Mechanical properties and platelet adhesion behavior of diamond-like carbon films synthesized by pulsed vacuum arc plasma deposition

Diamond-like carbon (DLC) is an attractive biomedical material due to its high inertness and excellent mechanical properties. In this study, DLC films were fabricated on Ti6Al4V and Si(1 0 0) substrates at room temperature by pulsed vacuum arc plasma deposition. By changing the argon flow from 0 to 13 sccm during deposition, the effects of argon flow on the characteristics of the DLC films were systematically examined to correlate to the blood compatibility. The microstructure and mechanical properties of the films were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) surface analysis, a nano-indenter and pin-on-disk tribometer. The blood compatibility of the films was evaluated using in vitro platelet adhesion investigation, and the quantity and morphology of the adherent platelets was investigated employing optical microscopy and scanning electron microscopy.The Raman spectroscopy results showed a decreasing sp³ fraction (an increasing trend in I_D/I_G ratio) with increasing argon flow from 0 to 13 sccm. The sp³:sp² ratio of the films was evaluated from the deconvoluted XPS spectra. We found that the sp³ fraction decreased as the argon flow was increased from 0 to 13 sccm, which is consistent with the results of the Raman spectra. The mechanical properties results confirmed the decreasing sp³ content with increasing argon flow. The Raman D-band to G-band intensity ratio increased and the platelet adhesion behavior became better with higher flow. This implies that the blood compatibility of the DLC films is influenced by the sp³:sp² ratio. DLC films deposited on titanium alloys have high wear resistance, low friction and good adhesion.     

Fluctuation of arc plasma in arc plasma torch with multiple cathodes

Fluctuation phenomena commonly exist in arc plasmas, limiting the application of this technology.In this paper,we report an investigation of fluctuations of arc plasmas in an arc plasma torch with multiple cathodes.Time-resolved images of the plasma column and anode arc roots are captured.Variations of the arc voltage, plasma column diameter, and pressure are also revealed.The results indicate that two well-separated fluctuations exist in the arc plasma torch.One is the high-frequency fluctuation(of several thousand Hz), which arises from transferring of the anode arc root.The other is the low-frequency fluctuation(of several hundred Hz), which may come from the pressure variation in the arc plasma torch.Initial analysis reveals that as the gas flow rate changes, the low-frequency fluctuation shows a similar variation trend with the Helmholtz oscillation.This oscillation leads to the shrinking and expanding of the plasma column.As a result, the arc voltage shows a sinusoidal fluctuation.     

Uncapped silver nanoparticles synthesized by DC arc thermal plasma technique for conductor paste formulation

Uncapped silver nanoparticles were synthesized by DC arc thermal plasma technique. The synthesized nanoparticles were structurally cubic and showed wide particle size variation (between 20–150 nm). Thick film paste formulated from such uncapped silver nanoparticles was screen-printed on alumina substrates and the resultant ‘green’ films were fired at different firing temperatures. The films fired at 600 °C revealed better microstructure properties and also yielded the lowest value of sheet resistance in comparison to those corresponding to conventional peak firing temperature of 850 °C. Our findings directly support the role of silver nanoparticles in substantially depressing the operative peak firing temperature involved in traditional conductor thick films technology.     

Morphology and electronic properties of carbon nanotubes synthesized by arc discharge in CF4gas

The morphology of carbon nanotubes synthesized by arc discharge in a CF₄gas atmosphere was investigated by scanning electron microscopy and transmission electron microscopy. The electronic properties of these nanotubes were investigated by electron spin resonance. The synthesis conditions in CF₄gas were then compared with those in CH₄, H₂and He based on these results. Furthermore, the mechanism of tube growth in CF₄gas was discussed briefly.     

Synthesis of carbides in the arc plasma

A method of synthesis of iron, silicon, titanium, and tungsten carbides in an argon arc between graphite electrodes is developed. It is found that iron, silicon, and titanium atoms introduced into the interelectrode gap cause the voltage drop across the gap to decrease, whereas tungsten atoms increase this voltage. The X-ray diffraction analysis of synthesized powders reveals carbide and graphite crystallites. Their relative concentrations are estimated from the intensities of the respective reflection peaks. The morphological examination of the synthesized particles shows that titanium carbide particles are the largest and iron carbide ones are the finest. Raman spectra taken of the powders confirm the presence of graphite and carbide crystallites.     

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采用简化阴极的一维边界层模型,将同轴磁旋转电弧等离子体发生器的阴极与弧柱耦合求解,使用FLUENT软件,数值模拟了不同锥角阴极的形状对磁分散电弧等离子体、阴极弧根和阳极弧根位形的影响.结果表明:阴极弧根具有扩散特征,其电流密度为107A·m-2量级;阴极形状的改变引起阴极弧根位形和电流密度分布变化,从而影响等离子体参数分布;随着阴极锥角的增大,阴极弧根从阴极前端移动到阴极侧面,等离子体区域向下游偏移,等离子体轴向厚度减小.     

Observation of arc modes in a magnetically rotating arc plasma generator

An arc plasma can present various forms under the influence of an external magnetic field. In this study, a magnetically rotating arc plasma generator has been developed to produce three arc modes, namely rigid arc, distorted arc, and diffuse arc, which are obtained by controlling the gas flow rate. The evolution of these arc modes are experimentally studied and discussed. Results show that, as the gas flow rate increases, the arc mode is first transformed from the rigid to the distorted mode, and then to the diffuse mode. Comparisons show that the location of the arc attachment is a key factor in determining the rigid and distorted modes. The diffuse arc is observed under larger gas flow rates, but the completely diffuse arc can exist only within a narrow range of gas flow rates. Compared to the distorted arc, the diffuse arc has not only better stability but also a wider high‐temperature plasma zone, which indicates that the diffuse mode may be more useful in industry.     

Electrostatic interaction in plasma with charged bose condensate

Screening in plasma with Bose-Einstein condensate is studied. Finite temperature effects are taken into account. It is shown that, due to condensate effects, the potential has several unusual features. It contains two oscillating terms, one of which is analogous to the fermionic Friedel oscillations in standard QED, and a power law decreasing term. In the T ?? 0 limit, only one of the oscillating terms survives. On the whole, any charge impurity is screened more efficiently than in ordinary plasma.     

Absorption characteristic of arc plasma in the infrared region

In this paper,argon arc plasma is chosen as an example to study the absorption characteristics of arc plasma in the infrared region.Firstly,the phase and the attenuation constants are deduced for the given temperature,pressure and probe wavelength regions.Based on those constants,the dependence of the attenuation constant on the temperature and pressure in the vicinity of a certain probe wavelength is found.Then,theoretical analysis and discussion are conducted.Maximal absorption occurs at the position where the contributions of neutral particles and electrons come to a balance in a physical point of view,which may provide some measures to take for decreasing or controlling the plasma absorption of electromagnetic waves.     

磁旋转弧等离子体中的弧电压突变现象

利用光学成像系统观察到了磁旋转弧等离子体实验中的电弧电压突变现象,电弧电压突变的范围约在40～100V之间。实验结果表明,电弧电压的变化与电弧弧长的变化密切相关。     

Evolution of magnetically rotating arc into large area arc plasma

An arc channel tends to shrink due to its conductivity increasing with the increase of temperature.In this study,to generate large area arc plasma,we construct a magnetically rotating arc plasma generator,which mainly consists of a lanthanide tungsten cathode(13 mm in diameter),a concentric cylindrical graphite anode chamber(60 mm in diameter)and a solenoid coil for producing an axial magnet field.By controlling the cold gas flow,the magnetically rotating arc evolves from constricted mode to diffuse mode,which almost fills the whole arc chamber cross section.Results show that the diffuse arc plasma has better uniformity and stability.The formation mechanism of large area arc plasma is discussed in this paper.     

Estimation of dynamic properties of attractors observed in hollow copper electrode atmospheric pressure arc plasma system

Understanding of the basic nature of arc root fluctuation is still one of the unsolved problems in thermal arc plasma physics. It has direct impact on myriads of thermal plasma applications being implemented at present. Recently, chaotic nature of arc root behavior has been reported through the analysis of voltages, acoustic and optical signals which are generated from a hollow copper electrode arc plasma torch. In this paper we present details of computations involved in the estimation process of various dynamic properties and show how they reflect chaotic behavior of arc root in the system.     

Effects of gravity on single-wall carbon nanotubes synthesized by arc in water

The method using arc discharge in liquid is a simple and inexpensive route for synthesis of carbon nanotubes and other related nano-materials. In this study, we report the synthesis of single-wall carbon nanotubes (SWCNTs) by means of the arc-in-water method under extremely low gravity conditions. The strong heat convection caused by the arc plasma is suppressed under such conditions. Therefore, the boiling flow behavior and temperature distribution have been stabilized in low gravity. As a result, the possibility of the chirality control of SWCNTs by applying extremely low gravity was revealed; namely, the yield of semiconducting SWCNTs was increased and several SWCNTs of specific diameters turned out to be prominent under extremely low gravity conditions. PACS 52.80.Wq; 68.37.Lp; 81.07.De; 81.70.Ha; 82.80.Gk     

Properties of high pressure arc plasma

High pressure argon arc discharges are investigated in the pressure range up to 1000 atm. Experimental values of radiative properties such as the frequency-dependent emission coefficient and the total radiation source strength are compared with theoretical predictions. Solutions of the energy balance of wall stabilized high pressure arcs are presented, the agreement with measurements is good. A comparison of measured electrical conductivities of non-ideal argon plasmas with order measurements and with computations following different theoretical approaches, confirms the poor agreement between theory and experiment found by other authors for this regime. Auszug aus einer Habilitationsschrift am Fachbereich für Elektrotechnik der TU München.     

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研究了滑动弧放电过程中电参数的变化,并对滑动弧等离子体中的非平衡度和各个参数之间的关系进行了讨论。应用双通道电弧模型,对电弧在气流作用下运动规律进行了数值模拟,模拟所得的结果有助于分析滑动弧非平衡等离子体的产生机理。     

On the application of the theory of Lorentzian plasma to calculation of transport properties of multicomponent arc plasmas

The application of the Lorentzian plasma theory for the calculation of the properties of multicomponent electric arc plasma is considered. It is shown that this model gives satisfactory results in the temperature range, which is corresponding to the weakly ionized arc plasma and arc plasma with dominant first ionization. The calculations are provided for the arc plasmas of noble gases and their mixtures between them and also that with metals. It is also pointed that the discrepancy between the electron temperature and gas temperature can be significant even at relatively weak electric fields, that fact must be taken into account under the simulation of arc discharges.     

O--ion radiation in the spectrum of an oxygen arc plasma

The radiation emitted from the axis of a wall-stabilized, low-current cylindrical arc in pure oxygen at temperatures around 9000 K was measured quantitatively in the wavelength range from 2000 to 9000 A. In the near i.r. region, the two first thresholds of the affinity continuum appear at 8615 and 8465 A, respectively, yielding an electron affinity (EA) of 1.465 eV and a ground-state splitting Δ = 26 meV for the negative oxygen ion. Another threshold occurs in the u.v. region at 3630 A and involves a transition to O^- from the first exited state of atomic oxygen. The continuous spectrum can be shown (Fig. 17) to be dominated in the u.v. and visible regions by the affinity continuum due to the negative oxygen ion. Additional contributions, which become increasingly important towards longer wave-lengths, are the Kramers-Unsöld continuum and O₂⁺-association radiation. In the u.v., the recombination of two neutral oxygen atoms forms a small contribution. A broad peak structure centered around 7000 A cannot be definitely explained. Applying Kirchhoff's law, the photodetachment cross section of O^- is obtained as a function of photon energy. Deviations from local thermodynamic equilibrium (LTE) are accounted for.     

Transport properties of the disordered charged bose condensate in two dimensions

Analytical results for the frequency-dependent conductivity of a disordered two-dimensional interacting Bose condensate are presented. Charged and uncharged impurities are considered. We find that for weak disorder the condensate is a superfluid while for strong disorder it is an insulator (a Bose glass). At the superfluid-insulator transition point (at the critical boson densityN _c) the condensate exhibits metallic tranport properties. An loffe-Regel criterion for the transition point is derived. The conductivity at the transition point is of ordere ²/h (h is Planck's constant) and depends on the kind of disorder. For charged impurities (with impurity densityN _i) the conductivity (for a condensate of particles with charge 2e and forN _i=2N _c) at the transition point is given by _c =0.26x(2e)²/h. We discuss recent experiments on superconducting ultra-thin films and on high-T _c superconductors.     

自旋-轨道耦合玻色-爱因斯坦凝聚势垒散射特性的研究

对自旋-轨道耦合玻色-爱因斯坦凝聚中的双势垒散射问题进行了研究, 得到了系统透射系数的解析表达式, 并对如何克服Klein隧穿以及如何束缚Dirac粒子进行了讨论并给出囚禁Dirac粒子的实验方案. 此外, 运用时间劈裂谱方法对Dirac粒子势垒散射问题进行了数值模拟. 分析了Dirac粒子分别在势垒Klein阻塞区域中心以及边缘的透射情况. 最后从排斥和吸引相互作用两方面研究了非线性相互作用对于Dirac粒子演化的影响, 结果表明弱非线性相互作用对散射特性的影响非常小, 而强非线性相互作用会彻底破坏波包的动量分布, 从而改变Dirac粒子的势垒散射效果． 关键词： 自旋-轨道耦合 Klein隧穿 势垒散射 玻色-爱因斯坦凝聚     

Coherence properties of a radiating electron-hole condensate

We analyze both the spatial as well as the temporal coherence of an electron-hole condensate and the radiation emitted from it. These coherences evolve from being full for the low density Bose-Einstein condensate to a chaotic behavior for a high density Bardeen-Cooper-Schrieffer-like state. Time coherence is transferred, to the emitted radiation in the ultrafast regime, in a damped oscillatory way.