Synthesis and characterization of Ti and N binary‐doped ɑ‐C films deposited by pulse cathode arc with ionic source assistant

Using ionic source assistant, Ti and N co‐doped amorphous C (α‐C:N:Ti) thin films were prepared by pulse cathode arc technique. Microstructure, composition, elemental distribution, morphology, and mechanical properties of α‐C:N:Ti films were investigated in dependence of nitrogen source, pulse frequency, and target current by Raman spectroscopy, X‐ray diffraction, scanning electron microscopy, X‐ray photoelectron spectroscopy, atomic force microscopy, nanoindentation, and surface profilometer. The results show the presence of titanium carbide and nitride in a‐C:N:Ti films. The α‐C:N⁺:Ti film (6 Hz, 60 A) shows the smaller size and the higher disordering degree of Csp² clusters. The α‐C:N⁺:Ti films present smoother surface and smaller particle size than for α‐C:N₂:Ti films. N ions facilitate the formation of N‐sp³C bonds in the α‐C:N⁺:Ti films, and α‐C:N⁺:Ti (10 Hz, 80 A) film possesses the more graphite‐like N bonds. Higher hardness and lower residual stress present in the α‐C:N₂:Ti (10 Hz, 80 A) film.     

Surface analysis of nitride layers formed on Fe‐based alloys through plasma nitride process

Nitriding phenomena that occur on the surfaces of pure Fe and Fe? Cr alloy (16 wt% Cr) samples were investigated. An Ar + N₂ mixture‐gas glow‐discharge plasma was used so that surface nitriding could occur on a clean surface etched by Ar⁺ ion sputtering. In addition, the metal substrates were kept at a low temperature to suppress the diffusion of nitrogen. These plasma‐nitriding conditions enabled us to characterize the surface reaction between nitrogen radicals and the metal substrates. The emission characteristics of the band heads of the nitrogen molecule ion (N₂⁺) and nitrogen molecule from the glow‐discharge plasma suggest that the active nitrogen molecule is probably the major nitriding reactant. AES and angle‐resolved XPS were used to characterize the thickness of the nitride layer and the concentration of elements and chemical species in the nitride layer. The thickness of the nitride layer did not depend on the metal substrate type. An oxide layer with a thickness of a few nanometers was formed on the top of the nitride layer during the nitriding process. The oxide layer consisted of several species of N_x‐Fe_y‐O, NO⁺, and NO₂^?. In the Fe? Cr alloy sample, these oxide species could be reduced because chromium is preferentially nitrided. Copyright © 2009 John Wiley & Sons, Ltd.     

Fast Imaging of Laser-induced Plasma Emission from a ZnO Target

The spatio-temporal evolution of plasma plume laser ablation zinc oxide target was investigated by ICCD camera fast imaging. The plasma was created by a KrF excimer laser of 248 nm wavelength and 25 ns pulse. The laser fluence was set at 2 J/cm². This study was performed under vacuum and oxygen atmosphere at a pressure range of 10^− 6 to 10 mbar.Free expansion, splitting and stopping of the plume were observed at different pressures and time delays following the laser pulse. Moreover, depending on the gas pressures, the photography shows some turbulence for given time delays in the front edge of the plasma while at 5 and 10 mbar the whole plasma edge is perturbed. Rayleigh–Taylor instability is proposed as an explanation to this observed effect. A time integrated emission spectroscopy diagnostic has been also used to identify plasma species. A plasma emission spectrum shows the presence of Zn⁺, Zn and O emission lines both in vacuum and in O₂ atmosphere. As the distance from the target surface increases the Zn⁺ emission line disappears.     

Production of nitrogen oxides in a positive column of a glow-type discharge in air flow

This paper deals with the investigations of a low-current glow-type discharge in air flow as applied to the problem of nitrogen oxide production. The electrode configurations correspond to the classical coaxial plasmatron and to the so-called gliding arc. The discharge burns in a regime of constricted positive column with a typical current density from 47 to 120 A/cm² and with the related electron density from 0.53?10¹⁴ to 2.3?10¹⁴ 1/cm³. The gas temperature changes from 3000 to 3610 K. The described conditions provide a flow of NO molecules from the plasma column with the energetic cost for production of one molecule of (30–50) eV. Maximum content of NO molecules [NO]?=?4 g/m³ (3500 ppm) was obtained. In spite of a rather high gas temperature, the plasma is still nonequilibrium. The high vibrational levels of the nitrogen molecules are populated, and the main channel of the nitric oxide production is associated with the reaction in which the vibrationally excited nitrogen interacts with atomic oxygen.

     

Room-temperature ammonia formation from dinitrogen on a reduced mesoporous titanium oxide surface with metallic properties

Mesoporous titanium oxide was treated with bis(toluene) titanium under nitrogen at room temperature in toluene, leading to a new blue black material possessing conductivity values of up to 10(-)(2) Omega(-)(1) cm(-)(1). XRD and nitrogen adsorption showed that the mesostructure was fully retained. Elemental analysis indicated that the material absorbed Ti from the organometallic, without any incorporation of the toluene ligand. There was also an increase of nitrogen from below the detection limit to 1.16%. XPS studies showed that the Ti framework was reduced by the organometallic and that the material had reduced nitride on the surface. There was also an emission at the Fermi level, suggesting metallic behavior. This was confirmed by variable-temperature conductivity studies, which showed a gradual decrease of resistivity with temperature. SQUID magnetometer studies revealed spin glass behavior with a degree of temperature independent paramagnetism, consistent with metallic properties. Solid-state (15)N NMR studies on materials synthesized in the presence of labeled dinitrogen showed that the source of the nitride was the reaction atmosphere. IR and (15)N NMR demonstrated that this nitrogen species was surface ammonia, suggesting that the initially formed nitride species had reacted with moisture imbedded in the walls of the mesostructure. The direct conversion of dinitrogen to ammonia is a very rare process and this work represents the first example of this process mediated by a molecular sieve.     

Influence of binders on infrared laser ablation of powdered tungsten carbide pressed pellets in comparison with sintered tungsten carbide hardmetals studied by inductively coupled plasma atomic emission spectrometry

Laser ablation (LA) was studied as a sample introduction technique for the analysis of powdered and sintered tungsten carbides (WC/Co) by inductively coupled plasma optical emission spectrometry (ICP–OES). The possibility to work with powdered and compact materials with close chemical composition provided the opportunity to compare LA sampling of similar substances in different forms that require different preparation procedures. Powdered WC/Co precursors of sintered hardmetals were prepared for the ablation as pressed pellets with and without powdered silver as a binder, while sintered hardmetal blocks were embedded into a resin to obtain discs, which were then smoothed and polished. A Q-switched Nd:YAG laser operated at its fundamental wavelength of 1064 nm with a pulse frequency of 10 Hz and maximum pulse energy of 220 mJ was used. A single lens was used for the laser beam focusing. An ablation cell (14 cm³) mounted on a PC-controlled XY-translator was connected to an ICP spectrometer Jobin Yvon 170 Ultrace (laterally viewed ICP, mono- and polychromator) using a 1.5-m tubing (4 mm i.d.). Ablation was performed in a circular motion (2 mm diameter). Close attention was paid to the study of the crater parametres depending on hardness, cohesion and Ag binder presence in WC/Co samples. The influence of the Co content on the depth and structure of the ablation craters of the binderless pellets was also studied. Linear calibration plots of Nb, Ta and Ti were obtained for cemented WC/Co samples, binderless and binder-containing pellets. Relative widths of uncertainty intervals about the centroids vary between ± 3% and ± 7%, and exceptionally reach a value above 10%. The lowest determinable quantities (LDQ) of Nb, Ta and Ti calculated from the calibration lines were less than 0.5% (m/m). To evaluate the possibility of quantitative elemental analysis by LA–ICP–OES, two real sintered WC/Co samples and two real samples of powdered WC/Co materials were analysed. The results of LA–ICP–OES real sample analysis correlated well with the results obtained by X-ray fluorescence (sintered samples) and pneumatic nebulization inductively coupled plasma optimal emmission spectrometry (powdered samples) with a bias not exceeding 6.5%.     

Surface modifications of PET in argon atmospheric pressure plasma: Gas flow rate effect

The correlation between plasma optical properties and the treated polyethylene terephthalate (PET) surface characteristics have been studied at various Ar flow rate. The rotational T_rot and vibrational T_vib temperatures of APPJ were determined from SPS emission band. The pristine and plasma-treated PET surfaces were characterized by several techniques including X-ray photoelectrons spectroscopy (XPS), Raman spectroscopy, contact angle (CA), and atomic force microscope (AFM). The CA decreased rapidly in the flow rate range 1–3 L/min and weakly dependent as flow rate > 3 L/min. XPS results showed that C 1s % of plasma-treated PET surfaces decreases and has a minimum for samples treated at 3–4 L/min, while O 1s has a maximum at the same flow rate range. The carbon C 1s peak of pristine and plasma treated PET samples resolved into five subcomponents: C–C, C–O, C=O, O–C=O, and π–π bonds with variable percentage ratio accordance to the plasma gas flow rate. Raman data revealed a partial loss in the crystallinity of the treated PET samples and also confirm the incremental of C–O band at Ar flow rate of 3 L/min. AFM images showed that the surface roughness of treated PET films increases as Ar flow rate increases.     

Niobium nitride films formed by rapid thermal processing (RTP): a study of depth profiles and interface reactions by complementary analytical techniques

The nitridation of niobium films approximately 250 and 650 nm thick by rapid thermal processing (RTP) at 800 °C in molecular nitrogen or ammonia was investigated. The niobium films were deposited by electron beam evaporation on silicon substrates covered by a 100 or 300 nm thick thermally grown SiO₂ layer. In these investigations the reactivity of ammonia and molecular nitrogen was compared with regard to nitride formation and reaction with the SiO₂ substrate layer. The phases formed were characterized by X-ray diffraction (XRD). Depth profiles of the elements in the films were recorded by use of secondary neutral mass spectrometry (SNMS). Microstructure and spatial distribution of the elements were imaged by transmission electron microscopy (TEM) and energy-filtered TEM (EFTEM). Electron energy loss spectra (EELS) were taken at selected positions to discriminate between different nitride, oxynitride, and oxide phases. The results provide clear evidence of the expected higher reactivity of ammonia in nitride formation and reaction with the SiO₂ substrate layer. Outdiffusion of oxygen into the niobium film and indiffusion of nitrogen from the surface of the film result in the formation of oxynitride in a zone adjacent to the Nb/SiO₂ interface. SNMS profiles of nitrogen reveal a distinct tail which is attributed to enhanced diffusion of nitrogen along grain boundaries.     

N-Decane Reforming by Gliding Arc Plasma in Air and Nitrogen

Plasma cracking of n-decane is carried out in a new type of gliding arc flow reactor in the atmosphere of nitrogen and air, at a flow range of 25–45 L/min with an interval of 5 L/min. The relationship between arc evolution and discharge voltage and current signals is established by synchronous recording with high-speed camera and oscilloscope. It is recorded that the rotating frequency of the gliding arc is in the range of 81–176 Hz, which increases with the rise of the flow rate and has no direct relationship with the type of gas. When air is used as the discharge medium, although the luminous intensity of the arc is weak, arc rotation is relatively stable, and the specific input energy is higher, which is 58% higher than that of nitrogen. In addition, the partial oxidation of n-decane provides extra heat for cracking, which is helpful to improve the efficiency of plasma cracking. The cracking products mainly include hydrogen, ethylene, acetylene, methane, propylene and ethane. The concentration of each component is higher, reaching the maximum value at the flow rate of 40 L/min, with the hydrogen selectivity of 23.1%. However, when nitrogen plasma is selected, the kinds of products are reduced, containing only hydrogen, ethylene and acetylene, and the concentrations are lower than 0.5%. Two parameters, energy conversion efficiency and carbon based characterization effective cracking rate, were proposed to evaluate the cracking effect of flow reactor.

     

Ethylene Epoxidation over Alumina- and Silica-Supported Silver Catalysts in Low-Temperature AC Dielectric Barrier Discharge

In this work, ethylene epoxidation reaction for ethylene oxide production over silver catalysts loaded on two different supports (silica and alumina particles) in a low-temperature AC dielectric barrier discharge (DBD) reactor was investigated. The DBD plasma system was operated under the following base conditions: an O₂/C₂H₄ feed molar ratio of 1/4, a total feed flow rate of 50 cm³/min, an electrode gap distance of 0.7 cm, an input frequency of 500 Hz, and an applied voltage of 19 kV. From the results, the presence of silver catalysts improved the ethylene oxide production performance. The silica support interestingly provided a higher ethylene oxide selectivity than the alumina support. The optimum Ag loading on the silica support was found to be 20 wt%, exhibiting the highest ethylene oxide selectivity of 30.6%.     

Au/Ti-MCM-41(H)催化丙烯气相直接环氧化

采用纳米组装法制备了一系列不同Ti含量的具有微孔-介孔复合结构(hybrid)的钛硅分子筛Ti-MCM-41(H)载体,继而用沉积-沉淀法制得纳米金催化剂.通过粉末X射线衍射(XRD)、氮气等温吸附-脱附、傅里叶变换红外(FT-IR)光谱、紫外-可见漫反射(DRUV-Vis)光谱、透射电镜(TEM)及等离子体原子发射光谱法(ICP-AES)对催化剂进行了表征,并考察了纳米金催化剂在氢气/氧气共存条件下丙烯气相直接氧化制环氧丙烷反应中的催化性能.结果表明:合成的微孔-介孔复合结构的钛硅分子筛Ti-MCM-41(H)具有典型的MCM-41结构,Ti(IV)以高分散的形式存在于分子筛的骨架结构中.在常压、423K反应温度下,以Ti/Si摩尔比为1%的Ti-MCM-41(H)为载体制备纳米金催化剂表现出了最佳的催化性能,反应30min,丙烯的转化率达5.4%,环氧丙烷的选择性为74.2%,环氧丙烷的生成速率为73.1g·h-1·kg-1;反应330min后,丙烯的转化率为4.9%,环氧丙烷的选择性为67.3%.     

Nitrogen Fixation as NOx Enabled by a Three-Level Coupled Rotating Electrodes Air Plasma at Atmospheric Pressure

In this paper, a three-level coupled rotating electrodes air plasma at atmospheric pressure is developed for evaluation of nitrogen fixation. Factors influencing the NO_x production rate and energy cost, including airflow rate, the input H₂O concentration, blade numbers at each rotating electrode and rotating speed, are examined. Air flow rates prove to have no effect on the rotational temperature of N₂ 337.1 nm and the emission intensities of N₂⁺ and N₂, but specific energy input (SEI) and species’ residence time can be shorter with higher air flow rates, resulting in lower NO_x concentration and energy cost. The addition of H₂O also has a positive effect on both NO_x concentration and energy cost. Optical emission spectrum (OES) shows that air?+?H₂O plasma has stronger 336 nm (NH) and 309 nm (OH) emission lines than air plasma, suggests NH and OH are the key species in NO_x enhancement. The most energy efficient conditions are found at airflow rate of 15 l min^?1, 12% H₂O concentration, with 4 blades on each rotating speed. Under these conditions, the lowest energy cost is observed to be 165 GJ/tN.

     

Emission characteristics of Grimm-style glow discharge plasmas with helium matrix plasma gas containing small amounts of nitrogen

Glow discharge plasmas with helium–(0–16%) nitrogen mixed gas were investigated as an excitation source in optical emission spectrometry. The addition increases the sputtering rate as well as the discharge current, because nitrogen molecular ions, which act as primary ions for the cathode sputtering, are produced through Penning-type ionization collisions between helium metastables and nitrogen molecules. The intensity of a silver atomic line, Ag I 338.29 nm, is monotonically elevated along with the nitrogen partial pressure added. However, the intensities of silver ionic lines, such as Ag II 243.78 nm and Ag II 224.36 nm, gave different dependence from the intensity of the atomic line: Their intensities had maximum values at a nitrogen pressure of 30 Pa when the helium pressure and the discharge voltage were kept at 2000 Pa and 1300 V. This effect is principally because the excitations of these ionic lines are caused by collisions of the second kind with helium excited species such as helium metastables and helium ion, which are quenched through collisions with nitrogen molecules added to the helium plasma. The sputtering rate could be controlled by adding small amounts of nitrogen to the helium plasma, whereas the cathode sputtering hardly occurs in the pure helium plasma.     

Schlieren High-Speed Imaging of a Nanosecond Pulsed Atmospheric Pressure Non-equilibrium Plasma Jet

The fluid-dynamic characterization by means of Schlieren high-speed imaging of the effluent region of a single electrode plasma jet is presented. The plasma source is powered by a high-voltage generator producing pulses with nanosecond rise time. Time evolution of fluctuations generated in a free flow regime and when the jet is impinging on substrates of different geometries (plain substrates, Petri dishes, etc.) and materials (metal, dielectric covered metal, polystyrene) has been investigated. Plasma ignition causes fluid-dynamic instabilities moving in the direction of the jet flow and correlated with the high-voltage pulses: for low pulse repetition frequency (PRF) (<125 Hz), the movement of the turbulent front between two voltage pulses can be tracked, whereas for higher PRF (1,000 Hz) the flow is completely characterized by turbulent eddies in the effluent region, without relevant changes between subsequent voltage pulses. When the jet is impinging on a substrate, turbulent fronts propagate over the surface starting from the gas impinging zone.     

Low energy ion bombardment of Ti and TiNx films

The influence of low energy ion bombardment on TiN_x film growth and film properties was investigated. The discharge was characterized using Langmuir probe technique as well as energy resolved mass spectrometry with a plasma monitor (Hiden HAL 301 S/EQP). The deposited films were investigated by means of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Increasing the N₂ gas flow as well as increasing the negative substrate voltage at constant gas flow effect an increase of the N/Ti ratio in the films determined by XPS. The influence of the energy flux to the surface due to ion bombardment was mainly recognized in the substructure of the films. In addition, pure Ti films were modified by nitrogen ion bombardment after deposition using an ion gun. An increase of the N/Ti ratio was observed with increasing ion energy. Finally saturation is reached.     

Composition of Ti-N films: EDX analysis during the sputtering process

Summary Energy dispersive X-ray (EDX) analysis was applied in-situ for measurements of composition, surface mass and deposition rate of Ti atoms during reactive sputtering. Electron beam excitation was used for the determination of composition and X-ray fluorescence (XRF) for the surface mass determination. Intensity measurements of the optical emission of Ti atoms agree well with the deposition rate of Ti atoms measured by XRF. The influences of nitrogen mass flow and negative bias substrate voltage on concentration and sputtering rate were investigated in homogeneous TiN_x films and TiN_x/TiN_y multilayers.     

Nitrogen-doped TiO2 mesosponge layers formed by anodization of nitrogen-containing Ti alloys

An alloy containing 5 at.% of N was produced by arc melting of Ti and TiN powders. By anodization of the alloy in a 10 wt.% K₂HPO₄/glycerol electrolyte at 140 °C, oxide mesosponge layers can be formed with thickness as up to several micrometers. X-ray photoelectron spectroscopy confirms nitrogen uptake in the oxide. Photoelectrochemical measurements show successful N-doping of these mesoporous anodic layers with a significant visible light photoresponse.     

Effect of excitation states of nitrogen on the surface nitridation of iron and steel in d.c. glow discharge plasma

The plasma nitriding phenomena that occur on the surfaces of iron and steel were investigated. In particular, the correlation between the kinds of nitrogen radicals and the surface nitriding reaction was investigated using a glow‐discharge apparatus. To control the excitation of nitrogen radicals, noble gas mixtures were used for the plasma gas. The highly populated metastables of noble gases selectively produce excited nitrogen molecules (N₂*) or nitrogen molecule ions (N₂⁺). The optical emission spectra suggested that the formation of N₂*‐rich or N₂⁺‐rich plasma was successfully controlled by introducing different kinds of noble gases. Auger electron spectroscopy and XPS were used to characterize the depth profile of the elements and chemical species on the nitrided surface. The nitride layer formed by a N₂⁺‐rich plasma had a much higher nitrogen concentration than that by a N₂*‐rich plasma, likely due to the larger chemical activity of the N₂⁺ species as well as the N₂⁺ sputtering bombardment to the cathode surface. The strong reactivity of the N₂⁺ species was also confirmed from the chemical shift of N 1s spectra for iron nitrides. An iron nitride formed by the N₂⁺‐rich plasma has higher stoichiometric quantity of nitrogen than that formed by the N₂*‐rich plasma. Besides the effect of nitrogen radicals on surface nitridation, the contribution of the chromium in steel to the nitriding reaction was also examined. This chromium can promote a nitriding reaction at the surface, which results in an increase in the nitrogen concentration and the formation of nitride with high nitrogen coordination. Copyright © 2010 John Wiley & Sons, Ltd.     

XPS study of a laser-nitrided iron surface using a focused pulsed Nd:YAG laser under various conditions

Laser nitridation of a pure iron (Fe) surface was conducted using a focused pulsed Nd:YAG laser under a nitrogen atmosphere, and the effects of nitrogen gas pressure, laser power, and repetition number of laser shots on the surface characteristics were analyzed using XPS. The laser-irradiated surface consisted of the topmost surface layer of Fe oxynitride (FeO_xN_y) and the underlayer beneath, which mainly comprised Fe nitride (Fe₄N). The topmost surface layer is a post-formed layer due to the oxidation of the nitride layer. The thickness of the underlayer corresponding to the original nitride layer drastically increased under nitrogen gas at atmospheric pressure. Increasing the repetition number of laser shots enhanced layer thickness up to 5 shots, after which no change was observed. Moreover, the layer thickness increased monotonically with increasing laser power. Nitridation through pulsed laser irradiation was likely predominated by the melting and resolidification of a specific surface area, as well as the convection of nitrogen therein. Thickness variation under various conditions can be explained appropriately using this assumption.     

Depth profile analysis of surface modified SnO2 gas sensors in a hollow cathode discharge

Depth profile analysis of a SnO₂/SiO₂/Si structure, modified with hexamethildisilazane and processed with rapid thermal annealing (RTA) in the temperature range of 800–1200 °C, is investigated in a hollow cathode discharge for the purpose of characterizing gas sensing solid state devices. The depth behavior of the elements tin, nitrogen, carbon and silicon in this structure is deduced from their emission spectra in the hollow cathode plasma. The hollow cathode used is a liquid nitrogen - cooled Al cylinder having 4 mm inner diameter and 12 mm length. Spectrally pure Ne at a pressure of 130 Pa is used as working gas. The hollow cathode discharge is supplied by a pulse generator with 10 μs pulse width, 4 kHz pulse frequency and 0.5 A pulse amplitude. The results are interpreted by possible reconstruction of hexamethyldisilazane molecule.