit) cathode has been experimentally studied. A regular periodic plasma structure has been observed during nanosecond pulsed discharge in helium at medium pressures. Conditions of the plasma structure formation with respect to the discharge voltage and current are determined. It is shown that the observed plasma structure differs from the known types of striations.     

Formation of a cathode plasma jet in a laser-induced vacuum discharge

The process of formation of micropinch structures in the plasma of a vacuum discharge initiated by a laser pulse on the cathode is studied. It is demonstrated that the micropinch formation takes place mainly in the substance evaporated by the laser pulse upon the discharge initiation. The size of the hot region of the plasma jet and the distance from the cathode to the micropinch increase with increasing laser pulse energy.     

PMMA基底含氢非晶碳膜的结构和摩擦学性能

分别用磁控溅射和等离子体增强化学气相沉积方法在PMMA基底上沉积硅膜和含氢非晶碳(a-C:H)膜.用氩离子溅射硅靶制备硅膜,以甲烷和氢气为反应气体在不同自偏压下制备非晶碳膜.分别用原子力显微镜、X射线光电子能谱和紫外拉曼光谱表征薄膜的形貌和结构,并分别用纳米压痕仪和栓盘摩擦磨损试验机测试其机械和摩擦学性能.结果表明,沉积碳膜的PMMA基底呈现出高硬度、低摩擦系数和低磨损率的特性.碳膜的显微结构、机械和摩擦学特性均显著依赖薄膜沉积过程中使用的自偏压,其摩擦系数和磨损率与其硬度和sp3含量密切相关.     

Preparation and comparison of a-C:H coatings using reactive sputter techniques

Amorphous hydrogenated carbon (a-C:H) coatings are widely used in several industrial applications. These coatings commonly will be prepared by plasma activated chemical vapor deposition (PACVD). The main method used to prepare a-C:H coating in industrial scale is based on a glow discharge in a hydrocarbon gas like acetylene or methane using a substrate electrode powered with medium frequency (m.f. — some 10 to 300 kHz). Some aims of further development are adhesion improvement, increase of hardness and high coating quality on complex geometries. A relatively new and promising technique to fulfil these requirements is the deposition of a-C:H coatings by a reactive d.c. magnetron sputter deposition from a graphite target with acetylene as reactive gas. An advancement of this technique is the deposition in a pulsed magnetron sputter process. Using these three mentioned techniques a-C:H coatings were prepared in the same deposition machine. For adhesion improvement different interlayer systems were applied. The effect of different substrate bias voltages (d.c. and d.c. pulse) was investigated. By applying the magnetron sputter technique in the d.c. pulse mode, plastic hardness values up to 40 GPa could be reached. Besides hardness other mechanical properties like resistance against abrasive wear were measured and compared. Cross sectional SEM images showed the growth structure of the coatings.     

Mechanical and tribological properties of gradient a-C:H/Ti coatings

The unusual combination of high hardness and very low friction coefficient are the most attractive tribological parameters of DLC (diamond-like carbon) layers. However, their usability is strongly restricted by the limited thickness due to high residual stress. The main goal of the presented work was to obtain thick, wear resistant and well adherent DLC layers while keeping their perfect friction parameters. As a proposed solution a Ti-Ti _x C _y gradient layer was manufactured as the adhesion improving interlayer followed by a thick diamond-like carbon film. This kind of combination seems to be very promising for many applications, where dry friction conditions for highly loaded elements can be observed. Both layers were obtained in one process using a hybrid deposition system combining PVD and CVD techniques in one reaction chamber. The investigation was performed on nitrided samples made from X53CrMnNiN21-9 valve steel. Structural features, surface topography, tribological and mechanical properties of manufactured layers were evaluated. The results of the investigation confirmed that the presented deposition technique makes it possible to manufacture thick and well adherent carbon layers with high hardness and very good tribological parameters. Preliminary investigation results prove the possibility of application of presented technology in automotive industry.     

Hydroxyl groups and a-C:H and a-C:H(Me) structures

IR absorption spectra of hydroxyl groups in a-C:H and a-C:H(Me) (Me = Cu, Co) films grown by magnetron cosputtering of graphite and metal targets in argon-hydrogen plasma were studied. The hydroxyl band shape was analyzed using published data on the dependence of the O-H stretching vibration frequency on the distance from the nearest oxygen atom. It is demonstrated that the hydroxyl band shape is related to the character of interaction between an encapsulated metal and a carbon backbone of the film.     

Tribological behaviour a-C and a-C:H films doped with Ti in biological solutions

The coatings were deposited in a multi magnetron Teer sputtering device with two C targets and a Ti target in Ar atmosphere, on steel and Si substrates. To deposit hydrogenated coatings methane was introduced in the discharge atmosphere. The films were deposited in a range of 7-14 at.% Ti content. X-ray diffraction patterns revealed the presence of a nanocrystalline TiC phase. The hardness varied from 8 to 9 GPa. The tribological tests were performed under dry sliding and lubricated (0.9% NaCl water solution, physiological solution, PS, and 10% fetal bovine serum dissolved in Ringer’s saline solution, FBS) conditions, using a 100Cr6 steel balls with a diameter of 6 mm, in a pin-on-disc wear test apparatus.     

Runaway electron beam generation by a plasma cathode in atmospheric air discharge

Electron beam generation in atmospheric air discharge with a flat cathode has been experimentally studied. The discharge was excited by voltage pulses of negative polarity with an amplitude of 220 kV, a full width at half maximum of 2 ns, and a leading front width of 0.7 ns. The electron beam was monitored using luminescence of a layer of ZnS-CdS:Ag phosphor placed behind a 20-μm-thick foil anode. It was found that the intensity and homogeneity of luminescence of the phosphor layer increased when a dielectric tube with a length smaller than half of the interelectrode distance was placed in the near-cathode part of the air gap. It is concluded that a plasma cathode is formed within the volume confined by the tube and electrons emitted from this region are accelerated in the open part of the gap. In addition, the dielectric tube decreases the divergence of the electron beam.     

空心阴极等离子体放电结构的优化设计

 低温等离子体表面处理可以有效克服液相处理法存在的环境污染、耗能大和成本高的缺点,对材料表面进行清洗、活化和接枝处理,而设计一个合理的低温等离子体放电结构能够较好地改进表面处理的质量．通过建立CRFHCP空心阴极等离子体放电的数学模型,分析影响低温等离子体放电的关键因素,并设计了不同电极配置方式、样品位置和不同远区空心阴极结构的众多方案．通过接触角测定、表面能计算、SEM照片等方式,对不同方案下处理前后的疏水性PP薄膜形态结构进行表征分析．实验结果发现：远区径向喷嘴式空心阴极等离子体放电结构处理的薄膜表面比其他处理方式具有较小的接触角和较大的表面能．这表明采用优化设计的CRFHCP空心阴极等离子体放电结构,可以较其他结构更为有效地改善材料表面的亲水性能．     

Non-equilibrium crystallization-aggregation mechanism of a-C:H layer in a-C:H/a-Se complex films

Also representing: CCAST (World Laboratory), Beijing 100080, People's Republic of China and the Structure Research Laboratory, University of Sciences and Technology of China, Hefei 230026, People's Republic of China.     

The influence of bias sputter parameters on thick copper coatings deposited using a hollow cathode

Experiments were conducted to examine the influence of bias sputtering on open boundary formation in thick (60–100 μm) OFHC copper coatings deposited on substrates with polished and bead-blasted surfaces at low (0.13 Pa) and high (4 Pa) argon pressures. Coatings were deposited on tubular substrates mounted on the axis of a hollow cathode sputtering apparatus in a configuration which (1) permitted a relatively wide combination of voltages and current densities to be maintained on the cathode and substrate and (2) provided sufficient control so that net deposition rates could be predicted from the cathode and substrate voltages and current densities. Most experiments were conducted with bias sputter voltages of - 100 V, -250 V, -500 V and -850 V using water-cooled substrates to eliminate thermal influences. Backsputter fractions covered the range 10–70%. Coating surface topographies, microhardnesses, preferred orientations and microstructures were influenced by bias conditions. At 0.13 Pa an intense ion bombardment suppressed open boundary formation on smooth but not on bead-blasted substrates. At 4 Pa intense ion bombardment largely suppressed open boundaries, even on the rough substrates. Sputter redistribution of coating material appears to be an important mechanism in bias suppression of open boundaries.     

Generation of a homogeneous plasma in a glow discharge with a hollow anode and a wide-aperture hollow cathode

The principles for designing electrode systems for sources of ion beams of large cross section on the basis of a glow discharge are considered, and a system with combined magnetic and electrostatic confinement of the fast electrons in a wide-aperture hollow cathode and the generation of an ion-emitting plasma in the anode cavity is proposed. It is shown that the system investigated generates a plasma with a nearly homogeneous distribution of the ion emission current density at low gas pressures and can be effectively used to obtain ion beams over a broad range of energies. Pis’ma Zh. Tekh. Fiz. 25, 83–88 (June 26, 1999)     

Mechanical properties of a-C:H thin films deposited by r.f. PECVD method

Internal stress, hardness and deposition rate were evaluated for hydrogenated amorphous carbon (a-C:H) films prepared by conventional r.f. plasma-enhanced chemical vapour deposition. The internal stress, hardness and deposition rate of 0.9, 18 and 58 nm/min, respectively, achieved at 40 Pa gas pressure for negative self-bias voltages (V_b) window (from −370 to −550 V). It was found that the negative self-bias voltage window was associated with the existence of two turning points, which shift to higher wavenumber of G band peak position of Raman spectroscopy (Raman) at different V_b in relation to the internal stress and hardness, and rapid decreasing of the relative total peak areas of Fourier Transform Infra-red absorption spectroscopy (FT-IR).The internal stress relaxed from approximately 35 eV ion energy when the energy is increased and rapidly decreased in comparison with the stress relaxation equation.     

Characterization of thick chromium-carbon and chromium-nitrogen films deposited by hollow cathode discharge

Both CrC and CrN films deposited by hollow cathode discharge show hard, wear-resistant and good anti-corrosion characteristics. The ranges of substrate temperature and molecular ratio of chromium atoms and reactant molecules (C₂H₂ and N₂) arriving at the substrate were mapped, with Vickers microhardness as the parameter, for substrate bias voltages of 0 V and ?50 V. The films were characterized using X-ray diffraction, transmission electron microscopy, electron diffraction, Auger electron spectroscopy and electron probe microanalysis. The hardness of these films did not decrease after vacuum annealing up to 820 °C but instead increased in some cases, the line broadening in X-ray diffraction becoming narrower. Comparison of the chemical compositions of these films by Auger electron spectroscopy and electron probe microanalysis gave linear correspondences.     

Long-term aging of Ag/a-C:H:O nanocomposite coatings in air and in aqueous environment

Abstract

Nanocomposite coatings of silver particles embedded in a plasma polymer matrix possess interesting properties depending on their microstructure. The film microstructure is affected among others also by the RF power supplied during the deposition, as shown by transmission electron microscopy. The optical properties are characterized by UV–vis–NIR spectroscopy. An anomalous optical absorption peak from the Ag nanoparticles is observed and related to the microstructure of the nanocomposite films. Furthermore, a long-term aging of the coatings is studied in-depth in ambient air and in aqueous environments. It is shown that the studied films are not entirely stable. The deposition conditions and the microstructure of the films affect the processes taking place during their aging in both environments.     

XPS study of the a-C:H/Ti and a-C:H/a-Si interfaces

In this study ultrathin hydrogenated amorphous carbon (a-C:H) films have been grown onto the titanium and amorphous silicon (a-Si) overlayers by direct ion beam deposition using acetylene gas as a hydrocarbon source. X-ray photoelectron spectroscopy (XPS) was used for study of the DLC-Ti and DLC-Si interfaces. It was revealed that a-Si is a good interlayer for improvement of adhesion in the case of diamond-like carbon film deposition onto the steel substrate at room temperature. a-C:H film growth without substantial intermixing occurred on the a-Si. On the other hand, adhesion between the Ti interlayer and the diamond like carbon film was very sensitive to the deposition conditions (presence of the pump oil) as well as structure and stress level of the Ti film. It was explained by strong intermixing between the growing carbon film and Ti. Bad adhesion between the growing DLC film and Ti interlayer was observed despite formation of the TiC. At the same time, formation of the TiO_x was not an obstacle for good adhesion. It is shown that composition of the used hydrocarbon gas, structure of the Ti thin film and mechanical stress in it had greater influence on adhesion with a-C:H film than elemental composition of the Ti interlayer surface.     

Spectral diagnostics of plasma discharge between a metal cathode and liquid anode

The results from studies of an electric discharge between a metal cathode and liquid anode at atmospheric pressure are presented. We investigate the discharge shape, the plasma emission spectrum, the electron concentration and temperature, and the molecule temperature; we analyze the continuous emission in the plasma spectrum and perform infrared thermography.