Effect of Fe ion implantation on tribological properties and Raman spectra characteristics of diamond-like carbon film

1 Introduction It is well known that DLC (diamond-like carbon)prepared by physical vapor deposition, plasma en-hanced chemical vapor deposition (PECVD) and otherplasma processing is an amorphous carbon materialcontaining sp2 and sp3 bonded carbon atoms. DLCfilm possesses some interesting properties, such ashigh hardness and Young's modulus, chemical inert-ness and low friction coefficient. The property andstructure of DLC film can be modified by addingsome metals. Ion implantation…     

Study on the Hydrogenated Diamond-Like Carbon Films Synthesized by RF-PECVD from n-decane

Using a mixture of n-decane and hydrogen, diamond-like carbon thin films (DLCTFs) with high growth rate of 35?nm/min are deposited by radio frequency plasma enhanced chemical vapor deposition. We show that n-decane can be considered as a promising carbon source in DLCTF deposition. The properties of the deposited films such as structure, hydrogen content, deposition rate and refractive index are studied for 20, 50 and 100?sccm hydrogen flow rates (HFRs). It is shown that the deposition rate has a maximum of 35?nm/min for HFR?=?20?sccm and by increasing hydrogen concentration, deposition rate drops to 19?nm/min for HFR?=?100?sccm. The Raman spectra reveal that the films represent hydrogenated diamond-like carbon features. The photoluminescence background of the Raman spectra is used as a measure for hydrogen content of the films. The hydrogen content varies from 29 to 46% which yields a various amount of sp³ fraction. The results of the spectroscopic ellipsometry indicate that by increasing HFR, refractive index decreases from 2.1 to 1.9 at 632?nm. The aforementioned trends are attributed to the increase of hydrogen content in DLCTFs which is in very good agreement with enhancing of the photoluminescence background of the Raman spectra.     

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.     

Simulation of a low energy beam transport line

A 2.45 GHz electron cyclotron resonance intense proton source and a low energy beam transport line with dual-Glaser lens were designed and fabricated by Institute of Modern Physics for a compact pulsed hadron source at Tsinghua. The intense proton beams extracted from the ion source are transported through the transport line to match the downstream radio frequency quadrupole accelerator. Particle-in-cell code BEAMPATH was used to carry out the beam transport simulations and optimize the magnetic field structures of the transport line. Emittance growth due to space charge and spherical aberrations of the Glaser lens were studied in both theory and simulation. The results show that narrow beam has smaller aberrations and better beam quality through the transport line. To better match the radio frequency quadrupole accelerator, a shorter transport line is desired with sufficient space charge neutralization.     

Analysis of Van de Graaff ion source with Rutherford backscattering spectroscopy

A radio frequency (RF) ion source is utilized at the University of Massachusetts Lowell accelerator facility to produce a plasma from which positive ions are extracted and then accelerated. The interior surface of the source becomes contaminated with a dark coating after several hundred hours of usage which reduces the current output of the source. Rutherford backscattering spectroscopy (RBS) was employed to analyze the constituents of this coating. Procedures have been carried out to etch chemically this film and to refurbish the ion source.     

First results of negative ion extraction with Cs for CRAFT prototype negative beam source

In order to understand the physics and pre-study the engineering issues for radio frequency(RF)negative beam source, a prototype source with a single driver and three-electrode accelerator was developed. Recently, the beam source was tested on the RF source test facility with RF plasma generation, negative ion production and extraction. A magnetic filter system and a Cs injection system were employed to enhance the negative ion production. As a result, a long pulse of 105 s negative ion beam with current density of 153 A m-2 was repeatedly extracted successfully. The source pressure is 0.6 Pa and the ratio of co-extracted electron and negative ion current is around0.3. The details of design and experimental results of beam source were shown in this letter.     

MoP with rich species generated via radio frequency thermal plasma for higher alcohols synthesis from syngas

In this paper, the molybdenum phosphide (MoP) catalysts (TPR-MoP and TPR-MoP-Pla) were prepared by the traditional method and the RF (radio frequency) thermal plasma technique respectively and characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), hydrogen temperature-programmed desorption (H₂-TPD) and carbon monoxide temperature-programmed desorption (CO-TPD) measurements, and their catalytic performance for HAS was evaluated. The results showed that the total and C₂₊ alcohols selectivity of the catalyst after plasma treatment (TPR-MoP-Pla) were enhanced. The enhanced catalytic performance could be related to more dislocation defects and the synergistic effect between Mo^0–2+ and Mo⁴⁺ valence species in the TPR-MoP-Pla catalyst. In addition, this work suggests that thermal plasma treatment can be used as a new preparation technique for the synthesis of materials with rich species.     

Analysis of the characteristics of the plasma of an RF driven ion source for a neutral beam injector

A radio frequency(RF)driven ion source is a very important component of a neutral beam injector for large magnetic confinement fusion devices.In order to study the key technology and physics of an RF driven ion source for a neutral beam injector in China,an RF ion source test facility was developed at the Institute of Plasma Physics,Chinese Academy of Sciences.In this paper,a two-dimensional fluid model is used to simulate the fundamental physical characteristics of RF plasma discharge.Simulation results show the relationship of the characteristics of plasma(such as electron density and electron temperature)and RF power and gas pressure.In order to verify the effectiveness of the model,the characteristics of the plasma are investigated using a Langmuir probe.In this paper,experimental and simulation results are presented,and the possible reasons for the discrepancies between them are given.This paper can help us understand the characteristics of RF plasma discharge,and give a basis for further R&D for an RF ion source.     

Electrostatic Modes of Dusty Plasmas in a Uniform Magnetic Field

Electrostatic dusty plasma waves in a uniform magnetic field are studied.Unless the magnetic field is extremely strong,the dust particles can hardly be magnetized,while however,electrons and ions are easily done so.Electrostatic modes in such dusty plasmas can then be investigated by making use of the “Moderately magnetized” assumption of magnetized electrons and ions,and unmagnetized dust particles.In a high frequency range,due to the existence of dust component.both frequencies of Langmuir waves(parallel to the magnetic field)and upper hybrid waves(perpendicular to the field) are reduced.In the frequency range of ion waves,besides the effect on dust-ion-acoustic waves propagating parallel to the magnetic field.the frequency of ion cyclotron waves perpendicular to the magnetic field is also enhanced.In a very low dust frequency range,we find an “ion-cyclotron-dust-acoustic” mode propagating across the field line with a frequency even slower than dust acoustic waves.     

Modeling of magnetized collisional plasma sheath with nonextensive electron distribution and ionization source

The properties of an atmospheric-pressure collisional plasma sheath with nonextensively distributed electrons and hypothetical ionization source terms are studied in this work. The Bohm criterion for the magnetized plasma is extended in the presence of an ion–neutral collisional force and ionization source. The effects of electron nonextensive distribution, ionization frequency, ion– neutral collision, magnetic field angle and ion temperature on the Bohm criterion of the plasma sheath are numerically analyzed. The fluid equations are solved numerically in the plasma–wall transition region using a modified Bohm criterion as the boundary condition. The plasma sheath properties such as charged particle density, floating sheath potential and thickness are thoroughly investigated under different kinds of ion source terms, contributions of collisions, and magnetic fields. The results show that the effect of the ion source term on the properties of atmosphericpressure collisional plasma sheath is significant. As the ionization frequency increases, the Mach number of the Bohm criterion decreases and the range of possible values narrows. When the ion source is considered, the space charge density increases, the sheath potential drops more rapidly, and the sheath thickness becomes narrower. In addition, ion–neutral collision, magnetic field angle and ion temperature also significantly affect the sheath potential profile and sheath thickness.     

Modification of DLC films by Ni ions implantation

Enhanced diamond-like carbon (DLC) multilayer films were produced by a method of alternating the magnetic filtered vacuum cathode arc deposition and the metal vapor vacuum arc (MEVVA) implantation of Ni⁺ ions. The microstructure and mechanical properties of these multilayer films were studied by XPS, Raman, SEM, AFM, XRD, nano-intender and internal stress measurement. The results reveal that with the increasing dose of implanted Ni⁺ ions, the sp³ contents are declining and reduction of the nanohardness and release of the internal stress are observed.     

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。     

Gas pressure effect on plasma transport in a magnetic-filtered radio-frequency plasma source

Volume negative ion production relies on a magnetic filter(MF), where the plasma downstream of the MF is characterized by a strip-like pattern that consists of a bright and dense plasma region. In this work, we study, in a radio-frequency plasma source, the effects of operating pressure on this strip. This investigation, conducted using a Langmuir probe, shows that the plasma uniformity might be controlled through the gas pressure. Moreover, the operating pressure determines on which hemi-cylinder(side of magnetic field lines) the strip forms. This side inversion of the high-density plasma hemi-cylinder is due to an inversion of an ambipolar electric field that changes the E?×?B drift direction.     

Simulations of first-orbit losses of neutral beam injection(NBI) fast ions on EAST

Simulations of first-orbit losses of neutral beam injection(NBI) fast ions in the EAST tokamak have been studied in detail by using the orbit-following code GYCAVA and the NBI code TGCO. Beam ion losses with the wall boundary are smaller than those with the last closed flux surface boundary. In contrast to heat loads on the wall without radio frequency wave(RFW)antennas, heat loads on the wall with RFW antennas are distributed more locally near the RFW antennas. The direction of the toroidal magnetic field dramatically affects the final positions of lost fast ions, which is related to the magnetic drift. The numerical results on heat loads of beam ions corresponding to different toroidal magnetic fields are qualitatively consistent with the experimental results. Beam ion losses increase with the beam energy for the co-current NBIs and the counter-perpendicular NBI. We have studied the behavior of fast ions produced by a small section neutral beam(beamlet) by using the numerical tool NBIT. The distributions of the loss fraction of beamlet fast ions peaked near the edge of the beam section for the counter-current NBIs, and they are related to the injection angle. This indicates that the first-orbit losses can be reduced by changing the shape of beam cross section.     

紧凑型强流ECR源

建立了１台紧凑型强流ＥＣＲ源。共振磁场由１个小电磁线圈及软铁回路产生,磁场可调,能保证放电处于最佳条件。研究了气压,微波功率及共振场对放电的影响。在５５０Ｗ的放电功率下,从直径４ｍｍ引出孔引出了３５ｍＡ的Ｈ＾＋离子束,引出Ｈ＾＋离子的质子比超过９０％,从源中还引出了７ｍＡＯ＾＋、８ｍＡＮ＾＋、１２ｍＡ Ａｒ＾＋的束流。     

Ion Extraction Characteristics from Photoionized Plasma by Radio-Frequency Resonance Method

In order to raise ion extraction efficiency in laser isotope separation, we have developed a radio-frequency (rf) resonance method. Then, to confirm feasibility of this method to a photoionized plasma, we experimentally studied the ion extraction characteristics.

When the rf frequency was swept under a weak magnetic field (5mT), the plasma-sheath resonance was found to occur at about 12MHz which was almost the same value as the theoretical one. Moreover, it was confirmed that the ion extraction time at the resonance frequency became the minimum.

When the magnetic field strength decreased from 5mT to zero, the ion extraction time became long. From the simulation results, this was because the plasma potential decreased with the magnetic field strength. Therefore, a magnetic field strength of more than 1mT was required to obtain a sufficient ion extraction efficiency.

To obtain the same extraction time as when applying a ?3kV dc voltage in the electrostatic method, the rf resonance method needed a voltage more than 70V_rms, in which the dc bias was ?1kV. Therefore, we confirmed that this method is feasible for the ion extraction from the photoionized plasma.     

Mechanism of high growth rate for diamond-like carbon films synthesized by helicon wave plasma chemical vapor deposition

A high growth rate fabrication of diamond-like carbon(DLC)films at room temperature was achieved by helicon wave plasma chemical vapor deposition(HWP-CVD)using Ar/CH_4gas mixtures.The microstructure and morphology of the films were characterized by Raman spectroscopy and scanning electron microscopy.The diagnosis of plasma excited by a helicon wave was measured by optical emission spectroscopy and a Langmuir probe.The mechanism of high growth rate fabrication for DLC films by HWP-CVD has been discussed.The growth rate of the DLC films reaches a maximum value of 54μm h~(-1)at the CH_4flow rate of 85 sccm,which is attributed to the higher plasma density during the helicon wave plasma discharge.The CH and H_αradicals play an important role in the growth of DLC films.The results show that the H_αradicals are beneficial to the formation and stabilization of C=C bond from sp~2to sp~3.     

Extraction Characteristics of Radio Frequency ICP Ion Source

An inductively coupled radio frequency ion source has been developed and its extraction characteristics measured. Beam current density up to 0.11 mA/ cm2 was obtained with argon at a rf discharge power of about 140 W. The dependences of ion beam on the discharge parameters such as rf source power, gas pressure and gas flow rate was studied.     

α+β两相区热处理对Zr-Sn-Nb合金微观组织和腐蚀性能的影响

对Zr-Sn-Nb合金在α+β两相区温度下不同工艺热处理后所得样品,在360 ℃/18.6 MPa纯水环境中进行均匀腐蚀试验,并采用扫描电子显微镜（SEM）观察样品微观形貌、聚焦离子束（FIB）和原子力显微镜（AFM）分析腐蚀后样品表面氧化膜。结果表明,Zr-Sn-Nb合金在α+β两相区温度下热处理时,锆合金中会形成条带状β-Zr第二相,再经过α相区温度最终退火后,β-Zr区域会分解为α-Zr和第二相粒子;经α相区最终退火的样品,在360 ℃/18.6 MPa纯水中的耐腐蚀性能优于未经最终退火的样品;未退火样品中条带状β-Zr第二相区域的氧化膜较α-Zr基体的氧化膜厚,而经过α相区温度退火后β-Zr发生分解,该区域的腐蚀氧化膜出现凹陷。     

Measurement of Ion Cyclotron Emissions by Using High-Frequency Magnetic Probes in the LHD

Two pairs of high-frequency magnetic probes were installed in the Large Helical Device (LHD). During the injection of a perpendicular neutral beam, ion cyclotron emissions (ICEs) with the fundamental frequency corresponding to the ion cyclotron frequency at the plasma edge were detected, which are the same type of ICE as measured with the former spare ion cyclotron range of frequencies (ICRF) heating antennas. This type of ICE was further investigated with regard to the phase and intensity of signals. Another type of ICE was found in the LHD, and these ICEs were synchronized with bursts of toroidicity induced Alfv¶en eigenmodes (TAE) and the rise of intensity of lost ion °ux. Therefore the source of these ICEs was thought to be the particles transferred from the core to the outer region of plasma by the TAE bursts. The frequency of ICEs induced by the TAE bursts increases linearly with the magnetic ¯eld strength, since the ion cyclotron frequency increases with the magnetic ¯eld strength.