Electron scattering and dissociative attachment by SF6 and its electrical-discharge by-products

Discrete electron-molecule processes relevant to SF₆ etching plasmas are examined. Absolute, total scattering cross sections for 0.2–12-eV electrons on SF₆, SO₂, SOF₂, SO₂F₂, SOF₄, and SF₄, as well as cross sections for negative-ion formation by attachment of electrons, have been measured. These are used to calculate dissociative-attachment rate coefficients as a function ofE/N for SF₆ by-products in SF₆.     

Identification of corona discharge-induced SF6 oxidation mechanisms using SF6/18O2/H2 16O and SF6/16O2/H2 18O gas mixtures

The absolute yields of gaseous oxyfluorides SOF₂, SO₂F₂, and SOF₄ from negative, point-plane corona discharges in pressurized gas mixtures of SF₆ with O₂ and H₂O enriched with¹⁸O₂ and H₂ ¹⁸O have been measured using a gas chromatograph-mass spectrometer. The predominant SF₆ oxidation mechanisms have been revealed from a determination of the relative¹⁸O and¹⁶O isotope content of the observed oxyfluoride by-product. The results are consistent with previously proposed production mechanisms and indicate that SOF₂ and SO₂F₂ derive oxygen predominantly from H₂O and O₂, respectively, in slow, gas-phase reactions involving SF₄, SF₃, and SF₂ that occur outside of the discharge region. The species SOF₄ derives oxygen from both H₂O and O₂ through fast reactions in the active discharge region involving free radicals or ions such as OH and O, with SF₅ and SF₄.     

Gas-phase reactions in plasmas of SF6 with O2: Reactions of F with SOF2 and SO2 and reactions of O with SOF2

The plasma chemistry of SF₆/O₂ mixtures is particularly complicated because of the large number of possible reactions. Over a wide range of conditions, products including SF₄, SOF₄, SOF₂, and SO₂F₂ can be formed but thre is considerable uncertainty about the major reactions which contribute to the formation of these species. In this work reactions of oxygen atoms with SOF₂ and fluorine atoms with SOF₂ and SO₂ have been studied in order to determine the principal sources of SO₂F₂ in these plasmas. Reactions were studied at 295 K in a gas flow reactor sampled by a mass spectrometer. No reaction could be detected between oxygen atoms and SOF₂, which for the conditions employed, means that the upper limit for the reaction rate coefficient is 1×10^–14 cm³ sec^–1. The reaction of fluorine atoms with SOF₂ was studied with the helium bath gas number density ranging from 3.1×10¹⁶ to 2.0×10¹⁷ cm^–3. Within this range the rate coefficient increased with increasing [He] from (4.1 to 10.8)×10^–14 cm³ sec^–1. SO₂ was found to react with fluorine atoms with a rate coefficient which appeared to be independent of the helium bath gas number density over the range given above. The possibility that this reaction occurred entirely on the walls of the reactor is discussed.     

By-product formation in spark breakdown of SF6/O2 mixtures

The yields of SOF₄, SO₂F₂, SOF₂, and SO₂ have been measured as a function of O₂ content in SF₆/O₂ mixtures, following spark discharges. All experiments were made at a spark energy of 8.7 J/spark, a total pressure of 133 kPa, and for O₂ additions of 0, 1, 2, 5, 10, and 20% to SF₆. Even for the case of no added O₂, trace amounts of O₂ and H₂O result in the formation of the above by-products. However, addition of O₂ significantly increases the yields of SOF₄ and SO₂F₂, while SOF₂ is only slightly affected. The net yields for SOF₄ and SO₂F₂ formation range from 0.18×10^–9 and 0.64×10^–10 mol·J^–1, respectively, at 1% O₂ content to 10.45×10^–9 and 7.15×10^–10 mol·J^–1, respectively, at 20% O₂ content. The mechanism for SOF₄ production appears to involve SF₄, an important initial product of SF₆, as a precursor. Comparison of the SOF₄ and SO₂F₂ yield from spark discharges (arc and corona) shows that the yields from other discharges (arc and corona) shows that the yields can vary by at least three orders of magnitude, depending on the type of discharge and on other discharge parameters.     

Mass spectrometric study of SF6-N2 plasma during etching of silicon and tungsten

The reaction products in the SF₆-N₂ mixture rf plasma during reactive ion etching of Si and W have been measured by a mass spectrometric method. Two kinds of cathode materials were used in this work; they were stainless steel for the Si etching, and SiO₂ for the W etching. The main products detected in the etching experiments of Si and W included SF₄, SF₂, SO₂, SOF₂, SOF₄, SO₂F₂, NSF, NF₃, N₂F₄, N_xS_y, NO₂, and SiF₄. In the W etching with the SiO₂ cathode, additional S₂F₂, N₂O, and WF₆ molecules were also obtained. The formation reactions about the novel NSF compound and the sulfur oxyfuorides were discussed.     

Negative ion formation in compounds relevant to SF6 decomposition in electrical discharges

Dissociative and nondissociative electron attachment in the electron impact energy range 0–14 eV are reported for SOF₂ SOF₄, SO₂F₂, SF₄, SO₂, and SiF₄ compounds which can be formed by electrical discharges in SF₆. The electron energy dependences of the mass-identified negative ions were determined in a time-of-flight mass spectrometer. The ions studied include F^– and SOF ₂ ^–* from SOF₂; SOF ₃ ^– and F^– from SOF₄; SO₂F ₂ ^–* , SO₂F^–, F ₂ ^– , and F^– from SO₂F₂; SF ₄ ^–* and F^– from SF₄; O^–, SO^–, and S^– from SO₂; and SiF ₃ ^– and F^– from SiF₄. Thermochemical data have been determined from the threshold energies of some of the fragment negative ions. Lifetimes of the anions SOF ₂ ^–* , SO₂F ₂ ^–* , and SF ₄ ^–* are also reported.     

Gas-phase reactions in plasmas of SF6 with O2 in He

Processes which occur in microwave discharges of dilute mixtures of SF₆ and O₂ in He have been examined using a flow reactor sampled by a mass spectrometer. Two classes of experiments were performed. In the first set of experiments, mixtures containing 6×10¹¹ cm^–3 SF₆, 6×10¹⁶ cm^–3 He, and O₂ in the range (0–3.6)×10¹³ cm^–3 were passed through a 20-W 2450-MHz microwave discharge. The gas mixtures arriving at a sample point downstream from the discharge were examined for SF₆, SF₄, SOF₂, SOF₄, SO₂F₂, SO₂, F, and O. In the second class of experiments, rate coefficients were measured for the reactions of SF₄ with O and O₂ and for the reaction of SF with O. The rate coefficient for the reaction of SF with O was found to be (4.2±1.5)×10^–11 cm^–3 s^–1. SF₄ was found to react so slowly with both oxygen atoms and oxygen molecules that only upper limits could be placed on the rate coefficients for these reactions. These values were 2×10^–14 cm³ s^–1 and 5×10^–15 cm³ s^–1 for reactions with O and O₂ respectively. The observed distribution of products from the discharged mixtures is discussed in terms of the measured rate coefficients.     

吸附法制备CuO-Ag/SiO2纳米复合物

利用吸附法原位制备CuO/SiO2、CuO-Ag/SiO2纳米复合物,研究了不同吸附质体系中预负载的纳米Ag粒子对CuO的影响。结果表明:Ag粒子对CuO的影响因吸附质的不同而不同。以Cu(Ac)2为吸附质,纳米Ag几乎没有影响;以NaOH为吸附质,纳米Ag使得CuO的晶粒粒径增大。这一结果与铜物种对Ag晶粒粒径的影响规律完全不同。通过比较不同吸附质的吸附行为,Cu(OH)2与硅胶表面的相互作用被认为是导致这一现象的原因。     

Automatic Carbon,Hydrogen, Nitrogen,Sulfur Analyzer Ciiemistry of Sulfur Reactions

Abstract

An automatic analyzer for the simultaneous microdetermination of carbon, hydrogen, nitrogen, and sulfur is described. The method is based on the uncatalyzed, dynamic, flash-combustion of the sample in an oxygen/helium atmosphere in a quartz tube. Separation of the combustion gases, N₂, CO₂, SO₂, and H₂O is accomplished by using gas chromatography and a thermal conductivity detector. Reactions of SO₂ formation are given in detail.     

Halogen displacement chemistry with silver and alkali metal salts: Preparation of SF5-esters, alcohols, aliphatic olefins, acids and an iodide

It has been found that treatment of SF₅-alkyl halides, especially SF₅(CH₂)₂Br, with silver salts such as CH₃C(O)OAg, p-CH₃C₆H₄SO₃Ag, CF₃SO₃Ag and AgNO₃ provides convenient pathways for preparing the following ester compounds: SF₅CH₂CH₂R (R = CH₃COO, TosO, CF₃SO₃, NO₃), SF₅(CH₂)₃OTos, and SF₅(CF₂)₄(CH₂)₂OAc. Important derivatives prepared from these esters include SF₅(CH₂)₂OH; SF₅(CF₂)₄(CH₂)₂OH. Several alkenes SF₅C(Br)CH₂ and SF₅CH₂(COOCH₃)CCHC(O)OCH₃ are obtained using silver salts. The use of alkali metals salts with SF₅(CH₂)₃Br is studied and yields SF₅(CH₂)₃I; also, a pathway has been developed that extends for SF₅(CH₂)₃₋ the chain by two-carbon atoms and also produces the first SF₅-containing malonic acid.     

SO2 Surface Chemistry on Metal Substrates

The surface chemistry, induced by thermal and non-thermal methods, of SO₂ on metal substrates is reviewed. The substrate temperature during dosing is important; regardless of metal, adsorption is dissociative at 300 K and molecular at 100 K. On Ni, Pd, and Pt, molecular adsorption occurs through the S and one O atom, and the molecular plane is perpendicular to the surface. However, on Ag and Cu, adsorption occurs only through the S with the molecular plane perpendicular to the surface. The differences can be attributed to the structure of the metal's molecular orbitals and their interactions with the SO₂ orbitals. Upon heating, SO₂ dissociates on all transition metal surfaces with the exception of Ag, Au, and Cu, where only molecular desorption occurs. On Pt, Fe, and Pd, additional reactions are observed between SO₂ and its dissociation products. The nonthermal reactions induced by photons and electrons for monolayer coverages of SO₂ on Ag (111) are dominated by molecular desorption. Desorption cross sections for 313 nm photons and 50eV electrons were 2.8 × 10^?20 cm² and ?1 × 10^?16 cm², respectively. Nonthermal excitation mechanisms and quenching processes as well as interesting characteristics of SO₂ under irradiation are also reviewed.     

Gas-phase reactions of SF5, SF2, and SOF with O(3 P): Their significance in plasma processing

Reactions of both SF₅ and SF₂ with O(³ P) and molecular oxygen have been studied at 295 K in a gas flow reactor sampled by a mass spectrometer. For reactions with O(³ P), rate coefficients of (2.0±0.5)×10^–11 cm³ s^–1 and (10.8±2.0)×10^–11 cm³ s^–1 were obtained for SF₅ and SF₂ respectively. The rate coefficients for reactions with O₂ are orders of magnitude lower, with an estimated upper limit of 5×10^–16 cm³ s^–1 for both SF₅ and SF₂. Reaction of SF₂ with O(³ P) leads to the production of SOF which then reacts with O(³ P) with a rate coefficient of (7.9±2.0)×10^–11 cm³ s^–1. Both SO and SO₂ are products in the reaction sequence initiated by reaction between SF₂ and O(³ P). Although considerable uncertainty exists for the heat of formation of SOF, it appears that SO arises only from reaction between SOF and O atoms which is also the source of SO₂. These results are discussed in terms of a reaction scheme proposed earlier to explain processes occurring during the plasma etching of Si in SF₆/O₂ plasmas. A comparison between the results obtained here and those reported earlier for reactions of both CF₃ and CF₂ with O and O₂ shows that there is a marked similarity in the free radical chemistry which occurs in SF₆/O₂ and CF₄/O₂ plasmas.     

Influence of Metallic Materials on SF<Subscript>6</Subscript> Decomposition Components under Positive DC Partial Discharge

Determination of the influence and mechanism of metallic materials on SF₆ decomposition under direct current (DC) partial discharge is one of the key aspects to improve SF₆ decomposition component analysis (DCA). In this study, three kinds of metallic materials, namely, aluminum, copper, and 18/8 stainless steel, were made into needle–plate electrons, and then used in the SF₆ positive DC partial discharge decomposition experiments. The influences of metallic materials on the five main decomposition components (i.e., CF₄, CO₂, SOF₂, SO₂F₂, and SO₂) were determined by gas chromatography–mass spectrometry. Results showed no significant correlation among the contents of CO₂ for the different kinds of metallic materials. However, the metallic materials considerably influenced the contents of the other four gases. The difference in SF₆ decomposition characteristics for the different metal electrodes was mainly due to the difference in anti-halogenation ability of metals and the passive film. Therefore, the impacts of different metallic materials should be considered when using SF₆ DCA for the condition monitoring and fault diagnosis of DC gas-insulated equipment.     

Inorganic volatile fluorides obtained from electrical decomposition of sulfur hexafluoride in a quartz tube

Recent investigations on sulfur hexafluoride decomposition have shown the need of a rapid and efficient method for the qualitative and quantitative analysis of the reaction products. An analytical method for characterizing the gas mixture obtained from the decomposition of sulfur hexafluoride in a quartz reactor submitted to an r.f. discharge, is presented. A combination of gas-chromatographic, mass spectrometric and infrared spectrophotometric techniques has shown the presence of SF₆, SO₂F₂, SOF₄, SOF₂, SiF₄ and F₂ in the gas mixtures examined. For quantitative purposes a gas-chromatographic method has been found to be most suitable.     

Microcalorimetric Studies of the Surface Reactivity of Pollutant Gas Atmospheres on Supported SnO2 and Ga2O3 Catalysts

The surface properties of gallium oxide and tin dioxide supported on alumina or titania have been studied by adsorption microcalorimetry. The differential heats of adsorption of various pollutant adsorbates such as sulfur dioxide, nitrogen monoxide, nitrogen dioxide and also ammonia were measured on these catalytic surfaces. NH₃, SO₂, NO₂ are strongly adsorbed while NO is only physisorbed. The supported Ga₂O₃ samples show a slight decrease in acidity as probed by ammonia adsorption, compared to alumina or titania. The addition of SnO₂ decreases the number of strong acid sites but creates a few weak and medium strength acid sites on alumina and does not modify the acidity of titania. In all cases, the basicity, probed by SO₂ adsorption, is very strongly affected by the deposition of Ga₂O₃ or SnO₂. The differential heats of NO₂ adsorption remain nearly constant on all samples. The heats of adsorption are discussed as a function of the coverage and of the amount of guest oxide. This revised version was published online in August 2006 with corrections to the Cover Date.     

Real-time monitoring traces of SF6 in near-source ambient air by ion mobility spectrometry

The leakage of sulphur hexafluoride (SF₆) gas threats the global climate changes and personnel safety. Monitoring the concentration of SF₆ in its application places is an industry regulation. In this study, ion mobility spectrometry (IMS) was developed for fast monitoring traces of SF₆ in near-source ambient air. Due to the water is an important part of the natural air and affects most atmospheric measurements, the operating parameters of IMS monitoring SF₆ were optimised for quantitative analysis of SF₆ at different relative humidity (RH). It is discovered two main product ions SF₆^? and SOF₄^? by IMS at different RH. The calibration curves of SF₆ were investigated by its relationship with the peak intensity of SOF₄^– for real application. The time resolution of the measurement was obtained less than 1 s and the limit of detection (LOD) achieved 0.16–0.68 ppm with a data averaging of 30 times. At last, the simulated application of monitoring SF₆ leakage was tested in the fume hood of our lab. The results showed a great potential application prospect of IMS in monitoring SF₆ in the ambient air of its application places.     

Interaction Between Two Similar Plane Parallel Double Layers for (NH4)2Fe(SO4)2 or (NH4)2Cu(SO4)2 Type Complex Salt Electrolytes at Positive Surface Potential

Interaction energies between two similar plane parallel double layers for (NH₄)₂Fe(SO₄)₂ or (NH₄)₂Cu(SO₄)₂ type complex salt electrolytes at positive surface potential were expanded in a power series and accurate numeral results were given for 0.1 ≤ y _e  < y ₀ ≤ 20. The general expressions were given for the interaction energies of A _ν +B _ν′ +C_ν? type complex salt electrolytes at y > 0. The interaction energies for simple salts NaCl, CaCl₂, Na₂SO₄, FeCl₃, Na₃PO₄, Mg₃(PO₄)₂, Al₂(SO₄)₃, and complex salts (NH₄)₂Fe(SO₄)₂ or (NH₄)₂Cu(SO₄)₂ at y ₀ = 1 were compared. There was hardly difference between these simple salts and this complex salt for the interaction energies. The interaction energy for complex salt (NH₄)₂Fe(SO₄)₂ was close to that for simple salt Na₃PO₄.

Supplemental files are available for this article. Go to the publisher's online edition of the Journal of Dispersion Science and Technology to view the free supplemental file.     

S 2p photoabsorption of the SF5CF3 molecule: Experiment,theory and comparison with SF6

The S 2p core excitation spectrum of the SF₅CF₃ molecule has been measured in the total ion yield mode. It resembles a lot the analogous spectrum of SF₆, also recorded in this study, displaying intense transitions to the empty molecular orbitals both below and above the S 2p ionization potential (IP) and weak transitions to the Rydberg orbitals. The S 2p photoabsorption spectra of SF₆ and SF₅CF₃ have been calculated using time-dependent density functional theory, whereby the spin–orbit coupling was included for the transitions below the S 2p IP. The agreement between experiment and theory is good for both molecules, which allows us to assign the main S 2p absorption features in SF₅CF₃.     

Monolayer oxide catalysts from alkoxide precursors, part IV. Vanadia, titania and stibia on SiO2, SnO2, and TiO2 in 2-propanol oxidation

Vanadia monolayer catalysts supported on SnO₂, ZrO₂, TiO₂, and SiO₂, similarly as titania and stibia monolayers deposited on SiO₂, have been synthesized by reacting the corresponding metal alkoxides with hydroxyls on the carrier surfaces. The metal ions loads in monolayer systems were determined. The catalysts activity was tested in 2-propanol transformations. The nature of carrier has a strong influence on the dehydrating to dehydrogenating activity ratio of vanadia monolayer.     

Preparation of ethyl levulinate from wheat stalk over Zr(SO4)2/SiO2

A series of Zr(SO₄)₂/SiO₂ solid acid catalysts with different Zr(SO₄)₂ loadings were prepared by water-soluble-impregnation method at room temperature. Then, the prepared catalysts were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectrum, X-ray diffraction, adsorption/desorption of N₂, and temperature-programmed desorption of NH₃. The results showed that the active component Zr(SO₄)₂ was successfully adhered to the mesoporous SiO₂, and the acid amount of Zr(SO₄)₂/SiO₂ increased with the increasing of the Zr(SO₄)₂ loadings. Finally, the wheat stalk was used as raw material and depolymerized over Zr(SO₄)₂/SiO₂ to produce ethyl levulinate (EL). The reaction mixture was separated and purified by filtration and vacuum distillation. The kinetic characteristics and the reaction pathway were also studied. A comparative study showed that 20 wt.% Zr(SO₄)₂/SiO₂ exhibited higher catalytic activity. When reaction temperature, time, catalyst dosage and Zr(SO₄)₂ loadings were 190 °C, 50 min, 20 wt.% and 30 wt.%, the EL yield reached a maximum of 17.14%. The relative content of EL exceeded 90% after three steps of distillation.