An optical emission spectroscopy study of the plasma generated in the DC HF CVD nucleation of diamond

Optical emission spectroscopy (OES) was used to study the plasma generated by the activation of the gas phase CH₄ + H₂ both by hot filaments and by a plasma discharge (DC HF CVD) during the nucleation of CVD diamond. The effects of nucleation parameters, such as methane concentration and extraction potential, on the plasma chemistry near the surface were investigated. The density of the diamond nucleation and the quality of the diamond films were studied by scanning electron microscopy (SEM) and Raman scattering, respectively. The OES results showed that the methane concentration influenced strongly the intensity ratio of H_β-H_α implying an increase of electron mean energy, as well as CH, CH⁺, C₂. A correlation between the relative increase of CH⁺ and the diamond nucleation density was found, conversely the increase of C₂ contributed to the introduction of defects in the diamond nuclei.     

Langmuir probe and optical emission spectroscopy studies for RF magnetron sputtering during TiON thin film deposition

Low-pressure plasma of gas mixture of Ar, O₂ and N₂ generated by RF magnetron sputtering was characterized by Langmuir probe and optical emission spectroscopy (OES). The electron temperature (T_e), ion density (n_i) and electron energy distribution function (EEDF) in Ar-O₂-N₂ plasma atmosphere were calculated from I-V characteristic of Langmuir probe. Boltzmann plot method was applied for calculating the vibrational temperature (T_vib) of the second positive system of N₂ (N₂SPS) in Ar-O₂-N₂ plasma. The T_e, n_i, EEDF and T_vib in Ar-O₂-N₂ plasma were studied as a function of O₂ percentages. It was found, the T_vib increased from 0.47 eV to 0.55 eV as the oxygen percentage in Ar-N₂-O₂ plasma increased from 10% to 40%. Further, the T_e increased from 1.6 eV to 3 eV as the O₂ concentration increased from 10% to 40%.     

射频感应耦合Ar-N2等离子体物理特性的Langmuir探针测量及理论研究

分别通过Langmuir探针测量和动力学模型模拟方法研究了射频感应耦合Ar-N₂等离子体中电子能量分布、电子温度、电子密度等物理量随N₂含量的变化规律.实验研究结果表明：电子能量分布呈现出非Maxwell型分布,并由双温分布向三温分布过渡;电子温度在不同的气压下随N₂含量的增加呈现出不同的变化规律.在放电气压小于1.3 Pa时,电子温度随N₂含量的增加而下降;当气压大于1.3 Pa时,电子温度随N₂关键词： 感应耦合等离子体 2混合气体放电')" href="#">Ar-N₂混合气体放电 电子能量分布 Langmuir探针     

Electron energy distribution function in a hollow-cathode glow discharge in mixtures of nitrogen with electronegative gases

The electron energy distribution function (EEDF) in a hollow-cathode glow discharge in mixtures of nitrogen with electronegative gases is investigated. It is shown that small admixtures of SF₆ or CCl₄ to nitrogen significantly increase the number of electrons in the energy range 2–6 eV, which corresponds to the inverse part of the EEDF. In nitrogen with small admixtures of F₂ or NF₃, the EEDF differ slightly from that calculated for pure nitrogen. The EEDF in these mixtures substantially depends on electron attachment to electronegative gas molecules.     

Positrons — an alternative probe to electron scattering

Interaction of positrons with atoms and molecules differs from electron interaction due to the difference in polarity of the charge. This makes positrons an alternative tool to study atomic and molecular structure. Recent measurements of the total cross-sections for positron scattering at low energies on He, Ar, H₂, N₂, C₆H₆, C₆H₁₂, C₆H₇N carried out at Trento University [Karwasz et al., Acta Phys. Pol. 127, 666 (2005)] are discussed and compared to electron scattering results. All measured total cross-sections exhibit an increase with decreasing positron energy in the limit of zero energy; H₂, N₂, Ar, show regions of constant cross-section which are a few eV-wide, characteristic of scattering on a hard-sphere potential. Helium shows two resonant structures much below the positronium formation threshold. They may be attributed to virtual positronium formation. In conclusion, positron scattering is complementary to electron scattering. The total cross-sections do not show Ramsuaer minima but constant values, and new resonances appear.     

Experimental and kinetic modeling study on auto-ignition properties of ammonia/ethanol blends at intermediate temperatures and high pressures

The auto-ignition properties of ammonia (NH₃)/ethanol (C₂H₅OH) blends close to engine operating conditions were investigated for the first time. Specifically, the ignition delay times (IDT) of ammonia/ethanol blends were measured in a rapid compression machine (RCM) at elevated pressures of 20 and 40 bar, five C₂H₅OH mole fractions from 0% to 100%, three equivalence ratios (ϕ) of 0.5, 1.0 and 2.0, and intermediate temperatures between 820 and 1120 K. The measurements reveal that ethanol can drastically promote the reactivity of ammonia, e.g., the auto-ignition temperature with merely 1% C₂H₅OH in fuel decreases accordingly around 110 K at 40 bar as compared to that of neat ammonia. Moreover, the promotion efficiency of ethanol is higher than hydrogen and methane with a factor of 5 and 10 under the same condition. Different dependences of IDT on the equivalence ratio were observed with different ethanol fractions in the blends, i.e., the IDTs of the 5%, 10% and 100% C₂H₅OH in fuel decrease with an increase of ϕ, but an opposite trend was observed in the mixture with 1% C₂H₅OH. A new chemical kinetic mechanism for NH₃/C₂H₅OH mixtures was developed and it is highlighted that the addition of cross-reactions between the two fuels is necessary to obtain reasonable simulations. Basically, the newly developed mechanism can reproduce the measurements of IDT very well, whereas it overestimates the reactivity of the stoichiometric and fuel-rich mixture with 1% C₂H₅OH in fuel. The sensitivity, reaction pathway, as well as rate of production analysis indicated that the ethanol addition to ammonia fuel blends provides key interaction pathways and enriches the O/H radical pool which further promotes the auto-ignition process.     

The scattering of He from adsorbed layers of gases on Ag(110)

The adsorption of gases on Ag(110) has been studied using inelastic He atom scattering. Vibrational spectra have been obtained for Kr, Xe, C₂H₆, C₂H₄, CH₄, CF₄, CHF₃, CO₂ and H₂O. Spectra have also been obtained for multilayers of Xe (2 layers) and C₂H₆ (3 and 4 layers) where the energy changes move to lower values. The scattering from Kr and Xe can be shown to be dispersionless as has been previously found for these adsorbates on Cu(100) and Cu(110). The energy changes for Kr and Xe are smaller than on Cu surfaces and attempts were made to account for this based on an Einstein model of the adsorbed atoms in the surface holding potential.     

Non-Maxwellian electron energy distribution function in He,He/Ar,He/Xe/H<Subscript>2</Subscript> and He/Xe/D<Subscript>2</Subscript> low temperature afterglow plasma

Experimental studies of the electron energy distribution function “EEDF” under well defined conditions in flowing afterglow plasma, using a Langmuir probe are reported. The EEDF is measured in He₂ ⁺ and Ar⁺ dominated plasmas and in XeH⁺ and XeD⁺ dominated recombining plasmas. He is used as a buffer gas at medium pressures in all experiments (1600 Pa, 250 K). The deviation of the measured EEDF from Maxwellian distribution is shown to depend on plasma composition and on the processes governing the plasma decay. The influence of energetic electrons produced during the plasma decay on the body and tail of the EEDF is observed. The mechanism of energy balance in afterglow plasma is discussed.     

Langmuir probe and spectroscopic studies of RF generated helium-nitrogen mixture plasma

This paper reports the effect of helium percentage variation in a capacitive RF helium-nitrogen mixture plasma on various plasma parameters and concentration of nitrogen active species (N₂(C³Π _u) and N₂ ⁺(B²Σ _u ⁺)). Langmuir probe is used for determination of electron energy distribution functions, effective electron temperature, plasma potential and electron density. Optical emission spectroscopy is used for determination of electron temperature from Boltzmann's plot of He–I lines and the relative changes in the concentration of active species by measuring the emission intensities of nitrogen (0-0) bands of the second positive and the first negative systems. The results demonstrate that electron temperature, electron density and concentration of active species increase significantly with increase in helium percentage in the mixture and RF power.     

Modification of polyethylene powder with an organic precursor in a spiral conveyor by hollow cathode glow discharge

Hexamethyldisiloxane (HMDSO) films were deposited on polyethylene (PE, (C₂H₄)_n) powder by hollow cathode glow discharge. The reactive species in different HMDSO/Ar plasmas were studied by optical emission spectroscopy (OES). Increasing the HMDSO fraction in the gas mixture additional compounds like CH_x, OH, SiC and SiO can be identified. After deposition the formed silicon and carbon containing groups (C–O, C=O, SiC and SiO) on the PE powder surface have been analyzed by X-ray photoemission spectroscopy (XPS). Changes in wettability depending on the HMDSO fraction were investigated by contact angle measurements (CAM). The free surface energy of the PE powder decreases with increasing HMDSO fraction in the process gas and encapsulation of the powder particles occurs. An aging effect of the plasma treated PE surface was observed depending on the process gas composition. The higher the HMDSO fraction the less is the aging effect of the plasma treated PE surface.     

Phenolic polymer–surface interactions from ab initio computations

Test calculations show that the diamond surface binding energy of C₁₃H₁₁O₂, the simplest model for phenolic, is virtually the same as that of C₆H₅. Using the C₆H₅ model, we compare the binding to a diamond surface, a graphene sheet, a (10, 0) nanotube, and a silica surface. The binding energy is more than 5?eV for the silica and 2.85?eV for the diamond surface. As expected, the binding energy of a second molecule at a site adjacent to the first molecule is larger than the first binding energy for the graphene sheet and the carbon nanotube, since the first C₆H₅ bond breaks a π bond and the second molecule bonds to the unpaired π electron created by adding the first molecule. For all of the systems, adding a C₂ unit between the surface and the C₆H₅ group increases the binding by at least 0.51?eV and up to 2.3?eV. Part of this increase is due to the intrinsically stronger bonding for the sp hybridization and part due to a decrease in the surface–C₆H₅ repulsion.     

Determination of gas temperature of high-frequency low-temperature electrodeless plasma using molecular spectra of hydrogen and hydroxyl-radical

In this study we determine gas temperature of He+H₂, Ar+H₂ and Ne+H₂ high frequency electrodeless lamps using intensity distribution in rotational spectra of hydrogen molecule and hydroxyl radical. The measurement results show that OH rotational spectra can be successfully used for estimation of gas temperature of the high-frequency electrodeless lamps at very small amounts of hydrogen present in plasma. The analysis of the measurement results leads to the conclusion that in “pure” plasma the applied energy is used to heat plasma, while for the plasma with hydrogen addition the energy is used in chemical reactions.     

A first-principles study on the adsorption behaviour of methanol and ethanol over C59B heterofullerene

In the present study, the adsorption behaviour of methanol (CH₃OH) and ethanol (C₂H₅OH) molecules over heterofullerene C₅₉B surface is studied by density functional theory calculations. This heterofullerene is obtained from C₆₀ by substituting a carbon atom with a boron atom and relaxing self-consistently the structure to the local minimum. The adsorption of CH₃OH and C₂H₅OH on the C₅₉B is exothermic and the relaxed geometries are stable. The CH₃OH and C₂H₅OH adsorption can also induce a change in the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy gap of the nanocage. The dehydrogenation pathways of CH₃OH and C₂H₅OH via O–H and C–H bonds scission are also examined. The results indicate that O–H bond scission is the most favourable pathway on the C₅₉B surface.     

Controlled synthesis of BaWO4 hierarchical nanostructures by exploiting oriented attachment in the solution of H2O and C2H5OH

Shape-controlled synthesis of BaWO₄ hierarchical nanostructures has been successfully achieved by exploiting oriented attachment in a mixture of water and ethanol. A controlled change in the volume ratio of C₂H₅OH and H₂O or the concentration of initial reagents has resulted in the synthesis of products of various morphologies, such as shuttle-like, ellipsoid-like, and flower-like ones. The obtained products are characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy. The altered nucleation and growth rates of primary particles that assembled to the final hierarchical nanostructures through oriented attachment are the main cause of the evolution of their morphologies. The room-temperature photoluminescent intensities of the products strongly depend on their morphology.     

Investigation on improving characteristics of two-cell SBS system with CCl4/C2H5OH liquid mixture

In order to improve the performance of the two-cell stimulated Brillouin scattering （SBS） system, this paper proposes the methods of using mixtures, which require amplifier media to have small absorption rate, and generator media to have high optical breakdown threshold and Brillouin frequency shift equal to that of the amplification media. The characteristics of the two-cell SBS system are studied experimentally by using CCl4 as amplifier medium and CCl4, C2H5OH and CCl4/C2H5OH liquid mixture as generator medium pumped by Nd：YAG Q-switched laser. The obtained results show that liquid mixture in generator cell improves the power load ability, phase conjugation fidelity, energy reflectivity （ER） and ER stability.     

Transmission of broadband saturable absorbing mixture for 10.6 μm nanosecond pulses

The transmission through a mixture consisting of sulphur hexafluoride (SF₆), ethyl alcohol (C₂H₅OH) and freon 502 (R502) was investigated with the 3-ns pulses of a TEA CO₂ laser operating at the 10P(20) line. The transmission characteristics of this mixture were measured. Thus, it was confirmed that the radiation beam traversing the gas-filled absorption cell exhibits self-interaction effects in a certain range of gas pressure, cell length and incident energy fluence. A more effective behavior of such an absorber was confirmed for mixtures under lower pressures and proportionally longer cells. Buffering behavior of the additives (C₂H₅OH and R502) was also assessed.     

Inelastic atom scattering from layers of atoms and molecules on Cu(110)

The vibrational properties of adsorbed layers have been studied using inelastic He atom scattering. The substrate was Cu(110) viewed along the [001] and [11&#x0304;0] azimuth. The adsorbates included, Kr, Xe, CH₄, CD₄, C₂H₆, CO, CO₂ and O₂ and covered the region of both physisorption and chemisorption. Despite a range of binding energies and mass ratios the vibrational frequencies showed no dependence on the momentum change, i.e. scattering was dispersionless, although intensity changes occurred in the inelastic peaks. There seemed to be no dependence of the adsorbate spectra on coverage below a monolayer. The peaks of CH₄ and C₂H₆ appeared broader than those of Kr and Xe suggesting molecular motions. Further, CH₄ and C₂H₆ gave very similar spectra. Both energy gain and loss events were observed in the inelastic spectrum. For those adsorbates which gave multilayer adsorption (Xe, C₂H₆) changes in the spectra were observed as the second layer developed. In the latter category also, mixed layers (Xe on C₂H₆, Xe on CO and C₂H₆ on Xe) were studied.     

Neutron inelastic spectroscopy of benzene chemisorbed on Raney platinum

The neutron inelastic scattering spectrum of benzene adsorbed at 300 K on Raney platinum has been measured between 350 and 2250 cm^?1. No deshydrogenation of the molecules is observed so that the benzene ring must be adsorbed parallel to the surface. Slight modifications of the force field of the model molecule (C₆H₆)Cr(CO)₃ were introduced to account for the vibrational frequency shifts. The benzene molecule is found less perturbed on platinum than on nickel. The calculated frequencies of adsorbed C₆H₆ and C₆D₆ are used to reassign some modes previously observed by electron loss spectroscopy.     

On the coupling of electron energy distribution function and excited state distributions in pulsed microwave H$\mathsf{_{2}}$ plasmas

Time evolution of vibrationally and electronically excited states and their coupling with the electron energy distribution function (EEDF) were calculated for microwave pulsed discharges. Different situations have been considered by changing the period and the duty cycle, and considering different pressure values.The main result of this study was to evidence the change in the non-equilibrium character and dynamics of the different distributions depending on the pressure and the pulse period. In particular EEDF strongly deviating from the Maxwell behaviour appear as a consequence of inelastic and superelastic collisions at relatively high pressure and long period. Also, strong oscillation appears on the tail of the H₂ vibrational distribution at high pressure discharge conditions. At low pressure, the effect of superelastic and inelastic collisions appears to be less significant and most of the plasma characteristics may be deduced from a time averaged electron energy distribution function.Received: 15 January 2004, Published online: 29 June 2004PACS: 52.25.Dg Plasma kinetic equations - 52.20.Hv Atomic, molecular, ion, and heavy-particle collisions - 52.27.Cm Multicomponent and negative-ion plasmas     

工作压强对射频辉光放电H2/C4H8等离子状态的影响

利用辉光放电技术采用等离子体质谱诊断的方法研究了不同工作 压强下H₂/C₄H₈混合气体等离子体中 主要正离子成分及其能量的变化规律, 并分析了压强对H₂/C₄H₈混合气体的离解机理以及主要正离子形成过程的影响. 结果表明: 随着工作压强的增加, 碳氢碎片离子的浓度和能量均逐渐减小. 当工作压强为5 Pa时, H₂/C₄H₈混合气体等离子体中C₃H₅⁺相对浓度最大; 压强为10 Pa时, C₃H₃⁺相对浓度最大; 压强为15, 20 Pa时, C₂H₅⁺相对浓度最大; 压强为25 Pa时, C₄H₉⁺相对浓度最大. 对H₂/C₄H₈等离子体中的主要组分及其能量分布所进行的定性分析, 将为H₂/C₄H₈混合气体辉光放电聚合物涂层的工艺参数优化提供参考技术基础. 关键词： 辉光放电技术 等离子体质谱诊断 工作压强