Discharge characteristics of a radio-frequency capacitively coupled Ar/O2 glow discharge at atmospheric pressure

In this study, the discharge characteristics of the developed atmospheric pressure homogeneous and cold plasma source in Ar/O₂ glow discharge driven by radio-frequency (13.56 MHz) are investigated experimentally by means of electric measurements. The electron density is estimated to be in the order of 10¹¹ cm^− 3 in the abnormal discharge regime and is reduced by half in amount when the oxygen is mixed into argon plasma at oxygen-to-argon ratio of 0.3 and 0.6 vol.% at the same input power. The estimated electron temperature assumes the value of 1.4 eV in the abnormal discharge regime and the addition of oxygen to the argon plasma at the oxygen-to-argon ratio smaller than 1.0 vol.% does not alter the electron temperature appreciably.     

Nanoimprint lithography patterns with a vertically aligned nanoscale tubular carbon structure

A nanoscale tubular carbon structure array was demonstrated as a mold for nanoimprint lithography (NIL), in which a vertically formed and hexagonally aligned nanoscale tubular carbon array was fabricated through carbon growth inside an anodic aluminum oxide (AAO) nanotemplate, followed by controlled chemical etching of the AAO layer. High density (over 10(10)?cm(-2)) of the nanoscale carbon pillars with their controlled diameters and protruded lengths was inversely replicated onto a UV-curable resist for the first time using the imprinting lithography technique.     

Operating characteristics of the hollow anode glow discharge ion source

In this work, a new shape of a glow discharge ion source with axial extraction has been designed and constructed. High output ion beam current can be extracted axially in a direction normal to the discharge region without using extraction system. Optimization of the distance between the anode and the cathode has been determined using argon gas. It is found that the optimum gap distance between the anode and the cathode is equal to 3.5 mm, where stable discharge current and maximum output ion beam current can be obtained. The discharge characteristics of the ion source at different operating gas pressures have been measured at this optimum distance between the anode and the cathode. A disk of Teflon insulator has been put between the anode and the cathode. This disk was covering the cathode area and reducing the discharge area on the cathode surface for discharge confinement, therefore, a higher output ion beam current could be obtained.     

Surface wettability of silicon rubber after irradiation with a glow discharge plasma

Silicon rubber, PDMS, was irradiated by Ar, Ar/H₂ and Ar/O₂ plasmas to increase the surface wettability to water which was found to increase with the irradiation time for every application of plasma irradiation. The use of Ar/O₂ plasma was found to be particularly effective in enhancing the surface wettability. The aging behavior due to exposure to air, ethanol or water was also measured. In the case of continuous exposure to water after plasma treatment, the wettability could be maintained for more than several months with the water immersion.     

Breakdown voltage of glow discharge of pin electrodes

One of the shortcomings of glow discharge tube is its high breakdown voltage. In this paper, 2-pin electrode, 3-pin electrodes and 4-pin electrode are fabricated. The breakdown voltages of glow discharge of these electrodes have been measured within the pressure range of 0.4-2.5 kPa. The breakdown voltages vary obviously for the different kinds of electrodes, and the maximum difference of the breakdown voltages is about 208 V. Electric fields of the electrodes are calculated and the results consist with the experimental results. It is concluded that the breakdown voltage can be significantly reduced by adjusting electrode structure without changing the distance between electrode pins. The proposed electrode structure has potential applications in devices of glow discharge.     

Study of rotational temperature of oxygen DC glow discharge in Silica and Pyrex discharge tubes

Active DC glow discharges in oxygen have been studied in Silica and Pyrex discharge tubes for medium pressures up to 550 Pa and for discharge currents up to 40 mA. Electric field strength measured by a double-probe technique was found to increase with the pressure and to decrease with the discharge current, which is typical for DC glow discharges. We have focused on the emitted radiation. The rotational temperature (T_rot) of molecular oxygen was determined from the ^PP and ^PQ branches of the well-resolved atmospheric A-band of molecular oxygen at 760 nm. Good agreement between values of T_rot obtained from particular branches was found. The increase of the rotational temperature with increasing pressure and discharge current has been observed in both discharge tubes, however, the values of rotational temperature were systematically higher in the tube made of Pyrex glass. This difference was explained by the particular thermal conductivity of the tube material.     

Modifying the properties of AISI 316L steel by glow discharge assisted low-temperature nitriding and oxynitriding

Apart from titanium, its alloys and CoCrMo alloys, austenitic steels are widely used in medical applications. In order to improve the frictional wear resistance of these steels, they are subjected to various surface treatments such that the good corrosion resistance of the steels is preserved.The paper analyzes the structure and phase composition of AISI 316L steel after subjecting it to low-temperature nitriding and oxynitriding under glow discharge conditions. The treatments produced diffusion-type surface layers composed of nitrogen-expanded austenite (known as the phase S, i.e. supersaturated solution of nitrogen in austenite) with a thin surface layer of chromium nitride (CrN) zone (after nitriding) or chromium oxide (Cr₂O₃) zone (after oxynitriding). It has been shown that the treatments substantially increase the hardness and frictional wear resistance of the steel without degrading its good corrosion resistance (examined in the Ringer physiological solution at a temperature of 37 °C).     

Growth of vertically aligned arrays of carbon nanotubes for high field emission

Vertically aligned multi-walled carbon nanotubes have been grown on Ni-coated silicon substrates, by using either direct current diode or triode plasma-enhanced chemical vapor deposition at low temperature (around 620 °C). Acetylene gas has been used as the carbon source while ammonia and hydrogen have been used for etching. However densely packed (∼ 10⁹ cm^− 2) CNTs were obtained when the pressure was ∼ 100 Pa. The alignment of nanotubes is a necessary, but not a sufficient condition in order to get an efficient electron emission: the growth of nanotubes should be controlled along regular arrays, in order to minimize the electrostatic interactions between them. So a three dimensional numerical simulation has been developed to calculate the local electric field in the vicinity of the tips for a finite square array of nanotubes and thus to calculate the maximum of the electron emission current density as a function of the spacing between nanotubes. Finally the triode plasma-enhanced process combined with pre-patterned catalyst films (using different lithography techniques) has been chosen in order to grow regular arrays of aligned CNTs with different pitches in the micrometer range. The comparison between the experimental and the simulation data permits to define the most efficient CNT-based electron field emitters.     

Role of ions in the abnormal glow of the plasma-cathode interface of neon glow discharges

Experimental and theoretical studies of the luminescence of cathode zone of Ne/(Fe cathode) glow discharges are reported. The dependence of line intensity I(λ) on the discharge parameters (gas pressure p, current density j_d and position x) was experimentally investigated by optical emission spectrometry (OES). The measured characteristics I(λ)=f(p, j_d, p, x) were discussed based on complex modeling of the plasma-cathode interface. A few examples of Ne species excitation such as the electron-atom interaction and the participation of metastable Ne^m atoms were considered. The fast Ne⁺ ions interaction with Ne atoms and the cathode surface is concluded finally to be the dominating process affecting the line emission of all neon species occurring in the plasma-cathode interface.     

Thin polymer films from polyimide vacuum thermal degradation with and without a glow discharge

Polyimide-like thin films were deposited by thermal degradation of polyimide with and without simultaneous activation by a glow discharge excited using an r.f. planar magnetron. The films deposited without discharge are similar in composition to conventional polyimide, whereas the deposition with plasma results in cross-linked coatings with composition typical for plasma polymers e.g. prepared by r.f. sputtering of polyimide. AFM reveals rough surface topography for the films evaporated without plasma. The application of plasma leads to very smooth plasma polymer films.     

Decoloration of aqueous Brilliant Green by using glow discharge electrolysis

This paper described a plasma degradation of Brilliant Green (BG) by glow discharge electrolysis. Various influencing factors such as the voltage, the distance between cathode and anode were examined. Ultraviolet (UV) absorption spectra, gas chromatogram-mass spectrum (GC-MS), and chemical oxygen demand (COD) were used to monitor the degradation process and to identify the major oxidation intermediates. It was confirmed that benzoic acid, 1,2,3,4,5,6-cyclohexanehexaol, and carboxylic acids (e.g., oxalic acid, succinic acid and hydroxyacetic acid) were produced in the degradation process. The results showed that BG rapidly underwent degradation and eventually mineralized into CO(2) and H(2)O.     

Effects of exo-electron emission from MgO thin film on statistical delay of glow discharge of ac-PDP

Relationship between exo-electron emission currents and statistical delay of glow discharges of ac-PDP was investigated by measuring exo-electron currents. The currents were measured as a function of time and doping elements. The measured results indicated that the exo-electron currents decrease exponentially with time, while the statistical delay increases with time. The results demonstrate that the statistical discharge delay is inversely proportional to the currents of exo-electron emission from MgO film in a time interval of 1 to 10 ms.     

Degradation of 2,4-dichlorophenol by using glow discharge electrolysis

Degradation of 2,4-dichlorophenol (2,4-DCP) in aqueous by glow discharge electrolysis (GDE) has been investigated. Ultraviolet (UV) absorption spectra, atomic force microscopy (AFM), high performance liquid chromatography (HPLC) and gas chromatogram-mass spectrum (GC/MS) are used to monitor the degradation process and to identify the major oxidation intermediate products. It has been found that 2,4-DCP undergoes a series of intermediate step, which leads to form a number of intermediate products, mainly isomeric chlorophenols and aliphatic acids. These products are further oxidized, eventually, mineralized into CO(2) and Cl(-). A degradation pathway for 2,4-DCP is proposed on the basis of detection of intermediate compounds.     

Rotational temperature of oxygen molecules in DC glow discharge in O2-Ar mixtures sustained in discharge tube made from Pyrex glass

The active DC glow discharge sustained in pure O₂ and O₂-Ar mixtures with Ar/O₂ concentration ratios up to 50% has been studied in a Pyrex discharge tube for pressures up to 500 Pa and for discharge currents up to 40 mA. The electric field strength and emission spectra parameters of the discharge were studied by means of the double-probe method and optical emission spectroscopy.The electric field strength was found to increase with the pressure and decrease with the discharge current, which is typical for DC glow discharges. Considering O₂-Ar mixtures, the values of electric field strength decreased with Ar/O₂ ratio.We have focused on the emitted radiation. The rotational temperature T_rot of molecular oxygen was determined from the well-resolved atmospheric A-band at 760 nm. The increase of the rotational temperature with increasing deposited power has been observed for all studied Ar/O₂ ratios. Moreover, it has been found that values of T_rot are independent of the mixture composition.     

Study of rotational temperature of oxygen molecules in H and T forms of DC glow discharge sustained in pure oxygen

The active DC glow discharge sustained in pure oxygen has been studied in a Silica discharge tube by means of optical emission spectroscopy and double-probe diagnostics for pressures 600, 750 and 1000 Pa and for discharge currents up to 40 mA. Two different forms of positive column of the discharge (high-gradient H form and low-gradient T form) were observed. Our investigation was focused on the variations of the rotational temperature T_rot determined from emission spectra of molecular oxygen (atmospheric A-band at 760 nm) in the dependence on the discharge current and on the pressure with respect to the existence of the two forms of the discharge. An increase of the rotational temperature with increasing discharge current has been observed. Moreover, higher values of T_rot were found in the H form compared with the T form.     

Effects of rf power on the structural properties of carbon nitride thin films prepared by plasma enhanced chemical vapour deposition

Carbon nitride (CN_x) thin films were deposited by radio frequency plasma enhanced chemical vapour deposition (rf PECVD) technique from a gas mixture of methane (CH₄), hydrogen (H₂) and nitrogen (N₂). The effects of rf power on the structural properties of CN_x thin films were discussed in this paper. It was found that rf power had significant effects on the growth rate, structural and morphological properties of the deposited films. The point of transition of the growth rate trend marked the equilibrium condition for primary and secondary reactions in growth kinetics of the film with respect to rf power. The films grown at this optimum rf power were most ordered in structure with high surface roughness and had the lowest N incorporation. This work showed that H etching effects and ion bombardment effects increase with increase in rf power and strongly influenced the structure of the CN_x films.     

Study on micro-patterning process of vertically aligned carbon nanotubes (VACNTs)

Vertically aligned carbon nanotubes (VACNTs) have drawn significant attention by the researchers because of their nanometric size and favorable material properties. Patterning of CNT forests in the micrometric domain is very important for their application in the area of microelectromechanical system (MEMS). For the first time this paper reports, detailed experimental investigation on a post growth μ-patterning process of VACNT forests. The micromechanical bending (M2B) process was locally applied at the targeted area in order to change the alignment of VACNT forests. Interestingly, the VACNT forest was transformed from typical black body absorber to reflective mirror as the M2B process was applied. Several parameters were identified that govern the resultant patterns such as rotational spindle speed, lateral bending speed, step size, tool morphology, and total depth of bend. Optimization of the parameters was carried out experimentally to obtain the best surface roughness and integrity of the microstructure. A minimum average surface roughness of Ra = 15 nm was achieved with 2000 rpm spindle speed, 1 mm/min bending speed and 1 µm step size.     

理论分析辉光放电对碳纳米管生长速率的影响

利用负偏压增强热丝化学气相沉积 ,在沉积过渡层Ta和催化剂NiFe层的Si衬底上制备了碳纳米管 ,并用扫描电子显微镜研究了它们的形貌。发现辉光放电后 ,碳纳米管的平均长度比无辉光放电时大 ,并且随着负偏压的增大而增大 ,即辉光放电增大了它们的生长速率。结合辉光放电和扩散理论分析了辉光放电对碳纳米管生长速率的影响 ,结果表明在生长碳纳米管的过程中 ,由于辉光放电的产生 ,碳在催化剂中的活度得到增强 ,从而增大了碳纳米管的生长速率。     

Fe-Mo/Al_2O_3催化剂催化分解甲烷制备碳纳米管:温度对碳管结构的影响

利用化学气相沉积法,以Fe-Mo/Al_2O_3为催化剂,催化分解甲烷气体制备碳纳米管(CNTs).研究了温度,反应时间和气体流速对碳纳米管结构的影响.结果显示:温度是影响碳纳米管壁厚的关键参数.低温导致壁厚为2 nm～7 nm的多壁碳纳米管(MWCNTs)的生成.相对地,高温有利于双壁碳纳米管(DWCNTs)的生长,而更高的温度促使单壁碳纳米管(SWCNTs)的产生.进一步升高温度,得到了壁厚为3 nm～15 nm的MWCNTs和大的炭颗粒.     

Effect of glow discharge plasma treatment on amorphous Co–B catalyst

Glow discharge plasma technique was firstly applied to treat amorphous Co–B catalyst. Both the amorphous Co–B particles before and after plasma treatment were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption, and CO temperature-programmed desorption (TPD). After plasma treatment, relatively larger uniform spherical Co–B particles with mesopores have been formed and the synergistic effect between Co and B enhanced. Furthermore, the mesopores formed on the surface of Co–B after plasma treatment enabled it with higher specific surface area. During the liquid-phase cinnamaldehyde (CMA) hydrogenation, Co–B after plasma treatment exhibited higher CMA conversion and cinnamyl alcohol (CMO) selectivity.